RU2286616C2 - Method for producing part incorporating silicon substrate whose surface is covered with silicon carbide film - Google Patents

Abstract

FIELD: manufacture of semiconductor materials for semiconductor devices.

SUBSTANCE: proposed method for manufacturing part incorporating silicon substrate with silicon carbide film on its surface includes synthesis of silicon carbide film on substrate surface by joint heating of substrate and carbon-containing material at temperature of 1100 to 1400 °C; used as carbon-containing material is solid material brought in mechanical contact with substrate.

EFFECT: facilitated procedure.

11 cl, 5 dwg

Description

The invention relates to a technology for producing semiconductor materials and can be used to create semiconductor devices.

Silicon carbide has a number of unique properties, such as chemical inertness, thermal stability, high mechanical and thermophysical characteristics [Gnesin G.G. Silicon carbide materials, M., 1977]. According to the electrophysical properties, silicon carbide is a semiconductor material with a band gap of 2.3-3.3 eV (wide-gap semiconductor) and retains the electrophysical characteristics at high temperatures [Silicon carbide as a material of modern optoelectronics and semiconductor technology, M., 1984]. In addition, silicon carbide is very effective as a substrate material for the epitaxial synthesis of promising semiconductor materials (for example, gallium nitride) [USP 6773508, 2004]. All of the above determines a significant interest in silicon carbide and methods for its preparation.

In the technologies for producing silicon carbide and silicon carbide materials, it is possible to single out the production of powders and grains, composites for technical applications (abrasives, heaters, refractories, etc.), as well as block silicon carbide materials, for example, wafers and single crystals with various degrees of structural perfection. These methods are well known [Gnesin G.G. Silicon carbide materials, M., 1977]. Note that the structural features and physicochemical properties of silicon carbide (especially block materials) make its preparation quite expensive and difficult from a technology point of view.

At the same time, for a number of applications, for example, in semiconductor technology, thin films of silicon carbide on various substrates can be used. Among them, silicon substrates are of interest. It is known that silicon is a widely used semiconductor material and its combination with silicon carbide in a single product is considered as very promising [Silicon carbide as a material of modern optoelectronics and semiconductor technology, M., 1984].

Known methods for producing silicon carbide films on various substrates can be divided into two groups. The methods of the first group use physicochemical processes in which silicon for the formation of silicon carbide is fed into the synthesis zone in the form of chemical compounds (hydrides, silicon halides, etc.). That is, use an "external" source of silicon. Another group of methods uses an “internal” silicon source, i.e. the source of silicon atoms forming silicon carbide during the process is the substrate itself, on which silicon carbide grows. In this case, the silicon substrate is used. As will be shown below, our proposed method belongs to this last group.

The formation of a SiC film by chemical reduction is known (US Pat. No. 3,386,866), in which the reaction product CCl ₄ and SiCl ₄ are precipitated in a hydrogen stream at T = 1700-1800 K at normal pressure on an α-SiC substrate (usually 6H-SiC).

Another method (US Pat. No. 3,382,113) precipitates the reaction product of SiH ₄ with propane on a substrate at a pressure of 10 ^-2 mm Hg, with a component ratio of 1.2: 1 and the absence of hydrogen and other carriers.

The method of US Pat. No. 3,520,740 makes it possible to obtain an article with epitaxial layers of α-SiC on an α-SiC substrate using convective heating of a graphite substrate at normal pressure. The film is deposited from a mixture of gases SiH ₄ , C ₃ H ₈ and H ₂ . As a result of pyrolysis in a mixture of gases, silicon carbide vapors are formed which condense on the substrate. Satisfactory film quality is realized in the temperature range 1700-1850 ° C.

The disadvantage of these methods is the complexity of the production technology and hardware design, namely: the need to use silicon hydrides and halides (difficult from the point of view of ecology and safety of reagents), the need to maintain the optimal composition of the components in the gas mixture, the difficulty of implementing the required process conditions in large reactors, where uneven concentration of reagents by volume due to the production of reagents and the allocation of reaction products.

The prior art method according to patent RU 2100870, comprising placing a substrate in a condensation zone of silicon carbide vapor and depositing silicon carbide in a plasma of a high-frequency gas discharge of silicon dioxide, a hydrocarbon compound and water vapor with a mass flow rate of the last 10-30% of the flow rate of the hydrocarbon compound. The method improves the reproducibility of the composition of the film, and the composition of the plasma reduces the influence of fluctuations in the technological parameters on the composition of the formed film of silicon carbide. However, the known technology is expensive and complicated in hardware design.

The prior art method for producing a silicon carbide film, comprising heating a silicon substrate to 1173-1573K in a C ₂ H ₂ hydrocarbon atmosphere (J. Vac. Sci. And Techn. 1970, 7, 490). The substrate material, interacting with a hydrocarbon, forms a carbide film.

