JP4100228B2 - Silicon carbide single crystal and manufacturing method thereof - Google Patents

Description

【００７０】
表１から、本発明の方法により、冷却法と温度勾配法のいずれの結晶成長方法おいても、2000℃以下の融液温度で、マイクロパイプ欠陥を含んでいない炭化珪素バルク単結晶を実用に十分な成長速度で製造することができることがわかる。冷却速度または温度勾配を大きくすると、炭化珪素単結晶の成長速度が増大する。この結果から、合金融液中に溶解したＣが基板表面に達する拡散が炭化珪素の結晶成長の律速過程になっているものと考察される。
【００７１】
なお、実施例１〜３(冷却法)では、冷却による結晶成長を１回しか実施しなかったため、成長時間がより長い実施例４〜６(温度勾配法)より結晶の厚みは小さくなった。実施例１〜３においても、加熱と冷却を繰り返すことにより結晶の厚みを大きくできることはいうまでもない。
【００７２】
実施例１〜６および比較例１〜４で得られた炭化珪素単結晶はいずれも、ラマン分光法および電子線回折により調べた結果、基板と同じ６Ｈ−ＳｉＣの結晶構造を有していた。
【図面の簡単な説明】
【図１】黒鉛坩堝中でＳｉ_０．８Ｔｉ_０．２融液を1850℃で、又はＳｉ_０．４Ｍｎ_０．６融液を1650℃で、坩堝から溶解したＣ濃度が飽和するまで均熱加熱した後に冷却して種結晶基板上に炭化珪素単結晶を成長させた場合の冷却速度と成長速度との関係を示すグラフである。
【図２】冷却法により炭化珪素単結晶を製造するために利用し得る結晶成長装置の一例を示す模式的断面図である。
【図３】温度勾配法により炭化珪素単結晶を製造するために利用し得る結晶成長装置の一例を示す模式的断面図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a high-quality large (bulk) single crystal of silicon carbide (SiC) particularly suitable as a substrate material for optical devices and electronic devices, and in particular, such carbonization at a temperature of 2000 ° C. or less which is preferable for operation. The present invention relates to a method capable of stably producing a silicon single crystal. The invention also relates to a good quality silicon carbide bulk single crystal thus produced.
[0002]
[Prior art]
Silicon carbide (SiC) is one of the thermally and chemically stable compound semiconductors. Compared to silicon (Si), the band gap is about 3 times, the breakdown voltage is about 10 times, and the electron saturation rate is It has the characteristics that the thermal conductivity is about twice as large as that of about twice. Because of these excellent features, silicon carbide is expected to be used as a substrate material for electronic devices such as power devices that break the physical limitations of Si devices and environmental devices that operate at high temperatures.
[0003]
On the other hand, in optical devices, gallium nitride (GaN) -based materials aiming at shorter wavelengths are being developed. Silicon carbide has attracted attention as a substrate material for epitaxial growth of a GaN layer, because lattice mismatch with GaN is much smaller than that of other compound semiconductors.
[0004]
It is well known that silicon carbide has a large number of crystal polymorphisms (polytypes) in which the stacking mode of atoms differs in the c-axis direction. Typical polytypes are 3C, 6H, 4H, 15R. Here, the symbol C represents a cubic crystal, H represents a hexagonal crystal, R represents a rhombohedral structure, and the number before the symbol represents the number of stacked molecules in one period. Therefore, 3C is a cubic crystal with a period of 3 molecules, 4H and 6H are hexagonal crystals with a period of 4 and 6 molecules, respectively, and 15R is a period of 15 molecules. Means rhombohedral structure.
[0005]
Application of silicon carbide to electronic or optical devices requires a good quality silicon carbide bulk single crystal that is free from defects or very few. In the sublimation method (a general method for producing a SiC single crystal) described later, other crystal forms are likely to be mixed due to polymorphic transition during the growth of the SiC single crystal. As a result, lattice defects such as micropipes and stacking faults are generated. A micropipe is a hollow penetration defect having a diameter of about 2 μm or more, a large Burgers vector for crystal transition, and a transition core that is hollow. A stacking fault is a disorder of stacking due to crystal transition. In particular, since a micropipe is a fatal defect, a portion with a micropipe defect cannot be used as a substrate.
[0006]
Conventionally known methods for producing a silicon carbide single crystal include sublimation, chemical vapor deposition (CVD), atchison, and liquid phase epitaxy (liquid phase epitaxy [LPE] methods) belonging to the vapor phase growth method. Solution growth method belonging to the above).
