USOO958.061 OB2

(12) United States Patent (10) Patent No.: US 9,580,610 B2 Koehler et al. (45) Date of Patent: Feb. 28, 2017

(54) OXIDE PASTES AND PROCESS (52) U.S. Cl. FOR THE USE THEREOF CPC ...... C09D 7/1216 (2013.01); C09D I/00 (2013.01); C09D 5/006 (2013.01); C09D (75) Inventors: Ingo Koehler, Reinheim (DE); Oliver 7/1233 (2013.01); C23C 18/1216 (2013.01); Doll, Dietzenbach (DE); Werner C23C 18/1245 (2013.01); C23C 18/1254 Stockum, Reinheim (DE); Sebastian (2013.01); HOIL 21/2225 (2013.01) Barth, Darmstadt (DE) (58) Field of Classification Search None (73) Assignee: MERCK PATENT GMBH, Darmstadt See application file for complete search history. (DE) (*) Notice: Subject to any disclaimer, the term of this (56) References Cited patent is extended or adjusted under 35 U.S. PATENT DOCUMENTS U.S.C. 154(b) by 99 days. 2008/0090101 A1 4/2008 Klipp et al. (21) Appl. No.: 14/003,467 2009,018951.0 A1 7/2009 Kanamori et al. (Continued) (22) PCT Filed: Feb. 9, 2012 FOREIGN PATENT DOCUMENTS (86). PCT No.: PCT/EP2012/000592 CN 101679.807. A 3, 2010 S 371 (c)(1), EP 1156024 A1 11 2001 (2), (4) Date: Sep. 6, 2013 (Continued)

(87) PCT Pub. No.: WO2012/119686 OTHER PUBLICATIONS PCT Pub. Date: Sep. 13, 2012 International Search Report for PCT/EP2012/000592 (Jun. 28, (65) Prior Publication Data 2013). US 2014/0000481 A1 Jan. 2, 2014 (Continued) (30) Foreign Application Priority Data Primary Examiner – Colin W Slifka (74) Attorney, Agent, or Firm — Millen White Zelano and Mar. 8, 2011 (EP) ...... 11 OO1921 Branigan, PC; Csaba Henter; Anthony Zelano Sep. 6, 2011 (EP) ...... 11 OO7205 (57) ABSTRACT (51) Int. Cl. C09D 7/12 (2006.01) The present invention relates to pastes and HOIL 2L/22 (2006.01) to a process for the use of the aluminium oxide pastes for the C23C 8/2 (2006.01) formation of Al-O coatings or mixed Al-O. hybrid layers. C09D I/00 (2006.01) C09D 5/00 (2006.01) 20 Claims, 2 Drawing Sheets

US 9,580,610 B2 Page 2

(56) References Cited L. Jiang et al., “Adsorption of Salicylic Acid, 5-Sulfosalicylic Acid and Tiron at the Alumina-Water Interface'. Colloids and Surfaces A: U.S. PATENT DOCUMENTS Physicochem. Eng. Aspects, vol. 211, No. 2-3 (Dec. 1, 2002) pp. 165-172. 2010/024.3221 A1 9/2010 Yamasaki et al. 2011/0076505 A1* 3/2011 Ishii ...... C23C 8/10 P.C. Hidber et al., “Influence of the Dispersant Structure on Prop 428,472 erties of Electrostatically Stabilized Aqueous Alumina Suspen sions”, Journal of the European Ceramic Society, vol. 17. No. 2 FOREIGN PATENT DOCUMENTS (1997) pp. 239-249. N. Ozer et al., “Preparation of Amorphous Al2O3 Films by the EP 2085411 A2 8, 2009 EP 2147957 A1 1, 2010 Sol-Gel Process”, Part of the SPIE Conference on Solar Optical JP 06-19129 A T 1994 Materials XVI, SPIE vol. 3789 (Jul 1999) pp. 77-83. JP 2010-254553 A 11 2010 M. Nocun et al., “Sodium Diffusion Barrier Coatings Prepared by TW 200819506 A 5, 2008 Sol-Gel Method”. Optica Applicata, vol. 38, No. 1 (2008) pp. TW 200936,717 A 9, 2009 171-179. Chinese Office Action dated May 15, 2015 issued in corresponding OTHER PUBLICATIONS CN 201280011955.6 application (pp. 1-12). English Abstract of JPH 06-191929 A published Jul. 12, 1994. L. Montanaro et al., “Set up of a Screen-Printing Procedure for the English Abstract of JP 2010-254553 A published Nov. 11, 2010. Production of a B Alumina-Based Gas Sensor'. Journal of Electroceramics, vol. 5, No. 3 (2000) pp. 253-259. * cited by examiner U.S. Patent Feb. 28, 2017 Sheet 1 of 2 US 9,580,610 B2

