JP2017154953A - Silicon carbide single crystal production apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon carbide single crystal production apparatus, in which the intrusion of sublimation gases to a radiant light passing hole for measuring the temperature of a crucible upper cover is suppressed in a non-contact manner so that the closure of the radiant light passing hole can be prevented.SOLUTION: In a silicon carbide single crystal production apparatus, a graphite crucible 3 is composed of a crucible body for filling a silicon carbide material, and an upper cover 4 for mounting a seed crystal 1 on the inner face. In the graphite crucible, the upper cover 4 is covered with an insulating material 7. The insulating material 7 has a through hole extending in the thickness direction. In the through hole, a cylindrical member 13 made of graphite is arranged to have its one end connected to the upper cover 4 and its other end protruding through the insulating material 7 by a length of 20-100 mm from the surface of the insulating material 7.SELECTED DRAWING: Figure 5

Description

  In the present invention, when a silicon carbide single crystal is produced by a sublimation recrystallization method using a graphite crucible including a crucible body and an upper lid, the temperature of the upper lid of the crucible can be stably measured. The present invention relates to a crystal manufacturing apparatus.

  Silicon carbide (SiC) has attracted attention as an environmentally resistant semiconductor material because of its excellent heat resistance and mechanical strength, and physical and chemical properties such as resistance to radiation. SiC is a typical material having a polymorphic polymorphic structure with many different crystal structures even though the chemical composition is the same. Polytype means that when a unit of Si and C bonded molecules in the crystal structure is considered as one unit, the unit structure molecule is different in the periodic structure when stacked in the c-axis direction ([0001] direction) of the crystal. Arise. Typical polytypes include 6H, 4H, 15R or 3C. Here, the first number indicates the repetition period of the lamination, and the alphabet represents a crystal system (H is a hexagonal system, R is a rhombohedral system, and C is a cubic system). Each polytype has different physical and electrical characteristics, and application to various uses is considered using the difference. For example, 6H is recently used as a substrate for short-wavelength optical devices from blue to ultraviolet, and 4H is considered to be used as a substrate wafer for high-frequency, high-voltage electronic devices.

  However, a crystal growth technology that can stably supply a high-quality SiC single crystal having a large area on an industrial scale has not been sufficiently established, and SiC has many advantages and possibilities as described above. Despite the semiconductor materials, there are still many problems to be put into practical use.

Conventionally, on a laboratory scale scale, for example, a SiC single crystal was grown by a sublimation recrystallization method (Rayleigh method) to obtain a SiC single crystal of a size capable of manufacturing a semiconductor element. However, with this method, the area of the obtained single crystal is small, and it is difficult to control its size and shape with high accuracy. Also, it is not easy to control the crystal polymorphism and impurity carrier concentration of SiC. In addition, a cubic SiC single crystal is grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using a chemical vapor deposition method (CVD method). With this method, a single crystal with a large area can be obtained, but only a SiC single crystal containing many defects (up to 10 ⁷ cm ^-2 ) can be grown due to the lattice mismatch of about 20% with the substrate. It is not easy to obtain a high-quality SiC single crystal.

  In order to solve these problems, an improved Rayleigh method has been proposed in which sublimation recrystallization is performed using a SiC single crystal {0001} plane substrate as a seed crystal (Non-patent Document 1). In this method, since the seed crystal is used, the nucleation process of the crystal can be controlled, and the growth rate of the crystal can be controlled with good reproducibility by controlling the atmospheric pressure to about 100 Pa to 15 kPa with an inert gas. . The principle of the improved Rayleigh method will be described with reference to FIG. The SiC single crystal that will be the seed crystal is placed on the inner surface of the crucible's upper lid (crucible lid), and the SiC crystal powder that is the raw material (usually the one that has been cleaned and pre-treated with the abrasive prepared by the Acheson method is used. Is filled in the lower part of the crucible (usually graphite), and the crucible is installed inside the double quartz tube and heated to 2000-2400 ° C in an inert gas atmosphere such as argon (133-13.3kPa). The At this time, the temperature gradient is set so that the seed crystal has a slightly lower temperature than the raw material powder. After sublimation, the raw material is diffused and transported in the direction of the seed crystal by a concentration gradient (formed by a temperature gradient). Single crystal growth is realized by recrystallization of the source gas that has arrived at the seed crystal on the seed crystal. At this time, the volume resistivity of the crystal is determined by adding an impurity gas in an atmosphere composed of an inert gas, or by mixing an impurity element or a compound thereof in the SiC raw material powder, It can be controlled by replacing the carbon atom position with an impurity element (doping). Typical substitutional impurities in SiC single crystals include nitrogen (n-type), boron, and aluminum (p-type). A SiC single crystal can be grown while controlling the carrier type and concentration by these impurities. Currently, SiC single crystal substrates having a diameter of 2 inches (50.8 mm) to 6 inches (150.0 mm) are cut out from the SiC single crystals produced by the above-described improved Rayleigh method, and are used for epitaxial thin film growth and device fabrication.

