RU2633909C1 - METHOD OF PRODUCING MONOCRYSTALLINE SiC - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes sublimation of a SiC source placed in a crucible onto a seed SiC single-crystal plate placed on a flat ring support, and one or more layers are applied to the seed SiC single-crystal plate from the side not intended for growth of the SiC single-crystal ingot, providing the thermochemical stability and given temperature conditions on the surfaces of the plate of the seed SiC single-crystal, and the holder with a seed SiC single-crystal plate is installed in a crucible in such a way, that the surface of the plate, intended for the growth of the SiC single-crystal ingot, is turned into the inside of the crucible and contacts with the gaseous medium inside the crucible during sublimation. On the circumference of the inner cylindrical surface of the holder flat ring, protrusions with a width of h=(1-3)⋅t and a length of S=(1-10)⋅h are periodically made, the ends of which are provided with ledges with a depth of k=0.3-1 mm and a width of t=0.5-2.0 mm, for placing a seed SiC single-crystal plate with a thickness H exceeding the depth of the ledge k, and on top of the holder with a plate with the deposited layers a plate of thermally expanded graphite with a thickness exceeding the value (H-k) is placed, and then is fixed with a clamping element in the form of a rigid plate of 1.5-8 mm thick and a retaining ring of thermostable materials.

EFFECT: improving the quality of the ingot, reducing the elastic stresses in the seed single-crystal plate, achieving a uniform growth rate over the entire surface of the seed single-crystal plate with the formation of an almost flat crystallization front.

6 dwg, 1 tbl

Description

The invention relates to microelectronics and relates to a technology for producing single-crystal SiC, a widely used material used for the manufacture of integrated circuits.

When obtaining single-crystal SiC by sublimation on the cover of a graphite crucible, the plate of the seed SiC single crystal is structurally fixed, a source of silicon carbide powder is placed in the crucible, the cap and crucible are combined with each other and sealed, and then the graphite crucible with the cap is placed in a growth chamber isolated from the atmosphere , mounted inside with a heat shield made of carbon materials. Next, the growth chamber is evacuated using a vacuum system, filled with an inert gas using a gas inlet system, heated with a heating element that provides a temperature sufficient to sublimate the source - silicon carbide powder and the formation of silicon-containing volatile compounds. During heating in the growth chamber using a heating element and a heat shield, a temperature gradient is created between the source - silicon carbide powder - and a SiC seed single crystal plate, with a temperature sufficient for sublimation, the growth chamber is pumped to a certain inert gas pressure at which the process is activated transfer of silicon-containing volatile compounds from a source to a seed single crystal plate and growth of a single-crystal SiC ingot.

After the process of growing a single-crystal silicon carbide ingot, the temperature in the growth chamber is gradually reduced to room temperature, after which the growth chamber is filled with an inert gas to atmospheric pressure. A crucible is removed from the growth chamber, and from it a seed single crystal plate with a single-crystal silicon carbide ingot grown on it.

To ensure the growth of a high-quality ingot of single-crystal silicon carbide, it is necessary:

- suppress the evaporation of the surface of the plate of the seed single crystal, not intended for growing a single crystal ingot SiC. Such evaporation is observed at a growth temperature and leads to the degradation of the properties of the plate of the seed single crystal ("eating" of the plate through, with the formation of through micropores);

to reduce the elastic stresses arising at the points of contact of the plate of the seed single crystal with the holder. Elastic stresses during the growth of a single-crystal SiC ingot lead to the appearance of dislocations, a failure of the growing polytype, and ultimately to degradation of the growing ingot;

- to ensure the same growth rate of a single-crystal ingot on the entire surface of the seed single crystal wafer, with the formation of an almost flat crystallization front, with layered single-crystal growth, which will minimize the defect density in the growing ingot and obtain a high-quality single-crystal silicon carbide ingot.

In addition, it is necessary to ensure simple and quick disassembly after the process of growing an ingot of a single-crystal SiC structure consisting of a plate of a seed single crystal SiC and a holder on which this plate is fixed in one way or another.

To fix the plate of the seed single crystal on the holder mainly use:

- fixation by gluing with adhesives - the plate is held due to the adhesive forces on a high-temperature adhesive, which retains its properties at a growth temperature of a single-crystal silicon carbide ingot;

- mechanical fixation without gluing - the plate is fixed due to additional devices located inside the crucible and supporting the plate.