[0007]
In the sublimation method, silicon carbide powder as a raw material is sublimated at a high temperature of 2200 to 2500 ° C., and silicon carbide is deposited on a seed crystal substrate made of a silicon carbide single crystal arranged in a low temperature part. In the CVD method, a silane gas and a hydrocarbon gas are used as raw materials, and a silicon carbide single crystal is epitaxially grown on a heated substrate such as Si by a gas phase chemical reaction.
[0008]
The Atchison method is a method of manufacturing silicon carbide by heating it to a high temperature of 2500-2700 ° C by charging and energizing a silicic acid and carbon around the carbon electrode. Industrial production of silicon carbide crystals for artificial abrasives It has been used for a long time. A silicon carbide single crystal is produced as a by-product.
[0009]
In the solution growth method, Si or a Si-containing alloy is melted in a graphite crucible, carbon is dissolved in the melt from the graphite crucible, and a silicon carbide single crystal layer is liquid phase deposited on a seed crystal substrate placed in a low temperature part. It is a method of growing by. As a solution growth method using an Si-containing alloy, there is also a method in which a silicon carbide single crystal is similarly grown from a solution in which C and Si are dissolved in molten Cr.
[0010]
A silicon carbide single crystal grown by a sublimation method contains many lattice defects such as micropipe defects and stacking faults. In the sublimation method, there is no SiC gas in the sublimation gas, and Si and Si vaporized from the silicon carbide powder. ₂ C, SiC ₂ And C vaporized from the graphite jig. The large number of lattice defects generated in the sublimation method is due to the fact that it is extremely difficult to stoichiometrically control these various gas partial pressures and that complicated reactions are involved.
[0011]
However, as will be described later, since other methods cannot stably produce a silicon carbide bulk single crystal at a sufficient growth rate, many of the silicon carbide bulk single crystals have been produced by a sublimation method. In the sublimation method, since the manufactured silicon carbide bulk single crystal includes a large number of micropipe defects, it is difficult to manufacture a semiconductor device of several mm square with a high yield. Research on sublimation methods aimed at reducing micropipe defects has also been vigorously conducted, but it has been reported that micropipe defect-free silicon carbide bulk single crystals substantially free of micropipe defects were obtained by the sublimation method. Is not yet.
[0012]
The CVD method supplies a raw material in a gas state, so that the supply amount of the raw material is small and is not suitable for manufacturing a bulk single crystal necessary for manufacturing a silicon carbide substrate. Therefore, the CVD method is exclusively used as a method for growing a thin film silicon carbide single crystal.
[0013]
The Atchison method cannot produce a high-purity silicon carbide single crystal due to a large amount of impurities in the raw material and cannot obtain a single crystal having a size required for the substrate material.
Since the solution growth method is crystal growth under a thermal equilibrium state, a high-quality silicon carbide single crystal with very few lattice defects and good crystallinity can be obtained. However, since the dissolution concentration of carbon from the graphite crucible into the melt is generally low, the growth rate of the silicon carbide crystal is very slow. In the Si melt method using Si as a melt, the growth rate of silicon carbide crystals is said to be 5 to 12 μm / hr at a melt temperature of 1650 ° C. This growth rate is 1 to 2 orders of magnitude smaller than that of the sublimation method. Although it is possible in principle to increase the growth rate by raising the melt temperature to 2000 ° C or higher and increasing the carbon concentration that can be dissolved in the melt, the evaporation of the Si melt is intense under normal pressure. If the pressure is applied, the apparatus becomes large, both of which have problems in industrial production.
[0014]
In order to increase the carbon concentration and increase the growth rate of the silicon carbide crystal while suppressing the evaporation of the Si melt, a transition metal such as Cr or Sc or a rare earth metal is also added to the melt. However, even in such a case, only a thin film having a thickness of about several μm has been realized so far by the Si melt method. Therefore, like the CVD method, the solution growth method is a method of forming a thin film on a seed crystal substrate, and has been considered to be unsuitable for growing a bulk single crystal.
[0015]
In Japanese Patent Laid-Open No. 2000-264790, a raw material containing at least one transition metal and Si and C is heated and melted in a carbonaceous crucible (actually a graphite crucible) to form a melt, and the melt is cooled. Alternatively, it is disclosed that a silicon carbide bulk single crystal is deposited and grown on a seed crystal substrate by forming a temperature gradient in the melt. As a specific example, in an atomic ratio of 31Mo-66Si-3C, 54Cr-23Si-23C or 29Co-65Si-6C, the growth rate at a growth temperature of 1750 to 2150 ° C. depends on the temperature gradient of the melt. The average was 200 to 800 μm / hr.
