RU1791429C - Method of producing parts from pyrolytic boron nitride - Google Patents

Abstract

Purpose: the invention relates to a technology for the manufacture of articles of pyrolytically pure boron nitride of high purity and high quality, used in the form of boats, crucibles and various devices in the production of compounds such as gallium arsenide. SUMMARY OF THE INVENTION: A method for producing articles from pyrolytic nitride of boron involves chemically depositing it on the surface of a graphite substrate by reacting gaseous boron halide and ammonia and removing the graphite substrate by heating in an oxidizing atmosphere. The substrate is made of dense graphite. A product from pyrolytic boron nitride is filled up on all sides with a powder of refractory oxide and graphite is removed at 700 - 900 ° C. Air or a mixture of air with an inert gas is used as the oxidizing atmosphere ohm The method provides 80 - 90% yield of suitable products, makes machining unnecessary. 2 tab.

Description

The invention relates to a technology for the production of high purity and high quality pyrolytic boron nitride products used in the form of boats, crucibles and various devices in the production of semiconductor compounds such as gallium arsenide.

High purity pyrolytic boron nitride (PNB) with excellent corrosion resistance is one practically irreplaceable material for the processes of growing single crystals of semiconductor compounds with a low content of impurities and excellent electrical resistance.

A known method for the synthesis of pyrolytic boron nitride using chemical vapor deposition on the surface

appropriate substrate using boron halide such as boron trichloride and ammonia at as initial components. temperature 1450 - 2300 ° С and pressure up to 50 Torr 1.

Providing peeling conditions; films of pyrolytic boron nitride obtained with. using chemical vapor deposition from the substrate, it is possible to obtain arbitrary-shaped products from PNB / ..- -.-. .; -...; -. . .: -: .. ..

Further, upon separation of the article from the BSS from the substrate, a portion of the backing material remains on the inner surface of the crucible. In this case, during the operation of the obtained crucibles, boats and various devices made of boron nitride during the preparation of semiconductor compounds, there is a month XI

Oh Ј

Yu

| H

This contamination of the semiconductors by the substrate material. .... .....

With known methods, the substrate material from sections of finished products from BSS is removed using sandpaper 2 or using chemical removal methods using acid 3 or oxidative treatment 4. These methods unusually extend the process. This process cannot ensure the complete removal of the residual substrate material, and in addition, since highly pure pyrolytic nitride has a layered structure with a high degree of orientation of the crystalline plane (001 plane), crucible stratification can occur parallel to the surface of the substrate, when using mechanical processing, which It threatens the penetration of the molten metal between the layers and the rapid destruction of the crucible in the evaporator of the molecular beam epitaxy. -...,.

However, by heating crucibles from PNB in an oxidizing atmosphere for a long time at temperatures above 750 ° C, B203 glass can form on open surfaces, which has a significantly higher vapor pressure and chemical activity than boron nitride.

The closest solution to the inventive method is a method for producing porous articles from pyrrleitic boron nitride (PNB), when PNB is deposited on a porous substrate by the reaction of ammonia and boron halide, in particular boron trichloride, and the substrate is then removed 5. About-; the deposition process is carried out at a temperature of 1100, - 200 r ° C, preferably 1700 - 2000 ° C, under reduced pressure below 67 x 10 Ra to obtain the desired amount of PNB, then cooling the substrate with a layer of PNB in a non-oxidizing atmosphere, separating the article from PNB from the substrate. ,; ; ..: ;; .., -. , / h: G,: /

Moreover, a porous carbon foam, such as, for example, carbonized plastic 1 foam, or glassy carbon net, is used as a substrate. which is then removed by oxidation in an oxidizing atmosphere; at a temperature of 500 to 700 ° C, more preferably 700 ° C. ,

This method is inconvenient when working with special grades of graphite; or pyrographite, which is expanded prior to the PNB deposition process for voro to obtain products suitable for use as molecular beam crucibles; single crystal growth:

The purpose of the invention is to obtain products of complex shape from vacuum tight boron nitride.

