JP4224908B2 - Method for producing silicon carbide single crystal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a silicon carbide (SiC) single crystal in which micropipe defects are blocked.
[0002]
[Prior art]
When a SiC single crystal is produced by an improved Rayleigh method (sublimation method) using an SiC single crystal as a seed crystal, a hollow through hole with a diameter of sub μm to several μm called a micropipe defect (hollow through defect) is substantially in the growth direction. Stretches along and is inherent in the growing crystal. Since the micropipe defect adversely affects the electrical characteristics of the device, the SiC single crystal having the micropipe defect is not suitable for a substrate for device formation. For this reason, reducing micropipe defects is an important issue.
[0003]
As methods for reducing micropipe defects, methods disclosed in US Pat. No. 5,679,153, Japanese Patent No. 2804860 and Japanese Patent No. 2876122 have been proposed.
[0004]
The method shown in US Pat. No. 5,679,153 utilizes the fact that micropipe defects are blocked during epitaxial growth when crystal growth is performed by liquid phase epitaxy using SiC melting in silicon. Te, a seed crystal having micropipe defects (defect density: 50~400cm ^-2) an epitaxial layer micropipe defects are reduced on (defect density: 0~50cm ^-2) are grown.
[0005]
In the method shown in Japanese Patent No. 2804860, a plane perpendicular to the (0001) plane is used as a growth surface of the seed crystal, so that no hexagonal etch pits are observed at the time of alkali etching, that is, micropipe defects. A single crystal that does not exist is grown on the seed crystal.
[0006]
In the method disclosed in Japanese Patent No. 2876122, β (cubic) -SiC or α- is formed on the surface of an α (hexagonal) -SiC single crystal substrate (seed crystal) by a thermochemical vapor deposition (CVD) method. A plurality of layers of β-SiC or α-SiC polycrystalline film is formed on an α-SiC single crystal substrate (seed crystal) by repeatedly forming a SiC polycrystalline film and heat-treating the composite obtained thereby. ) In the same orientation as the crystal axis (a kind of solid phase epitaxial growth) to grow high-quality and high-thickness single crystal SiC without crystal defects such as micropipe defects on the seed crystal. Yes.
[0007]
[Problems to be solved by the invention]
In each of the above three methods, a new single crystal is grown on the seed crystal, and micropipe defects are reduced in the growth layer.
[0008]
For this reason, in the first method, in order to obtain a portion free from micropipe defects, an epitaxial layer of 20 to 75 μm or more must be grown by the liquid phase epitaxy method. There is a problem that pipe defects exist. Further, when single crystal growth is performed again by the sublimation method using the epitaxial layer formed in this way as a seed crystal, since the portion where the micropipe defect is closed is thin, the closed portion is sublimated and microscopically again. There is a possibility that an opening of a pipe defect may occur, and there is a problem that it is difficult to prepare a seed crystal sample and to optimize the sublimation growth conditions.
[0009]
On the other hand, the second method is effective in suppressing the occurrence of micropipe defects, but a new stacking fault is introduced into the grown single crystal, causing anisotropy in the electrical characteristics of the substrate. There is a problem that it is not suitable as a substrate for electronic devices.
[0010]
On the other hand, in the third method, since a β-SiC or α-SiC polycrystalline film is formed on the surface of an α-SiC single crystal substrate (seed crystal) by a CVD method, an SiC composite having a grain boundary is obtained. It is done. When this composite is heat-treated and solid-phase epitaxially grown on the seed crystal, the crystallites in the β-SiC or α-SiC polycrystalline film overgrow and the clear crystal grain boundaries decrease with the heat treatment. However, there is a risk of introducing crystal defects due to internal strain at the crystal grain boundaries and crystal boundaries associated with inhomogeneous phase transformation. Since such a defect becomes a carrier trap source, there is a problem that it is not suitable as a substrate for an electronic device. Moreover, since it is necessary to repeat the film forming process, the heat treatment process, and the surface smoothing process several times in order to obtain the thickness of the practical substrate, there is a problem that the manufacturing cost increases.