[0016]
However, in this method, carbon is not supplied by melting from the graphite crucible, but a raw material containing carbon in a predetermined ratio is charged into the graphite crucible. Therefore, carbon from the crucible and carbon charged as a raw material inevitably compete and dissolve. As a result, a part of the carbon charged as a raw material remains undissolved in the melt, and this unresolved carbon can become the nucleus of silicon carbide precipitation, thereby inhibiting crystal growth on the seed crystal substrate immersed in the melt. The newly grown silicon carbide crystal is easily polycrystallized. Further, it was confirmed that only a growth rate of 100 μm / hr or less can be obtained at a temperature of 2000 ° C. or less.
[0017]
[Patent Document 1]
JP 2000-264790 A
[0018]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for stably producing a high-quality silicon carbide bulk single crystal with few lattice defects at a practical growth temperature and growth rate. The specific purpose is to stabilize a high-quality silicon carbide bulk single crystal substantially free of micropipe defects at a practical growth rate by a solution growth method at an operationally favorable melt temperature of 2000 ° C. or less. Is to manufacture.
[0019]
[Means for Solving the Problems]
According to the present invention, Si, C, and M (M: one of Mn or Ti) are included, and the atomic ratio of Si and M is Si. _1-x M _x When M is Mn, 0.1 ≦ x ≦ 0.7, and when M is Ti, 0.1 ≦ x ≦ 0.25. A silicon carbide single crystal is grown on the seed crystal substrate by immersing the seed crystal substrate and bringing SiC into a supersaturated state by supercooling the combined financial liquid at least around the seed crystal substrate A method for producing a single crystal is provided.
[0020]
“At least the cooling of the combined financial liquid around the seed crystal substrate” can be achieved by (1) cooling the combined financial liquid or (2) providing a temperature gradient in the combined financial liquid. Hereinafter, the method (1) is referred to as a “cooling method”, and the method (2) is referred to as a “temperature gradient method”.
[0021]
In the cooling method, the temperature of the combined financial liquid during substrate immersion is preferably 1650 ° C. or more and 2000 ° C. or less, and more preferably 1650-1850 ° C. The cooling rate is preferably 1 to 6 ° C./min. After cooling the combined liquid at a temperature higher than the solidus temperature of the alloy, the supercooling is repeated by repeatedly heating and cooling the melt, and the growth of the silicon carbide single crystal on the substrate is continued. Thus, large silicon carbide can be produced.
[0022]
In the temperature gradient method, the temperature gradient of the financial solution is preferably 5 to 100 ° C./cm, and the temperature of the financial solution near the substrate (hereinafter referred to as the growth interface temperature) is preferably 1450 ° C. or higher and 2000 ° C. or lower. More preferably, it is 1650-1850 degreeC.
[0023]
In either method, C in the combined financial liquid is preferably supplied by melting a carbonaceous crucible containing the combined financial liquid.
According to the method of the present invention, a silicon carbide bulk single crystal that has not been able to be produced in the prior art and is substantially free of micropipe defects, preferably having a diameter of about 2 μm or more by inspection with an optical microscope after etching with molten KOH. It becomes possible to provide a silicon carbide bulk single crystal free from micropipe defects in the sense that micropipes are not seen.
[0024]
Here, “silicon carbide bulk single crystal” means a silicon carbide single crystal having a thickness of 50 μm or more. In view of mechanical strength, the thickness of the silicon carbide bulk single crystal is preferably 200 μm or more, more preferably 500 μm or more, and most preferably 1500 μm or more, which is easy to handle as a single crystal of the substrate material.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
The present inventors repeated experiments on the formation behavior of a silicon carbide single crystal from a melt of a ternary alloy of Si-C-M, and added based on predictions from calculations of their ternary phase diagrams. The conditions such as metal species M, composition ratio, SiC crystal growth rate, temperature history, etc. were studied.
[0026]
As a result, M is Mn or Ti, and the atomic ratio between Si and M is Si _1-x M _x When M is Mn, 0.1 ≦ x ≦ 0.7, and when M is Ti, 0.1 ≦ x ≦ 0.25, the polymorphic transition at a melt temperature of 2000 ° C. or less. It has been found that a silicon carbide bulk single crystal can be stably produced at a growth rate sufficient for practical use without causing an increase in lattice defects.
