JP4706565B2 - Method for producing silicon carbide single crystal - Google Patents

Description

  The present invention relates to a method for producing a silicon carbide single crystal.

  Since silicon carbide single crystal has characteristics of high breakdown voltage and high electron mobility, it is expected as a semiconductor substrate for power devices. As a method for obtaining such a silicon carbide single crystal, for example, there is a single crystal growth method called a sublimation method (improved Rayleigh method) or a high temperature CVD method. Here, the improved Rayleigh method is to insert a silicon carbide raw material into a graphite crucible, place a seed crystal so as to face this raw material portion, and heat the raw material portion to 2200 to 2400 ° C. to generate sublimation gas. This is a method of growing a silicon carbide single crystal by recrystallization on a seed crystal that is at a temperature several tens to several hundreds of degrees C lower than the raw material part, and the high temperature CVD method is a CVD method at a high temperature, A silicon carbide single crystal is grown by epitaxially growing silicon carbide (see, for example, Patent Document 1).

  Furthermore, various methods have been proposed as a method for growing a silicon carbide single crystal having a desired crystal polymorph such as 4H type using a sublimation method or a high temperature CVD method.

  For example, in sublimation or high-temperature CVD, aluminum is added to the SiC raw material, and a single crystal is grown while controlling changes in atmospheric pressure in an inert gas atmosphere containing nitrogen, thereby controlling polymorphism. Patent Document 2 describes that a SiC single crystal can be obtained.

Further, Patent Document 3 describes that a high-quality 4H type SiC single crystal ingot can be manufactured with good reproducibility by introducing impurities at 5 × 10 ¹⁸ cm ⁻³ or more in the carbon atom position in the sublimation method. Yes.

Patent Document 4 describes a method of growing a silicon carbide single crystal containing arsenic by supplying a gas containing arsenic or an arsenic compound to a silicon carbide single crystal substrate in a sublimation method or a high temperature CVD method. . According to this, since arsenic controls the resistivity of a silicon carbide single crystal as an n-type dopant and has an atomic radius equivalent to that of silicon, it does not compress or expand the crystal and hardly causes intracrystalline strain. Therefore, generation of different polymorphs is suppressed, and a high-quality silicon carbide single crystal having a desired resistivity can be obtained.
Japanese National Patent Publication No. 11-508531 Japanese Patent Application Laid-Open No. 5-221796 Japanese Patent Laid-Open No. 9-157091 JP 2002-234800 A

  However, in the crystal growth method that introduces impurities or dopants described in Patent Documents 2 to 4 described above, different atoms are introduced into the SiC raw material, so that the obtained single crystal contains elements other than Si and C. Therefore, distortion occurs in the crystal, and a problem that a high-quality single crystal cannot be obtained occurs.

  In view of the above points, the present invention is capable of growing a single crystal that is higher in quality than a crystal growth method in which impurities or dopants are introduced and that is a desired crystal polymorph such as 4H type. It aims at providing the manufacturing method of a silicon carbide single crystal.

  In order to achieve the above object, the present invention provides a growth start time between a growth start time at which a single crystal starts growing on the surface of the seed crystal and a growth intermediate time during the growth of the single crystal after the growth start time. The starting time is characterized in that a single crystal having the same polymorph as the seed crystal is produced by setting the atomic ratio of the Si component to the C component in the raw material gas higher than that in the middle of the growth.

  Thus, by making the Si / C ratio of the raw material gas at the growth start time higher than that at the middle of growth, a single crystal having the same polymorph as the seed crystal can be produced stably.

  This is due to the following reason. That is, at the start of growth, by setting the Si / C ratio of the source gas to be higher than that during the growth period, an excessive number of silicon relative to the number of carbon atoms is directed toward the seed crystal than during the growth period. Will supply atoms. This excess silicon atom forms a Si—C bond with the SiC atom on the outermost surface of the seed crystal or becomes a Si—Si bond having a weak bond with respect to the Si—C bond. Easy to migrate. On the other hand, when the carbon atom becomes excessive, the Si—C bond is formed or the C—C bond having a strong bond is formed, so that the migration of atoms on the crystal surface is difficult. For this reason, this excessive silicon atom promotes the rearrangement of atoms on the surface of the seed crystal, and tends to form a SiC (0001) surface which is a stable surface on the surface of the seed crystal. As a result, an atomic step having a (0001) plane as a terrace can be generated on the surface of the seed crystal, and a single crystal can be grown along this atomic step. At this time, since the crystal polymorphism information of the seed crystal can be propagated to the single crystal from this atomic step, a single crystal having the same polymorph as the seed crystal can be manufactured stably.

  Therefore, according to the present invention, a single crystal which is a desired crystal polymorph can be grown by selecting a crystal polymorph of the seed crystal. For example, by selecting 4H type SiC as a seed crystal, a single crystal of 4H type SiC can be grown.

In addition, since no impurities or dopants are used in the present invention, high quality compared to the crystal growth method in which impurities and the like are introduced as in the techniques described in Patent Documents 2 to 4 described in the background art. Single crystal is obtained.
Furthermore, in the invention described in claim 1, the heat storage member (14) is disposed in the flow path of the source gas in the reaction vessel (6), the reaction vessel (6) is heated, and the inside of the reaction vessel (6) A single crystal is grown as a predetermined temperature atmosphere.
In the first and third aspects of the invention, at the growth start time, the reaction vessel (6) has a temperature atmosphere having a temperature gradient that becomes lower as it is closer to the seed crystal (7).
In the reaction vessel (6), a carbon ring material (9) is disposed so as to surround a region (8) where a single crystal on the surface of the seed crystal (7) grows, and of the ring material (9) It is characterized by using a reaction vessel (6) in which solid silicon carbide (10) is fixed to the surface on the high temperature side.
In the invention according to claim 2 , the temperature of the seed crystal (7) is 1800 ° C. at the temperature raising period in which the temperature of the seed crystal (7) is raised to the temperature of the growth start time higher than 1800 ° C. And before the start of sublimation of the seed crystal (7), the introduction of an etching gas for cleaning the surface (7a) of the seed crystal (7) into the reaction container (6) is started. (6) The introduction of the raw material gas into the inside is started.

