Method and apparatus for producing silicon carbide single crystal

Abstract

To provide a manufacturing method and a manufacturing apparatus for silicon carbide single crystal that reduce defects such as penetration dislocation, and a silicon carbide single crystal ingot.SOLUTION: A manufacturing method for silicon carbide single crystal in which a raw material gas is supplied into a reaction vessel 20 where a seed substrate 50 is arranged, and heated to a predetermined temperature comprises: a first process of controlling the temperature in the reaction vessel 20 to a first predetermined temperature to grow silicon carbide single crystal 51 on a surface of the seed substrate 50, and thus achieving pair annihilation or composition of penetration dislocation 55; and a second process of keeping the inside of the reaction vessel 20 at the first predetermined temperature after the first process, and putting a tip of the penetration dislocation close to the surface of the seed substrate 50.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for producing a silicon carbide single crystal, and a silicon carbide single crystal ingot. [Background technology]

[0002] Silicon carbide (hereinafter referred to as SiC) has excellent physical properties compared to Si, such as a band gap approximately three times larger, a saturated drift velocity approximately twice as large, and a dielectric breakdown field strength approximately ten times larger. It is also a semiconductor with high thermal conductivity, and is therefore expected to be a material that will realize the next generation of high-voltage, low-loss semiconductor elements that will greatly surpass the performance of currently used Si single crystal semiconductors.

[0003] The method for producing SiC single crystals is to use SiH 4 Gas containing Si such as C 3 H 8 or C 2 H 2 There is a manufacturing method known as the HTCVD method, in which a new SiC single crystal is obtained on a seed substrate using a gas containing C such as SiO2.

[0004] In order to realize high-performance semiconductor devices, it is necessary to reduce defects such as threading dislocations (threading screw dislocations and threading edge dislocations) that occur in SiC single crystals. In order to reduce threading dislocations, various techniques have been proposed for growing crystals using a plane that has a certain offset angle with respect to the basal plane as the growth plane (for example, Patent Document 1, etc.).

[0005] In the technology for producing SiC single crystals, techniques have been proposed to reduce defects such as threading dislocations (threading screw dislocations and threading edge dislocations), but the reality is that there is still room for further reduction in defects such as threading dislocations. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2006-1836 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and has an object to provide a method and apparatus for producing a silicon carbide single crystal, and a silicon carbide single crystal ingot, which are capable of obtaining a silicon carbide single crystal with reduced defects such as threading dislocations.

[0008] In order to achieve the above-mentioned object, the inventors conducted extensive research and discovered that by performing a specified heat treatment after crystal growth, the tips of threading dislocations can be brought closer to the surface of the seed substrate, thereby completing the present invention.

[0009] A first aspect of the present invention for achieving the above object resides in a method for producing a silicon carbide single crystal, which comprises supplying a raw material gas into a reaction vessel in which a seed substrate is placed and heating the reaction vessel to a predetermined temperature to grow a silicon carbide single crystal on a surface of the seed substrate, the method comprising: a first step of controlling the temperature inside the reaction vessel to a first predetermined temperature state to grow a silicon carbide single crystal on the surface of the seed substrate, thereby causing annihilation of threading dislocations or synthesis of threading dislocations; and a second step of, after the first step, maintaining the temperature inside the reaction vessel at the first predetermined temperature state to bring the tips of the threading dislocations closer to the surface of the seed substrate.

[0010] As a result, in the first step, the temperature in the reaction vessel is controlled to a first predetermined temperature state and silicon carbide single crystal is grown on the surface of the seed substrate, thereby annihilation of threading dislocations or synthesis of threading dislocations. In the second step, after the first step, the temperature in the reaction vessel is maintained at the first predetermined temperature state and raw material is supplied in an amount sufficient to compensate for sublimation and etching such as hydrogen gas. As a result, the vertical top end position of the threading dislocations can be brought closer to the surface of the seed substrate.

[0011] A second aspect of the present invention is the method for producing a silicon carbide single crystal according to the first aspect, characterized in that the second step is carried out such that a growth rate or an etching rate of the silicon carbide single crystal is within 0.1 mm / h.

[0012] As a result, by performing the growth rate or etching rate of the silicon carbide single crystal within 0.1 mm / h, heating can be performed without causing a significant change in the thickness of the silicon carbide single crystal.

