JP6119453B2 - Method for producing silicon carbide single crystal - Google Patents

Description

  The present invention relates to a method for producing a silicon carbide single crystal having few stacking faults and high crystal quality. A silicon carbide single crystal wafer manufactured from a silicon carbide single crystal obtained by the present invention through processing and polishing steps is mainly used as various semiconductor electronic devices or their substrates.

  Silicon carbide (SiC) is a wide band gap semiconductor having a wide forbidden bandwidth of 2.2 to 3.3 eV. Conventionally, SiC has been researched and developed as an environmentally resistant semiconductor material because of its excellent physical and chemical properties, but in recent years, short wavelength optical devices from blue to ultraviolet, high frequency electronic devices, SiC is attracting attention as a material for high-power electronic devices, and research and development is actively underway. However, until now, SiC has been considered difficult to produce high-quality large-diameter single crystals, which has hindered the practical application of SiC devices.

Conventionally, on a laboratory scale scale, for example, a SiC single crystal having a size capable of producing a semiconductor element by a sublimation recrystallization method (Rayleigh method) has been obtained. However, in this method, the area of the obtained single crystal is small, and it is not easy to control the size, shape, crystal polymorph (polytype), and impurity carrier concentration. On the other hand, a cubic SiC single crystal is also grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using chemical vapor deposition (CVD). With this method, large-area single crystals can be obtained, but only SiC single crystals containing many defects (up to 10 ⁷ / cm ² ) can be grown due to the lattice mismatch between SiC and Si of about 20%. High-quality SiC single crystals have not been obtained. In order to solve these problems, an improved Rayleigh method has been proposed in which sublimation recrystallization is performed using a SiC single crystal wafer as a seed crystal (see Patent Document 1). By using this improved Rayleigh method, it is possible to grow a SiC single crystal while controlling the polytype (6H type, 4H type, 15R type, etc.), shape, carrier type and concentration of the SiC single crystal.

  Currently, SiC single crystal wafers with a diameter of 51 mm (2 inches) to 100 mm are cut out from SiC single crystals produced by the modified Rayleigh method and used for device production in the field of power electronics. There are over 200 polytypes of SiC, but the 4H polytype is often used for electronic devices because of its physical properties and stability of crystal growth. Further, in the SiC single crystal, there are crystal defects such as hollow hole-like defects penetrating in the growth direction called “micropipes”, dislocation defects, and stacking faults. Since these crystal defects deteriorate device performance, reduction of these crystal defects is regarded as an important issue in SiC device application.

Among these, for stacking faults in SiC single crystals produced by the sublimation recrystallization method, for example, Siche et al. Reported that 15R and 6H type stacking faults occur in 4H polytypes (non-patent literature). 1). Nakabayashi et al. Have reported that 6H type stacking faults exist in 4H polytype (see Non-Patent Document 2). In addition, 3C type and 8H type stacking faults are known, especially when annealing nitrogen-doped substrates with a nitrogen atom number density of about 1 × 10 ²⁰ (/ cm ³ ) at 1000 to 1100 ° C. (See Non-Patent Document 3). Conversely, it has been reported that stacking faults hardly occur in nitrogen undoped crystals (see Non-Patent Document 4).

Incidentally, the resistivity of SiC single crystal substrates that are currently on the market is generally 0.012 to 0.030 (Ω / cm), and has the above-described resistivity from the relationship between the resistivity and the number density of nitrogen atoms. The number density of nitrogen atoms necessary for obtaining a SiC single crystal is about 5 × 10 ^{18 to} 1.1 × 10 ¹⁹ (/ cm ³ ) (see Non-Patent Document 5).

Japanese Patent Laid-Open No. 9-157091

D. Siche, et al., Materials Science and Forum, vols. 483-485 (2005), pp.39-42 M. Nakabayashi, et al., Materials Science and Forum, vols.645-648 (2010), pp9-12 Thomas A. Kuhr, et al., Journal of Applied Physics, vols. 92, (2002), pp. 5863-5871 Tomohisa. Kato, et al., Materials Science and Forum, vols. 556-557 (2007), pp.239-242 R. C. Glass, et al., Phys. Stat. Sol. (B), 202, (1997), pp.149-162

Since stacking faults in a SiC single crystal cause a decrease in the breakdown voltage of the device and a current leak path, it is necessary to reduce the stacking faults in manufacturing a high-performance device. As described in Non-Patent Document 4 described above, stacking faults are suppressed by undoped nitrogen, but it is necessary to supply nitrogen for controlling the resistivity of the SiC single crystal substrate. Therefore, a substrate having a nitrogen atom number density of 5 × 10 ¹⁸ (/ cm ³ ) or more is required so that the resistivity is 0.030 (Ω / cm) or less.

  The present invention has been made in view of the above circumstances, and it is possible to produce a SiC single crystal having a predetermined nitrogen atom number density but having few stacking faults, high crystal quality, and controlled resistivity. It provides a possible method.