  In the present invention, for example, it is preferable that a part of the surface of the seed crystal is at the lowest temperature in the surface of the seed crystal at the start of growth.

  As a result, a single crystal can be grown by forming a crystal nucleus on a part of the surface of the seed crystal, which is more stable than the case of crystal growth based on a plurality of nuclei generated in the surface of the seed crystal. This is because a single crystal having the same polymorph as the seed crystal can be produced.

  In addition, as a method of making a part of the surface of the seed crystal the lowest temperature within the surface of the seed crystal, for example, a heat-dissipating groove is provided in a portion of the outer surface of the reaction vessel facing the seed crystal, or inactive A method of applying gas can be adopted.

  In the present invention, for example, it is preferable to introduce an etching gas into the reaction vessel (6) and expose the clean surface of the seed crystal (7) with the etching gas before the start of growth.

  This is because it is possible to easily form an atomic step on the seed crystal surface for propagating the crystal polymorphism information of the seed crystal to the single crystal at the start of growth. That is, the surface of the seed crystal is etched before the crystal growth is started to obtain a clean surface, and then the Si / C ratio in the source gas is increased to start the crystal growth. Atomic steps that are not affected by can be formed on the surface of the seed crystal. Therefore, it is possible to grow a single crystal that inherits the crystal polymorph information of the high-quality seed crystal.

  In the present invention, for example, when the amount of Si component in the raw material gas is the same and the amount of C component is different between the growth start time and the growth middle time, the growth start time and the growth middle time are the same. This is preferable as compared with the case where the amount of the Si component in the source gas is varied and the amount of the C component is the same.

  In other words, at the growth start time, the ratio of the Si component to the C component can be set high by reducing only the C component amount of the Si component amount and the C component amount in the raw material gas compared to the growth intermediate time. preferable. This is to prevent Si clusters that do not contribute to the growth of the single crystal from the source gas as the Si component gas increases.

  In the present invention, for example, it is preferable to include a chlorine component in the source gas at the start of growth.

  Here, when Si clusters that do not contribute to the growth of the single crystal are formed from the raw material gas, the Si / C ratio in the raw material gas used for the growth of the single crystal is substantially reduced. For this reason, the substantial Si / C ratio at the start of growth may be lower than the set size.

  On the other hand, like this invention, even if Si cluster is formed from source gas by including a chlorine component in source gas, Si cluster can be decomposed | disassembled by this chlorine component. Thereby, the substantial Si / C ratio in the raw material gas at the growth start time can be maintained at the set size.

  In the present invention, for example, the surface (13a, 14a) in contact with the raw material gas flowing toward the seed crystal (7) inside the reaction vessel (6) at the start of growth is made of TaC or NbC. It is preferable to be in the state covered with (20).

  Here, when the surfaces (13a, 14a) in contact with the source gas are made of carbon and the surfaces are not covered with the coating material made of TaC or NbC, the surfaces in contact with the source gas (13a 14a), the C component is taken into the source gas, and the Si / C ratio in the source gas may be substantially reduced.

  On the other hand, according to the present invention, the incorporation of the C component into the raw material gas can be suppressed, and the substantial decrease in the Si / C ratio in the raw material gas can be suppressed.

  In the case of producing a single crystal whose crystal polymorph is 4H type, for example, as a seed crystal, a seed crystal whose surface crystal plane orientation is (000-1) C and whose crystal polymorph is 4H type SiC. Is preferably used.

  In addition, the code | symbol in the bracket | parenthesis of each means described in the claim and this column is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

(First embodiment)
In the present embodiment, the present invention is applied to a method for producing a silicon carbide single crystal by a high temperature CVD method.

  First, the manufacturing apparatus of the silicon carbide single crystal used by this embodiment is demonstrated. In FIG. 1, the schematic cross section of the manufacturing apparatus of the silicon carbide single crystal in 1st Embodiment of this invention is shown.

  In FIG. 1, the apparatus includes a vacuum container 1. The vacuum vessel 1 has a cylindrical shape, a container main body 2 that is fixed in a state where both end openings are positioned vertically, an upper lid member (flange) 3 that closes the upper surface opening of the container main body 2, It is comprised from the lower cover material (flange) 4 which blocks the lower surface opening part of the container main body 2. FIG. The container body 2 is made of, for example, quartz.

  A cylindrical heat insulating material 5 is arranged inside the vacuum container 1 so as to be along the inner wall of the container main body 2. Inside the heat insulating material 5, a cylindrical reaction vessel 6 is arranged along the inner wall of the heat insulating material 5. The internal space of the reaction vessel 6 becomes a reaction chamber (crystal growth chamber). The upper surface of the reaction vessel 6 is closed and the lower surface is opened.

  As a material for the reaction vessel 6, for example, high-purity graphite that can withstand high temperatures (about 2400 ° C.) can be used. By using such high purity graphite, it is possible to reduce the generation of impurities from the heated reaction vessel 6 and the incorporation of impurities into the crystal during crystal growth.

  Here, FIG. 2 shows an enlarged cross-sectional view of the upper portion of the reaction vessel 6. As shown in FIG. 2, a pedestal portion 6a is integrally formed on the ceiling surface in the reaction vessel 6 so as to protrude, and a seed crystal 7 made of silicon carbide faces downward on the lower surface of the pedestal portion 6a. It is joined. The pedestal portion 6a and the seed crystal 7 have the same diameter, and the seed crystal 7 is joined to the pedestal portion 6a with the outer edge of the pedestal portion 6a and the outer edge of the seed crystal 7 aligned. By supplying the source gas to the seed crystal 7 from below, a single crystal made of silicon carbide grows on the surface 7 a of the seed crystal 7.

  Further, as the seed crystal 7, for example, a single crystal substrate whose crystal polymorph is 4H type and whose crystal plane orientation of the surface 7a is a (000-1) C plane is used. This is because, in this case, a single crystal whose crystal polymorph is 4H type can be stably grown as compared with the case where the surface 7a has another crystal plane orientation.

  As shown in FIG. 2, a carbon ring material 9 is disposed in the reaction vessel 6 so as to surround a region 8 where the single crystal below the seed crystal 7 grows, and solid silicon carbide is formed on the lower surface of the ring material 9. 10 is fixed. The solid silicon carbide 10 is disposed in the vicinity of the outer periphery of the seed crystal 7 and on the higher temperature side (upstream side of the source gas) than the seed crystal 7 with a space from the seed crystal 7. Silicon carbide solid raw material (in powder form) or silicon carbide polycrystal is used as solid silicon carbide 10.

