CS201111B1 - Method of making the film creating solution - Google Patents

Description

The present invention relates to a process for the production of uranium film-forming solutions for the deposition of phosphorus-infused glassy films as a source for the diffusion of phosphorus into silicon. The invention is applicable in a semiconductor microelectric heater in the manufacture of transistor elements and integral circuits.

Processes for making film-forming solutions that are used to clarify optical products, optical coatings with different reflective properties, illumination and optical filters are known in the literature.

The processes described in the literature consist, for example, in the stepwise mixing of tetraethoxysilane and some organic solvent and water, and then the acid catalyst, mineral acids such as hydrochloric acid, nitric acid in an amount of 0.1 mol / l are added. then leave it to mature for several hours or days.

However, such solutions for coating films as sources of diffusion of donor and aseptor impurities into semiconductor materials are not suitable; they do not contain any corresponding infusion compounds.

It is also known to produce film-forming solutions for infusion of semiconductor materials

201 111 rials with spilled ingredients such as boron, antimony, arsenic and zinc ·

The process consists in dissolving tetramstoxysilane 1 infusion additive, such as triethoxyborane, and a catalyst such as titanium tetrachloride, individually in anhydrous ethanol. The hermetically sealed container is aged for about 48 hours.

However, this method of making film-forming solutions is associated with the need to use anhydrous ethanol or some other anhydrous solvent and is complicated. In addition, the solutions thus prepared are highly hygroscopic and contain excess acetic acid, which reduces the stability of the solutions and deteriorates

Yet another method of making film-forming solutions for infusing semiconductor materials with various impurities such as phosphorus is known.

The method consists in adding to the tetraethoxysilane some hydrophilic organic solvent, for example ethanol and water. In this case tetraethoxysilane is added in an amount of about 20% by weight, the amount of water being 7 moles per 1 mol of tetraethoxysilane.

After mixing the ingredients, the solution is allowed to stand for a period of time sufficient to allow the tetraetexysilane to undergo hydrolysis. Then, an infused additive, a chemical compound containing donor or acceptor impurities necessary for diffusion in the production of semiconductor systems, orthophosphoric.

The obtained film-forming solutions are used as follows:

(a) pipette the film-forming solution in an amount not exceeding 1 ml onto the surface of a plate of any semiconductor material, chaining onto a centrifuge;

b) The film-coated semiconductor plate is subjected to a heat treatment at 600 to 650 ° C in air for 30 seconds. · In the heat treatment, the decomposition of the polymeric orthosilicic acid and phosphoric acid esters forms phosphorosilicate glass;

The thickness of the obtained film can be controlled in the range of 0.1 to 0.3 µm by changing the spin speed of the centrifuge and the content of infusion ingredients by changing the concentration of infused ingredients in solution. The obtained films are used as diffusion sources in base and partition diffusion processes to form NPN transistor structures. for additional Infusion contact area transistor and other diffusion processes in semiconductor device manufacturing ·

The addition of a relatively large amount of phosphoric acid to the hydrolyzate leads to an active chemical reaction of the components of the solution, resulting in heating of the solution to temperatures where the reaction of hydrolysis and polycondensation of tetraethoxysilane proceeds by one or more orders. Applicability · Such flows are suitable for use within 2 to 3 days, while the possibility of their technical production is virtually impossible ·

The applicability of the solutions and the rapidly changing viscosity in semiconductor technology does not guarantee good reproducibility of the obtained silicon films (depending on the thickness and concentration of the impurities) and consequently leads to insufficient reproducibility of the electrophysical parameters of diffusion structures.

The use of the solutions obtained according to the above processes results in the production of relatively thick, uneven films, which often become cloudy when airborne, delaminated or cracked during diffusion annealing. · The parameters of the devices deteriorate accordingly and the percentage of usable devices decreases.

In addition, the process of manufacturing known solutions consists of two stages which are separated by an interval of several days, which is disadvantageous for the technical production of such solutions on a large scale.

The purpose of the invention is to overcome these disadvantages.

The main object of the present invention was to provide a process which makes it possible to obtain a film-forming solution containing polysiloxane chains of preferably linear configuration, which makes it possible to substantially inhibit the process of forming the solution in solution, increase stability of these solutions, increase reproducibility of electrophysical parameters. excluded on semiconductor materials *

The disadvantages of the above processes have been eliminated according to the invention by preparing a film-forming solution for infusing semiconductor materials by mixing 49.3 to 71.8% by weight of dioxane as a hydrophilic solvent with 4.5 to 13.5% by weight of water, to which is added 3.4 to 6.0% by weight of the infusion additive and finally 10.3 to 6.0%

31.2% by weight of tetraalkoxysilane.