[0027]
In the experiment, first, Si and an additive element M selected from various metals were charged into a graphite crucible, the crucible was heated to 1700 ° C. for 1 hour in a soaking furnace under Ar atmospheric pressure, and Si— was dissolved by elution of carbon from the crucible. A C-M ternary alloy melt was produced. Thereafter, the graphite crucible was cooled to 1500 ° C. at a cooling rate of 1 ° C./min, and the temperature below 1500 ° C. was allowed to cool to room temperature. The obtained coagulated mass is HF-HNO. ₃ Acid etching was performed with (1: 1), and silicon carbide crystals grown by the generation of natural nuclei were recovered. The effectiveness of the additive element on the growth rate of the silicon carbide single crystal was judged from the size of the obtained silicon carbide crystal. For comparison, the same experiment was performed with a melt charged with only Si without using an additive element.
[0028]
As a result, when the additive element was Mn or Ti, a very large crystal (2 mm or more) was obtained as compared with a crystal (several tens of μm) crystallized from a melt charged with only Si. These crystals were found to contain no micropipe defects by microstructure observation by molten KOH etching, and were found to have very few lattice defects by TEM (transmission electron microscope) observation.
[0029]
When a silicon carbide bulk single crystal is grown on a seed crystal substrate made of a silicon carbide single crystal using a combined financial liquid charged with Si-Mn or Si-Ti, Si and M (M is Mn or Ti). Atomic ratio (Si _1-x M _x When x) in the above condition satisfies the above conditions, sufficient C solubility can be ensured, a silicon carbide single crystal is crystallized as an initial crystal, and a high-quality bulk single crystal having no micropipe defects at a growth rate of several hundred μm / hr or more. It was confirmed that crystals could be produced.
[0030]
When the additive element M is Mn, Si _1-x Mn _x When the atomic ratio x of Mn represented by is less than 0.1, the solubility of C is low and the growth rate of the silicon carbide single crystal is low. On the other hand, when x exceeds 0.7, the solubility of C becomes too high, and there is a high possibility that C crystallizes on the seed crystal substrate and the crystal growth of silicon carbide is hindered. The atomic ratio x of Mn is preferably in the range of 0.35 to 0.65. When x is 0.35 or more, the effect of promoting the growth rate of silicon carbide due to an increase in the amount of dissolved C appears significantly. When x is 0.65 or less, the possibility that C crystallizes and inhibits the crystal growth of silicon carbide is reduced in a wider melt temperature region. A more preferable atomic ratio x of Mn is 0.45 to 0.65.
[0031]
When the additive element M is Ti, Si _1-x Ti _x When the atomic ratio x of Ti expressed by the formula is less than 0.1, the solubility of C is low, and the growth rate of the silicon carbide single crystal is low. When x exceeds 0.25, a Ti-containing layer is easily formed on the seed crystal substrate, and the possibility that the growth of the silicon carbide single crystal layer is hindered increases. This Ti-containing layer is considered to be titanium carbide (TiC). The atomic ratio x of Ti is preferably in the range of 0.15 to 0.25.
[0032]
The growth of the silicon carbide bulk single crystal in the method of the present invention can be carried out by either the cooling method or the temperature gradient method described above. In order to prevent undissolved C from being present in the melt, it is preferable that C of the raw material is supplied into the melt by melting from a carbonaceous crucible such as a graphite crucible. If it can be formed, a part or all of C may be put into a crucible together with other raw materials (Si and M). Hereinafter, a case where C is mainly supplied from a graphite crucible will be described as an example.
[0033]
In the case of the cooling method, raw materials Si and Ti or Mn and optionally C are charged into a crucible at a predetermined ratio, and then heated to the liquidus temperature or higher of the composition to melt, thereby forming a melt. Even after the melt is formed, soaking is continued at a constant temperature until the C concentration in the melt reaches or near the saturation concentration due to dissolution of C from the graphite crucible. When C is added to the crucible as an additive material, heating is continued until C is completely dissolved.
[0034]
When M is either Mn or Ti, the melt temperature is preferably 1650 ° C. or higher and 2000 ° C. or lower, more preferably 1650 to 1850 ° C. When the temperature is higher than 1850 ° C., in particular, higher than 2000 ° C., the evaporation of the melt becomes remarkable and inhibits the stable growth of the silicon carbide crystal. When the melt temperature is lower than 1650 ° C., the amount of dissolved C is reduced, and the production efficiency of the silicon carbide single crystal is lowered. Further, when M is Ti, the stability of the single crystal growth is also lowered because the temperature is close to the solidus temperature.
[0035]
A seed crystal substrate made of a SiC single crystal having the same crystal form (eg, 6H) as that of the single crystal to be manufactured is melted in the melt of the alloy of Si, M (M = Mn or Ti), and C. Immerse. The seed crystal substrate may be immersed at any point during the heating of the melt.