[0013] A third aspect of the present invention is the method for producing a silicon carbide single crystal according to the first or second aspect, characterized in that the first predetermined temperature is in the range of 2400°C to 2550°C, and a radial temperature difference of the silicon carbide single crystal is 10°C or less.

[0014] As a result, by setting the first predetermined temperature in the range of 2400°C to 2550°C, it is possible to make it easier for threading dislocations to move, and by setting the radial temperature difference of the silicon carbide single crystal to 10°C or less, it is possible to minimize the thermal stress applied to the silicon carbide single crystal.

[0015] A fourth aspect of the present invention is a method for producing a silicon carbide single crystal according to any one of claims 1 to 3, characterized in that in the first step, the SiH4 gas partial pressure is 7.0 kPa or more and the C3H8 gas partial pressure is 1.5 kPa or more, and in the second step, the SiH4 gas partial pressure is 2.0 kPa or more and the C3H8 gas partial pressure is 0.5 kPa or more.

[0016] A fifth aspect of the present invention resides in the method for producing a silicon carbide single crystal according to any one of the first to fourth aspects, characterized in that the silicon carbide single crystal having a reduced threading dislocation density by the second step is used as a seed substrate for growing the silicon carbide single crystal.

[0017] A sixth aspect of the present invention is a silicon carbide single crystal manufacturing apparatus for carrying out the silicon carbide single crystal manufacturing method according to any one of claims 1 to 5, characterized in that the apparatus has a function of detecting a gas flow rate and a temperature in the first step and the second step and controlling at least the gas flow rate and the temperature, and further includes a device for controlling the gas flow rate and the temperature according to a stored recipe. Effect of the Invention

[0018] According to the present invention, there are provided a method and apparatus for producing a silicon carbide single crystal, and a silicon carbide single crystal ingot, which are capable of bringing the tips of threading dislocations closer to the surface of a seed substrate by performing a predetermined heat treatment after crystal growth, thereby reducing defects such as threading dislocations. [Brief description of the drawings]

[0019] [Figure 1] 1 is a cross-sectional view of a manufacturing apparatus for manufacturing a silicon carbide single crystal according to an embodiment of the present invention. [Diagram 2] 2A to 2C are diagrams illustrating schematic vertical cross sections of a silicon carbide single crystal after a first step and a second step of a manufacturing process for a silicon carbide single crystal according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, the present invention will be described based on an embodiment.

[0021] (Embodiment 1) The present invention relates to a method for producing a silicon carbide single crystal, which comprises supplying a raw material gas into a reaction vessel in which a seed substrate is placed and heating the reaction vessel to a predetermined temperature to grow a silicon carbide single crystal on a surface of the seed substrate, the method comprising: a first step of controlling the temperature inside the reaction vessel to a first predetermined temperature to grow a silicon carbide single crystal on the surface of the seed substrate, thereby causing annihilation of threading dislocations or synthesis of threading dislocations; and a second step of, after the first step, maintaining the temperature inside the reaction vessel at the first predetermined temperature to bring the tips of the threading dislocations closer to the surface of the seed substrate.

[0022] First, an example of a manufacturing apparatus for silicon carbide (SiC) single crystal wafers will be described below. Fig. 1 is a schematic cross-sectional view of the manufacturing apparatus.

[0023] The manufacturing apparatus I is for bulk growing a SiC single crystal by a high temperature gas growth method. The manufacturing apparatus I is equipped with a reaction vessel 20 housed in a vacuum vessel 10. A raw material gas supplying apparatus 1 for supplying a raw material gas is connected to the manufacturing apparatus I.

[0024] The source gas supply device 1 is a device for supplying a source gas to a reaction vessel 20. The source gas has a composition for growing SiC, and as an example, SiH 4 , C as a carbon-based reactive species 3 H 8 , H as carrier gas 2 A mixture of various gases such as Ar and H2O can be used as the source gas.

[0025] The vacuum vessel 10 is a vessel that houses a reaction vessel 20 therein, and the pressure inside can be adjusted from vacuum to atmospheric pressure. The vacuum vessel 10 of this embodiment is formed in a cylindrical shape, with an opening at the bottom through which a pipe 2 is inserted. The vacuum vessel 10 is also provided with an exhaust path 13 that connects the inside to the outside. There is no limitation on the material of the vacuum vessel 10, and for example, quartz, metal, etc. can be used.