There is a known method for growing single-crystal silicon carbide ingots, in which a protective layer is formed on the side of the seed single-crystal plate not intended for growing single-crystal silicon carbide ingots, after which an adhesive layer is applied, the surfaces of the holder and plates of the seed single crystal are glued and single-crystal silicon carbide ingot is grown on free the surface of the seed plate of a single crystal (KR 20150075220, С30В 25/10, С30В 25/16, С30В 29/36, 2015).

There is a known method for producing single-crystal silicon carbide in which a seed plate of a single crystal is fixed to the holder by gluing, in which, to improve the quality of gluing, an exact amount of adhesive per unit interface is fixed (JP 2015129055, C30B 23/06, C30B 29/36, 2015).

Such methods of fixing the seed single crystal wafer are characterized by a low degree of reliability, heterogeneous thermal contact over the surface of the seed single crystal wafer, and the presence of stresses due to the difference in the temperature coefficients of the linear expansion of the materials of the SiC seed single crystal wafer and the holder material (graphite), which leads to a decrease in the quality of the grown single crystal silicon carbide ingot.

To improve the reliability of the contact of the plate of the silicon carbide seed crystal with the holder, a method is known according to which the side of the plate of the silicon carbide seed crystal not intended for growing a single-crystal SiC ingot is roughened, after which adhesive is applied and glued to the holder (JP 2010116275, C30B 23/02, C30B 29/36, H01L 21/205, 2010). Such a fixing method improves the reliability of the contact, but does not solve the problems associated with the presence of stresses at the interface "seed plate of a single crystal SiC holder".

To improve the reliability of the contact “SiC seed crystal single-wafer plate” contact, a method is known in which a damping metal film is placed between the SiC seed single crystal plate and the holder, the melting temperature of which is lower than the temperature of growing a single-crystal SiC ingot (US 2005166833, C30B 23/00; C30B 29/00 36, 2005), in particular, titanium can be used as such a metal (JP 2008019166, C30B 23/06, C30B 29/36, 2008; JP 2008280196 (A), C30B 29/36, 2008). For the same purpose, a film of molten silicon (JP 2016020306, C30B 15/32, C30B 19/00, C30B 29/36, 2016) can be placed between the plate of the seed single crystal and the holder, followed by its carbidization (JP 2011219337, C30B 29 / 36, 2011). Some improvement in the reliability of the contact provided by such technical solutions does not completely solve the problem of uniformity of thermal contact and, most importantly, the problem of the presence of elastic stresses at the interface.

To reduce the elastic stresses occurring in the wafer of the SiC single crystal due to bonding, it is known to use stress damping elements at the interface of the "wafer single crystal SiC holder" (JP 2015193494, C30B 29/36, 2015; JP 2015131744, C30B 23/02, C30B 29/36, 2015). In particular, there is presented a construction of a holder with an intermediate plate glued between the SiC seed crystal plate and the holder made of single-crystal silicon carbide (JP 2006143511, C30B 23/08, C30B 29/36, 2006) or an intermediate layer of polycrystalline SiC (CN104233458, C30B 23 / 00, C30B 29/36, 2014). In the design with an intermediate plate of single-crystal silicon carbide, the elastic stresses can be slightly reduced, however, it is necessary to use double the number of single-crystal silicon carbide plates. In addition, the removal of solvent from the adhesive during heating of the structure leads to local peeling and unevenness of thermal contact, since silicon carbide, unlike graphite, does not have any significant porosity.

When using an intermediate layer of polycrystalline silicon carbide, elastic stresses cannot be reduced, due to the anisotropy of the elastic modules in silicon carbide crystals. The proposed structures with voltage damping intermediate layers simplified the problem of removing a single-crystal SiC ingot from the holder (JP 2015131748, С30В 23/06, С30В 29/36, С30В 33/00, 2015), but, first of all, due to a decrease in adhesion and a decrease reliability of the contact, which leads to deterioration in the quality of the ingot of single-crystal silicon carbide.

Also, in order to reduce the elastic stresses arising in the plate of the SiC seed single crystal due to adhesive contact with the holder, it is known to fix the plate of the seed single crystal with adhesive-adhesive based on bakelite varnish on a graphite holder with an intermediate lining of thermally expanded graphite (UA 68293, H01L 21/205 H01L 21/36, 2004). In this case, the solvent vapor contained in the bakelite varnish can also not be effectively removed from the contact region of the “SiC single crystal chip-heat-expanded graphite gasket plate” contact during drying, due to the absence of porosity in the heat-expanded graphite gasket, which leads to non-uniformity of the adhesive contact and deterioration of the properties of the growing ingot of single crystal silicon carbide.

