JP4503736B2 - Method and apparatus for producing single crystal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for crystal growth of, for example, a SiC single crystal by a sublimation method and an apparatus therefor. In particular, there are few micropipes for wide-bandgap semiconductors such as silicon carbide (SiC), zinc selenide (ZnSe), gallium nitride (GaN), and aluminum nitride (AlN), and a large crystal diameter enlargement ratio. The present invention relates to a production method for continuously growing a high-quality single crystal having a long time and an apparatus therefor.
[0002]
[Prior art]
Semiconductors such as SiC are materials that are generally very thermally and chemically stable and have a wide energy band gap, and can be used even at high temperatures. It can be used for power control power element materials, short wavelength light emitting element materials, and the like.
For example, as a method for producing a SiC single crystal, a sublimation method requiring a high temperature using SiC powder as a raw material is generally used (Japanese Patent Publication No. 3-501118). In the sublimation method, a SiC raw material powder and a seed crystal substrate which is a SiC single crystal are placed facing each other in a graphite crucible and heated to 1800 to 2400 ° C. in an inert gas atmosphere. The sublimation chemical species (gas) generated when the SiC raw material powder is decomposed and sublimated by heating reaches the surface of the seed crystal substrate held in the growth temperature range, and grows epitaxially as a single crystal.
[0003]
In the method for producing a single crystal, the inside of the crucible filled with SiC is depressurized (for example, 10 Torr), and the entire apparatus is heated from room temperature to a growth temperature (for example, 2200 ° C.). In addition to sublimation gases such as Si, Si ₂ C, SiC ₂ , and SiC that contribute to crystal growth generated from raw materials as the temperature rises, fine particles of impurities (eg, Fe, Ti, etc.) contained in raw materials, etc. Interfering microparticles that hinder the growth of high-quality crystals (for example, carbon particles generated from the crucible wall) float in the crucible, adhere to the crystal on which they grow, and degrade the quality of the growing crystal, for example micro It is estimated that this is the cause of the occurrence of pipes (cavity defects), crystal dislocations, and the like.
Moreover, since the raw material SiC accommodated in the crucible is heated from the crucible wall side, the temperature is high on the crucible wall side and the temperature is low at the crucible center. For this reason, more sublimation gases such as Si, Si ₂ C, SiC ₂ , and SiC are generated from the contained raw material near the crucible wall side. As a result, the carbon concentration is high as the raw material composition of this part. Finally, it becomes a lump of carbon.
[0004]
Therefore, the composition distribution of the raw material in the crucible is generated from these surfaces because a surface with a non-uniform component distribution is formed in which the portion near the wall is rich in carbon and the central portion of the crucible is rich in SiC. The components of the sublimation gas differ in composition in terms of position. This means that when the crystal growth is continued for a long time, the concentration ratio of the sublimation gas component changes because the carbon concentration distribution changes with the reaction time. As a result, it becomes difficult to control the uniformity of the sublimation gas, and it becomes difficult to stably obtain high-quality crystals.
In a single crystal used as a semiconductor element raw material, it is considered practically preferable that the number of micropipes (cavity defects) is not more than several tens [pieces / cm ² ]. It is difficult to satisfy.
[0005]
In order to improve this, as a means of sublimation by improving the heating of the raw material in the center of the crucible, a uniform heat conductor is installed in the central part of the crucible to raise the temperature of the central part and make the sublimation uniformity of the raw material A SiC single crystal growth apparatus container that improves the above is disclosed (Japanese Patent Laid-Open No. 5-58774).
However, in this method, it is estimated that a large amount of electric power is required to obtain a predetermined temperature, resulting in poor efficiency. Further, not only the wall side of the crucible but also the periphery of the graphite in the center portion has a high carbon concentration immediately after the start of sublimation, and the uneven surface state cannot be resolved. This causes generation of disturbing fine particles, and carbon inclusion is likely to occur in the grown crystal. Further, since the heat conductor (such as graphite) is exposed to a high temperature and the surface deteriorates, disturbing particles are also emitted from the heat conductor itself.
