JP4853449B2 - SiC single crystal manufacturing method, SiC single crystal wafer, and SiC semiconductor device - Google Patents

Description

  The present invention relates to a method for producing a silicon carbide single crystal suitable as a substrate material for electronic devices and optical devices. In the present invention, a high-quality silicon carbide single crystal with few crystal defects (ie, low crystal defects) is grown on a surface of a seed crystal substrate made of a silicon carbide single crystal having a crystal plane inclined from the {0001} plane. The present invention relates to a method for producing a silicon carbide single crystal that can be stably grown by a method. By utilizing the method of the present invention, a crystal plane inclined silicon carbide single crystal substrate having a surface with low crystal defects, a silicon carbide single crystal epitaxial wafer with low crystal defects, and silicon carbide with high reliability and high productivity Products such as electronic devices can be realized. The invention also relates to such products.

  Silicon carbide (SiC) has a wide band gap, a large thermal conductivity, and a low dielectric constant, and has thermally and mechanically stable characteristics. Therefore, a semiconductor element using SiC has higher performance than a conventional semiconductor element using silicon (Si). Due to its excellent material properties, SiC is a device material in a wide range of power control materials for power control with low operating loss, high-voltage high-frequency device materials, environmental-resistant device materials used in high-temperature environments, and radiation-resistant device materials. Application as is expected.

  Regarding the crystal structure of SiC, in addition to 3C of zinc blende structure, wurtzite structure having over 200 types of polytypes including 2H, 4H, 6H, etc. has been confirmed, depending on the use and purpose of SiC. Various crystal structures can be selected.

As a typical example, a high-output power device includes a low-concentration n-type 4H—SiC crystal layer for high breakdown voltage operation on a high-concentration n-type 4H—SiC (tetragonal hexagonal crystal) substrate. A semiconductor element obtained by epitaxially growing the substrate by CVD (chemical vapor deposition) is used. In this case, since epitaxial growth of SiC by the CVD method is based on step flow growth, a substrate whose surface orientation is inclined by several degrees from the ( 0001) plane to the (11-20) direction is used.

  On the other hand, high-frequency devices require properties of high thermal conductivity and low dielectric constant, and HEMT (High Electron Mobility Transistor) made of a nitride-based material (GaN, AlN, etc.) on a high purity, high resistance 4H or 6H-SiC substrate. This is achieved by stacking the structures by heteroepitaxial growth.

  Further, an optical device aiming at shortening the wavelength from blue to ultraviolet light uses a high-concentration n-type 6H—SiC substrate that has a smaller lattice irregularity with respect to a GaN-based crystal than other semiconductor crystal substrates. It is formed by laminating a heteroepitaxial layer of a nitride material on top.

The main methods conventionally known as methods for producing SiC single crystals are a sublimation recrystallization method belonging to vapor phase growth and a solution growth method belonging to liquid phase growth.
The sublimation recrystallization method is suitable for growing a bulk single crystal that can be used as a substrate because it can be grown at a relatively high speed (up to 1 mm / hr), and is currently most widely used for the production of SiC single crystal substrates. ing. In this method, the raw SiC powder is placed in a graphite growth crucible facing the seed crystal (SiC single crystal), and the SiC raw material is heated to 1800-2400 ° C. in an inert gas atmosphere. The SiC sublimation gas is recrystallized as an SiC single crystal on a seed crystal maintained in a temperature range suitable for crystal growth.

  On the other hand, in the solution growth method, carbon is dissolved in a melt of silicon (silicon, Si) or silicon alloy (Si-M alloy), and a high-temperature SiC solution (solvent) in which SiC is dissolved in the melt. Prepare a melt of Si or Si alloy. An SiC seed crystal (SiC single crystal substrate) is immersed in this high temperature solution of SiC, and at least the solution near the seed crystal is brought into a supercooled state, thereby creating a supersaturated state of SiC near the seed crystal. Grow up.

  In the solution growth method, a temperature difference method in which a temperature gradient is set such that the temperature of the SiC solid phase surface, which is the growth interface, is lower than the solution temperature in the vicinity of the seed crystal (only the solution in the vicinity of the seed crystal is in a supercooled state). And a slow cooling method in which the entire solution in which the seed crystals are immersed is cooled to a supersaturated solution.

  The SiC single crystal grown by the sublimation recrystallization method has a problem that it includes dislocations inherited from the seed crystal and micropipe defects, and a large number of dislocations that are considered to have occurred during crystal growth. The reason for the generation of new dislocations that occur during crystal growth is that the sublimation recrystallization method is basically a reaction that proceeds in a closed system in a carbon crucible, so that the sublimation gas supplied by sublimation of the SiC raw material There are large temperature gradients in the growth environment due to the fact that the components fluctuate during crystal growth, and because of the solid phase / gas phase reaction. As a result, a large thermal stress is generated in the crystal. It is considered that the temperature environment and the concentration of sublimation gas as a raw material change with time because the growth interface moves in the crucible. Along with the growth, new defects are generated due to the above-mentioned inappropriate crystal growth conditions and fluctuations in growth conditions, so it is extremely difficult to obtain crystals with quality significantly higher than the seed crystal by the sublimation recrystallization method. It is.