Stable film-forming solutions with a high concentration of orthophosphoric acid can be obtained by the proposed process. · The shelf-life of these solutions guarantees the achievement of reproducible parameters of diffusion structures for three months or more. The films excluded from said solutions have an even thickness and concentration of impurities. No cracks appear after the heat treatment, indicating good adhesion of the deposited films to the semiconductor material. By eliminating the pre-hydrolysis stage of tetraalkoxysilane, the proposed process has been made to meet the technological requirements and is more suitable for production.

To improve the shelf-life of the proposed solutions, whereby said solutions guarantee up to approx. For example, according to the invention, tetraalkoxysilane is added to a mixture of dioxane with water and an infusion mixture cooled to a temperature not exceeding +3 ° C.

One embodiment of the invention consists in adding, after addition of tetraalkoxysilane to the mixture, an amount of 0.005 to 0.04 mol / l hydrochloric acid,

This also increases the stability of the solutions prepared according to the invention.

Other objects and advantages of the invention will become apparent from the detailed description of the process for making film-forming solutions and the examples of the process described below.

It has been found that the simultaneous change in the composition of the film-forming solution and the order of mixing of the ejection components of this solution makes it possible to overcome the inherent disadvantages of the known film-forming solution process for indunding semiconductor materials.

Furthermore, it has been found to be advantageous to add water in an amount of 3 to 5 moles per mole of the film-forming component, tetraalkoxysilane, found to have a beneficial effect on retarding polycondensation in solutions over prolonged storage.

In the process according to the invention, a non-polar or low-polar solvent is dioxane as the hydrophilic organic solvent. This solvent practically does not react with the components of the mixture and does not participate in the polycondensation reaction, which guarantees the stability of the solution obtained, as already pointed out above.

In addition, according to the invention it is proposed to add hydrochloric acid to the solution, since this acid slows the polycondensation reaction and stabilizes the solution.

A change in the order of mixing of the components of the obtained solution consists in adding orthophosphoric acid to a mixture of a hydrophilic non-polar organic solvent, dioxane with water, thereby causing a large dilution of the orthophosphoric acid with the solvent. This leads to a higher homogeneity of the solution, to equalization of the concentrations of the reactants in the volume. Previous cooling of the mixture to a temperature not exceeding +3 ° C prior to addition of tetraalkoxysilane is necessary to lower the temperature when the mixture is self-heating. This cooling slows the polycondensation rate of the obtained solution and increases the stability of the solution.

All of the proposed process changes compared to previously known processes are directed to carrying out the hydrolysis of the hydrolytic polycondensation of tetraalkoxysilane with the participation of orthophosphoric acid under strictly controllable conditions. That is, the inventors have sought to prevent the formation of three-dimensional polysiloxane chains that are prone to rapid formation of spatial structures and irreversible conversion of solution into gel.

It is the object of the present invention to slow down the branching effect of the polysiloxane chains and to virtually prevent the chain crosslinking while maintaining the possibility of forming linear chains that grow in length faster than in space.

It is known that in film-forming solutions prepared according to previously known methods, the polysiloxane chains grow rapidly in all directions (while trapping the molecules of the polar solvent used), which in turn causes an increase in the viscosity of the film-forming solution. orthophosphorus, and consequently the reproducibility of the diffusion structure parameters decreases.

The process for the production of the film-forming solutions according to the invention is carried out as follows:

201 111

The non-polar organic solvent (diox < n >) is mixed with water in an amount of 3 to 5 moles of water per mole of tetraalkoxysilane. The concentration of water in the solution is from 1.5 to 7 · 5 mol / l, depending on the concentration of tetraalkoxysilane. Less than 1.5 mol / l of water does not guarantee the necessary completeness of the hydrolysis. An amount of water greater than 7.5 mol / l results in a strong increase in viscosity and a decrease in solution stability.

To the solvent / water mixture is added orthophosphoric acid (d 1.69) in an amount as required by the technological instructions. In the semiconductor device technology, film-forming solutions containing orthophosphoric acid in the orthophosphoric acid / tetraalkoxysilane molar ratio of from 0.36 to 1.28, preferably from 0.57 to 0.86, are used for the emitter diffusion step.

