RU2811353C1 - METHOD FOR PRODUCING MONOCRYSTALLINE SiC - Google Patents

Abstract

FIELD: microelectronics.

SUBSTANCE: invention can be used in the manufacture of integrated circuits. The method for producing monocrystalline SiC involves sublimation of a source of silicon carbide - silicon carbide powder - onto a plate of a seed SiC single crystal with a diameter of D in a growth crucible, in the upper part of which a graphite shaper is placed. In the lower part of the growth crucible, a cylindrical insert made of dense graphite with a high thermal conductivity value of radius R is placed, in which vertical holes are made designed to accommodate silicon carbide powder, and the gaps between the holes have dimensions d2 such that d2≥0.1R, and the total cross-sectional area of all holes is at least 40% of the end area of the cylindrical insert, while the distance H between the upper surface of the cylindrical insert and the plate of the seed single crystal is such that d1 < H < D.

EFFECT: invention makes it possible to improve the quality of monocrystalline SiC ingots while reducing the cost of the method.

3 cl, 6 dwg, 1 tbl

Description

The invention relates to microelectronics and concerns the technology for producing monocrystalline SiC - a widespread material used in the manufacture of integrated circuits.

Single-crystalline SiC ingots are usually grown by the sublimation-condensation method (the so-called modified Lely method). In accordance with this method, in a growth crucible, usually made of graphite, a SiC seed single crystal plate and a silicon carbide source (silicon carbide powder) are placed opposite each other on top (see Fig. 1). The transfer of silicon carbide particles from a silicon carbide source to the surface of a SiC seed single crystal wafer is carried out at high temperatures (usually above 2000 °C) in a vacuum or an atmosphere of residual inert gas (argon, with a pressure of 50 Pa...1000 Pa), for which a temperature gradient is created ( the so-called axial temperature gradient) between a hotter silicon carbide source and a less heated SiC seed single crystal plate (temperature difference 20 K...200 K).

For the most efficient operation of the source during the growing process, the source must be located entirely in the temperature zone, at the same temperature. If this condition is not met, silicon carbide powder in one area of the source may evaporate and condense in another part of the source. As a result, the growth rate of the ingot decreases. In addition, the source operates unevenly - intense graphitization of individual parts of the source is observed, leading to the entry of graphite particles into the volume of the gas phase and onto the surface of the growing ingot.

The grown ingot of single-crystalline silicon carbide must have a minimum of structural defects, for which, during the growth process, the entire growth surface of the ingot must have a flat or slightly convex shape. The presence of concave areas on the surface of a single-crystal SiC ingot leads to degradation of the ingot - the appearance of dislocation clusters and failure of the growing polytype. The transfer of silicon carbide during the growth process occurs in the gap between the source and the seed single crystal plate. In order to ensure a slightly convex surface of a growing single-crystalline silicon carbide ingot, it is necessary to ensure the same temperature of the source surface facing the seed single-crystal plate, as well as to create a relatively small temperature gradient along the surface of the seed single-crystal plate (the so-called lateral temperature gradient - for growing the ingot) , with a minimum temperature in the center of the seed single crystal plate (see Figure 2, arrows indicate the direction of silicon carbide vapor transfer). Thus, the axial temperature gradient at the center of the seed single crystal wafer is slightly higher than at the periphery of the wafer.

Resistive heating elements are usually placed on the outside of the side walls of the growth crucible. Thus, during the process of growing an ingot, the side walls of the growth crucible, as well as the peripheral parts of the source adjacent to the side walls of the growth crucible, heat up most strongly. The deep parts of the source are heated due to the thermal conductivity of the silicon carbide powder.