  Efforts to reduce defects in SiC single crystals by the sublimation recrystallization method have been energetically made. As a method for obtaining a high-quality seed crystal with few defects, attention is paid to the fact that micropipe, which is a defect derived from the seed crystal, and certain dislocations have singularities in the propagation direction. Single crystal growth methods are known. However, in these methods, in order to obtain a seed crystal by cutting the ingot in a direction perpendicular to the crystal growth direction, in order to obtain a large-diameter seed crystal, an ingot having a length longer than the diameter is grown. There is a need. As described above, in the sublimation recrystallization method, the temperature environment and the gas composition are likely to fluctuate with growth, so that it is very difficult to obtain a complete crystal for a long ingot.

  On the other hand, as a method for suppressing the occurrence of dislocations during crystal growth, the crystal growth rate is reduced by reducing the growth rate to reduce the crystal defect occurrence rate, or shortening the growth time so that the fluctuation of the sublimation gas component does not increase. However, these methods have not yet achieved the quality and productivity of SiC single crystals that can be put to practical use.

  In the solution growth method, which is liquid phase growth, the growth temperature can be lowered by about 500 ° C. to 1000 ° C. compared with the sublimation recrystallization method, and therefore, the temperature controllability is excellent compared with the sublimation recrystallization method. . Therefore, the thermal stress in the crystal can be made extremely small, and the occurrence of dislocations can be suppressed. In addition, it is possible to substantially eliminate fluctuation factors such as solution composition during crystal growth. As a result, no dislocations newly generated during crystal growth can be eliminated.

  In Journal of Electronic Materials 27 (1998) p.292, when an on-axis (0001) SiC single crystal produced by a sublimation recrystallization method is used as a seed crystal, a SiC single crystal is grown on the seed crystal as a solution. It has been reported that crystal growth proceeds while reducing micropipe defects and dislocations contained in the seed crystal, and it is possible to improve the crystal quality of the seed crystal by reducing the dislocation of the seed crystal. It is shown.

In US Pat. No. 5,679,153, when a SiC single crystal is grown on a crystal (defect density: 50 to 400 cm ⁻² ) containing micropipe defects produced by a sublimation recrystallization method, micropipe defects are generated during the growth. A method for producing a SiC single crystal layer in which micropipe defects on the surface layer are reduced (defect density 0 to 50 cm ⁻² ) by utilizing blocking is disclosed. The method described in this US patent is a method for improving (reducing defects) the crystal quality of the surface layer of a SiC single crystal substrate produced by a sublimation recrystallization method having a problem in crystal quality by a solution growth method. Conceivable.

However, the surface orientation of the substrate surface, which is suitable for the growth of a SiC epitaxial layer by a CVD method in the manufacture of a SiC element for an electronic device such as a power device, is inclined in the ( 11-20) direction from the {0001} plane (that is, When a SiC single crystal solution is grown according to the technique disclosed in US Pat. No. 5,679,153 using a SiC single crystal substrate (off-plane), on a {0001} just plane that does not have such a plane orientation inclination. In contrast to the above growth, it has been found that there is a problem that instability occurs at the growth interface and three-dimensional growth occurs, and as a result, stable two-dimensional layer growth cannot be expected.

  The three-dimensionality observed in a solution growth experiment of a SiC single crystal on a 4H-SiC single crystal substrate having a SiC crystal plane of 8 ° off [8 ° tilt from {0001} plane] conducted by the present inventors. A cross-sectional optical micrograph of the grown SiC single crystal is shown in FIG. Immediately after solution growth, crystal growth proceeds by two-dimensional layer growth, but it can be seen that instability occurs at the growth interface and the transition to three-dimensional growth occurs.

Applied Surface Science 184 (2001) p.27 describes the growth of 0.1, 1 and 5 μm thick solutions on SiC single crystal substrates tilted 8 ° from the {0001} plane produced by sublimation recrystallization. The results are shown. Crystal defects from the substrate are inherited as they are in the 5 μm thick solution grown crystal layer. Further, it is shown that the crystal surface is uneven and the surface has already started to shift to three-dimensional growth despite the crystal thickness of 5 μm.
Journal of Electronic Materials 27 (1998) p.292 Applied Surface Science 184 (2001) p.27 US Pat. No. 5,679,153

  As described above, the SiC single crystal substrate tilted from the {0001} plane suitable as the substrate for electronic devices is intended to improve the surface quality of the substrate by growing a high-quality SiC single crystal on the surface by the solution growth method. Thus, there has been a demand for the development of a method for growing a SiC single crystal that can secure a crystal thickness that exhibits a surface quality improvement effect while suppressing three-dimensional growth using this substrate as a seed crystal substrate.

  The subject of this invention is providing the technique for performing stably the quality improvement of the surface layer of the SiC single crystal substrate suitable as a substrate for electronic devices, and the crystal plane inclined from the {0001} plane. Specifically, the present invention provides a manufacturing method capable of stably growing a SiC single crystal layer having a higher quality than that of a substrate on a SiC single crystal substrate whose crystal plane is inclined from the {0001} plane by a solution growth method. And a crystal plane inclined SiC single crystal substrate having a surface of low crystal defects that could not be realized by conventional techniques, a low crystal defect SiC single crystal epitaxial wafer, and high reliability It is an object of the present invention to provide a highly productive SiC electronic device.

  The present invention provides an SiC seed crystal substrate having a crystal plane inclined from the {0001} plane in an SiC solution using a melt of Si metal or Si-M alloy (M is one or more metals other than Si) as a solvent. The present invention relates to a method for producing a SiC single crystal, which comprises immersing and allowing at least the vicinity of the substrate to be supersaturated by supercooling to grow a SiC single crystal on the substrate. That is, the present invention relates to a method for growing a SiC single crystal on a SiC seed crystal substrate having the inclined crystal plane by a solution growth method.

