JP7005122B6 - SiC seeds and SiC ingots - Google Patents

Description

The present invention relates to SiC seeds and SiC ingots .

Silicon carbide (SiC) has excellent properties such as a dielectric breakdown field one order of magnitude larger, a band gap three times larger, and a thermal conductivity about three times higher than silicon (Si). Therefore, SiC is expected to be applied to power devices, high-frequency devices, high-temperature operation devices, and the like. In recent years, SiC wafers have come to be used in semiconductor devices such as those described above.

A SiC epitaxial wafer uses a SiC wafer processed from an SiC ingot as a substrate on which a SiC epitaxial film is formed, and the active region of a SiC semiconductor device is usually formed thereon by chemical vapor deposition (CVD). Manufactured by growing a SiC epitaxial film.

Further, SiC ingots are obtained by growing SiC seeds. SiC ingots are required to be of high quality with few defects and heterogeneous polymorphisms, and SiC seeds that serve as growth starting points are required to be capable of controlling defects and heterogeneous polymorphisms.

Previously, there were countless dislocations such as threading screw dislocations, threading edge dislocations, basal plane dislocations, etc. of 10 ⁴ or more per cm ² . The main challenge was to eliminate these micropipes, which are killer defects. However, with recent technological improvements, it has become possible to fabricate SiC wafers that have almost no micropipes and have less than 10 ⁴ dislocations/cm ² . In particular, regarding screw dislocations, by performing crystal growth using seeds prepared by a method such as RAF (repeated a-face method), which repeats a-plane growth, SiC wafers with a screw dislocation density of 10 pieces/cm2 ^or less can be grown. It has also been confirmed that the following can be obtained (Non-Patent Document 1). However, due to the extremely low screw dislocation density, another problem has arisen: generation of different polymorphisms.

Polymorphism means a difference in the crystal structure of SiC. SiC has polymorphisms such as 3C-SiC, 4H-SiC, and 6H-SiC. There is no difference in the outermost surface structure of these polymorphs when viewed from the c-plane direction (<0001> direction). Therefore, there is a problem that the crystal changes to a different polymorph (heterogeneous polymorph) during crystal growth in the c-plane direction.
On the other hand, the polymorphs have different outermost surface structures when viewed from the a-plane direction (<11-20> direction). Therefore, such polymorphic differences can be inherited during growth in the a-plane direction. That is, in growth in the a-plane direction, heterogeneous polymorphism is less likely to occur.

Therefore, the growth plane is made slightly deviated from the c-plane to suppress the occurrence of heterogeneous polymorphism. By shifting the growth plane from the c-plane, lateral growth (step-flow growth) from atomic steps (steps in the atomic plane) occurs, and polymorphism is preserved.
However, as the crystal grows, a plane parallel to the c-plane always appears on a part of the outermost surface of the crystal. The part that is parallel to the c-plane and exposed on the growth plane is called the c-plane facet. Since the c-plane facet is parallel to the c-plane, the crystal growth mode is different. Within the SiC single crystal after growth, the portions grown in different growth modes are referred to as facet growth regions.

Crystal growth on the c-plane facet is crystal growth in the c-plane direction. Therefore, when crystal growth is performed on a SiC single crystal having an extremely low screw dislocation density as described above, island-like growth occurs, and polymorphism cannot be inherited, resulting in generation of different polymorphisms.
On the other hand, if a screw dislocation exists in the c-plane facet, or if there is a starting point for the occurrence of a screw dislocation that is converted into a screw dislocation immediately after growth, screw growth occurs with the screw dislocation as the starting point. In helical growth, since the helical part forms a step, growth in the a-plane direction is possible and polymorphism can be inherited.
That is, in order to maintain the polymorphism, the c-plane facet requires a certain amount of screw dislocation or a screw dislocation origin, and a method for this purpose is required.

For example, in Patent Document 1, SiC is grown using a dislocation control seed crystal that has a plane within an offset angle of 60 degrees from the {0001} plane as a growth plane and has a region where screw dislocations can occur on the growth plane. A method for producing silicon carbide single crystals is disclosed.
By using the method for manufacturing a silicon carbide single crystal using a dislocation-controlled seed crystal having a screw dislocation generating region described in Patent Document 1, screw dislocations can be reliably formed within the c-plane facet, and heterogeneous polymorphism can be formed. It is possible to suppress the formation of crystals with different orientations.

