JPH1160389A - Production of silicon carbide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-quality silicon carbide single crystal in bulk state by preventing cracks or warpage produced in a silicon carbide single crystal layer becoming a seed crystal. SOLUTION: Plural grooves 4 crossing one another are formed in a silicon single crystal substrate 3 to divide the surface of the silicon single crystal substrate 3 into plural regions. The silicon carbide single crystal layer 5 is grown on the surface of the silicon single crystal substrate 3, and further, a silicon carbide single crystal 7 is grown on the silicon carbide single crystal layer 5. In this method, by forming the grooves 4 to have such a width that is twice or less than twice of the growing length of the silicon carbide single crystal layer 5 in the parallel direction to the surface of the silicon single crystal substrate 5, the silicon carbide single crystal layer 5 divided by the grooves 4 is joined to form a continuous large-size layer while the silicon carbide single crystal layer 5 grows. Therefore, by forming the silicon carbide single crystal 7 on the large-size silicon carbide single crystal layer 5 above described, the silicon carbide single crystal 7 can be grown into bulk state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a bulk silicon carbide single crystal and a method for producing a silicon carbide single crystal layer serving as a seed crystal for producing a silicon carbide single crystal.

[0002]

2. Description of the Related Art In recent years, a silicon carbide single crystal substrate has been developed as a semiconductor substrate of a high-breakdown-voltage high-power semiconductor device such as a high-breakdown-voltage power transistor or a high-breakdown-voltage diode. An α-type silicon carbide single crystal is used for the silicon carbide single crystal substrate. As a method for producing this α-type silicon carbide single crystal, as disclosed in Japanese Patent Application Laid-Open No. 9-77595, a silicon carbide single crystal layer grown on a silicon wafer is used as a seed crystal by a sublimation recrystallization method. A method of forming an α-type bulk silicon carbide single crystal having a large area equivalent to a silicon wafer on a crystal has been proposed.

[0003]

However, when a silicon carbide single crystal layer is grown on a silicon wafer, there is a difference in physical properties such as thermal expansion coefficient and elastic modulus between the silicon wafer and the silicon carbide single crystal layer. Due to the internal stress generated, cracks and warpage may occur between the silicon wafer and the silicon carbide single crystal layer, so that it is difficult to grow a large-area α-type bulk silicon carbide single crystal with high quality and high yield. It is.

The present invention has been made in view of the above problems, and is intended to manufacture a silicon carbide single crystal capable of obtaining a high quality bulk-like silicon carbide single crystal while preventing cracks and warpage occurring in the silicon carbide single crystal layer. It is a primary object to provide a method. It is a second object of the present invention to provide a silicon carbide single crystal layer serving as a seed crystal for obtaining a high quality bulk silicon carbide single crystal.

[0005]

In order to achieve the above object, the following technical means are employed. According to the first aspect of the present invention, a plurality of grooves (4) are formed in the silicon single crystal substrate (3) in the first step, and the surface of the silicon single crystal substrate (3) is divided into a plurality of regions. In the second step, a silicon carbide single crystal layer (5) is grown on the surface of the silicon single crystal substrate (3), and a silicon carbide single crystal (7) is further grown on the silicon carbide single crystal layer (5). It is characterized by having.

As described above, since the surface of silicon single crystal substrate (3) is divided into a plurality of regions by grooves (4) in the second step, even if silicon carbide single crystal layer (5) is grown. No cracking or warping occurs. Then, a silicon carbide single crystal (7) is grown on the silicon carbide single crystal layer (5) in the third step by using the silicon carbide single crystal layer (5) free of such cracks and warpages. Then, a high quality bulk-like silicon carbide single crystal can be obtained.

According to the second aspect of the present invention, the width (W1) of the groove (4) formed in the silicon single crystal substrate (3) is increased in a direction parallel to the surface of the silicon single crystal substrate (3). It is characterized in that the size is set to be twice or less the growth distance for growing the crystal layer (5). Thus, the width of the groove (4) (W
If the size of 1) is set to be equal to or less than twice the growth distance for growing the silicon carbide single crystal layer (5) in a direction parallel to the surface of the silicon single crystal substrate (3), the silicon carbide single crystal layer (5) Silicon carbide single crystal layer (5) divided by groove (4) when grown
Are joined to form a continuous, large-diameter layer. Therefore, when silicon carbide single crystal (7) is formed on such a large-diameter silicon carbide single crystal layer (5), bulk silicon carbide single crystal (7) can be grown.