  In one embodiment, the growth of the SiC single crystal by the solution growth method is performed by the temperature difference method. In this case, a supersaturated state is created in the vicinity of the substrate by forming a temperature gradient in the SiC solution at a low temperature in the vicinity of the seed crystal substrate, and this temperature gradient is set to 5 ° C./cm or less. In the temperature difference method, the single crystal can be continuously grown. The temperature gradient may be formed in the vertical (height) direction so that the upper part of the solution in which the substrate is immersed is at a low temperature and the lower part of the solution is at a high temperature by controlling the heating means provided in the crucible for storing the solution. Alternatively, the seed crystal substrate is cooled via a substrate holder that supports the seed crystal substrate (heat is removed from the substrate via the substrate holder), so that the solution around the substrate is locally cooled to both the horizontal and vertical directions. It is also possible to form a temperature gradient. Of course, you may use both together.

  In another aspect, a supersaturated state that is a driving force for crystal growth is realized by a slow cooling method that cools the entire solution. In this case, the entire SiC solution is cooled to create a supersaturated state, and the cooling rate at that time is set to 0.05 ° C./min or more and 1 ° C./min or less. The slow cooling method is basically batch growth. However, even in the slow cooling method, after the cooling of the SiC solution is finished at a temperature higher than the solidus temperature of the solution, the supersaturated state is repeatedly created by repeatedly heating and cooling the solution (to the supercooling temperature). The growth of the SiC single crystal on the substrate can be continued.

  In any of the methods, the SiC seed crystal substrate immersed in the SiC solution is preferably dissolved in the substrate surface layer before starting single crystal growth on the substrate. This is because the surface layer of a SiC substrate cut out from a bulk single crystal used as a seed crystal substrate has a work-affected layer, a natural oxide film, etc., which can be removed before crystal growth. Effective for improving crystal quality. Although the thickness which melt | dissolves changes with the processing state of the surface of the SiC single crystal substrate used as a seed crystal substrate, it is about 5-50 micrometers. If the dissolution thickness is less than 5 μm, the processed deteriorated layer and the natural oxide film may not be sufficiently removed depending on the processing state, and stable quality may not be realized.

  Dissolution of the surface layer of the seed crystal substrate can be realized by forming, in the solution, a temperature gradient in which the solution temperature in the vicinity of the seed crystal substrate is high, that is, a temperature gradient opposite to the single crystal growth. Even if SiC single crystal growth is performed by a slow cooling method and this temperature gradient cannot be formed by the heating means provided in the crucible containing the solution, for example, by heating the seed crystal substrate via a substrate holder that supports the seed crystal substrate. The required temperature gradient can be formed in the solution. The temperature gradient during dissolution of the substrate surface layer is preferably 5 ° C./cm or more and 50 ° C./cm or less. If the temperature gradient is 5 ° C./cm or less, the dissolution rate of the substrate surface layer becomes slow, so it takes time to start crystal growth. When the temperature gradient is 50 ° C./cm or more, the dissolution rate is too fast and it becomes difficult to control the amount of dissolution.

  Dissolution of the surface layer of the seed crystal substrate can also be achieved by continuously immersing the seed crystal substrate in a solution heated to a temperature higher than the liquidus temperature without forming a temperature gradient in the solution. In this case, the higher the 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.

  The maximum temperature difference in the in-plane temperature distribution of the growth interface during single crystal growth on the seed crystal substrate surface is preferably 2 ° C. or less, as will be exemplified later in Examples. Thereby, the three-dimensional growth at the time of crystal growth can be suppressed more effectively. Means for reducing the in-plane temperature distribution will be described later. When a SiC single crystal is grown on the {0001} just plane, even if the in-plane temperature distribution at the growth interface increases, the three-dimensional growth hardly occurs and the two-dimensional growth is sustained. However, it has been clarified that when a SiC single crystal is grown on an off-plane substrate by a solution method, a process window under a growth temperature condition that can sustain two-dimensional growth is narrow. Therefore, reducing the in-plane temperature distribution at the growth interface has an advantageous effect on sustaining two-dimensional growth.

  Since the growth interface is the surface of the seed crystal substrate before the start of growth, the growth interface temperature is substantially the same as the substrate temperature. Therefore, the temperature distribution of the substrate measured on the back side of the substrate may be the in-plane temperature distribution at the growth interface, and the temperature difference between the maximum temperature and the minimum temperature thus measured may be 2 ° C. or less.

  The melt serving as the solvent for the SiC solution is preferably a Si-M alloy rather than Si metal because the amount of C dissolved is higher and therefore the solubility of SiC can be increased. A particularly preferred Si-M alloy is a Si-Ti alloy.

  The seed crystal substrate is preferably a SiC substrate manufactured by a sublimation recrystallization method in which an inclination angle (also referred to as an off angle) of the crystal plane from the {0001} plane is 0.2 ° or more and 10 ° or less. If this inclination angle is smaller than 0.2 °, crystal growth proceeds in almost the same two-dimensional growth mode as that of the {0001} just plane, so there is no need to apply the method of the present invention. On the other hand, when this tilt angle is increased, the cut loss during the production of the substrate increases, and a crystal plane that is practically sufficiently flat is obtained at a tilt angle of 8 ° in CVD epitaxial growth. Therefore, the tilt angle is 10 ° or more. Since the SiC substrate is not practically used, there is no need to apply the method of the present invention. The crystal form of the seed crystal substrate is preferably 4H—SiC.