  The ring material 9 is detachable from the reaction vessel 6. Specifically, the reaction vessel 6 includes a lower member 61 having a cylindrical shape and an upper member 62 having a covered cylindrical shape. A screw portion 61 a is formed on the upper outer peripheral surface of the lower member 61 and a lower portion of the upper member 62 is formed. A screw portion 62a is formed on the inner peripheral surface. Then, by screwing the screw portion 61a of the lower member 61 and the screw portion 62a of the upper member 62 with the ring material 9 disposed between the lower member 61 and the upper member 62, as shown in FIG. In addition, the ring member 9 can be sandwiched between the lower member 61 and the upper member 62.

Moreover, as shown in FIG. 1, the recessed part 4a is formed in the center part of the lower cover material (flange) 4 so that it may protrude below. The inside of the recess 4a is a storage chamber R1 for storing foreign matter generated in the vacuum vessel 1. A mixed gas introduction pipe 11 is formed on the bottom surface of the recess 4a, and the mixed gas introduction pipe 11 extends in the vertical direction. The upper end side of the mixed gas introduction tube 11 extends inside the vacuum vessel 1, and the mixed gas introduction tube 12 extends upward from the upper end of the mixed gas introduction tube 11. The mixed gas is introduced into the vacuum vessel 1 from the outside of the vacuum vessel 1 through the mixed gas introduction pipes 11 and 12. This mixed gas is a gas that is a raw material for a single crystal, and is a mixture of a raw material gas containing a Si component (Si element) and a C component (C element), a carrier gas, and an etching gas. The mixing ratio of these gases can be adjusted. Specifically, for example, monosilane (SiH ₄ ), which is a gas containing a Si component, and propane (C ₃ H ₈ ), which is a gas containing a C component, are used as source gases. Moreover, argon gas or helium gas is used as carrier gas. Further, hydrogen gas is used as an etching gas.

  A bottomed cylindrical member 13 is connected and supported at the upper end of the mixed gas introduction pipe 12. The bottomed cylindrical member 13 is disposed along the inner wall of the reaction vessel 6 inside the reaction vessel 6. The inside of the mixed gas introduction pipe 12 and the inside of the bottomed cylindrical member 13 communicate with each other, and the gas introduced into the mixed gas introduction pipes 11 and 12 is guided to the inside of the bottomed cylindrical member 13. The upper surface of the bottomed cylindrical material 13 is open, and the gas that has passed through the bottomed cylindrical material 13 travels toward the seed crystal 7. Further, this gas flow reverses on the ceiling surface of the reaction vessel 6, moves downward along the side wall of the reaction vessel 6, and escapes to the outside of the reaction vessel 6 through the through holes S on the lower surface of the reaction vessel 6.

  In this way, the mixed gas introduction pipes 11 and 12 and the bottomed cylindrical member 13 are extended from below the reaction vessel 6 toward the seed crystal 7 in the reaction vessel 6, and the mixed gas (monosilane) is formed on the surface of the seed crystal 7. Propane, carrier gas and etching gas).

  In addition, a heat storage member 14 is disposed in the gas passage directly above the gas introduction pipe 12 inside the bottomed cylindrical member 13 so as to be separated from the side wall and the bottom surface of the bottomed cylindrical member 13. The mixed gas introduced into the bottomed cylindrical member 13 from the mixed gas introduction pipe 12 strikes (contacts) the heat storage member 14 and then moves toward the upper seed crystal 7. The heat storage member 14 as a temperature change prevention member makes it easier for the introduced gas to maintain a constant temperature when the flow rate of the mixed gas (source gas, carrier gas, etching gas) introduced by the gas introduction pipes 11 and 12 changes. This is to prevent the occurrence of crystal defects by suppressing changes in the atmospheric temperature (abrupt temperature changes in the reaction vessel 6). It is preferable that the heat storage member 14 has a large heat capacity, and the maximum size that can enter the bottomed cylindrical material 13 is preferable.

  The lower lid member (flange) 4, the concave portion 4a, and the mixed gas introduction pipe 11 are integrated, and are made of, for example, a stainless steel plate material (SUS material).

  The bottomed cylindrical member 13 and the heat storage member 14 are made of, for example, carbon (C), and the inner surface 13a of the bottomed cylindrical member 13 and the surface 14a of the heat storage member 14 are heated by the heating coil 19, Since the surface is in contact with the gas, it is covered with a covering material 20 made of TaC or NbC.

  Further, an exhaust pipe 15 is connected to a side surface portion of the concave portion 4a of the lower lid member (flange) 4, and the exhaust pipe 15 communicates with the storage chamber R1. An exhaust pump 17 is connected to the exhaust pipe 15 via a particle collector 16. The gas in the vacuum vessel 1 is discharged to the outside of the vacuum vessel 1 by the exhaust pump 17. At this time, the particle collector 16 captures foreign matters such as particles in the gas.

  On the other hand, an inert gas introduction pipe 18 is formed at the center of the upper lid member (flange) 3 located on the upper side in FIG. The lower end of the inert gas introduction pipe 18 extends to the notch portion 5 a in the heat insulating material 5 in the vacuum vessel 1. An inert gas (for example, argon gas) is introduced from the inert gas introduction pipe 18 and moves downward from the upper surface of the reaction vessel 6 through the side surface in the vacuum vessel 1. That is, an inert gas flows downward from the vicinity of the center of the upper lid member 3 through the inert gas introduction pipe 18 and flows downward around the reaction vessel 6 through the periphery of the reaction vessel 6. In this manner, an inert gas is introduced into the reaction vessel 6 from above the reaction vessel 6 in the vacuum vessel 1 and the gas (foreign matter) in the reaction vessel 6 is directed to the outside of the vacuum vessel 1 through the through holes S. Is made. The upper lid member (flange) 3 and the inert gas introduction pipe 18 are integrated, and are made of, for example, a stainless steel plate material (SUS material).