383.38 : *::::::: U.S. Patent Feb. 28, 2017 Sheet 2 of 2 US 9,580,610 B2

Change in viscosity •Example 1 &Exampl

93

7

Storage time days

E-3

E-4

SE-s

--screen printed A223

1.0E-38 r. ::::::::: of passivated Carries density A in US 9,580,610 B2 1. 2 ALUMNIUM OXDE PASTES AND PROCESS highly promising replacement for SiO2 layers to be obtained. FOR THE USE THEREOF Besides the above-mentioned uses, in which Al-O serves either as diffusion barrier and/or Sol-gel-based doping The present invention relates to aluminium oxide pastes Source, Al2O is also Suitable, owing to the hardness of its and to a process for the use of the aluminium oxide pastes crystalline modifications, for use as mechanical protection for the formation of Al-O coatings or mixed Al-O hybrid layer. layers. Surprisingly, it has now been found that it is possible to The synthesis of Sol-gel-based layers is attaining ever synthesise and formulate paste-form mixtures based on the greater importance in industrial production owing to their Al-O sol-gel process which meet the rheological require variety of possible uses. Thus, the following functional 10 ments of the screen-printing process. Unexpectedly, the layers or Surface finishes and modifications can be built up paste-form mixtures can be applied Surprisingly easily to or carried out by means of Sol-gel technology: silicon wafer Surfaces in the screen-printing process, where antireflection coatings, for example for optical compo they have high structure fidelity. nents and the like For use, in particular in the Solar sector, Sol-gel-based corrosion-protection coatings, for example of Steels and 15 layers have to meet particular requirements, and thus so too the like do the pastes based on them, meaning that these requirement Scratch-protection coatings S also have to be taken into account in the formulation of Surface seals compositions for the production of Such layers. hydrophobisation or hydrophilisation of surfaces On the one hand, Suitable having properties synthesis of membranes and membrane materials which are advantageous for the use. Such as, for example, no synthesis of Support materials for catalytic applications to low toxicity, adequate surface wetting, etc., should be precursors of sinter ceramics and sinter-ceramic compo selected. Furthermore, corrosive anions (Cl or NO, etc.) nents should not be present in the pastes, since they would greatly dielectric layers for electronic and microelectronic com limit the possible uses of the pastes. Corresponding pastes ponents having the following special applications, 25 could, for example, corrode the printing and deposition where the formation of one of the desired functional equipment used, but also later undesirably promote corro ities may be, but does not have to be, linked to specific sion of solder contacts when connecting up Solar cells which heat treatment, such as, for example, in a stream of O, are provided with Such layers, which would consequently N, O/N and/or forming gas: result in limited long-term stability of crystalline silicon spin-on-glass ("SoG) in the manufacture of integrated 30 Solar cells. circuits For the production of screen-printable pastes, the litera dielectric buffer layers between individual metallisa ture only discloses syntheses using rheological additives or tion planes in the manufacture of integrated circuits grinding of metal oxides precipitated by the sol-gel process (“porous MSQ) with Subsequent Suspension of these oxides. However, this printable dielectric layers for printed circuits, printable 35 type of paste production with post-treatment or admixture of electronics in general and printable organic electron rheological additives usually comprises contamination of ics in particular the actual active Substances. diffusion-barrier layers (cf. MERCK SolarFesist patent) Zhou et al. have investigated, for example, the synthesis for semiconductors in general of a CuZnSnS paste. Elemental copper, Zinc, tin and Sulfur for silicon in particular and especially for silicon wafers 40 were ground in a ball mill with addition of . After and in particular for those for the production of Subsequent drying, these were Suspended in isopropanol and crystalline silicon Solar cells mixed with a 10% ethylcellulose mixture in isopropanol. matrices for the binding of dopants (for example B. Ga, P. This mixture was ground again in a ball mill with addition AS, etc.) for the specific full-area and/or local doping of of terpineol, and the alcohol was removed in vacuo. The semiconductors in general 45 resultant viscous mass was employed for screen printing, silicon in particular and especially for silicon wafers and the layers obtained were investigated. {1 Z. Zhou, Y. and in particular for those for the production of Wang, D. Xu, Y. Zhang, Solar Energy Materials and Solar crystalline silicon Solar cells Cells, in press, (2010)} electronic passivation of semiconductor Surfaces in gen Hansch et al. in turn investigated the synthesis of a eral and of silicon Surfaces in particular, which results 50 screen-printable YO/ZrO mixed oxide. A YO/ZrO sol in a considerable reduction in the Surface recombina was obtained by mixing Zirconium n-propoxide stabilised by tion speed. means of acetylacetone and carboxylic acid (acetic acid, This list only represents a selection of the various possible propionic acid, caproic acid, nonanoic acid) in isopropanol applications. and an aqueous yttrium nitrate solution. In order to obtain a Most sol-gel processes known from the literature are 55 screen-printable paste, a calcined YO/ZrO powder was based on the use of silicon and alkoxides thereof (siloxanes), added to this sol (sol/powder 20/80-40/60 wt.%), and this the specific hydrolysis and condensation of which enables mixture was Subsequently ground by means of a ball mill for networks having various properties and coatings which can homogenisation. In the same way, pastes were prepared with be derived therefrom to be synthesised very easily, and addition of organic additives (terpineol or ethylcellulose), Smooth or porous films, or films in which particles are 60 but a paste was also prepared only from the calcined oxide. embedded, can be produced in this way. For certain appli These pastes were investigated for their suitability as elec cations, however, it would be desirable to be able to provide trolytic layer in fuel cells. 