JP2003183097A - Silicon carbide single crystal ingot and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a silicon carbide single crystal capable of producing a single crystal silicon carbide wafer having a very low micropipe density and a large diameter. <P>SOLUTION: This method for producing a silicon carbide single crystal ingot is characterized in the following: after a mask is formed on the crystal growth plane of a seed crystal, a silicon carbide single crystal is caused to grow across the mask; while the single crystal is growing, a new mask having such masking sections as to cover the positions of the mask openings on the seed crystal is set; and this mask setting is conducted at least once during the crystal growth. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide single crystal and a method for manufacturing the same, and in particular, it is used as a substrate wafer for blue light emitting diodes and electronic devices characterized by high breakdown voltage and high frequency operation. The present invention relates to a large-sized single crystal ingot with extremely few pipe defects and a method for manufacturing the same.

[0002]

2. Description of the Related Art Silicon carbide (SiC) has excellent heat resistance and mechanical strength, and also has excellent semiconductor characteristics exceeding that of silicon, which is a typical general-purpose semiconductor material. Therefore, it has a short wavelength range from blue to ultraviolet. As a substrate wafer for optical devices, high-frequency high-voltage electronic devices, etc., research aiming at industrial stable production thereof has been activated in recent years. However,
This material is apt to have a characteristic micropore defect called a micropipe, and when such a defect occurs,
It is known that when a device is fabricated on a substrate, it has a fatal effect such as causing leakage current that penetrates defects (eg, PG Neudeck et al., IEEE Ele.
ctron Device Letters, Vol.15 (1994) pp.63-65). Therefore, industrially, there is a demand for the production of a large-diameter and high-quality SiC single crystal ingot without such defects, but the crystal growth technology that enables it is still well established. However, the present situation is hindering the practical application of this material.

Generally, a SiC single crystal ingot is manufactured by a method called an improved Rayleigh method (Yu.
M. Tairov and VF Tsvetkov, Journal of Crystal Gr
owth, Vol.52 (1981) pp.146-150). In this method, SiC
Using a single crystal wafer as a seed crystal, a raw material SiC crystal powder was filled in a crucible mainly made of graphite, and the raw material was filled in an atmosphere of an inert gas such as argon (133 Pa to 13.3 Pa).
kPa) and heated to 2000-2400 ° C. At this time, the seed crystal and the raw material powder are arranged so that a temperature gradient in which the seed crystal is on the lower temperature side than the raw material powder is formed, whereby the raw material is sublimated, and then diffused and transported in the seed crystal direction,
Then, single crystal growth is realized by recrystallizing on the seed crystal.

On the other hand, when producing a SiC single crystal ingot by the improved Rayleigh method, it is known that defect groups such as micropipes existing in the seed crystal tend to be inherited by the grown crystal portion during growth. In the first place, this micropipe is considered to be formed when the dislocation Burgers vector in a screw dislocation becomes larger than a certain critical value, and the crystal growth is basically a spiral growth centered on the screw dislocation. In the silicon carbide realized by the method, the micropipe cannot be extinguished unless the operation of making the dislocation Burgers vector below the critical value is performed during crystal growth. Such an operation is a polymorphic crystal peculiar to the present system called a heterogeneous polytype, there is no occurrence of crystal grains in which the crystal orientation is greatly disturbed, so-called stable crystal growth is continuously repeated,
In that process, there is no effective method other than waiting for the screw dislocations having a huge Burgers vector to decompose into screw dislocation groups having a Burgers vector below the critical value, and therefore a large-diameter high-quality ingot with few defects is produced. In order to do so, the present situation is that either a seed crystal having an extremely low micropipe density is used, or stable crystal growth is repeated and waiting for the micropipes to be reduced. On the other hand, as a seed crystal having an extremely low micropipe density, as a crystal that can be tested, the existence of a crystal fragment called a Rayleigh crystal produced by the Rayleigh method is known, but this crystal fragment has a large size. Has a diameter of at most about 10 to 15 mm, which is far less than the industrially required diameter of 2 to 4 inches (about 50 to 100 mm). Therefore, basically, starting from the Rayleigh crystal, stable crystal growth is repeated, and the diameter is carefully expanded so as not to newly generate a micropipe, and a desired diameter of 2 to 4 inches (about 50 to 100 mm) is obtained. This is the basic guideline for manufacturing large diameter, high quality ingots. However, even if this method succeeds in expanding the diameter, it may be newly added to the growth ingot due to causes such as growth instability caused by accidental factors such as sudden changes in growth conditions while repeating stable growth. The probability that a large number of micropipes occur cannot be ignored, and in such a case, stable crystal growth must be repeated many times until the density of micropipes is reduced to the original level, as described above. Industrial production is hindered.

