(19) &  

(11) EP 2 298 955 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication: (51) Int Cl.: 23.03.2011 Bulletin 2011/12 C23C 16/24 (2006.01) H01L 31/18 (2006.01) H01L 31/20 (2006.01) (21) Application number: 10176489.2

(22) Date of filing: 13.09.2010

(84) Designated Contracting States: • Ridgeway, Robert Gordon AL AT BE BG CH CY CZ DE DK EE ES FI FR GB Quakertown, PA 18951 (US) GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO • Hutchison, Katherine Anne PL PT RO SE SI SK SM TR Sunnyvale, CA 94086 (US) Designated Extension States: • Langan, John Giles BA ME RS Breinigsville, PA 18031 (US)

(30) Priority: 11.09.2009 US 241466 P (74) Representative: Muir, Benjamin M. J. 31.08.2010 US 872806 Beck Greener Fulwood House (71) Applicant: AIR PRODUCTS AND CHEMICALS, INC. 12 Fulwood Place Allentown, PA 18195-1501 (US) London WC1V 6HR (GB)

(72) Inventors: • Hurley, Patrick Timothy Allentown, PA 18104 (US)

(54) Additives to for thin film silicon photovoltaic devices

(57) The objective of this invention is to use chemical current generating capability of the deposited films for additives to increase the rate of deposition processes for photoconductive films used in the manufacturing of Thin the amorphous silicon film ( αSi:H) and/or the microcrys- Film based Photovoltaic (TFPV) devices. talline silicon film (PCSi:H), and improve the electrical EP 2 298 955 A1

Printed by Jouve, 75001 PARIS (FR) 1 EP 2 298 955 A1 2

Description Silane; hydrogen; and BACKGROUND OF THE INVENTION at least one additive selected from:

[0001] Photovoltaic devices (PV) or solar cells are de- 5 (a) higher order straight chain , selected from; vices which convert sunlight into direct current (DC) elec- Si2H6, trisilane Si3H8, tetrasilane Si4H10, trical power. pentasilane Si5H12, hexasilane Si6H14, heptasilane [0002] Thin Film based Photovoltaic (TFPV) devices Si7H16, octasilane Si8H18, nonasilane Si9H20, de- have been using both amorphous silicon film ( αSi:H) and casilane Si10H22, other straight chain silanes of the 10 microcrystalline silicon film ( PCSi:H) for low cost thin film general formula Si xH2x+2 where x is 2 to 20, and mix- photovoltaic devices. Hydrogenated amorphous silicon tures thereof; (αSi:H) has been studied for applications in solar cells for several decades. More recently, microcrystalline sil- (b) higher order branched silanes, selected from; 2- icon (PCSi:H) has been studied because it is a suitable silyl-trisilane SiH3-Si(H)(SiH3)-SiH3, 2,2-disilyl-trisi- 15 material for the intrinsic layer in the bottom cell of thin- lane SiH3-Si(SiH3)2-SiH3, 2-silyl-tetrasilane SiH3-Si film tandem solar cells. (H)(SiH3)-SiH2-SiH3, 2,3-disilyltetrasilane SiH3-SiH [0003] The deposition of αSi:H and PCSi:H on large (SiH3)-SiH(SiH3)-SiH3, 2,2-disilyltetrasilane SiH3-Si substrate based photovoltaic (PV) panels has been ac- (SiH3)2-SiH2-SiH3, 3- silylpentasilane SiH 3-SiH2-SiH complished primarily using silane (SiH4) and hydrogen (SiH3)-SiH2-SiH3, silylpentasilane 2- SiH3-SiH 20 (H2) gas mixtures. The work have been done in the field (SiH3)-SiH2-SiH2-SiH3, 2,3-disilylpentasilane SiH3- includes: US2009/0077805 A1, US2007/0298590 A1), SiH(SiH3)-SiH(SiH3)-SiH2-SiH3, 2,4-disilylpentasi- US6855621 B2 and JP2005244037. A. Hammad et al lane SiH3-SiH(SiH3)-SiH2-SiH(SiH3)-SiH3, 2-silyl- (Thin Solid Films 451-452 (2004) 255-258) studied the hexasilane SiH3-SiH(SiH3)-(SiH2)3SiH3, 3-silylhex- hydrogenated microcrystalline silicon thin films using si- asilane SiH3-SiH2-SiH(SiH3)-(SiH2)2SiH3, 2,2-disi- 25 lane (SiH4), hydrogen gases ( H2 ) and disilane (Si2H6). lylpentasilane SiH3-Si(SiH3)2-(SiH2)2-SiH3, 3,3-dis- [0004] However, the deposition processes are rela- ilylpentasilane SiH3-SiH2-Si (SiH3)2-SiH2 -SiH3, tively slow (5- 10 Å/sec for αSi:H and 1-7 Å/sec for PCSi: 2,2,3-trisilyltetrasilane SiH3-Si(SiH3)2-SiH(SiH3)- H ) creating a bottle neck in the manufacturing of TFPV SiH3, 2-silylheptasilane SiH3-SiH(SiH3)-(SiH2)4- panels. This leads to a lower process tool through-put, SiH3, silylheptasilane 3- SiH3-SiH2-SiH(SiH3)- 30 which in turn leads to higher cost per Watt for the man- (SiH2)3-SiH3, 4-silylheptasilane SiH3-(SiH2)2-SiH ufactured panels. (SiH3)-(SiH2)2-SiH3, 2,2-disilylhexasilane SiH3-Si [0005] Additionally, deposition of αSi:H and PCSi:H on (SiH3)2-(SiH2)3-SiH3, 2,3-disilylhexasilane SiH 3-SiH large substrate based photovoltaic (PV) panels with the (SiH3) -SiH(SiH3)-(SiH2)2-SiH3, 2,4-disilylhexasi- existing chemistry of SiH4 and H2 yield solar cells with lane SiH3-SiH(SiH3)-SiH2-SiH(SiH3)-SiH2-SiH3, 2, 35 efficiencies ranging from 6% to 10%, depending on cell 5-disilylhexasilane 3 SiH-SiH(SiH3)-(SiH2)2-SiH design. The cell efficiency is dependent upon the quality (SiH3)- SiH3, 3,3-disilylhexasilane SiH3-SiH2-Si of the αSi:H and PCSi:H deposited, and more specifically (SiH3)2-(SiH2)2-SiH3, 3,4-disilylhexasilane SiH3- related to the grain size of crystallites in PCSi:H, number SiH2-SiH(SiH3)- SiH(SiH3)-SiH2-SiH3, 2,2,3-trisi- of defects and donor impurities present in the film. lylpentasilane SiH3-Si(SiH3)2-SiH(SiH3)-SiH2-SiH3, 40 [0006] Therefore, there is a need of a method for de- 2,2,4-trisilylpentasilane SiH3-Si(SiH3)2-SiH2-SiH positing an amorphous silicon film (αSi:H ) and a micro- (SiH3)-SiH3, 2,3,3-trisilylpentasilane SiH3-SiH crystalline silicon film (PCSi:H ) with increased deposi- (SiH3)-Si(SiH3)2-SiH2-SiH3, 2,3,4-trisilylpentasilane tion rate and increased cell efficiency. SiH3-SiH(SiH3)-SiH(SiH3)-SiH(SiH3)-SiH3, 2,2,3,3- tetrasilyltetrasilane SiH3-Si(SiH3)2-Si(SiH3)2-SiH3, BRIEF SUMMARY OF THE INVENTION 45 other branched silanes of the general formula SixH2x+2 where x is 4 to 20, and mixtures thereof; [0007] Accordingly, the present invention is directed to the use of chemical additives to increase the rate of (c) cyclic silanes, selected from; cyclotrisilane Si 3H6, deposition processes, and improve the electrical current cyclotetrasilane Si4H8, cyclopentasilane Si5H10, cy- 50 generating capability of the deposited films for photocon- clohexasilane Si6H10, other cyclic silanes of the gen- ductive films used in the manufacturing of Thin Film eral formula SixH2x where x is 3 to 20, and mixtures based Photovoltaic (TFPV) devices. thereof; [0008] In one embodiment, the invention provides a method of deposition for an amorphous silicon film ( αSi: (d) silyl substituted cyclic silanes, selected from; silyl 55 H) or microcrystalline silicon film P( CSi:H). Preferably, cyclotetrasilane SiH3-Si4H7, 1,2-disilyl cyclopen- the method is a method of deposition for a solar grade tasilane (SiH3)2-Si5H8, silyl cyclohexasilane amorphous silicon film ( αSi:H) as a photoconductive film SiH3-Si6H11, disilyl 1,3- cyclohexasilane on a substrate. The method in this embodiment uses (SiH3)2-Si6H10, other silyl substituted cyclosilanes of