  A heating coil (RF coil) 19 as a heating means is wound around the outer peripheral portion of the vacuum container 1 in the container body 2. The heating coil 19 includes an upper coil 19a and a lower coil 19b. The upper coil 19a can heat the upper portion of the reaction vessel 6, and the lower coil 19b can heat the lower portion of the reaction vessel 6. Moreover, the frequency of the alternating current applied to each coil 19a, 19b is different, and the temperature of the upper part and the lower part of the reaction vessel 6 can be controlled independently. Specifically, the heating coil 19 (upper coil 19 a and lower coil 19 b) has a temperature atmosphere having a lower temperature gradient in the upper part than in the lower part of the reaction vessel 6.

  The gas introduced into the reaction vessel 6 is heated in the reaction vessel 6, part of the gas is crystallized in the seed crystal 7, and the unreacted gas flows to the lower side of the reaction vessel 6.

  In this way, the seed crystal 7 is joined to the surface of the pedestal portion 6a in the reaction vessel 6, and a mixed gas containing at least Si-containing gas and C-containing gas is introduced into the reaction vessel 6. Then, in a gas flow path leading to the seed crystal 7, a single crystal made of silicon carbide is grown on the surface 7 a of the seed crystal 7 by sending the mixed gas to the seed crystal 7 in a temperature atmosphere having a lower temperature gradient toward the downstream. Can be done.

  Next, a method for producing a silicon carbide single crystal will be described.

  FIG. 3 is a time chart showing temporal changes in the temperature (growth atmosphere temperature), hydrogen flow rate, and source gas flow rate of the seed crystal 7.

  First, as shown in FIG. 1, the seed crystal 7 is placed in the reaction vessel 6 in the vacuum vessel 1.

  Then, as shown in FIG. 3, the temperature of the seed crystal (growth atmosphere temperature) is raised to 2300 ° C. (increase) by heating the reaction vessel 6 with the coils 19 a and 19 b during the period from t1 to t4. Warm process).

  The temperature raising process from t1 to t4 will be described in detail. T1 is the timing for starting the temperature raising. Further, since the seed crystal temperature (growth atmosphere temperature) exceeds 1800 ° C., carbonization of the surface 7a of the seed crystal 7 due to excessive escape of Si begins to occur with the generation of the SiC sublimation gas from the seed crystal 7. In order to clean the surface 7a of the seed crystal 7, supply of hydrogen gas as an etching gas is started at the timing t2 at a temperature of 1800 ° C. or lower. Further, the supply of the raw material gas is started at the timing t3 when the temperature reaches 1800 ° C. And the heating for temperature rising is continued until t4 from which the temperature of a seed crystal will be 2300 degreeC.

Subsequently, as shown in FIG. 3, in the period from t <b> 4 to t <b> 5, the flow rate of the gas containing Si and the gas containing C to be introduced into the reaction vessel 6 is set to a desired size, so that the raw material The atomic ratio (Si / C ratio) of the Si component to the C component in the gas is adjusted (Si / C ratio adjustment process). For example, when monosilane (SiH ₄ ) and propane (C ₃ H ₈ ) are used as source gases, silane 1 slm and propane 0.15 slm are set so that the Si / C ratio in the input raw material is about 2.2. To do. In order to grow a SiC single crystal, the propane flow rate is increased from 0.

  Subsequently, at the timing of t5, while keeping the seed crystal temperature and the supply amount of the source gas constant, the flow rate of the hydrogen gas is increased to a desired magnitude, and the hydrogen gas at a predetermined flow rate is increased to a certain time (timing of t6). Continue to supply. At this time, the flow rate of the hydrogen gas is set to 20 slm, for example. With this hydrogen gas, the crystal grown on the surface 7a of the seed crystal 7 in the temperature rising process is etched to expose the surface 7a of the seed crystal 7, that is, the clean surface (etch back process).

  In this etch back process, solid silicon carbide 10 is disposed around the seed crystal 7 with a space therebetween, and the solid silicon carbide 10 is at a higher temperature than the outer periphery of the seed crystal 7. SiC component gas sublimated from silicon carbide 10 is supplied to the outer periphery of seed crystal 7. For this reason, even in the etching process, the lower surface of the seed crystal 7 can be etched without the outer periphery of the seed crystal 7 disappearing by etching (without reducing the diameter). At the same time, disappearance of the outer peripheral portion of the seed crystal 7 due to sublimation can be prevented. Further, since the outer peripheral portion of the seed crystal 7 does not disappear, no crystal defect occurs in the outer peripheral portion of the seed crystal 7.

  Subsequently, during the period from t6 to t7, while keeping the supply amount of the source gas constant, the flow rate of the hydrogen gas is slowly decreased so that the ambient temperature does not change, or the change in the ambient temperature is minimized. Reduce the flow rate of hydrogen gas (etching gas reduction process).

  In this etching gas reduction process, the flow rate of the hydrogen gas is reduced to a predetermined size so as to shift from etching to single crystal growth on the seed crystal surface 7a at the timing of t7. At this time, the hydrogen gas has only to be reduced to such an extent that crystal growth occurs and does not necessarily have to be zero. The temperature of the etching process is preferably 2100 ° C. or higher at which sublimation is promoted, and the surface can be cleaned by etching in a relatively short time by hydrogen etching assisted by sublimation.

  At t7, the growth of the single crystal starts on the surface (clean surface) 7a of the seed crystal 7 exposed by the etching gas. After t7 is the growth process of the single crystal, and the timing of t7 corresponds to the growth start time described in the claims.

  Of the single crystal growth process, during the period from t7 to t8, the flow rate of the raw material gas is kept constant and the Si / C ratio in the charged raw material is kept at about 2.2. At this time, the heating temperature by the coils 19a and 19b is set so that the temperature of the raw material gas introduced into the reaction vessel 6 is higher by 50 ° C. or more than the seed crystal surface 7a. As a result, a 4H-type SiC single crystal starts to grow on the surface 7a of the seed crystal 7 (single crystal growth initial stage).

  The initial growth process of the single crystal from t7 to t8 is a period from when the 4H type SiC single crystal starts to grow on the surface 7a of the seed crystal 7 until the 4H type SiC single crystal is stabilized. , T7 to t8 is, for example, 20 minutes. The 4H type SiC single crystal stably grows when the same surface state is repeated and the single crystal grows, that is, on the 4H type SiC single crystal and subsequently the 4H type SiC. It means that a single crystal comes to grow.