For these reasons, in the method of manufacturing a large-diameter and high-quality silicon carbide single crystal ingot, it is not necessary to depend on the quality of the seed crystal, particularly the micropipe density, and the conventional repeated stable growth is required. Therefore, a new method that can realize a high-quality large-diameter ingot with extremely low micropipe density has been strongly desired.

[0006]

As described above, when stable growth is achieved during crystal growth, SiC is used.
Most of the micropipe defects existing in single crystals are those that existed in seed crystals and succeeded by grown crystals (Takahashi et al., Journal of Crystal Growth,
Vol.167 (1996) pp.596-606). Therefore, in order to realize a large-diameter ingot with a very small micropipe density, it is necessary to produce a large-diameter seed crystal with an extremely small micropipe density and ideally none. However, at present, there is no simple method for producing such a seed crystal.

In view of the above circumstances, the present invention provides a large-diameter silicon carbide single crystal ingot having a very small micropipe density even if many micropipes are present in the seed crystal, and a method for producing the same.

[0008]

According to the method for producing a SiC single crystal of the present invention, a raw material made of SiC is heated and sublimated to obtain S.
A method of supplying a seed crystal composed of an iC single crystal and growing a SiC single crystal on the seed crystal, which includes the step of (1) growing a silicon carbide single crystal on the seed crystal by a sublimation recrystallization method. A method of manufacturing a silicon carbide single crystal ingot, comprising: forming a mask layer having a mask portion and an opening on a crystal growth surface of a seed crystal, and then growing the silicon carbide single crystal through the mask layer. In the middle of the growth, a new mask layer including a mask portion arranged so as to include the opening of the mask layer is formed, and the single crystal growth is continued at least once. A method of manufacturing a silicon carbide single crystal ingot, wherein (2) a projection image obtained when the mask portions included in a plurality of mask layers are projected onto a seed crystal completely shields a crystal growth surface of the seed crystal, (1)
A method for producing a silicon carbide single crystal ingot described in (3).
The method for producing a silicon carbide single crystal ingot according to (1) or (2), wherein each of the plurality of mask layers independently includes one or more selected from the group consisting of graphite, tungsten, molybdenum, and tantalum. (4) The thickness of each of the plurality of mask layers is independently 0.1 to 3 m.
m, the method for manufacturing a silicon carbide single crystal ingot according to any one of (1) to (3), (5) the widths of the plurality of mask portions are each independently 1 to 5 mm ( 1) The method for manufacturing a silicon carbide single crystal ingot according to any one of the items (4) to (6), the mask aperture ratios (aperture area / mask area) of the plurality of mask layers are independent of each other. , 0.2 to 2, wherein the method for producing a silicon carbide single crystal ingot according to any one of (1) to (5),
(7) The aperture is 50 mm or more,
A silicon carbide single crystal ingot obtained by the manufacturing method according to any one of (1) to (6).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a method for producing a silicon carbide single crystal ingot, which comprises the step of growing a silicon carbide single crystal on a seed crystal by a sublimation recrystallization method, which comprises: After forming a mask layer consisting of a mask portion and an opening, the silicon carbide single crystal was grown over the mask layer, and was arranged so as to include the opening portion of the mask layer during the growth. A method for manufacturing a silicon carbide single crystal ingot, which comprises forming a new mask layer including a mask portion and continuing the single crystal growth at least once. According to this method, It is possible to obtain a large-diameter SiC single crystal ingot with almost no pipe defects. Furthermore, when the mask portion of each mask is projected onto the seed crystal growth surface, it is preferable that all projection images completely cover the seed crystal growth surface. In the present invention, the mask portion is formed on the growth surface of the seed crystal, and the micropipe grows during the growth of the single crystal.
It has the function of being taken over as an n-in defect and preventing the micropipe from penetrating. In addition, the opening is shown in FIG.
As shown in (a), it indicates a portion other than the mask portion in the mask layer.