  For the purpose of surface modification of a SiC single crystal substrate having an off angle produced by a sublimation recrystallization method, a SiC single crystal layer to be grown is grown on this substrate according to the method of the present invention. The thickness is preferably 10 μm or more and 100 μm or less. Unless the solution is grown to a thickness of 10 μm or more, the effect of improving the surface quality of the seed crystal substrate by the solution growth method according to the present invention is not sufficiently exhibited. There is no particular upper limit on the crystal thickness for solution growth, but when the purpose is to improve the quality of the surface layer of the SiC single crystal substrate produced by the sublimation recrystallization method, a crystal thickness of 100 μm is sufficient.

  According to the present invention, the SiC single crystal layer produced by the above method was produced by a sublimation recrystallization method in which the crystal plane inclination angle from the {0001} plane was 0.2 ° or more and 10 ° or less. An SiC single crystal substrate for device fabrication is provided, which is provided on the surface of an SiC substrate having a diameter of 50 mm or more and 100 mm or less. In this SiC single crystal substrate, the total etch pit density due to dislocations measured on a substrate tilted 8 ° or 4 ° from the {0001} plane is reduced as compared to the underlying SiC seed crystal substrate. With improved surface crystal quality as demonstrated by

  The present invention also provides an SiC single crystal epitaxial wafer having an SiC single crystal thin film epitaxially grown on the SiC single crystal substrate by a CVD method, and an SiC semiconductor device manufactured using the SiC single crystal epitaxial wafer. To do.

  According to the present invention, a SiC single crystal is grown by a solution growth method on a SiC single crystal substrate having a crystal plane inclined from the {0001} plane suitable as a substrate for epitaxial growth by CVD for electronic device applications. When surface quality is improved, three-dimensional growth can be suppressed and high-quality two-dimensional growth can be carried out stably, improving the quality of the surface layer of a SiC single crystal substrate fabricated by sublimation recrystallization. Can be performed efficiently.

  The present inventors have prepared an off-angle SiC seed crystal whose crystal plane is inclined from the {0001} plane in a high-temperature solution of SiC prepared by dissolving C to a nearly saturated concentration in a melt of Si or Si—Ti alloy. By immersing the substrate and supercooling at least the solution around the SiC seed crystal substrate by a solution growth method to bring it into a supersaturated state, new SiC is grown on the seed crystal substrate (hereinafter also referred to as SiC solution growth). ) Regarding the growth of the SiC single crystal, the conditions for suppressing the three-dimensional growth were studied repeatedly.

  As a result, by optimizing the growth temperature conditions for the SiC solution growth, it is possible to significantly suppress the three-dimensional growth that leads to a decrease in crystal quality, and it is possible to grow a high-quality SiC single crystal. I found out.

  Unlike the solution growth on the {0001} plane (just plane), step bunching occurs in the solution growth in which new SiC is grown on the surface of the off-angle SiC seed crystal substrate inclined from the {0001} plane by the solution growth method. There is a problem that it is easy to do. This step bunching becomes a macro step as the growth time is extended, and a step is generated at the growth interface. In this way, once the growth interface becomes three-dimensional, crystal growth in the portion protruding to the solution side proceeds preferentially, and the solvent component is taken into the gap between the crystal and the portion where the crystal growth is delayed. As a result, a high-quality SiC single crystal cannot be obtained.

  According to the present invention, when forming a temperature gradient such that the temperature of the seed crystal is lower from the seed crystal to the solution side during crystal growth, the temperature gradient is set to 5 ° C./cm or less, and When the driving force is applied by slow cooling, stable two-dimensional layer growth can be continued by setting the cooling rate of the entire solution to 0.05 ° C./min or more and 1 ° C./min or less. This is considered to be because the step forward speed can be made uniform between steps, and step bunching can be substantially prevented.

  An example of a single crystal manufacturing apparatus used for manufacturing a SiC single crystal by the solution growth method is schematically shown in FIG. The illustrated single crystal manufacturing apparatus includes a crucible 2 containing a high-temperature solution 1 in which SiC is dissolved in a melt of Si or Si-M alloy, and is attached to the tip of a seed shaft (substrate holder) 3 that can be moved up and down. The held seed crystal substrate 4 is immersed in the vicinity of the liquid surface of this high temperature solution. As shown, the crucible 2 and the seed shaft 3 are preferably rotated.

  The high temperature solution 1 is prepared by dissolving C (carbon) in a melt of Si or Si-M alloy (prepared by putting raw materials into a crucible and heating and melting them). In the illustrated example, the crucible is a carbonaceous crucible such as a graphite crucible or an SiC crucible, so that C is dissolved in the melt by melting the crucible and an SiC solution is formed. In this way, undissolved C does not exist in the high-temperature solution, 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 using another method such as injection of hydrocarbon gas or charging a solid C supply source together with the melt raw material, or by combining this with melting of the crucible. Good.

  The crucible 2 is substantially closed by a crucible lid 5 through which the seed shaft passes, and the outer periphery of the crucible 2 is covered with a heat insulating material 6 for heat insulation. A high frequency coil 7 for inductively heating the crucible and the high temperature solution is disposed on the outer periphery of the heat insulating material 6.