2 R. Hansch, M. R. R. coatings having improved properties compared with con Chowdhury, N. H. Menzler, Ceramics International, 35 ventional silicon dioxide layers, such as higher hardness and (2009), 803-811} modified behaviour towards etchants generally employed. 65 Laobuthee et al. obtained an MgAl2O (spinel) paste by By means of a number of experiments, it has been found mixing a ground (K"- or Na-doped) MgAl-O powder that the use of Al-O in corresponding layers enables a formed from a sol-gel synthesis with organic additives US 9,580,610 B2 3 4 (butylcarbitol acetate, terpineol, ethylcellulose). This paste gallium, silicon, germanium, Zinc, tin, phosphorus, titanium, was applied to aluminium oxide Substrates by means of Zirconium, yttrium, nickel, cobalt, iron, cerium, niobium, screen printing. The layers obtained in this way were inves arsenic and lead, where the pastes are obtained by the tigated for their suitability as atmospheric moisture sensors. introduction of corresponding precursors into the paste. {3 A. Laobuthee, N. Koonsaeng, B. Ksapabutr, M. Preference is given to the use of sterically stabilised Panapoy, C. Veranitisagul, International Journal of Materials pastes which are obtained by mixing with at least one & Structural Reliability, 3 (2005), 95-103} hydrophobic component and at least one hydrophilic com Riviere et al. at tempted to optimise a classical SnO. ponent and optionally with at least one chelating agent. screen-printing paste with inorganic thickeners and organic Furthermore, these pastes comprise at least one hydrophobic “vehicles' ( s) and to prepare a “gel ink', which 10 component selected from the group 1.3-cyclohexadione, consists only of active SnO2 (SnO gel obtained from sol-gel salicylic acid and structurally related compounds, and at systems with admixture of SnO powder). These two com least one hydrophilic compound selected from the group positions were investigated with respect to their suitability acetylacetone, dihydroxybenzoic acid and trihydroxyben as CO sensor. The inks without addition of organic and Zoic acid or structurally related compounds thereof, chelat inorganic additives exhibited significantly higher sensor 15 ing agents, such as ethylenediaminetetraacetic acid (EDTA). activity after heat treatment at 600° C. {4 B. Riviere, J.-P. diethylenetriaminepentaacetic acid (DETPA), nitrilotriacetic Viricelle, C. Pijolat, Sensors and Actuators B, 93 (2003), acid (NTA), ethylenediaminetetramethylene-phosphonic 531-537) acid (EDTPA) and diethylenetriaminepentamethylenephos After the classical Sol-gel process, there is no stable state phonic acid (DETPPA) or structurally related complexing between sol (low viscosity <100 mPas) and gel (high agents or corresponding chelating agents. Besides these viscosity >100 Pas) for the production of Al-O layers. The components, the pastes used comprise solvents selected literature only mentions stabilised sols or high-viscosity gels from the group of low-boiling alcohols, preferably selected for the formation of aluminium oxide fibres. from the group ethanol and isopropanol, and at least one Dressler et al. added ASB (Al tri-sec-butoxide) to an high-boiling solvent selected from the group of high-boiling aqueous solution of aluminium nitrate. At high ASB con 25 glycol ethers, preferably selected from the group diethylene centrations, phase separation (2-butanol phase and aqueous glycol monoethyl ether, ethylene glycol monobutyl ether phase) occurred. Polyvinylpyrrolidone was therefore added and diethylene glycol monobutyl ether or mixtures thereof, as binder. The rheology of the resultant sols and the chemical and optionally polar solvents selected from the group structure were investigated by means of NMR, and the acetone, DMSO, sulfolane and ethyl acetate, or similar polar correlating particle sizes were measured. 5 M. Dressler, 30 Solvents. Particularly advantageous is the use according to M. Nofz, J. Pauli, C. Jäger, Journal of Sol-Gel Science and the invention of corresponding pastes which have an acidic Technology (2008) 47, 260-267 pH in the range 4-5 and comprise, as acids, one or more Furthermore, Glaubitt et al. modified ASB firstly by organic acids, preferably acetic acid, which result in residue means of glycol ether and Subsequently by means of propi free drying. Particular preference is given to the use of these onic acid. After addition of 0.5 mol of water per mol of 35 pastes for the formation of impermeable, homogeneous aluminium, the viscosity increased rapidly (>2000 Pas), layers, to which water for hydrolysis is added in the molar while a clear sol(/gel) remained. The gel exhibited long ratio of water to precursor in the range from 1:1 to 1:9, stability, and long fibres could be drawn therefrom. The sol preferably between 1:1.5 and 1:2.5, where the solids content was investigated by means of Al-NMR before each modi is in the range 9 to 10% by weight. In particular, these pastes fication, and the drying was investigated by means of TGA. 40 can be used for the production of a diffusion barrier, a {6 W. Glaubitt, D. Sporn, R. Jahn, Journal of Sol-Gel printed dielectric, electronic and electrical passivation, an Science and Technology, 2 (1994), 525-528} antireflection coating, a mechanical protection layer against Shojaie-Bahaabad et al. in turn investigated the formation wear or a chemical protection layer against oxidation or the of YO/Al2O (YAG) sols. Yttrium oxide was dissolved in action of acid. These pastes are furthermore suitable for the aqueous HC1. AlCls and slowly aluminium powder were 45 preparation of hybrid materials comprising simple and poly added to this solution. This solution was heated at 98°C. for meric boron and phosphorus oxides and alkoxides thereof 6 h in order to dissolve the aluminium powder. The sol for the full-area and local doping of semiconductors, pref obtained was investigated rheologically for its gel behaviour erably silicon, or for the production of Al-O layers as as a function of the Al powder to AlCls content and the Y.O. Sodium and potassium diffusion barriers in LCD technology. and H2O/HC1 