1A to 1D show the outline of the manufacturing method of the present invention. In this figure, in crystal growth on the {0001} plane, a case where two mask layers are provided so that the projected image of each mask portion completely covers the seed crystal growth surface is shown. First, as a first-stage treatment, a mask layer is provided on the seed crystal (a), and a SiC single crystal is grown through the mask layer (b). At the initial stage of growth, crystal growth occurs in the opening in a direction substantially parallel to the c-axis, but as the crystal growth progresses thereafter, in the space directly above the mask, the crystal grows perpendicularly to the c-axis so as to occupy this space. Directional crystal growth progresses from the opening (b). At this time, in the grown crystal portion just above the opening, the micropipe existing in the seed crystal is gr
The micropipe penetrates because it is inherited as an own-in defect. On the other hand, JP-A-5-262599
As disclosed in Japanese Patent Laid-Open Publication No. JP-A-2003-264, in the space portion on the mask portion, crystal growth in the direction perpendicular to the c-axis is induced, so that extremely high quality crystal growth with almost no micropipe defects is realized. . A new mask layer is further formed on the surface of the single crystal thus produced.
The mask portion of the newly formed mask layer is installed so as to completely cover the opening portion of the mask layer formed previously. As a result, when the mask portions of these two mask layers are projected onto the seed crystal surface, the projected image completely covers the seed crystal growth surface (c). Subsequently, when single crystal growth is carried out over the newly formed mask layer, crystal growth continues from the portion where there is no micropipe, so that the micropipe is already formed in the opening of the newly formed mask layer. There is nothing, and as a result, a large-diameter ingot with almost no micropipe is realized over almost the entire part of the grown crystal (d). Although not illustrated, in the case where the seed crystal surface cannot be substantially covered by the two mask layers, a third mask layer is further formed, and the crystal layer is formed on the mask layer. Growth is carried out, and finally, as described above, by repeating this operation until the projection of the mask portion of each mask layer onto the seed crystal surface covers at least all of the seed crystal surface, growth similar to the above is performed. Large-diameter ingots with almost no micropipes can be manufactured over almost all parts of the crystal.

In addition, in the region where the generation of micropipe defects is suppressed (the region directly above the mask portion), Takahashi et a
l., Journal of Crystal Growth, Vol.181 (1997) pp.2
As shown in 29-240, there are (0001) area layer defects, but by continuing the growth and manufacturing a sufficiently thick ingot, in most of the region except directly above the mask, the c-axis is almost Since the crystal growth progresses in parallel with the above, the above-mentioned surface defect does not occur.

As the mask pattern shape of the mask layer,
The mesh shape or the lattice shape is preferable from the viewpoint of easiness of mask processing, but other shapes may be used as long as the above-described growth mode can be realized. Further, as the material of the mask layer, any material can be applied as long as it does not dissolve or decompose at the growth temperature and the contamination of the grown crystal with impurities does not matter, but it is made of graphite, tungsten, molybdenum and tantalum. It is preferable to include at least one selected from the group. Further, although a plurality of mask layers are formed in the present invention, they may be the same or different materials as long as they are selected from the above-mentioned substances.

The thickness of the mask layer is preferably 0.1 to 3.0 mm. Here, the mask thickness is 0.1 m
If it is less than m, the mask may be deformed or damaged during the growth preparation step or the growth experiment, which is not preferable. On the other hand, if it exceeds 3.0 mm, the portion of the grown crystal that can be taken out from the large-area wafer is unnecessarily shortened, which is also not preferable.

The shape of the mask portion is not particularly limited, but when the mask pattern is strip-shaped, for example, the band width of the mask portion is preferably 1.0 to 5.0 mm. Here, if the width of the mask portion is less than 1.0 mm, the growth in the direction perpendicular to the c-axis is not sufficiently performed (therefore, the micropipe defect cannot be completely suppressed), and the effect of the present invention can be obtained. Becomes difficult. On the other hand, if the width of the mask portion exceeds 5.0 mm, it becomes difficult to cover the entire area of the mask due to the growth in the direction perpendicular to the c-axis, and defects such as voids are formed right above the center of the mask portion. For example, a new defect is also generated, which is not preferable.

In the case of a mask pattern other than the above band-shaped mask, there is no adjacent opening in a region of less than 1.0 mm from the boundary between the opening and the mask toward the mask, and the mask is separated from the boundary. It is preferable that a region of 2.5 mm or less in the direction covers the entire mask portion. This state will be described in detail with reference to FIG. For example, in the case of a square lattice mask pattern, as shown in FIG.
From the boundary line between the opening A and the mask portion toward the mask portion 1.
It is preferable that there is no opening adjacent to the area of less than 0 mm, that is, the adjacent openings B and C do not enter the area of less than 1.0 mm, while FIG.
As shown in, 2.5m from the boundary line toward the mask part
It is preferable that the area of m or less covers the entire mask portion, that is, the mask portion is covered without a gap by the area of 2.5 mm or less in each of the openings A to D. Here, as shown in FIG. 3C, when the openings B and C are present in the area of the opening A that is less than 1.0 mm, the width between the openings is as narrow as less than 1.0 mm, and as described above. There is a possibility that the growth in the direction perpendicular to the c-axis does not occur for a sufficient length. On the other hand, as shown in FIG. 3D, when the area of 2.5 mm or less of the openings A to D cannot cover the entire mask portion and a gap is formed, the width of the mask portion is 5.0.
Since the thickness exceeds mm, it may be difficult to cover the entire mask due to growth in the direction perpendicular to the c-axis as described above.