[0011]
The present invention has been made in view of the above problems, and does not suppress the occurrence or inheritance of micropipe defects in a new growth layer, but blocks micropipe defects present in the silicon carbide single crystal within the silicon carbide single crystal. The purpose is to be able to make it.
[0012]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present inventors perform heat treatment in a state where the silicon carbide substrate crystal made of a silicon carbide single crystal having micropipe defects is coated, so that the micropipe defects are formed inside the silicon carbide substrate crystal. It was found that it can be occluded.
[0013]
However, when a coating layer is formed on a silicon carbide substrate crystal by normal epitaxial growth regardless of a gas phase or a liquid phase, crystal information of the silicon carbide substrate crystal is inherited, and micropipe defects may not be covered with the coating layer. . In such a case, since the micropipe defect is not blocked by the subsequent heat treatment, it is necessary to reliably cover the micropipe defect.
[0014]
From such a viewpoint, it has been found that when a polycrystal is deposited on the surface of a silicon carbide substrate crystal, a coating layer is formed regardless of the crystallinity of the silicon carbide substrate crystal.
[0015]
Therefore, in the invention described in claim 1, the step of depositing silicon carbide polycrystal (3) on the surface of the silicon carbide substrate crystal (1) containing the micropipe defect (1a) to cover the micropipe defect; performing a step of closing the micropipe defects within the silicon carbide substrate crystal by heat treatment to the coated silicon carbide polycrystalline silicon carbide substrate crystal, the step of depositing the unrealized silicon carbide polycrystal by liquid phase growth It is characterized by that.
[0016]
Thus, by depositing a silicon carbide polycrystal on the surface of the silicon carbide substrate crystal, the micropipe defect is reliably covered, and the micropipe defect is surely closed in the silicon carbide substrate crystal by the subsequent heat treatment. Can be. Specifically, the step of depositing silicon carbide polycrystal can be performed by liquid phase growth.
[0018]
In the second aspect of the present invention, the step of forming the coating layer (4) on the surface of the silicon carbide substrate crystal (1) containing the micropipe defect (1a), and the silicon carbide substrate crystal on which the coating layer is formed Depositing the silicon carbide polycrystal (3) to coat the micropipe defects with the silicon carbide polycrystal, and heat treating the silicon carbide substrate crystal coated with the silicon carbide polycrystals to carbonize the micropipe defects. It is seen containing a step of clogging in the silicon substrate crystal, and is characterized in that composed of carbon coating layer.
[0019]
Thus, after forming the coating layer on the surface of the silicon carbide substrate crystal and then forming the silicon carbide polycrystal on the silicon carbide substrate crystal on which the coating layer is formed, the silicon carbide polycrystal is formed using the coating layer as a nucleus. Can be formed. Thus, the effect similar to Claim 1 can be acquired by heat-processing with respect to the silicon carbide substrate crystal | crystallization covered with the silicon carbide polycrystal. Specifically, the coating layer can be made of carbon.
[0020]
Moreover, as shown in claim 3 or 4 , the step of depositing the silicon carbide polycrystal can be performed by liquid phase growth.
[0021]
In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
In FIG. 1, the manufacturing process of the silicon carbide single crystal to which 1st Embodiment of this invention is applied is shown. Hereinafter, a method for producing a silicon carbide single crystal will be described with reference to FIG.
[0023]
First, as shown in FIG. 1A, a silicon carbide substrate crystal 1 made of a silicon carbide single crystal having micropipe defects 1a is prepared. Then, as shown in FIG. 1B, particles 2 containing at least one of silicon carbide particles, silicon particles, and carbon particles are applied to the surface of silicon carbide substrate crystal 1. As the particles 2, for example, particles having a particle size of several μm to sub-μm are selected.
[0024]
Silicon carbide substrate crystal 1 coated with particles 2 is placed in a graphite crucible and subjected to heat treatment. Thereby, as shown in FIG.1 (c), the silicon carbide polycrystal 3 is formed in the surface of the silicon carbide substrate crystal 1 by making the particle | grains 2 into a nucleus.