That is, the present invention has the following configuration.
( 1 ) A silicon carbide single crystal in which nitrogen gas is supplied to a crucible containing raw material powder and seed crystal, and a silicon carbide single crystal having a nitrogen atom number density of a set density D ₁ is grown by a sublimation recrystallization method A manufacturing method of
A second pre-growth test for growing a silicon carbide single crystal including nitrogen contained in the growth crystal in advance in a crucible while supplying a certain amount of nitrogen gas from the outside is performed. For each of a plurality of nitrogen supply conditions in which the supply amount is changed, the number density of nitrogen atoms taken into the grown crystal is determined in relation to the height of the grown crystal,
In the second pre-growth test, a nitrogen supply condition A in which the nitrogen atom number density satisfies the range of the set density D ₁ until the middle of crystal growth, and thereafter the nitrogen atom number density falls below the set density D ₁ range; Until the middle of crystal growth, the nitrogen atom number density exceeds the range of the set density D ₁ , and thereafter, the nitrogen supply condition C that satisfies the set density D ₁ is selected.
Nitrogen atom number density of silicon carbide single crystal ^{5 × 10 18 (/ cm 3} ) or more ^{2.5 × 10 19 (/ cm 3} ) so as to set the density D ₁ of the below, the nitrogen supply conditions during the crystal growth A method for producing a silicon carbide single crystal, wherein crystal growth is performed by switching a supply amount of nitrogen gas from A to a nitrogen supply condition C.
( 2 ) In the second pre-growth test, the nitrogen atom number density exceeds the range of the set density D ₁ until the middle of crystal growth, and once the nitrogen atom number density satisfies the range of the set density D ₁ , and thereafter Furthermore by selecting the nitrogen supply condition B to the nitrogen atoms density is below the range of the set density D _1, so that the set density D _1, sequentially the nitrogen supply conditions during the crystal growth a, B, and C method for producing a silicon carbide single crystal according to claim (1), characterized in that the crystal growth is performed by switching.
( 3 ) The method for producing a silicon carbide single crystal according to ( 1 ) or ( 2 ), wherein the nitrogen gas in the growth atmosphere has a change amount of less than 10 vol% per hour when the nitrogen supply condition is switched. .
( 4 ) When the vertical section of the silicon carbide single crystal including the diameter of the seed crystal is viewed, the number of stacking faults included per unit length in the growth direction is 10 (/ cm) or less (1 )-( 3 ) The manufacturing method of the silicon carbide single crystal in any one of.
( 5 ) The method for producing a silicon carbide single crystal according to any one of (1) to ( 4 ), wherein the polytype of the silicon carbide single crystal is 4H.
( 6 ) The method for producing a silicon carbide single crystal according to any one of (1) to ( 5 ), wherein the stacking fault is a 6H type.
( 7 ) The method for producing a silicon carbide single crystal according to any one of (1) to ( 6 ), wherein a crystal diameter of the silicon carbide single crystal is 50 mm or greater and 300 mm or less.

  The SiC single crystal obtained by the method of the present invention has a predetermined nitrogen atom number density but has few stacking faults and is excellent in crystal quality. And since the wafer processed from this SiC single crystal (SiC single crystal substrate) is high quality and the resistivity is controlled, it exhibits high performance as a substrate for electronic devices.

The block diagram which shows an example of the single-crystal manufacturing apparatus used in manufacturing the crystal | crystallization of this invention. Explanatory drawing for demonstrating the mode of the stacking fault contained in a silicon carbide single crystal. Graph showing the relationship between the height of the growing crystal and the nitrogen atom number density of growing crystals obtained in advance growth test according to the first invention (basic density D _0). The graph which shows the relationship between the nitrogen atom number density in the growth crystal obtained by the prior growth test which concerns on 2nd invention, and the height of the growth crystal. The graph which shows the relationship between the nitrogen atom number density in the growth crystal obtained by the prior growth test which concerns on 2nd invention, and the height of the growth crystal.

In the present invention, as described below, the number density of nitrogen atoms in the SiC single crystal is 5 × 10 ¹⁸ (/ cm ³ ) or more and less than 2.5 × 10 ¹⁹ (/ cm ³ ), preferably 5 × 10 ¹⁸ (/ By making the set density D _{1 not} less than cm ³ ) and not more than 1.5 × 10 ¹⁹ (/ cm ³ ), it becomes possible to produce a SiC single crystal having few stacking faults and high crystal quality.

The mechanism that can reduce stacking faults is described below.
As a cause of stacking faults, Non-Patent Document 2 proposes 6H polytype two-dimensional nucleation on a (0001) plane terrace during SiC crystal growth. This is because 6H polytype two-dimensional nuclei are formed and taken into the crystal by increasing the terrace width of the (0001) plane of the growth surface, and 6H polytype stacking faults are generated. . One of the factors that increase the terrace width during growth is considered to be step bunching due to excessive supply of additive elements. Therefore, the present inventors thought that step bunching can be suppressed and stacking faults can be reduced by appropriately controlling the supply amount of the additive element.