Further, Patent Document 2 describes that the growth end face of the seed crystal has a convex shape with a predetermined curvature to form a c-plane facet region that performs spiral growth during the growth process.

Japanese Patent Application Publication No. 2004-323348 Patent No. 5171571

Yasushi Urakami et al. , Materials Science Forum (2012), 717-720, 9

However, the methods described in Patent Document 1 and Patent Document 2 cannot solve the following three problems. The first problem is that ``the generation of heterogeneous polymorphism cannot be sufficiently suppressed when crystal growth is performed using seeds with extremely low screw dislocation density'', and the second problem is that ``the introduced screw dislocations The third problem is that "heterogeneous polymorphism cannot be sufficiently suppressed when growing into long lengths with the aim of lowering costs." It is.

In the methods described in Patent Document 1 and Patent Document 2, it is considered that screw dislocations cannot be reliably inserted into the facet growth region formed at the initial stage of growth, and the area of the facet growth region where heterogeneous polymorphism may occur is An attempt was made to prevent heterogeneous polymorphism in the early stages of growth by making it as small as possible (points or lines). In this case, if no heterogeneous polymorphism occurs before the facet growth region gradually expands and screw dislocations are introduced, growth without heterogeneous polymorphism can be achieved. However, heterogeneous polymorphism inevitably occurs with a certain probability at the very early stages of growth. That is, the first problem mentioned above cannot be solved.

As a countermeasure to the first problem, it is conceivable to introduce screw dislocations at an extremely high density (several thousand pieces/cm ² or more) into the facet growth region. If a high density of screw dislocations is introduced, the probability of occurrence of heterogeneous polymorphism at the early stage of growth can be reduced. However, when high-density screw dislocations are introduced, the dislocations flow downstream of the offset, creating a large number of defects. That is, the second problem mentioned above occurs.

Furthermore, in order to simultaneously solve the first problem and the second problem, it is also possible to find an optimal density of screw dislocations to be introduced into the c-plane facet. However, even if the optimum density is found, there is a third problem that it cannot cope with the increase in the length of the SiC ingot. As the crystal growth progresses, screw dislocations of opposite signs attract each other and combine and disappear or are converted into defects in the basal plane, so the density of screw dislocations decreases as the crystal grows. That is, even if the screw dislocation density at the early stage of growth is optimal, the problem arises that the screw dislocation density is insufficient in the latter half of growth, resulting in heterogeneous polymorphism. On the other hand, if the screw dislocation density is set to the optimum condition in the latter half of growth, the screw dislocation density in the early stage of growth will be too high, resulting in the second problem.

As described above, these three problems are in a trade-off relationship with each other, and there is a problem that they cannot all be satisfied at the same time.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a SiC seed, a SiC ingot, and a SiC wafer that can solve the three problems at the same time.

The present inventors paid attention to the fact that when manufacturing a semiconductor device from a SiC wafer, the SiC wafer is divided into chips. They have also discovered that by introducing screw dislocations along the dicing lines when cutting into chips, the substantial quality within the semiconductor device obtained after cutting can be improved.
That is, the present invention provides the following means to solve the above problems.

(1) The SiC seed according to one aspect of the present invention includes an initial facet formation surface whose inclination angle θ with respect to the {0001} plane is less than 2° in any direction, and at least the initial facet formation surface has a first facet formation surface. It has a first screw dislocation generation line extending in the direction of.

(2) The SiC seed described in (1) above may further include a main surface having an offset angle of 2° or more and 20° or less with respect to the {0001} plane.

(3) In the SiC seed according to any one of (1) or (2) above, there are a plurality of first screw dislocation generation lines, and the plurality of first screw dislocation generation lines are arranged periodically at predetermined intervals. They may be arranged in a straight line.

(4) In the SiC seed according to any one of (1) to (3) above, the first direction is parallel to the {1-100} plane or parallel to the {11-20} plane. It may be in either direction.

(5) In the SiC seed according to any one of (1) to (4) above, the initial facet formation surface has a second screw dislocation extending in a second direction intersecting the first direction. It may further include a generation line.

(6) In the SiC seed described in (5) above, the second direction may be orthogonal to the first direction.

(7) In the SiC seed according to any one of (5) or (6) above, there are a plurality of second screw dislocation generation lines, and the plurality of second screw dislocation generation lines are arranged periodically at predetermined intervals. They may be arranged in a straight line.