  As described above, the SiC single crystal grows by recrystallizing, where the raw material sublimated at high temperature in the graphite crucible is diffused and transported by the concentration gradient formed by the temperature gradient and reaches the seed crystal. To do. For this reason, control of the temperature distribution in the crucible during crystal growth is a very important technique. As a method for heating a graphite crucible to a high temperature of 2000 to 2400 ° C., which is necessary for SiC single crystal growth by the modified Rayleigh method, induction heating by applying a high frequency is generally used. Specifically, it is utilized that the conductive material (in this case, a graphite crucible) itself generates heat due to an induced current generated in the conductive material by high frequency. As for the shape of the crucible, heat generation due to high-frequency induced current does not penetrate inside due to the shielding effect of the carrier of the conductive material and occurs on the surface of the conductive material (skin effect), so the temperature distribution in the crucible is made uniform. For ease of use, a cylindrical crucible is commonly used.

  Further, for the purpose of suppressing heat loss from graphite as a heating element and maintaining a high temperature of 2000 ° C. or higher, it is also generally used to cover the crucible periphery with a heat insulating material. At this time, it is necessary that the heat insulating material is a non-conductive material or a structure in which an induced current is not easily generated so that the high frequency acts directly on the crucible. In practice, graphite felt is generally used as a heat insulating material.

  When the heat insulating material is actually arranged, the heat insulating material is processed so that the temperature distribution inside the crucible during growth becomes an ideal distribution for crystal growth. Specifically, in order to maintain the convex shape of the ingot during crystal growth, a hole for heat extraction purposes is opened in the center of the heat insulating material (upper heat insulating material) that covers the crucible upper lid on which the seed crystal is attached to the inner surface. (By providing a through-hole penetrating in the thickness direction of the heat insulating material), the heat removal from the center of the upper lid is promoted more than the periphery, the temperature near the center is lower than the periphery, and the crystal growth rate is also increased. As a result, the growing convex shape can be maintained.

  Since it is extremely important to control the temperature of the crucible at the time of growth, actually, using the heat removal hole of the heat insulating material in the center of the upper lid opened for setting the temperature distribution as described above, By detecting the radiation from the visible graphite crucible, the temperature of the upper part of the crucible (top lid) is measured with a radiation thermometer, and the temperature is measured during growth and the power of the heating furnace is adjusted based on this (Fig. 3 (a)) ). However, part of the sublimation gas sublimated from the raw material during the growth leaks from the crucible and diffuses, and near the upper part of the heat removal hole, which is a lower temperature part (also used as a synchrotron radiation passage hole for temperature measurement) The phenomenon of adhering to the heat insulating material occurs (Fig. 3 (b)).

  Due to this phenomenon, the hole diameter is narrowed due to the deposits around the heat removal holes in the insulation material during the growth time, so the temperature measurement at the top of the crucible using the emitted light is disturbed and the accurate temperature is measured. The problem of being unable to do so became apparent. In other words, the crystal growth itself can be maintained even if temperature measurement is hindered, but since the actual temperature is not known from the middle, it is impossible to perform “control by temperature measurement over the entire growth”, which is the ideal ideal. Temperature control in the latter half was not possible, and it was difficult to continue stable crystal growth with excellent reproducibility.

Yu. M. Tairov and V.F.Tsvetkov, Journal of Crystal Growth, vol. 52 (1981) pp.146-150.

  As described above, the reason why the temperature of the graphite crucible upper lid could not be stably measured over the entire SiC single crystal growth time in the sublimation recrystallization method using the seed crystal is the sublimation generated from the raw material during the growth. When a part of the gas leaks out of the crucible, the sublimation gas enters the hole for heat removal provided in the heat insulating material that covers the top cover of the crucible (at the same time as the radiation passing hole from the crucible for temperature measurement). It was to stick and close the hole.