As additive elements for obtaining a SiC single crystal, for example, nitrogen (N), boron (B), aluminum (Al), and vanadium (V) are generally used. Among these, nitrogen can be used as an additive element because a gas source (N ₂ ) can be used and the supply amount can be easily controlled.

The present inventors investigated the relationship between the amount of nitrogen in the crystal (nitrogen atom number density) and the occurrence of stacking faults, and found that the nitrogen atom number density in the crystal was less than 2.5 × 10 ¹⁹ (/ cm ³ ). It was discovered that stacking faults hardly occur by controlling the nitrogen supply amount. Although the details have not been elucidated, it is considered that the generation of stacking faults was suppressed because the step bunching during crystal growth was suppressed by limiting the amount of additive elements.

  Here, regarding the number of stacking faults in the SiC single crystal, in the present invention, the number of stacking faults per unit length in the growth direction on the (1-100) plane perpendicular to the seed crystal is defined. In other words, stacking faults are surface defects that extend in a SiC single crystal (SiC single crystal ingot) in a direction substantially parallel to the growth direction, so many (1-100) plane samples parallel to the growth direction Stacking faults can be observed. Therefore, in the present invention, as shown in FIG. 2, in the (1-100) plane, which is a longitudinal section of an ingot that includes the diameter of the seed crystal (that is, a longitudinal section that includes the central portion of the ingot), The number of stacking faults included per unit length in the growth direction was evaluated. When the number of stacking faults in this (1-100) plane exceeds 10 / cm, the area containing stacking faults in the (0001) plane wafer cut out from the same crystal becomes wider. Yield decreases. Accordingly, the number of stacking faults is desirably 10 / cm or less, and more desirably 5 / cm or less.

  Incidentally, the number density of nitrogen atoms in the SiC single crystal depends on the amount of nitrogen in the growth atmosphere. As the nitrogen content in the growth atmosphere, in addition to nitrogen gas or a mixed gas containing nitrogen supplied from the high-purity gas pipe 9 in the SiC single crystal growth apparatus as shown in FIG. 1, graphite constituting the crystal growth space Examples include nitrogen released from the crucible 3 or the SiC raw material powder (sublimation raw material) 2. This is because nitrogen existing in the atmosphere or in the double quartz tube before crystal growth adheres to the graphite crucible 3 or SiC raw material powder 2 and is released into the growth atmosphere by detaching in a high temperature environment during crystal growth. What can be considered. Since the amount of nitrogen released from the components of this SiC single crystal growth device varies depending on the temperature and pressure during crystal growth, it is difficult to predict how much it will be incorporated into the SiC single crystal, and the resulting SiC single crystal It is difficult to precisely control the nitrogen atom number density.

Therefore, in the present invention, in order to reduce the number of stacking faults included in the SiC single crystal while having a predetermined resistivity, the SiC single crystals obtained by the manufacturing methods according to the first and second inventions as described below are used. The number density of nitrogen atoms in the crystal is controlled accurately.
First, in the first invention, a first pre-growth test is performed in which a SiC single crystal is grown without supplying nitrogen gas from the outside, and is taken into the grown crystal based on the nitrogen content previously present in the crucible. The basic density D ₀ obtained is determined in relation to the height of the grown crystal, and nitrogen gas corresponding to the difference from the basic density D ₀ is crystallized so that the number density of nitrogen atoms of the SiC single crystal becomes the set density D _1. SiC single crystal is manufactured by supplying from outside during growth.

That is, in the first invention, crystal growth is performed under the condition that the amount of nitrogen gas supplied from the outside is 0 (mL / min) intentionally, and the amount of nitrogen in the obtained SiC single crystal is subjected to secondary ion mass spectrometry. By measuring with (SIMS) or the like, the amount of nitrogen taken into the crystal by nitrogen released from the constituent elements of the SiC single crystal growth apparatus is investigated in advance. Specifically, as shown in FIG. 3, the basic density D ₀ derived from the nitrogen content preliminarily present in the crucible and taken into the growth crystal is expressed as a function of the height of the growth crystal. At this time, except that nitrogen gas is not supplied from the outside, the conditions (temperature, pressure) for growing the SiC single crystal in actual production may be used. Based on the function of the basic density D ₀ thus obtained, the nitrogen gas supplied from the high-purity gas pipe 9 or a mixed gas containing nitrogen is adjusted by the mass flow controller 10 to control the amount of nitrogen in the growth atmosphere. Thus, the number density of nitrogen atoms in the crystal can be made 5 × 10 ¹⁸ (/ cm ³ ) or more and less than 2.5 × 10 ¹⁹ (/ cm ³ ), and as a result, stacking faults can be suppressed.