It is known that silicon carbide in the form of a bulk single crystal has extremely high thermal conductivity (up to 120-150 W/m⋅K), but decreases significantly at temperatures above 1000 °C [Khin Maung Soe Composite ceramics based on silicon carbide with eutectic additives in Al systems ₂ O ₃ -TiO ₂ -MnO, Al ₂ O ₃ -MnO-SiO ₂ , MgO-SiO ₂ , Al ₂ O ₃ (MgO)-MgO-SiO ₂ // Diss. for the candidate...candidate of technical sciences. M., Russian Chemical Technical University named after. DI. Mendeleev. 2019. 109 p.]. The thermal conductivity of sintered silicon carbide powders is relatively low (λ = 13 W/(m⋅K) at a temperature of 2200 K) [https://shaxsu.ru/runy/karborund-formula.html], and is difficult to calculate analytically [Volchenko T S.S., Yalovets A.P. Calculation of the effective thermal conductivity of powder materials from spherical particles in a gas atmosphere // Journal of Technical Physics. 2016. Volume 86, issue. 3. P.8-19]. Temperature inhomogeneities usually occur in the growth crucible - both in the volume of the source and on its surface facing the plate of the seed single crystal (see Figure 3, T ₁ >T ₂ ). As a result, in the central part of the source surface facing the seed single crystal wafer, the temperature is lower, the corresponding axial gradient will also be lower, as well as the growth rate of the silicon carbide ingot in the central part of the seed single crystal wafer. Accordingly, vapor transfer will occur not only in the direction of the seed single crystal plate, but also from the periphery of the source to its central part (see Fig. 3, shown by arrows). On the surface of the source, this will lead to the growth of material on the surface of the source, in its central part, and to rapid carbonization of the peripheral part of the surface of the source. The silicon carbide ingot will have a concavity in the central part, which will lead to the appearance of numerous defects in the form of dislocation bushes or failure of the growing polytype. In addition, the growth rate of the ingot will decrease, and the efficiency of using the source will also decrease. The effect considered is insignificant for small diameters of the growth crucible (correspondingly, for small plates of seed crystals, up to 76 mm in diameter). For larger diameters of seed crystal plates (from 100 mm in diameter and above), the dip in growth rate in the central part of the ingot will already be significant, due to the significant distance of the heater from the central part of the ingot.

There are known methods for producing single-crystal SiC that make it possible to partially eliminate these disadvantages.

Thus, there is a known method for growing silicon carbide single crystals, in which the source (silicon carbide powder) is heated using two coaxial heaters, one of which is located on the outside of the growth crucible, and the second in the central part of the growth crucible, in the area where the powder is placed (RU2770838 , C30B23/00, C30B33/02, C30B29/36, 2021). When installing a seed single crystal plate at a given distance from the source surface, defects such as polytype inclusions, dislocations, micropores and graphite inclusions can be minimized. Obviously, this method, with correctly selected power on both heaters, makes it possible to partially level out the concavity in the central part of the ingot, but does not solve the problem entirely, since the surface of the source between the heaters will also have temperature inhomogeneities, only smaller in absolute value. In addition, the method is labor-intensive due to the need to select power on the heaters. Creating a central heater, which must be relatively small in size and operate in the space of a vacuum chamber, presents significant difficulties.

Another way to improve the structural quality of single-crystalline SiC ingots is to grow a single-crystalline silicon carbide ingot in thermal contact with polycrystalline SiC, which equalizes the surface temperature of the single-crystalline SiC ingot to prevent the formation of microcracks and other defects (JP 2001114598, C30B 29/36, C30B 29/10 , 2001). The method partially solves the problem of temperature inhomogeneities, but is ineffective for large-diameter seed crystal plates. In addition, contact with a polycrystal can lead to stress injection into the growing single-crystalline SiC ingot and its subsequent degradation.

As a means for leveling the axial temperature gradient over the surface area of a growing single-crystalline SiC ingot and, accordingly, for the growth of an ingot with a flat or slightly convex surface, it is known to use a heat screen in the form of a set of shielding plates made of different grades of graphite installed in the SiC vapor phase transfer space (JP 2000264795, С30В 23/00, С30В 29/36, С30В 29/10, 2000). This method helps to reduce temperature inhomogeneity, but has low reproducibility, since the screen is difficult to install accurately enough. In addition, the screen becomes overgrown with polycrystalline silicon carbide and effectively reduces the useful growth rate of the single-crystalline SiC ingot. Also, the use of a screen leads to an effective redistribution of vapor flows in the growth crucible, which increases the likelihood of defects appearing in the growing single-crystal SiC ingot.