[0006]
In order to improve the quality of these single crystals, the generation of impurities is currently suppressed by increasing the purity of raw materials and equipment used for crystal growth, such as crucibles and raw materials, but the cost is high. ing. In addition, the gas situation accompanying the change in the reaction situation (temperature change, change in gas state) due to the crystal surface growing with crystal growth approaching the raw material, and the lowering of the purity of the raw material (the carbon concentration in the raw material increases with time) The operating conditions for crystal growth are controlled by taking into account the change in empirical rules, but sufficient and optimal control cannot be achieved, and high-quality crystals are not obtained.
[0007]
[Problems to be solved by the invention]
The present invention makes it possible to ensure uniform temperature in the crucible, uniform sublimation gas even when continuously growing for a long time while suppressing the change in the raw material concentration in the crucible, the grown single crystal has few micropipes, crystal diameter An object of the present invention is to develop a manufacturing method and an apparatus therefor for continuously growing a high-quality single crystal having a large expansion ratio for a long time.
[0008]
[Means for Solving the Problems]
The present invention
[1] In the crystal growth method by the sublimation method, a hollow heat transfer body having a thin upper part and a thick lower part is installed in the crucible, and a raw material is filled between the crucible and the hollow heat transfer body to perform crystal growth. A method for producing a single crystal, characterized in that the temperature distribution on the surface of the raw material is made more uniform, and high quality crystals are obtained with less adhesion of impurities and adhesion obstruction particles from the raw material,
[2] Enlarging crystal diameter, characterized in that the diameter of the upper opening of the hollow heat transfer body (the diameter of the circumscribed circle if not circular) is 0.2 to 5 times the diameter of the seed crystal The method for producing a single crystal according to the above [1] having a high rate,
[0009]
[3] The method for producing a single crystal according to the above [1] or [2], wherein the single crystal is a crystal for a wide band gap semiconductor,
[4] In the crystal growth method using silicon carbide sublimation, a hollow heat transfer body with a thin upper part and a thick lower part is provided in the crucible, and raw material silicon carbide is filled between the crucible and the hollow heat transfer body. , A method for producing a silicon carbide single crystal with few cavity defects, characterized by heating to 1800 to 2400 ° C. in a rare gas atmosphere or a nitrogen gas atmosphere or a mixed atmosphere thereof,
By solving this problem, the above problems were solved.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
According to the method of the present invention, the isothermal surface in the depth direction inside the heated raw material in the crucible can be brought closer to the sublimation surface (raw material surface).
In the present invention, the wide band gap semiconductor includes optical crystals, crystals for high frequency devices, and crystals for power devices. For example, silicon carbide (SiC), zinc selenide (ZnSe), gallium nitride (GaN), aluminum nitride ( AlN) means a crystal made by a sublimation method.
[0011]
Hereinafter, the production of a SiC single crystal will be described as a representative, but the present invention is not limited to this and can be applied to a method for producing a semiconductor single crystal.
In the study of the growth of various semiconductor crystals such as SiC, the present inventors have measured the crystal growth of the seed crystal substrate by hollowing through the bottom of the crucible and the center of the heat conductor installed at the center of the crucible. When the temperature distribution was measured, the SiC crystal that was generated unexpectedly has few micropipes, and a high-quality single crystal with a large crystal diameter and a large expansion rate is continuously grown for a long time. I realized I could do it. If the heat conductor is hollow, the cause is effective. In particular, the effect is great by installing a hollow heat transfer body with a thin upper part and a thick lower part in a crucible (no hole is required at the bottom). I understood it.
Although this mechanism is unknown, it is presumed to be based on the following principle based on the obtained phenomenon.