[0036]
Thereafter, the combined financial liquid is slowly cooled at a constant cooling rate, so that the melt temperature is lower than the liquidus temperature but higher than the solidus temperature, thereby bringing SiC into a supersaturated state. Thereby, the SiC crystal is epitaxially grown on the seed crystal substrate, and a silicon carbide single crystal having the same crystal form as the substrate is generated on the substrate. The cooling rate at this time is an important factor that determines the growth rate.
[0037]
FIG. 1 shows a Si-Ti melt (Si _0.8 Ti _0.2 ) At 1850 ° C. or Si-Mn melt (Si _0.4 Mn _0.6 ) Is heated at 1650 ° C. in a graphite crucible to dissolve C to a saturated concentration, and the relationship between the growth rate of the silicon carbide single crystal on the seed crystal substrate is shown. As can be seen from this figure, when the cooling rate is lower than 1 ° C./min, the growth rate of the silicon carbide crystal decreases. On the other hand, when the cooling rate is higher than 6 ° C./min, crystal growth of silicon carbide due to the generation of natural nuclei occurs, and such crystal growth occurs in the vicinity of the substrate, and many silicon carbide crystals grown on the substrate. It becomes easy to crystallize. Accordingly, the cooling rate is preferably in the range of 1 to 6 ° C./min, more preferably in the range of 2 to 5 ° C./min.
[0038]
When cooling is completed, the driving force for crystallizing silicon carbide is lost. If the silicon carbide single crystal grown on the seed crystal substrate is large enough, pull the substrate out of the melt and adjust the composition if necessary to use the melt for the next crystal growth, Alternatively, the whole is solidified by cooling to a temperature lower than the solidus temperature.
[0039]
However, normally, it is not possible to obtain a sufficiently large silicon carbide bulk single crystal by one growth. In that case, while the substrate is immersed in the financial solution or once pulled out of the melt, the melt is again heated to a soaking temperature before cooling to dissolve C from the graphite crucible (and / or C Is added and completely dissolved), and the thickness of the silicon carbide single crystal grown on the substrate can be increased by repeating cooling or dipping and cooling the substrate again. By repeating this soaking and cooling many times, a bulk single crystal (ingot) that is long in the thickness direction can be obtained on the substrate. In that case, the seed crystal substrate is moved little by little as necessary as the growth thickness increases.
[0040]
In the temperature gradient method, a silicon carbide single crystal is formed on a seed crystal substrate formed in a melt of an alloy of Si, M (M = Mn or Ti) and C in a crucible and immersed in a low temperature portion of the temperature gradient. Grow. This temperature gradient is usually a vertical gradient, but can also be a horizontal gradient. The temperature gradient can be formed by controlling the heating means arranged around the crucible and optionally using the cooling means arranged around the low temperature part of the crucible. As for the temperature gradient in the vertical direction, it is more convenient for the upper part of the melt to be a low temperature part because the seed crystal substrate does not have to be exposed to the high temperature part.
[0041]
The growth interface temperature (temperature in the vicinity of the substrate in the low temperature portion) of the temperature gradient method is preferably in the range of 1650 to 2000 ° C., more preferably in the range of 1650 to 1850 ° C. when M = Ti. On the other hand, when M = Mn, since the liquidus temperature is lower, the growth interface temperature is preferably in the range of 1450 to 2000 ° C, more preferably in the range of 1650 to 1850 ° C. As the temperature difference between the temperature of the high temperature part and the growth interface temperature increases, the C solubility in the melt increases and the growth rate increases. From the viewpoint of controllability of the temperature difference, It is preferable to set the temperature higher by several ° C. to several hundred ° C. If the temperature of the high-temperature part greatly exceeds 2000 ° C, stable growth is hindered by the evaporation of the melt, etc. It is preferable not to greatly exceed ° C.
[0042]
The temperature gradient is preferably in the range of 5 to 100 ° C./cm. When the temperature is less than 5 ° C./cm, the driving force for diffusion of silicon carbide, which is the solute in the melt, is small, and the growth rate of the silicon carbide crystal is small. When the temperature gradient exceeds 100 ° C./cm, a silicon carbide crystal is generated near the substrate due to the generation of natural nuclei, and the silicon carbide crystal grown on the substrate is easily polycrystallized. The temperature gradient is more preferably 5 to 50 ° C./cm.