  After the growth of the 4H-type SiC single crystal is stabilized, the monosilane flow rate is kept constant so that the Si / C ratio approaches 1 in the period from t8 to t9 in order to improve the growth rate of the single crystal. However, the propane flow rate is increased (Si / C ratio adjustment process).

  After t9, since the Si / C ratio of the supplied source gas is 1, the 4H-type SiC single crystal grows faster than the initial growth process (single crystal high-speed growth process). Note that the period from t9 to the end of growth corresponds to the mid-growth period described in the claims.

  And although not shown in figure, after growing a single crystal to the target ingot length, supply of a raw material is stopped, it cools and a single crystal is taken out. In this way, a silicon carbide single crystal is manufactured.

Next, main features of the present embodiment will be described.
(1) In this embodiment, when producing a silicon carbide single crystal, in the initial growth process of the single crystal from t7 to t8, the Si / C ratio in the input raw material is set to about 2.2, and from t8 to t9 In the single crystal high-speed growth process, the Si / C ratio in the input raw material is set to about 1, so that the Si / C ratio in the input raw material in the initial growth process of the single crystal is higher than that in the single crystal high-speed growth process. Is also high.

  Here, in FIG. 4, the conceptual diagram showing the surface state of the seed crystal 7 in the growth initial stage of the single crystal of t7-t8 in the manufacturing method of this embodiment is shown. 2A is a plan view of the seed crystal 7, FIG. 2B is a perspective view of the seed crystal 7, and FIG. 2C is a cross-sectional view taken along the line AA of the seed crystal 7 in FIG.

  In addition, as a comparative example, FIG. 5 shows a case where, unlike the present embodiment, the Si / C ratio in the input raw material is set to about 1 in the initial stage of the growth of the single crystal, as in the high-speed growth process of the single crystal. The conceptual diagram showing the surface state of the seed crystal in the initial stage of the growth of a single crystal is shown. 2A is a plan view of the seed crystal 7, FIG. 2B is a perspective view of the seed crystal 7, and FIG. 2C is a cross-sectional view of the seed crystal 7 in FIG.

  As in the present embodiment, when the Si / C ratio in the input raw material is set higher than in the single crystal high-speed growth process at the initial stage of single crystal growth, the number of carbon atoms is increased toward the seed crystal 7. An excessive number of silicon atoms will be supplied. This excess silicon atom forms a Si—C bond with the SiC atom on the outermost surface of the seed crystal or becomes a Si—Si bond having a weak bond with respect to the Si—C bond. Easy to migrate. On the other hand, when the carbon atom becomes excessive, the Si—C bond is formed or the C—C bond having a strong bond is formed, so that the migration of atoms on the crystal surface is difficult. For this reason, this excessive silicon atom promotes the rearrangement of atoms on the seed crystal surface 7a, and tends to form a SiC (0001) plane which is a stable surface on the seed crystal surface 7a. As a result, as shown in FIG. 4C, an atomic step 22 having the SiC (0001) plane as the terrace 22a occurs on the seed crystal surface 7a. As shown in FIGS. 4A and 4B, the atomic steps 22 are formed concentrically.

  A single crystal grows on the seed crystal surface 7a while causing the atomic step to occur on the outermost surface. At this time, since the crystal polymorphism information of the seed crystal 7 can be propagated to the single crystal from the atomic step 22 on the seed crystal surface 7a, the 4H type of 4H type which is the same polymorph as the 4H type SiC seed crystal 7 can be obtained. A SiC single crystal can be stably grown.

  Further, in the high-speed growth process of single crystals, 4H-type SiC single crystals having atomic steps are growing in the initial growth process, so even if the Si / C ratio in the input material is set to about 1. The SiC single crystal can be grown at high speed while maintaining the 4H type.

  Unlike the present embodiment, when the Si / C ratio in the input material is set to the same magnitude as that in the high-speed growth process of the single crystal at the initial stage of the growth of the single crystal, FIGS. 5 (a) and 5 (b). As shown in FIG. 5, no atomic step is formed on the seed crystal surface 7a, and as shown in FIG. 5C, the single crystal 21 grows according to the temperature distribution and gas concentration distribution generated on the seed crystal surface 7a. At this time, the crystal polymorphism information of the seed crystal 7 is not propagated to the growing single crystal 21, and a 6H-type SiC single crystal having a crystal polymorphism different from the seed crystal grows.

Therefore, in the present embodiment, in the period from t7 to t8, the Si / C ratio in the input material is set high as about 2.2 so that the atomic step 22 is formed on the seed crystal surface 7a.
After t9, the Si / C ratio in the input material is set to about 1 so that a single crystal of a desired size can be formed at an early stage.

  In addition, according to the present embodiment, since a 4H type SiC single crystal can be manufactured without using impurities or dopants, impurities and the like are removed as in the techniques described in Patent Documents 2 to 4 described in the background art. Compared with the crystal growth method to be introduced, a high-quality single crystal can be obtained.

  In the present embodiment, the Si / C ratio in the input material is set to about 2.2 in the initial growth process of the single crystal from t7 to t8, but the C component used for the growth of the SiC crystal is By adding an excessive Si component to the raw material gas, the Si / C ratio in the input raw material can be changed to an arbitrary size as long as the atomic step 22 can be formed on the seed crystal surface 7a. The Si / C ratio at this time may be optimized depending on the shape and material of the reaction vessel 6. As the magnitude of the Si / C ratio, for example, other magnitudes such as 3 larger than 1 can be used.

  (2) In this embodiment, hydrogen gas is introduced into the reaction vessel 6 in the etch back process from t5 to t6, and the crystal grown on the surface 7a of the seed crystal 7 in the temperature rising process is etched by this hydrogen gas. (Clean) to expose the clean surface of the seed crystal 7.

  Thereby, in the initial growth process of the single crystal, the atomic step 22 for propagating the crystal polymorph information of the seed crystal 7 to the single crystal can be easily formed on the seed crystal surface 7a. That is, by making the surface of the seed crystal a clean surface and then increasing the Si / C ratio in the source gas and starting crystal growth, the atomic step 22 that is not affected by surface strain such as dirt, impurities, damage, It can be formed on the seed crystal surface 7a. Therefore, it is possible to grow a single crystal that inherits the crystal polymorph information of the seed crystal 7.