[0012]
The hollow heat transfer body is heated by heat conduction through the graphite from the crucible body whose side surface generates heat by high-frequency heating, but the graphite heats up due to its higher thermal conductivity than the raw material, and heat conduction from the bottom of the graphite crucible. Although the hollow heat transfer body is heated, since the heat transfer body has a hollow shape whose upper part is thinner than the lower part, the radiation effect from the bottom of the graphite crucible, which is a heating element, is also improved at the upper part of the heat transfer body. It can be received efficiently, and the entire installed hollow heat transfer body can be heated efficiently. In addition, since a hollow heat transfer body is used, the surface area in contact with the raw material layer can be increased more than when a solid heat transfer body using the same mass is used as the heat transfer body, and a larger amount of heat can be supplied to the raw material layer. . As a result, the raw material can be efficiently heated from the center side, and since the heat transfer surface area is large, the temperature can be controlled more reliably than a solid cylindrical heat transfer body. It is estimated that the temperature can be easily controlled to near parallel.
[0013]
As a result, the sublimation gas can be generated more uniformly from the crucible as a whole, and the occurrence of uneven bias in the carbon concentration of the raw material SiC layer can be suppressed even in a long-time crystal growth reaction. A sublimation gas such as Si, Si ₂ C, SiC ₂ , or SiC generated from the raw material layer reaches the seed crystal substrate surface by diffusion and grows epitaxially as a single crystal, but the crystal obtained because the sublimation gas is uniform The shape is flatter than that of the conventional method (the conventional method makes the crystal plane almost spherical and the crystallinity of the periphery is poor, but the crystallinity improves to the periphery by flattening. In addition, the operation conditions can be easily controlled, and a single crystal having a stable quality can be obtained.
[0014]
On the other hand, since the temperature distribution of the gas phase close to the raw material also follows the raw material surface temperature, the temperature of the entire crucible becomes more uniform, and as a result, a uniform ascending airflow across the isothermal surface is generated on the raw material surface that sublimates. it is believed that the crucible center downdraft reversed for the temperature is low (hollow heat transfer hollow upper part of) the that has occurred. In such a situation, the transport force of the substance works due to the rising air flow that crosses the isothermal surface of the outer periphery of the crucible, so that solid impurities released from the raw material and adhesion-blocking particles are directed to the lid around the crystal above the sublimation surface. It is presumed that solid impurities and adhesion hindering particles that have reached the lid are fixed to the peripheral edge of the lid controlled at a low temperature and rarely reach the crystal growth surface.
Because of the diffusion effect in the transport of sublimation gas, solid impurities (eg, Fe, Ti, etc.) contained in the raw material, etc., or other fine particles that interfere with the growth of high quality crystals (eg, generated from the crucible wall) Carbon particles) can be prevented from scattering into the crucible and adhering to the crystals on which they grow.
[0015]
Furthermore, by generating an even sublimation gas by making the isothermal surface in the depth direction of the heated raw material close to parallel to the sublimation surface (raw material surface), the generation of uneven carbon concentration in the raw material layer results. It is possible to suppress the generation of carbon clumps that can be disturbing fine particles by suppressing. This is presumably because the heat transfer body is a hollow body and there is no dust generation source below the seed crystal.
From the above, it is presumed that high quality single crystals can be obtained by reducing the deterioration of the quality of the growing crystal, for example, the occurrence of micropipes, crystal dislocations, etc. and producing for a long time.
[0016]
In order to describe the present invention more specifically, an example of an embodiment will be described.
For the crucible and crucible lid for containing and heating the SiC raw material used in the present invention, a carbon material, usually graphite, is preferably used, but any material from crystalline to amorphous can be used as long as it is a carbon material. . In addition, as long as the carbon material is used for the member for holding the seed crystal substrate of the crucible lid and the peripheral member, any material from crystalline to amorphous can be used. For holding, there is a method in which a SiC seed crystal is attached to a holding member or mechanically bonded.