  When crystal growth is performed by the temperature difference method, the height direction (vertical) of the high-temperature solution is adjusted by adjusting the number of windings and intervals of the high-frequency coil and the positional relationship between the high-frequency coil 7 and the crucible 2 in the height direction. Direction) temperature gradient. The temperature gradient at this time is 5 ° C./cm or less as described above. Thereby, two-dimensional growth can be continued stably. A preferable range of the temperature gradient is 1 to 3 ° C./cm.

  Since these crucible 2, heat insulating material 6, and high-frequency coil 7 become high temperature, they are disposed inside the water-cooled chamber 8. The water cooling chamber 8 includes a gas introduction port 9 and a gas exhaust port 10 so that the atmosphere in the apparatus can be adjusted. A plurality of pyrometers (pyrometers) may be disposed through the heat insulating material 6 through the gaps of the high frequency coil so that the side surface temperatures at a plurality of height points of the crucible 2 can be measured. Since the side temperature of the crucible is substantially equal to the high temperature solution temperature, the heating by the high frequency coil 7 can be adjusted by the measured temperature value. In addition, the radial temperature measurement at the crucible bottom can be performed by inserting a plurality of thermocouples with the crucible shaft holding the crucible hollow.

  The in-plane temperature distribution at the growth interface during single crystal growth can be obtained by measuring the in-plane temperature of the seed axis in contact with the back surface of the seed crystal substrate immersed in the high temperature solution. The in-plane temperature of the seed shaft in contact with the seed crystal substrate back surface can be measured by inserting a plurality of thermocouples into the hollow seed shaft. The temperature distribution in the growth surface can be adjusted, for example, by arranging a heat insulating material structure above the free surface of the high temperature solution 1 or adding a heat insulating material structure inside the seed shaft.

The solvent of the high temperature solution 1 is composed of Si metal or Si-M alloy. The type of the metal M 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 M include Ti, Mn, Cr, Co, V, Fe and the like. Ti and Mn are preferable, and Ti is particularly preferable. The preferable atomic ratio of the alloy element M is expressed as Si _1-x M _x in the composition of the Si—M alloy, and 0.1 ≦ x ≦ 0.25 when M is Ti, and 0.1 when M is Mn. ≦ x ≦ 0.7.

  In addition to realizing the supersaturated state, which is the driving force for crystal growth, by the temperature difference method, it is also possible to realize it by gradually cooling the entire solution in which the seed crystal is immersed. As described above, the cooling rate in the slow cooling method is 0.05 ° C./min or more and 1 ° C./min or less. When the cooling rate of the whole solution is 1 ° C./min or less, stable two-dimensional layer growth can be continued. When this cooling rate is 0.05 ° C./min or less, it takes too much growth time per batch. A preferable range of the cooling rate is 0.1 to 1 ° C./min.

  The slow cooling method is a batch type, but after the slow cooling of the high temperature solution is finished at a temperature higher than the solidus temperature of the solution, the supersaturated state is repeatedly created by repeating the heating and slow cooling of the high temperature solution, The growth of the SiC single crystal on the substrate can be continued.

In any method, as described above, the SiC single crystal immersed in the high temperature solution is preferably removed by dissolving the surface layer in the high temperature solution before the growth.
The seed crystal substrate is not particularly limited as long as it is a SiC single crystal substrate. However, when the method for producing a SiC single crystal of the present invention is used for the purpose of improving the crystal quality of the substrate surface, as described above, the SiC by the CVD method is used. This is an off-angle substrate suitable for epitaxial growth of which the crystal plane has an inclination angle of 0.2 ° to 10 °.

  A SiC single crystal layer is grown on a surface of a SiC single crystal substrate having a diameter of 50 to 100 mm and having the above-described off-angle produced by a sublimation recrystallization method according to the method of the present invention to a thickness of 10 to 100 μm. Defects (which can be expressed by etch pit density) that inevitably occur on the surface of the substrate prepared by the recrystallization method can be reduced. A high-quality SiC single crystal epitaxial wafer can be manufactured by epitaxially growing a SiC single crystal thin film on the SiC single crystal substrate whose surface crystal quality has been modified in this manner by a known CVD method. This wafer is used for the manufacture of SiC semiconductor devices. The manufacture of the SiC semiconductor device may be performed according to a known method.

  In this example, a solution growth experiment of a SiC single crystal by a temperature difference method was performed using the single crystal manufacturing apparatus shown in FIG. The high-temperature solution 1 stored in the crucible 2 is controlled in the vertical (height) direction so that the upper part of the solution in which the substrate is immersed is at a low temperature and the lower part of the solution is at a high temperature by controlling the heating means provided in the crucible for storing the solution. A gradient is formed, and the vicinity of the seed crystal substrate 4 is at a low temperature. Due to the temperature gradient of this solution, the solution near the substrate becomes supersaturated, and the growth of the SiC single crystal proceeds.

  The single crystal manufacturing apparatus includes a high-purity graphite crucible 2 having an inner diameter of 130 mm and a height of 150 mm that contains the solution 1, and the crucible 2 is disposed in a water-cooled stainless steel chamber 8. The outer periphery of the graphite crucible is kept warm by a heat insulating material 6, and a high frequency coil 7 for induction heating is provided on the outer periphery. The atmosphere in the single crystal manufacturing apparatus is adjusted using the gas inlet 9 and the gas outlet 10.