The mixture of organic solvent and water with orthophosphoric acid is then conveniently cooled in a thermostatic vessel (water and ice) to a temperature to prevent spontaneous heating of the solution when tetraalkoxysilane is added and the temperature of the solution after mixing does not exceed +25 ° C. Indeed, at higher temperatures, the reaction rate of the hydrolytic polycondensation increases strongly. The particular cooling temperature depends on the volume of solvent used and the heat transfer conditions. However, the temperature of the mixture must not exceed +3 ° C prior to the addition of tetraalkoxysilane.

Tetraalkoxysilane, for example tetramethoxytetraethoxy or tetrapropoxysilane, is added to the cooled mixture of organic solvent and water with orthophosphoric acid without interruption of smoothing. The concentration of tetraalkoxysilane in the solution may be in the range of 0.4 to 1.5 mol / l, depending on the desired film thickness. At a concentration of less than 0.4 mol / l, the hydrolytic process proceeds very slowly and films of good quality cannot be obtained from such solutions for a long time. In addition, thin porous films are practically not used in technology. At a concentration greater than 1.5 mol / l, the stability of the solution decreases sharply and the characteristic values of the films also deteriorate.

After mixing tetraalkoxysilane with the other constituents of the solution, make up the volume of the solution with dioxane to the mark (at room temperature) and additionally add hydrochloric acid (d 4 1.19) in an amount of from 0.005 to 0.4 mol / k. The amount of acid depends on the tetraalkoxysilane and water in the solution. This concentration range guarantees stability of the solution on the one hand and does not deteriorate the quality of the deposited films on the one hand (excess acid inhibits the deposition of films from the solution and decreases their adhesion and strength).

The finished solution is stored in a hermetic package after filtration.

The film-forming solutions prepared according to the invention have the following advantages »

The decrease in the water content of the solutions, the replacement of the polar solvent with a non-polar solvent and the addition of hydrochloric acid as a stabilizer, further changing the mixing order and process conditions allow the production of phosphoric acid film forming solutions whose viscosity changes very slowly.

This leads to a significant increase in the stability of the film-forming solutions. The solutions have a reproducibility of diffusion structures of more than 3 months at a high concentration of orthophosphoric acid, the transverse reproducibility of the electrophysical properties of the diffusion layers being sufficiently high throughout the storage period. The dispersion of the specific surface resistance of the diffusion layer R is from < = 5% from process to process &lt; 5% &gt; · Films excluded from the solutions have a uniform thickness and concentration of impurities and no cracks appear after heat treatment. This is indicative of an increase in adhesion and masking ability of the solutions obtained, and the density increases as evidenced by the absence of clear pores in the film.

Mean variance

Uniformity according to film thickness ...................................

The uniformity according to conoentraoe is characterized by a slight dispersion of the specific surface resistance of the diffusion layer R. - 3% (after diffusion) above the plate

By eliminating the pre-hydrolysis stage of tetraalkoxysilane (hydrolyzate production), the proposed process better meets the technological requirements and is more suitable for production.

Example 1

In a 100 ml volumetric flask, mix 50 to 55 ml of dioxane and 7,2 ml of deionized water, add 4,7 ml of orthophosphoric acid (85% density d 1,69) and cool the solution ee with stirring ( cold water and ice) to +3 ° C. Thereafter, 22.3 ml of tetraethoxysilane are added under vigorous stirring and without interruption of smoothing. When the temperature of the solution is equal to room temperature, make up the volume of the solution with dioxane to the 100 ml mark, then add 0.15 ml (37%) of hydrochloric acid, mix, filter and seal hermetically. The solution guarantees the production of phosphorus silicon films with a phosphorus pentoxide concentration of about 50% by weight *, which are suitable for performing phosphorus emitter diffusion in integral micro-circuit technology.

The shelf life of the solution is 3 to 4 months.

Example 2

In a 100 ml volumetric flask, mix 50 to 55 ml of dioxane and 7.2 ml of deionized water, add 4.7 ml of orthophosphoric acid (85%) and cool the solution to +1 ° 0 with stirring, then Add 14.3 ml of tetramethoxysilane without interruption. When the temperature of the solution is equal to room temperature, make up the volume of the dio201 solution with 111 xane to the 100 ml mark, then add 0.15 ml (37%) of hydrochloric acid, mix, filter and hermetically seal. The solution guarantees the production of silicon films having a phosphorus pentoxide concentration of about 50% by weight. The shelf life of the solution is about 3 months.

