WO2006085798A2

WO2006085798A2 - Method for manufacturing of article comprising silicon substrate with silicon carbide film on its surface

Info

Publication number: WO2006085798A2
Application number: PCT/RU2006/000067
Authority: WO
Inventors: Sergey Konstantinovich Gordeev; Svetlana Borisovna Korchagina; Sergey Arsenievich Kukushkin; Andrey Victorovich Osipov
Original assignee: Ooo 'upravlyaushaya Kompaniya 'sozvezdie'; Fond Podderzki Nauki I Obrazovaniya
Priority date: 2005-02-10
Filing date: 2006-02-10
Publication date: 2006-08-17
Also published as: RU2005103321A; RU2286616C2; WO2006085798A3

Abstract

The present invention relates to technologies for obtaining semiconductor materials and can be used for creation of semiconductor devices. Technical result is achieved owing to that in the method for manufacturing of an article comprising silicon substrate with silicon-carbide film on its surface, including synthesis of silicon-carbide film on the surface of the substrate by means of joint heating of the substrate and carbon-containing material, as the carbon- containing material a solid material is used which is brought into mechanical contact with the substrate while heating is carried out at a temperature 1100- 14OO °C.

Description

METHOD FOR MANUFACTURING OF ARTICLE COMPRISING SILICON

SUBSTRATE

WITH SILICON CARBIDE FILM ON ITS SURFACE

TECHNICAL FIELD

The present invention relates to technologies for obtaining semiconductor materials and can be used for creation of semiconductor devices.

PRIOR ART

Silicon carbide possesses a number of unique properties, such as chemical inertness, thermal stability, high mechanical and thermophysical characteristics [Gnesin G.G. Silicon-carbide materials, Moscow, 1977]. As for electrophysical properties, silicon carbide is a semiconducting material with forbidden gap width of 2.3-3.3 eV (i.e. wide-gap semiconductor) and retains its electrophysical characteristics at high temperatures [Silicon carbide as a material for modern optoelectronics and semiconductor engineering, Moscow, 1984]. Moreover, silicon carbide is extremely effective as a material for substrate at epitaxial synthesis of advanced semiconductor materials (e.g. gallium nitride) [USP 6,773,508. 2004]. All aforesaid features determine considerable interest for silicon carbide and methods for production of the latter.

In techniques for production of silicon carbide and silicon-carbide materials there can be distinguished production of powders and grains, composites for technical applications (abrasives, heaters, refractories etc.) as well as modular silicon-carbide materials, such as plates and single crystals with different perfection degrees of structure. These methods are well known [Gnesin G.G. Silicon-carbide materials, Moscow, 1977]. It should be noticed that peculiarities of structure and physicochemical properties of silicon carbide (particularly in the form of modular materials) make its production rather expensive and complicated from technological point of view.

On the other hand, for some applications, e.g. in semiconductor engineering, there can be used thin films of silicon carbide on various substrates. Among the latters silicon substrates are of interest. It is known that silicon is a semiconductor material of wide application and its combination with silicon carbide in a single common article is considered as a very promising direction [Silicon carbide as a material for modern optoelectronics and semiconductor engineering, Moscow, 1984].

Known methods for obtaining silicon-carbide films on different substrates can be divided into two groups. The methods of the first group use physicochemical processes where silicon necessary for silicon carbide formation is fed into synthesis zone in the form of chemical compounds (silicon hydrides, halogenides etc.). That is, "external" source of silicon is used. In another group of methods "internal" source of silicon is used, i.e. silicon carbide grows on the backing, the latter being itself a source of silicon atoms for formation of silicon carbide. In this case silicon substrate must be certainly used. As will be shown below, the claimed method relates to the latter group. A method is known where SiC film is formed by means of chemical reduction (US Patent 3,386,866), the reaction products CCl₄ and SiCl₄ being deposited in the hydrogen flow at a temperature T= 1700- 1800K and normal pressure onto the substrate of α-SiC (usually 6H-SiC).

Another method is known (US Patent 3,382,113) where product of reaction between SiH₄ and propane at pressure of 10^"2 mm Hg is deposited onto the substrate at relation between the components 1.2: 1 without hydrogen or other carrier.

A method according to US Patent 3,520,740 makes it possible to obtain an article with epitaxial layers of α-SiC on α-SiC substrate using convective heating of graphite substrate at normal pressure. The film is being deposited from the mixture of gases SiH₄, C₃H₈ and H₂. As a result of pyrolysis silicon carbide vapours are being formed in the gas mixture condensing on the substrate. Satisfactory quality of the film is achieved in the temperature range of 1700-1850⁰C.

Drawback of the aforementioned methods is complicated technology and apparatus, namely: necessity of usage silicon hydrides and halogenides (which create problems from ecology and safety points of view), necessity of maintaining optimum composition of gas mixture, complication of realization desired process conditions in large reactors where non-uniformity of reactants concentration through the volume exerts influence due to exhaustion of the reactants and emission of reaction products.