Further, in the second invention, a second pre-growth test for growing a SiC single crystal including nitrogen contained in advance in a crucible while supplying a constant amount of nitrogen gas from the outside. To do. At that time, such a pre-growth test was conducted under a plurality of nitrogen supply conditions in which the amount of nitrogen gas supplied from the outside was changed, and the number density of nitrogen atoms incorporated into the grown crystal was related to the height of the grown crystal. I ask for it. Then, as shown in FIG. 4, in the second pre-growth test, the nitrogen atom number density satisfies the set density D ₁ until the middle of the crystal growth, and thereafter the nitrogen atom number density becomes the set density D _1. Nitrogen supply condition A (below the lower limit of the set density D ₁ ), and the number density of nitrogen atoms exceeds the range of the set density D ₁ until the middle of crystal growth (above the upper limit of the set density D ₁ ), Thereafter, after selecting the nitrogen supply condition C in which the nitrogen atom number density satisfies the range of the set density D ₁ , the nitrogen atom density is increased during crystal growth so that the nitrogen atom number density of the SiC single crystal becomes the set density D _1. The SiC single crystal is manufactured by performing crystal growth by switching the supply amount of nitrogen gas from the supply condition A to the nitrogen supply condition C.

That is, in the second invention, the crystal growth is performed under different conditions of the amount of nitrogen gas supplied from the outside, and the amount of nitrogen in the crystal is adjusted in a state including the nitrogen content released from the components of the SiC single crystal growth apparatus. Measurement is performed by the method as described above, and the number density of nitrogen atoms taken into the grown crystal is expressed as a function of the height of the grown crystal. At this time, except for the supply of nitrogen gas from the outside, the conditions (temperature, pressure) for growing the SiC single crystal in actual production may be used. Based on at least the nitrogen supply conditions A and C as described above, the number density of nitrogen atoms in the crystal from the start to the end of the growth is 5 × 10 ¹⁸ (/ cm ³ ) or more and 2.5 × 10 ^19. By switching the amount of nitrogen gas supplied from the outside so as to be less than (/ cm ³ ), stacking faults can be suppressed.

In the second invention, from the result of the pre-growth test, the nitrogen atom number density exceeds the range of the set density D ₁ until the middle of the crystal growth, and once the nitrogen atom number density satisfies the range of the set density D ₁ , Thereafter, the crystal growth may be performed by further selecting the nitrogen supply condition B in which the nitrogen atom number density falls below the range of the set density D ₁ . That is, as shown in FIG. 5, the nitrogen supply conditions are changed from A → B → C so that the number density of nitrogen atoms in the crystal from the start to the end of growth is within the set density D ₁ . It is also possible to obtain a SiC single crystal in which stacking faults are suppressed by sequentially switching the crystal growth. In the second invention, when the nitrogen supply condition is switched from A → C (or A → B → C), the amount of nitrogen gas in the growth atmosphere is preferably less than 10 vol% per hour. It is better to do so. If the nitrogen gas changes suddenly during growth, lattice mismatch may occur due to the difference in the number density of nitrogen atoms in the crystal, and dislocation defects may occur. It is better to switch.

Since the SiC single crystal obtained by the present invention has few stacking faults, when an electronic device is manufactured, it is possible to suppress a decrease in breakdown voltage due to stacking faults and generation of leakage current. In general, the amount of nitrogen in crystals required for electronic devices is 5 × 10 ^{18 to} 1.1 × 10 ¹⁹ (/ cm ³ ), so the SiC single crystal obtained by the production method of the present invention is used for electronic devices. Can be suitably used.

  Further, regarding the polytype of the silicon carbide single crystal to which the production method according to the present invention is applied, the 4H polytype that has a high electron mobility and is capable of producing a high-performance device is preferable.

Furthermore, in the present invention, many of the stacking faults that occur when the nitrogen content exceeds 2.5 × 10 ¹⁹ (/ cm ³ ) by identifying the stacking fault type by observing the lattice image using a transmission electron microscope (TEM). Was found to be 6H type. Therefore, 6H type stacking faults can be suppressed by the manufacturing method of the present invention.

  The suppression of stacking faults in the present invention is performed by controlling the amount of nitrogen supply, so there is no limitation on the crystal diameter in the application range, and for example, it can be applied to a crystal growth process with a diameter of 50 mm or more and 300 mm or less.

  Hereinafter, the present invention will be specifically described based on examples.

  FIG. 1 shows a SiC single crystal growth apparatus by an improved Rayleigh method used for manufacturing a SiC single crystal according to an embodiment of the present invention. Crystal growth is performed by sublimating the sublimation raw material 2 accommodated in the graphite crucible 3 provided with the lid 4 by induction heating and recrystallizing the seed crystal 1. The seed crystal 1 is attached to the inner surface of the graphite lid 4, and the sublimation raw material 2 is filled in the graphite crucible 3. The graphite crucible 3 is covered with a felt made of graphite 7 for heat shielding together with the lid 4 and is placed on a graphite support rod 6 inside the double quartz tube 5. After the inside of the quartz tube 5 is evacuated by the evacuation device 11, high purity Ar gas and nitrogen gas are allowed to flow through the pipe 9 while being controlled by the mass flow controller 10, and the pressure inside the quartz tube during crystal growth is 1.3 kPa. Crystal growth was carried out by applying a high-frequency current to the work coil 8 while heating the graphite crucible 3. The temperature of the graphite crucible 3 was measured with a two-color thermometer from the brightness of the upper part of the crucible by providing an optical path with a diameter of 6 mm at the center of the heat insulating material covering the upper part of the crucible. The amount of nitrogen incorporated into the SiC crystal was adjusted by changing the amount of nitrogen supplied to the atmospheric gas.