A known method of mechanically fixing a seed single crystal plate, according to which a coating, for example, of metal carbide, is formed on the surface of a SiC seed single crystal plate not intended for SiC single crystal growth, after which the seed single crystal plate is pressed to the holder and held by brackets (CN 103088411, С30В 23/00, С30В 29/36, 2013). This method is quite complicated, since it assumes a very good flatness of the mating surfaces of the holder and the seed plate of a single crystal, which leads to an increase in the requirements for mating surfaces and possible irreproducibility and unevenness in the area of contact properties.

A method is known in which a metal carbide coating is formed on the back side of a seed single crystal plate not intended for growing a single-crystal SiC ingot, after which the seed single crystal plate is suspended on a bracket in the form of brackets (WO 2015182474, C30B 23/06, C30B 29 / 36, 2015). The disadvantage of this method is not sufficiently homogeneous heat removal on the surface of the plate of the seed single crystal. In the place of contact of the seed plate of the single crystal with the holder, a so-called "edge influx" is observed, that is, a local increase in the growth rate due to better heat removal at the point of contact with the holder. Such an increase in the growth rate will lead to a deterioration in the quality of the ingot of single-crystal silicon carbide due to an increase in the elastic stresses in the ingot.

A known method of mechanically fixing a plate of a seed single crystal on a holder (JP 2011184209, C30B 23/06, C30B 29/36, 2011), in which a supporting element is laid on a ledge formed on the inside of the crucible wall, which has the shape of a truncated cone. The side of the seed single crystal plate, not intended for growing a single crystal silicon carbide ingot, is coated with a protective layer to prevent evaporation of the seed single crystal plate during the growth of a single crystal SiC ingot, after which the seed single crystal plate is mounted on a support element and pressed on top of the crucible lid, by means of a threaded connection with the latter the wall of the crucible.

The disadvantage of this method is a local increase in the growth rate at the point of contact of the supporting element with the seed single crystal plate, which can lead to malfunctions of the polytype composition of the growing ingot of single-crystal silicon carbide, uneven growth rate over the surface of the plate of the seed single crystal and deterioration of the quality of the ingot. In addition, the disadvantage of this method is the complexity of high-quality and reliable assembly of the holder-plate of the seed single crystal design, since the plate of the seed single crystal is not fixed, and in contact with the holder rotating when turning the thread can be displaced from its original position. The result is the irreproducibility of the assembly process and the deterioration in the quality of the growing ingot of single-crystal silicon carbide.

Closest to the claimed invention in technical essence is a method for producing single-crystal SiC, which provides for the sublimation of a source of SiC placed in a crucible onto a plate of a SiC seed single crystal (acting as a substrate) placed on a holder made in the form of a flat ring of elastic material, the values of the elastic modules which is less than the value of the elastic moduli of single-crystal SiC, at least one protective layer is applied to the SiC seed crystal single wafer, providing thermochemical stability, the SiC seed single crystal plate is attached on the side of the deposited layer to the holder, completely overlapping the region bounded by the inner side surface of the holder ring to form the surface of the seed single crystal plate, not intended for the growth of a single crystal SiC ingot, on which several layers additionally predetermined temperature conditions on the surface of the plate of the seed single crystal, then the holder with a fixed plate The seed single crystal SiC is installed in the crucible so that the surface of the plate intended for the growth of a single-crystal SiC ingot is turned inside the crucible and is in contact with the gas medium inside the crucible (RU 2557597, C30B 23/00, C30B 29/36, 2015).

This method does not allow to obtain an ingot of monocrystalline silicon carbide, characterized by a fairly high quality. At the place of sticking of the seed single crystal plate to the holder, a local increase in the growth rate (the so-called "edge influx") is always observed, leading to a nonuniform growth rate of the ingot of single-crystal SiC and, as a result, to a deterioration in the quality of the growing ingot. In addition, the heterogeneity of bonding of the seed single crystal plate to the holder over the surface area, as well as the irreproducibility of the bonding process itself, lead to significant elastic stresses in the plate of the seed single crystal SiC, which also leads to a deterioration in the quality of the growing ingot of single crystal silicon carbide.

The objective of the invention is to provide a method for producing single-crystal SiC, which provides a technical result, which consists in improving the quality of an ingot of single-crystal SiC due to a decrease in elastic stresses in the plate of a seed single crystal of SiC and to achieve a uniform growth rate over the entire surface of the plate of a seed single crystal with the formation of an almost flat crystallization front.