A hollow heat transfer body is installed in the crucible, and SiC raw material powder is accommodated around it. The lower horizontal cross-sectional shape of the hollow heat transfer body is preferably a circle or a regular polygon in terms of thermal symmetry and crystal system shape. The thickness of the hollow heat transfer member is not particularly limited, but is preferably 0.5 mm to 10 mm, more preferably 1 mm to 3 mm from the viewpoint of thermal conductivity and material strength. The material of the hollow heat transfer body is preferably a carbon material, usually graphite, but any material from crystalline to amorphous can be used as long as it is a carbon material. The diameter of the circumscribed circle of the upper cross-sectional shape of the hollow heat transfer body is the ratio of the diameter of the seed crystal and the diameter of the circumscribed circle of the cross-sectional shape of the upper hollow part of the hollow heat transfer body. The relationship is preferably 0.2 to 5, and preferably 0.5 to 2 from the efficiency of the apparatus.
[0017]
The inner diameter of the inner cross section of the crucible and the diameter of the circumscribed circle of the upper cross section of the hollow heat transfer body are not particularly limited as long as the amount of raw materials to be accommodated and a predetermined temperature setting and control are possible. The height of the hollow heat transfer body can be adjusted by adjusting the distance between the surface of the SiC raw material and the seed crystal to optimum crystal growth conditions. The positional relationship between the center of gravity of the cross-sectional shape in the crucible, the center of gravity of the upper cross-sectional shape of the hollow heat transfer body, and the center of gravity of the lower cross-sectional shape of the hollow heat transfer body is preferably as identical as possible from the point of symmetry. The fixing method of the hollow heat transfer body is mechanically fitted or adhesive (phenol resin or a mixture of carbon powder or the like) if the thermal bonding is appropriate and the strength is appropriate. Can be used.
[0018]
For example, as shown in FIG. 1, the bottom of a graphite crucible 1 having an inner diameter of 50 mm and a depth of 95 mm is 77 mm high, an upper inner diameter is 14.2 mm, and a lower inner diameter is 30 mm. Shape) hollow heat transfer body 2 is fixed and installed at the center position of the bottom of the crucible by a mechanical fitting method, and the raw material SiC powder 3 is filled to a height of 70 mm between the crucible and the hollow heat transfer body. .
This graphite crucible is wrapped with a heat insulating material 4 and set in a reaction tube 6 in a heating furnace 5 (a high frequency heating furnace is exemplified). The reaction tube 6 can introduce a rare gas such as helium or argon or an inert gas such as nitrogen, and can also control the pressure in the reaction tube.
The seed crystal substrate 7 used in the present invention has the same crystal structure as the crystal to be grown. The growth crystal plane can be used in any plane orientation. For example, a C-axis vertical plane ({0001} plane), a C-axis parallel plane ({1-100} plane), a plane with an off angle introduced, and the like can be used. If the surface of the seed crystal substrate 7 is polished and planarized, it is desirable because the quality of the grown single crystal can be improved.
[0019]
The seed crystal substrate 7 is attached to the crucible lid 8, and is preferably installed in the central portion away from the side surface of the inner wall of the crucible. In order to recrystallize the sublimation gas, it is necessary to install the seed crystal substrate in a locally low temperature region in order to lower the temperature of the seed crystal substrate 7 relative to the peripheral portion.
As a heating method, a general method such as high-frequency heating or resistance heating can be used. In the high-frequency heating method, if the coil is divided and installed above and below the crucible 1, the temperature distribution above and below the crucible 1 can be controlled more appropriately. The temperature of the surface of the seed crystal substrate 7 is, for example, in the range of 1500 to 2500 ° C., and is preferably 1700 to 2300 ° C., more preferably 1900 to 2300 ° C., for ease of temperature control.
If the seed crystal substrate temperature is lower than 1500 ° C. or higher than 2500 ° C., the precipitated crystal is likely to be mixed with polymorphic crystals. If the seed crystal substrate 7 is rotated during the growth, the temperature, gas composition and the like are homogenized, and the effect of suppressing undesired crystal growth can be obtained.
[0020]
Seed crystal substrate 7 is not in contact with SiC raw material powder 3. Further, as the single crystal grows, if the seed crystal substrate 7 or the SiC raw material surface is adjusted and moved in order to keep the distance between the seed crystal substrate 7 and the SiC raw material powder 3 constant, the growth conditions such as temperature become stable and homogeneous. Single crystal can be grown. As the raw material SiC powder, it is desirable to use a material that has been previously cleaned with an acid or the like to remove impurities as much as possible.
