JP2013006739A - Method for producing single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing single crystal, which can suppress dropping of atoms from a side or a surface outer peripheral part of a seed crystal and can produce high quality single crystal.SOLUTION: There is provided the method for producing single crystal in which a raw material 6 is positioned in a crucible 7 sealed by a crucible lid 8 to which the seed crystal 9 is fixed and the raw material 6 is sublimated to produce the single crystal. The method includes: a film-forming process of forming a crystal thin film 15 in advance in a temperature region in which the seed crystal 9 is not sublimated so as to cover an exposed surface of the seed crystal 9 fixed to the crucible lid 8; and a growing process of sublimating the raw material 6 to grow the single crystal by sealing the crucible 7 with the crucible lid 8 on which the crystal thin film 15 is formed.

Description

  The present invention relates to a method for producing a single crystal using a sublimation method. More specifically, the present invention relates to a method for producing a sublimable single crystal such as AlN (aluminum nitride) or SiC (silicon carbide).

  A compound semiconductor crystal is a semiconductor crystal obtained by combining a plurality of elements as materials, and is useful as a material for forming a semiconductor device such as a light emitting element, an electronic element, or a semiconductor sensor. Compound semiconductors are attracting attention as materials for high-efficiency power semiconductor devices because they have a larger band gap than single-element semiconductors such as Si and Ge, and therefore have a higher dielectric breakdown voltage.

  Since compound semiconductors often have higher vapor pressures when melted than single element semiconductors, it is known that when heated at atmospheric pressure, they do not become melts but sublime and decompose. For this reason, a sublimation method is generally used as a method for producing a compound semiconductor crystal. In the sublimation method, the crucible is heated to sublimate the powder raw material placed in the crucible at a high temperature, and the generated sublimation gas is diffused and transported in the direction of the seed crystal fixed to the upper lid. At this time, the diffusion direction of the sublimation gas can be controlled in the direction of the seed crystal by setting the temperature gradient so that the seed crystal has a lower temperature than the powder raw material as the raw material. As a result, the sublimation gas that has arrived at the seed crystal is recrystallized on the seed crystal, whereby single crystal growth is performed. Here, examples of the seed crystal used include AlN and SiC. Note that the sublimation method has a higher growth rate than the MOCVD method (metal organic vapor phase epitaxy method) and the MBE method (molecular beam epitaxy method), and thus is an effective method for producing a bulk crystal.

  In order to obtain a high-quality single crystal, it is necessary to grow at a relatively high temperature so that surface migration of adsorbed atoms can be promoted. However, there is a problem peculiar to a seed crystal when growing.

  One such problem is that atoms are difficult to escape from the seed crystal plane when the crystal growth temperature is above a certain level. As an example of the seed crystal to be used, in the case of SiC, when the crystal growth temperature is 1500 ° C. or higher, the saturation vapor pressure is higher for Si atoms than for C atoms. Atoms are preferentially escaped. As a result, holes (voids) from which Si atoms have escaped are generated in the seed crystal. If these voids are generated on the SiC seed crystal surface, the crystal quality of the single crystal to be grown is affected. Therefore, it is desirable that the seed crystal plane used during single crystal growth be as flat as possible.

  A method for forming a protective film by applying a photosensitive resist, which is an organic film, to the rear surface of the seed crystal and then performing carbonization is described in Patent Document 1 below. When crystal growth is performed using the SiC seed crystal with the protective film, the elimination of Si atoms from the back surface of the seed crystal is suppressed by the protective film, and generation of voids can be prevented.

JP 2003-226600 A

  However, in the method for producing a single crystal described in Patent Document 1, when the protective film covers the back surface of the seed crystal SiC, Si atoms are removed from the side surface of the seed crystal and the outer periphery of the surface instead of detaching Si atoms from the back surface. Desorption is promoted. Therefore, as the growth of the single crystal by the sublimation method proceeds, Si atoms are desorbed from the side surface of the seed crystal and the outer peripheral portion of the surface, and as a result, a void is generated on the side surface of the seed crystal and the outer peripheral portion of the surface.

  The present invention has been made in view of the above circumstances, and can produce a high-quality single crystal that can suppress the detachment of atoms from the side surface and the outer peripheral portion of the seed crystal. The purpose is to provide.

