JP6060863B2 - SiC single crystal and method for producing the same - Google Patents

Description

  The present invention relates to a SiC single crystal suitable as a semiconductor element and a method for manufacturing the same, and more particularly to a SiC single crystal having a large thickness and few defects, and a method for manufacturing a SiC single crystal by a solution method.

  SiC single crystals are very thermally and chemically stable, excellent in mechanical strength, resistant to radiation, and have excellent physical properties such as higher breakdown voltage and higher thermal conductivity than Si single crystals. . Therefore, it is possible to realize high power, high frequency, withstand voltage, environmental resistance, etc. that cannot be realized with existing semiconductor materials such as Si single crystal and GaAs single crystal, and power devices that enable high power control and energy saving. Expectations are growing as next-generation semiconductor materials in a wide range of materials, high-speed and large-capacity information communication device materials, in-vehicle high-temperature device materials, radiation-resistant device materials and the like.

  Conventionally, as a method for growing a SiC single crystal, a gas phase method, an Acheson method, and a solution method are typically known. Among the vapor phase methods, for example, the sublimation method has a defect that a grown single crystal is liable to cause a lattice defect such as a hollow through defect called a micropipe defect or a stacking fault and a crystal polymorphism, but the crystal growth. Due to the high speed, many of SiC bulk single crystals are conventionally produced by a sublimation method. Attempts have also been made to reduce defects in the grown crystal, and the dislocation density propagates in the <0001> direction by repeatedly growing crystals on the (11-20) plane and the (1-100) plane by the sublimation method. Has been proposed (Patent Document 1). In the Atchison method, since silica and coke are used as raw materials and heated in an electric furnace, it is impossible to obtain a single crystal with high crystallinity due to impurities in the raw materials.

  In the solution method, an Si melt or an alloy is melted into the Si melt in a graphite crucible, C is dissolved in the melt, and a SiC crystal layer is deposited on a seed crystal substrate placed in a low temperature portion to grow. Is the method. Since the crystal growth is performed in the solution method in a state close to thermal equilibrium as compared with the gas phase method, it can be expected to reduce defects. For this reason, recently, several methods for producing a SiC single crystal by a solution method have been proposed. A method for obtaining a SiC single crystal having a growth surface with excellent flatness (Patent Document 2), a SiC single crystal with few crystal defects, and the like. A method of obtaining a crystal (Patent Document 3) and a SiC single crystal manufacturing apparatus (Patent Document 4) for suppressing the generation of polycrystals have been proposed.

Japanese Patent Laid-Open No. 2003-119097 JP 2007-197231 A JP-A-6-227886 JP 2012-136386 A

  As described in Patent Documents 1 to 4, attempts have been made to reduce defects in grown crystals in the sublimation method or the solution method. However, in order to stably obtain a high-quality SiC single crystal that can be used as a semiconductor element, the above method is still insufficient, and in particular, an SiC single crystal that does not contain threading dislocations is manufactured with a high yield. That is still difficult. In the sublimation method, it is difficult to obtain a SiC single crystal containing almost or no threading dislocations. In the solution method, the dislocation of the seed crystal is easily propagated, and almost or not including threading dislocations. It is difficult to obtain no SiC single crystal. Furthermore, it is very difficult to obtain a SiC single crystal that contains almost no threading dislocations or no threading dislocation and has a large thickness.

  The present invention solves the above-described problems, and has a small single threading dislocation density such as threading screw dislocations, threading edge dislocations, and micropipe defects, and a large growth thickness. An object is to provide a manufacturing method.

The present invention is a method for producing a SiC single crystal, wherein a SiC single crystal is grown by bringing a SiC seed crystal substrate into contact with a Si-C solution having a temperature gradient that decreases in temperature from the inside toward the surface,
When the SiC single crystal is grown with the (1-100) plane as the growth surface, the SiC single crystal having a growth thickness of 4 mm or more is obtained by increasing the temperature gradient of the surface region of the Si-C solution at least once. Grow,
It is a manufacturing method of a SiC single crystal.

The present invention is also a SiC single crystal having a threading dislocation density of 10 pieces / cm ² or less and a growth thickness of 4 mm or more.

  According to the present invention, a SiC single crystal having a small threading dislocation density and a large growth thickness can be obtained.

FIG. 1 is a graph showing the relationship between the thickness of the seed crystal substrate and the crystal growth rate due to the temperature gradient of the surface region of the Si—C solution when SiC crystal growth is continuously performed for 15 hours. FIG. 2 is a graph showing the relationship between the thickness of the seed crystal substrate and the crystal growth rate according to the temperature gradient in the surface region of the Si—C solution when SiC crystal growth is continuously performed for 24 hours. FIG. 3 is a schematic diagram showing the relationship between the crystal thickness and the crystal growth rate that can be obtained in the present invention. FIG. 4 is a schematic cross-sectional view of an example of a single crystal production apparatus that can be used in the present invention. FIG. 5 is a cross-sectional transmission image of the SiC crystal grown in the example. FIG. 6 is a cross-sectional transmission image of the SiC crystal grown in the example. FIG. 7 is a photomicrograph of the etched surface of the seed crystal substrate produced by the sublimation method used in the example and the SiC growth crystal grown from the seed crystal substrate.

  In the present specification, “−1” in the notation of the (1-100) plane and the like is a place where “−1” is originally written with a horizontal line on the number.

  As described in Patent Document 1, the RAF growth method has hitherto been considered effective for reducing defects in crystals, and (11-20) plane (also referred to as a-plane) growth and (1- A crystal with reduced dislocations is produced by repeating 100) plane (also referred to as m-plane) growth. However, it is difficult to obtain a dislocation-free single crystal even by the RAF method, and it is necessary to repeatedly grow the (11-20) plane and the (1-100) plane, and the dislocation density can be further reduced and simplified. New manufacturing methods are desired.