  In a high-purity graphite crucible 2, Si and Ti are charged as a melt raw material at a molar ratio of 80:20, and the high-frequency coil 7 is energized to melt the raw material in the crucible by induction heating. A melt was formed. During the heating, the melting of the graphite crucible as a container melted the carbon into a high temperature solution, and a high temperature solution of SiC was formed. Before the growth of the single crystal, the produced melt was heated at 1650 ° C. for 2 hours so that a sufficient amount of carbon was dissolved in the melt.

  The temperature distribution in the height direction of the high-temperature solution was controlled by adjusting the number of turns of the high-frequency coil 7, the winding interval, and the relative positional relationship between the graphite crucible and the high-frequency coil. High temperature so that the temperature gradient at the location where the seed crystal is planned to be immersed (in this example, near the liquid surface of the solution) is 3 ° C./cm so that the temperature gradient is lower than the solution at other locations. The temperature distribution of the solution was adjusted. In the prior art, the temperature gradient is greater than 5 ° C./cm in order to provide a large driving force for crystal growth. The heating temperature of 1650 ° C. is the maximum temperature of the solution (that is, the solution temperature at the crucible bottom).

  When heated for 2 hours under the above conditions, sufficient carbon was dissolved from the graphite crucible 2 to make the solution supersaturated, and the SiC concentration in the solution 1 in the vicinity of the seed crystal substrate 4 reached the supersaturated state. SiC solution 1 was formed in the crucible. Thereafter, a 4H—SiC seed crystal substrate 4 having a diameter of 50 mm and having a crystal plane tilted by 8 ° (with an 8 ° off angle) in the (11-20) direction from the {0001} plane is held at the tip of the seed shaft 3. Then, it was immersed in the vicinity of the surface layer of Solution 1 and kept in the immersed state for 1 hour, and SiC crystal growth was performed by a temperature difference method. The crystal growth time was 15 hours. During this time, the crucible 2 and the seed shaft 3 were rotated at 10 rpm in opposite directions.

  When the in-plane temperature distribution of the seed crystal substrate 4 before being inserted into the graphite crucible 2 and immersed in the high temperature solution 1 was measured, the temperature was lowest at the center of the seed crystal substrate 4 and highest at the outer periphery. The temperature difference was 4 ° C.

  After completion of the growth experiment, the seed shaft 3 was raised, and the seed crystal substrate 4 was separated from the solution 1 and collected. The solution in the crucible was cooled to room temperature and solidified. This seed crystal was washed with hydrofluoric acid to remove the coagulated substance of the attached solution. On the seed crystal substrate 4, a SiC crystal was newly grown to a thickness of about 200 μm by the solution growth method.

Subsequently, an n-type (1 × 10 ¹⁶ cm ⁻³ ) SiC epitaxial layer having a thickness of 10 μm was stacked on the surface of the SiC crystal layer of the planarized substrate by a CVD method using silane and propane as raw material gases. For the CVD growth, a normal pressure CVD apparatus using hydrogen (H ₂ ) as a carrier gas was used, and the susceptor was heated by high frequency induction heating. After the SiC single crystal substrate was placed in the reaction furnace, gas replacement and high vacuum evacuation were repeated several times, and then H ₂ carrier gas was introduced into the reaction furnace. The temperature was raised to 1500 ° C., and raw materials silane and propane were introduced to start epitaxial growth. During the growth, nitrogen gas was added to control n-type conductivity.

  The thickness of the solution-grown SiC crystal grown on the SiC seed crystal substrate and the thickness of the SiC crystal grown thereon by the CVD method were determined from observation of an optical microscope of the crystal cross section. Further, regarding the crystallinity of the obtained single crystal, after polishing the (0001) plane, it is subjected to a molten KOH etching (500 ° C., 2 minutes) treatment, and the number of etch pits appearing on the crystal plane is counted, The density was calculated, and the etch pit density was compared among the CVD SiC crystal, the solution grown SiC crystal, and the seed crystal substrate 4. Etch pit density comparison was performed by repeating polishing and molten KOH etching on the crystal and examining the etch pit density distribution in the growth thickness direction. These results are summarized in Table 1.

The etch pit density was determined according to the following criteria:
A: The etch pit density of the CVD crystal and the solution growth outermost layer is decreased by one digit or more with respect to the etch pit density of the seed crystal substrate;
○: The etch pit density of the CVD crystal and the solution growth outermost layer is decreased by less than one digit with respect to the etch pit density of the seed crystal substrate;
X: The etch pit density of the CVD crystal solution growth outermost layer is the same or increased with respect to the etch pit density of the seed crystal substrate.

  In this example, a solution growth experiment of a SiC single crystal by a slow cooling method was performed using the single crystal manufacturing apparatus shown in FIG. The vicinity of the seed crystal substrate is at substantially the same temperature as the temperature of the entire solution, and crystal growth proceeds by cooling the entire solution.

  The single crystal manufacturing apparatus includes a high-purity graphite crucible 2 having an inner diameter of 130 mm and a height of 150 mm that contains the solution 1, and the crucible 2 is disposed in a water-cooled stainless steel chamber 8. The outer periphery of the graphite crucible is kept warm by a heat insulating material 6, and a high frequency coil 7 for induction heating is provided on the outer periphery. The atmosphere in the single crystal manufacturing apparatus is adjusted using the gas inlet 9 and the gas outlet 10.