[0026] The reaction vessel 20 is a vessel in which a source gas is supplied to a seed substrate 50 made of SiC housed therein to grow a SiC single crystal. Specifically, the reaction vessel 20 is formed in a cylindrical shape with openings at the top and bottom, and a pipe 2 is connected to the opening at the bottom. In addition, a susceptor 15, which is a pedestal, is disposed from the opening side of the top so as to be located inside the reaction vessel 20.

[0027] The reaction vessel 20 is formed of, for example, a heat insulating material. The heat insulating material is not particularly limited, but may be, for example, a high melting point metal such as tantalum (Ta), niobium (Nb), zirconium (Zr), titanium (Ti), tungsten (W), or a carbide thereof, or graphite.

[0028] The susceptor 15 is a device that holds a seed substrate 50 made of SiC. Specifically, the susceptor 15 has a holding surface 16 that faces downward in the figure, and the seed substrate 50 is bonded to this holding surface 16.

[0029] A raw material gas supply device 1 for supplying raw material gas is connected to a pipe 2 provided in the center below the reaction vessel 20, and the raw material gas from the raw material gas supply device 1 is supplied into the internal space of the reaction vessel 20 and then to the growth surface on the lower surface of the seed substrate 50.

[0030] Incidentally, various gas supply means for supplying the source gas uniformly in the surface direction and at high speed to the growth surface of seed substrate 50 may be provided inside reaction vessel 20 .

[0031] A first insulating material 11 and a second insulating material 12 are disposed inside the vacuum vessel 10. Specifically, the first insulating material 11 is configured to cover the outer peripheral portion of the pipe 2 that appears inside the vacuum vessel 10. The second insulating material 12 is configured in a cylindrical shape to accommodate the reaction vessel 20 therein. The material of these insulating materials is not particularly limited, but for example, alumina, zirconia, pyrolytic carbon, graphite, felt carbon, etc. can be used.

[0032] The first insulating material 11 maintains the temperature of the raw material gas in the pipe 2, and the second insulating material 12 maintains the temperature in the reaction vessel 20.

[0033] A coil 30 is disposed on the outside of the vacuum vessel 10 as an example of a temperature adjustment means for setting the temperature inside the reaction vessel 20 .

[0034] The coil 30 performs induction heating on the reaction vessel 20. Although not shown, the coil 30 is connected to an AC power source and is supplied with high-frequency AC current. The coil 30 can raise the temperature inside the reaction vessel 20 to a temperature suitable for growing SiC single crystal, for example, a high temperature of 1500° C. or higher. When a vacuum vessel 10 made of metal is used, the coil 30 is disposed inside the vacuum vessel 10 and outside the reaction vessel 20.

[0035] Although not shown, the susceptor 15 is provided with a heat dissipation mechanism, which dissipates heat from the seed substrate 50 and makes it possible to keep the temperature of the seed substrate 50 relatively lower than that of the source gas.

[0036] In the SiC single crystal manufacturing apparatus I having the above-mentioned configuration, the inside of reaction vessel 20 is set to a high temperature by coil 30. On the other hand, seed substrate 50 is set to a relatively low temperature by the heat dissipation mechanism of susceptor 15.

[0037] Then, the raw material gas is supplied from the raw material gas supply device 1 through the pipe 2 to the seed substrate 50 held on the susceptor 15 inside the reaction vessel 20, and the SiC single crystal is grown. The raw material gas is then exhausted to the outside from the top opening of the reaction vessel 20 through the exhaust path 13 of the vacuum vessel 10.

[0038] In manufacturing apparatus I, a raw material gas is supplied to seed substrate 50 to grow a SiC single crystal on seed substrate 50. In the present invention, the temperature inside reaction vessel 20 is controlled to a first predetermined temperature to grow a silicon carbide single crystal on the surface of seed substrate 50, thereby carrying out a first step of annihilation of threading dislocations or synthesis of threading dislocations, and after the first step, a second step of bringing the tips of the threading dislocations closer to the surface of the seed substrate by maintaining the temperature inside the reaction vessel at the first predetermined temperature.

[0039] In carrying out the first and second steps, it is necessary to control the temperature and gas flow rate in the reaction vessel 20 to predetermined values ​​in the first and second steps, and such control is executed by the control device 70. In addition, in order to control the temperature and gas amount, a detection device (not shown) is provided for detecting the temperature and gas partial pressure in the reaction vessel 20, particularly in the vicinity of the growth surface of the seed substrate 50, and the control device 70 is adapted to control the gas flow rate and temperature in accordance with a pre-stored recipe based on the detection value of the detection device.