  In order to solve the above-mentioned problems, the inventors studied diligently by paying attention to the seed crystal itself. As a result, it has been found that the above problem can be solved by forming a crystal thin film on the seed crystal, and the present invention has been completed. That is, the present invention is a method for producing a single crystal in which a raw material is placed in a crucible sealed with a crucible lid to which a seed crystal is fixed, and the raw material is sublimated to produce a single crystal, which is fixed to the crucible lid. In order to cover the exposed surface of the seed crystal, the crystal thin film is formed in advance in a temperature region where the seed crystal does not sublimate, and the crucible is sealed with the crucible lid on which the crystal thin film is formed to sublimate the raw material. And a growth process for growing the single crystal.

  According to this method for producing a single crystal, before growing the single crystal by the sublimation method, the crystal thin film is previously formed in a temperature region where the seed crystal is not sublimated so as to cover the exposed surface of the seed crystal fixed to the crucible lid. By forming the single crystal by the sublimation method, the seed crystal is covered with the crystal thin film even in the temperature range where the seed crystal is sublimated, so that desorption of atoms from the seed crystal is suppressed. Can do. For this reason, desorption of atoms from the side surface of the seed crystal and the outer peripheral portion of the surface can be suppressed, and a single crystal can be produced on a flatter seed crystal surface. As a result, a high-quality single crystal can be produced.

  The present invention is also a method for producing a single crystal, wherein the film forming step uses a CVD method, a PVD method, or an LPE method.

  According to this single crystal manufacturing method, the growth rate can be made slower than the sublimation method, and the film thickness can be controlled on the atomic layer order, so that a higher quality crystal interface can be obtained. . For this reason, it is possible to produce a high-quality single crystal in the growth step of growing the single crystal by the sublimation method.

  In the method for producing a single crystal, the crystal thin film is preferably a single crystal.

  In this case, when a single crystal is grown by a sublimation method, a high-quality single crystal can be manufactured by using a single crystal thin film.

  In the method for producing a single crystal, the crystal thin film and the single crystal are preferably the same kind of substance.

  Here, when a single crystal is grown using the same kind of material as the crystal thin film, the lattice constants of the seed crystal and the crystal to be grown coincide. For this reason, compared to the case of using different kinds of materials, the degree of lattice mismatch between the single crystal and the crystal thin film can be further reduced, and the crystal can be prevented from cracking due to strain. Fabrication is possible.

  ADVANTAGE OF THE INVENTION According to this invention, the detachment | leave of the atom from the side surface and surface outer peripheral part of a seed crystal can be suppressed, and the manufacturing method of the single crystal which can produce a high quality single crystal is provided.

It is the schematic of an example of the manufacturing apparatus used for the manufacturing method of the single crystal which concerns on this invention. It is a flowchart which shows the manufacturing method of the single crystal which concerns on this invention. It is a conceptual diagram explaining the effect | action in this embodiment, Comprising: (a) is a conceptual diagram which shows the state of a seed crystal at the time of using the cover body of FIG. 1, (b) is a seed in the manufacturing method of the conventional single crystal. It is a conceptual diagram which shows the state of a crystal | crystallization. It is the schematic which shows the state of the seed crystal at the time of using the cover body of the manufacturing apparatus used for other embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 1, a single crystal manufacturing apparatus (hereinafter, simply referred to as “manufacturing apparatus”) 100 accommodates a crystal growth unit 1 in which a single crystal 4 is grown and a crystal growth unit 1. The heating furnace body 2 is a place where heating is performed, and the high-frequency coil 3 is wound around the heating furnace body 2.

  The crystal growth unit 1 includes a growth vessel 5 for growing a single crystal 4, and the growth vessel 5 includes a crucible 7 in which a raw material 6 is accommodated and a lid 8 that seals the crucible 7.

  The lid 8 is formed with a seed crystal accommodating portion 10 in which the seed crystal 9 is accommodated. The opening shape of the seed crystal accommodating portion 10 matches the outer shape of the seed crystal 9 to be accommodated, and is processed so that the seed crystal 9 can be accommodated without a gap. In addition, the dimension in the depth direction of the seed crystal accommodating portion 10 matches the thickness dimension of the seed crystal 9. Therefore, in the state where the seed crystal 9 is accommodated, the exposed surface of the seed crystal 9 matches the surface of the lid 8.