  In a high-purity graphite crucible 2, Si and Ti are charged as a melt raw material at a molar ratio of 80:20, and the high-frequency coil 7 is energized to melt the raw material in the crucible by induction heating. A melt was formed. During the heating, the melting of the graphite crucible as a container melted the carbon into a high temperature solution, and a high temperature solution of SiC was formed. Prior to the growth of the single crystal, the resulting melt was kept heated at 1650 ° C. for 2 hours so that a sufficient amount of carbon was dissolved in the melt. The number of turns of the high-frequency coil and the winding interval, the relative positions of the graphite crucible and the high-frequency coil, and the structure of the heat insulating material 6 were adjusted so that the temperature in the height direction in the solution became substantially uniform.

  When heated for 2 hours under the above conditions, sufficient carbon was dissolved in the melt from the graphite crucible 2, and a high-temperature solution 1 in which SiC was dissolved to a saturation concentration was formed in the crucible. Then, after the 4H-SiC seed crystal substrate 4 having an 8 ° off angle of 50 mm held at the tip of the seed shaft 3 was immersed in the solution 1 and held for 1 hour, the solution temperature was stabilized, By reducing the temperature of the entire solution to 1450 ° C. while reducing the output of the high-frequency coil 7, SiC crystal growth was performed by a slow cooling method. The cooling rate was 0.2 ° C./minute (cooling time 1000 minutes). During this time, the crucible 2 and the seed shaft 3 were rotated at 10 rpm in opposite directions. At this time, the in-plane temperature of the seed crystal substrate was lowest at the center of the seed crystal substrate 4 and highest at the outer periphery, and the temperature difference had a temperature distribution of 4 ° C.

  After completion of the growth experiment, the seed shaft 3 was raised, separated from the seed crystal substrate 4 and the solution 1 and collected. The solution in the crucible was cooled to room temperature and solidified. This seed crystal substrate was washed with hydrofluoric acid to remove the coagulated substance in the attached solution. Others were the same as in Example 1.

  A SiC single crystal was grown on a seed crystal substrate by a temperature difference method in the same manner as in Example 1 except that the melt raw material charged in the graphite crucible 2 was Si.

  A SiC single crystal was grown on a seed crystal substrate by a slow cooling method in the same manner as in Example 2 except that the melt raw material charged in the graphite crucible 2 was Si.

  The in-plane temperature distribution of the seed crystal substrate immersed in the solution 1 is the lowest at the center of the seed crystal substrate 4 and the highest at the outer periphery, and the temperature difference is adjusted to 2 ° C. A SiC single crystal was grown on a seed crystal substrate by a temperature difference method. The in-plane temperature distribution was adjusted by inserting a heat insulating material sheet into the tip of the seed shaft 3 holding the seed crystal substrate and adjusting its structure.

  The in-plane temperature distribution of the seed crystal substrate immersed in the solution 1 is lowest at the center of the seed crystal substrate 4 and highest at the outer periphery, and the temperature difference is adjusted to 2 ° C. A SiC single crystal was grown on a seed crystal substrate by a slow cooling method.

  Before starting the growth of the single crystal, when the temperature at the center of the melt bottom in the crucible is adjusted to 1650 ° C. and heating is continued for 2 hours so that a sufficient amount of carbon is dissolved from the crucible, A temperature gradient in the direction of the height of the solution opposite to that during growth was formed. That is, a gradient in the height direction is formed such that the temperature in the solution surface layer, which is the planned immersion location of the seed crystal substrate, is higher than the solution at the bottom, and the temperature gradient at this time is 15 ° C./cm. The surface layer of the seed crystal substrate 4 was dissolved by about 5 μm before crystal growth. Thereafter, the temperature gradient in the height direction of the solution is returned to the temperature gradient for crystal growth (the same as in Example 1, a temperature gradient of 3 ° C./cm in the direction where the solution surface layer is at a low temperature and the bottom portion is at a high temperature). A SiC single crystal was grown on a seed crystal substrate by a temperature difference method in the same manner as in Example 1 except that it was started.

Before starting the growth of the single crystal, when the temperature at the center of the melt bottom in the crucible is adjusted to 1650 ° C. and heating is continued for 2 hours so that a sufficient amount of carbon is dissolved from the crucible, A temperature gradient in the direction of the height of the solution opposite to that during growth was formed. That is, a gradient in the height direction is formed such that the temperature in the solution surface layer, which is the planned immersion location of the seed crystal substrate, is higher than the solution at the bottom, and the temperature gradient at this time is 15 ° C./cm. The surface layer of the seed crystal substrate 4 was dissolved by about 5 μm before crystal growth. Thereafter, a SiC single crystal was grown on the seed crystal substrate by a slow cooling method in the same manner as in Example 2 except that the temperature in the solution at the time of crystal growth was soaked.
(Comparative Example 1)

A SiC single crystal was grown on the seed crystal substrate by the temperature difference method in the same manner as in Example 1 except that the temperature gradient in the vicinity of the solution in which the seed crystal substrate 4 was immersed during crystal growth was 15 ° C./cm. .
(Comparative Example 2)

A SiC single crystal was grown on the seed crystal substrate by a slow cooling method in the same manner as in Example 2 except that the cooling rate of the whole solution was 2 ° C./min (cooling time 100 minutes).
Table 1 summarizes the crystal growth conditions, the SiC crystal thickness two-dimensionally grown on the seed crystal substrate, and the etch pit density determination result in the outermost layer of the two-dimensionally grown portion for the above examples and comparative examples.