The hollow heat transfer body installed inside is a hexagonal spindle having a height of 77 mm, an upper inner diameter of 14.2 mm, and a lower inner diameter of 14.2 mm as an example of a regular polygon. When the growth was carried out, the same effect was obtained as when a conical hollow heat transfer body was installed.
[0021]
FIG. 3 shows a case where the cross section of the hollow heat transfer body is curved. Again the like crucible temperature distribution similar effect can be obtained, further hollow heat transfer section could be performed for a long time crystal growth than for raw material powder often be filled compared with the case of the straight line.
Even in the cross-sectional shape as shown in FIG. 4, the same effect as in FIG. 2 is obtained.
As described above, the reason could not be clarified at the time of the present invention, but even if the crystal growth by the sublimation method is performed in the graphite crucible in which the raw material and the growing single crystal coexist, the raw material is added to the growing single crystal. It was found that impurities / adhesion-preventing particles from the metal hardly reach the seed crystal surface, and only the sublimation gas that contributes to crystal growth reaches the crystal surface and can produce high-quality crystals.
[0022]
In addition, the temperature distribution on the surface of the raw material becomes uniform, the sublimation gas is supplied uniformly from the surface of the raw material for a long time, and the crystal growth temperature is not affected by the temporal deterioration of the purity of the raw material. Therefore, the crystal shape (the shape of the crystal growth surface) is flattened and a crystal with less distortion can be obtained, and furthermore, a high quality crystal that is stable for a long time that has not been conventionally available can be manufactured.
The method of the present invention and the apparatus therefor are characterized in that the crystal growth on the seed crystal can be monitored from the hollow portion of the hollow heat transfer body, and is not limited to the SiC single crystal manufacturing method and apparatus, but other semiconductor raw material single crystals It can be applied to a crystal manufacturing method by sublimation crystal growth.
[0023]
【Example】
Example 1
It implemented using the apparatus shown in FIG. 1 which is an example of the crystal growth apparatus by this invention. For crystal growth, a graphite crucible is used as a portion for storing and heating the SiC raw material. A 6H-SiC single crystal produced by the Atchison method is used as a seed crystal substrate (6H-SiC single crystal (Si) surface, 10 mm diameter, 0.5 mm thickness) at the center of the lower surface of the crucible lid made of graphite. Pasted and held.
A hollow heat transfer body having a height of 77 mm, an upper inner diameter of 14.2 mm, and a lower inner diameter of 30 mm is placed in a graphite crucible having an inner diameter of 50 mm and a depth of 95 mm, and SiC powder (# 240 manufactured by Showa Denko) is used as a raw material around the crucible. ) Was stored until the height reached 70 mm. This graphite crucible was wrapped with a heat insulating material and set in a reaction tube in a high-frequency heating furnace.
[0024]
After evacuating from the gas discharge port 9 and reducing the pressure in the reaction tube to 5 × 10 ⁻⁵ torr, the inert gas introduction port 10 is filled with argon gas to normal pressure, and then exhausted from the gas discharge port again to 5 × 10 ⁻⁵ torr. The pressure in the reaction tube was reduced, and the air in the reaction tube was expelled. Then, argon gas is again filled up to 700 Torr from the inert gas inlet, and the graphite crucible is heated to 2300 ° C. Thereafter, the SiC single crystal was grown in a state where the gas was exhausted from the gas outlet and the argon atmosphere pressure was reduced to 10 torr. The crystal growth time was 8 hours. The temperature setting was controlled while measuring the temperature on the outer wall side of the graphite crucible using a radiation thermometer.
The grown thickness of the grown single crystal in the length direction was 3 mm, and the resulting diameter was 16 mm. From the peak position of the obtained single crystal measured by Raman spectroscopy and the peak pattern of X-ray diffraction, it was confirmed that the single crystal was 6H-SiC and was free of other polymorphs.