content. Fibres were spun from the gels 50 The present invention also relates, in particular, to a (mid-2000 Pas), and these were investigated by means of SEM process for the production of pure, residue-free, amorphous and XRD. {7 M. Shojaie-Bahaabad, E. Taheri-Nassaj, R. Al-O layers on mono- or multicrystalline silicon wafers, Naghizadeh, Ceramics International, 34 (2008), 1893-1902} Sapphire wafers, thin-film Solar modules, glasses coated with Object: functional materials (for example ITO, FTO, AZO, IZO or The object of the present invention is therefore to develop 55 the like), uncoated glasses, steel elements and alloys, and on and Stabilise a screen-printable aluminium oxide paste while other materials used in microelectronics, in which, after avoiding interfering, highly corrosive anions. Such as, for application of the paste, the drying is carried out at tem example, chloride and nitrate, and further rheological addi peratures between 300 and 1000° C., preferably at 300 to tives, which can result in the introduction of further impu 400° C., particularly preferably at 350° C. rities, where the long-term stability of the paste should 60 Drying and heat treatment of the printed-on pastes at simultaneously be retained. temperatures from 1000° C. forms hard, crystalline layers Subject-Matter of the Invention having comparable properties to corundum. The object is achieved by the use of printable, sterically Application of a Suitable amount of paste per unit area stabilised pastes for the formation of Al-O coatings and also gives, over the course of a drying time of less than minutes, mixed Al-O. hybrid layers. Pastes according to the invention 65 a layer thickness of less than 100 nm. The process according comprise precursors for the formation of Al2O and one or to the invention preferably enables pure, residue-free, amor more oxides of the elements selected from the group boron, phous, structurable Al2O3 layers to be produced if, after US 9,580,610 B2 5 6 application of a thin layer of paste, the drying is carried out aliphatic, Saturated and unsaturated, mono- to polybasic, at temperatures between 300 and 500° C. Correspondingly functionalised and non-functionalised alcohols, produced layers which have been dried at temperatures Such as methanol, ethanol, propanol, butanol, amyl <500° C. can be etched by most mineral acids, but prefer alcohol, propargyl alcohol and homologues having ably by HF and HPO, and by many organic acids, such as Cs10 acetic acid or propionic acid, or post-structured. Such as alkylated, secondary and tertiary alcohols with Surprisingly, experiments have shown that it is possible to any desired degree of branching, for example iso synthesise and formulate paste-form mixtures based on the propanol, 2-butanol, isobutanol, tert-butanol and Al-O sol-gel process which meet the rheological require homologues, preferably isopropanol and 2-butanol 10 Such as glycol, pinacols, 1,2-propanediol. 1,3-propane ments of the screen-printing process and can thus be found diol, 1,2,3-propanetriol and further branched homo precisely in the viscosity window which is described above logues and has hitherto not been acquired/occupied. Unexpectedly, Such as monoethanolamine, diethanolamine and tri the paste-form mixtures can be deposited, for example on ethanolamine silicon wafer Surfaces, by means of the screen-printing 15 glycol ethers and condensed glycol ethers, and propylene process on the one hand Surprisingly easily and on the other glycol ethers and condensed propylene glycol ethers, hand very well with retention of high structure fidelity, and branched homologues thereof, corresponding to the screen definition or characteristic used Such as methoxyethanol, ethoxyethanol, propoxyetha for printing, as shown by the examples given below. Cor nol, butoxyethanol, pentoxyethanol, phenoxyethanol responding aluminium oxide pastes form impermeable, i.e. and others diffusion-impermeable or -resistant, Smooth layers on the diethylene glycol, diethylene glycol monomethyl ether, Surface of silicon wafers. This means that, on combined diethylene glycol monoethyl ether, diethylene glycol drying and heat treatment at below 400° C., the pastes monopropyl ether, diethylene glycol monobutyl formed by a sol-gel process form stable and Smooth layers ether, diethylene glycol monopentyl ether, diethyl which are free from organic contaminants after drying and 25 ene glycol dimethyl ether, diethylene glycol diethyl heat treatment. ether, diethylene glycol dipropyl ether, diethylene The present invention thus relates to acidic, sterically glycol dibutyl ether, diethylene glycol dipentyl ether stabilised Al-O pastes having a pH in the range 4-5, and others preferably having a pH-4.5 , which comprise sterically propylene glycol, methoxy-2-propanol, propylene gly stabilised Al-O precursors with small amounts of polyoxy 30 col monomethyl ether, propylene glycol dimethyl lated Solvents having very good wetting and adhesion prop ether, propylene glycol monoethyl ether, propylene erties on SiO2- and silane-terminated silicon wafer surfaces, glycol diethyl ether, phenoxypropylene glycol and and which result in the formation of homogeneous, imper others. meable, in particular diffusion-impermeable, layers. Suitable polar aprotic solvents can be: FIG. 1 shows a photomicrograph of an Al-O layer 35 dimethyl sulfoxide, Sulfolane, 1,4-dioxane, 1,3-dioxane, according to the invention which has been applied by Screen acetone, acetyl-acetone, dimethylformamide, dimethy printing to a polished (100) silicon wafer and has a layer lacetamide, ethyl methyl ketone, diethyl ketone and thickness of 600 nm at the crown. It is apparent to the person others. skilled in the art that the achievable layer thickness is In the case of the use of aluminium alkoxides, the variable through suitable and careful selection and setting of 40 synthesis of the sol furthermore requires the addition of characteristic parameters of the paste used and through the water in order to achieve hydrolysis for the formation of the choice of the screen used for the printing process. aluminium nuclei and precondensation thereof. The water Correspondingly, FIG. 1 shows in the present case a required can be added in Sub- to SuperStoichiometric photomicrograph of a screen-printed Al-O layout after amounts. Substoichiometric addition is preferred. drying for 5 minutes at 300° C. (left) and after 10 minutes 45 The alkoxides liberated on hydrolysis of the aluminium at 600° C. (right). The very good resolution of the line nuclei are converted into the corresponding alcohols by (printed: 500 um, after drying: 500 um) is evident. The addition of an organic acid and/or mixtures of organic acids. splinters within the screen-printed layer presumably arise The acid or acid mixture is added in such a way that a pH through bursting of the layer with a thickness of about 600 in the range between 4-5, preferably <4.5, can be achieved. . 