  The present inventors have a large growth thickness with a small threading dislocation density such as screw dislocations, edge dislocations, and micropipe defects that can occur in a grown crystal due to a seed crystal in the production of a SiC single crystal by a solution method. Intensive research was conducted on the production method of SiC single crystals.

  As a result, an SiC single crystal having significantly lower threading dislocation density than the seed crystal is obtained by performing m-plane growth using the (1-100) plane (also referred to as m-plane) of the seed crystal as a base point using a solution method. It was found that can be obtained.

  An SiC single crystal containing little or no threading dislocations can be obtained by growing the SiC single crystal by m-plane growth using a solution method. According to this method, there is no need to repeatedly grow the single crystal by changing the growth surface, and an SiC single crystal with significantly reduced threading dislocations compared to the seed crystal can be obtained only by m-plane growth.

  Furthermore, when growing a SiC single crystal with the (1-100) plane as the growth surface, increasing the temperature gradient of the surface region of the Si—C solution at least once increases the m-plane growth with a large thickness. It was found to be effective for obtaining crystals.

  The present invention is a method for producing a SiC single crystal, wherein a SiC single crystal is grown by bringing a SiC seed crystal substrate into contact with a Si-C solution having a temperature gradient that decreases in temperature from the inside toward the surface. 100) When the SiC single crystal is grown with the growth surface as the growth surface, the temperature gradient of the surface region of the Si-C solution is increased at least once to grow a SiC single crystal having a growth thickness of 4 mm or more. The manufacturing method of a SiC single crystal is an object.

  In the method for producing a SiC single crystal according to the present invention, a solution method is used. The solution method for producing a SiC single crystal is to supersaturate the surface region of the Si-C solution by forming a temperature gradient in the crucible that decreases in temperature from the inside of the Si-C solution toward the surface of the solution. In this method, an SiC single crystal is grown on the seed crystal substrate using the seed crystal substrate brought into contact with the Si-C solution as a base point.

  In this method, a SiC single crystal of a quality generally used for the production of an SiC single crystal can be used as a seed crystal. For example, a SiC single crystal generally prepared by a sublimation method can be used as a seed crystal. The SiC single crystal generally produced by such a sublimation method generally contains many threading dislocations.

  In this method, an SiC seed crystal having a (1-100) plane is used, and a SiC single crystal is grown on a (1-100) plane by using the solution method with the (1-100) plane as a base point. The threading dislocation density of the obtained (1-100) plane grown SiC single crystal is significantly smaller than the threading dislocation density of the seed crystal.

According to this method, the threading dislocation density having a growth thickness of 4 mm or more and including threading screw dislocations, threading edge dislocations, and micropipe defects is 10 pieces / cm ² or less, preferably 5 pieces / cm ^2. Hereinafter, it is possible to obtain a SiC single crystal that is more preferably 1 piece / cm ² or less, and still more preferably 0 piece / cm ² .

  In order to obtain an m-plane grown crystal having a large thickness, a method of increasing the growth rate or extending the growth time can be mentioned. However, in m-plane growth, it is difficult to increase the growth rate because Si-C solution inclusion is likely to occur, and even if the growth time is lengthened, the crystal growth takes a very long time, or a predetermined amount is required. Crystal growth sometimes did not exceed the thickness.

  In addition, in order to obtain an m-plane grown crystal having a large thickness, a method in which growth is repeated a plurality of times can also be mentioned. However, even if the growth is repeated a plurality of times, it takes a very long time to grow the m-plane to a thickness of 4 mm or more, or the crystal does not grow beyond a predetermined thickness.

  Although it is not bound by theory that the crystal growth takes a very long time or does not grow beyond a predetermined thickness, the SiC single crystal is more thermally conductive than the graphite axis. Since the rate is high, it is considered that as the crystal growth thickness increases, the temperature gradient in the interface region between the SiC crystal growth surface and the Si—C solution decreases, and the crystal growth rate decreases.

  FIG. 1 shows the relationship between the crystal thickness and the crystal growth rate depending on the temperature gradient of the surface region of the Si—C solution when SiC crystal growth is continuously performed for 15 hours with (1-100 plane) as the growth surface. Show. In FIG. 1, the temperature gradient in the surface region of the Si—C solution is an average value of the temperature gradient in a range of 3 mm from the surface of the Si—C solution, and the crystal thickness is the SiC used as a seed crystal before the start of growth. The thickness of a single crystal, and the crystal growth rate is a value obtained by dividing the thickness of a crystal grown in 15 hours by 15 hours, and is an average crystal growth rate. FIG. 1 shows that the crystal growth rate decreases as the crystal thickness increases. It can also be seen that the crystal growth rate can be increased by increasing the temperature gradient of the surface region of the Si-C solution.

  FIG. 2 shows the crystal thickness and the crystal growth rate depending on the temperature gradient of the surface region of the Si—C solution when the SiC crystal growth was performed under the same conditions as in FIG. The relationship is shown. As in the case where the SiC crystal growth of FIG. 1 is continuously performed for 15 hours, the crystal growth rate tends to decrease as the crystal thickness increases.

  It can be seen that m-plane growth has such a tendency, and in the middle of m-plane growth, increasing the temperature gradient of the surface region of the Si-C solution at least once can produce an m-plane grown crystal having a large growth thickness. It is effective in obtaining. By this method, an m-plane grown crystal having a thickness of 4 mm or more, preferably 5 mm or more, more preferably 6 mm or more, and even more preferably 7 mm or more can be obtained satisfactorily.

