~™ mi mi ii ii mi mini ii ii iii (19) J European Patent Office Office europeen des brevets (11) EP 0 759 481 A1 (12) EUROPEAN PATENT APPLICATION (43) Date of publication:ation: (51) |nt. CI.6: C23C 16/40, H01 L 21/316 26.02.1997 Bulletin 1997/09 (21) Application number: 96201647.3 (22) Date of filing : 1 3.06.1 996 (84) Designated Contracting States: • Schuchmann, Shari CH DE FR GB IT LI NL Sunnyvale, CA 94086 (US) (30) Priority: 23.06.1995 US 494616 (74) Representative: Van kan, Johan Joseph Hubert, Ir. et al (71) Applicant: Novellus Systems, Inc. Algemeen Octrooibureau San Jose, CA 951 34 (US) P.O. Box 645 5600 AP Eindhoven (NL) (72) Inventors: • Carl, Daniel A. Mountain View, CA 94040 (US) (54) Method of depositing a stable f luorinated TEOS film (57) A plasma enhanced chemical vapor deposition parallel plate reactor is provided with a dual frequency RF power source. The low frequency RF power source provides more power than the high frequency power source during deposition of a fluorine-doped silicon dioxide film from TEOS, oxygen, and fluorine. The ratio of oxygen partial pressure to TEOS partial pressure is substantially high. The resulting film is stable and has excellent step coverage and planarity. < CO <7> LO o Q_ LU Printed by Rank Xerox (UK) Business Services 2.13.15/3.4 1 EP 0 759 481 A1 2 Description et al, "Low Dielectric Constant Interlayer Using Fluo- rine-Doped Silicon Oxide", Japan. J. Appl Phys., Vol 33, BACKGROUND OF THE INVENTION 1994, pp. 408-412, and T. Matsudada et al., "Dual Fre- quency Plasma CVD Fluorosilicate Glass Deposition for Field of the Invention 5 0.25 urn Interlevel Dielectrics," 1995 DUMIC Confer- ence Proceedings, 1995, pp. 22-28. Good Si-F bond This invention relates to a method of depositing stability is necessary if an F-TEOS film is to be success- material using chemical vapor deposition (hereinafter fully integrated into a the structure of a device such as, "CVD"), and more particularly to a method of depositing for example, a semiconductor device for electronic inte- a fluorine-doped silicon dioxide film from tetraethyl- 10 grated circuits, since free fluorine in the film reacts with orthosilicate (hereinafter "TEOS") using plasma water or other materials in the device to pose potential enhanced chemical vapor deposition (hereinafter reliability concerns. Moreover, water absorption must be "PECVD"). minimized, least the dielectric constant reduction other- wise achieved by incorporation of fluorine into the Si02 Description of Related Art 15 film be counteracted by the polarizability of water and Si-OH in the film. Polarization of water and Si-OH in the As device dimensions continue to decrease, the film can lead to effective dielectric constants greater need for high quality dielectric films that can fill aspect than 4.0 even when fluorine is incorporated into the film. ratios greater than 1:1 becomes more critical. This is Accordingly, what is desired is a production-viable particularly true of the 0.35 urn technologies and 20 intermetal dielectric F-TEOS film that has an equivalent beyond, which demand stringent intermetal dielectric or superior stability to currently available gap fill films so gap fill and lower dielectric constants. that it can be used without requiring barrier or cap films. The term "aspect ratio" means the ratio of the depth of the gap to the width of the gap. A gap 1 1 0 having a SUMMARY OF THE INVENTION 2:1 aspect ratio, for example, is shown in Figure 1 , con- 25 trasted with a gap 120 having a 1 :1 aspect ratio and a Advantageously, the present invention provides a gap 1 30 having a 1 :2 aspect ratio. Figure 2 shows a gap stable fluorine-doped silicon dioxide film having excel- 200 that is filed with an ideally conformal film 202. The lent step coverage and planarity. portion of the film 202 filling the gap 200 contains no In many embodiments, the present invention seams or voids, and the surface of the film 202 is planar. 30 extends gap fill capability to an aspect ratio in excess of Figure 3 shows another gap 300 that is filled with a non- 1.5:1, provides a lower dielectric constant oxide, stabi- conformal film 302. In contrast with film 202, the portion lizes the fluorine in the film, produces a film having min- of the film 302 filling the gap 300 contains a seam 306 imal stress hystersis, achieves excellent particle and and a void 308, and the surface of the film 302 is process reproducibility, simplifies process integration, depressed over the gap 300 (depressed region 304). 