50 In addition, the added acid and/or acid mixture acts as The aluminium sols can be formulated using correspond catalyst for the precondensation and crosslinking commenc ing alkoxides of aluminium as precursors. These can be ing therewith of the aluminium nuclei hydrolysed in the aluminium triethoxide, aluminium triisopropoxide and alu Solution. Suitable organic acids can be: minium tri-sec-butoxide. Alternatively, readily soluble formic acid, acetic acid, acetoacetic acid, trifluoroacetic hydroxides and oxides of aluminium can be employed. All 55 acid, mono-chloro- to trichloroacetic acid, phenoxy organic aluminium compounds which are suitable for the acetic acid, glycolic acid, pyruvic acid, glyoxylic acid, formation of Al-O in the presence of water under acidic Oxalic acid, propionic acid, chloropropionic acid, lactic conditions at a pH in the range from about 4-5 are suitable acid, B-hydroxypropionic acid, glyceric acid, Valeric per se as precursors in paste formulations. acid, trimethylacetic acid, acrylic acid, methacrylic Corresponding alkoxides are preferably dissolved in a 60 acid, vinylacetic acid, crotonic acid, isocrotonic acid, suitable solvent mixture. This solvent mixture may be com glycine and further C.-amino acids, 3-alanine, malonic posed both of polar protic solvents and also polar aprotic acid, Succinic acid, maleic and fumaric acid, malic acid, Solvents, and mixtures thereof. In addition and in accordance tartronic acid, mesoxalic acid, acetylenedicarboxylic with the pre-specified application conditions, the solvent acid, tartaric acid, citric acid, oxalacetic acid, benzoic mixtures can be adapted within broad limits by the addition 65 acid, alkylated and halogenated, nitrated and hydroxy of non-polar solvents, for example in order to influence their lated benzoic acids, such as Salicylic acid, and further wetting behaviour. Suitable polar protic solvents can be: homologues US 9,580,610 B2 7 8 The stabilisation of the aluminium sol can be carried out (2-hydroxyethyl)glycine, bis(2-hydroxyethyl)imino either by means of the above-mentioned organic acids and tris(hydroxymethyl)-methane, N-(tris(hydroxym mixtures thereof, or alternatively achieved or increased by ethyl)methyl)glycine, ethylenediaminetetra-2- the specific addition of complexing and/or chelating addi propanol, N,N-bis(2-hydroxyethyl)-2- tives. Complexing agents for aluminium which can be used aminoethanesulfonic acid, N-(tris(hydroxymethyl) are the following Substances: methyl)-2-aminoethanesulfonic acid, nitrilotriacetic acid, nitrilotris(methylenephosphonic pentaerythritol, N-butyl-2,2'-iminodiethanol, acid). ethylene-diaminetetraacetic acid, ethylenedi monoethanolamine, diethanolamine, trietha aminetetrakis(methylenephos-phonic acid), diethylene nolamine, acetylacetone, 1.3-cyclohexanedione. glycol diaminetetraacetic acid, diethylene-triaminepen 10 Furthermore, it is possible to employ substituted (for taacetic acid, diethylene glycol triaminetetrakis(meth example alkylated, halogenated, nitrated, Sulfonated, ylene-phosphonic acid), carboxylated) homologues and derivatives of the diethylenetetraminepentakis(methylenephosphonic above-mentioned complexing and chelating agents, acid), triethylene-tetraminehexaacetic acid, triethyl and salts thereof, preferably ammonium salts and com enetetraminehexakis(methylene-phosphonic acid), 15 plexing and chelating agents which are able to coordi cyclohexanediaminetetraacetic acid, cyclohexane nate Al. diaminetetrakis(methylenephosphonic acid), Furthermore, further additives can be added to the alu etidronic acid, imino-diacetic acid, iminobis(meth minium Sol for specific setting of desired properties, which ylenephosphonic acid), hexamethylene-diaminetet can be, for example, Surface tension, Viscosity, wetting rakis(methylenephosphonic acid), methyliminodi behaviour, drying behaviour and adhesion capacity. Such acetic acid, methyliminobis(methylenephosphonic additives can be: acid), dimethyliminoacetic acid, dimethyliminom Surfactants and Surface-active compounds for influencing ethylenephosphonic acid, hydroxyethyliminodi the wetting and drying behaviour, acetic acid, hydroxyethylethylenediaminetetraacetic antifoams and deaerating agents for influencing the drying acid, trimethylene-dinitrilotetraacetic acid, 2-hy 25 behaviour, droxytrimethylenedinitrilotetraacetic acid, maltol, further high- and low-boiling polar protic and aprotic ethylmaltol, isomaltol, kojic acid, mimosine, solvents for influencing the particle-size distribution, mimosinic acid, mimosine methyl ether, 1,2-dim the degree of precondensation, the condensation, wet ethyl-3-hydroxy-4-pyridinone, 1,2-diethyl-3-hy ting and drying behaviour and the printing behaviour, droxy-4-pyridinone, 1-methyl-3-hydroxy-4-pyridi 30 further high- and low-boiling non-polar solvents for influ none, 1-ethyl-2-methyl-3-hydroxy-4-pyridinone, encing the particle-size distribution, the degree of pre 1-methyl-2-ethyl-3-hydroxy-4-pyridinone, 1-propyl condensation, the condensation, wetting and drying 3-hydroxy-4-pyridinone, 3-hydroxy-2-pyridinones, behaviour and the printing behaviour, 3-hydroxy-1-pyridinethiones, 3-hydroxy-2-pyri polymers for influencing the rheological properties (struc dinethiones, lactic acid, maleic acid, D-gluconic 35 tural viscosity, thixotropy, flow point, etc.), acid, tartaric acid, 8-hydroxyquinoline, catechol, particulate additives for influencing the rheological prop 1,8-dihydroxynaphthalene, 2,6-dihydroxynaphtha erties, lene, naphthalic acid (naphthalene-1,8-dicarboxylic particulate additives (for