  Therefore, the present invention solves the above-described problems in the prior art and prevents the heat removal hole of the heat insulating material that is also a radiation light passage hole from being blocked over the entire crystal growth time, thereby realizing stable temperature measurement. It aims to provide a method.

That is, the gist of the present invention is as follows.
(1) For manufacturing a silicon carbide single crystal by a sublimation recrystallization method in which the outer side of a graphite crucible comprising a crucible body filled with a silicon carbide raw material and an upper lid on which seed crystals are placed on the inner surface is covered with a heat insulating material. A silicon carbide single crystal manufacturing apparatus, characterized in that a heat insulating material covering the surface of the upper lid is provided with a through hole penetrating in a thickness direction, and a graphite cylindrical member is disposed in the through hole. A silicon carbide single crystal manufacturing apparatus,
(2) The silicon carbide single crystal manufacturing apparatus according to (1), wherein an inner diameter of the cylindrical member is 5 mm or more and 25 mm or less,
(3) The cylindrical member protrudes from the surface of the heat insulating material with a length of 20 to 100 mm in a state where the cylindrical member is disposed in the through hole of the heat insulating material (1) or (2) A silicon carbide single crystal manufacturing apparatus according to claim 1,
(4) One end of the cylindrical member is connected to the center of the surface of the upper lid, The silicon carbide single crystal manufacturing apparatus according to any one of (1) to (3),
It is.

  According to the manufacturing apparatus of the present invention, in the SiC single crystal growth by the sublimation recrystallization method using induction heating by applying high frequency, the temperature measurement of the upper part of the crucible (upper lid) can be stably performed over the entire crystal growth. Thus, it is possible to produce a SiC single crystal having good crystallinity with a high yield.

FIG. 1 is a schematic view showing a state of a cylindrical member of a SiC single crystal manufacturing apparatus according to the present invention, wherein (a) shows a relationship between a crucible upper lid and a cylindrical member, and (b) shows a crucible upper lid and heat insulation. The relationship between a material and a cylindrical member is shown. FIG. 2 is a diagram for explaining the improved Rayleigh method. FIG. 3 is a diagram for explaining a state change during the growth time in the conventional SiC single crystal manufacturing apparatus. FIG. 4 is a diagram for explaining a state change during the growth time in the SiC single crystal manufacturing apparatus according to the present invention. FIG. 5 is a schematic view of the SiC single crystal production apparatus used in the examples.

Embodiments according to the present invention will be described below.
The present invention is to manufacture a silicon carbide single crystal by a sublimation recrystallization method in which the outside of a graphite crucible composed of a crucible body filled with a silicon carbide raw material and an upper lid on which seed crystals are placed on the inner surface is covered with a heat insulating material. The silicon carbide single crystal manufacturing apparatus of the present invention, the inventors of the present invention, with respect to the heat removal hole of the heat insulating material that becomes a passage hole for the synchrotron radiation for measuring the temperature of the crucible upper lid corresponding to the crucible upper portion with a non-contact thermometer If the invasion of the sublimation gas as described above can be suppressed, the problem that the radiated light passage hole is blocked can be solved. That is, a heat insulating material that covers the surface of the crucible upper cover is provided with a through hole penetrating in the thickness direction, and a graphite cylindrical member is disposed in the through hole.

  More specifically, as illustrated in FIG. 1, a graphite cylindrical member is provided so as to be in contact with the center of the surface of the crucible upper lid, and one end of the graphite cylindrical member is connected to the upper lid. It is preferable to penetrate the heat insulating material provided on the upper lid and protrude the other end. In this way, if the inside of the cylindrical member is used as a passage hole for synchrotron radiation, the graphite cylindrical member is in contact with the crucible top lid at the root (the root portion), and sublimation gas intrudes at the joint. Since the temperature can be controlled stably over the entire crystal growth time, heat removal from the center of the crucible upper lid can be promoted more than the peripheral portion, which is suitable for the seed crystal. The convex shape of the grown crystal can be maintained.

  Conventionally, in the production of a silicon carbide single crystal by the sublimation recrystallization method, as shown in FIG. 3, the sublimation gas leaking from the crucible diffuses in the double quartz tube as the growth proceeds, and the low temperature portion is compared with the others. There are problems such as adhering to the heat removal hole of the heat insulating material and blocking the hole or blocking the emitted light. On the other hand, according to the present invention, the sublimation gas diffused to the position of the hole for transmitting radiated light is provided with the graphite cylindrical member penetrating the heat insulating material on the crucible upper lid surface. As shown in Fig. 4, even if the leaked sublimation gas adheres, it stays on the outside (outer periphery) of the cylindrical member, and the radiation inside the cylindrical member can always pass through without being blocked. Thus, stable temperature measurement is possible throughout growth.