According to the third aspect of the present invention, the width (W3) of the groove (4) formed in the silicon single crystal substrate (3) is increased in a direction parallel to the surface of the silicon single crystal substrate (3). It is characterized in that the size is set to be not more than twice the growth distance for growing the crystal (7). Thus, the width of the groove (4) (W
If the size of the silicon carbide single crystal layer (5) is set to be less than twice the growth distance of the silicon carbide single crystal (7) growing in a direction parallel to the surface of the silicon single crystal substrate (3), the silicon carbide single crystal layer (5) will However, when the silicon carbide single crystal (7) grows, the silicon carbide single crystal (7) joins to form a continuously connected large-diameter layer. Therefore, a bulk silicon carbide single crystal (7) can be grown.

According to a fourth aspect of the present invention, the depth (d) of the groove (4) formed in the silicon single crystal substrate (3) is set to a depth not less than the growth thickness of the silicon carbide single crystal (5). It is characterized by doing. As described above, when the depth (d) of the groove (4) is set to be equal to or greater than the thickness of the silicon carbide single crystal layer (5), the silicon carbide single crystal layer (5) can be moved from the bottom of the groove (4). It can be prevented from contacting the growing polycrystalline silicon carbide single crystal.

In a third step, the silicon carbide raw material powder (2) is heated and sublimated in an inert gas atmosphere in a graphite crucible (1) to form a silicon carbide raw material powder (2). ) Lower temperature silicon carbide single crystal layer (5)
It is effective to grow the silicon carbide single crystal (7) on the surface of the substrate because the thickness of the silicon carbide single crystal (7) can be increased.

According to a sixth aspect of the present invention, the growth distance of the silicon carbide single crystal layer (5) on the silicon single crystal substrate (3) in a direction parallel to the surface of the silicon single crystal substrate (3) is twice or less. Forming a plurality of trenches (4) having a width (W1) having a length of to divide the surface of the silicon single crystal substrate (3) into a plurality of regions;
Silicon carbide single crystal layer (5) on the surface of silicon single crystal substrate (3)
Is characterized by growing.

As described above, while dividing the surface of silicon single crystal substrate (3) into a plurality of regions by grooves (4), silicon carbide single crystal layer (5) is formed on the surface of silicon single crystal substrate (3). When formed, the silicon carbide single crystal layer (5) serving as a seed crystal for forming a high quality bulk-like silicon carbide single crystal (7) can be prevented from being generated in the silicon carbide single crystal layer. Can be formed.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows a graphite crucible 1 used in the present embodiment. The graphite crucible 1 sublimes the silicon carbide raw material powder 2 provided in the graphite crucible 1 by heat treatment, and forms a silicon carbide single crystal layer 5 as a seed crystal.
A silicon carbide single crystal 7 is grown thereon.

The graphite crucible 1 includes a crucible body 1a having an open upper surface, and a lid 1b for closing the opening of the crucible body 1a. Then, in this graphite crucible 1, the lid 1b serves as a pedestal for supporting the silicon carbide single crystal layer 5 as a seed crystal. The graphite crucible 1 can be heated by a heater in a vacuum vessel into which an arcon gas can be introduced. By adjusting the power of the heater, the temperature of the silicon carbide single crystal layer 5 as a seed crystal can be reduced. The temperature is maintained at about 100 ° C. lower than the temperature of silicon carbide raw material powder 2.

Next, a method for producing a silicon carbide single crystal is shown in FIG.
A description will be given based on (a) to (f). First, FIG.
As shown in (1), a silicon single crystal substrate (silicon wafer) 3 having a diameter of 4 inches and a (111) plane orientation as a substrate surface is prepared. Then, a resist is formed on the silicon single crystal substrate 3 and the resist is used as a mask material by a reactive ion etching (RIE) apparatus using SF6 gas as shown in FIG. The groove 4 is formed on the surface of. Specifically, the width W1 of the groove 4 is 5 μm,
The depth d is 20 μm, and the interval W2 between the grooves 4 is 5
mm. (See Fig. 3)

Next, as shown in FIG. 2C, a silicon carbide single crystal layer 5 serving as a seed crystal is formed on a silicon single crystal substrate 3 having a groove 4 formed thereon by a chemical vapor phase epitaxy (CVD).
Method). More specifically, a chemical vapor deposition method using a chemical reaction between a carbon supply source gas such as propane and a silicon supply source gas such as silane is used. At this time, silicon carbide single-crystal layer 5 has a thickness t of 20 μm, and silicon carbide single-crystal layer 5 also grows in a direction parallel to the surface of silicon single-crystal substrate 3 (hereinafter, referred to as a substrate parallel direction) and is adjacent thereto. Silicon carbide single crystal layers 5 joined together to form a single
Trench 4 having width W1 is covered with silicon carbide single crystal layer 5 after growth of silicon carbide single crystal layer 5 is completed.