  The SiC single crystal grown by (1-100) plane by the method according to the present invention may contain basal plane dislocations and stacking faults, but the threading dislocation density is very low or zero. When the crystal is further grown with the {0001} plane as the base point, a very high quality SiC single crystal not only containing threading dislocations but also containing basal plane dislocations and stacking faults can be obtained.

  More specifically, from the SiC single crystal grown by (1-100) plane by the method according to the present invention, the crystal is cut out so as to expose the {0001} plane, preferably (000-1) plane, By using it as a seed crystal, {0001} plane growth, preferably (000-1) plane growth can be performed. The {0001} plane grown crystal, preferably the (000-1) plane grown crystal, obtained in this way contains little or no threading dislocations, basal plane dislocations, and stacking faults.

  This is because there are very few or no threading dislocations in the {0001} plane which is the growth base point of the seed crystal, so there is very little or no threading dislocation propagating from the seed crystal to the growing crystal, and This is because the basal plane dislocations and stacking faults that can be included in the crystal are difficult to propagate to the {0001} plane growth crystal. {0001} plane growth can be performed using a solution method, or can be performed using a sublimation method. When the {0001} plane growth is performed by the sublimation method, the growth may be performed with an off angle of several degrees from the {0001} plane.

  Therefore, since the SiC crystal having a large (000-1) plane can be obtained as the growth thickness of the SiC single crystal grown on the m-plane is increased, use this as a seed crystal for {0001} plane growth. Thus, it is possible to obtain a {0001} plane grown crystal having a large diameter and containing little or no defects.

  In the method according to the present invention, when the temperature gradient of the surface region of the Si—C solution is increased, it is preferable not to exceed the initially set crystal growth rate. Usually, at the initial stage of crystal growth, the temperature gradient of the surface region of the Si—C solution is set so that the highest growth rate is obtained in a range where no inclusion occurs.

  In the method according to the present invention, it is preferable that the crystal is grown so that the inclusion of the Si—C solution does not enter. In order to suppress the occurrence of inclusion, it is effective to grow the crystal at a predetermined growth rate or lower. When the crystal is grown continuously for 15 hours, the crystal is grown at an average growth rate of 93 μm / h or lower. In the case where the crystal is grown continuously for 24 hours, the crystal is preferably grown at an average growth rate of 87 μm / h or less.

  In the method according to the present invention, when the crystal is grown continuously for 15 hours or 24 hours, the lower limit of the average growth rate of the SiC crystal is larger than 0 μm / h, preferably 20 μm / h or more, more preferably It is 40 μm / h or more, more preferably 60 μm / h or more, and even more preferably 80 μm / h or more.

  The upper limit of the average growth rate of the SiC crystal when the crystal is grown continuously for 15 hours is preferably 93 μm / h or less, and may be 90 μm / h or less or 80 μm / h or less with a margin. The upper limit of the average growth rate of the SiC crystal when the crystal is grown continuously for 24 hours is preferably 87 μm / h or less, and may be 80 μm / h or less or 70 μm / h or less with a margin.

  In the method according to the present invention, it is preferable to increase the temperature gradient of the surface region of the Si—C solution before the growth thickness of the SiC single crystal reaches 4 mm. This is because when the crystal growth is performed continuously, the growth rate of the SiC single crystal becomes about 4 mm, as shown in FIG. 1, the growth rate becomes very small.

  Before the SiC single crystal growth thickness reaches 3 mm, more preferably 2 mm, even more preferably 1 mm, the temperature gradient of the surface region of the Si-C solution is increased. May be. For example, the temperature gradient may be increased before the growth thickness reaches 1 mm, and then the temperature gradient may be further increased before the growth thickness reaches 1 mm.

  If the growth thickness cannot be monitored during the SiC crystal growth, the crystal thickness and the crystal growth rate due to the temperature gradient of the surface region of the Si-C solution as shown in FIG. The relationship is investigated, and the temperature gradient of the surface region of the Si—C solution may be increased so that a predetermined crystal growth rate is obtained at a timing when the predetermined crystal thickness is reached.

  When the relationship shown in FIG. 1 is obtained, for example, a 2.6 mm thick seed crystal is prepared, and the average temperature gradient in the range of 3 mm depth from the surface of the Si—C solution is 10 ° C./cm. When grown at an average growth rate of 93 μm / h for 15 hours, the crystal grows 1.4 mm, so that a crystal thickness of 4.0 mm is obtained. If the growth is continued for another 15 hours, only an average growth rate of 42 μm / h can be obtained, and a total crystal thickness of 4.6 mm can be obtained by a crystal growth of 0.6 mm. However, when a crystal thickness of 4.0 mm is obtained, if the average temperature gradient in the depth range of 3 mm from the surface of the Si—C solution is increased to 21 ° C./cm and the growth is continued for another 15 hours. The crystal can be grown at an average growth rate of 85 μm / h, and the crystal grows 1.3 mm, so that a total crystal thickness of 5.3 mm is obtained.

  Further, data is collected in advance in advance, and, for example, as schematically shown in FIG. 3, the crystal length (or so as to obtain a substantially constant crystal growth rate within a range below the upper limit growth rate indicated by a broken line) It is also possible to grow a crystal by setting a program of a growth time) and a temperature gradient.

  As described above, in the method according to the present invention, it is possible to increase the temperature gradient of the surface region of the Si—C solution at least once or twice or more during the SiC crystal growth.