Effective equalization of the axial temperature gradient can be achieved using barrier carbon traps located between the silicon carbide source and the SiC seed single crystal wafer. A barrier trap in the form of a partition made of porous carbon, installed in the space between the silicon carbide source and the seed SiC single crystal (US 4866005, H01L 21/205, H01L 21/36, 1989; CN 202430332, C30B 23/02, C30B 29/02, 2012 ), evens out the axial temperature gradient over the surface area of the seed single crystal of silicon carbide, but effectively reduces the growth rate of the single-crystal SiC ingot to commercially unacceptable values. The barrier trap in the form of two or more overlapping plates made of heat-resistant material (RU 2405071, C30B 23/00, C30B 29/36, 2010) has the same disadvantages, due to an increase in the flow path. In addition, the barrier traps themselves in the space inside the growth crucible can be a source of contamination of the growing single-crystalline silicon carbide ingot with particles of carbon or refractory metals.

The closest to the claimed technical essence is a method for producing a single crystal SiC ingot (JP2015212207 (A), “Method for manufacturing silicon carbide single crystal ingot”, C30B29/36, 2015), in which a single crystal of silicon carbide is grown by sublimation, and on the surface of the source , in its central part, a graphite element is placed in the shape of a plate or cone, pointing downwards. The element lies on the surface of the source or is partially buried in the source and serves for more efficient use of the source material when growing large-diameter ingots.

The prototype method partially solves the problem of adjusting the growth profile of a single-crystalline SiC ingot in its central part, but is also characterized by insufficiently high quality of the grown single-crystalline silicon carbide ingots.

Firstly, the graphite element lies on the surface and does not affect the temperature distribution deep in the source. In the middle of the source, there is still a transfer of source material from the periphery of the source to the central region.

Secondly, a graphite plate lying on the surface of the source will be overgrown with polycrystalline silicon carbide, which also reduces the growth rate of the single-crystalline SiC ingot and reduces the efficiency of the source.

Thirdly, the graphite element on the surface of the source actively changes the direction of movement of gas flows in the space between the plate of the seed single crystal and the surface of the source, which can lead to the injection of various defects or carbon inclusions into the surface of the growing single-crystal silicon carbide ingot.

Fourth, the surface of the graphite element lying opposite the surface of the growing single-crystalline SiC ingot can serve as a source of inclusions in the growing single-crystalline silicon carbide ingot.

Thus, the prototype method creates new sources of defects in a growing ingot of single-crystal SiC and - in addition - reduces the efficiency of the source.

The objective of the present invention is to create a method for producing single-crystalline SiC ingots, providing a technical result consisting in improving the quality of single-crystalline SiC ingots while reducing the cost of carrying out the method.

The essence of the invention lies in the fact that in the method of producing single-crystal SiC, including sublimation of a source of silicon carbide onto a plate of a seed SiC single crystal with a diameter D, a cylindrical insert of dense graphite with a radius R is placed in the lower part of the growth crucible, in which vertical holes are structurally made for placement in source - silicon carbide powder, with characteristic hole sizes d1, such that d1 < R, and gaps between holes with sizes d2, such that d2 ≥ 0.1R, and the total cross-sectional area of all holes is at least 40% of the area the end of the cylindrical insert, and the distance H between the upper surface of the cylindrical insert and the plate of the seed single crystal is selected from the approximate condition d1 < H < D.

The cylindrical insert is made of dense structural graphite with a high thermal conductivity (> 100 W/(m⋅K)) and has a diameter that allows it to be placed inside the growth crucible, in its lower part.