[0043]
When C is supplied by melting a carbonaceous crucible such as a graphite crucible, heating of the melt produced in the crucible is continued as in the cooling method, so that at least the C in the melt has a saturated concentration or Try to reach that vicinity. Subsequent or during heating of the melt, the substrate is immersed in the low temperature part of the crucible. Since the amount of C dissolved in the melt depends on the melt temperature, a C concentration gradient is formed in the melt due to the temperature gradient of the melt. This concentration difference becomes a driving force, and C in the melt diffuses from the high temperature side to the low temperature side. C transported by diffusion becomes supersaturated on a silicon carbide seed crystal substrate immersed in a low-temperature melt in a supercooled state lower than the liquidus temperature, and crystallizes as silicon carbide. Grow.
[0044]
Even when a part or all of C is added to the crucible, since the saturation concentration of C dissolved in the melt depends on the temperature, a C concentration gradient is generated in the melt, and the same result as above is obtained. In this case, after the added C is completely dissolved, the seed crystal substrate is immersed in the low temperature portion of the temperature gradient of the melt.
[0045]
The crucible containing the combined financial liquid may be made of a refractory material that does not cause leakage of the melt due to deterioration due to reaction with the melt and does not enter the melt as impurities. When supplying C by melting from a crucible, a carbonaceous crucible, particularly a graphite crucible, is used. When it is not necessary to dissolve C from the crucible (addition of the entire amount of C), a crucible in which a crucible made of graphite or other refractory is covered with high-purity silicon carbide can be used.
[0046]
In order to prevent oxidation of the melt, it is preferable that the periphery of the crystal growth apparatus including the crucible and its heating means is sealed and the inside of the sealed space is a non-oxidizing atmosphere (eg, a rare gas atmosphere).
[0047]
Doped silicon carbide bulk single crystals can also be produced by the method of the present invention. For example, when silicon carbide is doped with Al or B, it becomes a p-type semiconductor, and when doped with N or P, it becomes an n-type semiconductor. The doping element may be added to the crucible. In the case of N, the doping element can be introduced from the atmospheric gas.
[0048]
Since the silicon carbide single crystal produced by the method of the present invention does not produce crystal polymorphism, it has significantly fewer lattice defects than the single crystal produced by the sublimation method. Moreover, the method of the present invention can produce a silicon carbide single crystal at a growth rate sufficient for practical use at an operationally preferable temperature of 2000 ° C. or less. Therefore, according to the present invention, it is possible to produce a silicon carbide bulk single crystal that does not contain micropipe defects. This silicon carbide bulk single crystal is suitable as a substrate for optical devices and electronic devices.
[0049]
[Example 1]
This example illustrates the production of a silicon carbide bulk single crystal by a cooling method using the crystal growth apparatus shown in FIG.
[0050]
The crystal growth apparatus shown in FIG. 2 includes a graphite crucible 3 containing the combined financial liquid 1, and the crucible 3 is surrounded by a resistance heater 2 a made of high-purity graphite. The resistance heater 2 a and the graphite crucible 3 Is surrounded by a heat insulating material 9. The side surface of the graphite crucible 3 is directly measured by a plurality of optical pyrometers 4 through the observation holes provided in the heater 2 a and the heat insulating material 9. The heater 2a is controlled based on the temperature measurement values of the pyrometer 4, and the crucible 3 is heated to a substantially uniform temperature. The atmosphere in the crystal growth apparatus is adjusted to an Ar atmosphere using the gas inlet 7 and the gas outlet 8.
[0051]
Si in the graphite crucible 3 _0.8 Ti _0.2 The alloy raw material (Si and Ti) having the following composition is charged, and the crucible is heated to 1850 ° C. in an Ar atmosphere at atmospheric pressure to melt it. Then, C is introduced into the generated melt from the inner wall of the graphite crucible 3. The melt temperature of 1850 ° C. was maintained for 5 hours so as to dissolve to the saturated concentration. Thereafter, a seed crystal substrate 6 made of 6H—SiC single crystal held by a graphite holding jig 5 was immersed in the melt 1. The graphite crucible 3 and the holding jig 5 were rotated in opposite directions. One hour after the immersion of the substrate 6, cooling was started at a rate of 0.5 ° C./min by controlling the temperature heater 2 a and continued until the temperature of the entire melt 1 reached 1650 ° C. (cooling time 400 minutes) . Thereafter, the holding jig 5 was raised, the substrate 6 was pulled up from the melt 1 and collected, and then the crucible was allowed to cool to room temperature.
[0052]
The thickness (μm) of the silicon carbide bulk single crystal grown on the substrate was measured and divided by the cooling time (hr) to obtain the crystal growth rate (μm / hr).
In addition, after cutting and polishing this silicon carbide bulk single crystal to obtain a [0001] plane, it was treated in molten KOH (450-500 ° C.) for 10 minutes, and then thoroughly washed with water. The number of hexagonal etch pits having a size of about 2 μm or more peculiar to the above was counted. Micropipe defects were determined according to the following criteria.