(8) In the SiC seed according to any one of (1) to (7) above, the area ratio occupied by the first screw dislocation generation line and/or the second screw dislocation generation line is 50% or less. It may be.

(9) A SiC ingot according to one aspect of the present invention includes the SiC seed according to any one of (1) to (8) above, and a growth portion grown on the SiC single crystal seed, The growth portion has a facet growth region extending from the initial facet formation surface of the SiC seed over the entire growth direction, and the facet growth region extends from the first screw dislocation generation line in the SiC growth direction. It has a first screw dislocation dense region.

(10) In the SiC ingot according to (9) above, the SiC seed has a second screw dislocation generation line extending in a second direction intersecting the first direction, and the facet growth region , a second screw dislocation dense region may be provided extending from the second screw dislocation generation region in the SiC growth direction.

(11) In the SiC ingot according to any one of (9) or (10) above, the c-plane facet on the outermost surface of the facet growth region and the initial facet formation surface of the SiC seed are the same as the c-plane facet. When viewed in plan from a direction perpendicular to the plane, at least a portion thereof may overlap.

(12) In the SiC ingot according to any one of (9) to (11) above, the thickness of the growth portion in the c-axis direction may be 30 mm or more.

(13) The SiC wafer according to one aspect of the present invention has facet growth scars in at least a portion thereof, and the facet growth scars have first dense screw dislocation lines extending in a first direction.

(14) In the SiC wafer according to (13) above, there may be a plurality of the first dense screw dislocation lines, and the plurality of first dense screw dislocation lines may be arranged periodically at predetermined intervals. good.

(15) In the SiC wafer according to any one of (13) or (14) above, the first direction is a direction parallel to the {1-100} plane or a direction parallel to the {11-20} plane. There may be.

(16) In the SiC wafer according to any one of (13) to (15) above, the facet growth traces have a second screw dislocation density extending in a second direction intersecting the first direction. It may further include a line.

(17) In the SiC wafer according to (16) above, the second direction may be orthogonal to the first direction.

(18) In the SiC wafer according to any one of (16) or (17) above, there is a plurality of the second dense screw dislocation lines, and the plurality of second dense screw dislocation lines are arranged periodically at predetermined intervals. They may be arranged in a straight line.

(19) In the SiC wafer according to any one of (13) to (18) above, the area ratio occupied by the first screw dislocation dense line and/or the second screw dislocation dense line is 50% or less. It may be.

(20) In the SiC wafer according to any one of (13) to (19) above, a dicing planned area, a device fabrication area surrounded by the dicing planned area, and a dicing planned area and the device fabrication area at least a portion of the region to be diced coincides with the first screw dislocation dense line, and the outer peripheral region has a higher screw dislocation density than the device fabrication region. good.

(21) A semiconductor device according to one aspect of the present invention has an active region that is driven as a device, and an outer peripheral region surrounding the active region, and the screw dislocation density of the outer peripheral region is higher than the screw dislocation density of the active region. It's also big.

(22) A method for manufacturing a semiconductor device according to one aspect of the present invention includes the steps of preparing the SiC wafer according to any one of (13) to (20) above, and performing a first screw dislocation in the SiC wafer. dividing the SiC wafer along the dense line and/or the second dense screw dislocation line.

The SiC seed according to one aspect of the present invention has a screw dislocation generation line at a predetermined position. Therefore, a SiC wafer having dense screw dislocation lines at predetermined positions can be obtained. By performing dicing along the screw dislocation dense lines of this SiC wafer, it is possible to obtain semiconductor devices with a low abundance of defects and heterogeneous polymorphisms.