  The lid 8 is fixed so as to seal the crucible 7 so that the seed crystal 9 is inside, in a state where the seed crystal 9 is fixed to the seed crystal accommodating portion 10. The fixed surface of the lid 8 is defined as the surface. As a material constituting the crucible 7 and the lid 8, it is sufficient if it is made of a heat conductive material. For example, graphite, alumina, magnesia, zirconia, quartz and the like are used. Here, it is preferable to use graphite from the viewpoint of economical and high temperature heat resistance. If graphite is used, the single crystal is decomposed and sublimated by the carbon atmosphere generated during firing. To prevent this, the inner wall surface 7a of the crucible 7 and the surface of the lid 8 are made of a metal nitride such as tungsten nitride. It is preferable to coat with.

  A gas inlet 11 and a gas outlet 12 are formed in the heating furnace body 2, and metal nitrides coated on the inner wall surface 7 a of the crucible 7 and the surface of the lid 8 are formed during crystal growth. In order to prevent sublimation, the insides of the crucible 7 and the heating furnace body 2 are filled with gas. The inert gas is introduced (F1) from the inert gas supply device (not shown) through the gas introduction port 11, and the gas in the heating furnace main body 2 is discharged through the gas discharge port 12 by a decompression device (for example, a vacuum pump). (F2). Here, examples of the inert gas include a rare gas such as argon, helium, or neon, or a nitrogen gas. The heating furnace body 2 is also formed with an opening (not shown) for accommodating the crystal growth part 1. Furthermore, radiation thermometers 13 for measuring the temperatures of the lower surface and the upper surface of the growth vessel 5 are provided at the upper and lower ends of the heating furnace body 2.

  The high-frequency coil 3 is spirally wound around the heating furnace main body 2 and has a role of generating heat from the growth vessel 5 made of a heat conductive material by induction heating by applying a high-frequency current.

  In the above embodiment, the crucible 7 generates heat by induction heating of the high frequency coil 3, but the high frequency coil 3 is not necessarily required. For example, the crucible 7 can be heated by resistance heating.

  Furthermore, although the manufacturing apparatus 100 includes the heating furnace body 2 and the high-frequency coil 3 in addition to the crystal growth unit 1 in the above embodiment, the manufacturing apparatus 100 may include only the crystal growth unit 1.

  Next, with reference to FIG. 2, the manufacturing method of the single crystal which concerns on this embodiment using the said manufacturing apparatus 100 is demonstrated. FIG. 2 is a flowchart showing a method for producing a single crystal according to the present invention.

  First, the seed crystal 9 is fixed to the lid 8 (step S1). The seed crystal 9 is adhered by a protective film 14 to be described later, and is fixed so that the seed crystal housing portion 10 and the seed crystal 9 are not separated from each other. Here, a protective film 14 is provided on the back surface of the seed crystal 9 for the purpose of preventing the detachment of atoms. The material constituting the protective film 14 is not particularly limited as long as the material has a sublimation rate equal to or lower than that of the seed crystal at the growth temperature of the single crystal. Examples thereof include a carbon thin film obtained by carbonizing an organic thin film such as a photosensitive resist.

The seed crystal 9 is not particularly limited as long as a single crystal can be grown. For example, the seed crystal 9 is made of a semiconductor crystal substrate made of a single element semiconductor such as Si or Ge, or a group IV compound semiconductor such as SiC or SiGe. Semiconductor crystal substrate or semiconductor crystal substrate made of an oxide semiconductor such as Al ₂ O ₃ , MgAl ₂ O ₄ , ZnO, MgO or SiO _2, GaAs, GaP, InP, BN, or Al _x In _y Ga _{(1-x− y) A} semiconductor crystal substrate made of a III-V group compound semiconductor such as N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ x + y ≦ 1) can be used. Among these, from the viewpoint of efficiently producing a high-quality single crystal with few defects, a seed crystal having excellent thermal characteristics is preferable. For example, SiC, Al ₂ O ₃ or Al _x In _y Ga _(1-xy) is preferable. It is preferable to use a semiconductor crystal substrate composed of N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ x + y ≦ 1).