A method is known from the state of the at (Patent RU 2100870) including placement of substrate in the zone of condensation of silicon carbide vapours and deposition of silicon carbide in the plasma of high-frequency gaseous discharge from silicon dioxide, hydrocarbon compound and water vapours, mass consumption of the latters being 10-30% of hydrocarbon compound consumption. The method makes it possible to enhance reproducibility of the film composition while composition of plasma allows to decrease influence of variations of technological parameters upon composition of the silicon carbide film being formed. However, the known technology is expensive and demands complicated apparatus.

A method for obtaining silicon-carbide film is also known from the state of the art including heating of silicon substrate up to 1173-1573K in atmosphere of hydrocarbon C₂H₂ (J.Vac.Sci. and Techn. 1970, 7, 490). Material of the substrate, interacting with hydrocarbon, forms carbide film.

It should be noticed that the method does not allow to obtain the film of uniform thickness and density because of impossibility to control hydrocarbon diffusion into layers of silicon carbide. The most close to the claimed concept is invention according to US Patent

US 6,773,508, publ. 08.10.2004, Cl. C30B25/04, C30B25/02. The known method includes the following stages:

• Placement of the silicon substrate in the reaction chamber;

• Passing gaseous mixture containing hydrogen and hydrocarbon, proportion of the latter being l-5%vol., through the reaction chamber;

• Heating of the reaction chamber to 1200 - 1405°C;

• Decomposition of hydrocarbon with deposition of pyrocarbon onto the substrate accompanied by formation of SiC film;

• Control of single-crystal SiC formation; . Removal of excessive pyrocarbon by oxidation with oxygen (C+O₂ =>

CO₂) under the following conditions: 1. displacement of hydrogen by argon flow;

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

3. treatment with flow of gas mixture Ar + O₂ (oxygen flow rate about 100 cm³ /min, argon flow rate about 1000 cm³ /min).

The principal disadvantage of the method chosen as a prototype is its complexity. In fact, formation of silicon-carbide film occurs by means of two simultaneous processes: formation of carbon on the surface of silicon (due to decomposition of hydrocarbon) and interaction of carbon with silicon. It demands precise control of many parameters at the same time, namely temperature, reactants concentration, time of their contact with the substrate, time of reactants dwell in the reaction chamber, etc. The latter circumstance must be taken into account because under conditions of realization of the method process of carbon formation takes place not only on the substrate surface but also on all the heated parts of the reaction chamber. It causes considerable change of reagents concentration in the system. Moreover, obligatory usage of hydrogen as a reactant makes the technology more sophisticated.

DISCLOSURE

It is an object of the present invention to eliminate aforementioned drawbacks and assure simplification of technology for manufacturing of article containing silicon-carbide film on the surface of a silicon substrate.

The technical result is achieved owing to that in the method for manufacturing of an article comprising silicon substrate with silicon-carbide film on its surface, including synthesis of silicon-carbide film on the surface of the substrate by means of joint heating of the substrate and carbon-containing material, as the carbon-containing material a solid material is used which is brought into mechanical contact with the substrate while heating is carried out at a temperature 1100-1400°C. At realization of the method, as carbon-containing material a material with carbon content at least 90%mass should be preferably used and said mechanical contact should be carried out by means of application of pressure at least 1.5 Pa, Choice of carbon-containing materials with carbon content over 90% is preferable by two reasons. High carbon content makes it possible to intensify process of silicon carbide formation. Moreover, high content of carbon predetermines low content of other elements in the material, which could otherwise contaminate silicon carbide being formed. Mechanical contact of the silicon substrate and carbon-containing material means that in the zone of contact of these two solid bodies a mechanical stress (mutual mechanical pressure) exists. This pressure must be preferably at least 20 Pa. In such a case sufficiently close contact between the bodies is assured as well as their mutual fixation which is desirable.

The method for manufacturing of the article can be realized in such a way that mechanical contact between substrate and carbon-containing material is accomplished only at a part of substrate surface. In such a case an article is obtained where only a part of substrate has silicon-carbide film on its surface.

For manufacturing of an article various carbon materials can be used as the carbon-containing material. Group of these materials includes (but not restricted with) such materials as artificial graphite, glasscarbon, pyrolitic graphite, graphite foil, carbon pyroceram.

In some cases, in order to change properties of obtained articles, additional etching and/or heat treatment of the articles is carried out after heating. Such operations are preferably carried out in the following cases. Heat treatment in vacuum or inert atmosphere is used in order to enhance degree of structural order of the film. Heat treatment in oxygen-containing atmosphere and etching in acids is carried out for cleaning of substrate from carbon and other contaminants as well as for creation of oxyfunctional groups on the film surface. Etching is preferably carried out in oxidizing acids such as nitric, perchloric and some other acids as well in mixtures of these acids with other reagents. Heat treatment can be carried out in vacuum or in inert gas atmosphere at a temperature of 1100-1400⁰C or in oxygen- containing atmosphere at a temperature of 500-800⁰C. As an oxygen-containing medium it is convenient to use ambient air.