The essence of the invention lies in the fact that in the method of producing single-crystal SiC, including the sublimation of the source of SiC placed in the crucible, on the plate of the seed single crystal placed on the holder and on the side of which is not intended for growing an ingot of single-crystal SiC, one or more layers are applied, which provide both the thermochemical stability of the SiC surface and the specified temperature conditions on the plate surfaces of the SiC seed single crystal, the holder is made in the form of a flat ring, around the circumference of the inner cylindrical surface of which protrusions are made, the ends of which have ledges to accommodate the SiC seed single crystal plate, install the holder inside the crucible, place the seed single crystal plate in the holder on the ledges so that the layers previously deposited on the surface of the seed single crystal plate, not intended for growth of a single-crystal SiC ingot, facing up, then onto a holder with a seed single crystal plate equipped with with abrasive layers, a plate is installed on top that provides uniform thermal contact of the surfaces from thermally expanded graphite and is fixed with a clamping element in the form of a rigid plate and a retaining ring made of thermostable materials.

The seed single crystal plate does not have adhesive mates with the holder, but is mounted on the holder freely and is pressed only from above, as a result of which the level of elastic stresses in the seed single crystal plate decreases. A plate that provides uniform thermal contact of the surfaces and is pressed from above to the seed single crystal plate is made of thermally expanded graphite, which is a plastic material that provides uniform thermal contact of the mating surfaces even with some non-flatness of the seed single crystal plate or installation inaccuracy due to plastic deformation, which leads to uniformity of the growth rate of the ingot of a single crystal of SiC over the entire surface of the plate of the seed single crystal.

The thermally expanded graphite plate is pressed against the surface of the SiC seed single crystal plate by a clamping element consisting of a rigid plate and a retaining ring, which allows a simple and reliable preloaded and fixation system to ensure reproducible and uniform contact over the entire surface of the SiC seed single crystal plate, thereby improving the quality growing ingots of single-crystal silicon carbide.

The fastening of the SiC seed crystal plate in the holder on the ledges allows redistributing the growth rate at the peripheral sections of the single-crystal SiC ingot and, as a result, reduces the local increase in the growth rate of the single-crystal SiC ingot at the initial growth stage, at the points of contact of the holder with the SiC seed crystal plate (to eliminate edge flows ), which allows to achieve a uniform growth rate over the entire surface of the seed plate of a single crystal and to improve the quality of single crystal ingots whom SiC.

The method is illustrated by drawings.

FIG. 1 is a diagram of a sublimation apparatus for implementing the proposed method.

FIG. 2 - used in the inventive method, the holder for the plate of the seed single crystal with protrusions, the ends of which have ledges.

FIG. 3 - holder for comparison, with an annular ledge made directly on the inner cylindrical surface of the ring.

FIG. 4 is a perspective view of an edge-ingot ingot obtained using the holder of FIG. 3.

FIG. 5 is a perspective view of an ingot without edge sag obtained by using the holder of FIG. 2.

FIG. 6 is a general view of the retaining ring.

The table shows the technical characteristics of the ingot and the method and its preparation, depending on the values of the structural parameters.

As a technical means for implementing the proposed method, a crucible can be used (Fig. 1), having a cylindrical body, side wall 1 and bottom 2 of which are made of dense MPG-6 graphite. On the inner surface of the side wall 1 in its upper part, a step 3 is structurally made for mounting the holder (the structural arrangement of the holder can be implemented differently).

On the side wall 1 of the crucible, a spiral 4 of a resistive electric heater and a heat-insulating layer 5 made of graphite felt are sequentially located outside from the outside. Elements 1-5 are placed in a cylindrical growth chamber 6 of a sublimation unit. On the ledge 3, a holder is installed in the form of a flat graphite ring 7, on which a plate of the seed single crystal 8 is placed, with layers previously provided on the surface not intended for growth providing thermochemical stability (not shown in Fig. 1). On the holder 7 with the plate of the seed single crystal 8 is located on top of the plate of the TRG 9, providing a uniform thermal contact of the mating surfaces. Tight and reliable contact of the mating surfaces is carried out using a clamping element consisting of a rigid plate 10 and a retaining ring 11 mounted on top. At the bottom 2 of the crucible, the feedstock 12 is located - polycrystals of silicon carbide, which serve as a source of the obtained ingot of single-crystal silicon carbide.

When carrying out the method, a holder 7 is used, made in the form of a flat graphite ring (Fig. 2), around the circumference of the inner cylindrical surface of which there are protrusions 13, the ends of which have ledges 14, on which the seed plate is mounted and held from lateral displacement during assembly and implementation of the method single crystal 8.