2 3 EP 2 298 955 A1 4

the general formula SiyH3y-SixH2x-y where x is 3 to (H)(SiH3)-SiH2-SiH3, 2,3-disilyltetrasilane SiH3-SiH 20 and y is 1 to 2x, and mixtures thereof; (SiH3)-SiH(SiH3)-SiH3, 2,2-disilyltetrasilane SiH3-Si (SiH3)2-SiH2-SiH3, 3- silylpentasilane SiH 3-SiH2-SiH (e) silyl substituted silenes, selected from; 2-tetra- (SiH3)-SiH2-SiH3, silylpentasilane 2- SiH3-SiH 5 silene SiH3-SiH=SiH-SiH3, 2,3-disilyltetrasil-2-ene (SiH3)-SiH2-SiH2-SiH3, 2,3-disilylpentasilane SiH3- SiH3-Si(SiH3)=Si(SiH3)-SiH3, 2,3-disilylpentasil-2- SiH(SiH3)-SiH(SiH3)-SiH2-SiH3, 2,4-disilylpentasi- ene SiH3-Si(SiH3)=Si(SiH3)-SiH2-SiH3, 2,5-disilyl- lane SiH3-SiH(SiH3)-SiH2-SiH(SiH3)-SiH3, 2-silyl- hexasil-2-ene SiH3-Si(SiH3)=SiH-SiH2-SiH(SiH3)- hexasilane SiH3-SiH(SiH3)-(SiH2)3SiH3, 3-silylhex- SiH3, 2,3,4-trisilylhexasil-2-ene SiH3-Si(SiH3)=Si asilane SiH3-SiH2-SiH(SiH3)-(SiH2)2SiH3, 2,2-disi- 10 (SiH3)-SiH(SiH3)-SiH2-SiH3, other silyl substituted lylpentasilane SiH3-Si(SiH3)2-(SiH2)2-SiH3, 3,3-dis- silenes of the general formula Si yH3y-SixH2x-y where ilylpentasilane SiH3-SiH2-Si (SiH3)2-SiH2 -SiH3, x is 2 to 20 and y is 1 to 2x, and mixtures thereof; 2,2,3-trisilyltetrasilane SiH3-Si(SiH3)2-SiH(SiH3)- SiH3, 2-silylheptasilane SiH3-SiH(SiH3)-(SiH2)4- (f) halogen substituted silanes and silenes, selected SiH3, silylheptasilane 3- SiH3-SiH2-SiH(SiH3)- 15 from; 1,1-dichlorodisilane SiHCl2SiH3, 1,1,1,2- (SiH2)3-SiH3, 4-silylheptasilane SiH3-(SiH2)2-SiH tetrafluorodislane SiF3-SiH2F, 1,2-dichloro-1,2-dif- (SiH3)-(SiH2)2-SiH3, 2,2-disilylhexasilane SiH3-Si luorotetrasilane SiHClF-SiClF-SiH2-SiH3, 1,1,1- (SiH3)2-(SiH2)3-SiH3, 2,3-disilylhexasilane SiH 3-SiH trichlorotrisilane SiCl3-SiH2-SiH3, 1,1-difluoro-1,2,2- (SiH3) -SiH(SiH3)-(SiH2)2-SiH3, 2,4-disilylhexasi- trichlorosilane SiF2Cl-SiCl2-SiH3, chloropentasilane lane SiH3-SiH(SiH3)-SiH2-SiH(SiH3)-SiH2-SiH3, 2, 20 SiH2Cl-(SiH2)3-SiH3, and other compounds of the 5-disilylhexasilane 3 SiH-SiH(SiH3)-(SiH2)2-SiH general formula SiwH2w+2-zXz where X = F, Cl, Br, I, (SiH3)- SiH3, 3,3-disilylhexasilane SiH3-SiH2-Si w is 1 to 20 and z is 1 to 2w+2; and 2- chlorotetrasil- (SiH3)2-(SiH2)2-SiH3, 3,4-disilylhexasilane SiH3- 2-ene SiH3-SiCl=SiH-SiH3, 1,1-dichloro-2-fluoro- SiH2-SiH(SiH3)- SiH(SiH3)-SiH2-SiH3, 2,2,3-trisi- pentasil-2-ene SiHCl2-SiF=SiH2-SiH2-SiH3, 2,3- lylpentasilane SiH3-Si(SiH3)2-SiH(SiH3)-SiH2-SiH3, 25 dichlorotetrasil-2-ene SiH3-SiCl=SiCl-SiH3, and oth- 2,2,4-trisilylpentasilane SiH3-Si(SiH3)2-SiH2-SiH er compounds of the general formula SiwH2w-zX’z (SiH3)-SiH3, 2,3,3-trisilylpentasilane SiH3-SiH where X’ = F, Cl, Br, I, w is 2 to 20 and z is 1 to 2w; (SiH3)-Si(SiH3)2-SiH2-SiH3, 2,3,4-trisilylpentasilane and mixtures thereof; and SiH3-SiH(SiH3)-SiH(SiH3)-SiH(SiH3)-SiH3, 2,2,3,3- tetrasilyltetrasilane SiH3-Si(SiH3)2-Si(SiH3)2-SiH3, (g) halogen substituted cyclic silanes, selected from; 30 other branched silanes of the general formula chlorocyclopentasilane Si5H9Cl, dodecachlorocy- SixH2x+2 where x is 4 to 20, and mixtures thereof; clohexasilane Si6Cl12, 1-chloro-1fluorocyclopen- (c) cyclic silanes, selected from; cyclotrisilane Si 3H6, tasilane Si5H8FCl, other cyclic silanes of the general cyclotetrasilane Si4H8, cyclopentasilane Si5H10, cy- formula SiwH2w-zX’z where X’ = F, Cl, Br, I, w is 3 to clohexasilane Si6H10, other cyclic silanes of the gen- 35 20 and z is 1 to 2w, and mixtures thereof. eral formula SixH2x where x is 3 to 20, and mixtures thereof; [0009] In another embodiment, the invention provides (d) silyl substituted cyclic silanes, selected from; silyl a deposited, preferably solar grade, amorphous silicon cyclotetrasilane SiH3-Si4H7, 1,2-disilyl cyclopen- film (αSi:H) made by the method of the preceding em- tasilane (SiH3)2-Si5H8, silyl cyclohexasilane SiH3- 40 bodiment. Si6H11, 1,3-disilyl cyclohexasilane (SiH3)2-Si6H10, [0010] In another embodiment, the invention provides other silyl substituted cyclosilanes of the general for- a method of deposition for amorphous silicon film (αSi: mula SiyH3y-SixH2x-y where x is 3 to 20 and y is 1 to H) or microcrystalline silicon film P( CSi:H) as a photo- 2x, and mixtures thereof; conductive film on a substrate, using (e) silyl substituted silenes, selected from; 2-tetra- 45 Silane; silene SiH3-SiH=SiH-SiH3, 2,3-disilyltetrasil-2-ene hydrogen; SiH3-Si(SiH3)=Si(SiH3)-SiH3, 2,3-disilylpentasil-2- at least one additive selected from: ene SiH3-Si(SiH3)=Si(SiH3)-SiH2-SiH3, 2,5-disilyl- hexasil-2-ene SiH3-Si(SiH3)=SiH-SiH2-SiH(SiH3)- (a) higher order straight chain silanes, selected from; SiH3, 2,3,4-trisilylhexasil-2-ene SiH3-Si(SiH3)=Si 50 disilane Si2H6, trisilane Si3H8, tetrasilane Si4H10, (SiH3)-SiH(SiH3)-SiH2-SiH3, other silyl substituted pentasilane Si5H12, hexasilane Si6H14, heptasilane silenes of the general formula Si yH3y-SixH2x-y where Si7H16, octasilane Si8H18, nonasilane Si9H20, de- x is 2 to 20 and y is 1 to 2x, and mixtures thereof; casilane Si10H22, other straight chain silanes of the and general formula Si xH2x+2 where x is 2 to 20, and mix- at least one additional additive selected from: tures thereof; 55 (h) halogen substituted silenes, selected from; mon- (b) higher order branched silanes, selected from; 2- ochlorosilane SiH 3Cl, dichlorosilane SiH 2Cl2,trichlo- silyl-trisilane SiH3-Si(H)(SiH3)-SiH3, 2,2-disilyl-trisi- rosilane SiHCl3, tetrachlorosilane (SiCl4), chlorodis- lane SiH3-Si(SiH3)2-SiH3, 2-silyl-tetrasilane SiH3-Si ilane SiH3-SiH2Cl, and mixtures thereof; and

3 5 EP 2 298 955 A1 6

(i) halogen containing gases, selected from; chlorine DRAWINGS Cl2, HCl, chlorine trifluoride ClF 3, nitrogen trifluoride NF3, fluorine F2, hydrogen fluo- [0015] ride HF, bromine Br 2, HBr, hydro- gen iodide HI and mixtures thereof; 5 Figure 1. The Empirical Microstructure Factor R* of hydrogenated silicon αSi:H versus SiH 4 flow rate un- [0011] In another embodiment, the invention provides der different power densities. The hydrogenated sil- a deposited amorphous silicon film ( αSi:H) or microcrys- icon αSi:H was deposited using silane and hydro- talline silicon film (PCSi:H) made by the method of the gen. preceding embodiment. 10 [0012] In yet another embodiment, the invention pro- Figure 2. The deposition rate of hydrogenated silicon vides a method of deposition for a solar grade amorphous αSi:H versus SiH4 flow rate under different power silicon film (αSi:H), preferably of solar grade, or a micro- densities. The hydrogenated silicon αSi:H was de- crystalline silicon film (PCSi:H), preferably having high posited using silane and hydrogen. microcrystalline fraction, as a photoconductive film on a 15 substrate, using Figure 3. The deposition rate of hydrogenated silicon Silane; αSi:H versus the flow rate of the mixture of SiH4 and hydrogen; and disilane under different power densities. The hydro- at least one additive selected from: genated silicon αSi:H was deposited using silane, 20 disilane and hydrogen. (f) halogen substituted higher order silanes and si- lenes, selected from; 1,1-dichlorodisilane Figure 4. The Empirical Microstructure Factor R* of SiHCl2SiH3, 1,1,1,2-tetrafluorodislane SiF3-SiH2F, hydrogenated silicon αSi:H versus the flow rate of 1,2-dichloro-1,2-difluorotetrasilane SiHClF-SiClF- the mixture of SiH4 and disilane under different pow- 25 SiH2-SiH3, 1,1,1-trichlorotrisilane SiCl3-SiH2-SiH3, er densities. The hydrogenated silicon αSi:H was de- 1,1-difluoro-1,2,2-trichlorosilane SiF2Cl-SiCl2-SiH3, posited using silane, disilane and hydrogen. chloropentasilane SiH2Cl-(SiH2)3-SiH3, and other compounds of the general formula w SiH2w+2-zXz Figure 5. The microcrystalline fraction versus the where X = F, Cl, Br, I, w is 1 to 20 and z is 1 to 2w+2; mole fraction SiH3Cl / (SiH3Cl + SixHy). 30 and 2-chlorotetrasil-2-ene SiH3-SiCl=SiH-SiH3, 1,1- dichloro-2-fluoropentasil-2-ene Figure 6. The Activation Energy for deposited micro- SiHCl2-SiF=SiH2-SiH2-SiH3, 2,3-dichlorotetrasil-2- crystalline film versus the mole fractions of halogen- ene SiH3-SiCl=SiCl-SiH3, and other compounds of ated silanes SiH3Cl / (SiH3Cl + SixHy). the general formula Si wH2w-zX’z where X’ = F, Cl, Br, I, w is 2 to 20 and z is 1 to 2w; and mixtures thereof; 35 DETAILED DESCRIPTION OF THE INVENTION and [0016] In prior arts, Plasma power, frequency, temper- (g) halogen substituted cyclic higher order silanes, ature, gas mixing ratios and pressure have been used to selected from; chlorocyclopentasilane Si5H9Cl, do- control film structure, thickness and electrical properties. 40 decachlorocyclohexasilane 6Cl Si12, chloro- 1- [0017] The present invention further discloses the use 1fluorocyclopentasilane Si5H8FCl, other cyclic si- of chemical additives to increase the rate of deposition lanes of the general formula Si wH2w-zX’z where X’ = processes, and improve the electrical current generating F, Cl, Br, I, w is 3 to 20 and z is 1 to 2w, and mixtures capability of the deposited films for photoconductive films thereof. used in the manufacturing of Thin Film based Photovolta- 45 ic (TFPV) devices. [0013] In another embodiment, the invention provides [0018] Increasing the module efficiency is one ap- a deposited, preferably solar grade, amorphous silicon proach for reducing manufacturing costs. The present film (αSi:H) or microcrystalline silicon film ( PCSi:H), pref- invention discloses the reduction of manufacturing costs erably having high microcrystalline fraction, made by the through the addition of additives to the mixture of SiH4 50 method of the preceding embodiment. and H2. [0014] The deposited films in the embodiments dis- [0019] In present invention, the additives are used to closed above, provide high deposition rates, enhanced increase the deposition rate, and in addition, to control photoconductivity, solar grade for amorphous silicon film film structure to achieve better grade for practical use, to (αSi:H), and high microcrystalline fraction for microcrys- optimize crystalline grain sizes, reduce the number of talline silicon film (PCSi:H). 55 defects and/or minimize or neutralize the effects of im- purities present as a result of contamination from the BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE processing environment; thus reducing manufacturing costs.