35 and extends to processes at or under 0.5 urn. The film 302 is illustrative of the type of a silicon dioxide In one embodiment, the present invention is a film formed from the CVD or the PECVD of silane method of depositing a fluorine-doped silicon dioxide (SiH4), for example. film. A substrate is maintained in a plasma-enhanced PECVD TEOS oxide films have long been used in chemical vapor deposition reactor. A gas mixture com- the VLSI industry as the intermetal dielectric film of 40 prising a TEOS component, an oxygen component, and choice due to superior physical and electrical properties a fluorine component is introduced into the reactor, coupled with excellent conformal deposition. Void-free wherein the ratio of the oxygen partial pressure to the fill using PECVD TEOS has worked well up to and TEOS partial pressure is high. Alternating current including aspect ratios of 0.8:1 in larger than 0.5 urn energy is applied to the gas mixture to excite the gas process integration schemes. However, above aspect 45 mixture into a plasma proximate the substrate. ratios of 0.8:1, conventional PECVD TEOS alone can- In another embodiment, a method of process inte- not be relied upon to provide a void free fill. gration comprises the steps of the aforementioned While fluorinated tetraethylorthosilicate, or F- method and excludes depositing an encapsulation layer TEOS, films have been recognized for their gap fill abil- associated with the film. ities and have attained nearly ideal characteristics, 50 including an effective dielectric constant of below 4.0, BRIEF DESCRIPTION OF THE DRAWINGS the stability of these films has not been entirely satisfac- tory. See, e.g., M.B. Anand etal., "Fully Integrated Back In the drawings, in which like reference characters End of the Line Interconnected Process for High Per- refer to like parts, formance ULSIs," 1994 VMIC Conference Proceedings, 55 June 7, 1994, pp. 15-21; K. Shimokawa, "Fluorine Figure 1 shows cross-sectional views of gaps hav- Doped Si02 with Low Dielectric Constant for Multilevel ing various aspect ratios; Interconnection," Semicon Japan Technical Session Proceedings, December 1, 1993, pp. 211-216; T. Usami Figure 2 is a cross-sectional view of a gap filed with 2 3 EP 0 759 481 A1 4 an ideally conformal film; sus time in a 100% RH, 65 degree Centigrade oven, as found in the high low power study; Figure 3 is a cross-sectional view of a gap filed with a non-conformal film; Figure 17 is a plot of HOH atomic percent for three 5 Si-F content cases versus time in a 100% RH, 65 Figure 4 is a schematic diagram of an illustrative degree Centigrade oven, as found in the high low radio frequency system useful for depositing films power study; in accordance with the present invention; Figure 18 and Figure 19 are expansions of the por- Figure 5 is a schematic diagram of response cubes 10 tion of the FTIR spectrum where SiOH and HOH for the parameters varied in the process factorial of absorbencies were observed for a 2.5% Si-F con- a low power study; tent Hi LF F-TEOS film after boiling in water for 100 minutes, as found in the high low power study; Figure 6 is a plot of the Si-F/Si-0 bond ratio versus 02:C2F6 ratio at a constant low frequency power, 15 Figure 20 is a plot of dielectric constant versus Si- high frequency power, and reactor pressure, as F/Si-0 bond ratios for several illustrative cases; and found in the low power study; Figure 21 is a plot of refractive index versus Si-F/Si- Figure 7 is a plot of stress versus Si-F/Si-0 bond O bond ratios for several illustrative cases. ratio as a function of the percentage of low fre- 20 quency power, as found in the low power study; DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 8 is a plot of all refractive index data points in We have found that key factors to controlling the the factorial analysis versus the Si-F/Si-0 bond film stability in a F-TEOS PECVD process is the energy ratio, as found in the low power study; 25 flux of the ion bombardment divided by the deposition rate, high 02:TEOS mole ratios and low PECVD pres- Figure 9 is a representative gap fill of an aspect sures. The energy flux is controllable by using a high ratio line/space of about 1 .4:1 and a Si-F/Si-0 ratio amount of total power, a high percentage of low fre- of about 2.5%, as found in the low power study;. quency power and, high 02:TEOS mole ratios, and low 30 PECVD pressures. Instead of using dual frequency, a Figure 1 0 is a representative gap fill of an aspect high amount of single frequency power at an optimal ratio line/space of about 1 .4:1 and a Si-F/Si-0 ratio frequency may be used.