It should be noted that the method does not allow to obtain a film of uniform thickness and density due to the impossibility of controlling the diffusion of hydrocarbon in the layers of silicon carbide.

The closest to the claimed solution is the invention according to patent US 6773508, publ. 10/08/2004, class C 30 V 25/04, C 30 V 25/02. The known method includes the following stages:

- Placing the silicon substrate in the reaction chamber.

- Passing through the reaction chamber a stream of a gaseous mixture containing hydrogen and hydrocarbon, with a content of the latter of 1-5 vol.%.

- Heating the reaction chamber to 1200-1405 ° C.

- Decomposition of a hydrocarbon with the deposition of pyrocarbon on a substrate, accompanied by the formation of a SiC film.

- Control over the formation of single-crystal SiC.

- Removing excess pyrocarbon by oxidizing it with oxygen (C + O ₂ ⇒CO ₂ ) under the following conditions:

1. displacement of hydrogen by a stream of argon;

2. cooling the substrate with SiC to 550 ° C;

3. treatment with a stream of a mixture of gases Ar + O ₂ (oxygen flow rate of about 100 cm ³ / min, argon flow rate of about 1000 cm ³ / min).

The main disadvantage of the method selected as a prototype is its complexity. Indeed, the formation of a silicon carbide film occurs due to two simultaneously proceeding processes: the formation of carbon on the silicon surface (due to the decomposition of the hydrocarbon) and the interaction of carbon with silicon. This requires accurate control of many process parameters at the same time, namely: temperature, reagent concentration, time of their contact with the substrate surface, residence time of the reagents in the reaction chamber, etc. Consideration of the latter circumstance is important, because under the conditions of the method, the process of carbon formation occurs not only on the surface of the substrate, but also on all heated parts of the reaction chamber. This leads to a significant change in the concentration of reagents in the system. In addition, the mandatory use of hydrogen as a reagent complicates the technology.

The invention is aimed at eliminating these disadvantages and provides a simplification of the manufacturing technology of an article containing a silicon carbide film on the surface of a silicon substrate.

The technical result is achieved by the fact that in the method of manufacturing an article containing a silicon substrate with a silicon carbide film on its surface, comprising synthesizing a silicon carbide film on the surface of a substrate by co-heating the substrate and a carbon-containing material, a solid material is used as the carbon-containing material, which result in mechanical contact with the substrate, and heating is carried out at a temperature of 1100-1400 ° C.

When implementing the method, it is preferable to use a material with a carbon content of more than 90 wt.% As a carbon-containing material, and to carry out mechanical contact by applying a pressure of more than 1.5 Pa. The choice of carbon-containing materials with a carbon content of more than 90% is preferred for two reasons. The high carbon content makes it possible to intensify the process of silicon carbide formation. In addition, the high carbon content determines the low content of other elements in the material that can contaminate the formed silicon carbide. The mechanical contact of the silicon substrate and the carbon-containing material implies that in the contact zone of these two solids there is mechanical stress (mutual mechanical pressure). This pressure should preferably be at least 1.5 Pa. In this case, a more snug fit of the bodies to each other, their mutual fixation, which is preferred.

A method of manufacturing the product can be carried out in such a way that the mechanical contact of the substrate and the carbon-containing material is carried out only with part of the surface of the substrate. In this case, an article is obtained in which only part of the substrate has a silicon carbide film on its surface.

For the manufacture of the product as a carbon-containing material can be used various carbon materials, the group of which includes (but is not limited to) such materials as artificial graphite, glassy carbon, pyrographite, graphite foil, carbon-metal.

In some cases, to change the properties of the obtained products after heating, additional etching and / or heat treatment of the products is carried out. Such operations are preferably carried out in the following cases. Heat treatment in a vacuum or inert gas medium - to increase the degree of structural ordering of the film. Heat treatment in an oxygen-containing atmosphere and etching in acids - to clean the substrate from carbon and other contaminants, as well as to create oxyfunctional groups on the film surface. Etching is preferably carried out in acid oxidizing agents, such as for example nitric, perchloric and other acids, as well as mixtures thereof with other reagents. Heat treatment can be carried out in vacuum or inert gas at a temperature of 1100-1400 ° C or in an oxygen-containing medium at a temperature of 500-800 ° C. It is convenient to use air as an oxygen-containing medium.

The description of the invention is illustrated by the following drawings:

Figure 1. Electron diffraction pattern obtained from the surface of the sample made according to example 1.

Figure 2. X-ray diffraction pattern (Cu Kα) obtained from a sample made according to example 2.