Here, the relationship between the width W1 and the depth d of the groove 4, the distance W2 between the grooves 4, and the thickness t of the silicon carbide single crystal layer 5 to be formed will be described with reference to FIG. As described above, when silicon carbide single-crystal layer 5 grows, silicon carbide single-crystal layer 5 also grows in the direction parallel to the substrate. In order for the groove 4 to be covered with the silicon carbide single crystal layer 5, the sum of the growth (spread) of the silicon carbide single crystal layer 5 on both sides of the groove 4 in the substrate parallel direction is equal to the groove. 4 must be larger than the width W1.

Accordingly, the angle when silicon carbide single crystal layer 5 spreads in the direction parallel to the substrate (the inclination angle of silicon carbide single crystal layer 5 with respect to the normal direction of the surface of silicon carbide single crystal substrate 3)
Is the spread angle θ, the width W1, the depth d, and the interval W2
And the relationship between the film thickness t and the spread angle θ is W1 ≦ 2 · t · tan.
θ must be satisfied. Further, a silicon carbide layer may be deposited also on the bottom surface of groove 4, but since the bottom surface of groove 4 is not uniform, the silicon carbide layer becomes polycrystalline. Therefore, the relationship between the depth d of groove 4 and the thickness t of silicon carbide single crystal layer 5 is set so that d ≧ t so that the layer of polycrystalline silicon carbide does not contact silicon carbide single crystal layer 5. Is preferably satisfied.

In consideration of such conditions, in the present embodiment, the width W1 of the groove 4 is 5 μm, the depth d is 20 μm, and the thickness t of the silicon carbide single crystal layer 5 is 20 μm. Also,
The reason why the interval W2 between the grooves 4 is 5 mm is that the interval between the grooves 4 is
Is reduced, silicon single crystal substrate 3 and silicon carbide single crystal layer 5
Can be reduced, but since a crystal defect occurs at a portion where the silicon carbide single crystal layer 5 is joined at the upper portion of the groove 4, an element manufactured using the silicon carbide single crystal substrate 3 An interval W2 between the grooves 4 larger than the size is set.

Thus, the surface of silicon carbide single crystal layer 5 is continuously connected, and silicon carbide single crystal layer 5 having a large area is obtained. During the growth of silicon carbide single crystal layer 5, silicon carbide single crystal 5 is divided into small areas, and the occurrence of internal stress due to a difference in thermal expansion coefficient from silicon single crystal substrate 3 and the like is reduced. Thus, silicon carbide single crystal layer 5 on silicon single crystal substrate 3 having no surface is obtained.

Thereafter, the silicon single crystal substrate 3 is removed, and FIG.
As shown in (d), the silicon carbide single crystal layer 5 is bonded to the lid 1b of the graphite crucible 1 with an adhesive 6 as shown in FIG.
Is fixed to the lid 1b of the graphite crucible. When fixing silicon carbide single crystal layer 5 to lid 1b of a graphite crucible, a polycrystalline silicon layer or a polycrystalline silicon carbide layer may be formed on silicon carbide single crystal layer 5 to reinforce it.

Further, the lid 1b of the graphite crucible to which the silicon carbide single crystal layer 5 is fixed is disposed in the opening of the graphite crucible body 1a. Then, the pressure in the graphite crucible 1 is set to 1 Torr in an argon gas atmosphere, the temperature of the silicon carbide raw material powder 2 is maintained at 2330 ° C., and the temperature of the silicon carbide single crystal layer 5 as a seed crystal is maintained at 2210 ° C. Silicon carbide single crystal 7 is sublimated and recrystallized on silicon carbide single crystal layer 5.

As a result, as shown in FIG. 2E, a diameter of 4 inches having a diameter substantially equal to the diameter of the silicon single crystal substrate 3 and a thickness of 2 mm were formed on the silicon carbide single crystal layer 5 as a seed crystal.
Silicon carbide single crystal (silicon carbide single crystal ingot) 7 is formed with high yield. Thus, a high-quality large-diameter bulk silicon carbide single crystal ingot can be obtained.
When silicon single crystal substrate 3 has a diameter of 8 to 10 inches, silicon carbide single crystal 7 can have a large diameter of 8 to 10 inches.