4 7 EP 2 298 955 A1 8

[0020] More specifically, the present invention uses (SiH3)-SiH3, 2,3,3-trisilylpentasilane SiH3-SiH the mixture of silane and hydrogen as the primary source (SiH3)-Si(SiH3)2-SiH2-SiH3, 2,3,4-trisilylpentasilane of silicon, and uses additives as the process enhancing SiH3-SiH(SiH3)-SiH(SiH3)-SiH(SiH3)-SiH3, 2,2,3,3- feature. The process enhancements are significantly tetrasilyltetrasilane SiH3-Si(SiH3)2-Si(SiH3)2-SiH3 greater than the potential additional cost afforded by the 5 and any other higher branched silanes under the use of higher value additives. These enhancements lead general formula SixH2x+2 where x can be 4-20; to a lower cost per unit of energy through: (i) a faster deposition rate and better control of film grade resulting (c) Cyclic silanes, including; cyclotrisilane Si 3H6, cy- from the addition of relatively low mole fractions of higher clotetrasilane Si4H8, cyclopentasilane Si5H10, cy- 10 order silanes; and, (ii) a more photoconductive film clohexasilane Si6H10, and other cyclic silanes con- through the addition of a halogen containing gas or a sisting of the general formula Si xH2x where x can be halogen substituted silane containing gas. 3-20; [0021] The deposition processes include but are not limited to Chemical Vapor Deposition (CVD), Plasma En- (d) Silyl substituted cyclic silanes, including; silyl cy- 15 hanced Chemical Vapor Deposition (PECVD), Low Pres- clotetrasilane SiH3-Si4H7, 1,2-disilyl cyclopentasi- sure Chemical Vapor Deposition (LPCVD), Hot Wire lane (SiH3)2-Si5H8, silyl cyclohexasilane 3 SiH- Chemical Vapor Deposition (HWCVD), Initiated Chemi- Si6H11, 1,3-disilyl cyclohexasilane (SiH3)2-Si6H10, cal Vapor Deposition (ICVD) and Sub Atmospheric and other silyl substituted cyclosilanes of the general Chemical Vapor Deposition (SA-CVD). formula SiyH3y-SixH2x-y where x can be 3 to 20 and [0022] Process enhancing additives include, but are 20 y can be 1 to 2x. not limited to: (e) Silyl substituted silenes, including; 2-tetrasilene (a) Higher order straight chain silanes, including; dis- SiH3-SiH=SiH-SiH3, 2,3-disilyltetrasil-2-ene SiH3-Si ilane Si2H6, trisilane Si3H8, tetrasilane Si4H10, pen- (SiH3)=Si(SiH3)-SiH3, 2,3-disilylpentasil-2-ene 25 tasilane Si5H12, hexasilane Si6H14, heptasilane SiH3-Si(SiH3)=Si(SiH3)-SiH2-SiH3, 2,5-disilylhexas- Si7H16, octasilane Si8H18, nonasilane Si9H20, de- il-2-ene SiH3-Si(SiH3)=SiH-SiH2-SiH(SiH3)-SiH3, 2, casilane Si10H22 and other straight chain silanes fol- 3,4-trisilylhexasil-2-ene SiH3-Si(SiH3)=Si(SiH3)-SiH lowing the general formula Si xH2x+2 where x can be (SiH3)-SiH2-SiH3, and other silyl substituted silenes 2-20; of the general formula SiyH3y-SixH2x-(y+2) where x 30 can be 2 - 20 and y can be 1 to 2x. (b) Higher order branched silanes, including; 2- silyl- trisilane SiH3-Si(H)(SiH3)-SiH3, 2,2-disilyl-trisilane (f) Halogen substituted higher order silanes and si- SiH3-Si(SiH3)2-SiH3, 2-silyl-tetrasilane SiH3-Si(H) lenes, including; 1,1-dichlorodisilane SiHCl2SiH3, (SiH3)-SiH2-SiH3, 2,3-disilyltetrasilane SiH3-SiH 1,1,1,2-tetrafluorodislane SiF3-SiH2F, 1,2-dichloro- 35 (SiH3)-SiH(SiH3)-SiH3, 2,2-disilyltetrasilane SiH3-Si 1,2-difluorotetrasilane SiHClF-SiClF-SiH2-SiH3, 1, (SiH3)2-SiH2-SiH3, 3- silylpentasilane SiH 3-SiH2-SiH 1,1-trichlorotrisilane SiCl3-SiH2-SiH3, 1,1-difluoro- (SiH3)-SiH2-SiH3, silylpentasilane 2- SiH3-SiH 1,2,2-trichlorosilane SiF2Cl-SiCl2-SiH3, chloropen- (SiH3)-SiH2-SiH2-SiH3, 2,3-disilylpentasilane SiH3- tasilane SiH2Cl-(SiH2)3-SiH3, and other compounds SiH(SiH3)-SiH(SiH3)-SiH2-SiH3, 2,4-disilylpentasi- of the general formula Si wH2w+2-zXz where X = F, Cl, 40 lane SiH3-SiH(SiH3)-SiH2-SiH(SiH3)-SiH3, 2-silyl- Br, I; where w can be 1 to 20 and z can be 1 to 2w+2; hexasilane SiH3-SiH(SiH3)-(SiH2)3SiH3, 3-silylhex- 2-chlorotetrasil-2-ene SiH3-SiCl=SiH-SiH3, 1,1- asilane SiH3-SiH2-SiH(SiH3)-(SiH2)2SiH3, 2,2-disi- dichloro-2-fluoropentasil-2-ene SiHCl2-SiF=SiH2- lylpentasilane SiH3-Si(SiH3)2-(SiH2)2-SiH3, 3,3-dis- SiH2-SiH3, 2,3-dichlorotetrasil-2-ene SiH3-SiCl=Si- ilylpentasilane SiH3-SiH2-Si (SiH3)2-SiH2 -SiH3, Cl-SiH3, and other compounds of the general formu- 45 2,2,3-trisilyltetrasilane SiH3-Si(SiH3)2-SiH(SiH3)- la SiwH2w-zX’z where X’ = F, Cl, Br, I; and, w can be SiH3, 2-silylheptasilane SiH3-SiH(SiH3)-(SiH2)4- 2 to 20 and z can be 1 to 2w. SiH3, silylheptasilane 3- SiH3-SiH2-SiH(SiH3)- (SiH2)3-SiH3, 4-silylheptasilane SiH3-(SiH2)2-SiH (g) Halogen substituted cyclic higher order silanes, (SiH3)-(SiH2)2-SiH3, 2,2-disilylhexasilane SiH3-Si including; chlorocyclopentasilane 5H Si9Cl, do- 50 (SiH3)2-(SiH2)3-SiH3, 2,3-disilylhexasilane SiH 3-SiH decachlorocyclohexasilane 6 SiCl12, 1-chloro-1 (SiH3) -SiH(SiH3)-(SiH2)2-SiH3, 2,4-disilylhexasi- fluorocyclopentasilane Si 5H8FCl, and other cyclic si- lane SiH3-SiH(SiH3)-SiH2-SiH(SiH3)-SiH2-SiH3, 2, lanes of the general formula Si wH2w-zX’z where X’ = 5-disilylhexasilane 3 SiH-SiH(SiH3)-(SiH2)2-SiH F, Cl, Br, I; where w can be 3 to 20 and z can be 1 (SiH3)- SiH3, 3,3-disilylhexasilane SiH3-SiH2-Si to 2w. 55 (SiH3)2-(SiH2)2-SiH3, 3,4-disilylhexasilane SiH3- SiH2-SiH(SiH3)- SiH(SiH3)-SiH2-SiH3, 2,2,3-trisi- (h) Halogen substituted silanes, including; mono- lylpentasilane SiH3-Si(SiH3)2-SiH(SiH3)-SiH2-SiH3, chlorosilane SiH3Cl, dichlorosilane SiH2Cl2, trichlo- 2,2,4-trisilylpentasilane SiH3-Si(SiH3)2-SiH2-SiH rosilane SiHCl3, tetrachlorosilane (SiCl4), and chlo-

5 9 EP 2 298 955 A1 10

rodisilane SiH3-SiH2Cl. silylheptasilane 3-(SiH SiH2)2-SiH(SiH3)- (SiH2)2-SiH3, 2,2-disilylhexasilane SiH3-Si (i) Halogen containing gases, including; chlorine Cl 2, (SiH3)2-(SiH2)3-SiH3, 2,3-disilylhexasilane hydrogen chloride HCl, chlorine trifluoride ClF3, ni- SiH3-SiH(SiH3) -SiH(SiH3)-(SiH2)2-SiH3, 2,4- 5 trogen trifluoride NF3, fluorine F2, disilylhexasilane SiH3-SiH(SiH3)-SiH2-SiH HF, bromine Br2, hydrogen bromide HBr, hydrogen (SiH3)-SiH2-SiH3, 2,5-disilylhexasilane SiH3- iodide Hl and other compounds of these types. SiH(SiH3)-(SiH2)2-SiH(SiH3)- SiH3, 3,3-disilyl- hexasilane SiH3-SiH2-Si(SiH3)2-(SiH2)2-SiH3, [0023] To increase the deposition rate and improve the 3,4-disilylhexasilane SiH3-SiH2-SiH(SiH3)- SiH 10 photoconductivity of the film, one embodiment of the (SiH3)-SiH2-SiH3, 2,2,3-trisilylpentasilane SiH3- present invention uses at least one additive selected from Si(SiH3)2-SiH(SiH3)-SiH2-SiH3, 2,2,4-trisi- the groups (a) to (g) shown above in addition of SiH 4 and lylpentasilane SiH3-Si(SiH3)2-SiH2-SiH(SiH3)- H2; yet another embodiment of the present invention us- SiH3, 2,3,3-trisilylpentasilane SiH3-SiH(SiH3)- es the combinations of additives from groups (a) to (e) Si(SiH3)2-SiH2-SiH3, 2,3,4-trisilylpentasilane 15 and additives from groups (h) and (i) to further enhance SiH3-SiH(SiH3)-SiH(SiH3)-SiH(SiH3)-SiH3, 2,2, the photoconductivity of the film. 3,3-tetrasilyltetrasilane 3-Si(SiH SiH 3)2-Si [0024] The depositions use 5 to 10% silane; from 0.01 (SiH3)2-SiH3 and mixtures thereof; to 5% an additive from groups (a) to (g); 0.01 to 5% an additive from groups (h) and (i) (where used); and the (c) cyclic silanes, selected from the group con- 20 remainder hydrogen; the flow of hydrogen, silane, and sisting of; cyclotrisilane Si3H6, cyclotetrasilane appropriate additive or additives totalling 100% (all said Si4H8, cyclopentasilane Si5H10, cyclohexasi- percentages being by volume). lane Si6H10, and mixtures thereof; [0025] Aspects of the invention include: (d) silyl substituted cyclic silanes, selected from #1. A method of deposition for a solar grade amor- 25 the group consisting of; silyl cyclotetrasilane phous silicon film (αSi:H) as a photoconductive film SiH3-Si4H7, 1,2-disilyl cyclopentasilane on a substrate, using (SiH3)2-Si5H8, silyl cyclohexasilane 3- SiH Silane; Si6H11, 1,3-disilyl cyclohexasilane (SiH3)2- hydrogen; and Si6H10, and mixtures thereof; at least one additive selected from the group con- 30 sisting of: (e) silyl substituted silenes, selected from the group consisting of; tetrasilene 2- SiH3-SiH= (a) higher order straight chain silanes, compris- SiH-SiH3, 2,3-disilyltetrasil-2-ene SiH3-Si(SiH3) ing; disilane Si2H6, trisilane Si3H8, tetrasilane =Si(SiH3)-SiH3, 2,3-disilylpentasil-2-ene SiH3- 35 Si4H10, pentasilane Si5H12, hexasilane Si6H14, Si(SiH3)=Si(SiH3)-SiH2-SiH3, 2,5-disilylhexasil- heptasilane Si7H16, octasilane Si8H18, nonasi- 2-ene SiH3-Si(SiH3)=SiH-SiH2-SiH(SiH3)- lane SigH20, decasilane Si10H22 and mixtures SiH3, 2,3,4-trisilylhexasil-2-ene SiH3-Si(SiH3) thereof; =Si(SiH3)-SiH(SiH3)-SiH2-SiH3, and mixtures thereof; (b) higher order branched silanes, comprising; 40 2-silyl-trisilane SiH3-Si(H)(SiH3)-SiH3, 2,2-disi- (f) halogen substituted silenes, including; 1,1- lyl-trisilane SiH3-Si(SiH3)2-SiH3, 2-silyl-tetrasi- dichlordisilane SiHCl2SiH3, 1,1,1,2-tetrafluoro- lane SiH3-Si(H)(SiH3)-SiH2-SiH3, 2,3-disilyltet- dislane SiF 3-SiH2F,1,2-dichloro-1,2-difluorotet- rasilane SiH3-SiH(SiH3)-SiH(SiH3)-SiH3, 2,2- rasilane SiHClF-SiClF-SiH2-SiH3, 1,1,1-trichlo- 45 disilyltetrasilane SiH3-Si(SiH3)2-SiH2-SiH3, 3- rotrisilane SiCl3-SiH2-SiH3, 1,1-difluoro-1,2,2- silylpentasilane 3 SiH-SiH2-SiH(SiH3)-SiH2- trichlorosilane SiF2Cl-SiCl2-SiH3, chloropen- SiH3, 2-silylpentasilane SiH3-SiH(SiH3)-SiH2- tasilane SiH2Cl-(SiH2)3-SiH3, and other com- SiH2-SiH3, 2,3-disilylpentasilane SiH3-SiH pounds of the general formula w SiH2w+2-zXz (SiH3)-SiH(SiH3)-SiH2-SiH3, 2,4-disilylpentasi- where X = F, Cl, Br, I; w can be 1 to 20 and z 50 lane SiH3-SiH(SiH3)-SiH2-SiH(SiH3)-SiH3, 2-si- can be 1 to 2w+2; 2-chlorotetrasil-2-ene lylhexasilane SiH3-SiH(SiH3)-(SiH2)3SiH3, 3-si- SiH3-SiCl=SiH-SiH3, 1,1-dichloro-2-fluoropen- lylhexasilane 3-SiH SiH 2-SiH(SiH3)-(SiH2)2 tasil-2-ene SiHCl2-SiF=SiH2-SiH2-SiH3, 2,3- SiH3, 2,2-disilylpentasilane SiH3-Si(SiH3)2- dichlorotetrasil-2-ene SiH3-SiCl=SiCl-SiH3, and (SiH2)2-SiH3, 3,3-disilylpentasilane SiH3-SiH2- other compounds of the general formula 55 Si (SiH3)2-SiH2 -SiH3, 2,2,3-trisilyltetrasilane SiwH2w-zX’z where X’ = F, Cl, Br, I; and, w can SiH3-Si(SiH3)2-SiH(SiH3)-SiH3, 2-silylheptasi- be 2 to 20 and z can be 1 to 2w; and mixtures lane SiH3-SiH(SiH3)-(SiH2)4-SiH3, 3-silylhep- thereof; and tasilane SiH3-SiH2-SiH(SiH3)-(SiH2)3-SiH3, 4-