(3) In the present embodiment, in the single crystal growth process after t7, the monosilane flow rate of monosilane (SiH ₄ ) and propane (C ₃ H ₈ ), which are source gases, is kept constant, and t8 to t9. By increasing the flow rate of propane over time, the Si / C ratio in the feedstock is reduced from 2.2 to 1. In other words, in the initial growth process of the single crystal, the Si / C ratio in the input raw material is increased by reducing the flow rate of propane as compared with the high-speed growth process of the single crystal.

Here, as a method for increasing the Si / C ratio in the raw material in the initial growth process of the single crystal, compared with the high-speed growth process of the single crystal, the single crystal high-speed growth process and the flow rate of propane (C ₃ H ₈ ). And a method of increasing the flow rate of monosilane (SiH ₄ ) in comparison with the single crystal high-speed growth process.

However, monosilane (SiH ₄ ), which is a gas containing Si, is heated and pyrolyzed when supplied to the seed crystal 7, but forms Si clusters that do not contribute to the growth of the single crystal in this pyrolysis process. It's easy to do. The Si cluster is mainly a collection of a plurality of Si atoms or molecules, and is visually recognized as smoke.

For this reason, when the flow rate of monosilane (SiH ₄ ) is increased, a large number of Si clusters are formed, so that the substantial Si / C ratio of the raw material gas used for the single crystal is lowered and the Si rich state is obtained. There is a fear of not becoming.

  Therefore, as in this embodiment, in the single crystal growth initial process, it is preferable to reduce the flow rate of propane and increase the Si / C ratio in the input raw material, compared to the single crystal high-speed growth process.

(4) In this embodiment, in order to increase the thermal decomposition of monosilane (SiH ₄ ) in the reaction vessel 6 in the initial growth process of the single crystal from t7 to t8, the gas temperature is 50 with respect to the seed crystal surface 7a. Higher than ℃. Thus, in the case where monosilane (SiH ₄₎ is supplied to the seed crystal 7, likely to be thermally decomposed, it can suppress the formation of the Si clusters.

  (5) In the present embodiment, in the manufacturing apparatus used when manufacturing a silicon carbide single crystal, the bottomed cylindrical member 13 and the heat storage member 14 disposed inside the reaction vessel 6 are made of carbon (C). The inner surface 13a of the bottomed cylindrical member 13 and the surface 14a of the heat storage member 14 are surfaces that are heated by the heating coil 19 and contact with the source gas flowing toward the seed crystal 7, so that the coating made of TaC or NbC It is covered with a material 20.

  Here, unlike this embodiment, when the inner surface 13a of the bottomed cylindrical material 13 and the surface 14a of the heat storage member 14 are not covered with the covering material 20 made of TaC or NbC, the bottomed The C component is taken into the raw material gas from the inner surface 13a of the cylindrical member 13 and the heat storage member 14, and the Si / C ratio in the raw material gas may be substantially lowered.

  Thus, as in this embodiment, the inner surface 13a of the bottomed cylindrical member 13 and the surface 14a of the heat storage member 14 are covered with the covering material 20 made of TaC or NbC, so that the C component from the reaction vessel to the source gas is obtained. Can be suppressed. Thereby, the substantial fall of Si / C ratio in source gas can be controlled.

  (6) In the present embodiment, in a manufacturing apparatus used when manufacturing a silicon carbide single crystal, a carbon ring material 9 is provided in the reaction vessel 6 so as to surround a region 8 where the single crystal below the seed crystal 7 grows. Is disposed, and solid silicon carbide 10 is fixed to the lower surface of the ring material 9.

  When producing a silicon carbide single crystal, as shown in FIG. 1, there is a temperature gradient in the reaction vessel 6, and basically, the raw material gas flows from high temperature to low temperature. When the silicon 10 is not fixed, C (carbon) constituting the ring material 9 may be taken into the source gas from the lower surface of the ring material 9. For this reason, in the initial growth process of the single crystal, the component ratio in the source gas supplied to the seed crystal 7 changes.

  On the other hand, as in this embodiment, solid silicon carbide 10 is fixed to the lower surface of the ring material 9, thereby suppressing the incorporation of C (carbon) constituting the ring material 9 into the source gas. In addition, the Si / C ratio in the source gas can be maintained in a Si-rich state in the initial growth process of the single crystal.

(Second Embodiment)
In FIG. 6, the elements on larger scale of the manufacturing apparatus of the silicon carbide single crystal in this embodiment are shown. FIG. 6 is an enlarged cross-sectional view of the upper part of the reaction vessel 6 and corresponds to FIG.

  In the present embodiment, with respect to the silicon carbide single crystal manufacturing apparatus of FIG. 1 described in the first embodiment, as shown in FIG. A heat radiating groove 63 is provided. The groove 63 is disposed at a portion facing the central portion of the pedestal 6a (seed crystal surface 7a) so that the central portion of the seed crystal surface 7a has the lowest temperature due to heat dissipation, for example. In addition, about the other structural part of a manufacturing apparatus, and the manufacturing method of a silicon carbide single crystal, it is the same as that of 1st Embodiment.

  In the present embodiment, since the groove 63 is provided on the upper surface of the reaction vessel 6 as described above, when a silicon carbide single crystal is manufactured by the same method as in the first embodiment, in the growth process of the single crystal from t7 to t8. The seed crystal surface 7a has a temperature distribution in which the central portion has a lower temperature than the surroundings. For this reason, as shown in FIG. 4A, along the temperature distribution, the atomic steps 22 can be evenly and concentrically formed from the central portion on the seed crystal surface 7a.

  For this reason, a single crystal can be grown concentrically on the seed crystal surface 7a with the central portion as a base point. That is, a crystal nucleus can be formed at the center of the seed crystal surface 7a, and a single crystal can be grown using this nucleus as a base point.

  By the way, when the temperature of the seed crystal surface 7a is uniform, since the atomic step 22 is formed at various locations on the seed crystal surface 7a, crystal nuclei are formed at a plurality of locations. In addition, the single crystal may grow. In this case, there is a possibility that the 4H type SiC single crystal cannot be stably grown.