example aluminium hydroxides acid), 3,4-dihydroxynaphthalene, 2-hydroxy-1- and aluminium oxides, silicon dioxide) for influencing naphthoic acid, 2-hydroxy-3-naphthoic acid, dop 40 the dry-film thicknesses resulting after drying, and the amine, L-dopa, desferal or desferriferrioxamine-B, morphology thereof, acetonehydroxamic acid, 1-propyl- and 1-butyl- and particulate additives (for example aluminium hydroxides 1-hexyl-2-methyl-3-hydroxy-4-pyridinone, 1-phe and aluminium oxides, silicon dioxide) for influencing nyl- and 1-p-tolyl- and 1-p-methoxy-phenyl and 1-p- the scratch resistance of the dried films, nitrophenyl-2-methyl-3-hydroxy-4-pyridinone, 45 oxides, hydroxides, basic oxides, alkoxides and precon 2-(2-hydroxyphenyl)-2-oxazoline, 2-(2-hydroxy densed alkoxides of the elements selected from the phenyl)-2-benzoxazole, 2, X-dihydroxybenzoic acid group boron, gallium, silicon, germanium, Zinc, tin, (where X=3, 4, 5, 6), other alkylated, halogenated, phosphorus, titanium, Zirconium, yttrium, nickel, nitrated 2.X-dihydroxybenzoic acids, salicylic acid cobalt, iron, cerium, niobium, arsenic, lead and further and alkylated, halogenated and nitrated derivatives 50 compounds and mixtures thereof which are suitable for thereof. Such as 4-nitro- and 5-nitrosalicyic acid, the formulation of corresponding hybrid sols, enabling 3,4-dihydroxybenzoic acid, other alkylated, haloge all mixed forms resulting therefrom to be possible. In nated, nitrated 3,4-dihydroxybenzoic acids, 2,3,4- particular, these are simple and polymeric oxides, trihydroxybenzoic acid, other alkylated, haloge hydroxides, alkoxides of boron and phosphorus for the nated, nitrated 2,3,4-trihydroxybenzoic acids, 2.3- 55 formulation of formulations which have a doping dihydroxyterephthalic acid, other alkylated, action on semiconductors, in particular on silicon lay halogenated, nitrated 2,3-dihydroxyterephthalic CS. acids, mono-, di- and trihydroxyphthalic acids, and In this connection, it goes without saying that each other alkylated, halogenated, nitrated derivatives print-coating method makes its own requirements of the thereof, 2-(3', 4'-dihydroxyphenyl)-3,4-dihydro-2H 60 paste to be printed and/or of the paste resulting from a 1-benzopyran-3,5,7-triol (componentfrom tannin), corresponding ink. Depending on the particular printing malonic acid, oxydiacetic acid, oxal-acetic acid, tar method, the individual parameters to be set for the paste tronic acid, malic acid, Succinic acid, hippuric acid, relate to the surface tension, the viscosity and the total glycolic acid, citric acid, tartaric acid, acetoacetic vapour pressure of the paste. acid, ethanolamines, glycine, alanine, B-alanine, ala 65 Apart from their use for the production of scratch-pro ninehydroxamic acid, C.-aminohydroxamic acids, tection and corrosion-protection layers, for example in the rhodotorulic acid, 1,1'1"-nitrilo-2-propanol, N.N-bis production of components in the metal industry, the print US 9,580,610 B2 10 able pastes can preferably be used in the electronics industry, Al-O (hybrid) layers which have been dried at tempera and in particular here in the manufacture of microelectronic, tures <500° C. can be etched using most inorganic mineral photo-voltaic and microelectromechanical (MEMS) compo acids, but preferably using HF or HPO, but also by many nents. Photovoltaic components in this connection are taken organic acids, such as acetic acid, propionic acid and the to mean, in particular, Solar cells and modules. Thus, the 5 like. Simple post-structuring of the layers obtained is thus pastes according to the invention can be used for the possible. manufacture of thin-film solar cells from thin-film solar Suitable substrates for the coating with the pastes accord modules, the production of organic Solar cells, the produc ing to the invention are mono- or multicrystalline silicon tion of printed circuits and organic electronics, the produc wafers (cleaned with HF or RCA), sapphire wafers, thin-film tion of display elements based on the technologies of 10 thin-film transistors (TFTs), liquid crystals (LCDs), organic Solar modules, glasses coated with functional materials (for light-emitting diodes (OLEDs) and contact-sensitive capaci example ITO, FTO, AZO, IZO or the like), uncoated glasses, tive and resistive sensors. steel elements and alloys, especially in the automobile The present invention thus also consists in the provision sector, and other Surfaces used in microelectronics. of printable, sterically stabilised pastes for the formation of 15 In accordance with the substrates selected, the layers Al-O coatings and also mixed Al-O hybrid layers. formed through the use of the pastes according to the Suitable hybrid materials are mixtures of Al-O with the invention can serve as diffusion barrier, printable dielectric, oxides of the elements boron, gallium, silicon, germanium, electronic and electrical passivation, antireflection coating, Zinc, tin, phosphorus, titanium, Zirconium, yttrium, nickel, mechanical protection layer against wear, chemical protec cobalt, iron, cerium, niobium, arsenic and lead, where the tion layer against oxidation or the action of acid. pastes are obtained by the introduction of the corresponding The pastes according to the invention which are described precursors into the paste. Steric stabilisation of the pastes is here can be deposited in a simple manner on semiconducting effected here by mixing with hydrophobic components, such materials, preferably on silicon, and particularly preferably as 1.3-cyclohexadione, Salicylic acid and structural relatives, on silicon wafers, where they induce electronic Surface and moderately hydrophilic components, such as acetylac 25 passivation after corresponding treatment. This already etone, dihydroxybenzoic acid, trihydroxybenzoic acid and increases the charge-carrier lifetime, i.e. after application of structural relatives thereof, or with chelating agents, such as a thin layer of paste and Subsequent drying. If not only ethylenediamine-tetraacetic acid (EDTA), diethylenetri drying, but also so-called heat treatment is carried out at a aminepentaacetic acid (DETPA), nitrilo-triacetic acid temperature in the range 350-550° C., either in an