[0040] Here, in the first step, a source gas is supplied at a predetermined flow rate for growing a silicon carbide single crystal on a seed substrate at a first predetermined temperature. The conditions for this first step are not critical as long as they are conditions for growing a silicon carbide single crystal, but for the sake of productivity, it is preferable to set conditions for growing at as high a growth rate as possible.

[0041] In such a first step, it is desirable that the first predetermined temperature is in the range of 2400° C. to 2550° C., and the temperature difference in the planar direction of the growth surface of the silicon carbide single crystal is 10° C. or less, preferably 5° C. or less.

[0042] In the first step, a source gas is supplied. Examples of the source gas include hydrogen gas, monosilane, and hydrocarbon gas. Specifically, as described above, SiH 4 , C as a carbon-based reactive species 3 H 8 , H as carrier gas 2 A mixture of various gases such as Ar and H2O can be used as the source gas.

[0043] Here, the source gas is SiH 4 Gas partial pressure is 7.0kPa or more, C 3 H 8 A gas partial pressure of 1.5 kPa or more is desirable.

[0044] The time for the first step is not particularly limited, and can be continued as long as there is space available for the silicon carbide single crystal 51 to grow.

[0045] In such a first step, a silicon carbide single crystal grows on the growth surface of the seed substrate at a predetermined rate of 1 mm / h or more to form a silicon carbide single crystal 51. However, even if conditions are set to minimize the occurrence of defects, threading dislocations are formed.

[0046] Here, the threading dislocations are threading screw dislocations and threading edge dislocations, and are formed so as to penetrate silicon carbide single crystal 51 along the growth direction.

[0047] Such threading dislocations are shown typically in Fig. 2. Fig. 2(a) is a schematic diagram of a vertical cross section of silicon carbide single crystal 51 at the time when the first step is completed, and there is a region (hereinafter, low defect region) where no or extremely few threading dislocations 55 are present on the tip side of silicon carbide single crystal 51, and there are a first region a1 where relatively many threading defects are present, and a second region a2 where relatively few or no threading dislocations 55 are present.

[0048] In FIG. 2(a), the boundary line L1 between the first region a1 and the second region a2 is set to the position of the tip of the most extended threading dislocation 55 in the first region a1.

[0049] The type of threading dislocation is defined by the direction of the crystal misalignment (Burgers vector). For example, it is known that there are right-handed (plus c) and left-handed (minus c) threading screw dislocations.

[0050] The direction of the stress field acting around the dislocation also differs depending on the type. The stress fields acting on the right-handed and left-handed threading screw dislocations mentioned above are in opposite directions, and an attractive force acts between the two opposite-handed threading screw dislocations (plus c and minus c). It is thought that this attractive force causes the threading dislocations to attract each other and annihilate each other.

[0051] A similar mechanism exists for threading edge dislocations, which result in dislocation synthesis. Experimental results have revealed that they occur primarily during crystal growth. On the other hand, it is known that the energy of a dislocation itself depends on its length.

[0052] In other words, a dislocation with a long dislocation line is in a high energy state, and therefore a force acts to shorten it. Here, the threading dislocation 55 in FIG. 2, which shows the annihilation of dislocation pairs, is more likely to gain in terms of energy by moving in a direction that shortens its half loop.

[0053] In a high-temperature state where dislocations can move, the dislocation loop shortens, and it is considered that the half-loop moves upward and in the shortening direction in Fig. 2. Taking the dislocation half-loop shown in the figure as an example, the point of boundary line L1 in Fig. 2(a) rises to the point of boundary line L2 in Fig. 2(b), and the length of the first region a1 shrinks to the length of the first region A1.

[0054] The present invention utilizes the mechanism by which a half loop formed by annihilation of two dislocations shrinks by maintaining the crystal at a high temperature that allows the movement of dislocations.

[0055] In addition, the second regions a2, A2, which are low defect regions, have a threading dislocation density that is half or less of that in the first regions a1, A1.

[0056] Next, in the second step performed after the first step of the present invention, the supply of the source gas is reduced and conditions are maintained such that the growth rate or etching rate of the silicon carbide single crystal 51 is within 0.1 mm / h. By such a second step, the tips of the threading dislocations formed in the silicon carbide single crystal 51 grown in the first step are brought closer to the surface of the seed substrate.