  When the growth thickness can be monitored during the SiC crystal growth, the crystal growth rate can be calculated by measuring the crystal growth time. When the growth rate falls, it can be fed back to the setting of the temperature gradient of the surface region of the Si—C solution so that a predetermined crystal growth rate is obtained. For example, the crystal growth rate is measured every short time such as 1 hour or less or in real time, and the temperature gradient of the surface region of the Si-C solution is increased so as to keep the growth rate almost constant regardless of the crystal growth thickness. Also good. In this case, crystal growth as shown in FIG. 3 or crystal growth with a constant growth rate can be performed more easily. When the crystal growth rate can be measured in a short time such as 1 hour or less or in real time, the upper limit of the growth rate is preferably 170 μm / h or less.

  The growth rate of the SiC single crystal can be controlled by controlling the degree of supersaturation of the Si—C solution. Increasing the supersaturation degree of the Si—C solution increases the growth rate of the SiC single crystal, and decreasing the supersaturation degree decreases the growth rate of the SiC single crystal.

  The supersaturation degree of the Si-C solution can be controlled mainly by the surface temperature of the Si-C solution and the temperature gradient of the surface region of the Si-C solution. For example, the surface temperature of the Si-C solution is kept constant. However, if the temperature gradient of the surface region of the Si—C solution is reduced, the degree of supersaturation can be reduced, and if the temperature gradient of the surface region of the Si—C solution is increased, the degree of supersaturation can be increased.

  The method for controlling the temperature gradient of the surface region of the Si—C solution will be described in detail later with reference to the drawings, but the arrangement and configuration of a heating device such as a high-frequency coil arranged around the crucible of the single crystal manufacturing apparatus, By adjusting the output and the like, a predetermined temperature gradient in the vertical direction can be formed on the surface of the Si-C solution.

  Alternatively, the temperature gradient in the surface region of the Si—C solution can be increased by cooling the seed crystal holding shaft. Examples of the method for cooling the seed crystal holding shaft include blowing a gas, flowing cooling water, or bringing a low-temperature member closer to the seed crystal holding shaft. Moreover, the temperature gradient of the surface region of the Si—C solution can be increased also by cooling the grown SiC single crystal. As a method of cooling the grown SiC single crystal, for example, a gas is blown onto at least a part of the grown crystal, or a low temperature member is brought closer.

  The seed crystal used in the method according to the present invention can have any shape such as a plate shape, a disk shape, a columnar shape, a prism shape, a truncated cone shape, or a truncated pyramid shape. The (1-100) plane of the seed crystal can be used as the lower surface of the seed crystal that makes contact with the Si-C solution surface, and the upper surface on the opposite side can be used as a surface that is held by a seed crystal holding shaft such as a graphite shaft. .

  The (1-100) plane of the seed crystal substrate used in the method according to the present invention includes a plane having an offset angle of preferably within ± 10 °, more preferably within ± 5 °, and even more preferably within ± 1 °, Even more preferred is a just surface.

In this specification, the temperature gradient of the surface region of the Si—C solution is a temperature gradient in the vertical direction of the surface of the Si—C solution, and the temperature decreases from the inside of the Si—C solution toward the surface of the solution. It is a temperature gradient. The temperature gradient consists of a temperature A on the surface of the Si—C solution on the low temperature side, a temperature B on the high temperature side at a predetermined depth perpendicular to the solution side from the surface of the Si—C solution, and Si for the seed crystal substrate. It can be calculated as an average value by measuring in advance using a thermocouple before contacting with the -C solution and dividing the temperature difference by the distance between the positions where temperature A and temperature B are measured. For example, when measuring the temperature gradient between the surface of the Si—C solution and the position of the depth Dcm perpendicular to the solution side from the surface of the Si—C solution, the surface temperature A of the Si—C solution and Si -C Difference from temperature B at a position of depth Dcm perpendicular to the solution side from the surface of the solution divided by Dcm:
Temperature gradient (° C./cm)=(B−A)/D
Can be calculated.

  The control range of the temperature gradient is preferably a range from the surface of the Si—C solution to a depth of 3 mm. In this case, in the above formula, the value obtained by dividing the difference between the surface temperature A of the Si—C solution and the temperature B at a depth of 3 mm perpendicular to the solution side from the surface of the Si—C solution by 3 mm is the temperature gradient. (° C./cm).

  If the control range of the temperature gradient is too shallow, the range for controlling the temperature gradient is shallow and the range for controlling the degree of supersaturation of C becomes shallow, and the growth of the SiC single crystal may become unstable. Further, if the range for controlling the temperature gradient is deep, the range for controlling the degree of supersaturation of C is also deep and effective for stable growth of the SiC single crystal. In practice, however, the depth contributing to the growth of the single crystal is Si −. It is sufficient to control the temperature gradient very close to the surface of the C solution and from the surface to a depth of a few millimeters. Therefore, in order to stably perform the growth of the SiC single crystal and the control of the temperature gradient, it is preferable to control the temperature gradient in the depth range.

  Observation of the presence or absence of inclusion in the SiC crystal can be performed using a microscope. When the grown SiC crystal is sliced to a thickness of about 1 mm and observed from below, the SiC single crystal portion appears transparent, and the portion where inclusion exists appears black. Judgment can be made. If it is easy to determine the presence or absence of inclusion, the appearance of the grown crystal may be simply observed.

  Measurement of threading dislocation density including threading screw dislocations, threading edge dislocations, and micropipe defects in SiC crystal is mirror-exposed to expose a surface tilted in the <1-100> direction from the (0001) plane of SiC crystal. It can be performed by polishing and performing molten alkali etching using molten potassium hydroxide, sodium peroxide or the like, emphasizing dislocations, and observing the etched surface with a microscope. The angle inclined from the (0001) plane in the <1-100> direction is preferably 2 to 8 °, more preferably 3 to 8 °, and for example, 4 °.

