Aluminium oxide pastes and process for the use thereof

Abstract

The present invention relates to aluminium oxide pastes and to a process for the use of the aluminium oxide pastes for the formation of Al.sub.2O.sub.3 coatings or mixed Al.sub.2O.sub.3 hybrid layers.

Claims

1. A printable, sterically stabilized paste suitable for the formation of a diffusion-impermeable homogeneous Al.sub.2O.sub.3 coating or a mixed Al.sub.2O.sub.3 hybrid layer, comprising a precursor for the formation of Al.sub.2O.sub.3 and one or more oxides of the elements selected from the group consisting of boron, gallium, silicon, germanium, zinc, tin, phosphorus, titanium, zirconium, yttrium, nickel, cobalt, iron, cerium, niobium, arsenic and lead, and at least one hydrophobic component selected from the group consisting of 1,3-cyclohexadione and salicylic acid and at least one hydrophilic component selected from the group consisting of acetylacetone, dihydroxybenzoic acid and trihydroxybenzoic acid and one or more organic acids and optionally at least one chelating agent selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DETPA), nitrilotriacetic acid (NTA), ethylenediaminetetramethylenephosphonic acid (EDTPA), diethylenetriaminepentamethylenephosphonic acid (DETPPA), and corresponding chelating agents, wherein said paste has an acidic pH of 4-5 and results in residue-free drying.

2. A paste according to claim 1, which is obtained by the introduction of the corresponding precursor into the paste.

3. A paste according to claim 1, which comprises at least one chelating agent.

4. A paste according to claim 1, which comprises at least one hydrophobic component selected from the group consisting of 1,3-cyclohexadione and salicylic acid, and at least one hydrophilic compound selected from the group consisting of acetylacetone, dihydroxybenzoic acid and trihydroxybenzoic acid, and optionally at least one chelating agent selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DETPA), nitrilotriacetic acid (NTA), ethylenediaminetetramethylenephosphonic acid (EDTPA), and diethylenetriaminepentamethylenephosphonic acid (DETPPA).

5. A paste according to claim 1, further comprising a solvent selected from the group consisting of ethanol, isopropanol, diethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, polar solvents, acetone, DMSO, sulfolane and ethyl acetate.

6. A paste according to claim 1, further comprising water for hydrolysis in the molar ratio of water to precursor in the range of 1:1 to 1:9, where the solids content is in the range of 9 to 10% by weight.

7. A diffusion barrier, a printed dielectric, electronic or electrical passivation, an antireflection coating, a mechanical protection layer against wear, a chemical protection layer against oxidation or the action of acid, which has been prepared from a paste according to claim 1.

8. A hybrid material that contains simple and polymeric boron and phosphorus oxides and alkoxides thereof, which has been prepared from a paste according to claim 1.

9. An Al.sub.2O.sub.3 layer as a sodium and potassium diffusion barrier in LCD technology, which has been prepared from a paste according to claim 1.

10. A process for preparing a pure, residue-free, amorphous Al.sub.2O.sub.3 layer on a product, which is a mono- or multicrystalline silicon wafer, sapphire wafer, thin-film solar module, a glass coated with a functional material, which is optionally ITO, FTO, AZO, IZO or the like, an uncoated glass, a steel element or alloy, or a material for microelectronics, comprising applying a paste according to claim 1 to said product and drying at a temperature of 300 to 1000 C.

11. A process according to claim 10, wherein the drying is carried out over the course of less than 5 minutes, giving a layer having a thickness of less than 100 nm.

12. A process according to claim 10 for the production of pure, residue-free, amorphous, structurable Al.sub.2O.sub.3 layer, wherein the drying is carried out at a temperature X, wherein 300 C.<X<500 C.

13. A process according to claim 12, further comprising structuring the layer by HF, H.sub.3PO.sub.4, an organic acid, acetic acid or propionic acid.