At the upper end of the cylindrical insert, through or blind holes of a round shape are structurally made, which do not lead to loss of integrity of the cylindrical insert, that is, they are made with gaps between them. If round holes have different diameters, size d1 refers to the diameter of the maximum hole. Holes with a shape other than round, for example grooves, can also be made. In this case, the characteristic hole size d1 is the smaller of the groove dimensions. If the grooves have different sizes, d1 means the smaller size of the widest groove.

The gaps between the holes can have different sizes, but to implement the claimed method, the size of the smallest of them must satisfy the approximate condition d2 ≥ 0.1R.

The cylindrical insert can be pre-coated with a film of tantalum carbide or pyrolytic carbon.

The proposed method has differences that make it possible to improve the quality of grown single-crystalline SiC ingots while reducing the cost of carrying out the method.

In the space inside the growth crucible, in its lower part, a cylindrical insert made of dense structural graphite, which has high thermal conductivity, is placed. All holes made in this insert contain silicon carbide powder - a source divided into sections. The use of a heat-conducting cylindrical insert, taking into account geometric restrictions on the holes and gaps between them, makes it possible to effectively equalize the temperature of all parts of the source located in all sections and eliminate temperature inhomogeneities - both in the volume of all parts of the source and on their surface. As a result, at the upper end of the cylindrical insert the temperature at all points, both in the central part and at the periphery, will be approximately the same. Accordingly, at a constant temperature at all points of the seed single crystal plate, vapor transfer will occur only in the direction from the cylindrical insert to the seed single crystal plate. When restrictions are met on the size of the holes, the gaps between them and on the distance from the seed single crystal plate to the upper end of the cylindrical insert, the growing ingot of single crystal SiC will have a slightly convex or flat shape at all points of the surface, which will lead to a decrease in the density of defects such as dislocations, micropores and inclusion of other polytypes and improving the quality of single-crystal SiC ingots. At the same time, in order to ensure an approximately uniform density of holes over the area of the cylindrical insert, the total cross-sectional area of all holes (source sections) must be at least 40% of the end area of the cylindrical insert.

The proposed method has differences that make it possible to reduce the cost of carrying out the method.

When the temperature on the surface and in the volume of the source is equalized when using a cylindrical insert, the source operates evenly, there is no mass transfer from one part of the source to another (for example, from the periphery to the central region of a single source), the growth rate of a single-crystalline silicon carbide ingot increases even with a smaller volume of the source, which increases the source resource in hours and thus reduces the cost of carrying out the method. The presence of gaps between the holes can reduce the total surface area of the source and reduce the growth rate of the single-crystal SiC ingot, therefore the total cross-sectional area of all holes (source sections) must be at least 40% of the end area of the cylindrical insert.

The present invention is illustrated by the following drawings.

Figure 1 is a schematic representation of a growth crucible with an external heater and a single source, cross-sectional side view;

Figure 2 is a schematic representation of a growth crucible with a grown ingot of single-crystalline SiC of small diameter with a single source, side sectional view;

Figure 3 is a schematic representation of a growth crucible with a grown ingot of large-diameter single-crystalline SiC with a single source, side sectional view;

Figure 4 is a schematic representation of a growth crucible with a grown ingot of single-crystal SiC with a cylindrical insert, (a) a side view in section, (b) a section of a sectioned source;

Figure 5 - cylindrical insert with holes, top view with characteristic dimensions;

Fig.6 - cylindrical insert with grooves, top view with characteristic dimensions.

The numbers in the figures (Fig. 1-6) indicate: 1 - growth crucible, 2 - source, 3 - seed holder, 4 - seed monocrystal plate, 5 - external heater, 6 - heat-insulating screen, 7 - hole in the heat-insulating screen, 8 - ingot of monocrystalline silicon carbide, 9 - cylindrical insert, 10 - holes in the cylindrical insert.