  As described above, the seed crystal substrate can be installed in the single crystal manufacturing apparatus by holding the upper surface of the seed crystal substrate on the seed crystal holding shaft. A carbon adhesive can be used for holding the seed crystal substrate on the seed crystal holding shaft.

  The contact of the seed crystal substrate with the Si-C solution is such that the seed crystal holding axis holding the seed crystal substrate is lowered toward the Si-C solution surface, and the lower surface of the seed crystal substrate is parallel to the Si-C solution surface. Can be carried out by contacting the Si-C solution. Then, the SiC single crystal can be grown by holding the seed crystal substrate in a predetermined position with respect to the Si—C solution surface.

  The holding position of the seed crystal substrate is such that the position of the lower surface of the seed crystal substrate coincides with the Si-C solution surface, is below the Si-C solution surface, or is relative to the Si-C solution surface. It may be on the upper side. When the lower surface of the seed crystal substrate is held at a position above the Si-C solution surface, the seed crystal substrate is once brought into contact with the Si-C solution, and the Si-C solution is brought into contact with the lower surface of the seed crystal substrate. Then, pull it up to a predetermined position. The position of the lower surface of the seed crystal substrate may coincide with the Si-C solution surface or be lower than the Si-C solution surface, but in order to prevent the occurrence of polycrystals, It is preferable to prevent the Si—C solution from coming into contact. In these methods, the position of the seed crystal substrate may be adjusted during the growth of the single crystal.

  The seed crystal holding axis may be a graphite axis that holds the seed crystal substrate on its end face. The seed crystal holding shaft may be in an arbitrary shape such as a columnar shape or a prismatic shape, and a graphite shaft having the same end surface shape as the shape of the upper surface of the seed crystal substrate may be used.

  In the present invention, the Si—C solution refers to a solution in which C is dissolved using a melt of Si or Si / X (X is one or more metals other than Si) as a solvent. X is one or more kinds of metals, and is not particularly limited as long as it can form a liquid phase (solution) in thermodynamic equilibrium with SiC (solid phase). Examples of suitable metals X include Ti, Mn, Cr, Ni, Ce, Co, V, Fe and the like. The Si—C solution preferably has a composition containing Si and Cr.

  The Si—C solution is more preferably a Si—C solution using a melt of Si / Cr / X (X is one or more metals other than Si and Cr) as a solvent. Furthermore, a Si—C solution using a melt of Si / Cr / X = 30 to 80/20 to 60/0 to 10 in terms of atomic composition percentage as a solvent is more preferable because there is little variation in the dissolved amount of C. For example, in addition to Si, Cr, Ni, or the like can be charged into the crucible to form a Si—Cr solution, a Si—Cr—Ni solution, or the like.

  In the method according to the present invention, the temperature of the Si—C solution refers to the surface temperature of the Si—C solution. The lower limit of the surface temperature of the Si—C solution is preferably 1800 ° C. or higher, and the upper limit is preferably 2200 ° C. Within this temperature range, the amount of C dissolved in the Si—C solution can be increased. Furthermore, when growing an n-type SiC single crystal, the lower limit of the temperature of the surface of the Si—C solution is more preferably 2000 ° C. or higher in that the amount of nitrogen dissolved in the Si—C solution can be increased.

  The temperature of the Si—C solution can be measured using a thermocouple, a radiation thermometer, or the like. Regarding the thermocouple, from the viewpoint of high temperature measurement and prevention of impurity contamination, a thermocouple in which a tungsten-rhenium strand coated with zirconia or magnesia glass is placed in a graphite protective tube is preferable.

  FIG. 4 shows an example of a SiC single crystal manufacturing apparatus suitable for carrying out the method of the present invention. The illustrated SiC single crystal manufacturing apparatus 100 includes a crucible 10 containing a Si-C solution 24 in which C is dissolved in a Si or Si / X melt, and is provided on the surface of the solution from the inside of the Si-C solution. A SiC single crystal can be grown by forming a temperature gradient that decreases toward the surface and bringing the seed crystal substrate 14 held at the tip of the graphite shaft 12 that can be moved up and down into contact with the Si-C solution 24. It is preferable to rotate the crucible 10 and the graphite shaft 12.

  The Si-C solution 24 is prepared by charging a raw material into a crucible and dissolving C in a Si or Si / X melt prepared by heating and melting. By making the crucible 10 a carbonaceous crucible such as a graphite crucible or an SiC crucible, C is dissolved in the melt by melting the crucible 10 to form an Si-C solution. In this way, undissolved C does not exist in the Si—C solution 24, and waste of SiC due to precipitation of the SiC single crystal in the undissolved C can be prevented. The supply of C may be performed by, for example, a method of injecting hydrocarbon gas or charging a solid C supply source together with the melt raw material, or combining these methods with melting of a crucible. Also good.

  In order to keep warm, the outer periphery of the crucible 10 is covered with a heat insulating material 18. These are collectively accommodated in the quartz tube 26. A high frequency coil 22 for heating is disposed on the outer periphery of the quartz tube 26. The high frequency coil 22 may be composed of an upper coil 22A and a lower coil 22B, and the upper coil 22A and the lower coil 22B can be independently controlled.

  Since the crucible 10, the heat insulating material 18, the quartz tube 26, and the high frequency coil 22 become high temperature, they are disposed inside the water cooling chamber. The water-cooled chamber includes a gas inlet and a gas outlet in order to make it possible to adjust the atmosphere in the apparatus to Ar, He, or the like.