(Example 1)
First, from a previously grown SiC single crystal ingot, a 4H type SiC single crystal substrate having a (0001) plane with a diameter of 50 mm as a main surface was cut out, polished, and used as a seed crystal. After the inside of the double quartz tube 5 was evacuated, high-purity Ar gas was introduced as an atmospheric gas, and the pressure in the quartz tube was set to 80 kPa. Under this pressure, a current was passed through the work coil 16 to increase the temperature, and the temperature of the seed crystal 1 was increased to 2200 ° C. Thereafter, the growth atmosphere pressure was reduced to 1.3 kPa over 30 minutes, and crystal growth was performed for 60 hours using the (000-1) plane of the seed crystal 1 as the crystal growth plane. The nitrogen supply during this period is 0 (mL / min).

The crystal diameter of the obtained crystal was about 50 mm, and the crystal height was about 10 mm. Regarding the obtained SiC single crystal, the measurement result of the nitrogen amount by SIMS is that the nitrogen amount at a height of 2 mm from the seed crystal is 1 × 10 ¹⁹ (/ cm ³ ), and the position at a height of 6 mm from the seed crystal. The amount of nitrogen was 1 × 10 ¹⁷ (/ cm ³ ), and the amount of nitrogen at a height of 10 mm from the seed crystal was 1 × 10 ¹⁷ (/ cm ³ ). Under this growth condition (first pre-growth test), the relationship between the height t1 from the seed crystal and the nitrogen amount N1 from the seed crystal to 6 mm is “N1 = −0.2475 × 10 ¹⁹ × t1 + 1.495 × 10 ¹⁹ ” Can be derived. Despite the fact that the nitrogen supply during crystal growth is 0 (mL / min), nitrogen is present in the crystal because the nitrogen attached to the graphite crucible and SiC raw material powder is released into the growth atmosphere. It was because it was taken in. The amount of nitrogen was the same at 6 mm and 10 mm from the seed crystal because all the nitrogen adhering to the graphite crucible and the SiC raw material powder was released from the start of growth until the crystal height reached 6 mm. This suggests that growth has occurred in a non-existent environment.

Subsequently, crystal growth was performed for 60 hours under the condition that 6.7% by volume of nitrogen in the supply gas was contained. The conditions are the same as above except for the amount of nitrogen to be supplied. The crystal diameter of the obtained crystal was about 50 mm, and the crystal height was about 10 mm. The measurement result of nitrogen amount by SIMS is that the amount of nitrogen at 2 mm from the seed crystal is 2.5 × 10 ¹⁹ (/ cm ³ ), the amount of nitrogen at 6 mm from the seed crystal is 1.5 × 10 ¹⁹ (/ cm ³ ), The amount of nitrogen at 10 mm from the crystal was 1.5 × 10 ¹⁹ (/ cm ³ ). The relationship between the height t2 (0 ≦ t2 ≦ 6) from the seed crystal under this growth condition and the nitrogen amount N2 can be derived as “N2 = −0.25 × 10 ¹⁹ × t1 + 3.0 × 10 ¹⁹ ”.

Based on the results measured in advance, the nitrogen supply rate is 0 (mL) immediately after the start of growth in order to set the set density D1 to 5 × 10 ¹⁸ (/ cm ³ ) or more and less than 2.5 × 10 ¹⁹ (/ cm ³ ). / min), the nitrogen supply amount was changed to 6.7% by volume over 36 hours (the time required for the crystal to grow 6 mm), and crystal growth was performed for 60 hours. The conditions are the same as above except for the amount of nitrogen to be supplied. The crystal diameter of the obtained crystal was about 50 mm and the crystal height was about 10 mm. Nitrogen content of the measurement result of the SIMS, the nitrogen content is ^{1.5 × 10 19 (/ cm 3} ) of 0mm position from the seed crystal, the nitrogen in position of 2mm is ^{1.5 × 10 19 (/ cm 3} ), 6mm from the seed crystal The nitrogen amount at the position of 1.5 × 10 ¹⁹ (/ cm ³ ) was 1.5 × 10 ¹⁹ (/ cm ³ ) at the position 10 mm from the seed crystal. A (1-100) plane wafer containing a longitudinal section including the diameter of the seed crystal was cut out, and after mirror polishing, the stacking faults included per unit length in the growth direction were measured by a photoluminescence microscope and molten KOH etching. The number (stacking fault density) was measured. As a result, the stacking fault density was 0 (lines / cm) at any position of 0, 2, 6, and 10 mm from the seed crystal.