[0025]
Since the silicon carbide polycrystal 3 formed in this manner does not inherit the crystal form of the silicon carbide substrate crystal 1 made of a silicon carbide single crystal, the micropipe defect 1a formed in the silicon carbide substrate crystal 1 is also present. The micropipe defect 1a can be reliably covered with the silicon carbide polycrystal 3 without being inherited.
[0026]
Then, the silicon carbide substrate crystal 1 thus coated with the micropipe defect 1a by the silicon carbide polycrystal 3 is embedded in silicon carbide or silicon powder, and heat treatment is performed while suppressing carbonization from the surface of the silicon carbide substrate crystal 1. I do.
[0027]
Thereby, micropipe defect 1a formed in silicon carbide substrate crystal 1 is closed and becomes closed hole 1b.
[0028]
The mechanism by which the micropipe defect 1a is blocked is estimated as follows.
[0029]
The micropipe defect is considered to be that a screw dislocation core having a large Burgers vector is formed into a hollow through-hole in order to relax large elastic strain energy (FC Frank Acta Cryst. 4 (1951)). 497).
[0030]
It is estimated that the blocking phenomenon of the micropipe defect 1a is a phenomenon opposite to the mechanism of the micropipe defect 1a. A blockage estimation model of the micropipe defect 1a will be described with reference to FIG.
[0031]
Consider the case where silicon carbide substrate crystal 1 including micropipe defects 1a is covered with silicon carbide polycrystal 3 (FIG. 2A). When placed in the heat treatment apparatus shown in FIG. 1 in this state and subjected to heat treatment under appropriate temperature and pressure conditions, in order to maintain the equilibrium vapor pressure at that temperature, the periphery of the micropipe defect 1a, the 3C-SiC film And vapor species such as Si, SiC ₂ and Si ₂ C sublimate from the graphite of the lid as shown by arrows in the figure. (FIG. 2 (b)).
[0032]
After that, although the reason is not yet clear, the micropipe defect formed from the screw dislocation (Super Screw Dislocation) having a large Burgers vector at the interface with the silicon carbide polycrystal 3 from the observation result of the transmission electron microscope of the blocked portion. After being decomposed, an assembly of several screw dislocations (stacking faults, 1c (in the case of 6H-SiC, c = 1.5 nm, c corresponds to the c-axis length of the unit cell)) or less Burgers vector It is presumed that SiC was precipitated in the hollow holes.
[0033]
This is because, in that place, SiC is precipitated rather than a hollow hole having a surface, and surface energy disadvantage due to the formation of the surface is eliminated, and molecules in the environmental phase (gas phase) are also present in the crystal. Since the reduction in free energy due to incorporation into the substrate exceeds the loss due to strain energy in the crystal caused by SiC precipitation, the entire system has a gain in free energy. For this reason, it is presumed that the sublimation-reprecipitation (/ rearrangement) has progressed (FIGS. 2C and 2D).
[0034]
As in this embodiment, covering at least one surface of the silicon carbide substrate crystal 1 having the micropipe defect 1a and performing a heat treatment serve to decompose the Burgers vector of the micropipe defect 1a (screw dislocation), As a result, it is estimated that the micropipe defect 1a has an effect of being blocked.
[0035]
Thus, after completely covering the micropipe defect 1a, the silicon carbide polycrystal 3 is embedded with silicon carbide or silicon powder, and heat treatment is performed while suppressing the silicon carbide substrate crystal 1 from being carbonized from the surface. As shown in FIG. 1D, the micropipe defect 1a formed in the silicon carbide substrate crystal 1 is closed to form a closed hole 1b.
[0036]
When the silicon carbide polycrystal 3 and the carbon 4 are removed from the silicon carbide substrate crystal 1 having the micropipe defect 1a as the closed hole 1b as described above, the silicon carbide substrate crystal 1 is exposed. A silicon carbide single crystal in which all la is closed can be obtained.