The method is as follows. At the bottom of crucible 1, a source — polycrystalline silicon carbide 12 — is placed, and on a ledge 3 of the inner surface of the side wall of the crucible 1, a holder 7 is arranged in the form of a flat ring with protrusions, the ends of which have ledges, so that the ledges face up. After applying all the layers that provide thermochemical stability of the surface of the plate of the seed single crystal 8, not intended for growth, the plate of the seed single crystal 8 is fixed on top of the holder 7, placing it on the ledges, with the surface that is intended for growth, facing down. Next, the holder 7 with the plate of the seed single crystal 8 is covered with a plate TRG 9, which should provide uniform thermal contact. On top of the plate, the TRG 9 is closed with a rigid plate 10 and the surfaces are pressed against each other, leading the retainer ring 11 into the cavity bounded by the inner surface of the wall of the crucible 1, until it contacts the rigid plate 10 around the entire perimeter of the retainer ring 11.

After that, the crucible 1 is placed in a cylindrical growth chamber 6, which is vacuumized using a vacuum system, filled with an inert gas using a gas inlet system, heated with a heating element 4, which provides a temperature sufficient to sublimate the source 12, and the growth chamber is pumped to a certain inert pressure gas, in which the process of transferring silicon-containing volatile compounds from source 12 to the plate of the seed single crystal 8 and the growth of a single-crystal SiC ingot is activated.

After carrying out the process of growing a single-crystal silicon carbide ingot, the crucible is cooled and, after argon inlet, is removed from the growth chamber. After removing the retaining ring 11 and the plates 9 and 10, the seed plate of a single crystal 8 with a grown ingot of single-crystal silicon carbide is removed from the holder 7.

The holder 7 in the form of a ring for a SiC seed single crystal wafer can be made of graphite or carbon graphite materials (ТРГ - thermally expanded graphite, graphite composites), as well as from refractory metals with sufficient heat resistance (tantalum, niobium, etc.) or from graphite with a metal dusting. The most optimal, in our opinion, is the manufacture of a holder made of graphite, since this material is relatively cheap and has a fairly high strength. The protrusions 13, made on the inner diameter of the holder, contain ledges 14 on the surface of the ring, of width t and depth k, necessary for installing and fixing the seed single crystal in the plate holder. The width and depth of the step on the protrusions of the holder determine the reliability of fixing the plate of the SiC seed single crystal on the holder, they are respectively t = 0.5-2 mm and k = 0.3-1 mm. In addition, the magnitude of the step depth k should not exceed the thickness H of the used plate of the SiC seed crystal, to ensure a uniform pressed plate of the TEG 9 located above. Reducing the width of the used ledge to less than 0.5 mm is impractical, since the reliability of fixing the plate of the seed single crystal decreases: the ledge may collapse during preloading. Accordingly, to ensure the necessary mechanical strength, the total thickness of the holder ring is 1.5-2 mm.

In a number of experiments, for growing an ingot of monocrystalline silicon carbide, they used - to compare the parameters of the grown ingots of a monocrystalline SiC holder with an annular step made directly on the inner cylindrical surface of the ring (Fig. 3). When using such a holder, a fairly uniform distribution of the growth rate of a single-crystal silicon carbide ingot is achieved, but in the initial period of growth, regions with an increased growth rate are usually observed at the points of contact of the SiC 8 seed single crystal plate with the holder 7 (edge sagging 15 in the single-crystal silicon carbide 16, fig. . 4), leading to an increase in elastic stresses in the growing ingot. To exclude such areas and achieve a completely uniform distribution of the growth rate of a single-crystal SiC ingot over the surface of the seed single crystal plate in the ring of the holder 7, protrusions are made around the circumference of the inner cylindrical surface. A general view of an ingot grown using a holder with protrusions whose ends have ledges (FIG. 2) is shown in FIG. 5. In this case, there are no edge flows in the single crystal silicon carbide 16 ingot and a uniform distribution of the growth rate of the single crystal SiC 16 ingot over the plate area of the seed single crystal can be obtained 8. Additional deposition regions of polycrystalline silicon carbide 17 are observed in this case on the TEG plate 9, c the space between the protrusions (Fig. 5). These regions do not adversely affect the growing ingot of single-crystal silicon carbide, since they lag behind the growth rate from the central single-crystal region.