Example 3

In a 100 ml volumetric flask, mix 50 to 55 ml of dioxane and 7.2 ml of deionized water, add 4.7 ml of orthophosphoric acid (85%) and cool the solution to 0 ° 0 with stirring, with stirring and without interruption of cooling, 26.8 ml of tetraprepoxysilane are added. When the temperature of the solution equals room temperature, make up the volume of the solution with dioxane to the 100 ml mark, then add 0.15 (37%) hydrochloric acid, mix, filter and seal hermetically. The solution guarantees the production of phosphorus silicon films having a phosphorus pentoxide concentration of about 50% by weight. The shelf life of the solution is about 3 to 4 months.

Example 4

In a 100 ml volumetric flask, mix 50 to 55 ml of dioxane and 5.4 ml of deionized water, add 4.7 ml of orthophosphoric acid (85%) and cool to -2 ° C with stirring. 22.3 ml of tetraethoxysilane are added without stirring. When the temperature of the solution equals room temperature, make up the volume with dioxane to 100 ml, then add 0.15 ml (37%) of hydrochloric acid, mix, filter and seal. The solution guarantees the production of phosphorus silicon films having a phosphorus pentoxide concentration of about 50% by weight. The shelf life of the solution is about 3 months.

Example 5

In a 100 ml volumetric flask, mix 50 to 55 ml of dioxane and 13,5 ml of deionized water, add 7,05 ml (85%) of orthophosphoric acid and cool to -3 ° C with stirring, then 21.5 ml of tetramethoxysilane are added without stirring. When the temperature of the solution equals room temperature, make up to 100 ml with dioxane, then add 0.15 ml (37%) of hydrochloric acid, mix, filter and hermetically seal. The solution guarantees the production of phosphorous silicon films with phosphorus pentoxide concentration about 50 wt. The shelf life of the solution is about 2 months.

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Example 6

In a 100 ml ee volumetric flask with an emission of 50 to 55 µl dioxane and 4.5 ml of deionized water, add ee 2.35 µl (85%) of orthophosphoric acid, stir the solution and add at a temperature of +3 ° C eet tetraethoxyellan 11.15 ml · Then make up to 100 ml with dioxane, add 0.15 ml (37%) hydrochloric acid, mix, filter and seal. The solution guarantees the production of phosphorus silicon films having a phosphorus pentoxide concentration of about 50% by weight. The shelf life of the solution is one year.

Example 7

50-55 ml of dioxane and 13.5 ml of deionized water are mixed in a 100 ml volumetric flask, 7.05 ml (85%) of orthophosphoric acid are added, the solution is stirred and 33.5 ml of tetraethoxysilane are added at room temperature. Then (after cooling to room temperature) the volume of the solution is made up to 100 ml with dioxane, mixed, filtered and hermetically sealed. The solution guarantees the production of phosphorus silicon films having a phosphorus pentoxide concentration of about 50% by weight. The shelf life of the solution is 1 month.

Example 8

In a 100 ml volumetric flask, mix 50 to 55 ml of dioxane and 13.5 ml of deionized water, add 7.05 µl (85%) of orthophosphoric acid and add 33.5 ml of tetraethoxysilane with stirring at room temperature. The volume of the solution is then made up to 100 ml with dioxane, 0.15 ml (37%) of hydrochloric acid is added, mixed, filtered and sealed. The solution guarantees the production of phosphorus silicon films having a phosphorus pentoxide concentration of about 50% by weight. The shelf life of the solution is 40 days (1.3 months).

Claims (3)

SUBJECT OF THE INVENTION 1. A process for producing a film-forming solution for infusing semiconductor materials by mixing a hydrophilic organic solvent with water, a tetraalkoxysilane of the general formula Si (OR) ₄ , in which R is a C 1 -C 3 alkyl group and an infusion additive, phosphoric acid, characterized in that it is mixed with 49.3 to 201 111 71-8% by weight of dioxane as a hydrophilic solvent with 4-5.5 to 13.5% by weight of water, 3.4-6.0% by weight of the infusion additive and finally 10.3-31.2% by weight of said tetraalkoxysilane are added. 2. The process of claim 1 wherein tetraalkoxysilane is added to the mixture of dioxane, water and the infusion additive at a temperature of between -5 and 3 ° C. 3. A process according to claim 1, wherein, after addition of tetraalkoxysilane, hydrochloric acid is added in an amount of 0.005 to 0.4 mol / l.