[0053]
A: The micropipe of the seed crystal is blocked and there are no micropipe defects.
○: The micropipe of the seed crystal is blocked and reduced, but micropipe defects remain.
X: A micropipe is seen as much as a seed crystal.
[0054]
[Example 2]
Si charged in the graphite crucible 3 _0.4 Mn _0.6 A silicon carbide bulk single crystal was grown on the seed crystal substrate 6 by the cooling method in the same manner as in Example 1 except that the alloy raw material was heated and melted at 1650 ° C. and cooled from this temperature to 1450 ° C. I let you.
[0055]
[Example 3]
A silicon carbide bulk single crystal was grown on the seed crystal substrate 6 by the cooling method in the same manner as in Example 2 except that the cooling rate was increased to 2 ° C./min.
[0056]
[Example 4]
This example illustrates the production of a silicon carbide bulk single crystal by the temperature gradient method using the crystal growth apparatus shown in FIG.
[0057]
The crystal growth apparatus shown in FIG. 3 is provided with a graphite crucible 3 containing the combined financial liquid 1, and this crucible 3 is arranged in a reaction tube 10 made of quartz glass, and the graphite crucible 3 is placed on the outer periphery of the reaction tube 10. A high frequency coil 2b for induction heating is provided. Also in the apparatus of FIG. 3, the side surface of the crucible 3 is directly measured by a plurality of optical pyrometers 4. The high frequency induction heating is controlled based on the temperature measurement value on the side surface of the crucible 3. Due to the relative positional relationship between the crucible 3 and the high frequency coil 2b, a temperature difference is formed in the vertical direction of the crucible 3. Specifically, the temperature gradient formed by changing the number of turns and the interval of the coil 2b can be adjusted. In order to obtain a large temperature gradient, it is effective to forcibly cool the low temperature portion of the crucible 3 with a water cooling jig.
[0058]
In this example, the upper part of the graphite crucible 3 is a low temperature part. The temperature of the melt 1 in the vicinity of the seed crystal substrate 6 immersed in the low temperature part was determined by measuring the temperature of the side surface at the substrate position level of the crucible 3 with the pyrometer 4. The temperature gradient was calculated from the temperature difference between the side surface temperature at the position level of the substrate 6 and the highest temperature level and the separation distance.
[0059]
Si in the graphite crucible 3 _0.8 Ti _0.2 The side surface temperature (growth interface temperature) at the position level where the seed crystal substrate 6 on the upper side should be immersed in an Ar atmosphere at atmospheric pressure is 1650 ° C. The alloy raw material was melted by heating. By adjusting the number of turns of the coil 2b and the interval, a temperature gradient of 5 ° C./cm was set from the position level of the substrate 6 toward the lower side of the crucible 3 which is the high temperature side. The maximum temperature at the bottom of the crucible was about 1660 ° C.
[0060]
The combined liquid produced in the graphite crucible 3 was heated for 5 hours while maintaining the above temperature gradient so that C was dissolved in the melt from the inner wall of the crucible to the saturated concentration. After that, the seed crystal substrate 6 made of 6H—SiC single crystal held by the graphite holding jig 5 was immersed in the low temperature portion (side temperature is 1650 ° C. level) above the melt. The graphite crucible 3 and the holding jig 5 holding the single crystal were rotated in opposite directions. After 20 hours from the immersion of the seed crystal substrate 6, the support jig 5 was raised and the substrate 6 was pulled up and collected from the melt 1, and then the melt was allowed to cool to room temperature.
[0061]
The thickness (μm) of the silicon carbide bulk single crystal grown on the substrate was measured and divided by the growth (immersion) time (= 20 hr) to obtain the crystal growth rate (μm / hr). Moreover, it determined similarly to Example 1 about the micropipe defect.
[0062]
[Example 5]
The alloy raw material charged in the graphite crucible 3 is Si. _0.4 Mn _0.6 A silicon carbide bulk single crystal was grown on the seed crystal substrate 6 by the temperature gradient method in the same manner as in Example 4 except that the composition was as follows.
[0063]
[Example 6]
A silicon carbide bulk single crystal was grown on the seed crystal substrate 6 by a temperature gradient method in the same manner as in Example 5 except that the temperature gradient was increased to 20 ° C./cm by increasing the heating temperature of the high temperature part.
[0064]
[Comparative Example 1]
The alloy material charged in the graphite crucible 3 is Si _0.95 Ti _0.05 A silicon carbide bulk single crystal was grown on the seed crystal substrate 6 by the cooling method in the same manner as in Example 1 except that the composition was as follows.