14. A process for preparing a pure, residue-free, amorphous Al.sub.2O.sub.3 layer on a product, which is a mono- or multicrystalline silicon wafer, sapphire wafer, thin-film solar module, a glass coated with a functional material, which is optionally ITO, FTO, AZO, IZO or the like, an uncoated glass, a steel element or alloy, or a material for microelectronics, comprising applying a paste according to claim 1 to said product and drying at a temperature above 1000 C., wherein a hard, crystalline layer having comparable properties to corundum is formed.

15. A method for a full-area or local doping of a semiconductor or silicon, comprising applying to said semiconductor or silicon a hybrid material that contains simple and polymeric boron and phosphorus oxides and alkoxides thereof, which has been prepared from a paste according to claim 1.

16. An method for forming an Al.sub.2O.sub.3 layer as a sodium and potassium diffusion barrier barriers in LCD technology, comprising applying a paste according to claim 1 to form said barrier.

17. A printable, sterically stabilized paste suitable for the formation of a diffusion-impermeable homogeneous Al.sub.2O.sub.3 coating or a mixed Al.sub.2O.sub.3 hybrid layer, comprising a precursor for the formation of Al.sub.2O.sub.3 and one or more oxides of the elements selected from the group consisting of boron, gallium, silicon, germanium, zinc, tin, phosphorus, titanium, zirconium, yttrium, nickel, cobalt, iron, cerium, niobium, arsenic and lead, and at least one hydrophobic component selected from the group consisting of 1,3-cyclohexadione and salicylic acid and at least one hydrophilic component selected from the group consisting of acetylacetone, dihydroxybenzoic acid and trihydroxybenzoic acid and one or more organic acids and optionally at least one chelating agent selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DETPA), nitrilotriacetic acid (NTA), ethylenediaminetetramethylenephosphonic acid (EDTPA), diethylenetriaminepentamethylenephosphonic acid (DETPPA), and corresponding chelating agents, wherein said paste has an acidic pH of 4-5 and results in residue-free drying and wherein said paste does not contain corrosive anions NO.sub.3.sup..

18. A paste according to claim 17, further comprising water for hydrolysis in the molar ratio of water to precursor in the range of 1:1 to 1:9, where the solids content is in the range of 9 to 10% by weight.

19. A paste according to claim 17, which comprises at least one chelating agent.

20. A paste according to claim 17, further comprising a solvent selected from the group consisting of ethanol, isopropanol, diethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, polar solvents, acetone, DMSO, sulfolane and ethyl acetate.

Description

FIGURES AND DIAGRAMS

(1) FIG. 1: Photomicrograph of a screen-printed Al.sub.2O.sub.3 layout after drying for 5 minutes at 300 C. (left) and after 10 minutes at 600 C. (right).

(2) FIG. 2: Photomicrograph of an Al.sub.2O.sub.3 layout applied by screen printing after about 1000 pre-prints.

(3) FIG. 3 Change in viscosity of screen-printable aluminium oxide pastes in accordance with Examples 1 and 2

(4) FIG. 4 Charge-carrier lifetimes of p-doped FZ wafer samples in accordance with Example 5

EXAMPLES

Example 1

(5) 4.6 g of salicylic acid and 1.7 g of acetylacetone in 22 ml of diethylene glycol monoethyl ether and 2 g of acetic acid are initially introduced in a 100 ml round-bottomed flask. 14.1 g of aluminium tri-sec-butoxide are added to the solution, and the mixture is stirred for 10 minutes. 2.8 g of water are added for hydrolysis of the partially protected aluminium alkoxide, and the yellow solution is stirred for 10 minutes and left to stand for one day for ageing. The liquid ink is evaporated in a rotary evaporator at a temperature of 50 C. and a pressure of 20 mPa and, after distillation of all the 2-butanol formed from the hydrolysis, kept under these conditions for a further 2 hours. The viscous mass obtained exhibits a viscosity of 4.3 Pas. The resolution of the layout applied by screen printing exhibits slightbleeding of the paste, causing a printed 100 m line to be about 150 m wide after drying.