[0057] The gas partial pressure in the second step is not particularly limited as long as the growth rate or etching rate of the silicon carbide single crystal 51 is within 0.1 mm / h. For example, the gas partial pressure may be SiH 4 Gas partial pressure is 2.0kPa or more, C 3 H 8 A gas partial pressure of 0.5 kPa or more is desirable.

[0058] The time for the second step is not particularly limited, and may be appropriately set as necessary since the longer the time, the more the tip position of the threading dislocation 55 retreats. For example, it is desirable to set the time to 0.5 to 4 hours, preferably 2 to 3 hours.

[0059] 2(b) is a schematic diagram showing a vertical cross section of silicon carbide single crystal 51 after the second step, in which the tip positions of threading dislocations 55 in first region A1 move away from growth surface 51a and retreat toward the seed substrate. Thus, boundary line L2 retreats from boundary line L1, and second region a2 expands by the amount of region A3 to become second region A2.

[0060] By carrying out the above first and second steps, silicon carbide single crystal 51 with extremely few threading dislocations 55 can be produced, and by cutting out a silicon carbide single crystal wafer from second region A2, a silicon carbide single crystal wafer with extremely few threading dislocations can be obtained.

[0061] In addition, the second region A2 after the second step can be used as a seed substrate in addition to being used to cut out silicon carbide single crystal wafers. When such a seed substrate is used to carry out the above-mentioned first and second steps, a silicon carbide single crystal with even fewer threading dislocations can be produced, and the second regions a2, A2 in this case can be further increased.

[0062] (Other embodiments) In the above-described embodiment, the second step is carried out in the reaction vessel 20 in which the first step is carried out, but the second step may be carried out in a separate vessel. [Industrial Applicability]

[0063] The present invention can be utilized in the industrial field of producing silicon carbide single crystals. [Explanation of symbols]

[0064] I Manufacturing equipment 1. Raw gas supply device 10 Vacuum container 11 First insulation material 12 Second insulation material 13 Exhaust channel 15 Susceptor 20 Reaction vessel 30 Coil 50 types of substrates 51 Silicon carbide single crystal 55 Threading dislocations

Claims

1. A source gas is supplied into a reaction vessel in which a seed substrate is placed, The inside of the reaction vessel is heated to a predetermined temperature, A method for producing a silicon carbide single crystal by growing a silicon carbide single crystal on a surface of the seed substrate, a temperature inside the reaction vessel is controlled to a first predetermined temperature while the source gas is being supplied, thereby growing a silicon carbide single crystal on the surface of the seed substrate; A first step of annihilation of threading dislocations or synthesis of threading dislocations; After the first step, a supply of a raw material gas for growing the silicon carbide single crystal is set under conditions such that a growth rate or an etching rate of the silicon carbide single crystal is within 0.1 mm / h, and the temperature inside the reaction vessel is maintained at a first predetermined temperature; and a second step of bringing the tips of the threading dislocations closer to a surface of the seed substrate.

2. The method for producing a silicon carbide single crystal according to claim 1, 2. A method for producing a silicon carbide single crystal, comprising the steps of: forming a silicon carbide single crystal having a first crystal layer and a second crystal layer;

3. The method for producing a silicon carbide single crystal according to claim 1 or 2, The SiH ４ Gas partial pressure is 7.0 kPa or more, C ３ H ８ The gas partial pressure is 1.5 kPa or more, and the SiH ４ Gas partial pressure is 2.0 kPa or more, C ３ H ８ A method for producing a silicon carbide single crystal, wherein the gas partial pressure is 0.5 kPa or more.

4. The method for producing a silicon carbide single crystal according to any one of claims 1 to 3, a silicon carbide single crystal having a reduced threading dislocation density by the second step, the silicon carbide single crystal being used as a seed substrate for growing a silicon carbide single crystal;

5. A manufacturing apparatus for carrying out the method for producing a silicon carbide single crystal according to any one of claims 1 to 4, Detecting a gas flow rate and a temperature in the first step and the second step, and A function of controlling at least the gas flow rate and the temperature; and An apparatus for producing a silicon carbide single crystal, comprising: a device for controlling the gas flow rate and the temperature in accordance with a stored recipe.

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