  Therefore, it is preferable to arrange the groove 63 on the upper surface of the reaction vessel 6 so that the atomic step 22 is formed concentrically at the center of the seed crystal surface 7a as in the present embodiment. Thereby, a single crystal having the same polymorph as the seed crystal can be stably produced based on a plurality of nuclei generated in the surface of the seed crystal as compared with the case where the single crystal grows.

  In the present embodiment, the heat radiating groove 63 has been described as an example of the case where the groove 63 for heat dissipation is disposed at a portion facing the central portion of the pedestal portion 6a (seed crystal surface 7a). If the single crystal can be grown from the base point, the heat dissipating groove 63 may not necessarily be disposed at a position facing the central portion of the pedestal portion 6a (seed crystal surface 7a). Any part may be used as long as it faces a part of (seed crystal surface 7a).

  Here, FIG. 7 shows an enlarged cross-sectional view of the vicinity of seed crystal 7 and pedestal portion 6a in the silicon carbide single crystal manufacturing apparatus. For example, as shown in FIG. 7, when using a seed crystal 7 in which the crystal surface of the seed crystal surface 7a is tilted from the (0001) plane, the position of the heat radiation groove 63 is set according to the tilt angle. Shift from the center of 7a. That is, the heat radiating groove 63 is disposed at a portion facing the facet surface 71 so that the center of the facet surface 71 generated on the seed crystal surface 7a is cooler than the periphery thereof.

  Further, in the present embodiment, as means for lowering a part of the seed crystal surface 7a lower than its surroundings, means for providing the heat radiation groove 63 on the upper surface of the reaction vessel 6 is adopted, but other means are adopted. You can also. For example, a seed crystal can be obtained by allowing the inert gas to strike only a part of the upper surface of the reaction vessel 6 from the inert gas introduction pipe 18 provided in the silicon carbide single crystal production apparatus shown in FIG. It is also possible to make part of the surface 7a cooler than its surroundings.

(Third embodiment)
In the first and second embodiments described above, the case where the gas containing the Si component and the gas containing the C component are used as the source gas has been described as an example. However, in this embodiment, the Si component and the C component are used. In addition, the case where the source gas contains a Cl component will be described. Others are the same as in the first embodiment.

As source gas, as gas containing Si component, for example, monosilane (SiH ₄ ) is used, and as gas containing C component, for example, propane (C ₃ H ₈ ) is used as gas containing Cl component. For example, a chlorine compound such as hydrogen chloride (HCl) or chlorine (Cl ₂ ) gas can be used. At this time, the flow rates of monosilane and propane are the same as those in the first embodiment.

Si components and Cl components such as tetrachlorosilane (SiCl ₄ ), dichlorosilane (SiH ₂ Cl ₂ ), trichlorosilane (SiHCl ₃ ), etc., instead of the gas containing Si component and the gas containing Cl component A gas containing can also be used.

  Here, as described in the first embodiment, the gas containing the Si component in the source gas is easy to form Si clusters in the thermal decomposition process when the source gas is supplied to the seed crystal 7, and the gas is simply separated from the source gas. When Si clusters that do not contribute to crystal growth are formed, the Si / C ratio in the source gas used for single crystal growth is substantially reduced. For this reason, the substantial Si / C ratio in the initial stage of the growth of the single crystal may be lower than the set size. Further, when Si clusters adhere to the seed crystal surface 7a, there arises a problem that the quality of the growing single crystal is deteriorated.

  On the other hand, like this invention, even if Si cluster is formed from source gas by including a chlorine component in source gas, Si cluster can be decomposed | disassembled by this chlorine component. Thereby, the substantial Si / C ratio in the raw material gas at the initial stage of the growth of the single crystal can be maintained at a set size. Moreover, since it can suppress that Si cluster adheres to the seed-crystal surface 7a, a high quality single crystal is obtained.

  In the present embodiment, the case where the chlorine component is always included in the source gas has been described as an example. However, the generation of the Si clusters is particularly performed during the period until the single crystal grows stably. Since it becomes a problem, it is sufficient that the source gas contains a chlorine component at least in the initial stage of growth of the single crystal.

(Other embodiments)
(1) Regarding the etching in the manufacturing process of the single crystal, in the first embodiment, the timing for starting the supply of the hydrogen gas as the etching gas is set to t2 of 1800 ° C. or lower, but may be changed to the timing of t5. .

  If a single crystal having the same polymorph as the seed crystal can be grown, the etch-back process may be omitted.

  (2) Regarding the supply of the raw material gas in the process of manufacturing the single crystal, the first embodiment has described the case where the Si / C ratio in the raw material gas is set higher than the time after t9 during t5 to t8. However, the timing at which the Si / C ratio in the source gas is made higher than that after t9 may be other timing than t4 to t5 as long as it is before the start of single crystal growth.

  (3) As a means for setting the Si / C ratio in the source gas to be higher than that after t9, in the first embodiment, as an example, the flow rate of propane is reduced as compared with the high-speed growth process after t9. As described above, the Si / C ratio may be increased by including another Si-containing gas in the source gas only at the initial growth stage of the single crystal.

  (4) Regarding the raw material gas supply in the manufacturing process of the single crystal, in the first embodiment, the case where the Si / C ratio in the raw material gas is set to about 1 in the high-speed growth process after t9 has been described as an example. The Si / C ratio in the source gas at this time may be appropriately set to a size suitable for the growth of the 4H type SiC single crystal (high growth rate) according to the temperature at which the single crystal is grown. The appropriate size is such that the Si component and the C component in the raw material gas are used without excess or deficiency and a single crystal grows. For example, when the seed crystal temperature is 1800 ° C., the Si / C ratio can be set to 0.8.

  (5) Regarding the raw material gas supply in the manufacturing process of the single crystal, in the first embodiment, the case where the Si / C ratio in the raw material gas is changed to 1 at t8 to t9 has been described. For example, it may be maintained at 2.2 without changing the Si / C ratio.

  (6) In each of the above-described embodiments, a case where a 4H type SiC single crystal is manufactured has been described as an example. However, a 6H type SiC single crystal can also be manufactured by a similar method. In this case, a seed crystal 7 composed of a 6H type SiC single crystal is used.