Only the most general restrictions can be imposed on the shape of the protrusions, their number and location, which are generally arbitrary, in general:

(a) The location of the protrusions is periodic around the circumference of the inner cylindrical surface of the flat ring of the holder to provide a uniform pre-pressed plate of the seed single crystal 8 to the plate of thermally expanded graphite 9 located above;

(b) The number of protrusions N is arbitrary, but not less than 3;

(c) The width of the protrusion h = (1-3) ⋅t, where t is the width of the ledge on the holder ring;

(d) The length of the protrusion s = (1-10) ⋅h.

(e) The total length of the protrusions along the circumference D of the inner hole of the holder ring is less than 50% of the circumference, that is, N⋅h <πD / 2, where π = 3.14159.

The SiC seed single crystal wafer used in the method can generally be non-circular, in this case, the manufacturing process of the hole in the holder, which should repeat the profile of the seed single crystal wafer, as well as the process of manufacturing protrusions and ledges, is somewhat more complicated. Accordingly, all the ledges located around the perimeter of the holes of the holder must have the same parameters. The SiC single crystal wafer, in the general case, may have deviations from flatness, since it is pressed against the thermally expanded graphite 9 plate, which allows sufficiently large plastic deformations, repeating the surface profile of the SiC single crystal wafer.

The thermally expanded graphite plate (TEG plate) 9 has a circular shape, with a diameter generally allowing to cover the entire surface of the seed single crystal plate 8. Typically, a TEG plate 9 with a diameter matching the diameter of holder 7 was used. In order to avoid shrinkage during the growing process and changes in the shape of the TEG plate, it is preliminarily subjected to high-temperature annealing in vacuum at a temperature of 2000-2200 ° C.

As is known, the TEG plate is characterized by relatively high thermal conductivity in the direction tangent to its surface and significantly lower thermal conductivity in the direction normal to the surface. This allows, firstly, to effectively equalize the temperature over the entire surface of the seed single crystal plate 8, to which the TEG plate 9 is pressed, and secondly, the use of TEG plates of different thicknesses allows you to effectively change the axial temperature gradient in the growth crucible and, ultimately, control the growth rate of a single-crystal SiC ingot. The thickness of the used TEG wafers in our experiments lay in the range 0.3–2.0 mm; in the general case, the thickness of the TEG wafer should exceed H-k, where H is the thickness of the SiC seed crystal single wafer, k is the step depth in the holder hole (see above) , for a more uniform pressing to the surface of the plate of the seed single crystal SiC.

The rigid plate 10, mounted on top of the plate of the TEG 9, has a round shape, it must have flatness to ensure a fairly uniform compression of the plate of the TGG 9 to the plate of the seed single crystal 8, and a thickness that provides mechanical strength during compression. The plate 10 can be made of graphite or other material with sufficient rigidity and thermochemical stability at the temperature of growth (tantalum, niobium). The thicknesses of graphite plates 10 in our experiments ranged from 1.5 mm to 8 mm. The diameter of the graphite plate is generally slightly smaller than the internal diameter of the growth crucible at the installation site.

Preloading all the plates in the above order to the holder is carried out by means of a snap split ring 11 shown in FIG. 6, made of structural graphite (tantalum or niobium) and subjected to preliminary high-temperature annealing at a temperature of 2000-2200 ° С.

The diameter of the retaining ring in the free state slightly (2-8%) exceeds the inner diameter of the growth crucible at the installation location of the retaining ring, the thickness of the retaining ring (4-10 mm) should be sufficient to ensure its mechanical strength. By compressing the retaining ring, it can be installed in the body of the crucible, effectively pressing all the plates located below to the body of the holder. The use of a retaining ring instead of the commonly used threaded joints makes it easier to assemble the crucible and make it more reproducible.

A modification of the method is possible in which several plates of seed single crystals are mounted on one holder 7. In this case, the holder is pre-made in the form of a flat disk with a set of holes, the number of plates of seed single crystals used, each with protrusions and ledges. In this case, in the process of sublimation, a single ingot of single-crystal SiC is grown on each of the plates of seed single crystals. An additional requirement, which is imposed on the geometric dimensions of the plates of the seed single crystals in this case: all plates of the seed single crystals should be approximately the same thickness, to simplify the process of their simultaneous preload. In the most general case, it is possible to use plates of seed single crystals of different thicknesses, by using an individual step depth for each of the plates of the seed single crystal, while maintaining the value of H-k, where H is the thickness of the plate of the seed single crystal SiC, k is the depth of the step in the holder hole (cm . above).