Next, a crystal thin film 15 is formed so as to cover the exposed surface of the seed crystal 9 fixed to the lid 8 (step S2; film forming step). The method for forming the crystal thin film 15 is not particularly limited as long as the crystal thin film 15 can be formed at a temperature range where the seed crystal 9 does not sublime, that is, at a temperature lower than the temperature at which desorption of atoms in the seed crystal 9 starts to occur. Although there is no, for example, CVD method (chemical vapor deposition method) such as HVPE method (hydride vapor deposition method) or MOCVD method, PVD method (physical vapor deposition method) such as MBE method, or LPE method (liquid phase growth method) ) And the like. According to this, the growth rate can be made slower than the sublimation method, and the film thickness can be controlled on the atomic layer order, so that a higher quality crystal interface of the crystal thin film 15 can be obtained. These film forming methods are preferably grown in a high vacuum region with a degree of vacuum of 10 ⁻² Pa or less so that high-quality single crystals can be produced.

  Moreover, it is preferable that the deposited crystal thin film 15 is a single crystal so that a high-quality single crystal 4 can be obtained during the single crystal growth by the sublimation method. Furthermore, it is preferable that the crystal thin film 15 and the single crystal 4 are the same kind of substance. When the single crystal 4 is grown using the same kind of material as the crystal thin film 15, the lattice constants of the seed crystal and the crystal to be grown coincide. For this reason, compared to the case of using a different kind of substance, the degree of lattice mismatch between the single crystal 4 and the crystal thin film 15 can be further reduced, and the crystal can be prevented from cracking due to strain. Crystals can be produced.

  And the raw material 6 is accommodated in the growth container 5 (step S3). Examples of the single crystal 4 obtained by the present embodiment include a SiC single crystal, an AlN single crystal, and a GaN single crystal. As these raw materials, crystals of these powders are used.

  Further, the crucible 7 is sealed with the lid body 8 on which the crystal thin film 15 is formed (step S4). At this time, the crucible 7 is sealed with the surface of the lid 8 facing the inner wall surface 7 a of the crucible 7. In this state, the crystal growth part 1 is accommodated inside from the opening of the heating furnace body 2.

  Next, the heating furnace body 2 is evacuated by vacuuming with a decompression device (step S5). Thereafter, an inert gas is introduced into the heating furnace body 2 from the gas inlet 11 and the gas in the heating furnace body 2 is discharged from the gas outlet 12. Thus, the periphery of the crystal growth part 1 is placed in an inert gas atmosphere.

  Next, a high frequency magnetic field is applied to the growth vessel 5 by applying a high frequency current to the high frequency coil 3. Then, an induced current flows through the growth vessel 5 and the growth vessel 5 generates heat. At this time, by controlling the temperature of the raw material 6 to be higher than the temperature of the seed crystal 9 and setting a temperature gradient inside the growth vessel 5, the heat of the crucible 7 is transferred to the raw material 6, and the raw material 6 is heated and decomposed. Sublimated. The growth temperature is desirably higher than that during the film formation step so that surface migration of adsorbed atoms can be promoted. Specifically, for example, when obtaining an AlN single crystal, the temperature is about 1500 to 2000 ° C. Thereby, the sublimated raw material gas is mixed with the inert gas flowing in from the gas inlet 11. Then, the mixed gas adheres to the crystal thin film 15 covering the seed crystal 9 fixed to the lid 8 and recrystallizes to grow the single crystal 4 (step S6; growth process). Since the atmosphere temperature inside the crucible 7 is higher than the temperature of the seed crystal 9, the mixed gas is less likely to adhere to the side surface of the crucible 7 and is likely to adhere toward the seed crystal 9. The single crystal 4 grown by the manufacturing apparatus 100 may be any as long as it is a sublimable single crystal.

  Hereinafter, the function and effect of this embodiment will be described with reference to FIG. Here, the case where SiC is used for the seed crystal 9 and AlN is used for the crystal thin film 15 and the single crystal 4 will be described as an example.

  3A and 3B are conceptual diagrams for explaining the operation in the present embodiment. FIG. 3A is a conceptual diagram showing the state of the seed crystal 9 when the lid 8 of FIG. 1 is used, and FIG. It is a conceptual diagram which shows the state of the seed crystal 9 in the manufacturing method of a crystal.