oxygen, (NTA), ethylenediaminetetramethylenephosphonic acid 30 oxygen/nitrogen, nitrogen or forming-gas stream (for (EDTPA), diethylenetriaminepentamethylenephosphonic example 5% V/v of H/95% V/v of N), the surface passi acid (DETPPA) and structurally related complexing agents vation of the underlying layer can be greatly increased. or chelating agents. Pastes according to the invention in the form of hybrid Solvents which can be employed in the pastes are mix materials comprising simple and polymeric boron and phos tures of at least one low-boiling alcohol, preferably ethanol 35 phorus oxides and alkoxides thereof can be used for the or isopropanol, and at least one high-boiling glycol ether, inexpensive full-area and local doping of semiconductors, preferably diethylene glycol monoethyl ether, ethylene gly preferably silicon, especially in the electrical and electronics col monobutyl ether or diethylene glycol monobutyl ether, industry in general, and in the photovoltaics industry, in or a suitable pure glycol ether. However, other polar media, particular in the production of crystalline silicon Solar cells such as acetone, DMSO, sulfolane or ethyl acetate and the 40 and Solar modules. like, can also be used. The coating property can be matched The pastes according to the invention are printable, and to the Substrate through its mixing ratio. formulations and rheological properties thereof can be Addition of acids establishes an acidic pH in the pastes. matched within broad limits to the needs necessary in each The pastes for precondensation are therefore in an acidic case of the printing method to be used. These pastes are medium (pH 4-5). The acids used for adjustment of the pH 45 preferably printed by means of flexographic and/or screen can be organic acids, preferably acetic acid, which result in printing, particularly preferably by means of screen printing. residue-free drying. The pastes according to the invention in the form of For the formation of the desired impermeable, homoge hybrid sols comprising Al2O/BO can be employed for the neous layer, water for hydrolysis is added, where the molar specific doping of semiconductors, preferably of silicon ratio of water to precursor is between 1:1 and 1:9, preferably 50 wafers. Silicon wafers which can be employed for this between 1:1.5 and 1:2.5. purpose have preferably been cleaned with the RCA or an In order to prepare the pastes according to the invention, alternative comparable cleaning sequence. Suitable wafer the layer-forming components are employed in a ratio to one surfaces may be in hydrophilically or hydrophobically ter another such that the solids content of the pastes is between minated form. Simplified cleaning is preferably carried out 9 and 10% by weight. 55 before application of the Al-O layer; the wafers to be Suitable formulation of the compositions gives pastes treated are preferably cleaned and etched by means of HF having a storage stability of >3 months, where no detectable Solutions. The layer remaining on the wafer after the doping changes in the pastes with respect to viscosity, particle size process can be removed simply by means of etching in dilute or coating behaviour are detectable within this time. HF. The residue-free drying of the pastes after coating of the 60 Al-O layers produced in this way can be used as Sodium surfaces results in amorphous Al-O layers, where the dry and potassium diffusion barrier in LCD technology. A thin ing is carried out at temperatures between 300 and 1000°C., layer of Al-O on the cover glass of the display here can preferably at about 350° C. On suitable coating, the drying prevent diffusion of ions from the cover glass into the takes place within <5 minutes. If the drying is carried out liquid-crystalline phase, enabling the lifetime of the LCDs to under so-called heat-treatment conditions above 1000° C., 65 be increased considerably. hard, crystalline layers form which have a comparable The present description enables the person skilled in the structure to corundum. art to use the invention comprehensively. Even without US 9,580,610 B2 11 12 further comments, it is therefore assumed that a person aluminium alkoxide, and the yellow solution is stirred for 10 skilled in the art will be able to utilise the above description minutes and left to stand for one day for ageing. The Viscous in the broadest scope. ink is evaporated in a rotary evaporator at a temperature of If anything should be unclear, it goes without saying that 50° C. and a pressure of 20 mPa and, after distillation of all the cited publications and patent literature should be con the 2-butanol formed from the hydrolysis, kept under these Sulted. Accordingly, these documents are regarded as part of conditions for a further 2 hours. The viscous mass obtained the disclosure content of the present description. exhibits a viscosity of 14 Pas. For better understanding and in order to illustrate the invention, two examples are given below which are within Example 3 the scope of protection of the present invention. These 10 examples also serve to illustrate possible variants. Owing to After cleaning with HF, a multicrystalline silicon wafer is the general validity of the inventive principle described, printed with an aluminium oxide paste in accordance with however, the examples are not suitable for reducing the Example 2 by means of screen printing. In order to simulate Scope of protection of the present application to these alone. long-term print loading, about 1000 pre-prints are carried Furthermore, it goes without saying to the person skilled 15 outwit the paste before the actual print. The paste exhibits in the art that, both in the examples given and also in the very good resolution even after this long-term test. remainder of the description, the component amounts pres FIG. 2 shows a photomicrograph of an Al-O layout ent in the compositions always add up only to 100% by applied by screen printing after about 1000 pre-prints. The weight or 100 mol %, based on the composition as a whole, very good resolution even after long-term printing is evident and cannot exceed this, even if higher values could arise from the per cent ranges indicated. Unless indicated other in both pictures (left printed 50 lum, after drying