[0037]
As described above, by growing silicon carbide polycrystal 3 as a coating layer on the surface of silicon carbide substrate crystal 1, the coating layer may take over the micropipe defect 1a, so that the micropipe defect 1a may not be completely covered. The micropipe defect 1a can be completely closed by the subsequent processing.
[0038]
By using silicon carbide substrate crystal 1 in which micropipe defect 1a is closed hole 1b in this manner as a device substrate, a high-performance device can be produced. Further, by using silicon carbide substrate crystal 1 in which micropipe defect 1a is closed as a seed crystal, it is possible to newly create a high-quality crystal without micropipe defect 1a.
[0039]
(Second Embodiment)
In the above embodiment, in order to form a nucleus for forming silicon carbide polycrystal 3, particles 2 in which a carbon material, a silicon material, and a silicon carbide material are mixed are applied to the surface of silicon carbide substrate crystal 1. However, nuclei for polycrystalline growth may be formed by the method of this embodiment.
[0040]
FIG. 3 shows a closing process of the micropipe defect 1a in the present embodiment.
[0041]
First, as shown in FIG. 3A, a silicon carbide substrate crystal 1 including a micropipe defect 1a is prepared. Then, as shown in FIG. 3 (b), the surface of the silicon carbide substrate crystal 1 is covered with carbon 4. For example, the surface of the silicon carbide substrate crystal 1 is coated by depositing carbon 4.
[0042]
Thereafter, as shown in FIG. 3C, a silicon carbide polycrystal 3 is grown with carbon 4 as a nucleus. For example, after silicon carbide substrate crystal 1 covered with carbon 4 is placed in a graphite crucible together with silicon (Si) powder and subjected to heat treatment, silicon adhering to silicon carbide substrate crystal 1 is mixed with a mixed acid of hydrofluoric acid and nitric acid. When melted and the silicon carbide substrate crystal 1 is taken out, the silicon carbide polycrystal 3 grown in the liquid phase in the silicon melt can be deposited on the surface of the carbon 4. Thereby, micropipe defect 1a can be completely covered with silicon carbide polycrystal 3.
[0043]
Then, when the same process as the process shown in FIGS. 1D and 1E of the first embodiment shown in FIGS. 3D and 3E is performed, the micropipe defect 1a becomes the same as in the first embodiment. A silicon carbide single crystal that is completely blocked can be obtained. Thereby, the effect similar to 1st Embodiment can be acquired.
[0044]
(Third embodiment)
In the first and second embodiments, the heat treatment in the step of forming the silicon carbide polycrystal 3 on the silicon carbide substrate crystal 1 and the step of closing the micropipe defect 1a are performed separately. You may go on. Even in this manner, a silicon carbide single crystal in which all the micropipe defects 1a are closed can be obtained as in the first and second embodiments, and the same effect as in the first and second embodiments can be obtained. .
[0045]
(Other embodiments)
In the second embodiment, vapor deposition is used to form carbon 4. However, other methods such as carbonization of organic matter, application of carbon particles, and carbonization of silicon carbide substrate crystal 1 itself may be used.
[0046]
In the first and second embodiments, the carbon layer, the silicon carbide powder, the carbon powder, and the silicon powder are exemplified as the coating layer serving as a nucleus for forming the silicon carbide polycrystal 3, but other substances such as, for example, A ceramic such as a refractory metal or silicon nitride may be used.
[0047]
In the second embodiment, the liquid phase growth is exemplified as the method for forming the silicon carbide polycrystal 3. However, it may be performed by a solid phase method or a vapor phase method. The crystal polymorph of the silicon carbide single crystal can be applied to any of 6H, 4H, 15R, and the plane orientation of the substrate crystal 1 is not limited.
[0048]
【Example】
Examples based on the above embodiments will be described below.
Example 1
This example shows the experimental results for the first embodiment.