The letters in the figures (Fig. 1-6) indicate: H is the distance from the upper end of the source 2 or the upper end of the cylindrical insert 9 to the seed single crystal plate 4, d1 is the characteristic size of the holes 10, d2 is the size of the gaps between the holes 10, R is the radius cylindrical insert, T1, T2 - temperatures of different sections of the source.

Arrows in the growth crucible show the directions of mass flows in different parts of the source.

The design of a growth crucible, historically used for growing single-crystalline silicon carbide ingots, is schematically presented in Figure 1 [Tairov Yu.M. Growth of bulk SiC // Materials Science and Engineering: B. 1995. Vol.29. N1-3. P.83-89]. Inside the growth crucible 1 there are usually located: in the lower part of the growth crucible 1 - source 2 (silicon carbide powder), a seed holder 3 with a seed single crystal plate 4, as well as a heat-insulating screen 6 with hole 7 for the formation of axial and lateral gradients. Heating is carried out using a resistive heater 5 located near the outer side wall of the growth crucible 1.

A grown single-crystalline SiC 8 ingot having a diameter of less than 76 mm and a convex growth surface at all points is shown schematically in FIG. 2. An ingot of single-crystalline SiC with a diameter of 100 mm or more, having a concave section in the central part of the growth surface, is shown schematically in Fig. 3.

As a technical means for implementing the proposed method, growth crucible 1 (Figure 4 a, b), having a cylindrical body made of dense structural graphite, can be used. In the lower part of the growth crucible 1 there is a cylindrical insert 9, also made of dense structural graphite, with high thermal conductivity (> 100 W/(m⋅K)). The outer diameter of the cylindrical insert is slightly smaller than the inner diameter of the growth crucible 1, which ensures a free fit of the cylindrical insert 9 in the body of the growth crucible 1. The cylindrical shape of the insert 9 is determined by the cylindrical symmetry of the heater 5 and the growth crucible 1 and ensures uniform heating of the insert in all directions normal to the axis growth crucible 1.

In the body of the cylindrical insert 9, on the upper end side, vertical holes 10 are structurally made. In all holes 10, a source 2 is placed - silicon carbide powder. A graphite seed holder 3 with a glued plate of a seed single crystal 4 is placed above the cylindrical insert 9 at a distance H from the upper edge of the cylindrical insert. A heat-insulating screen 6 made of graphite felt is placed above the seed holder 3, made of graphite felt, with a hole 7 - to form axial and lateral gradients in the area plates of seed single crystal 4.

During the growth process, a silicon carbide ingot 8 is formed on the seed single crystal plate 4.

The holes 10 can have any shape. The most technologically advanced and easiest to manufacture are round-shaped holes (Fig. 5) or in the form of grooves (Fig. 6). Holes 10 can be through or blind.

The cylindrical insert 9 is characterized by a radius R, as well as the characteristic dimensions of the holes d1 and the gaps between them d2. In the case of round holes, d1 is the diameter of the hole; for grooves, d1 is the width of the groove.

The limitation imposed on the size of the holes (d1 < R), as well as on the total area of the holes (at least 40% of the end area of the cylindrical insert), determines the approximately uniform distribution of holes (source sections) over the end area of the cylindrical insert.

The limitation imposed on the size of the gaps between the holes (d2 ≥ 0.1R) determines the conditions for equalizing the temperature over the surface of the upper end and the entire volume of the cylindrical insert, and, consequently, over the volume of all sections of the source.

The limitation imposed on the distance H between the upper surface of the cylindrical insert and the seed single crystal plate limits the scope of the invention:

1) To eliminate the heterogeneity in the growth rate of a single-crystal SiC ingot caused by the presence of discrete holes in the body of the cylindrical insert (the presence of source sections), it is necessary that H > d1;

2) To prevent the loss of the effect of equalizing the growth rate of the single-crystal SiC ingot and the loss in the value of the growth rate due to too large a distance from the source sections to the seed single-crystal SiC wafer, it is necessary that H < D.