The mask aperture ratio (aperture area / mask area) of the mask layer is preferably 0.2 to 2.0. If the aperture ratio is less than 0.2, it becomes difficult to inherit the growth orientation from the seed crystal, and polycrystals and the like are likely to occur. On the other hand, when it exceeds 2.0, the portion covered by the mask portion becomes small and the masking effect of the micropipe defects by the mask becomes small, which is not preferable.

Finally, the present invention is basically independent of the diameter of the seed crystal and is effective for seed crystals of all diameters, but is extremely effective especially for large single crystal ingots having a diameter of 50 mm or more. Is obtained. In the case of such a large single crystal ingot, in the conventional method, as described above, a high quality small diameter seed crystal having a small micropipe density is carefully expanded to a diameter of 50 mm, or a diameter of 50 mm having a high micropipe density is used. It can be produced only by any one of the methods of repeating stable growth using the seed crystal of 1) until the micropipe density decreases to a predetermined value. According to the method of the present invention, eg, shown in FIG.
A high quality ingot large single crystal ingot with an extremely low micropipe density can be obtained by performing single crystal growth only twice.

The manufacturing method of the present invention makes it possible to easily manufacture a high-quality large-diameter SiC single crystal ingot with almost no micropipe defects, regardless of the micropipe density of the seed crystal.

[0019]

EXAMPLES Examples of the present invention will be described below. FIG. 2 shows an outline of the growth apparatus. A hexagonal SiC single crystal wafer having a (0001) plane with a diameter of about 76 mm (= 3 inches) was used as a seed crystal. When the micropipe density of this wafer was examined by molten KOH etching, it was about 1
The number was 00 / cm ² . Next, this seed crystal wafer was attached to the inner surface of the graphite lid (21), and a mesh mask layer made of graphite was formed thereon to cover the seed crystal,
The seed crystal with a mask layer (22) was used. FIG. 2B shows a top view of this mask layer. Mask layer thickness is 0.5 mm
The width (30) of the graphite mask portion and the width (31) of the slit-shaped opening portion were both set to 1 mm (mask opening ratio 1.0, mask portion width 1.0 mm). Graphite crucible (21)
A high-purity SiC powder (23) for a raw material is filled in the above, and then a lid (21) equipped with the seed crystal (22) with a mask layer is attached.
It was then sealed with, covered with a graphite felt (25) for heat insulation, subjected to heat insulation treatment, and then installed inside a water-cooled double quartz tube (24). After the inside of the quartz tube was evacuated, Ar gas was introduced through the vacuum evacuation device Ar gas pipe (26) to replace the atmosphere, and an electric current was applied to the work coil (27) while maintaining the quartz tube internal pressure at about 80 kPa. High purity S for sink material
The temperature of the iC powder (23) was raised to 2000 ° C. After that, while reducing the pressure to 1.3 kPa which is a growth pressure over about 30 minutes, the raw material temperature was raised to a target temperature of 2400 ° C., and the growth was carried out while maintaining the growth at that temperature for about 1 hour. At this time, the temperature gradient in the crucible is 5 ° C / cm. The diameter of the obtained crystal was 76 mm, and the average thickness of the ingot was increased by about 1.5 mm.

Next, the surface of this ingot was mechanically ground to form a flat surface, and then mirror-finished by mechanical polishing using a polishing liquid containing diamond abrasive grains.
Further, this ingot was attached as a seed crystal to a new graphite lid, and a mesh mesh mask layer made of graphite was attached thereon so as to cover the seed crystal. At this time, the newly formed mesh-shaped mask portion was arranged so that the opening portion was moved in parallel in the diagonal direction so as to completely cover the opening portion of the mask layer formed during the initial growth. Hereinafter, single crystal growth was performed under almost the same conditions as the initial growth. However, the growth treatment time was 20 hours, and the growth rate was about 1 mm / hour. After the growth treatment was completed, the ingot was taken out from the crucible, and the obtained crystal had a diameter of 77 mm and an ingot thickness of about 13 mm.