6 11 EP 2 298 955 A1 12

(g) halogen substituted cyclic silanes, selected lane SiH3-Si(H)(SiH3)-SiH2-SiH3, 2,3-disilyltet- from the group consisting of; chlorocyclopen- rasilane SiH3-SiH(SiH3)-SiH(SiH3)-SiH3, 2,2- tasilane Si5H9Cl, dodecachlorocyclohexasilane disilyltetrasilane SiH3-Si(SiH3)2-SiH2-SiH3, 3- Si6Cl12, 1-chloro-1fluorocyclopentasilane Si 5H8 silylpentasilane 3 SiH-SiH2-SiH(SiH3)-SiH2- 5 FCl, and mixtures thereof. SiH3, 2-silylpentasilane SiH3-SiH(SiH3)-SiH2- SiH2-SiH3, 2,3-disilylpentasilane SiH3-SiH #2. A method of deposition for a solar grade amor- (SiH3)-SiH(SiH3)-SiH2-SiH3, 2,4-disilylpentasi- phous silicon film (αSi:H) according to #1, wherein lane SiH3-SiH(SiH3)-SiH2-SiH(SiH3)-SiH3, 2-si- the silane used is at 5 to 10 %, and the at least one lylhexasilane SiH3-SiH(SiH3)-(SiH2)3SiH3, 3-si- 10 additive used is at 0.01 to 5 %, and the rest is hy- lylhexasilane 3-SiH SiH 2-SiH(SiH3)-(SiH2)2 drogen. SiH3, 2,2-disilylpentasilane SiH3-Si(SiH3)2- #3. A method of deposition for a solar grade amor- (SiH2)2-SiH3, 3,3-disilylpentasilane SiH3-SiH2- phous silicon film (αSi:H) according to #1, wherein Si (SiH3)2-SiH2 -SiH3, 2,2,3-trisilyltetrasilane the deposition is performed at a substrate tempera- SiH3-Si(SiH3)2-SiH(SiH3)-SiH3, 2-silylheptasi- 15 ture of 25° -500° C, and pressure of 0.01 torr to 15 lane SiH3-SiH(SiH3)-(SiH2)4-SiH3, 3-silylhep- torr (1.33 to 2000 Pa). tasilane SiH3-SiH2-SiH(SiH3)-(SiH2)3-SiH3, 4- #4. A method of deposition for a solar grade amor- silylheptasilane 3-(SiH SiH2)2-SiH(SiH3)- phous silicon film (αSi:H) according to #3, wherein (SiH2)2-SiH3, 2,2-disilylhexasilane SiH3-Si the substrate temperature is at 150°- 250° C. (SiH3)2-(SiH2)3-SiH3, 2,3-disilylhexasilane 20 #5. A method of deposition for a solar grade amor- SiH3-SiH(SiH3) -SiH(SiH3)-(SiH2)2-SiH3, 2,4- phous silicon film (αSi:H) according to #1, wherein disilylhexasilane SiH3-SiH(SiH3)-SiH2-SiH the deposition is a process selected from the group (SiH3)-SiH2-SiH3, 2,5-disilylhexasilane SiH3- consisting of Chemical Vapor Deposition (CVD), SiH(SiH3)-(SiH2)2-SiH(SiH3)-SiH3, 3,3-disilyl- Plasma Enhanced Chemical Vapor Deposition hexasilane SiH3-SiH2-Si(SiH3)2-(SiH2)2-SiH3, 25 (PECVD), Low Pressure Chemical Vapor Deposition 3,4-disilylhexasilane SiH3-SiH2-SiH(SiH3)- SiH (LPCVD), Hot Wire Chemical Vapor Deposition (SiH3)-SiH2-SiH3, 2,2,3-trisilylpentasilane SiH3- (HWCVD), Initiated Chemical Vapor Deposition Si(SiH3)2-SiH(SiH3)-SiH2-SiH3, 2,2,4-trisi- (ICVD) and Sub Atmospheric Chemical Vapor Dep- lylpentasilane SiH3-Si(SiH3)2-SiH2-SiH(SiH3)- osition (SA-CVD). SiH3, 2,3,3-trisilylpentasilane SiH3-SiH(SiH3)- 30 #6. A method of deposition for a solar grade amor- Si(SiH3)2-SiH2-SiH3, 2,3,4-trisilylpentasilane phous silicon film (αSi:H) according to #1, wherein SiH3-SiH(SiH3)-SiH(SiH3)-SiH(SiH3)-SiH3, the deposition is a plasma enhanced chemical vapor 2,2,3,3-tetrasilyltetrasilane SiH3-Si(SiH3)2-Si deposition at a plasma power density ranging from (SiH3)2-SiH3 and mixtures thereof; 0.19-1.6 W/cm2 and a plasma frequency ranging from 13.56 to 40.68 MHz. 35 (c) cyclic silanes, selected from the group con- #7. A method of deposition for a solar grade amor- sisting of; cyclotrisilane Si3H6, cyclotetrasilane phous silicon film ( αSi:H) according to #6, the meth- Si4H8, cyclopentasilane Si5H10, cyclohexasi- od having a deposition rate ranging from 10 - 200 lane Si6H10, and mixtures thereof; Å/sec. #8. A method of deposition for a solar grade amor- 40 (d) silyl substituted cyclic silanes, selected from phous silicon film (αSi:H) according to #6, wherein the group consisting of; silyl cyclotetrasilane the deposited film provides a single junction solar SiH3-Si4H7, 1,2-disilyl cyclopentasilane cell having efficiencies of 5 -15%; or a tandem junc- (SiH3)2-Si5H8, silyl cyclohexasilane 3- SiH tion solar cell having efficiencies of 7 - 20 %. Si6H11, 1,3-disilyl cyclohexasilane (SiH3)2- 45 #9. A solar grade amorphous silicon film ( αSi:H) de- Si6H10, and mixtures thereof; posited using silane, hydrogen and at least one ad- ditive selected from the group consisting of: (e) silyl substituted silenes, selected from the group consisting of; tetrasilene 2- SiH3- (a) higher order straight chain silanes, compris- SiH=SiH-SiH3, 2,3-disilyltetrasil-2-ene SiH3-Si 50 ing; disilane Si2H6, trisilane Si3H8, tetrasilane (SiH3)=Si(SiH3)-SiH3, 2,3-disilylpentasil-2-ene Si4H10, pentasilane Si5H12, hexasilane Si6H14, SiH3-Si(SiH3)=Si(SiH3)-SiH2-SiH3, 2,5-disilyl- heptasilane Si7H16, octasilane Si8H18, nonasi- hexasil-2-ene 3 SiH-Si(SiH3)=SiH-SiH2-SiH lane Si9H20, decasilane Si10H22 and mixtures (SiH3)-SiH3, 2,3,4-trisilylhexasil-2-ene SiH3-Si thereof; (SiH3)=Si(SiH3)-SiH(SiH3)-SiH2-SiH3, and mix- 55 tures thereof; (b) higher order branched silanes, comprising; 2-silyl-trisilane SiH3-Si(H)(SiH3)-SiH3, 2,2-disi- (f) halogen substituted higher order silenes, in- lyl-trisilane SiH3-Si(SiH3)2-SiH3, 2-silyl-tetrasi- cluding; 1,1-dichlordisilane SiHCl 2SiH3, 1,1,1,2-

7 13 EP 2 298 955 A1 14

tetrafluorodislane SiF3-SiH2F, 1,2-dichloro-1,2- according to #15 which was deposited with a depo- difluorotetrasilane SiHClF-SiClF-SiH2-SiH3, sition rate of 10 - 200 Å/sec. 1,1,1-trichlorotrisilane SiCl3-SiH2-SiH3, 1,1-dif- #17. A solar grade amorphous silicon film α(Si:H) luoro-1,2,2-trichlorosilane SiF2Cl-SiCl2-SiH3, according to #15 providing a single junction solar cell 5 chloropentasilane SiH2Cl-(SiH2)3-SiH3, and having efficiencies of 5 -15%; or providing a tandem other compounds of the general formula junction solar cell having efficiencies of 7 - 20 %. SiwH2w+2-zXz where X = F, Cl, Br, I; w can be 1 #18. A method of deposition for amorphous silicon to 20 and z can be 1 to 2w+2; 2-chlorotetrasil- film (αSi:H) or microcrystalline silicon film (PCSi:H) 2-ene SiH 3-SiCl=SiH-SiH3, 1,1-dichloro-2-fluor- as a photoconductive film on a substrate, using 10 opentasil-2-ene SiHCl2-SiF=SiH2-SiH2-SiH3, Silane; 2,3-dichlorotetrasil-2-ene SiH3-SiCl=SiCl-SiH3, hydrogen; and other compounds of the general formula at least one additive selected from the group con- SiwH2w-zX’z where X’ = F, Cl, Br, I; and, w can sisting of: be 2 to 20 and z can be 1 to 2w; and mixtures thereof; and 15 (a) higher order straight chain silanes, compris- ing; disilane Si2H6, trisilane Si3H8, tetrasilane (g) halogen substituted cyclic higher order si- Si4H10, pentasilane Si5H12, hexasilane Si6H14, lanes, selected from the group consisting of; heptasilane Si7H16, octasilane Si8H18, nonasi- chlorocyclopentasilane Si5H9Cl, dodecachloro- lane Si9H20, decasilane Si10H22 and mixtures 20 cyclohexasilane Si6Cl12, 1-chloro-1fluorocy- thereof; clopentasilane Si5H8FCl, and mixtures thereof. (b) higher order branched silanes, comprising; #10. A solar grade amorphous silicon film α(Si:H) 2-silyl-trisilane SiH3-Si(H)(SiH3)-SiH3, 2,2-disi- according to #9 wherein the silane was used at 5 to lyl-trisilane SiH3-Si(SiH3)2-SiH3, 2-silyl-tetrasi- 25 10 % and the at least one additive used at 0.01 to 5 lane SiH3-Si(H)(SiH3)-SiH2-SiH3, 2,3-disilyltet- %, the rest being hydrogen. rasilane SiH3-SiH(SiH3)-SiH(SiH3)-SiH3, 2,2- #11. A solar grade amorphous silicon film α(Si:H) disilyltetrasilane SiH3-Si(SiH3)2-SiH2-SiH3, 3- according to #9 which was deposited at a substrate silylpentasilane 3 SiH-SiH2-SiH(SiH3)-SiH2- temperature of 25° -500° C, and pressure of 0.01 SiH3, 2-silylpentasilane SiH3-SiH(SiH3)-SiH2- 30 torr to 15 torr (1.33 to 2000 Pa). SiH2-SiH3, 2,3-disilylpentasilane SiH3-SiH #12. A solar grade amorphous silicon film α(Si:H) (SiH3)-SiH(SiH3)-SiH2-SiH3, 2,4-disilylpentasi- according to # 11 which was deposited using a sub- lane SiH3-SiH(SiH3)-SiH2-SiH(SiH3)-SiH3, 2-si- strate temperature of 150° - 250° C. lylhexasilane SiH3-SiH(SiH3)-(SiH2)3SiH3, 3-si- #13. A solar grade amorphous silicon film α(Si:H) lylhexasilane 3-SiH SiH 2-SiH(SiH3)-(SiH2)2 35 according to #9 which provides an Empirical Micro- SiH3, 2,2-disilylpentasilane SiH3-Si(SiH3)2- structure Factor R* less than 20%, (SiH2)2-SiH3, 3,3-disilylpentasilane SiH3-SiH2- * wherein the Empirical Microstructure Factor R is de- Si (SiH3)2-SiH2 -SiH3, 2,2,3-trisilyltetrasilane * fined as R = IHSM/(ILSM +IHSM); SiH3-Si(SiH3)2-SiH(SiH3)-SiH3, 2-silylheptasi- wherein IHSM and ILsm correspond to the integrated lane SiH3-SiH(SiH3)-(SiH2)4-SiH3, 3-silylhep- 40 absorption strength of Si-H2, or the High Stretching tasilane SiH3-SiH2-SiH(SiH3)-(SiH2)3-SiH3, 4- -1 Mode (HSM) at 2070-2100 cm and the integrated silylheptasilane 3-(SiH SiH2)2-SiH(SiH3)- absorption strength of Si-H, or the Low Stretching (SiH2)2-SiH3, 2,2-disilylhexasilane SiH3-Si -1 Mode (LSM) at 1980-2010 cm . (SiH3)2-(SiH2)3-SiH3, 2,3-disilylhexasilane #14. A solar grade amorphous silicon film α(Si:H) SiH3-SiH(SiH3) -SiH(SiH3)-(SiH2)2-SiH3, 2,4- 45 according to #9 which was deposited with a process disilylhexasilane SiH3-SiH(SiH3)-SiH2-SiH selected from the group consisting of Chemical Va- (SiH3)-SiH2-SiH3, 2,5-disilylhexasilane SiH3- por Deposition (CVD), Plasma Enhanced Chemical SiH(SiH3)-(SiH2)2-SiH(SiH3)- SiH3, 3,3-disilyl- Vapor Deposition (PECVD), Low Pressure Chemical hexasilane SiH3-SiH2-Si(SiH3)2-(SiH2)2-SiH3, Vapor Deposition (LPCVD), Hot Wire Chemical Va- 3,4-disilylhexasilane SiH3-SiH2-SiH(SiH3)- SiH 50 por Deposition (HWCVD), Initiated Chemical Vapor (SiH3)-SiH2-SiH3, 2,2,3-trisilylpentasilane SiH3- Deposition (ICVD) and Sub Atmospheric Chemical Si(SiH3)2-SiH(SiH3)-SiH2-SiH3, 2,2,4-trisilyl- Vapor Deposition (SA-CVD). pentasilane SiH3-Si(SiH3)2-SiH2-SiH(SiH3)- #15. A solar grade amorphous silicon film α(Si:H) SiH3, 2,3,3-trisilylpentasilane SiH3-SiH(SiH3)- according to #9 which was deposited with a plasma Si(SiH3)2-SiH2-SiH3, 2,3,4-trisilylpentasilane 55 enhanced chemical vapor deposition at a plasma SiH3-SiH(SiH3)-SiH(SiH3)-SiH(SiH3)-SiH3, 2 power density ranging from 0.19-1.6 W/cm and a 2,2,3,3-tetrasilyltetrasilane SiH3-Si(SiH3)2-Si plasma frequency ranging from 13.56 to 40.68 MHz. (SiH3)2-SiH3 and mixtures thereof; #16. A solar grade amorphous silicon film α(Si:H)