SPECIFICATION DRAWINS The invention will be further described with reference to the following figures:

Fig.l . Electron diffraction pattern obtained from the surface of a specimen manufactured according to Example 1 ;

Fig.2. X-ray pattern (Cu Ka) obtained from a specimen manufactured according to Example 2; plotted on the abscissa are degrees, on the ordinate - intensity..

Fig.3. Electron diffraction pattern obtained from the surface of a specimen manufactured according to Example 2;

Fig.4. Electron diffraction pattern obtained from the surface of a specimen manufactured according to Example 3; Fig.5. Distribution of elements through depth of an article obtained by Auger spectroscopy method.

Essence of the invention consists in the following.

For realization of the method a silicon substrate representing e.g. a single- cryslal silicon plate cut in accordance with crystal-lattice orientation is put into mechanical contact with a carbon material. As the carbon material artificial graphites, glasscarbon, pyrolitic graphite, graphite foil and other types of artificial and natural materials can be used in which carbon content exceeds preferably 90%mass while other elements and compounds contained therein does not form undesirable compounds with silicon or silicon carbide under conditions of realization of the method. Mechanical contact between silicon and the carbon material is accomplished e.g. by means of pressing a block (plate, disk etc.) made of a carbon material to polished (ground) surface of the silicon substrate, the surface of the block contacting with the substrate being flat which assures close fit of the surfaces. For partial covering of the substrate surface with silicon-carbide film mechanical contact is accomplished at only a part of the substrate surface. Hence, it is possible to create desirable "pattern" of film on the substrate surface.

The described assembly is being placed into furnace and heated in vacuum or inert atmosphere at temperature 1100-1400⁰C. During the treatment interaction takes place between silicon and carbon in the zone of contact between silicon plate and carbon block. It is established by experiments that under these conditions silicon-carbide film is being formed on the surface of the silicon substrate. Structure of the film can be various. It can be island-type film or continuous film of various thickness. Said features of the film are determined by temperature and time of the process.

After termination of heating and cooling of the furnace the obtained article is being removed. Afterwards, if necessary, the silicon substrate with the formed silicon-carbide film may be subjected to additional operations of etching and heat treatment. Depending on desired quality of the film obtained, it can be additionally treated in liquid or gaseous etching agents, e.g. in the air at 500-800⁰C, for elimination of contaminants, as well as for formation of surface silicon oxide upon it. As liquid etching agents oxidizing acids can be used, such as nitric or perchloric acid. Treatment at boiling in these acids makes it possible to clean the surface of silicon carbide from technological contaminants. It is also possible to carry out additional heat treatment of the substrate with film at temperatures up to 1400⁰C in order to exert influence upon structural features of silicon carbide film.

PREFERRED EMBODIMENTS

The following examples characterize essence of the invention.

Example 1. As substrate a plate of single-crystal silicon Mark KDB- 10 (silicon of semiconductor qualification alloyed with boron) is used with dimensions 15x15 mm and surface orientation (111). As carbon material necessary as a source of carbon for formation of silicon-carbide film graphite foil GraFlex (NPO Unichimtech) is used manufactured by rolling of thermo-expanded graphite, 0.3 mm thick, with carbon content 99%. A piece of foil, 15>< 15 mm in size, is being put on the surface of the silicon substrate and fixed by loading with a cylindrical graphite block (diameter 30 mm, height 20 mm, mass 25 g). It results in pressure between the substrate and graphite 1.1 kPa. The assembly is placed into vacuum furnace and heated in vacuum (residual pressure 10 Pa) to the temperature 1370+20⁰C, held at this temperature during 10 minutes, then the furnace is cooled down. The assembly is removed from the furnace and dismounted. On the surface of the silicon substrate the formed film can be distinguished using method of optical microscopy. Structure of the surface of the obtained specimen is examined by electron diffractometry method. Electron diffraction pattern of the specimen is shown in Fig.l. Interpretation of the diffraction pattern given in the Table shows that silicon-carbide film is formed on the surface of silicon substrate. As can be seen from Fig.l, the film has considerable texture, i.e. preferable orientation of blocks as indicated by bright points on the electron diffraction pattern. Investigations by means of scanning microscope show that the film is a continuous one. Its thickness is about 0.3 μm. So, an article is obtained representing a silicon plate with silicon-carbide film on its surface.