Further, as shown in FIG. 2 (f), the silicon carbide single crystal (silicon carbide single crystal ingot) 7 is removed from the lid 1b of the graphite crucible, and the obtained crystal is sliced.
The semiconductor substrate is completed by polishing. The crystal plane orientation and the crystal structure (polymorphism) of this substrate were determined by X-ray diffraction and Raman spectroscopy.
It was confirmed that it had an H-type (0001) plane orientation.

Using the substrate thus completed, a semiconductor device such as a vertical MOSFET, a pn diode, and a Schottky diode for high power can be manufactured. In this embodiment, the width W1 of the groove 4 is 5 μm, the depth d is 20 μm, and the thickness t of the silicon carbide single crystal layer 5 is 20 μm. However, the width W1, the depth d, the thickness t, and the spread angle If .theta. satisfies the above-described relationship, other values can be selected. (Second Embodiment) In the first embodiment, a large area silicon carbide single crystal layer 5 is formed by joining silicon carbide single crystal layer 5 at the upper part of groove 4, and is formed on silicon carbide single crystal layer 5. Although a large-area silicon carbide single crystal 7 is formed, in the present embodiment, a large-area silicon carbide single crystal 7 can be formed even when silicon carbide single-crystal layer 5 is not joined. That is, in the present embodiment, the grooves 14 formed in the silicon single crystal substrate 3
Is determined so that the silicon carbide single crystal 7 can be joined at the upper portion of the groove 14.

FIG. 5 shows a method for producing a silicon carbide single crystal.
A description will be given based on (a) to (f). FIG. 5 (a),
As shown in (b), a silicon single crystal substrate 3 is prepared, and lattice-shaped grooves 14 are formed on the surface of the silicon single crystal substrate 3.
Next, as shown in FIG. 5C, a silicon carbide single crystal layer 5 serving as a seed crystal is grown on silicon single crystal substrate 3. At this time, since width W3 of groove 14 is wider than growth of silicon carbide single crystal layer 5 in the direction parallel to the substrate, silicon carbide single crystal layer 5
The groove 14 is not joined at the upper part of the groove 4 and is not covered with the silicon carbide single crystal layer 5.

Then, the silicon single crystal substrate 3 is removed, and FIG.
As shown in (d), the silicon carbide single crystal layer 5 is joined to the lid 1b of the graphite crucible 1, and the silicon carbide single crystal layer 5 is fixed to the lid 1b of the graphite crucible. Thereafter, silicon carbide single crystal 7 is sublimated and recrystallized on silicon carbide single crystal layer 5 by the same sublimation recrystallization method as in the first embodiment. At this time, silicon carbide single crystal 7 also grows in the direction parallel to the substrate, and silicon carbide single crystal 7 is joined at the upper portion of groove 14 to have a large diameter.
As described above, even when silicon carbide single crystal 7 is bonded to the upper portion of groove 14 by growing silicon carbide single crystal 7 in the direction parallel to the substrate, high-quality large-diameter silicon carbide single crystal 7 with high yield can be obtained. be able to.

Specifically, as shown in FIG. 6, the width W3 of groove 14 is set to the angle (in relation to the normal direction of the surface of silicon carbide single crystal substrate 3) when silicon carbide single crystal 7 spreads in the direction parallel to the substrate. Assuming that the angle of inclination of the silicon carbide single crystal 7) is the spread angle φ, the relationship between the thickness T of the silicon carbide single crystal 7 and the spread angle φ of the silicon carbide single crystal 7 satisfies W3 ≦ 2 · T · tan φ. Then, large-diameter silicon carbide single crystal 7 can be obtained.

At this time, since polycrystalline silicon carbide grows from the lid 1b of the graphite crucible below the void existing between the silicon carbide single crystal layers 5 divided into small areas, the polycrystalline silicon carbide is divided into small areas. If groove 24 is formed in lid 1b of graphite crucible below the gap existing between silicon carbide single crystal layers 5 thus formed, polycrystalline silicon carbide does not contact silicon carbide single crystal 7 on which silicon carbide has grown. , A high quality silicon carbide single crystal 7 can be grown.