  (7) In each of the above-described embodiments, the example in which the present invention is applied to the high-temperature CVD method has been described. However, the present invention can also be applied to the sublimation method. In this case, for example, a gas introduction passage or the like can be provided in the graphite crucible so that Si / C in the raw material gas can be changed. Further, in this case, the sublimation gas from the raw material portion arranged in the graphite crucible corresponds to the raw material gas containing the Si component and the C component described in the claims.

It is sectional drawing of the manufacturing apparatus of the silicon carbide single crystal in 1st Embodiment of this invention. It is an expanded sectional view of the upper part of the reaction container 6 in FIG. It is a time chart showing the time change about the temperature of the seed crystal 7 at the time of manufacturing the silicon carbide single crystal in 1st Embodiment of this invention, a hydrogen flow rate, and a raw material gas flow rate. It is a conceptual diagram showing the surface state of the seed crystal 7 in the growth initial stage of the single crystal of t7-t8 in the manufacturing method of this embodiment, (a) is a top view of the seed crystal 7, (b) is the seed crystal 7 A perspective view and (c) are AA line sectional views of seed crystal 7 in (a). In the initial stage of single crystal growth, a conceptual diagram showing the surface state of the seed crystal at the initial stage of single crystal growth when the Si / C ratio in the raw material is set to 1 as in the high-speed growth process of the single crystal. (A) is a plan view of the seed crystal 7, (b) is a perspective view of the seed crystal 7, and (c) is a cross-sectional view taken along the line BB of the seed crystal 7 in (a). It is a fragmentary sectional view of the reaction container 6 of the manufacturing apparatus of the silicon carbide single crystal in the 1st example of 2nd Embodiment of this invention. It is a fragmentary sectional view of the reaction container 6 of the manufacturing apparatus of the silicon carbide single crystal in the 2nd example of 2nd Embodiment of this invention.

Explanation of symbols

6 ... reaction vessel, 6a ... pedestal, 7 ... seed crystal, 8 ... single crystal (growth planned region),
9 ... Ring material, 10 ... Solid silicon carbide.

Claims (9)

A seed crystal (7) made of silicon carbide is placed in the reaction vessel (6), and the seed crystal (7) is obtained using a raw material gas containing Si component and C component introduced into the reaction vessel (6). In the method for producing a silicon carbide single crystal, a single crystal made of silicon carbide is grown on the surface of
The heat storage member (14) is disposed in the flow path of the source gas in the reaction vessel (6), the reaction vessel (6) is heated, and the reaction vessel (6) is set to a predetermined temperature atmosphere, It is designed to grow single crystals,
Of the growth start time at which the single crystal starts growing on the surface of the seed crystal and the growth intermediate time during the growth of the single crystal after the growth start time, By setting the atomic ratio of the Si component to the C component in the raw material gas higher than halfway, the single crystal that is the same crystal polymorph as the seed crystal is produced ,
At the time of starting the growth, the inside of the reaction vessel (6) is a temperature atmosphere having a temperature gradient that becomes lower as the seed crystal (7) is closer,
In the reaction vessel (6), a carbon ring material (9) is disposed so as to surround a region (8) where a single crystal on the surface of the seed crystal (7) grows, and the ring material (9 method for producing a silicon carbide single crystal, wherein said Rukoto using a reaction vessel (6) on the surface of the high temperature-side solid silicon carbide (10) is fixed among). In the temperature raising period in which the temperature of the seed crystal (7) is raised to the temperature of the growth start time which is higher than 1800 ° C., the temperature of the seed crystal (7) exceeds 1800 ° C. and the seed crystal (7 ) Starts to be introduced into the reaction vessel (6) before the introduction of an etching gas to clean the surface (7a) of the seed crystal (7) and the reaction vessel (6) The method for producing a silicon carbide single crystal according to claim 1 , wherein the introduction of the source gas into the substrate is started. A seed crystal (7) made of silicon carbide is placed in the reaction vessel (6), and the seed crystal (7) is obtained using a raw material gas containing Si component and C component introduced into the reaction vessel (6). In the method for producing a silicon carbide single crystal, a single crystal made of silicon carbide is grown on the surface of
Of the growth start time at which the single crystal starts growing on the surface of the seed crystal and the growth intermediate time during the growth of the single crystal after the growth start time, By setting the atomic ratio of the Si component to the C component in the raw material gas higher than halfway, the single crystal that is the same crystal polymorph as the seed crystal is produced,
At the growth start time, the inside of the reaction vessel (6) is a temperature atmosphere having a temperature gradient that becomes lower as the seed crystal (7) is closer,
In the reaction vessel (6), a carbon ring material (9) is disposed so as to surround a region (8) where a single crystal on the surface of the seed crystal (7) grows, and the ring material (9 ), The reaction vessel (6) having solid silicon carbide (10) fixed to the surface on the higher temperature side than the seed crystal is used. Wherein in the growth start time, the portion of the surface of the seed crystal, the silicon carbide single crystal according to any one of claims 1 to 3, characterized in that the lowest temperature in the surface of the seed crystal Production method. Before the start of the growth, an etching gas is introduced into the reaction vessel (6), and after the clean surface of the seed crystal (7) is exposed by the etching gas, the growth of the single crystal is started. The method for producing a silicon carbide single crystal according to any one of claims 1 to 4 , wherein: And said growth start time, and in the growth midway timing and the amount of the same city Si component in the feed gas, as claimed in any one of claims 1 to 5, wherein varying the amount of component C A method for producing a silicon carbide single crystal. The method for producing a silicon carbide single crystal according to any one of claims 1 to 6 , wherein a chlorine component is included in the source gas at the growth start time. At the growth start time, the surfaces (13a, 14a) in contact with the source gas flowing toward the seed crystal (7) inside the reaction vessel (6) are covered with a covering material (20) made of TaC or NbC. The method for producing a silicon carbide single crystal according to any one of claims 1 to 7 , wherein the silicon carbide single crystal is in a state of being formed. The seed crystal according to any one of claims 1 to 8 , wherein a seed crystal having a crystal plane orientation of (000-1) C and a crystal polymorph of 4H type is used as the seed crystal. A method for producing a silicon carbide single crystal.

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