FIG. 1 is a schematic plan view of a portion of a SiC seed according to one embodiment of the present invention. This is a cut surface of a part of the SiC seed in FIG. 1 taken along the A-A' plane. FIG. 2 is an enlarged plan view of a part of the SiC seed according to one embodiment of the present invention, and is a schematic diagram showing the inclination direction and inclination angle θ of the main surface and the initial facet formation surface with respect to the {0001} plane. It schematically shows a cross section of a SiC ingot grown from SiC seeds, and also shows an enlarged photograph of the interface between the step flow growth region and the facet growth region. FIG. 3 is a schematic plan view and a schematic three-dimensional view before and after producing an initial facet formation surface of a SiC seed according to one embodiment of the present invention. (a) is a diagram schematically showing step flow growth, (b) is a diagram schematically showing facet growth, and (c) is a diagram schematically showing facet growth when screw dislocation is present. This is a diagram. FIG. 3 is a diagram schematically showing the state before and after the growth of a SiC ingot grown from a SiC seed, and (a) is a diagram schematically showing a cross section of a facet growth region where crystals have grown from the facet formation surface of the SiC sheet. , (b) is a schematic plan view in which a part of the initial facet formation surface is enlarged, and (c) is a schematic plan view in which a part of the c-plane facet is enlarged. FIG. 3 is a schematic plan view of a portion of a modified example of the SiC seed according to one aspect of the present invention. FIG. 3 is a schematic plan view of a portion of a modified example of the SiC seed according to one aspect of the present invention. FIG. 3 is a schematic plan view of a portion of a modified example of the SiC seed according to one aspect of the present invention. 1 is a diagram schematically showing a cross section of a part of a SiC ingot according to one embodiment of the present invention. 12 is a diagram schematically showing the vicinity of the facet growth region of a cut surface of the SiC ingot taken along the B-B' plane in FIG. 11. FIG. FIG. 1 is a schematic plan view of a SiC wafer according to one embodiment of the present invention. FIG. 1 is a schematic plan view enlarging a portion of a SiC wafer according to one embodiment of the present invention.

Hereinafter, one embodiment of the present invention will be described in detail with appropriate reference to the drawings.
In the drawings used in the following explanation, characteristic parts of the present invention may be shown enlarged for convenience in order to make it easier to understand, and the dimensional ratio of each component may differ from the actual one. be. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be practiced with appropriate changes within the scope of the invention.

[SiC seed]
FIG. 1 is a schematic plan view of a portion of a SiC seed according to one embodiment of the present invention. FIG. 2 is a cross section of a part of the SiC seed shown in FIG. 1 taken along the AA' plane. FIG. 1 shows only a certain area circled around the initial facet forming surface 20. As shown in FIG.

SiC seed 100 has a main surface 10 and an initial facet formation surface 20. Further, a sub-growth surface 30 may be provided which is cut out to form the initial facet forming surface 20. The main surface 10 has an offset angle of 2° or more and 20° or less with respect to the {0001} plane. The initial facet forming surface 20 has an inclination angle θ of less than 2° in absolute value with respect to the {0001} plane in any direction. A screw dislocation generation line 21 is formed on the initial facet forming surface 20 . The screw dislocation generation line 21 consists of a first screw dislocation generation line 21a extending in a first direction and a second screw dislocation generation line 21b orthogonal to the first direction.

Here, the "screw dislocation generation line" means a region where a plurality of screw dislocation generation starting points exist in a line. Further, the term "screw dislocation originating point" refers to an originating point that can become a screw dislocation in the process of crystal growth. For example, screw dislocations that originally exist in the SiC seed are threading dislocations that are inherited as they are in the c-plane direction, and therefore are normally inherited as they are in the growing crystal. Therefore, the screw dislocation that is present in the SiC seed from the beginning is the origin of screw dislocation generation.

Screw dislocation starting points can also be artificially created by subjecting the surface of the SiC seed to some kind of treatment. For example, if a layer with a disordered crystal structure is created on the surface by machining, ion implantation, etc., screw dislocations will occur there during the growth process. This is because, in order for a layer with a well-ordered crystal structure to grow on a layer with a disordered crystal structure, the disorder must be absorbed in some way. For example, disturbances in the <0001> direction parallel to the growth direction can occur in screw dislocations, micropipes, Frank-type stacking faults, etc. that have Burgers vectors parallel to <0001>, and in the <11-20> direction perpendicular to the growth direction. It is thought that disturbances in the <1-100> and <1-100> directions are absorbed by being converted into threading edge dislocations, basal plane dislocations, Shockley-type stacking faults, etc. that have Burgers vectors in those directions.

Furthermore, in the following, "offset upstream side" means the side that is the starting point of step flow growth. To give a specific example, the −X direction in FIG. 1 corresponds to the offset upstream side, and the +X direction corresponds to the offset downstream side.

(main surface)
The main surface 10 is a surface having an offset angle of 2° or more and 20° or less with respect to the {0001} plane. That is, as shown by the dashed line in FIG. 2, the {0001} plane has an inclination with respect to the main surface 10. Therefore, when the SiC seed 100 is crystal-grown in the +Z direction in FIG. 2, the main surface 10 can undergo step-flow growth.