Example 2

(6) 4.6 g of salicylic acid and 2.5 g of acetylacetone in 28 ml of diethylene glycol monoethyl ether and 1 g of acetic acid are initially introduced in a 100 ml round-bottomed flask. 21.4 g of aluminium tri-sec-butoxide are added to the solution, and the mixture is stirred for 10 minutes. 3.7 g of water are added for hydrolysis of the partially protected aluminium alkoxide, and the yellow solution is stirred for 10 minutes and left to stand for one day for ageing. The viscous ink is evaporated in a rotary evaporator at a temperature of 50 C. and a pressure of 20 mPa and, after distillation of all the 2-butanol formed from the hydrolysis, kept under these conditions for a further 2 hours. The viscous mass obtained exhibits a viscosity of 14 Pas.

Example 3

(7) After cleaning with HF, a multicrystalline silicon wafer is printed with an aluminium oxide paste in accordance with Example 2 by means of screen printing. In order to simulate long-term print loading, about 1000 pre-prints are carried outwit the paste before the actual print. The paste exhibits very good resolution even after this long-term test.

(8) FIG. 2 shows a photomicrograph of an Al.sub.2O.sub.3 layout applied by screen printing after about 1000 pre-prints. The very good resolution even after long-term printing is evident in both pictures (left printed 50 m, after drying about 53 m; right printed 100 m, after drying about 105 m).

Example 4

(9) In order to be able to assess the stability of the paste, the viscosity is investigated over a period of at least 6 weeks. FIG. 3 shows the change in viscosity of a paste in accordance with Examples 1 and 2.

(10) From the viscosity curve, it can be seen that the paste thickens somewhat, especially within the first days after the synthesis, but the viscosity changes only little in the remainder of the storage time (<2% after 3 days). The viscosity can be re-set at any time by addition of a small amount of solvent.

Example 5

(11) After cleaning, a p-doped (100) FZ silicon wafer piece polished on both sides is printed on both sides with an aluminium oxide sol paste in accordance with Examples 1 and 2 by means of screen printing, and each printed side is dried in each case at 450 C. for 30 minutes on a hotplate. The print layout consists of a square with an edge length of 4 cm. The charge-carrier lifetime of the wafer is subsequently investigated by means of a WCT-120 photoconductance lifetime tester (QSSPC, quasi steady-state photoconductance; measurement window 3 cm). The references used are identical wafer samples which are either uncoated or have been treated with the aid of the wet-chemical quinhydrone/methanol process. The quinhydrone/methanol process (mixture of 1,4-benzoquinone, 1,4-benzohydroquinone and methanol) is a wet-chemical and temporarily effective, i.e. non-long-term-stable, electronic surface passivation. All wafer samples are etched (pre-cleaned) in advance by means of dilute HF.

(12) FIG. 4 shows charge-carrier lifetimes of p-doped FZ wafer samples graphically: uncoated sample (yellow, bottom), sample coated with aluminium oxide (blue, middle) and chemically passivated sample (magenta, top). The life-times are, in this sequence (injection density: 1E+15 cm.sup.3, equals carrier density): 8 s, 275 s and >>3000 s.

(13) An increase in the lifetime by a factor of 34 is determined compared with the uncoated sample. The increase in the carrier lifetime is at tributable to the action of the aluminium oxide as electronic surface passivation of the semi-conducting material.

(14) It should be noted in this context that the sample is dried exclusively under ambient conditions. An increase in the carrier lifetime can be expected after treatment of the sample in either an oxygen, oxygen/nitrogen, nitrogen or forming-gas atmosphere (for example in 5% v/v of nH2/95% v/v of N2). Furthermore, edge effects and influences cannot be excluded in the passivation action, and an influence of potential flaws in the front and back coatings cannot be excluded.