  As shown in FIG. 3B, conventionally, by providing the protective film 14 on the back surface of the SiC seed crystal, Si atoms are desorbed from the back surface of the SiC seed crystal even at high temperature growth of 1500 ° C. or higher. Can be suppressed. However, by covering the back surface with the protective film 14, the desorption of Si atoms from the side surface or main surface of the SiC seed crystal is promoted instead of desorbing Si atoms from the back surface. For this reason, voids are generated on the side surfaces and the main surface of the seed crystal due to the elimination of Si atoms.

  Therefore, as shown in FIG. 3A, the SiC seed crystal is placed in the seed crystal accommodating portion 10 without a gap. Then, when the AlN crystal thin film is formed so that the SiC seed crystal covers the exposed main surface, the exposed surface of the SiC seed crystal 9 is covered with the AlN crystal thin film. Furthermore, since the side surface and the back surface of the SiC seed crystal 9 are protected by the lid 8, Si atoms to be desorbed are blocked and cannot be removed, so that generation of voids is suppressed. Therefore, desorption of Si atoms from the side surface or main surface of the seed crystal SiC can be suppressed, and a high-quality AlN single crystal can be produced. It should be noted that an appropriate film formation temperature condition for the AlN crystal thin film using the CVD method, the PVD method, or the LPE method is desirably 1500 ° C. or less at which Si atoms are not desorbed from the SiC seed crystal.

  Next, another embodiment will be described. FIG. 4 is a schematic view showing the state of the seed crystal 9 when the lid of the manufacturing apparatus used in another embodiment is used. That is, as shown in FIG. 4, a lid 8 in which the seed crystal 9 is directly fixed to the surface may be used. In this case, by adhering with the protective film 14 described above, fixing is performed so that no gap is formed between the surface of the lid 8 and the back surface of the seed crystal 9. Then, a crystal thin film 15 is formed on the exposed surface of the seed crystal 9, that is, the main surface opposite to the fixed surface of the seed crystal 9 and the side surface. The crucible 7 may be hermetically fixed with the lid 8 and a single crystal may be manufactured in the same procedure as in the above embodiment.

  Hereinafter, effects of other embodiments will be described. Here, the case where SiC is used for the seed crystal 9 and AlN is used for the crystal thin film 15 and the single crystal 4 will be described as an example.

  As shown in FIG. 4, the SiC seed crystal is adhered to the lid 8 with the protective film 14 described above, and directly fixed to the surface. Then, when an AlN crystal thin film is formed so as to cover the side surface of SiC seed crystal 9 and the exposed surface of the main surface, the side surface and main surface of SiC seed crystal 9 are covered with the AlN crystal thin film, so let's desorb. The generation of voids is suppressed because the Si atoms are blocked and cannot escape. Therefore, desorption of Si atoms from the side surface or main surface of the seed crystal SiC can be suppressed, and a high-quality AlN single crystal can be produced.

  DESCRIPTION OF SYMBOLS 1 ... Crystal growth part, 2 ... Heating furnace main body, 3 ... High frequency coil, 4 ... Single crystal, 5 ... Growth vessel, 6 ... Raw material, 7 ... Crucible, 8 ... Lid (crucible lid), 9 ... Seed crystal, 10 DESCRIPTION OF SYMBOLS ... Seed crystal accommodating part, 11 ... Gas inlet, 12 ... Gas outlet, 13 ... Radiation thermometer, 14 ... Protective film, 15 ... Crystal thin film, 100 ... Single crystal manufacturing apparatus.

Claims (4)

  A method for producing a single crystal in which a raw material is placed in a crucible sealed with a crucible lid to which a seed crystal is fixed, and the raw material is sublimated to produce a single crystal, the seed fixed to the crucible lid Forming a crystal thin film in advance in a temperature region where the seed crystal does not sublime so as to cover the exposed surface of the crystal, and sealing the crucible with the crucible lid on which the crystal thin film is formed, And a growth step of growing the single crystal by sublimating the substrate.   The method for producing a single crystal according to claim 1, wherein the film forming step uses a CVD method, a PVD method, or an LPE method.   3. The method for producing a single crystal according to claim 1, wherein the crystal thin film is a single crystal. The method for producing a single crystal according to any one of claims 1 to 3 , wherein the crystal thin film and the single crystal are the same kind of substance.

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