about 53 wise, '% data are regarded as % by weight or mol %, with the um; right printed 100 um, after drying about 105 um). exception of ratios, which are given in Volume data. The temperatures given in the examples and description Example 4 25 and in the Claims are always in C. In order to be able to assess the stability of the paste, the FIGURES AND DIAGRAMS Viscosity is investigated over a period of at least 6 weeks. FIG. 3 shows the change in viscosity of a paste in accor FIG. 1: Photomicrograph of a screen-printed Al-O layout dance with Examples 1 and 2. after drying for 5 minutes at 300° C. (left) and after 10 30 From the viscosity curve, it can be seen that the paste minutes at 600° C. (right). thickens somewhat, especially within the first days after the FIG. 2: Photomicrograph of an Al-O layout applied by synthesis, but the Viscosity changes only little in the remain screen printing after about 1000 pre-prints. der of the storage time (<2% after 3 days). The viscosity can FIG. 3 Change in viscosity of screen-printable aluminium be re-set at any time by addition of a small amount of oxide pastes in accordance with Examples 1 and 2 35 solvent. FIG. 4 Charge-carrier lifetimes of p-doped FZ wafer samples in accordance with Example 5 Example 5 EXAMPLES After cleaning, a p-doped (100) FZ silicon wafer piece 40 polished on both sides is printed on both sides with an Example 1 aluminium oxide Sol paste in accordance with Examples 1 and 2 by means of screen printing, and each printed side is 4.6 g of salicylic acid and 1.7 g of acetylacetone in 22 ml dried in each case at 450° C. for 30 minutes on a hotplate. of diethylene glycol monoethyl ether and 2 g of acetic acid The print layout consists of a square with an edge length of are initially introduced in a 100 ml round-bottomed flask. 45 4 cm. The charge-carrier lifetime of the wafer is subse 14.1 g of aluminium tri-sec-butoxide are added to the quently investigated by means of a WCT-120 photoconduc solution, and the mixture is stirred for 10 minutes. 2.8 g of tance lifetime tester (QSSPC, quasi steady-state photocon water are added for hydrolysis of the partially protected ductance; measurement window 3 cm). The references used aluminium alkoxide, and the yellow solution is stirred for 10 are identical wafer samples which are either uncoated or minutes and left to stand for one day for ageing. The liquid 50 have been treated with the aid of the wet-chemical quinhy ink is evaporated in a rotary evaporator at a temperature of drone/methanol process. The quinhydrone/methanol process 50° C. and a pressure of 20 mPa and, after distillation of all (mixture of 1,4-benzoquinone, 1,4-benzohydroquinone and the 2-butanol formed from the hydrolysis, kept under these methanol) is a wet-chemical and temporarily effective, i.e. conditions for a further 2 hours. The viscous mass obtained non-long-term-stable, electronic Surface passivation. All exhibits a viscosity of 4.3 Pas. The resolution of the layout 55 wafer samples are etched (pre-cleaned) in advance by means applied by screen printing exhibits slight"bleeding of the of dilute HF. paste, causing a printed 100 umline to be about 150 um wide FIG. 4 shows charge-carrier lifetimes of p-doped FZ after drying. wafer samples graphically: uncoated sample (yellow, bot tom), sample coated with aluminium oxide (blue, middle) Example 2 60 and chemically passivated sample (magenta, top). The life times are, in this sequence (injection density: 1E+15 cm. 4.6 g of salicylic acid and 2.5g of acetylacetone in 28 ml equals carrier density): 8 us, 275 us and >3000 us. of diethylene glycol monoethyl ether and 1 g of acetic acid An increase in the lifetime by a factor of -34 is deter are initially introduced in a 100 ml round-bottomed flask. mined compared with the uncoated Sample. The increase in 21.4 g of aluminium tri-sec-butoxide are added to the 65 the carrier lifetime is at tributable to the action of the solution, and the mixture is stirred for 10 minutes. 3.7 g of aluminium oxide as electronic Surface passivation of the water are added for hydrolysis of the partially protected semi-conducting material. US 9,580,610 B2 13 14 It should be noted in this context that the sample is dried 8. A hybrid material that contains simple and polymeric exclusively under ambient conditions. An increase in the boron and phosphorus oxides and alkoxides thereof, which carrier lifetime can be expected after treatment of the sample has been prepared from a paste according to claim 1. in either an oxygen, oxygen/nitrogen, nitrogen or forming 9. An Al-O layer as a sodium and potassium diffusion gas atmosphere (for example in 5% V/v of nH2/95% V/v of 5 barrier in LCD technology, which has been prepared from a N2). Furthermore, edge effects and influences cannot be paste according to claim 1. excluded in the passivation action, and an influence of 10. A process for preparing a pure, residue-free, amor potential flaws in the front and back coatings cannot be phous Al-O layer on a product, which is a mono- or excluded. multicrystalline silicon wafer, sapphire wafer, thin-film solar 10 module, a glass coated with a functional material, which is The invention claimed is: optionally ITO, FTO, AZO, IZO or the like, an uncoated 1. A printable, sterically stabilized paste suitable for the glass, a steel element or , or a material for microelec formation of a diffusion-impermeable homogeneous Al-O tronics, comprising applying a paste according to claim 1 to coating or a mixed Al-O hybrid layer, comprising said product and drying at a temperature of 300 to 1000° C. a precursor for the formation of Al-O and 15 11. A process according to claim 10, wherein the drying one or more oxides of the elements selected from the is carried out over the course of less than 5 minutes, giving group consisting of boron, gallium, silicon, germa a layer having a thickness of less than 100 nm. nium, Zinc, tin, phosphorus, titanium, Zirconium, 12. A process according to claim 10 for the production of yttrium, nickel, cobalt, iron, cerium, niobium, arsenic pure, residue-free, amorphous, structurable Al-O layer, and lead, and wherein the drying is carried out at a temperature X, wherein at least one hydrophobic component selected from the 300° C.