  The temperature of the Si—C solution usually has a temperature distribution in which the surface temperature is lower than the inside of the Si—C solution due to radiation or the like. Further, the number and interval of the high frequency coil 22, the high frequency coil 22 and the crucible 10 By adjusting the positional relationship in the height direction and the output of the high-frequency coil 22, the Si—C solution 24 is immersed in the Si—C solution 24 so that the upper part of the solution is low and the lower part of the solution is hot. A predetermined temperature gradient in the vertical direction can be formed on the surface of the C solution 24. For example, the output of the upper coil 22A can be made smaller than the output of the lower coil 22B, and a predetermined temperature gradient can be formed in the Si—C solution 24 such that the upper part of the solution is low and the lower part of the solution is high.

  C dissolved in the Si-C solution 24 is dispersed by diffusion and convection. The vicinity of the lower surface of the seed crystal substrate 14 is lower than the lower part of the Si—C solution 24 due to the output control of the upper / lower stages of the coil 22, the heat radiation from the surface of the Si—C solution 24, and the heat removal through the graphite shaft 12. A temperature gradient that is low in temperature is formed. When C dissolved in the lower part of the solution having a high solubility at a high temperature reaches near the lower surface of the seed crystal substrate having a low solubility at a low temperature, a supersaturated state is obtained, and an SiC single crystal grows on the seed crystal substrate using this supersaturation as a driving force.

  In some embodiments, before the growth of the SiC single crystal, meltback may be performed to dissolve and remove the surface layer of the SiC seed crystal substrate in the Si—C solution. The surface layer of the seed crystal substrate on which the SiC single crystal is grown may have a work-affected layer such as dislocations or a natural oxide film, which must be dissolved and removed before the SiC single crystal is grown. However, it is effective for growing a high-quality SiC single crystal. Although the thickness to melt | dissolves changes with the processing state of the surface of a SiC seed crystal substrate, about 5-50 micrometers is preferable in order to fully remove a process deterioration layer and a natural oxide film.

  The meltback can be performed by forming a temperature gradient in the Si-C solution in which the temperature increases from the inside of the Si-C solution toward the surface of the solution, that is, a temperature gradient opposite to the SiC single crystal growth. it can. The temperature gradient in the reverse direction can be formed by controlling the output of the high frequency coil.

  Melt back can also be performed by immersing the seed crystal substrate in a Si—C solution heated to a temperature higher than the liquidus temperature without forming a temperature gradient in the Si—C solution. In this case, the higher the Si-C solution temperature, the higher the dissolution rate, but it becomes difficult to control the amount of dissolution, and the lower the temperature, the slower the dissolution rate.

  In some embodiments, the seed crystal substrate may be preheated before contacting the seed crystal substrate with the Si-C solution. When a low-temperature seed crystal substrate is brought into contact with a high-temperature Si—C solution, heat shock dislocation may occur in the seed crystal. Heating the seed crystal substrate before bringing the seed crystal substrate into contact with the Si—C solution is effective for preventing thermal shock dislocation and growing a high-quality SiC single crystal. The seed crystal substrate can be heated by heating the entire graphite axis. Alternatively, instead of this method, the Si—C solution may be heated to a temperature at which crystals grow after contacting the seed crystal substrate with a relatively low temperature Si—C solution. This case is also effective for preventing heat shock dislocation and growing a high-quality SiC single crystal.

The present invention is also directed to a SiC single crystal having a threading dislocation density including threading screw dislocations, threading edge dislocations, and micropipe defects of 10 pieces / cm ² or less and a growth thickness of 4 mm or more.

In the SiC single crystal according to the present invention, the threading dislocation density is preferably 5 pieces / cm ² or less, more preferably 1 piece / cm ² or less, and further preferably 0 piece / cm ² .

  The SiC single crystal can be further grown using the SiC single crystal according to the present invention as a seed crystal. The SiC single crystal grown by (1-100) plane by this method contains little or no threading dislocations. Therefore, when the crystal is further grown from the (000-1) plane of this SiC single crystal, It is possible to obtain a very high quality SiC single crystal not including dislocations but also basal plane dislocations and stacking faults. This is because there is very little or no threading dislocations in the (000-1) plane which is the growth base point of the seed crystal, so there is very little or no threading dislocation propagating from the seed crystal to the growth crystal; This is because basal plane dislocations and stacking faults that can be included in the seed crystal are difficult to propagate to the (000-1) plane grown crystal.

(Example 1)
Prepared is a 4H-SiC single crystal in the shape of a rectangular parallelepiped having a length of 10 mm, a width of 10 mm, and a thickness of 1.5 mm, and a bottom surface having a (1-100) plane (just plane). And used as a seed crystal substrate. The upper surface of the seed crystal substrate was bonded to the substantially central portion of the end surface of the columnar graphite shaft using a graphite adhesive.

  Using the single crystal manufacturing apparatus shown in FIG. 4, Si / Cr / Ni was charged as a melt raw material at a ratio of atomic composition percentage of 50:40:10 into a graphite crucible containing the Si—C solution 24. The air inside the single crystal manufacturing apparatus was replaced with helium. The high-frequency coil 22 disposed around the graphite crucible 10 was energized and heated to melt the raw material in the graphite crucible 10 to form a Si / Cr / Ni alloy melt. Then, a sufficient amount of C was dissolved from the graphite crucible 10 in the Si / Cr / Ni alloy melt to form a Si—C solution 24.