8 15 EP 2 298 955 A1 16

(c) cyclic silanes, selected from the group con- pheric Chemical Vapor Deposition (SA-CVD). sisting of; cyclotrisilane Si3H6, cyclotetrasilane #22. Amethod of depositionfor an amorphous silicon Si4H8, cyclopentasilane Si5H10, cyclohexasi- film (αSi:H) or a microcrystalline silicon film (PCSi: lane Si6H10, and mixtures thereof; H) according to #18, wherein the deposition is a plas- 5 ma enhanced chemical vapor deposition at a plasma (d) silyl substituted cyclic silanes, selected from power density ranging from 0.19-1.6 W/cm2 and a the group consisting of; silyl cyclotetrasilane plasma frequency ranging from 13.56 to 40.68 MHz. SiH3-Si4H7, 1,2-disilyl cyclopentasilane #23. Amethod of depositionfor an amorphous silicon (SiH3)2-Si5H8, silyl cyclohexasilane 3- SiH film (αSi:H) or a microcrystalline silicon film (PCSi: 10 Si6H11, 1,3-disilyl cyclohexasilane (SiH3)2- H) according to #18, the method having a deposition Si6H10, and mixtures thereof; rate of 10 - 200 Å/sec for amorphous silicon film ( αSi: H) and 10-100 Å/sec for microcrystalline silicon film (e) silyl substituted silenes, selected from the (PCSi:H). group consisting of; tetrasilene 2- SiH3- #24. Amethod of depositionfor an amorphous silicon 15 SiH=SiH-SiH3, 2,3-disilyltetrasil-2-ene SiH3-Si film (αSi:H) or a microcrystalline silicon film (PCSi: (SiH3)=Si(SiH3)-SiH3, 2,3-disilylpentasil-2-ene H) according to #18, wherein the deposited amor- SiH3-Si(SiH3)=Si(SiH3)-SiH2-SiH3, 2,5-disilyl- phous silicon film (αSi:H) provides a single junction hexasil-2-ene SiH3-Si(SiH3)=SiH-SiH2-SiH solar cell having efficiencies of 5 -15%; or the de- (SiH3)-SiH3, 2,3,4-trisilylhexasil-2-ene SiH3-Si posited amorphous silicon film ( αSi:H) or microcrys- 20 (SiH3)=Si(SiH3)-SiH(SiH3)-SiH2-SiH3, and mix- talline silicon film (PCSi:H) provides a tandem junc- tures thereof; tion solar cell having efficiencies of 7 - 20 %. and #25. A solar grade amorphous silicon film ( αSi:H) or at least one another additive selected from the microcrystalline silicon film ( PCSi:H) having high mi- group consisting of: crocrystalline fraction deposited using 25 Silane; (f) halogen substituted silenes, selected from hydrogen; the group consisting of; monochlorosilane at least one additive selected from the group con- SiH3Cl, dichlorosilane SiH2Cl2, trichlorosilane sisting of: SiHCl3, tetrachlorosilane (SiCl4), chlorodisilane 30 SiH3-SiH2Cl, and mixtures thereof; and (a) higher order straight chain silanes, compris- ing; disilane Si2H6, trisilane Si3H8, tetrasilane (g) halogen containing gases, selected from the Si4H10, pentasilane Si5H12, hexasilane Si6H14, group consisting of; chlorine Cl 2, hydrogen chlo- heptasilane Si7H16, octasilane Si8H18, nonasi- ride HCl, chlorine trifluoride ClF 3, nitrogen triflu- lane Si9H20, decasilane Si10H22 and mixtures 35 oride NF3, fluorine F2, hydrogen fluoride HF, thereof; bromine Br2, hydrogen bromide HBr, Hl and mixtures thereof. (b) higher order branched silanes, comprising; 2-silyl-trisilane SiH3-Si(H)(SiH3)-SiH3, 2,2-disi- #19. Amethod of depositionfor an amorphous silicon lyl-trisilane SiH3-Si(SiH3)2-SiH3, 2-silyl-tetrasi- 40 film (αSi:H) or a microcrystalline silicon film (PCSi: lane SiH3-Si(H)(SiH3)-SiH2-SiH3, 2,3-disilyltet- H) according to #18, wherein the silane used is at 5 rasilane SiH3-SiH(SiH3)-SiH(SiH3)-SiH3, 2,2- to 10 %, the at least one additive used is at 0.01 to disilyltetrasilane SiH3-Si(SiH3)2-SiH2-SiH3, 3- 5 %, and at least one another additive is used at 0.01 silylpentasilane 3 SiH-SiH2-SiH(SiH3)-SiH2- to 5 %, and the rest is hydrogen. SiH3, 2-silylpentasilane SiH3-SiH(SiH3)-SiH2- 45 #20. Amethod of depositionfor an amorphous silicon SiH2-SiH3, 2,3-disilylpentasilane SiH3-SiH film (αSi:H) or a microcrystalline silicon film (PCSi: (SiH3)-SiH(SiH3)-SiH2-SiH3, 2,4-disilylpentasi- H) according to #18, wherein the deposition is per- lane SiH3-SiH(SiH3)-SiH2-SiH(SiH3)-SiH3, 2-si- formed at a substrate temperature of 25° -500° C, lylhexasilane SiH3-SiH(SiH3)-(SiH2)3SiH3, 3-si- and pressure of 0.01 torr to15 torr (1.33 to 2000 Pa). lylhexasilane 3-SiH SiH 2-SiH(SiH3)-(SiH2)2 50 #21. Amethod of depositionfor an amorphous silicon SiH3, 2,2-disilylpentasilane SiH3-Si(SiH3)2- film (αSi:H) or a microcrystalline silicon film (PCSi: (SiH2)2-SiH3, 3,3-disilylpentasilane SiH3-SiH2- H) according to #18, wherein the deposition is a proc- Si (SiH3)2-SiH2 -SiH3, 2,2,3-trisilyltetrasilane ess selected from the group consisting of Chemical SiH3-Si(SiH3)2-SiH(SiH3)-SiH3, 2-silylheptasi- Vapor Deposition (CVD), Plasma Enhanced Chem- lane SiH3-SiH(SiH3)-(SiH2)4-SiH3, 3-silylhep- 55 ical Vapor Deposition (PECVD), Low Pressure tasilane SiH3-SiH2-SiH(SiH3)-(SiH2)3-SiH3, 4- Chemical Vapor Deposition (LPCVD), Hot Wire silylheptasilane SiH3-(SiH2)2-SiH(SiH3)- Chemical Vapor Deposition (HWCVD), Initiated (SiH2)2-SiH3, 2,2-disilylhexasilane SiH3-Si Chemical Vapor Deposition (ICVD) and Sub Atmos- (SiH3)2-(SiH2)3-SiH3, 2,3-disilylhexasilane

9 17 EP 2 298 955 A1 18

SiH3-SiH(SiH3)- SiH(SiH3)-(SiH2)2-SiH3, 2,4- additive used at 0.01 to 5 %, and the rest being hy- disilylhexasilane SiH3-SiH(SiH3)-SiH2-SiH drogen. (SiH3)-SiH2-SiH3, 2,5-disilylhexasilane SiH3- #27. A solar grade amorphous silicon film ( αSi:H) or SiH(SiH3)-(SiH2)2-SiH(SiH3)- SiH3, 3,3-disilyl- a microcrystalline silicon film (PCSi:H) having high 5 hexasilane SiH3-SiH2-Si(SiH3)2-(SiH2)2-SiH3, microcrystalline fraction according to #25, which was 3,4-disilylhexasilane SiH3-SiH2-SiH(SiH3)- SiH deposited at a substrate temperature of 25° -500° (SiH3)-SiH2-SiH3, 2,2,3-trisilylpentasilane SiH3- C, and pressure of 0.01 torr to15 torr (1.33 to 2000 Si(SiH3)2-SiH(SiH3)-SiH2-SiH3, 2,2,4-trisilyl- Pa). pentasilane SiH3-Si(SiH3)2-SiH2-SiH(SiH3)- #28. A solar grade amorphous silicon film ( αSi:H) or 10 SiH3, 2,3,3-trisilylpentasilane SiH3-SiH(SiH3)- a microcrystalline silicon film (PCSi:H) having high Si(SiH3)2-SiH2-SiH3, 2,3,4-trisilylpentasilane microcrystalline fraction according to #25, which was SiH3-SiH(SiH3)-SiH(SiH3)-SiH(SiH3)-SiH3, deposited with a process selected from the group 2,2,3,3-tetrasilyltetrasilane SiH3-Si(SiH3)2-Si consisting of Chemical Vapor Deposition (CVD), (SiH3)2-SiH3 and mixtures thereof; Plasma Enhanced Chemical Vapor Deposition 15 (PECVD), Low Pressure Chemical Vapor Deposition (c) cyclic silanes, selected from the group con- (LPCVD), Hot Wire Chemical Vapor Deposition sisting of; cyclotrisilane Si3H6, cyclotetrasilane (HWCVD), Initiated Chemical Vapor Deposition Si4H8, cyclopentasilane Si5H10, cyclohexasi- (ICVD) and Sub Atmospheric Chemical Vapor Dep- lane Si6H10, and mixtures thereof; osition (SA-CVD). #29. A solar grade amorphous sil- 20 icon film ( αSi:H) or a microcrystalline silicon film ( PC- (d) silyl substituted cyclic silanes, selected from Si:H) having high microcrystalline fraction according the group consisting of; silyl cyclotetrasilane to#25, which was deposited with a plasma enhanced SiH3-Si4H7, 1,2-disilyl cyclopentasilane chemical vapor deposition process at a plasma pow- 2 (SiH3)2-Si5H8, silyl cyclohexasilane 3- SiH er density ranging from 0.19 -1.6 W/cm and a plas- 25 Si6H11, 1,3-disilyl cyclohexasilane (SiH3)2- ma frequency ranging from 13.56 to 40.68 MHz, at Si6H10, and mixtures thereof; a deposition rate of 10 - 200 Å/sec for amorphous silicon film (αSi:H) and 10- 100 Å/sec for microcrys- (e) silyl substituted silenes, selected from the talline silicon film (PCSi:H). group consisting of; tetrasilene 2- SiH3-SiH= #30. A solar grade amorphous silicon film α(Si:H) 30 SiH-SiH3, 2,3-disilyltetrasil-2-ene SiH3-Si(SiH3) according to #29, which provides an Empirical Micro- * =Si(SiH3)-SiH3, 2,3-disilylpentasil-2-ene SiH3- structure Factor R < 20%, and the microcrystalline Si(SiH3)=Si(SiH3)-SiH2-SiH3, 2,5-disilylhexasil- silicon film P ( CSi:H) having high microcrystalline 2-ene SiH3-Si(SiH3)=SiH-SiH2-SiH(SiH3)- fraction provides a microcrystalline fraction of >40% SiH3, 2,3,4-trisilylhexasil-2-ene SiH3-Si(SiH3) and a dark current activation energy (Eact) of 0.55 - 35 =Si(SiH3)-SiH(SiH3)-SiH2-SiH3, and mixtures 0.65 eV; thereof; wherein the Empirical Microstructure Factor R * is de- * and fined as R = IHSMl at least one additive selected from the group (ILSM +IHSM); consisting of: wherein IHSM and ILsm correspond to the integrated 40 absorption strength of Si-H2, or the High Stretching (f) halogen substituted silenes, selected from Mode (HSM) at 2070-2100 cm-1 and the integrated the group consisting of; monochlorosilane absorption strength of Si-H, or the Low Stretching -1 SiH3Cl, dichlorosilane SiH2Cl2, trichlorosilane Mode (LSM) at 1980-2010 cm . SiHCl3, tetrachlorosilane (SiCl4), chlorodisilane #31. A solar grade amorphous silicon film α(Si:H) 45 SiH3-SiH2Cl, and mixtures thereof; and according to #29, providing a single junction solar cell having efficiencies of 5 -15%, or a tandem junc- (g) halogen containing gases, selected from the tion solar cell having efficiencies of 7 - 20 %; or a group consisting of; chlorine Cl 2, hydrogen chlo- microcrystalline silicon film ( PCSi:H) having high mi- ride HCl, chlorine trifluoride ClF 3, nitrogen triflu- crocrystalline fraction according to #29, providing a 50 oride NF3, fluorine F2, hydrogen fluoride HF, tandem junction solar cell having efficiencies of 7-20 bromine Br2, hydrogen bromide HBr, hydrogen %. iodide Hl and mixtures thereof. #32. A method of deposition for a solar grade amor- phous silicon film (α Si:H) or a microcrystalline silicon #26. A solar grade amorphous silicon film ( αSi:H) or film (PCSi:H) having high microcrystalline fraction a microcrystalline silicon film (PCSi:H) having high 55 as a photoconductive film on a substrate, using microcrystalline fraction according to #25, wherein Silane; the silane was used at 5 to 10 %, the at least one hydrogen; and additive used at 0.01 to 5 %, the at least one another at least one additive selected from the group con-