The essence of the proposed technical solution lies in the fact that products from

arbitrary form pyrolytic boron nitride is obtained by the chemical method. deposition from the gas phase, including boron halide and ammonia, on the surface of the graphite substrate at a temperature of 1800 - 2100 ° C, is cooled, the product is removed from the PNB from the reactor and burned in a furnace. in air, or in an air mixture with inert additives, pre-filled with the product from PNB powder of highly pure refractory oxide.

The proposed method allows to obtain a cleaner surface of products made of pyrolytic nitride boron (see table), prevents the formation of boron oxide and other impurity oxides, reduces the time of oxidative annealing due to the possibility of annealing at higher temperatures. When using this method, the possibility of the formation of no black dots of boron carbide particles, as in the prototype, is excluded. Example 4 in the application descriptions, there is no need for machining the products, resulting in micro-seizures that cannot be removed by grinding with sandpaper. Example 6 of the prototype. Examples of practical use.-.-: -. ;; : (::: ..; -. ..;, -.- :, - - .::

Example 1. A graphite substrate of the desired shape is introduced into a reaction chamber with cooled walls. Heat up

the substrate by microwave radiation up to 1950 ° C; gaseous boron trichloride, ammonia and a nitrogen carrier gas are admitted from above. When maintaining a vacuum of 2 Torr in the furnace and the specified temperature of the substrate

the substrate forms a 0.5 mm thick layer of pyrolytic boron nitride. Then the product, together with the substrate, is slowly cooled, the product is removed from the reactor, visually assess the presence of cracks and fill; angle: p 6 a and | 16: djör g a1ot: thermal, with 1 bm

burning in air to remove carbon

particles and organic pollutants, possible with products from

NSA. The crucible is preliminarily filled with powdered powder AABM, put in a quartz lid a glass that is pre-coated with alumina to prevent the crucible from sticking due to the formation of boron oxide on the surface of the crucible, and then the crucible is completely covered with oxide. Then, the filled crucible is introduced into the furnace and annealed at a temperature of 750 ° C for 30 minutes in an atmosphere of air.

LI me R 2. The product of pyrolytic boron nitride receive similarly

Example 1, only magnesium oxide is used as a refractory oxide, and oxidative annealing is carried out at a temperature of 700 ° C for 40 minutes.

PRI me R 3. Products from PNB receive analogously to example 1 at a pressure in the reactor of 3 Torr and a temperature of 1980 ° C. A layer of pyrolytic boron nitride with a thickness of 0.8 mm is formed. Then the product is cooled, removed from the reactor and subjected to thermal annealing in heli in an atmosphere of a mixture of air with pure argon at a temperature of 800 ° C for 20 minutes.

Example 4. Products from pyrolytic boron nitride are obtained analogously to example 3. Thermal annealing of products from pyrolytic boron nitride is carried out in an atmosphere of a mixture of air with high purity nitrogen at 900 ° C for 15 minutes.

In the table. Figure 1 shows the comparative characteristics of PNB crucibles obtained by the proposed solution and the prototype for molecular beam epitaxy. The values of total boron, free boron, boron oxide and metallic impurities were obtained by atomic absorption analysis.

The relative standard deviation of the determination of microimpurities in the BSS is 0.05-0.10.

This method allows you to increase the number of suitable products by 30-40%, whereas with simple annealing at 500 - 700 ° C, 50% of the products are rejected, and the mechanical removal of carbon residues is strictly contraindicated, as described in the application materials, for scoring of the PNB layered material, which leads to melt flowing under the PN6 layers, destruction of the crucible,

and sometimes to the pollution of the growth chamber. A comparison of yield is given in

. table 2. . ..:. ; ...; ; : :: -: - r m u l a s a t s and -1. A method for producing articles from pyrolytic boron nitride, including its deposition on a graphite forming substrate by reaction of gaseous halide. boron, and ammonia, and removal

graphite substrate by heating in an oxidizing atmosphere, characterized in that, in order to obtain products of complex shape from vacuum-tight boron nitride, the substrates are made of dense

graphite, and their removal is carried out at 700 - 900 ° C in the filling of a powder of refractory oxide .:

2. The method according to p. T, and so on and with the fact that air or its mixture with an inert gas, nitrogen, is used as the oxidizing atmosphere.

Table 1