Figure 3. Electron diffraction pattern obtained from the surface of the sample made according to example 2.

Figure 4. Electron diffraction pattern obtained from the surface of the sample made according to example 3.

Figure 5. The distribution of elements along the depth of the product obtained by Auger spectroscopy. (The inscriptions on the axes: the abscissa axis - “depth, nm”; the ordinate axis - “element content, at.%.” The symbols of the elements are plotted on the curves.)

The invention consists in the following.

To implement the method, a silicon substrate, which is, for example, a single-crystal silicon wafer cut taking into account the crystallographic orientation, is brought into mechanical contact with the carbon material. As the carbon material can be used artificial graphites, glassy carbon, pyrographite, graphite foil and other types of artificial and natural materials, the carbon content of which preferably exceeds 90 wt.%, And additional elements and compounds do not form undesirable compounds with silicon and silicon carbide under the conditions of the method. The mechanical contact between silicon and the carbon material is, for example, by pressing a block (plate, disk, etc.) of carbon material to the polished (ground) surface of the silicon substrate. Moreover, the surface of the block adjacent to the substrate is flat, which ensures a tight fit of the surfaces. To partially cover the surface of the substrate with a silicon carbide film, mechanical contact is not carried out over the entire surface of the substrate. This makes it possible to create the desired "pattern" of the film on the surface of the substrate.

The specified assembly is placed in an oven and heated in vacuum or inert gas at a temperature of 1100-1400 ° C. During processing, silicon and carbon interact in the contact zone of the silicon wafer and the carbon block. It was experimentally established that, under these conditions, the formation of a silicon carbide film occurs on the surface of a silicon substrate. The structure of the film may be different. This can be an island film or a continuous film of various thicknesses. The specified features of the film are determined by the temperature and time of the process.

After heating and cooling the furnace, the resulting product is recovered. In the future, if necessary, the silicon substrate with the formed silicon carbide film can be subjected to additional etching and heat treatment operations. Depending on the required quality of the obtained film, it can be further processed in liquid or gaseous etchants, for example, in air at 500-800 ° C to remove unwanted contaminants, as well as to obtain surface silicon oxide on it. As liquid etchants, oxidizing acids, for example nitric and perchloric acids, can be used. Boiling in these acids makes it possible to clean the surfaces of silicon carbide from technological impurities. It is also possible to conduct additional heat treatment of the substrate with the film at temperatures up to 1400 ° C to affect the structural features of the silicon carbide film.

The following examples characterize the invention.

Example 1. As a substrate, a KDB-10 brand single-crystal silicon wafer (semiconductor grade silicon doped with boron) with a size of 15 × 15 mm with a surface orientation of (111) is used. As a carbon material serving as a carbon source for the formation of a silicon carbide film, graphite foil of the GraFlex brand (NPO Unihimteh) made by rolling thermally expanded graphite with a carbon content of 99% and a thickness of 0.3 mm is used. A 15 × 15 mm foil is applied to the surface of the silicon substrate and fixed with a 25 g mass loaded with a graphite block (cylinder with a diameter of 30 mm and a height of 20 mm) of 25 g. Due to this, the pressure between the substrate and the graphite foil is 1.1 kPa. The assembly is placed in a vacuum oven and heated in vacuum (residual pressure 10 Pa) to a temperature of 1370 ± 20 ° C. It is kept at the indicated temperature for 10 minutes. After which the furnace is cooled. The assembly is removed from the furnace and disassembled. Optical microscopy fixes the formation of a film on the surface of a silicon substrate. The surface structure of the obtained sample was studied by electron diffraction. Figure 1 shows the electron diffraction pattern of the sample. The decoding of the electron diffraction pattern shown in the table shows that a silicon carbide film is formed on the surface of the silicon substrate. Figure 1 shows that the film has a noticeable texture, i.e. preferred orientation of the blocks - this is indicated by bright points on the electron diffraction pattern. Scanning microscope studies show that the film is continuous. The film thickness is about 0.3 microns. Thereby, an article is obtained which is a silicon wafer with a silicon carbide film on its surface.

Example 2. The example is carried out analogously to example 1. The heating temperature is 1150 ± 20 ° C. After the operations, the sample is heat treated in air at a temperature of 650 ° C for 20 minutes. On the surface of the silicon substrate, the formation of an island film is microscopically recorded. The size of the islands is 1-3 microns. Structural studies carried out on an electron diffractograph indicate the formation of a silicon carbide film on the surface of a silicon substrate (see Figure 3 and table). Figure 2 presents the x-ray obtained from the surface of the sample. One can see reflections determined by x-ray diffraction on silicon and silicon carbide. This confirms the receipt of the product, which is a silicon wafer with a silicon carbide film on its surface.