The method is carried out as follows.

A cylindrical insert 9 is first created from dense structural graphite (usually isostatic) with a radius R, allowing it to be placed in the body of the growth crucible 1. Holes 10 are formed in the body of the cylindrical insert 9. The cylindrical insert 9 is characterized by a radius R, a characteristic hole size d1 and a characteristic gap size between holes d2, and

d2 ≥ 0.1R and d1 < R.

Next, the cylindrical insert 9 is covered with a film of passivating material (for example, tantalum carbide or pyrocarbon) to prevent corrosion of graphite surfaces in the atmosphere of the growth crucible 1 during the growth of the single-crystal SiC ingot, and both the outer surfaces of the cylindrical insert 9 and the inner surfaces of the holes 10 are treated. After this, the cylindrical insert 9 is placed inside the growth crucible 1, at its bottom. Powder - source 2 - is poured into all holes 10, level to the upper end of the cylindrical insert 9.

The plate of seed material 4 is preliminarily etched in molten alkali and washed from contaminants. On the side of the seed single crystal plate 4, not intended for the growth of a single crystal SiC ingot, protective layers are applied that prevent its evaporation during the growth of the single crystal SiC ingot.

A seed holder 3 of a conical or cylindrical shape with a bottom, made of graphite, is also processed by applying a layer of passivating material, after which a seed single crystal plate 4 is fixed on its bottom, on the inside. The seed holder 3 itself is installed in the space of the growth crucible 1 like this in such a way that the plate of the seed single crystal appears in the internal space limited by the seed holder 3 and the cylindrical insert 9. The distance H between the upper end of the cylindrical insert 9 and the plate of the seed single crystal 4 is determined by the height of the side wall of the seed holder 3, and

d1 < H < D,

where D is the diameter of the seed single crystal plate.

Above the seed holder 3, in the upper part of the growth crucible 1, a heat-insulating screen 6 with a hole 7 is placed to form the necessary gradients - axial and lateral.

Growth crucible 1 is placed in a vacuum chamber, inside the space of a cylindrical heater 5.

An ingot of single-crystalline SiC 8 is grown, after which the growth crucible 1 is cooled and, after filling with argon, removed from the vacuum chamber and disassembled. An ingot of single-crystalline SiC 8 is removed and the shape of the crystallization front is measured. After sawing the ingot into plates, the average dislocation density is determined using the method of selective liquid etching in molten alkali, followed by microscopic examination of the etching patterns. Parasitic inclusions of polytypes are determined visually, by the color of various sections of the plates in the light.

Examples of implementation of the proposed method are presented below.

Example. The method was carried out in growth crucible 1 with a height of 400 mm and an internal diameter of 170 mm, made of dense structural graphite MPG-8. Cylindrical insert 9, also made of MPG-8 graphite, had an outer radius of 84 mm and a height of 200 mm. The cylindrical insert 9 had the form shown in Fig.5. The dimensions of the through holes were d1 = 50 mm, the gaps d2 = 8.5 mm. The total cross-section of the holes is 62% of the end area of the cylindrical insert.

For hole sizes, the following condition is met:

d1 = 50 mm < R = 84 mm,

and for gaps, respectively,

d2 = 8.5 mm ≥ 0.1R = 8.4 mm.

The surfaces of the cylindrical insert were pre-passivated, covered with a thin film of polycrystalline tantalum carbide (20-30 microns thick) - to protect against the action of carbide vapors and increase the service life of the cylindrical insert 9. Next, the cylindrical insert 9 was placed inside a growth crucible, and the source 10 was poured into the through holes - Silicon carbide powder of our own production (size 200 - 300 microns, bulk density 1.2 g/cm ³ ), level - up to the upper end of the cylindrical insert, with a total weight of 3100 g.