[0065]
[Comparative Example 2]
The alloy material charged in the graphite crucible 3 is Si _0.95 Mn _0.05 A silicon carbide bulk single crystal was grown on the seed crystal substrate 6 by the cooling method in the same manner as in Example 2 except that the composition was as follows.
[0066]
[Comparative Example 3]
The alloy material charged in the graphite crucible 3 is Si _0.95 Ti _0.05 A silicon carbide bulk single crystal was grown on the seed crystal substrate 6 by the temperature gradient method as in Example 4 except that the composition was as follows.
[0067]
[Comparative Example 4]
The alloy material charged in the graphite crucible 3 is Si _0.95 Mn _0.05 A silicon carbide bulk single crystal was grown on the seed crystal substrate 6 by the temperature gradient method in the same manner as in Example 5 except that the composition was as follows.
[0068]
Table 1 summarizes the manufacturing conditions and the measurement results of the single crystal grown on the substrate for the above Examples and Comparative Examples.
[0069]
[Table 1]

[0070]
From Table 1, by the method of the present invention, a silicon carbide bulk single crystal that does not contain micropipe defects is put to practical use at a melt temperature of 2000 ° C. or lower in both the cooling method and the temperature gradient method. It can be seen that it can be produced at a sufficient growth rate. Increasing the cooling rate or the temperature gradient increases the growth rate of the silicon carbide single crystal. From this result, it is considered that the diffusion of C dissolved in the combined financial liquid to the substrate surface is the rate-determining process of silicon carbide crystal growth.
[0071]
In Examples 1 to 3 (cooling method), the crystal growth by cooling was performed only once, so that the crystal thickness was smaller than in Examples 4 to 6 (temperature gradient method) having a longer growth time. In Examples 1 to 3, it goes without saying that the thickness of the crystal can be increased by repeating heating and cooling.
[0072]
All of the silicon carbide single crystals obtained in Examples 1 to 6 and Comparative Examples 1 to 4 had the same 6H—SiC crystal structure as the substrate as a result of investigation by Raman spectroscopy and electron diffraction.
[Brief description of the drawings]
FIG. 1 Si in a graphite crucible _0.8 Ti _0.2 Melt at 1850 ° C or Si _0.4 Mn _0.6 The relationship between the cooling rate and the growth rate when a silicon carbide single crystal is grown on a seed crystal substrate by soaking at 1650 ° C. until the C concentration dissolved from the crucible is saturated and then cooled is shown. It is a graph.
FIG. 2 is a schematic cross-sectional view showing an example of a crystal growth apparatus that can be used for producing a silicon carbide single crystal by a cooling method.
FIG. 3 is a schematic cross-sectional view showing an example of a crystal growth apparatus that can be used for manufacturing a silicon carbide single crystal by a temperature gradient method.

Claims (8)

A method for producing a silicon carbide single crystal, comprising Si, C and M (M: one of Mn or Ti), wherein the atomic ratio of Si and M is represented by the formula Si _1-x M _x , in the melt but not containing C undissolved alloy when a Mn 0. 35 ≦ x ≦ 0 . 65, when M is Ti is 0. 15 ≦ x ≦ 0. 25, silicon carbide A method of growing a silicon carbide single crystal on the seed crystal substrate by immersing the seed crystal substrate and bringing SiC into a supersaturated state by supercooling the combined liquid at least around the seed crystal substrate .   The method of claim 1, wherein the supercooling of the combined financial liquid is achieved by cooling the combined financial liquid.   3. The method according to claim 2, wherein the temperature of the financial solution when immersed in the substrate is in a temperature range of 1650 ° C. or more and 2000 ° C. or less, and the cooling rate is 1 to 6 ° C./min.   After the cooling of the combined liquid is finished at a temperature higher than the solidus temperature of the alloy, the supercooling is repeated by repeating heating and cooling of the melt, and the growth of the silicon carbide single crystal on the substrate is continued. The method of claim 2.   The method according to claim 1, wherein the supercooling of the combined financial liquid is achieved by a temperature gradient provided in the combined financial liquid. The method according to claim 5 , wherein the temperature gradient of the combined liquid is 5 to 50 ° C./cm , and the temperature of the combined liquid in the vicinity of the seed crystal substrate is 1450 ° C. or higher and 2000 ° C. or lower.   The method according to claim 3 or 6, wherein the temperature range is 1650 to 1850 ° C.   The method according to claim 1, wherein C in the combined financial liquid is supplied by melting a carbonaceous crucible containing the combined financial liquid.

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