Example 3. As the substrate using a plate of single-crystal silicon grade KDB-10 with a size of 15 × 30 mm As a carbon material, which serves as a carbon source for producing a silicon carbide film, use MPG-6 artificial graphite in the form of a cylindrical block with a diameter of 50 mm and a thickness of 25 mm. One of the planes of the block is ground (Rz = 0.1 μm). The block is combined with a polished surface with a silicon wafer so that the block is on top of the wafer and presses it, providing mechanical contact. The assembly thus obtained is placed in an oven and heated at a temperature of 1250 ± 20 ° C for 10 minutes. After cooling the furnace, the assembly is disassembled and the samples obtained are recovered. Optical microscopy recorded the formation of a continuous film on the surface of a silicon substrate. Electron diffraction studies indicate the formation of a film of silicon carbide (Figure 4, table) on the surface of the silicon substrate. At the same time, a high degree of crystallographic ordering of the film structure was noted — only point reflections are visible in the electron diffraction pattern.

Example 4. The example is carried out analogously to example 3. The difference is that the silicon substrate is fixed with a carbon block so that only part of its surface (about half) has mechanical contact with the carbon block (the substrate protrudes from under the block). Microscopic studies indicate the formation of a silicon carbide film on the surface of a silicon substrate in the zone of its contact with the carbon block. The rest of the surface is free of carbide film.

Example 5. The example is carried out analogously to example 1. The heating temperature is 1250 ± 20 ° C. After the operations performed, the sample is heat-treated in vacuum at a temperature of 1350 ± 20 ° C for 10 minutes. Research of the surface of the obtained product was carried out by Auger spectroscopy. In this case, the dependence of the distribution of carbon and silicon over the depth of the product is obtained - Figure 5. It can be seen that on the surface of the product (to a depth of about 100 nm), the silicon and carbon contents are equal to each other and equal to 50 at.%. This corresponds to the composition of silicon carbide - SiC.

At a depth of more than 1000 nm, the composition of the product corresponds to pure silicon, i.e. composition of the original substrate.

Table.
Identification of electron diffraction patterns of samples according to examples 1-3 (interplanar distances d / n (nm) calculated from the electron diffraction angles on an electron diffractometer are indicated) Example / Reflex No. one 2 3 four 5 6 Example 1 0.250 0.215 0.155 0.130 0.125 0,110 Example 2 0.254 0.221 0.156 0.132 - - Example 3 0.251 0.218 0.155 0.130 0.127 0.113 Table Values for SiC 0.251 0.217 0.154 0.131 0,126 0.109

Thus, the implementation of the proposed method allows to manufacture products consisting of a silicon substrate and a silicon carbide film formed on its surface. The high structural perfection of carbide films indicates the possibility of their use for the formation of various types of semiconductors on their surface, such as, for example, gallium nitride. In comparison with known methods, the proposed technical solution provides a significant simplification of the manufacturing technology of products. In addition, it is possible to form a film of silicon carbide not on the entire surface of the substrate, but only in certain places.

Claims (11)

1. A method of manufacturing a product containing a silicon substrate with a silicon carbide film on its surface, comprising synthesizing a silicon carbide film on the surface of a substrate by co-heating the substrate and a carbon-containing material, characterized in that a solid material is used as the carbon-containing material, which is brought into mechanical contact with the substrate by applying pressure, and heating is carried out at a temperature of 1100-1400 ° C. 2. The method of manufacturing the product according to claim 1, characterized in that as a carbon-containing material using a material with a carbon content of more than 90 wt.%. 3. The method of manufacturing the product according to claim 1, characterized in that the mechanical contact is carried out by applying a pressure of more than 1.5 Pa. 4. The method of manufacturing the product according to claim 1, characterized in that the mechanical contact is carried out with part of the surface of the substrate. 5. The method of manufacturing the product according to claim 1, characterized in that as a carbon-containing material use material from the group of artificial graphite, glassy carbon, pyrographite, carbon-metal, graphite foil. 6. A method of manufacturing a product according to any one of claims 1 to 5, characterized in that after heating, additional etching and / or heat treatment is carried out. 7. The method of manufacturing the product according to claim 6, characterized in that the etching is carried out in acid oxidizing agents. 8. The method of manufacturing the product according to claim 7, characterized in that the etching is carried out in perchloric or nitric acid. 9. The method of manufacturing the product according to claim 6, characterized in that the heat treatment is carried out in vacuum or inert gas at a temperature of 1100-1400 ° C. 10. The method of manufacturing the product according to claim 6, characterized in that the heat treatment is carried out in an oxygen-containing medium at a temperature of 500-800 ° C. 11. The method of manufacturing the product according to claim 10, characterized in that the heat treatment is carried out in air.

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