A seed holder 3 was made in the shape of a truncated cone, with a bottom (see Fig. 1-4) 80 mm high. We used SiC 4 seed single crystal plates made of silicon carbide of the 4H polytype with a nominal orientation (0001) and a deviation of 4° in the azimuth direction [11-20] with an average surface density of micropores in the SiC seed single crystal plate of the order of 10 cm ^-2 , with a diameter of 105 mm. The prepared plate of the seed single crystal 4 was glued to the bottom of the seed holder 3 in such a way that when installing the seed holder 3 into the growth crucible 1 in accordance with Fig. 1, the plate of the seed single crystal 4 ended up in the internal cavity formed by the upper end of the cylindrical insert 9 and the inner walls and bottom holder 3 of the seed single crystal plate 4.

In this case, the distance from the surface of the seed single crystal plate 4 to the upper end of the cylindrical insert 9 is H = 80 mm. Conditions are met:

d1 = 50 mm < H = 80 mm < D = 105 mm.

The upper part of the growth crucible 1 was assembled by installing a heat-insulating screen 6 on the outer surface of the holder 3 of the seed single crystal plate 4.

After this, the growth crucible 1 assembly was placed in the growth chamber and an ingot of single-crystalline silicon carbide was grown. To do this, the growth chamber was evacuated using a vacuum system, filled with inert gas using a gas injection system, and heated using heating elements 5, providing a temperature sufficient for sublimation of the silicon carbide source 2. At a temperature sufficient for sublimation of the silicon carbide source 2 (T = 2000 ..2200°C), thermal stabilization of the growth crucible was carried out for 2-3 hours. The inert gas pressure in the growth chamber was 10-50 kPa. After this, the inert gas was pumped out to pressures at which the growth of a single-crystalline SiC ingot was possible at an acceptable speed (0.4-0.5 mm/hour). The duration of the process of growing a single-crystal SiC ingot was 10 hours.

After the process of growing the single-crystalline silicon carbide ingot 8, the growth crucible 1 was cooled and, after filling with argon, was removed from the growth chamber. Next, the growth crucible 1 was disassembled, an ingot of single-crystalline silicon carbide 8 and a cylindrical insert 9 with a spent source 2 were removed. The spent source of silicon carbide 2 was sent for annealing, which was carried out in air at a temperature of 900°C for 4-10 hours to remove carbon . The silicon carbide source was then reused with the addition of fresh silicon carbide powder to restore the mass of the source.

The ingot of single-crystalline silicon carbide 8 was separated from the seed holder 3. The growth rate of the ingot of single-crystalline silicon carbide 8 was determined by direct measurement of the thickness of the ingot, as well as gravimetrically (by the change in the weight of holder 3 with the plate of the seed single crystal SiC 4 and the ingot of single-crystal SiC 8 grown on it). The profile of the growth front of a single-crystal SiC ingot, as well as the presence or absence of concavity in the central part of the growth front of the ingot, was determined using a micrometer table.

The ingot was subjected to standard mechanical processing (calibration, cutting into plates, grinding and polishing).

The density of micropores and dislocations in silicon carbide wafers (and, accordingly, in an ingot of single-crystalline silicon carbide) was determined under a microscope after alkaline etching of the surface of silicon carbide wafers (KOH, 500 °C, 20 minutes). Parasitic inclusions of polytypes were determined visually, by the color of the material in the light or under UV irradiation.

The growth rate of the single-crystalline silicon carbide ingot was 0.5 mm/hour, the density of micropores in the plates of the grown single-crystalline SiC ingot was less than 5 cm ^-2 .

The ingot has a convex growth front (20-30 mm from the edge), in the central part the growth front is visually flat (40-50 mm in the center, curvature is not determined).

The test results of the method for various values of design parameters are presented in the table (cylindrical insert with a height of 200 mm, radius R = 84 mm, diameter of the silicon carbide seed single crystal plate D = 105 mm).