  The graphite crucible 10 was heated by adjusting the outputs of the upper coil 22A and the lower coil 22B to form a temperature gradient in which the temperature decreased from the inside of the Si—C solution 24 toward the surface of the solution. Confirmation that the predetermined temperature gradient was formed was performed by measuring the temperature of the Si-C solution 24 using a thermocouple capable of moving up and down. By controlling the output of the high frequency coils 22A and 22B, the temperature on the surface of the Si—C solution 24 is raised to 2000 ° C., and the temperature gradient is 10 to decrease from the inside of the solution toward the solution surface within a range of 3 mm from the solution surface. The output of the high-frequency coil 22 was adjusted to be ° C./cm.

  While maintaining the lower surface (m-plane) of the seed crystal substrate bonded to the graphite shaft in parallel with the Si-C solution surface, the position of the lower surface of the seed crystal substrate is arranged at a position corresponding to the liquid surface of the Si-C solution. Then, seed touch was performed in which the lower surface of the seed crystal substrate was brought into contact with the Si—C solution. Next, the graphite shaft was pulled up so that the position of the lower surface of the seed crystal substrate was located 1.5 mm above the liquid level of the Si—C solution. The SiC crystal was grown by holding for 15 hours at the position pulled up by 1.5 mm.

  After crystal growth for 15 hours, the graphite axis was raised, and the SiC crystal grown from the seed crystal substrate and the seed crystal substrate as a base point was recovered separately from the Si-C solution and the graphite axis. The obtained growth crystal was a single crystal and had a growth thickness of 2.0 mm. The total thickness of the seed crystal substrate and the grown crystal was 3.5 mm. The growth rate was 133 μm / h.

(Example 2)
The 3.5 mm-thick SiC crystal obtained in Example 1 was grown as (1-100) planes under the same conditions as Example 1 by using it as a seed crystal without polishing.

  The obtained growth crystal was a single crystal and had a growth thickness of 0.9 mm. The total thickness of the seed crystal and the grown crystal was 4.4 mm. The growth rate was 60 μm / h.

(Example 3)
The 4.4 mm-thick SiC crystal obtained in Example 2 was used as a seed crystal without being polished as it was, except that the temperature gradient was 21 ° C./cm and the growth time was 24 hours. (1-100) plane growth was performed under the same conditions.

  The obtained growth crystal was a single crystal and had a growth thickness of 2.1 mm. The total thickness of the seed crystal and the grown crystal was 6.5 mm. The growth rate was 87 μm / h.

(Example 4)
The same conditions as in Example 1 except that the 6.5 mm-thick SiC crystal obtained in Example 3 was used as a seed crystal without polishing, and the temperature gradient was 21 ° C./cm (1 -100) plane growth.

  The obtained growth crystal was a single crystal and had a growth thickness of 0.6 mm. The total thickness of the seed crystal and the grown crystal was 7.1 mm. The growth rate was 40 μm / h.

(Example 5)
A 4H-SiC single crystal having a rectangular parallelepiped shape having a size of 10 mm, a width of 10 mm, and a thickness of 1.5 mm, and a SiC single crystal produced by a sublimation method having a (1-100) plane (just plane) on the bottom surface is prepared. Used as a seed crystal substrate. (1-100) plane growth was performed under the same conditions as in Example 1 except that the temperature gradient was 13 ° C./cm and the growth time was 10 hours.

  The obtained growth crystal was a single crystal and had a growth thickness of 1.7 mm. The total thickness of the seed crystal substrate and the grown crystal was 3.2 mm. The growth rate was 170 μm / h.

(Example 6)
Under the same conditions as in Example 5 except that the 3.2 mm-thick SiC crystal obtained in Example 5 was used as a seed crystal without polishing, and the growth time was 24 hours, (1-100) The surface was grown.

  The obtained growth crystal was a single crystal and had a growth thickness of 0.8 mm. The total thickness of the seed crystal substrate and the grown crystal was 4.0 mm. The growth rate was 33 μm / h.

(Example 7)
The growth surface of the SiC crystal obtained in Example 6 was mirror-polished to obtain an SiC crystal having a thickness of 3.7 mm, which was used as a seed crystal and was the same as Example 5 except that the growth time was 24 hours. (1-100) plane growth was performed under the conditions.

  The obtained growth crystal was a single crystal and had a growth thickness of 0.4 mm. The total thickness of the seed crystal substrate and the grown crystal was 4.1 mm. The growth rate was 17 μm / h.

(Example 8)
Under the same conditions as in Example 5, except that the 4.1 mm-thick SiC crystal obtained in Example 7 was used as a seed crystal without polishing, and the growth time was set to 15 hours. (1-100) The surface was grown.

  The obtained growth crystal was a single crystal and had a growth thickness of 0.9 mm. The total thickness of the seed crystal substrate and the grown crystal was 5.0 mm. The growth rate was 60 μm / h.

(Example 9)
Same as Example 5 except that the SiC crystal of 5.0 mm thickness obtained in Example 8 is used as it is as a seed crystal without polishing, the temperature gradient is 21 ° C./cm, and the growth time is 24 hours. (1-100) plane growth was performed under the conditions.

  The obtained growth crystal was a single crystal and had a growth thickness of 1.3 mm. The total thickness of the seed crystal substrate and the grown crystal was 6.3 mm. The growth rate was 54 μm / h.

(Example 10)
A SiC single crystal having a rectangular parallelepiped 4H—SiC single crystal having a thickness of 10 mm, a width of 10 mm, and a thickness of 3.4 mm was prepared by a sublimation method having a (1-100) plane (just plane) on the bottom surface. Used as a seed crystal substrate. (1-100) plane growth was performed under the same conditions as in Example 1 except that the temperature gradient was 21 ° C./cm.