At least one protective layer must be applied to the surface of the SiC seed single crystal plate, not intended for growth of a single crystal SiC ingot, which provides thermochemical stability of the surface of the seed single crystal plate, i.e., it blocks the thermal evaporation of silicon carbide from the surface of the seed single crystal plate, not intended for single-crystal SiC ingot growth. In addition, a protective layer deposited on the surface of the plate of the seed single crystal prevents the chemical interaction of gaseous components (primarily silicon) with the surface of the plate of the seed single crystal. Such a layer usually consists of synthetic resins of various nature, adhesive and solvent. Various alcohols (isopropyl or isovinyl or ethyl) or acetone were used as solvents.

The number of applied protective layers, their composition and thickness can be, generally speaking, arbitrary.

One or several layers can also be deposited on the surface of the seed single crystal wafer, which is not intended for the growth of a single crystal SiC ingot, providing, due to changes in the thermal radiation absorption conditions, the specified temperature conditions on the surfaces of the SiC seed single crystal wafer. Such a layer usually consists of a suspension of carbon (graphite powder or carbon black) with the addition of solvents and plasticizers. Changing the thickness of the layer and its degree of blackness allows you to vary the temperature of the plate of the seed single crystal and, accordingly, change the growth rate of the ingot of single-crystal SiC.

Such a layer usually consists of a suspension of carbon (graphite powder or carbon black) with the addition of solvents and plasticizers. Changing the thickness of the layer and its degree of blackness allows you to vary the temperature of the plate of the seed single crystal and, accordingly, change the growth rate of the ingot of single-crystal SiC.

The design parameters of the devices used in carrying out the actions of the method are given in the above example.

For experimental verification of the method, a plate of a seed crystal 8 of SiC polytype 4H of nominal orientation (0001) and a deviation of 4 ° in the azimuth direction [11–20] with an average surface density of micropores of 10–30 cm ^{–3 with a} diameter of 3 inches and a thickness of 0 was used. 8 mm. This material was subjected to etching in molten KOH alkali for 10 min at 600 ° C and ultrasonic washing in deionized water to remove the defective surface layer remaining after preliminary machining of the seed single crystal plate. To create layers for various functional purposes, deposited on a wafer surface of a SiC seed single crystal, not intended for growth of a single-crystal SiC ingot, solutions of synthetic phenol-formaldehyde resins were used, a high-purity graphite powder from Grafi (Russia) and / or soot from Mitsubishi Chemical Corp was used as a carbon source . (Japan) and as a solvent various alcohols or acetone.

The components of each layer were mixed in the desired proportion and mixed thoroughly. The deposition of layers was carried out on a thoroughly cleaned fat-free surface of a seed single crystal plate, not intended for growth of a single-crystal SiC ingot. Several layers of various functional purposes were applied sequentially, they were annealed and cooled on the surface of a seed single crystal plate, not intended for growth of a single-crystal SiC ingot. The duration and temperature of the deposition, drying and cooling depended on the nature of the dispersion medium and binder used.

In the above example, a seed single crystal plate with 6 successively deposited layers was used.

The holder is made of structural graphite MPG-6 with a thickness of 1.5 mm, with linear dimensions of the ring 180 mm at D = 74 mm, where D is the diameter of the circle inscribed in the inner hole of the ring (see Fig. 2). Thus, the step width t for mounting a seed plate of a single crystal with a diameter of 3 inches (= 76.2 mm) is slightly more than 1 mm. The depth of the step on the surface of the holder is 0.5 mm, so the plate of the seed silicon carbide single crystal will protrude 0.8-0.5 = 0.3 mm above the surface of the holder. The width of the protrusion h was 3 mm, the length s was 6 mm.

To implement the method, a crucible with an inner diameter of 170 mm was used, on the inner surface of the wall of which a ledge was made in the upper part. The inner diameter of the growth crucible above the ledge was 180 mm. SiC powder was poured into the crucible (item 12 in FIG. 1). As SiC powder, high-purity pre-sintered powdery silicon carbide manufactured by Saint-Gobain (Norge), with a grain size of ≈100 μm, was used. A holder 7 was installed on the ledge 3 of the crucible wall 1. After the holder was installed in the holder’s inner hole, a seed single crystal plate 8 was deposited with layers of various functional purposes so that the surface intended for the growth of a single-crystal silicon carbide was facing the inner space of the crucible. After installing the seed single crystal plate, the holder was covered with a preliminary annealed TRG plate with a diameter of 180 mm and a thickness of 0.8 mm (pos. 9 in Fig. 1), then with a MPG-6 graphite plate with a thickness of 4 mm and a diameter of 180 mm (pos. 10 in Fig. 1). All plates were pressed by means of a retaining ring (pos. 11 in Fig. 1) made of graphite of the same grade with a diameter of 188 mm, with a cross section of 10 × 10 mm, which was mounted on top of the crucible space.