Therefore, the width of the groove 24 formed in the lid 1b of the graphite crucible is limited to the width of the groove 2 formed in the silicon single crystal substrate 3.
4 and the depth D of the groove 24 is D ≧ W3 /
A value that satisfies the relationship of 2.tanφ is preferable. (Other Embodiments) In the first and second embodiments, the powdered silicon carbide raw material powder 2 is used as the silicon carbide raw material, but other forms such as a sintered body are used instead of the powder as the silicon carbide raw material. May be used.

Further, in the first and second embodiments, the silicon carbide single crystal is formed by the sublimation recrystallization method, but may be formed by other methods. That is, the source gas to be supplied is not limited to a sublimation gas generated by a method of sublimating a material to be a single crystal by heating and sublimation (sublimation method), and may be a gas of a raw material to be a single crystal adjusted by a method other than the sublimation method. However, when a silicon carbide single crystal is formed by the sublimation recrystallization method, it is preferable to form the silicon carbide single crystal using the sublimation recrystallization method because the silicon carbide single crystal is easily grown.

Although a crucible made of graphite is used, a material other than graphite, such as a refractory metal such as tungsten or tantalum, may be used as the material of the crucible.

[Brief description of the drawings]

FIG. 1 is a schematic view of a graphite crucible used in an embodiment of the present invention.

FIG. 2 is a cross sectional view for illustrating a manufacturing process of a silicon carbide single crystal.

FIG. 3 is a top view of the silicon single crystal substrate 3.

FIG. 4 is a schematic diagram for describing bonding conditions for silicon carbide single crystal 5;

FIG. 5 is a cross-sectional view for illustrating a manufacturing process of a silicon carbide single crystal in a second embodiment.

FIG. 6 is a schematic diagram for explaining bonding conditions for silicon carbide single crystal 7;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Graphite crucible, 1a ... Crucible body, 1b ... Lid member,
2 ... silicon carbide raw material powder, 3 ... silicon single crystal substrate, 4 ... groove,
5 ... silicon carbide single crystal layer, 7 ... silicon carbide single crystal, 14 ...
Groove, W1, W3: groove width, d: groove depth, t: film thickness of silicon carbide single crystal layer, T: thickness of silicon carbide single crystal.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Shoichi Onda 1-1-1, Showa-cho, Kariya-shi, Aichi Pref.

Claims (6)

[Claims] 1. A silicon single crystal substrate (3) is prepared, a plurality of grooves (4) intersecting the silicon single crystal substrate (3) are formed, and the surface of the silicon single crystal substrate (3) is formed by a plurality of grooves. A first step of dividing the silicon carbide single crystal layer (5) on the surface of the silicon single crystal substrate (3); and a seed crystal of the silicon carbide single crystal layer (5). A third step of growing a bulk silicon carbide single crystal (7) on the silicon carbide single crystal layer (5). 2. A silicon single crystal substrate (3) in the first step.
The silicon carbide single crystal layer (5) formed in the second step grows in a direction parallel to the surface of the silicon single crystal substrate (3). The method for producing a silicon carbide single crystal according to claim 1, wherein the size is set to be twice or less the growth distance. 3. A single crystal silicon substrate (3) in the first step.
The width (W3) of the groove (4) to be formed in the growth is such that the silicon carbide single crystal (7) formed in the third step grows in a direction parallel to the surface of the silicon carbide single crystal layer (5). 2. The method for producing a silicon carbide single crystal according to claim 1, wherein the size is not more than twice the distance. 4. A single crystal silicon substrate (3) in said first step.
3. The method of manufacturing a silicon carbide single crystal according to claim 2, wherein a depth (d) of the groove (4) formed in the silicon carbide single crystal layer is made deeper than a growth thickness of the silicon carbide single crystal layer (5). 5. In the third step, the silicon carbide raw material powder (15) is heated and sublimated in an inert gas atmosphere in the graphite crucible (1), and the silicon carbide raw material powder (2) is heated.
5. The silicon carbide according to claim 1, wherein the silicon carbide single crystal is grown on a surface of the silicon carbide single crystal layer at a lower temperature. 6. Single crystal production method. 6. A method for growing a silicon carbide single crystal layer (5) as a seed crystal for forming a silicon carbide single crystal (7) on a surface of a silicon single crystal substrate (3), comprising: A plurality of grooves (4) having a width of not more than twice the growth distance for growing the silicon carbide single crystal layer (5) in a direction parallel to the surface of the crystal substrate (3) are formed in the silicon single crystal substrate (3). Forming a surface of the silicon single crystal substrate (3) and dividing the surface of the silicon single crystal substrate (3) into a plurality of regions.