The obtained ingot was found by analysis by X-ray diffraction and Raman scattering to be a hexagonal silicon carbide single crystal having the same structure as the seed crystal. A {0001} plane wafer with a thickness of about 1 mm was cut out from the ingot, and after polishing, the wafer surface was etched with molten KOH and observed under a microscope. As a result, the number of large hexagonal etch pits corresponding to micropipe defects was found to be almost all over the surface. 1.1 pieces across
It was below cm ² .

As a comparative example, a seed crystal having a micropipe density (about 100 pieces / cm ² ) substantially equal to that of the seed crystal wafer was used, and a single crystal obtained by a conventional sublimation recrystallization method without a mask layer. After the growth, the {0001} plane wafer was cut out from the ingot, and the single crystal growth and the {0001} plane wafer cut out were repeated about 19 times, 20 times in total. Then, similarly to the above, a {0001} plane wafer having a thickness of about 1 mm was cut out, and after polishing, the wafer surface was etched with molten KOH and observed under a microscope. As a result, the number of large hexagonal etch pits corresponding to micropipe defects was found. Was about 60 pieces / cm ² over almost the entire surface. That is, in the present invention, a high quality single crystal ingot that cannot be realized by repeating the single crystal growth and the seed crystal wafer slicing step 20 times in total in the conventional method is used in the present invention. It could be realized by single crystal growth.

[0023]

As described above, according to the present invention, the improved Rayleigh method using a seed crystal enables stable production of a large-sized large-sized silicon carbide single crystal having very few micropipe defects. By using such a silicon carbide single crystal wafer, a blue light emitting element having excellent optical characteristics and a high breakdown voltage / environment resistant electronic device having excellent electric characteristics can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an outline of a method for manufacturing a silicon carbide ingot of the present invention.

FIG. 2A is a diagram illustrating an outline of a silicon carbide ingot manufacturing apparatus, and FIG. 2B is a diagram illustrating an example of a pattern of a mask installed on a seed crystal.

FIG. 3 is a diagram for explaining an example of a pattern of a mask installed on a seed crystal in the present invention.

[Explanation of symbols]

11 graphite mask 12 SiC seed crystal 13 Micropipe defect 21 Graphite Lid and Crucible 22 Seed crystal with mask layer 23 High-purity SiC powder for raw materials 24 Water-cooled double quartz tube 25 Graphite felt for heat insulation 26 Vacuum exhaust device Ar gas pipe 27 work coil 28 Mask 29 opening 30 Mask width 31 Width of opening

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masakazu Katsuno             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division (72) Inventor Hirokatsu Yashiro             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division F-term (reference) 4G077 AA02 BE08 DA02 DA19 EA02                       EA03 ED01 HA02 HA06 SA04

Claims (7)

[Claims] 1. A method for producing a silicon carbide single crystal ingot, which comprises a step of growing a silicon carbide single crystal on a seed crystal by a sublimation recrystallization method, the method comprising the steps of:
After forming a mask layer composed of a mask portion and an opening, a silicon carbide single crystal is grown over the mask layer, and a mask portion arranged to include the opening of the mask layer in the middle of the growth. A method of manufacturing a silicon carbide single crystal ingot, which comprises forming a new mask layer containing the above and further continuing the single crystal growth at least once. 2. The silicon carbide single crystal according to claim 1, wherein a projection image obtained when the mask portions included in a plurality of mask layers are projected onto a seed crystal completely shields a crystal growth surface of the seed crystal. A method for manufacturing a crystal ingot. 3. The silicon carbide single crystal ingot according to claim 1, wherein the plurality of mask layers each independently include one or more selected from the group consisting of graphite, tungsten, molybdenum, and tantalum. Manufacturing method. 4. The method for manufacturing a silicon carbide single crystal ingot according to claim 1, wherein the plurality of mask layers each independently have a thickness of 0.1 to 3 mm. 5. The method for manufacturing a silicon carbide single crystal ingot according to claim 1, wherein the plurality of mask portions each independently have a width of 1.0 to 5.0 mm. 6. The mask aperture ratios (aperture area / mask area) of the plurality of mask layers are independently 0.
The method for producing a silicon carbide single crystal ingot according to any one of claims 1 to 5, which is 2 to 2. 7. The silicon carbide single crystal ingot obtained by the manufacturing method according to claim 1, having a diameter of 50 mm or more.