  Here, if the length of the cylindrical member made of graphite is too short, there is a phenomenon that the sublimation gas that has passed through a slight gap between the cylindrical member and the heat insulating material wraps around and enters the inside of the cylindrical member. Preferably, the length of the cylindrical member protruding from the surface of the heat insulating material is at least 20 mm (that is, 20 mm larger than the thickness of the upper heat insulating material) with the cylindrical member disposed in the through hole of the heat insulating material. On the other hand, even if the same part (protruding part) is too long, there is a problem in carrying the crucible and the like, so it is preferable that the length is 100 mm or less. The length of the cylindrical member protruding from the heat insulating material is more preferably 30 mm to 70 mm.

  Further, regarding the inner diameter of the cylindrical cylindrical member made of graphite, it is necessary to satisfy the conditions for obtaining a sufficient amount of light for heat extraction and temperature measurement, and it is desirable that the inner diameter is preferably 5 mm or more and too large. In order to affect the temperature distribution due to heat removal, the thickness is desirably 25 mm or less, and more desirably 10 mm to 16 mm.

  The SiC single crystal manufacturing apparatus in the present invention can be the same as a conventionally known manufacturing apparatus except that a cylindrical member is provided by penetrating the heat insulating material covering the crucible upper lid as described above. Here, for example, the shape of the crucible may be any shape such as a cylinder, a cone, a polygonal column, a polygonal pyramid, etc., as long as it can hold the seed crystal and can accommodate the SiC raw material powder. A cylindrical shape that is excellent in the uniformity of heat radiation in the circumferential direction is optimal. The same applies to other cases, and a known production apparatus used in a sublimation recrystallization method in which a SiC raw material is sublimated in a crucible and recrystallized on a seed crystal can be used.

  Examples of the present invention will be described below. The present invention is not limited to these contents.

Example 1
First, the single crystal growth apparatus (SiC single crystal manufacturing apparatus according to the present invention) used in this example will be briefly described with reference to FIG. The crystal growth is the same as in the conventional sublimation recrystallization method using a seed crystal. The SiC single crystal 1 used as a seed crystal is obtained by sublimating the SiC crystal powder 2 charged in the crucible body constituting the graphite crucible 3. This is done by recrystallization. The seed crystal SiC single crystal 1 is attached to the inner surface of an upper lid 4 constituting a crucible 3 made of high purity graphite. The raw material SiC crystal powder 2 is filled in the lower part of the crucible body constituting the high-purity graphite crucible 3. Such a graphite crucible 3 is placed in a double quartz tube 5 and installed by a graphite support rod 6. Further, around the graphite crucible 3, a graphite felt (heat insulating material) 7 for improving heat insulation is installed.

Here, the double quartz tube 5 can be evacuated to high vacuum (10 ⁻³ Pa or less) by the vacuum evacuation device 11, and Ar gas introduced through the gas flow rate controller 10 into the internal atmosphere. The pressure can be controlled. Various doping gases (nitrogen, trimethylaluminum, trimethylboron) can also be introduced through the gas flow controller 10. In addition, a work coil 8 is installed on the outer periphery of the double quartz tube 5 to heat the graphite crucible 3 by flowing a high-frequency current and to heat the SiC raw material 2 and the seed crystal 1 to a desired temperature. Can do. Furthermore, in order to adjust the temperature distribution on the crystal surface during the growth to a convex shape downward, a heat removal hole (22 mm in diameter) is provided in the center of the felt covering the upper lid 4 on the upper part of the crucible. The temperature of the crucible upper lid 4 is measured by using a radiation thermometer (not shown) with radiation light that can be detected from a through hole penetrating in the thickness direction of the felt. Here, the cylindrical member 13 made of graphite is arranged in the heat removal hole 12 in the felt central portion. In detail, the cylindrical member 13 made of graphite was arranged so that one end thereof was connected to the center of the surface of the crucible upper lid 4. As shown in FIG. 1B, the connecting method is such that a male screw part is formed on a part of the outer periphery of the tip of the cylindrical member 13, a female screw part is formed on the crucible upper lid 4, and these are screwed together. (Fixed). The graphite cylindrical member has an inner diameter of 16 mm and an outer diameter of 22 mm. Further, the thickness of the graphite felt 7 covering the surface of the crucible upper lid 4 is 10 mm, and the graphite cylindrical member 13 is a hole of this heat insulating felt (having a hole for heat removal and temperature measurement). 12 parts were penetrated and it protruded on the heat insulating material felt, and the length of the part which protruded from the heat insulating material 7 was 60 mm.