[0049]
A silicon carbide substrate crystal 1 (thickness 1 mm, micropipe defect density 100 / cm ² ) made of 6H polymorphic silicon carbide single crystal containing micropipe defects 1a was prepared. The surface of the silicon carbide substrate crystal 1 was embedded in particles 2 (particle size: several μm to sub μm) mixed with silicon carbide particles, silicon particles, and carbon particles, and then heat-treated in a graphite crucible. The heat treatment conditions for this time were an argon (Ar) atmosphere, a temperature of 1400 to 2000 ° C., a pressure of 6.65 × 10 ⁴ Pa (500 Torr), and a heating time of 6 hours.
[0050]
By this heating, silicon carbide polycrystal 3 grew on the surface of silicon carbide substrate crystal 1. In this silicon carbide polycrystal 3, no hole extending from the micropipe defect 1 a formed in the silicon carbide substrate crystal 1 is observed, and the end of the micropipe defect 1 a is completely covered with the silicon carbide polycrystal 3. It was.
[0051]
Silicon carbide substrate crystal 1 covered with silicon carbide polycrystal 3 was embedded in silicon carbide or silicon powder, and heat treatment was performed while suppressing carbonization from the surface of silicon carbide substrate crystal 1. The heat treatment conditions for the heat treatment at this time were an argon atmosphere, a temperature of 2400 ° C., a pressure of 6.65 × 10 ⁴ Pa, and a heating time of 24 hours.
[0052]
Thereafter, silicon carbide substrate crystal 1 covered with silicon carbide polycrystal 3 was processed and removed from the surface of silicon carbide polycrystal 3 to expose silicon carbide substrate crystal 1. Then, the surface of silicon carbide substrate crystal 1 was observed with a microscope. As a result, it became clear that there were no micropipe defects 1a opened on the surface of the silicon carbide substrate crystal 1, and all the micropipe defects 1a that were initially present were closed to form closed holes 7. It was.
[0053]
(Example 2)
This example shows the experimental results for the second embodiment.
[0054]
A silicon carbide substrate crystal 1 (thickness 1 mm, micropipe defect density 100 / cm ² ) made of 6H polymorphic silicon carbide single crystal containing micropipe defects 1a was prepared. After carbon 4 was deposited to a thickness of about 50 nm on the surface of silicon carbide substrate crystal 1, silicon carbide substrate crystal 1 was placed in a graphite crucible together with silicon powder and heated. The heat treatment conditions at this time were an argon (Ar) atmosphere, a temperature of 1800 to 2200 ° C., a pressure of 6.65 × 10 ⁴ Pa, and a heating time of 6 hours.
[0055]
After this heat treatment, silicon was dissolved with a mixed acid of hydrofluoric acid and nitric acid, and silicon carbide substrate crystal 1 was taken out. As a result, silicon carbide polycrystal 3 grew with carbon 4 as a nucleus in the silicon melt, and silicon carbide polycrystal 3 of about 50 μm on one side was deposited on silicon carbide substrate crystal 1. In this silicon carbide polycrystal 3, no hole extending from the micropipe defect 1 a formed in the silicon carbide substrate crystal 1 is observed, and the end of the micropipe defect 1 a is completely covered with the silicon carbide polycrystal 3. It was.
[0056]
Silicon carbide substrate crystal 1 covered with silicon carbide polycrystal 3 was embedded in silicon carbide or silicon powder, and heat treatment was performed while suppressing carbonization from the surface of silicon carbide substrate crystal 1. The heat treatment conditions for the heat treatment at this time were an argon atmosphere, a temperature of 2400 ° C., a pressure of 6.55 × 10 ⁴ Pa, and a heating time of 24 hours.
[0057]
Thereafter, 100 μm of the silicon carbide substrate crystal 1 covered with the silicon carbide polycrystal 3 was processed and removed from the surface of the silicon carbide polycrystal 3 to expose the silicon carbide substrate crystal 1. Then, the surface of silicon carbide substrate crystal 1 was observed with a microscope. As a result, it became clear that there were no micropipe defects 1a opened on the surface of the silicon carbide substrate crystal 1, and all the micropipe defects 1a that were initially present were closed to form closed holes 7. It was.
[0058]
(Example 3)
This example shows the experimental results for the third embodiment.