This crystal was subjected to component analysis using SIMS. As a result, the peak of Fe was smaller than that of the conventional example. When this crystal was cut in the crystal growth direction, polished and observed with a microscope, the number of hollow defects called micropipes was 15 [pieces / cm ² ]. The enlargement ratio of the diameter of the crystal was 16/10 = 1.6 times.
Further, when nitrogen was introduced at the same time interval and marked in the crystal, it was found that the crystal speed was constant.
[0025]
(Comparative example)
Crystal growth was performed in the same manner as in Example 1 except that a crucible in a conventional state in which a hollow heat transfer body was not installed in the crucible was used.
The grown crystal had a growth thickness in the length direction of 4 mm and a diameter of 12 mm as a result of growth. From the peak position by Raman spectroscopic measurement and the peak pattern of X-ray diffraction, it was confirmed that the single crystal was 6H-SiC and had no other polymorphic contamination.
As a result of component analysis of this crystal in the same manner as in the example, the Fe peak was larger than that in the example. When this crystal was cut in the crystal growth direction, polished, and observed with a microscope, the number of hollow defects called micropipes was several thousand [pieces / cm ² ]. Further, the enlargement ratio of the diameter of the crystal was 12/10 = 1.2 times.
In addition, when nitrogen was introduced at the same time interval and marked in the crystal, it was confirmed that the crystal growth rate was slow at the beginning of growth and increased as it approached the end (crystal uniformity was lost). It was.
[0026]
【The invention's effect】
According to the present invention, when performing crystal growth by a sublimation method in a graphite crucible having a hollow heat transfer body in which a raw material and a crystal to grow coexist, a single crystal from which impurities and adhesion-preventing particles from the raw material are obtained by growth Since only the sublimation gas that contributes to crystal growth reaches the crystal without reaching directly, it is possible to produce a high-quality crystal with a flat crystal shape with little distortion. Also, by using this crucible, the temperature distribution on the raw material surface becomes uniform, the sublimation gas is supplied uniformly from the raw material surface for a long time, the temperature dependency of the raw material purity is reduced, and the crystal growth temperature is deteriorated with time of the raw material. As a result, crystal growth can be performed for a long time at a constant and uniform temperature.
[Brief description of the drawings]
FIG. 1 is a flowchart of an apparatus for producing a single crystal according to the present invention.
FIG. 2 is a cross-sectional view of a crucible used in the apparatus of the present invention.
FIG. 3 is another cross-sectional view of the crucible used in the apparatus of the present invention.
FIG. 4 is another cross-sectional view of the crucible used in the apparatus of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Crucible 2 Hollow heat transfer body 3 SiC powder 4 Heat insulating material 5 High-frequency heating furnace 6 Reaction tube 7 Seed crystal substrate 8 Crucible lid 9 Gas outlet 10 Gas inlet

Claims (4)

  In the crystal growth method by the sublimation method, by installing a hollow heat transfer body with a thin upper part and a thick lower part in the crucible, filling the raw material between the crucible and the hollow heat transfer object, and performing crystal growth, A method for producing a single crystal, characterized in that the temperature distribution on the surface of the raw material is made more uniform, and high quality crystals are obtained with less adhesion of impurities and adhesion obstructing particles from the raw material.   The diameter of the upper opening of the hollow heat transfer body (the diameter of the circumscribed circle when it is not circular) is 0.2 to 5 times the diameter of the seed crystal, and has a large crystal diameter expansion rate The method for producing a single crystal according to claim 1.   The method for producing a single crystal according to claim 1 or 2, wherein the single crystal is a crystal for a wide band gap semiconductor.   In the crystal growth method by sublimation method of silicon carbide, a hollow heat transfer body with a thin upper part and a thick lower part is provided in the crucible, and raw material silicon carbide is filled between the crucible and the hollow heat transfer substance, and a rare gas A method for producing a silicon carbide single crystal with few cavity defects, characterized by heating to 1800 to 2400 ° C in an atmosphere, a nitrogen gas atmosphere or a mixed atmosphere thereof.

Images