10 19 EP 2 298 955 A1 20 sisting of: #37. A method of deposition for a solar grade amor- phous silicon film (α Si:H) or a microcrystalline silicon (a) halogen substituted higher order silenes, in- film (PCSi:H) having high microcrystalline fraction cluding; 1,1-dichlordisilane SiHCl 2SiH3, 1,1,1,2- according to #35, wherein the deposited amorphous 5 tetrafluorodislane SiF3-SiH2F, 1,2-dichloro-1,2- silicon film (αSi:H) provides a single junction solar difluorotetrasilane SiHClF-SiClF-SiH2-SiH3, cell having efficiencies of 5 -15%; or the deposited 1,1,1-trichlorotrisilane SiCl3-SiH2-SiH3, 1,1-dif- amorphous silicon film ( αSi:H) or microcrystalline sil- luoro-1,2,2-trichlorosilane 2 SiFCl-SiC2SiH3, icon film (PCSi:H) provides a tandem junction solar chloropentasilane SiH2Cl-(SiH2)3-SiH3, and cell having efficiencies of 7 - 20 %. other compounds of the general formula10 #38. A solar grade amorphous silicon film ( αSi:H) or SiwH2w+2-zXz where X = F, Cl, Br, I; w can be 1 microcrystalline silicon film ( PCSi:H) having high mi- to 20 and z can be 1 to 2w+2; 2-chlorotetrasil- crocrystalline fraction deposited using 2-ene SiH 3-SiCl=SiH-SiH3, 1,1-dichloro-2-fluor- Silane; opentasil-2-ene SiHCl2-SiF=SiH2-SiH2-SiH3, hydrogen; 15 2,3-dichlorotetrasil-2-ene SiH3-SiCl=SiCl-SiH3, at least one additive selected from the group con- and other compounds of the general formula sisting of: SiwH2w-zX’z where X’ = F, Cl, Br, I; and, w can be 2 to 20 and z can be 1 to 2w; and mixtures (a) halogen substituted higher order silenes, in- thereof; and cluding; 1,1-dichlordisilane SiHCl 2SiH3, 1,1,1,2- 20 tetrafluorodislane SiF3-SiH2F, 1,2-dichloro-1,2- (b) halogen substituted cyclic higher order si- difluorotetrasilane SiHCIF-SiCIF-SiH2-SiH3, lanes, selected from the group consisting of; 1,1,1-trichlorotrisilane SiCl3-SiH2-SiH3, 1,1-dif- chlorocyclopentasilane Si5H9Cl, dodecachloro- luoro-1,2,2-trichlorosilane SiF2Cl-SiCl2-SiH3, cyclohexasilane 6Cl12 Si, 1-chioro- chloropentasilane SiH2Cl-(SiH2)3-SiH3, and 25 1fluorocyclopentasilane Si 5H8FCl, and mixtures other compounds of the general formula thereof. SiwH2w+2-zXz where X = F, Cl, Br, I; w can be 1 to 20 and z can be 1 to 2w+2; 2-chlorotetrasil- #33. A method of deposition for a solar grade amor- 2-ene SiH3-SiCI=SiH-SiH3, 1,1-dichloro-2- phous silicon film (α Si:H) or a microcrystalline silicon fluoropentasil-2-ene 30 film (PCSi:H) having high microcrystalline fraction SiHCl2-SiF=SiH2-SiH2-SiH3, 2,3-dichlorotet- according to #32, wherein the silane used is at 5 to rasil-2-ene SiH3-SiCI=SiCI-SiH3, and other 10%, and the at least one additive used is at 0.01 to compounds of the general formula SiwH2w-zX’z 5 %, and the rest is hydrogen. where X’ = F, Cl, Br, I; and, w can be 2 to 20 and #34. A method of deposition for a solar grade amor- z can be 1 to 2w; and mixtures thereof; and phous silicon film (α Si:H) or a microcrystalline silicon 35 film (PCSi:H) having high microcrystalline fraction (b) halogen substituted cyclic higher order si- according to #32, wherein the deposition is a process lanes, selected from the group consisting of; selected from the group consisting of Chemical Va- chlorocyclopentasilane Si5H9Cl, dodecachloro- por Deposition (CVD), Plasma Enhanced Chemical cyclohexasilane Si6Cl12, 1-chloro-1 fluorocy- 40 Vapor Deposition (PECVD), Low Pressure Chemical clopentasilane Si5H8FCl, and mixtures thereof. Vapor Deposition (LPCVD), Hot Wire Chemical Va- por Deposition (HWCVD), Initiated Chemical Vapor #39. A solar grade amorphous silicon film α(Si:H) Deposition (ICVD) and Sub Atmospheric Chemical according to #38 which provides an Empirical Micro- Vapor Deposition (SA-CVD). structure Factor R* < 20%, or a microcrystalline sil- #35. A method of deposition for a solar grade amor- 45 icon film (PCSi:H) having high microcrystalline frac- phous silicon film (α Si:H) or a microcrystalline silicon tion according to #38 which provides a microcrystal- film (PCSi:H) having high microcrystalline fraction line fraction of >40% and a dark current activation according to #32, wherein the deposition is a plasma energy (Eact) of 0.55 - 0.65 eV; enhanced chemical vapor deposition at a plasma wherein the Empirical Microstructure Factor R * is de- 2 50 * power density ranging from 0.19 -1.6 W/cm and a fined as R = IHSM/ (ILSM +IHSM); plasma frequency ranging from 13.56 to 40.68 MHz. wherein IHsM and ILSM correspond to the integrated #36. A method of deposition for a solar grade amor- absorption strength of Si-H2, or the High Stretching phous silicon film (α Si:H) or a microcrystalline silicon Mode (HSM) at 2070-2100 cm-1 and the integrated film (PCSi:H) having high microcrystalline fraction absorption strength of Si-H, or the Low Stretching according to #35, the method having a deposition 55 Mode (LSM) at 1980-2010 cm-1. rate of 10 - 200 Å/sec for amorphous silicon film ( αSi: #40. A solar grade amorphous silicon film ( αSi:H) or H) and 10 - 100 Å/sec for microcrystalline silicon film a microcrystalline silicon film (PCSi:H) having high (PCSi:H). microcrystalline fraction according to #38, wherein

11 21 EP 2 298 955 A1 22

the silane was used at 5 to 10% and the at least one and formation of hydrogenated silicon (Si:H) networks. additive used at 0.01 to 5 %, the rest being hydrogen. Examples of this would be in the metastability of the op- #41. A solar grade amorphous silicon film ( αSi:H) or toelectronic properties in amorphous hydrogenated sili- a microcrystalline silicon film (PCSi:H) having high con which is also known as the Staebler-Wronski Effect microcrystalline fraction according to #38, which was 5 (SWE). Another example would be in the crystallization deposited at a substrate temperature of 25° -500° of Si-Si bonds during microcrystalline Si:H growth. C, and pressure of 0.01 torr to 15 torr (1.33 to 2000 [0027] Infrared (IR) spectroscopy is a commonly ap- Pa). plied analytical technique used to detect the different #42. A solar grade amorphous silicon film ( αSi:H) or bending, wagging, and stretching modes (SM) of hy- a microcrystalline silicon film (PCSi:H) having high 10 drides in amorphous hydrogenated and microcrystalline microcrystalline fraction according to #38, which was silicon. In the bulk layer of amorphous hydrogenated sil- deposited with a process selected from the group icon there are three characteristic absorptions modes; consisting of Chemical Vapor Deposition (CVD), wagging modes at 640 cm -1, a scissors doublet or bend- Plasma Enhanced Chemical Vapor Deposition ing mode at 840-890 cm-1 which is assigned to the di- (PECVD), Low Pressure Chemical Vapor Deposition 15 hyrides, and the stretching modes in the range of (LPCVD), Hot Wire Chemical Vapor Deposition 1895-2130 cm-1. The stretching modes are of great in- (HWCVD), Initiated Chemical Vapor Deposition terest due to the fact that they reflect detailed information (ICVD) and Sub Atmospheric Chemical Vapor Dep- related to the bonding environment of hydrogen in the osition (SA-CVD). film. #43. A solar grade amorphous silicon film ( αSi:H) or 20 [0028] It is well understood that by using IR to analyze a microcrystalline silicon film (PCSi:H) having high amorphous hydrogenated silicon for the Si-H x stretching microcrystalline fraction according to #38, which was modes between 1895-2130 cm -1one can back out ratios deposited with a plasma enhanced chemical vapor of Si-H2 which is also called the High Stretching Mode deposition process at a plasma power density rang- (HSM) at 2070-2100 cm -1 and Si-H which is also call the ing from 0.19 -1.6 W/cm2 and a plasma frequency 25 Low Stretching Mode (LSM) at 1980-2010 cm-1. Amor- ranging from 13.56 to 40.68 MHz, at a deposition phous hydrogenated silicon intrinsic layers with inferior rate of 10 - 200 Å/sec for amorphous silicon film ( αSi: opto-electronic properties typically are dominated by Si- H) and 10-100 Å/sec for microcrystalline silicon film H2 stretching modes. (PCSi:H). [0029] The Empirical Microstructure Factor (R*) is a #44. A solar grade amorphous silicon film α(Si:H) 30 calculation where one can back out ratios of HSM and according to #43, which provides an Empirical Micro- LSM. The Empirical Microstructure Factor is defined as * * structure Factor R < 20%, and the microcrystalline R = IHSMl (ILSM +IHSM) where IHSM and ILSM correspond silicon film P ( CSi:H) having high microcrystalline to the integrated absorption strength of the LSM and fraction provides a microcrystalline fraction of >40% HSM. By definition, the R * value is the fraction or percent 35 * and a dark current activation energy (Eact) of 0.55 - Si-H2 in the film. The smaller the R value is, the less 0.65 eV; percent of Si-H2 is in the film. In general for amorphous wherein the Empirical Microstructure Factor R * is de- hydrogenated silicon to be classified as solar grade ma- * * fined as R = IHSMl terial you need R < 0.2, or less than 20%. (ILSM +IHSM); [0030] Plasma Enhanced Chemical Vapor Deposition 40 wherein IHSM and ILSM correspond to the integrated (PECVD) was used in the present invention to deposit absorption strength of Si-H2, or the High Stretching thin films of αSi:H for single junction solar cells and αSi: Mode (HSM) at 2070-2100 cm-1 and the integrated H and PCSi:H for tandem solar cells , using silane with absorption strength of Si-H, or the Low hydrogen and additives. Stretching Mode (LSM) at 1980-2010 cm-1. #45. A solar grade amorphous silicon film α(Si:H) 45 Deposition of Amorphous Silicon Film (αSi:H) according to #43, which provides a single junction solar cell having efficiencies of 5 -15%, or a tandem [0031] The Empirical Microstructure Factor * (R) in junction solar cell having efficiencies of 7 - 20 %; or amorphous hydrogenated silicon intrinsic layers pro- a microcrystalline silicon film (PCSi:H) having high duced by using Silane (SiH4) and hydrogen can be ma- microcrystalline fraction according to #43, which pro- 50 nipulated by changing the total flow of chemical by vol- vides a tandem junction solar cell having efficiencies ume and power density in a Plasma Enhanced Chemical of 7 - 20 %. Vapor Deposition chamber (PECVD). [0032] Materials used to produce αSi:H and PCSi:H Working Examples based solar cells include from 5 to 10% silane; from 0.9 55 to 1.8% of an additive or additives. Process conditions Deposition of Amorphous Silicon Film (αSi:H) include a substrate temperature of 25° -500° C with pre- ferred temperatures of 150° - 250° C. Process conditions [0026] Hydrogen plays a critical role in the properties include plasma powers from 10 - 10,000 watts, power