Next, an example will be described for the production of an SiC single crystal using the crystal growth apparatus of the present invention. First, as a seed crystal 1, a 4H polytype SiC single crystal wafer having a (0001) plane with a diameter of 150 mm was prepared. The seed crystal had an offset angle of 4 ° from the {0001} plane. Next, the seed crystal 1 was attached to the inner surface of the upper lid 4 of the graphite crucible 3. The lower part of the graphite crucible 3 was filled with SiC crystal powder (SiC raw material) 2 produced by the Atchison method. Next, the graphite crucible 3 filled with the SiC raw material 2 was closed with the upper lid 4, covered with the graphite felt 7, placed on the graphite support rod 6, and installed inside the double quartz tube 5. Then, after the inside of the double quartz tube 5 was evacuated, a current was passed through the work coil 8 to raise the raw material temperature to 2000 ° C. Thereafter, high-purity Ar gas (purity 99.9995%) was introduced as the atmospheric gas, and the pressure in the double quartz tube 5 was maintained at 1.3 kPa throughout the growth. Under this pressure, the raw material temperature was increased from 2000 ° C. to the target temperature of 2400 ° C., and then the crystal growth was continued for about 20 hours while maintaining the same temperature. During this growth time, the nitrogen flow rate is 0.5 × 10 ⁻⁶ m ³ / sec at the start of growth (at the same flow rate, the nitrogen concentration in the grown crystal is 1 × 10 ¹⁹ cm ^−3, which is equivalent to the concentration in the seed crystal). Therefore, this flow rate was used) and kept until the end of growth. The obtained SiC single crystal had a diameter of 151 mm and a height of about 30 mm.

  With respect to the silicon carbide single crystal thus obtained, the production of the SiC single crystal was repeated, and the crystal quality of the obtained single crystal was examined after 20 experiments. Defects occurred and the crystal quality was deteriorated only twice, and 90% was obtained as a yield of good growth.

(Comparative Example 1)
SiC was used in the same manner as in Example 1, except that the graphite cylindrical member 13 was not attached to the heat removal hole 12 (diameter 22 mm) provided in the heat insulating material 7 covering the crucible upper cover, and the temperature was measured as it was. Single crystal growth was performed.

  With respect to the silicon carbide single crystal having the same size as that of Example 1 thus obtained, the crystal quality of the single crystal obtained after 20 experiments was examined. There were eight defects in which the crystal quality deteriorated due to defects, and the yield of good growth was 60% as a result of reflecting the instability of the temperature distribution.

1 seed crystal (SiC single crystal)
2 SiC crystal powder (SiC raw material)
3 Graphite crucible
4 Crucible top lid
5 Double quartz tube
6 Support rod
7 Graphite felt (insulation)
8 Work coil
9 Gas piping
10 Mass flow controller
11 Vacuum exhaust system
12 Heat removal hole (also radiation transmission hole)
13 Graphite cylindrical member
14 Radiation thermometer
15 Synchrotron radiation from a crucible
16 Deposits from sublimation gas solidification

Claims (4)

  A silicon carbide single crystal for producing a silicon carbide single crystal by a sublimation recrystallization method in which the outside of a graphite crucible consisting of a crucible body filled with a silicon carbide raw material and an upper lid on which a seed crystal is placed on the inner surface is covered with a heat insulating material. A silicon carbide characterized by being provided with a through-hole through which a heat insulating material covering the surface of the upper lid penetrates in the thickness direction, and a graphite cylindrical member is disposed in the through-hole. Single crystal manufacturing equipment.   The silicon carbide single crystal manufacturing apparatus according to claim 1, wherein an inner diameter of the cylindrical member is 5 mm or more and 25 mm or less.   3. The silicon carbide according to claim 1, wherein the cylindrical member protrudes with a length of 20 to 100 mm from the surface of the heat insulating material in a state where the cylindrical member is disposed in the through hole of the heat insulating material. Single crystal manufacturing equipment.   The silicon carbide single crystal manufacturing apparatus according to claim 1, wherein one end of the cylindrical member is connected to the center of the surface of the upper lid.

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