Substrates were cut from the same crystal in the (0001) plane, and the polytype and dislocation density were investigated. Visual observation of coloration revealed that it was a 4H single polytype. When the dislocation density was measured from observation with an optical microscope after the molten KOH etching, the dislocation density was 8.0 × 10 ³ (/ cm ² ). This value is equivalent to a commercially available product and can be said to be a high-quality substrate.

(Example 2)
First, a 4H type SiC single crystal substrate having a (0001) plane of 50 mm in diameter as a main surface was cut out from a previously grown SiC single crystal ingot and polished to obtain a seed crystal. Next, crystal growth was carried out for 60 hours under the condition that 3.4% by volume of nitrogen was included in the nitrogen supply gas supplied from the outside. Conditions other than the amount of nitrogen are the same as in Example 1. The crystal diameter of the obtained crystal was about 50 mm and the crystal height was about 10 mm. Regarding the obtained SiC single crystal, the measurement result of the nitrogen amount by SIMS is that the amount of nitrogen at a height of 0 mm from the seed crystal is 2.0 × 10 ¹⁹ (/ cm ³ ), and the position of the height of 2 mm from the seed crystal is The amount of nitrogen is 1.5 × 10 ¹⁹ (/ cm ³ ), the amount of nitrogen at a height of 6 mm from the seed crystal is 4 × 10 ¹⁸ (/ cm ³ ), the amount of nitrogen at a height of 10 mm from the seed crystal is 4 × 10 ¹⁸ (/ cm ³ ).

Subsequently, crystal growth was performed for 60 hours under the condition that 6.7% by volume of nitrogen was included in the nitrogen supply gas supplied from the outside. Conditions other than the amount of nitrogen are the same as in Example 1. The crystal diameter of the obtained crystal was about 50 mm and the crystal height was about 10 mm. Regarding the obtained SiC single crystal, the measurement result of the nitrogen amount by SIMS is that the nitrogen amount at the height of 0 mm from the seed crystal is 3.0 × 10 ¹⁹ (/ cm ³ ), the nitrogen amount at the position of 2 mm from the seed crystal. The amount of nitrogen is 2.5 × 10 ¹⁹ (/ cm ³ ), the amount of nitrogen at a height of 6 mm from the seed crystal is 1.5 × 10 ¹⁹ (/ cm ³ ), the amount of nitrogen at a height of 10 mm from the seed crystal is 1.5 × 10 ¹⁹ (/ cm ³ ).

Based on the above results, in order to set the set density D1 to 5 × 10 ¹⁸ (/ cm ³ ) or more and less than 2.5 × 10 ¹⁹ (/ cm ³ ), first, 3.4 volumes of nitrogen is supplied into the nitrogen supply gas supplied from the outside. % (Supply condition A) for 12 hours of crystal growth, then change the nitrogen in the supply gas to 6.7% by volume (supply condition C) over 20 minutes, and further crystal growth for 48 hours It was. The crystal diameter of the obtained crystal was about 50 mm and the crystal height was about 10 mm. Regarding the obtained SiC single crystal, the measurement result of the nitrogen amount by SIMS is that the amount of nitrogen at the height of 0 mm from the seed crystal is 2.0 × 10 ¹⁹ (/ cm ³ ) , and the amount of nitrogen at the position of 2 mm from the seed crystal is 1.5 × 10 ¹⁹ (/ cm ³ ), the amount of nitrogen at 6 mm from the seed crystal is 1.5 × 10 ¹⁹ (/ cm ³ ), the amount of nitrogen at a height of 10 mm from the seed crystal is 1.5 × 10 ¹⁹ (/ cm ³ ).

Further, for the obtained SiC single crystal, a (1-100) plane wafer including a longitudinal section including the diameter of the seed crystal was cut out, and after mirror polishing, the growth direction was measured by a photoluminescence microscope and molten KOH etching. The number of stacking faults included per unit length (stacking fault density) was measured. As a result, the stacking fault density is 5 (lines / cm) at the position of 0 mm from the seed crystal, the stacking fault density is 0 (lines / cm) at the position of 2 mm from the seed crystal, and the stacking fault density is 6 mm from the seed crystal. The stacking fault density was 0 (lines / cm) at a position of 0 (lines / cm) and 10 mm from the seed crystal. In addition, a substrate was cut out from the same crystal in the (0001) plane, and the polytype and dislocation density were investigated. Visual observation of coloration revealed that it was a 4H single polytype. When the dislocation density was measured from observation with an optical microscope after the molten KOH etching, the dislocation density was 9.0 × 10 ³ (/ cm ² ). This value is equivalent to a commercially available product and can be said to be a high-quality substrate.