  From Table 1, in Examples 1 to 8, the growth temperature condition is 3 ° C./cm or less in the case of the temperature difference method, and 3 ° C./min or less in the case of the slow cooling method by setting the cooling rate to 1 ° C./min or less. It can be seen that the dimensional growth can be suppressed, and as a result, the quality improvement effect of the SiC crystal by the solution growth method is manifested. Further, in the example in which the SiC single crystal is grown under the growth temperature condition according to the present invention, even in the SiC single crystal film epitaxially grown by the CVD method on the formed SiC single crystal layer, the etch pit density ( That is, the dislocation density was reduced as compared with the sublimation recrystallized substrate, and a high-quality SiC single crystal epitaxial wafer could be manufactured.

  As shown in Examples 5 and 6, it can be seen that when the in-plane temperature distribution of the seed crystal substrate is 2 ° C. or less, the effect of suppressing the three-dimensional growth is increased. In addition, as shown in Examples 7 and 8, when the surface layer of the seed crystal substrate substrate is dissolved and removed in the solution before starting the crystal growth, the quality improvement of the solution growth can be more effectively expressed. I understand.

  Although the present invention has been described above with reference to preferred embodiments and examples, it is to be understood that the above description is illustrative in all respects and not restrictive. The scope of the invention is limited only by the claims.

It is an optical microscope photograph of the cross section of the three-dimensionally grown SiC single crystal grown on a crystal having an off angle by a conventional solution growth method. Explanatory drawing which shows the basic composition of the crystal growth apparatus (SiC single crystal manufacturing apparatus) used in the Example of this invention.

Claims (15)

By immersing the SiC seed crystal substrate in an SiC solution using a melt of Si metal or Si-M alloy (M is one or more metals other than Si) as a solvent, and at least the vicinity of the substrate is supersaturated by supercooling. A method for producing a SiC single crystal comprising growing a SiC single crystal on a substrate,
The SiC seed crystal substrate has a crystal plane inclined in the (11-20) direction from the {0001} plane, and this inclined crystal plane is used as a growth plane.
A SiC single crystal is produced, wherein a supersaturated state is created in the vicinity of the substrate by forming a temperature gradient in the SiC solution at a low temperature in the vicinity of the seed crystal substrate, and the temperature gradient is 5 ° C./cm or less. Method. By immersing the SiC seed crystal substrate in an SiC solution using a melt of Si metal or Si-M alloy (M is one or more metals other than Si) as a solvent, and at least the vicinity of the substrate is supersaturated by supercooling. A method for producing a SiC single crystal comprising growing a SiC single crystal on a substrate,
The SiC seed crystal substrate has a crystal plane inclined in the (11-20) direction from the {0001} plane, and this inclined crystal plane is used as a growth plane.
A method for producing a SiC single crystal, wherein the entire SiC solution is cooled to create a supersaturated state, and the cooling rate at that time is 0.05 ° C./min or more and 1 ° C./min or less.   After the cooling of the SiC solution is finished at a temperature higher than the solidus temperature of the solution, a supersaturated state is repeatedly created by repeating heating and cooling of the SiC solution, and the growth of the SiC single crystal on the substrate The method of claim 2, wherein the method continues.   The method according to claim 1, wherein the maximum temperature difference in the in-plane temperature distribution of the growth interface during single crystal growth is 2 ° C. or less.   Immediately after the SiC seed crystal substrate is immersed in the SiC solution, a temperature gradient is formed in the solution so that the temperature of the substrate is higher than that of the SiC solution, and the substrate surface layer is dissolved in the SiC solution. The method according to claim 1, wherein the growth is performed.   The method according to claim 5, wherein the dissolution thickness of the surface layer of the SiC seed crystal substrate is 5 μm or more.   The method according to claim 1, wherein the melt is a Si—M alloy and M is Ti.   The SiC seed crystal substrate is produced by a sublimation recrystallization method having a crystal plane inclined at an angle of 0.2 ° or more and 10 ° or less from the {0001} plane. The method according to claim 1.   The method of claim 8, wherein the SiC seed crystal substrate has a 4H-SiC crystal structure.   The method according to claim 9, wherein the thickness of the SiC single crystal grown on the substrate is in the range of 10 to 100 μm.   It has having the layer of the SiC single crystal manufactured by the method of any one of Claims 8-10 on the SiC single crystal substrate manufactured by the sublimation recrystallization method of 50 mm or more and 100 mm or less in diameter. A SiC single crystal substrate for device fabrication, which is characterized. The total etch pit density due to dislocations measured on a substrate tilted 8 ° in the (11-20) direction from the {0001} plane is reduced compared to a SiC substrate fabricated by sublimation recrystallization. The SiC single crystal substrate according to claim 11. The total etch pit density due to dislocations measured on a substrate tilted 4 ° in the (11-20) direction from the {0001} plane is reduced compared to a SiC substrate fabricated by sublimation recrystallization of the base. The SiC single crystal substrate according to claim 11.   A SiC single crystal epitaxial wafer comprising a SiC single crystal thin film epitaxially grown by a CVD method on the SiC single crystal substrate according to any one of claims 11 to 13.   A SiC semiconductor device manufactured using the SiC single crystal epitaxial wafer according to claim 14.

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