12 23 EP 2 298 955 A1 24 densities from 019 W/cm2 to 1.6W/cm2 and chamber Hydrogen was at 91%. The flow rate of the mixture of pressures from 0.01 torr to 15 torr (1.33 to 2000 Pa). SiH4 and trisilane ranged from 0 to 125 sccm; and the [0033] Figure 1 is a graph showing the Empirical Micro- power densities were at 0.197, 0.394, 0.592, 0.789, structure Factor R * of hydrogenated silicon αSi:H depos- 0.987, 1.184, 1.382 and 1.58 W/cm2. 5 ited versus SiH 4 flow rate under different power densities. [0044] Figure 4 shows that as the flow rates of the mix- * The percentage of SiH 4 used was 9.0% and H 2 was 91%. ture of silane and trisilane increased, R value, that is, [0034] The flow rate of the SiH4 ranged from 0 to 125 the % of Si-H 2 in the film decreased to less than 20% for sccm; and the power densities were at 0.197, 0.789, all power densities greater than and equal to 0.789 1.382 and 1.58 W/cm2. W/cm2. This gave the added benefit of increased growth [0035] As the power density increased at lower flow 10 rate with an Empirical Microstructure Factor * R below rate range (see the flow rates < 50 sccm), the Empirical 20% to produce a suitable solar grade material. Microstructure Factors R* tended to be above 20% for [0045] However, the R* values did not reach <20% for all power densities. As the flow rate increased > 50 sccm, the power densities less than and equal to 0.5923 W/cm 2. as power density increased, the Empirical Microstructure This indicated that these films would not be a suitable Factors R* started to decrease for all power densities, 15 solar grade material. except for 0.197 W/ cm 2. However, it’s interesting to point [0046] Thus, to deposit a suitable solar grade silicon out that the Empirical Microstructure Factors R* did not film, both the Empirical Microstructure Factor R* value get below 20% at higher flow rates (100 and 125 sccm) and the deposition rate are important factors. for all power densities, except at 0.789 W / cm2 , which [0047] As shown above in Figure 4, although the dep- led to the conclusion that these films would not produce 20 osition rates were higher at power densities less than a suitable solar grade material. and equal to 0.5923 W/cm2 (comparing with the data [0036] The added value of producing the Empirical shown in Figure 2-no disilane used), however, due to the Microstructure Factors R * below 20% at high power den- higher R* values (>20%), no suitable solar grade films sities and high flow rates was the benefit of increased can be deposited with trisilane as an additive at those growth rates of the intrinsic films. 25 power densities. [0037] Figure 2 is a graph showing the deposition (growth) rate versus SiH 4 flow rate under different power Deposition of Microcrystalline Silicon Film (PCSi:H) densities. The Empirical Microstructure Factor R * for the data was at 10%. The percentage of SiH 4 used was 9.0% [0048] The dual benefit of faster deposition and higher 30 and H2 was 91 %. The flow rate of the SiH 4 ranged from photoconductance can be achieved through the use of 0 to 125 sccm; and the power densities were at 0.197, dual functional additives designed to incorporate the 0.394,0.592, 0.789, 0.987, 1.184, 1.382 and 1.58 W/cm 2. chemical features required to achieve both types of proc- [0038] Figure 2 shows that as flow rates and power ess enhancement. densities were increased, the deposition rates also in- [0049] The enhancement of growth rate and mainte- creased. 35 nance of photoconductivity can be achieved through ad- [0039] Disilane was used as the at least one of addi- dition of at least one higher order silane from groups (a) tives for higher order silanes shown above in group (a). to (e), while by incorporating at least one additional moi- The disilane used ranged from 0.9% to 1.8%. ety from groups (h) and (i), such as a halogen, on the [0040] The deposition rate versus the flow rate of the silane or higher order silane, microcrystaline fraction is mixture of silane with disilane under different power den- 40 increased and the impact of film defects and impurities sities had been shown in figure 3. The percentage of is reduced. disilane was 0.9%, silane was 8.1 %, and hydrogen was [0050] For example, molecules such as monchlorosi- 91%. lane (SiH3Cl or MCS), dichlorosilane (SiH2Cl2), chloro- [0041] The flow rate of the mixture of SiH 4 and disilane disilane (Si2H5Cl2) can be used as the at least one ad- ranged from 0 to 125 sccm; and the power densities were 45 ditional additives, in addition to growth rate enhancing at 0.197, 0.394, 0.592, 0.789, 0.987, 1.184, 1.382 and higher order silane, such as disilane and trisilane to the 2 1.58 W/cm . process yielding higher fractions of microcrystalinity in [0042] By using at least one of these higher order si- the deposited film. lanes as an additive to silane in the deposition process, [0051] PECVD process is used in depositing the mi- the amorphous phase deposition(growth) rate signifi- 50 crocrystalline silicon film (PCSi:H). cantly increased as the flow rate increased at all power [0052] For the data obtained in Figure 5, monchlorosi- densities compared to the neat silane films shown in Fig- lane (SiH3Cl) was used as the at least one additional ure 2. additive, the higher order silanes being represented in [0043] Figure 4 illustrates Empirical Microstructure the Figure by SixHy, wherein x = 2 to 20 and y= 6 to 42. * 55 Factor R as a function of the flow rate of a mixture of [0053] The mixture of the halogenated silane SiH3Cl silane with trisilane at different power densities (the tris- with silane (SiH 4) and higher order silanes (Si XHy) is rep- ilane being used as the at least one additive). The per- resented by (SiH3Cl + SiXHY), wherein x = 2 to 20 and centage of Trisilane was 0.9%, Silane was at 8.1%, and y= 6 to 42. The mole fraction SiH3Cl / (SiH3Cl + SiXHY)

13 25 EP 2 298 955 A1 26 is the ratio of the halogenated silane SiH3Cl (MCS) to fractions from 0.10 to 0.40 of halogenated silanes SiH 3Cl the mixture of the halogenated silane SiH 3Cl with silane / (SiH3Cl + SiXHy), compared to the absence of added (SiH4) and higher order silanes (SiXHy), chlorine. [0054] The flow rate of H 2 ranges from 91 to 99 %, the [0063] As shown in Figure 6, at high chlorine mole frac- 5 flow rate of the mixture ranges from 1% to 9%. The pre- tions > 0.5 , EACT increases as the film transitions from ferred embodiment of the example is (SiH3Cl + SiXHY) microcrystalline to amorphous phase. flows of 1 - 2 % and H2 flows of 98 - 99% based on the [0064] Those results are believed to be attributed to reactor plasma frequency of 13.56 MHz. Cl acting as an impurity scavenger reducing the doping [0055] Those skilled in the art will realize that higher capacity of impurities. The enhancement in photocon- plasma frequencies, such as 40.68 MHz, will permit high- 10 ductivity is realized by shifting the Fermi level to mid band er, relative (SiH3Cl + SiXHY) flows. gap for the enhanced growth rate intrinsic microcrystal- [0056] The film deposition in Figure 5 is performed at line film. 13.56 MHz using 1-9% silane, 1-9% higher order silane, [0065] The shift in Fermi level to the middle of the band and 1-9% SiH3Cl, with total Si containing moieties not gap at ca. 0.6 eV provides the optimal electrical bias for 15 exceeding 9 % ((SiH 4 + SiH 3Cl + Si XHY) < or equal 9 %). a p-i-n type photovoltaic device that is the subject of this The preferred embodiment of the present example is to invention. The electrical bias inherent to the p-i-n struc- use 1-2% silane, 0.1 - 0.2 % higher order silane (Si XHY), ture aids in separation of charge carriers created in the 0.1 - 0.2 % MCS, and with balance being hydrogen. intrinsic Si layer thus leading to higher degree of current [0057] Figure 5 shows the results of the change of the extraction and higher degree of solar cell efficiency. The microcrystalline fraction as the function of the mole frac- 20 use of the appropriate quantity of halogen during depo- tion of SiH3Cl / (SiH3Cl + SiXHY). Applicants have found sition, from 0.1 to 0.4 mole fraction of the silane contain- that all the higher order silanes functioned the same. ing moieties, yields a film that is less impacted from the [0058] When no SiH3Cl is added, the Microcrystalline defects, such as impurity incorporation, that can occur fraction is around 38%. The microcrystalline fraction during higher deposition rates. reaches an optimum value about 51% at approximately 25 [0066] Figures 5 and 6 demonstrate that the use of 0.18 mole fraction of SiH3Cl / (SiH3Cl + SiXHy) %, and higher order silanes and Halogen substituted silanes will trends down until the film becomes amorphous at > 0.5 increase the deposition rate, the microcrystalline fraction, mole fraction. An optimal amount of Cl added to the dep- and enhance the photoconductivity of the film. The osition aids in the nucleation process for microcrystalline present invention has demonstrated that the deposition formation. As more Cl is added the film trends towards 30 of αSi:H and PCSi:H at deposition rates 2- 20 times high- the amorphous phase. The specific mechanisms yielding er than industry averages reported above. These include optimized microcrystaline fractions at a given Cl partial deposition rates for αSi:H of 10 - 200 Å/sec and for PCSi: pressure in the plasma are not fully understood but are H of 2 - 100 Å/sec. suspected of being related to Cl aiding in the microcrys- [0067] The deposited αSi:H films for formation of sin- talline seeding process. Excess Cl disrupts the structured 35 gle junction solar cells had efficiencies of 5 -15 %. The deposition of microcrystalline yielding higher degrees of deposited αSi:H and PCSi:H films for forming tandem amorphous silicon fractions within the deposited film. junction solar cells had efficiencies of 7 - 20 %. Solar cell [0059] Figure 5 clearly indicates that the use of halo- efficiency is defined as: Solar cell efficiency (%) = ( Power gen substituted silanes in addition of higher order silanes out (W) x 100%) / (Area (m2) x 1000 W/m2). These effi- will increase the microcrystalline fraction, providing an 40 ciency improvements were the result of the addition of optimal band gap for the microcrystalline layer of 1.2 eV additives to the deposited films yielding enhanced pho- as part of the tandem solar cell. toconductivity. [0060] The film deposition conditions used in Figure 6 [0068] The foregoing examples and description of the were the same as in Figure 5. embodiments should be taken as illustrating, rather than [0061] Figure 6 shows the dark current activation en- 45 as limiting the present invention as defined by the claims. ergy versus the mole fractions of halogenated silanes As will be readily appreciated, numerous variations and SiH3Cl / (SiH3Cl + SiXHY) %, wherein SiXHY = SiH4 + combinations of the features set forth above can be uti- SixHy wherein x = 2 - 20 and y = 6 - 42. The dark current lized without departing from the present invention as set activation energy is the energy required to generate forth in the claims. Such variations are intended to be charge carriers in the absence of light for deposited mi- 50 included within the scope of the following claims. crocrystalline [0062] As demonstrated in Figure 6, the dark current activation energy (EACT) is impacted by the addition of Claims chlorine to the process. The effect of chlorine addition 55 increases dark current E ACT from 0.2 eV to approximately 1. A method of deposition for an amorphous silicon film 0.6 eV indicating that the effects of chlorine addition are (αSi:H) or microcrystalline silicon film ( PCSi:H) as a reduction of the effects of donor impurities such as oxy- photoconductive film on a substrate, using gen on the deposited microcrystalline film at low mole Silane;