The vacuum chamber 6 was pumped out to a pressure of 8⋅10 ^-6 mm Hg, and the crucible was heated to 1000 ° C using a spiral 4 resistive heater and kept at this temperature for 3 hours to remove residual contaminants. After that, the vacuum chamber 6 was filled with argon to a pressure of 100 mm Hg. and heated to a source temperature of SiC equal to 2250 ° C. The temperature of the plate of the seed single crystal was 2150 ° C. It was held at the indicated temperature and pressure for 1 h, after which the vacuum chamber 6 was pumped out to an argon pressure of 3 mm Hg, at which a single-crystal SiC ingot grew on the seed single crystal plate 8 for 2-48 hours. At the end of growing the single-crystal SiC ingot, the vacuum chamber 6 was cooled to room temperature and depressurized. The crucible was removed from the space of the growth chamber, and a plate of a seed single crystal with a grown ingot of monocrystalline silicon carbide of polytype 4H was removed from the growth crucible.

The growth rate of the ingot was determined by direct measurement of the thickness of the single-crystal ingot, as well as gravimetrically (by changing the weight of the plate of the seed single crystal 8 with a single-crystal silicon carbide ingot 16 grown on it). The density of micropores and dislocations in a single-crystal ingot was determined under a microscope after cutting the ingot into plates, followed by alkaline etching of the surface of single-crystal silicon carbide plates. The uniformity of the thermal contact and the presence of edge flows were evaluated visually, by the method of expert estimates, by the shape and uniformity of the growth profile of a single-crystal SiC ingot at the initial stages of growth (1-2 hours of growth).

The results of 8-fold tests of the method in argon atmosphere at the indicated temperatures of the SiC source and the seed single crystal wafer equal to 2250 ° C and 2150 ° C, respectively, the pressure in the vacuum chamber 6, equal to 3 mm RT.article, and various values of the structural parameters are given in the table.

As can be seen from the table, the use of the proposed method allows to obtain the claimed technical result, which consists in improving the quality of a single-crystal SiC ingot due to a decrease in the elastic stresses in the plate of a seed single crystal of SiC and achieving a uniform growth rate over the entire surface of the plate of a seed single crystal with the formation of an almost flat crystallization front. If the depth of the step 14 exceeds the thickness of the plate of the seed single crystal 8, to achieve a uniform high-quality compression of the plate of the seed single crystal 8 and the plate TRG 9, as a rule, fails. This leads to non-uniform growth and evaporation of the surface of the plate of the seed single crystal 8. Also, uniform deposition cannot be achieved if the plate of the TEG 9 is completely absent.

Other limitations of the method are associated with the structural dimensions of the protrusions 13 and ledges 14: very narrow protrusions begin to spring and do not provide a good compression of the surfaces. Narrow ledges (at t <1 mm) are fragile and can collapse. When using very wide protrusions (as well as generally without protrusions), edge sagging at the contacts of the holder 7 with the plate of the seed single crystal 8 cannot be avoided.

Claims (1)

A method for producing single-crystal SiC, including the sublimation of a source of SiC placed in a crucible onto a plate of a SiC seed single crystal placed on a flat-ring holder, wherein one or more of the SiC seed single crystal is applied from the side not intended for growth of a single crystal SiC ingot layers providing thermochemical stability and predetermined temperature conditions on the surfaces of the plate of the seed single crystal SiC, and the holder with the plate of the seed single crystal SiC they are mounted in the crucible so that the surface of the plate intended for the growth of a single-crystal SiC ingot faces inside the crucible and contacts during sublimation with the gaseous medium inside the crucible, characterized in that protrusions of width h = are periodically made around the circumference of the inner cylindrical surface of the holder’s flat ring (1-3) ⋅t and length S = (1-10) ⋅h, the ends of which are equipped with ledges with a depth of k = 0.3-1 mm and a width of t = 0.5-2.0 mm, to accommodate a plate of a seed single crystal SiC thickness H exceeding depth mortar k, and on top of the plate holder with applied layers is placed a plate of expanded graphite thickness exceeding the value (N-k), and further fixed clamping element in the form of a rigid 1.5-8 mm thick plate and the locking ring of thermostable materials.

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