  The obtained growth crystal was a single crystal and had a growth thickness of 1.5 mm. The total thickness of the seed crystal substrate and the grown crystal was 4.9 mm. The growth rate was 100 μm / h.

(Example 11)
A SiC single crystal having a rectangular parallelepiped 4H-SiC single crystal having a thickness of 10 mm, a width of 10 mm, and a thickness of 2.9 mm was prepared by a sublimation method having a (1-100) plane (just plane) on the bottom surface. Used as a seed crystal substrate. (1-100) plane growth was performed under the same conditions as in Example 1 except that the temperature gradient was 11 ° C./cm.

  The obtained growth crystal was a single crystal and had a growth thickness of 1.4 mm. The total thickness of the seed crystal substrate and the grown crystal was 4.3 mm. The growth rate was 93 μm / h.

(Evaluation of threading dislocation density)
The threading dislocation density of the SiC single crystal grown in each example was measured.

  The SiC single crystal grown in each example was sliced in a plate shape with a diamond saw so as to expose a surface inclined by 4 ° in the <1-100> direction from the (0001) plane, and the sliced crystal was Polishing was performed with two types of diamond slurries (slurry particle size: 6 μm and 3 μm) to finish a mirror surface. Next, etching was performed by immersing each SiC single crystal in a melt at 510 ° C. mixed with potassium hydroxide (manufactured by Nacalai Tesque Co., Ltd.) and sodium peroxide (manufactured by Wako Pure Chemical Industries, Ltd.) for 5 minutes. Similarly, for a SiC single crystal produced by a sublimation method used as a seed crystal substrate, etching was performed on a surface inclined by 4 ° in the <1-100> direction from the (0001) plane. Each etched SiC single crystal was taken out of the mixed melt, ultrasonically washed in pure water, and then observed for threading dislocations by microscopic observation (manufactured by Nikon). Although the SiC single crystal grown continuously in Examples 1 to 4 is a continuous crystal, since the thickness grown in each example is known, the threading dislocation density of the portion grown in each example was analyzed. The threading dislocation density of the SiC single crystal grown in Examples 5 to 9 was similarly analyzed.

  FIG. 7 is a micrograph of the etched surface in which the seed crystal substrate 14 produced by the sublimation method used in Example 1 and the threading dislocations of the grown crystal 16 in the portion grown in Example 1 using the seed crystal substrate 14 as a starting point were evaluated. Indicates. A straight broken line indicates an interface between the seed crystal substrate 14 and the grown crystal 16. Although threading screw dislocations (TSD) and threading edge dislocations (TED) were detected on the etched surface of the seed crystal substrate 14, threading dislocations were found on the etched surface of the grown crystal 16 in the portion grown in Example 1. Not detected. Similarly, threading dislocations were not detected on the etched surface of the SiC single crystal grown in Examples 2 to 11.

(Observation of inclusion)
The presence or absence of inclusion of the SiC single crystal grown in each example was evaluated. The SiC single crystal used for the measurement of the threading dislocation density was irradiated with light from below and observed with a microscope, and a cross-sectional transmission image was observed.

  FIG. 5 shows a cross-sectional transmission image of a portion of the SiC crystal grown in Example 1. As shown in FIG. 5, the SiC crystal in the portion grown in Example 1 contained inclusions. FIG. 6 shows a cross-sectional transmission image of a portion of the SiC crystal grown in Example 2. As shown in FIG. 6, the SiC crystal in the portion grown in Example 2 did not contain inclusions. Similarly, the following Table 1 shows the results of observing the presence or absence of inclusion of SiC crystals in the portions grown in Examples 3 to 11.

  Table 1 summarizes the growth conditions of Examples 1 to 11, the thickness of the grown crystal, the growth rate, the threading dislocation density, and the presence or absence of inclusion.

  FIG. 1 shows the relationship between the thickness of the seed crystal and the crystal growth rate when the growth is performed for 15 hours in Examples 1, 2, 4, 8, 10, and 11. Further, FIG. 2 shows the relationship between the thickness of the seed crystal and the crystal growth rate when the growth is performed for 24 hours in Examples 3, 6, 7, and 9.

  In m-plane growth, the crystal growth rate tends to decrease as the crystal thickness increases, but it was found that the growth rate can be increased by increasing the temperature gradient in the surface region of the Si-C solution. .

DESCRIPTION OF SYMBOLS 10 Graphite crucible 12 Graphite shaft 14 Seed crystal substrate 16 Growth crystal 18 Heat insulating material 22 High frequency coil 22A Upper high frequency coil 22B Lower high frequency coil 24 Si-C solution 26 Quartz tube 100 Single crystal manufacturing apparatus

Claims (5)

A method for producing a SiC single crystal, wherein a SiC single crystal is grown by bringing a SiC seed crystal substrate into contact with a Si-C solution having a temperature gradient that decreases from the inside toward the surface,
When a SiC single crystal is grown using the (1-100) plane as a growth surface, the temperature gradient of the surface region of the Si-C solution is increased at least once, and the SiC single crystal has a growth thickness of 4 mm or more. Grow,
A method for producing a SiC single crystal.   The manufacturing method of the SiC single crystal of Claim 1 which enlarges the temperature gradient of the surface area | region of the said Si-C solution before the growth thickness of the said SiC single crystal reaches 4 mm.   The manufacturing method of the SiC single crystal of Claim 1 or 2 whose average growth rate when growing the said SiC single crystal continuously for 15 hours is larger than 0 micrometer / h and below 93 micrometer / h. A SiC single crystal having a threading dislocation density of 10 pieces / cm ² or less and a growth thickness of 4 mm or more. The SiC single crystal according to claim 4, wherein the threading dislocation density is 0 / cm ² .