(Example 3)
First, crystal growth was performed for 60 hours with an externally supplied nitrogen amount of 0 (mL / min). Conditions other than the amount of nitrogen are the same as in Example 1. The crystal diameter of the obtained crystal was about 50 mm and the crystal height was about 10 mm. Regarding the obtained SiC single crystal, the measurement result of the nitrogen amount by SIMS shows that the nitrogen amount at the height of 0 mm from the seed crystal is 1.5 × 10 ¹⁹ (/ cm ³ ), and the position at the height of 2 mm from the seed crystal. The amount of nitrogen is 1 × 10 ¹⁹ (/ cm ³ ), the amount of nitrogen at a height of 6 mm from the seed crystal is 1 × 10 ¹⁷ (/ cm ³ ), and the amount of nitrogen at the position of 10 mm from the seed crystal is 1 × 10 ¹⁷ (/ cm ³ ).

Next, crystal growth was performed for 60 hours under the condition that 3.4% by volume of nitrogen was included in the nitrogen supply gas supplied from the outside. Conditions other than the amount of nitrogen are the same as in Example 1. The crystal diameter of the obtained crystal was about 50 mm and the crystal height was about 10 mm. Regarding the obtained SiC single crystal, the measurement result of the nitrogen amount by SIMS is that the amount of nitrogen at a height of 0 mm from the seed crystal is 2.0 × 10 ¹⁹ (/ cm ³ ), and the position of the height of 2 mm from the seed crystal is The amount of nitrogen is 1.5 × 10 ¹⁹ (/ cm ³ ), the amount of nitrogen at a height of 6 mm from the seed crystal is 4 × 10 ¹⁸ (/ cm ³ ), the amount of nitrogen at a height of 10 mm from the seed crystal is 4 × 10 ¹⁸ (/ cm ³ ).

Subsequently, crystal growth was performed for 60 hours under the condition that 6.7% by volume of nitrogen was included in the nitrogen supply gas supplied from the outside. Conditions other than the amount of nitrogen are the same as in Example 1. The crystal diameter of the obtained crystal was about 50 mm and the crystal height was about 10 mm. Regarding the obtained SiC single crystal, the measurement result of the nitrogen amount by SIMS is that the nitrogen amount at the height of 0 mm from the seed crystal is 3.0 × 10 ¹⁹ (/ cm ³ ), the nitrogen amount at the position of 2 mm from the seed crystal. The amount of nitrogen is 2.5 × 10 ¹⁹ (/ cm ³ ), the amount of nitrogen at a height of 6 mm from the seed crystal is 1.5 × 10 ¹⁹ (/ cm ³ ), the amount of nitrogen at a height of 10 mm from the seed crystal is 1.5 × 10 ¹⁹ (/ cm ³ ).

Based on the above result, in order to set the set density D1 to 5 × 10 ¹⁸ (/ cm ³ ) or more and 1.5 × 10 ¹⁹ (/ cm ³ ) or less, first, the amount of nitrogen supplied from the outside is 0 (mL / min). Crystal growth was performed for 12 hours (the time required for the crystal to grow 2 mm) under the conditions (nitrogen supply condition A), and then the nitrogen in the supply gas was changed to 3.4% by volume (nitrogen supply condition B) over 20 minutes. , 24 hours (the time it takes for the crystal to grow 4mm), and then change the nitrogen in the supply gas to 6.7% by volume (nitrogen supply condition C) over 20 minutes, then 24 hours (crystal The crystal growth of 4 mm is required. The crystal diameter of the obtained crystal was about 50 mm and the crystal height was about 10 mm.

Regarding the obtained SiC single crystal, the measurement result of the nitrogen amount by SIMS shows that the nitrogen amount at the height of 0 mm from the seed crystal is 1.5 × 10 ¹⁹ (/ cm ³ ), and the position at the height of 2 mm from the seed crystal. The amount of nitrogen is 1.5 × 10 ¹⁹ (/ cm ³ ), the amount of nitrogen at a height of 6 mm from the seed crystal is 1.5 × 10 ¹⁹ (/ cm ³ ), the amount of nitrogen at a height of 10 mm from the seed crystal Was 1.5 × 10 ¹⁹ (/ cm ³ ).

Further, for the obtained SiC single crystal, a (1-100) plane wafer including a longitudinal section including the diameter of the seed crystal was cut out, and after mirror polishing, the growth direction was measured by a photoluminescence microscope and molten KOH etching. The number of stacking faults included per unit length (stacking fault density) was measured. As a result, the stacking fault density was 0 (lines / cm) at any position of 0 mm, 2 mm, 6 mm, and 10 mm from the seed crystal. Substrates were cut from the same crystal in the (0001) plane, and the polytype and dislocation density were investigated. Visual observation of coloration revealed that it was a 4H single polytype. When the dislocation density was measured from observation with an optical microscope after the molten KOH etching, the dislocation density was 8.0 × 10 ³ (/ cm ² ). This value is equivalent to a commercially available product and can be said to be a high-quality substrate.