14 27 EP 2 298 955 A1 28 hydrogen; and lanes of the general formula yH Si3y-SixH2x-y at least one additive selected from: where x is 3 to 20 and y is 1 to 2x, and mixtures thereof; (a) higher order straight chain silanes, selected (e) silyl substituted silenes, selected from; 2- tet- 5 from; disilane Si2H6, trisilane Si3H8, tetrasilane rasilene SiH3-SiH=SiH-SiH3, 2,3-disilyltetrasil- Si4H10, pentasilane Si5H12, hexasilane Si6H14, 2-ene SiH3-Si(SiH3)=Si(SiH3)-SiH3, 2,3-disi- heptasilane Si7H16, octasilane Si8H18, nonasi- lylpentasil-2-ene SiH3-Si(SiH3)=Si(SiH3)-SiH2- lane SigH20, decasilane Si10H22, other straight SiH3, 2,5-disilylhexasil-2-ene SiH3-Si(SiH3)- chain silanes of the general formula SixH2x+2 SiH-SiH2-SiH(SiH3)-SiH3, 2,3,4-trisilylhexasil- 10 where x is 2 to 20, and mixtures thereof; 2-ene SiH3-Si(SiH3)=Si(SiH3)-SiH(SiH3)-SiH2- (b) higher order branched silanes, selected SiH3, other silyl substituted silenes of the gen- from; 2-silyl-trisilane SiH3-Si(H)(SiH3)-SiH3, eral formula SiyH3y-SixH2x-y where x is 2 to 20 2,2-disilyl-trisilane SiH3-Si(SiH3)2-SiH3, 2-silyl- and y is 1 to 2x, and mixtures thereof; tetrasilane SiH 3-Si(H)(SiH3)-SiH2-SiH3,2,3- dis- (f) halogen substituted silanes and silenes, se- 15 ilyltetrasilane SiH3-SiH(SiH3)-SiH(SiH3)-SiH3, lected from; 1,1-dichlorodisilane SiHCl2SiH3, 2,2-disilyltetrasilane SiH3-Si(SiH3)2-SiH2-SiH3, 1,1,1,2-tetrafluorodislane SiF3-SiH2F, 1,2- 3-silylpentasilane SiH3-SiH2-SiH(SiH3)- dichloro-1,2-difluorotetrasilane SiHCIF-SiCIF- SiH2-SiH3, 2-silylpentasilane SiH3-SiH(SiH3)- SiH2-SiH3, 1,1,1-trichlorotrisilane SiCl3-SiH2- SiH2-SiH2-SiH3, 2,3- disilylpentasilane SiH 3-SiH SiH3, 1,1-difluoro-1,2,2-trichlorosilane SiF2Cl- 20 (SiH3)-SiH(SiH3)-SiH2-SiH3, 2,4-disilylpentasi- SiCl2-SiH3, chloropentasilane SiH2Cl-(SiH2)3- lane SiH3-SiH(SiH3)-SiH2-SiH(SiH3)-SiH3, 2-si- SiH3, and other compounds of the general for- lylhexasilane SiH3-SiH(SiH3)-(SiH2)3SiH3, 3-si- mula SiwH2w+2-zXz where X = F, Cl, Br, I, w is 1 lylhexasilane SiH3-SiH2-SiH(SiH3)-(SiH2)2- to 20 and z is 1 to 2w+2; and 2- chlorotetrasil-2- SiH3, 2,2-disilylpentasilane SiH3-Si(SiH3)2- ene SiH3-SiCl=SiH-SiH3, 1,1-dichloro-2-fluoro- 25 (SiH2)2-SiH3, 3,3-disilylpentasilane SiH3-SiH2- pentasil-2-ene SiHCl2-SiF=SiH2-SiH2-SiH3, Si (SiH3)2-SiH2 -SiH3, 2,2,3-trisilyltetrasilane 2,3-dichlorotetrasil-2-ene SiH3-SiCl=SiCl-SiH3, SiH3-Si(SiH3)2-SiH(SiH3)-SiH3, 2-silylheptasi- and other compounds of the general formula lane SiH3-SiH(SiH3)-(SiH2)4-SiH3, 3-silylhep- SiwH2w-zX’z where X’ = F, Cl, Br, I, w is 2 to 20 tasilane SiH3-SiH2-SiH(SiH3)-(SiH2)3-SiH3, 4- and z is 1 to 2w; and mixtures thereof; and 30 silylheptasilane SiH3-(SiH2)2-SiH(SiH3)- (g) halogen substituted cyclic silanes, selected (SiH2)2-SiH3, 2,2-disilylhexasilane SiH3-Si from; chlorocyclopentasilane 5H Si9Cl, do- (SiH3)2-(SiH2)3-SiH3, disilylhexasilane 2,3- decachlorocyclohexasilane Si6Cl12, 1-chloro- SiH3-SiH(SiH3) -SiH(SiH3)-(SiH2)2-SiH3, 2,4- 1fluorocyclopentasilane Si5H8FCl, other cyclic disilylhexasilane SiH3-SiH(SiH3)-SiH2-SiH silanes of the general formulaw H Si2w-zX’z 35 (SiH3)-SiH2-SiH3, 2,5-disilylhexasilane SiH3- where X’ = F, Cl, Br, I, w is 3 to 20 and z is 1 to SiH(SiH3)-(SiH2)2-SiH(SiH3)- SiH3, 3,3-disilyl- 2w, and mixtures thereof. hexasilane SiH3-SiH2-Si(SiH3)2-(SiH2)2-SiH3, 3,4-disilylhexasilane SiH3-SiH2-SiH(SiH3)- SiH 2. The method of Claim 1, the method using (SiH3)-SiH2-SiH3, 2,2,3-trisilylpentasilane SiH 3- Silane; 40 Si(SiH3)2-SiH(SiH3)-SiH2-SiH3, 2,2,4-trisilyl- hydrogen; pentasilane SiH3-Si(SiH3)2-SiH2-SiH(SiH3)- at least one additive selected from (a) to (e); SiH3, 2,3,3-trisilylpentasilane SiH3-SiH(SiH3)- and Si(SiH3)2-SiH2-SiH3, 2,3,4-trisilylpentasilane at least one additional additive selected from: SiH3-SiH (SiH3)-SiH (SiH3)-SiH (SiH3)-SiH3, 45 2,2,3,3-tetrasilyltetrasilane SiH3-Si(SiH3)2-Si (h) halogen substituted silenes, selected from; (SiH3)2-SiH3, other branched silanes of the gen- monochlorosilane SiH3Cl, dichlorosilane eral formula SixH2x+2 where x is 4 to 20, and SiH2Cl2, trichlorosilane SiHCl3, tetrachlorosi- mixtures thereof; lane (SiCl4), chlorodisilane SiH3-SiH2Cl, and (c) cyclic silanes, selected from; cyclotrisilane mixtures thereof; and 50 Si3H6, cyclotetrasilane Si4H8, cyclopentasilane (i) halogen containing gases, selected from; Si5H10, cyclohexasilane Si6H10, other cyclic si- chlorine Cl2, hydrogen chloride HCl, chlorine tri- lanes of the general formula SiXH2X where x is fluoride ClF3, nitrogen trifluoride NF3, fluorine 3 to 20, and mixtures thereof; F2, hydrogen fluoride HF, bromine Br2, hydro- (d) silyl substituted cyclic silanes, selected from; gen bromide HBr, hydrogen iodide HI and mix- 55 silyl cyclotetrasilane SiH3-Si4H7, 1,2-disilyl cy- tures thereof. clopentasilane (SiH3)2-Si5H8, silyl cyclohexasi- lane SiH3-Si6H11, 1,3-disilyl cyclohexasilane 3. The method of Claim 1, the method using (SiH3)2-Si6H10, other silyl substituted cyclosi- Silane;

15 29 EP 2 298 955 A1 30

* hydrogen; and fined as R = IHSM / (ILSM +IHSM); at least one additive selected from (f) and (g). wherein IHSM and ILSM correspond to the integrated absorption strength of Si-H2, or the High Stretching 4. The method of Claim 1 or Claim 3, wherein the silane Mode (HSM) at 2070-2100 cm-1 and the integrated used is at 5 to 10 % (v/v), the at least one additive 5 absorption strength of Si-H, or the Low Stretching used is at 0.01 to 5 % (v/v), and the rest is hydrogen. Mode (LSM) at 1980-2010 cm-1.

5. The method of Claim 2 wherein the silane used is at 14. A microcrystalline silicon film ( PCSi:H) deposited us- 5 to 10 % (v/v), the at least one additive used is at ing a method according to any one of claims 1 to 11. 0.01 to 5 % (v/v), the at least one additional additive 10 used is at 0.01 to 5 % (v/v), and the rest is hydrogen. 15. The microcrystalline silicon film P (CSi:H) of claim 14, wherein the film has a microcrystalline fraction 6. The method of any one of the preceding claims, of >40% and a dark current activation energy (Eact) wherein the deposition is performed at a substrate of 0.55 - 0.65 eV. temperature of 25° -500° C, and pressure of 1.33 to 15 2000 Pa (0.01 torr to 15 torr).

7. The method of Claim 6, wherein the substrate tem- perature is at 150° - 250° C. 20 8. The method of any one of the preceding claims, wherein the deposition is a process selected from the group consisting of Chemical Vapor Deposition (CVD), Plasma Enhanced Chemical Vapor Deposi- tion (PECVD), Low Pressure Chemical Vapor Dep- 25 osition (LPCVD), Hot Wire Chemical Vapor Deposi- tion (HWCVD), Initiated Chemical Vapor Deposition (ICVD) and Sub Atmospheric Chemical Vapor Dep- osition (SA-CVD). 30 9. The method of any one of the preceding claims, wherein the deposition is a plasma enhanced chem- ical vapordeposition at a plasmapower density rang- ing from 0.19-1.6 W/cm2 and a plasma frequency ranging from 13.56 to 40.68 MHz. 35

10. The methodof claim 9, wherein the methodis a meth- od for deposition of an amorphous silicon film (αSi: H) at a deposition rate of 10 - 200 Å/sec, or is a method for deposition of a microcrystalline silicon 40 film (PCSi:H) at a deposition rate of 10 - 100 Å/sec.

11. The method of claim 9 or 10, wherein the method is a method for deposition of an amorphous silicon film (αSi:H) to provide a single junction solar cell having 45 efficiencies of 5 -15%; or is a method for deposition of an amorphous silicon film ( αSi:H) or microcrystal- line silicon film ( PCSi:H) to provide a tandem junction solar cell having efficiencies of 7 - 20 %. 50 12. A solar grade amorphous silicon film ( αSi:H) depos- ited using a method according to any one of the pre- ceding claims.

13. The solar grade amorphous silicon film α(Si:H) of 55 claim 12, wherein the film has an Empirical Micro- structure Factor R* less than 20%, wherein the Empirical Microstructure Factor R * is de-

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• US 20090077805 A1 [0003] • US 6855621 B2 [0003] • US 20070298590 A1 [0003] • JP 2005244037 B [0003]

Non-patent literature cited in the description

• A. Hammad et al. Thin Solid Films, 2004, vol. 451-452, 255-258 [0003]

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