Table.
Technical characteristics of the method depending on design parameters NN Variant of holes according to Fig. d1, mm d2, mm H, mm Area of holes, % of the area of the end of the insert / Weight of the source, kg Convex (+), concave (-), flat front (0) in the central part Spurious inclusions Micro-pore density,
cm ^-2 Growth rate, mm/min 1 5 50 8.5 80 62
3.1 0 No 2-10 0.5 2 5 48 10.5 80 57
2.9 + No 5-10 0.5 3 5 40 18.5 80 40
1.9 + No 2-5 0.3 4 3 (without insert) - - 80 100
4.9 - There is 10-30 0.6 5 5 50 8.5 120 62
3.1 - No 5-20 0.35 6 5 50 8.5 40 62
3.1 -* There is 5-20 0.5** 7 6 15 9.0 80 50
2.2 + No 5-10 0.4 8 6 20 4 80 67
3.4 - There is 30-50 0.6 9 6 15 7.3 50 50
2.6 - There is 5-20 0.4 10 6 15 8.5 110 50
2.1 0 No 5-15 0.4 eleven 6 15 20 80 25
1.3 + No 5-15 0.15 Note. * - multiple concave sections, ** - average speed.

As can be seen from the table, the proposed method eliminates the presence of a concave section in the central part of the growth front of an ingot of single-crystalline silicon carbide 8, compared to the prototype method (without a cylindrical insert, example 4).

During testing of the method, the limiting values of the design parameters of the installation were established to ensure the effectiveness of the proposed method. When the distance from the surface of the wafer of the seed single crystal 4 to the upper end of the cylindrical insert 9 decreases below the value d1 (H < d1, where d1 is the characteristic size of the hole), multiple concave areas begin to appear on the surface of the growing single-crystal silicon carbide ingot 8 caused by uneven injection of material onto the surface of a growing single-crystalline silicon carbide ingot 8. In this case, the growth rate of a single-crystalline SiC ingot can be measured on average and very approximately. As the distance H increases above the value D (H > D, where D is the diameter of the silicon carbide seed single crystal plate 4), the efficiency of the method decreases, since in this case the growth front profile depends only on the general temperature distribution in the growth crucible 1.

Reducing the size of the gaps d2 below a certain value (d2 < 0.1R, where R is the radius of the cylindrical insert 9) leads to insufficient temperature equalization over the source area, which does not make it possible to eliminate the dip in the growth rate in the central part of the ingot (concave section). Reducing the total cross-sectional area of all holes below approximately 40% of the end area of the cylindrical insert makes it possible to implement the method, but significantly reduces the growth rate, below commercially acceptable values. In addition, at low values of the total cross-sectional area of the holes, the velocity distribution over the surface of the single-crystalline silicon carbide ingot 8 will depend on the uniformity (or unevenness) of the arrangement of the holes at the end of the cylindrical insert 9.

The presence of concave areas on the surface of a growing ingot of single-crystalline silicon carbide is always accompanied by polytype inclusions and an increase in the density of micropores in the growing ingot.

Thus, the proposed method provides a technical result consisting in improving the quality of single-crystalline SiC ingots while reducing the cost of carrying out the method.

Claims (3)

1. A method for producing single-crystalline SiC, including sublimation of a source of silicon carbide - silicon carbide powder onto a plate of a seed SiC single crystal with a diameter of D in a growth crucible, in the upper part of which a graphite shaper is placed, characterized in that a cylindrical insert made of dense graphite is placed in the lower part of the growth crucible with a high thermal conductivity value of radius R, in which vertical holes are made, designed to accommodate silicon carbide powder, while the gaps between the holes have dimensions d2 such that d2 ≥ 0.1R, and the total cross-sectional area of all holes is at least 40% from the area of the end of the cylindrical insert, while the distance H between the upper surface of the cylindrical insert and the plate of the seed single crystal is such that d1 < H < D. 2. The method according to claim 1, characterized in that the insert has round holes with a diameter d1 such that d1 < R. 3. The method according to claim 1, characterized in that the insert has holes in the form of grooves, and the smaller of the groove dimensions is equal to d1 such that d1 < R.