(Comparative Example 1)
Without measuring the amount of nitrogen released into the atmosphere in advance, the mass flow controller was adjusted so that the supply gas contained 6.7% by volume of nitrogen, and crystal growth was performed for 60 hours. Other growth conditions are the same as in Example 1. The diameter of the obtained crystal was 52 mm and the height was about 10 mm.

  A (1-100) plane wafer was cut out from the obtained SiC single crystal in the same manner as in Example 1, and after mirror polishing, the stacking fault density was measured by a photoluminescence microscope and molten KOH etching. As a result, the stacking fault density at the position 2 mm from the seed crystal was 60 (lines / cm). The stacking fault density was 0 (lines / cm) at a position of 6 mm from the seed crystal.

In addition, for the obtained SiC single crystal, the measurement result of the nitrogen amount by SIMS is that the nitrogen amount at a height of 2 mm from the seed crystal is 2.5 × 10 ¹⁹ (/ cm ³ ), and the height of 6 mm from the seed crystal is The nitrogen content at the position was 1.4 × 10 ¹⁹ (/ cm ³ ). Despite the fact that the nitrogen in the supply gas during crystal growth was constant at 6.7% by volume, the amount of nitrogen in the crystal was different because the nitrogen adhering to the graphite crucible and SiC raw material powder was released into the growth atmosphere. This is because the amount of nitrogen in the growth atmosphere is increased, and the amount of nitrogen taken into the crystal is increased accordingly.

  When we tried to identify the stacking fault type by observing the lattice image with a transmission electron microscope (TEM), it was found to be a 6H type stacking fault. If 6H type stacking faults are present in the substrate, it will cause a reduction in device breakdown voltage and a leakage current path. Therefore, it was found that the yield of high-quality substrates is poor because it cannot be used for the production of high-performance devices using a substrate cut out from a region from a seed crystal where a large number of stacking faults occurred to a height of 6 mm. did.

1 Seed crystal (SiC single crystal)
2 Sublimation raw material 3 Graphite crucible 4 Lid 5 Double quartz tube 6 Support rod 7 Graphite felt 8 Work coil 9 High purity gas piping
10 Mass flow controller for high purity gas
11 Vacuum exhaust system

Claims (7)

A method for producing a silicon carbide single crystal in which nitrogen gas is supplied to a crucible containing raw material powder and seed crystal, and a silicon carbide single crystal having a nitrogen atom number density of a set density D ₁ is grown by a sublimation recrystallization method Because
A second pre-growth test for growing a silicon carbide single crystal including nitrogen contained in the growth crystal in advance in a crucible while supplying a certain amount of nitrogen gas from the outside is performed. For each of a plurality of nitrogen supply conditions in which the supply amount is changed, the number density of nitrogen atoms taken into the grown crystal is determined in relation to the height of the grown crystal,
In the second pre-growth test, a nitrogen supply condition A in which the nitrogen atom number density satisfies the range of the set density D ₁ until the middle of crystal growth, and thereafter the nitrogen atom number density falls below the set density D ₁ range; Until the middle of crystal growth, the nitrogen atom number density exceeds the range of the set density D ₁ , and thereafter, the nitrogen supply condition C that satisfies the set density D ₁ is selected.
Nitrogen atom number density of silicon carbide single crystal ^{5 × 10 18 (/ cm 3} ) or more ^{2.5 × 10 19 (/ cm 3} ) so as to set the density D ₁ of the below, the nitrogen supply conditions during the crystal growth A method for producing a silicon carbide single crystal, wherein crystal growth is performed by switching a supply amount of nitrogen gas from A to a nitrogen supply condition C. In the second pre-growth test, the nitrogen atom number density exceeds the range of the set density D ₁ until the middle of the crystal growth, once the nitrogen atom number density satisfies the range of the set density D ₁ , and thereafter the nitrogen atom number A nitrogen supply condition B whose number density falls below the range of the set density D ₁ is further selected, and the nitrogen supply condition is sequentially switched to A, B, and C during crystal growth so that the set density D ₁ is obtained. The method for producing a silicon carbide single crystal according to claim 1 , wherein the growth is performed. The method for producing a silicon carbide single crystal according to claim 1 or 2 , wherein the nitrogen gas in the growth atmosphere has a change amount of less than 10 vol% per hour when the nitrogen supply condition is switched. When viewed a longitudinal section of a silicon carbide single crystal to include the diameter of the seed crystal, according to claim 1 to 3 the number of stacking faults contained per unit length in the growth direction is 10 (/ cm) or less The manufacturing method of the silicon carbide single crystal in any one of these. Method for producing a silicon carbide single crystal according to any one of claims 1-4 polytype of the silicon carbide single crystal is 4H. Method for producing a silicon carbide single crystal according to claim 1-5 wherein the stacking fault is a 6H-type. Method for producing a silicon carbide single crystal according to any one of claims 1 to 6 crystal diameter of the silicon carbide single crystal is 50mm or more 300mm or less.

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