Example 2. It is realized similarly to Example 1. Heating temperature is 1150+20⁰C. After all the operations the specimen is subjected to heat treatment in the air at the temperature 65O⁰C during 20 min. On the surface of the silicon substrate formation of an island-type film can be ascertained by microscope. Island size is 1-3 μm. Structural investigations carried out by electron diffractometer indicate formation of silicon-carbide film on the surface of the silicon substrate (see Fig.3 and Table). In Fig.2 X-ray pattern of the surface of the specimen is presented. There can be seen reflexes caused by diffraction of X-rays on silicon and silicon carbide. It corroborates manufacture of the article representing a silicone plate with silicon-carbide film on its surface.

Example 3. As substrate a plate of single-crystal silicon Mark KDB-IO is used having dimensions 15x30 mm. As carbon material necessary as a source of carbon for formation of silicon-carbide film artificial graphite Mark MPG-6 is used in the form of a cylindrical block having diameter 50 mm and thickness 25 mm. One of the planes of the block is ground (Rz=O.1 μm). The block is put on top of the silicon plate, the ground surface down, so that the block can press the plate assuring mechanical contact. The assembly obtained in such a way is placed into the furnace and heated at the temperature 1250+20⁰C during 10 min. After cooling down of the furnace the assembly is removed and dismounted. By optical microscopy formation of continuous film on the surface of the silicon substrate can be indicated. Electron diffractometric investigations indicate formation of silicon-carbide film (see Fig.4 and Table) on the surface of the silicon substrate. High degree of crystallographic order of the film structure is also noted: on the electron diffraction pattern only dot reflexes are seen.

Example 4. It is realized similarly to Example 3. The difference consists in that the silicon substrate is fixed with carbon block in such a way that only part of its surface (about a half) has mechanical contact with the carbon block (the substrate projects from under the block). Microscopic examinations indicate formation of silicon-carbide film on the surface of the silicon substrate in the zone of contact with carbon block. The rest of the surface is free from carbide film.

Example 5. It is realized similarly to Example 1. Temperature of heat treatment is 1250+20⁰C. After all the operations the specimen is treated in vacuum at temperature 1350+20⁰C during 10 min. Examination of the surface of the obtained article is carried out by Auger spectroscopy method. There was obtained dependence of carbon and silicon distribution through depth of the article (see Fig. 5). It can be easily seen that on the surface of the article (down to depth about 100 nm) proportions of silicon and carbon ,are equal - 50%at. It corresponds to composition of silicon carbide - SiC. At the depth beyond 1000 nm composition of the article corresponds to pure silicon, i.e. material of initial substrate.

Table. Identifications of electron diffraction patterns (Examples 1 - 3).

Values of interplanar distance d/n (nm) are given calculated on the basis of electron diffraction angles on electron diffractometer.

Thus, realization of the proposed method makes it possible to manufacture articles consisting of silicon substrate and silicon-carbide film formed on its surface. High structural perfection of carbide films allows to use them for formation on their surface various types of semiconductors, such as gallium nitride. In comparison with the known methods the proposed technical concept provides for substantial simplification of technology for production of articles. Moreover, it is possible to form silicon-carbide film not only at the whole surface of substrate but also at desired places alone.

Claims

1. Method for manufacturing of an article comprising silicon substrate with silicon- carbide film on its surface, including synthesis of silicon-carbide film on the surface of the substrate during joint heating of the substrate and a carbon-containing material, characterized in that as the carbon-containing material a solid material is used which is brought into mechanical contact with the substrate by means of application of pressure while heating is carried out at temperature 1100-1400°C.

2. Method for manufacturing of an article according to Claim 1 characterized in that as carbon-containing material a material is used with carbon proportion over of

90%mass.

3. Method for manufacturing of an article according to Claim 1 characterized in that mechanical contact is accomplished by application of pressure over 1.5 Pa.

4. Method for manufacturing of an article according to Claim 1 characterized in that mechanical contact is accomplished at a portion of substrate surface.

5. Method for manufacturing of an article according to Claim 1 characterized in that as carbon-containing material a material is used out of the group: artificial graphite, glasscarbon, pyrolitic graphite, carbon pyroceram, graphite foil.

6. Method for manufacturing of an article according to any of Claims 1 - 5 characterized in that after heating additional etching and/or heat treatment is carried out.

7. Method for manufacturing of an article according to Claim 6 characterized in that etching is carried out in oxidizing acids.

8. Method for manufacturing of an article according to Claim 7 characterized in that etching is carried out in perchloric or nitric acid.

9. Method for manufacturing of an article according to Claim 6 characterized in that heat treatment is carried out in vacuum or in inert gas atmosphere at temperature 1100-1400⁰C.

10. Method for manufacturing of an article according to Claim 6 characterized in that heat treatment is carried out in oxygen-containing atmosphere at temperature

500-800⁰C.

11. Method for manufacturing of an article according to Claim 10 characterized in that heat treatment is carried out in the air.