[0059]
A silicon carbide substrate crystal 1 (thickness 1 mm, micropipe defect density 100 / cm ² ) made of 6H polymorphic silicon carbide single crystal containing micropipe defects 1a was prepared. After carbon 4 was deposited to a thickness of about 50 nm on the surface of silicon carbide substrate crystal 1, silicon carbide substrate crystal 1 was placed in a graphite crucible together with silicon powder and heated. The heat treatment conditions at this time were an argon (Ar) atmosphere, a temperature of 2400 ° C., a pressure of 6.65 × 10 ⁴ Pa, and a heating time of 30 hours.
[0060]
After this heat treatment, silicon was dissolved with a mixed acid of hydrofluoric acid and nitric acid, and silicon carbide substrate crystal 1 was taken out. As a result, silicon carbide polycrystal 3 was grown with carbon 4 as a nucleus in the silicon melt, and silicon carbide polycrystal 3 of about 250 μm on one side was deposited on silicon carbide substrate crystal 1.
[0061]
About 300 μm of the silicon carbide substrate crystal 1 covered with the silicon carbide polycrystal 3 was processed and removed from the surface of the silicon carbide polycrystal 3 to expose the silicon carbide substrate crystal 1. Then, the surface of silicon carbide substrate crystal 1 was observed with a microscope. As a result, it became clear that there were no micropipe defects 1a opened on the surface of the silicon carbide substrate crystal 1, and all the micropipe defects 1a that were initially present were closed to form closed holes 7. It was.
[Brief description of the drawings]
FIG. 1 is a diagram showing a manufacturing process of a silicon carbide single crystal in a first embodiment of the present invention.
FIG. 2 is a diagram for explaining a mechanism of blocking a micropipe defect 1a.
FIG. 3 is a diagram showing a process for manufacturing a silicon carbide single crystal in a second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Silicon carbide substrate crystal, 1a ... Micropipe defect, 1b ... Closure hole,
2 ... particles as nuclei, 3 ... polycrystalline silicon carbide, 4 ... carbon.

Claims (5)

Depositing silicon carbide polycrystal (3) on the surface of the silicon carbide substrate crystal (1) containing the micropipe defect (1a) to cover the micropipe defect;
See containing and a step of closing the said micropipe defects in said silicon carbide substrate crystal by heat treatment to the coated the silicon carbide substrate crystal silicon carbide polycrystal
A method for producing a silicon carbide single crystal, wherein the step of depositing the silicon carbide polycrystal is performed by liquid phase growth . Forming a coating layer (4) on the surface of the silicon carbide substrate crystal (1) containing micropipe defects (1a);
Coating the micropipe defects with the silicon carbide polycrystal by depositing silicon carbide polycrystal (3) on the silicon carbide substrate crystal on which the coating layer is formed;
See containing and a step of closing the said micropipe defects in said silicon carbide substrate crystal by heat treatment to the coated the silicon carbide substrate crystal silicon carbide polycrystal,
A method for producing a silicon carbide single crystal, wherein the coating layer is made of carbon . The method for producing a silicon carbide single crystal according to claim 2, wherein the step of depositing the silicon carbide polycrystal is by liquid phase growth. Forming a coating layer (4) on the surface of the silicon carbide substrate crystal (1) containing micropipe defects (1a);
Coating the micropipe defects with the silicon carbide polycrystal by depositing silicon carbide polycrystal (3) on the silicon carbide substrate crystal on which the coating layer is formed;
See containing and a step of closing the said micropipe defects in said silicon carbide substrate crystal by heat treatment to the coated the silicon carbide substrate crystal silicon carbide polycrystal,
The method for producing a silicon carbide single crystal, wherein the step of depositing the silicon carbide polycrystal is by liquid phase growth . A silicon carbide substrate crystal having a closed hole in which micropipe defects are closed, manufactured using the method for manufacturing a silicon carbide single crystal according to any one of claims 1 to 4 , is used as a seed crystal. A method for producing a silicon carbide single crystal, comprising growing a silicon carbide single crystal on the substrate.

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