The offset angle of the main surface 10 with respect to the {0001} plane is 2° or more and 20° or less, and preferably 3° or more and 9° or less. If the offset angle is too small, it will be difficult for defects to flow downstream of the offset. If the defects do not flow offset downstream (in the +X direction in FIG. 2) and remain at the same location, there is a problem that the defects are difficult to reduce during growth. Furthermore, if the offset angle is too small, there is also the problem that facets will occur in unexpected locations when a slight deviation occurs in the growth shape. In facet growth areas, the risk of developing heterogeneous polymorphisms increases.
On the other hand, if the offset angle is too large, there is a problem that stress is applied in the direction in which the c-plane slides (direction parallel to the {0001} plane) due to the temperature gradient, making basal plane dislocation more likely to occur. Moreover, the difference from the offset angle of a SiC wafer (usually 4° or less) used when manufacturing semiconductor devices and the like becomes large. Therefore, it is necessary to cut the SiC wafer diagonally from the SiC ingot, and the number of SiC wafers obtained is reduced.

Here, the SiC seed itself becomes a nucleus and crystal grows to produce a SiC ingot. Therefore, it is necessary to consider the state of crystal growth in the SiC seed. As briefly explained above, "facet" and "facet growth region" refer to a surface and a portion formed when a SiC seed grows a crystal. More precisely, a "facet" is a crystal surface that is flat on an atomic scale in accordance with the geometric regularity of the crystal, and is a surface that appears as a flat surface due to differences in the growth mechanism during crystal growth. means. For example, a {0001} plane facet (c-plane facet) is a plane parallel to the {0001} plane, and appears as a plane during crystal growth. Moreover, the "facet growth region" refers to a region consisting of an aggregate of portions in which facets are formed on the outermost surface of a SiC ingot in the growth process. The facet growth region has a different impurity concentration than other regions that undergo step-flow growth due to the difference in the growth mechanism. Therefore, the facet growth region can also be determined from the crystal after growth.

(Sub-growth surface, initial facet formation surface)
"Sub-growth surface" refers to the surface facing the growth direction excluding the main surface with the widest area. The "initial facet formation surface" is an example of a sub-growth surface, and has an inclination angle θ of less than 2° in absolute value with respect to the {0001} plane in any direction. The sub-growth surfaces 30 other than the initial facet forming surface 20 are not essential.

Here, the fact that "the inclination angle θ with respect to the {0001} plane is less than 2 degrees in absolute value in any direction" will be explained. FIG. 3 is an enlarged plan view of a part of the SiC seed according to one embodiment of the present invention, and is a schematic diagram showing the inclination direction and the inclination angle θ of the main surface and the initial facet formation surface with respect to the {0001} plane. .

The direction in which the initial facet formation surface 20 is inclined with respect to the {0001} plane may be any direction as shown by the arrow in FIG. 3(a). For example, FIG. 3(b) shows the case where the initial facet formation surface is inclined with respect to the {0001} plane in the ±X direction of FIG. 3(a), and FIG. 3(c) shows the case where the initial facet formation surface is inclined with respect to the FIG. 6 is a diagram schematically showing a case where the initial facet formation surface is inclined with respect to the {0001} plane in the Y direction. The inclination angle θ means the internal angle at which the {0001} plane and the initial facet formation surface 20 intersect, as shown in FIGS. 3(b) and 3(c).
When the initial facet formation surface 20 is substantially parallel to the {0001} plane, crystal growth directly above the initial facet formation surface 20 cannot be step-flow growth, and facets are formed. The inside of the initial facet forming surface may be a curved surface or an uneven surface as long as the inclination angle θ with respect to the {0001} plane is less than 2° in absolute value in any direction. By having the initial facet formation surface 20, the position where the facets are formed can be controlled.

For example, when the SiC seed has a rectangular parallelepiped shape and does not have an initial facet formation surface, the following problem occurs when crystal growth is performed on the SiC seed. When the SiC seed has a rectangular parallelepiped shape, a facet is formed near the most upstream corner of the offset (in the -X direction of the SiC seed). This is because step flow growth is performed except near the most upstream corner of the offset. When facets are formed at points such as the corners mentioned above, it is difficult to keep the position where the facets are formed constant regardless of the growth state, and the position where the facets are formed may shift as the facets grow. be. That is, without an initial facet forming surface, the position where the facets are formed cannot be sufficiently controlled.

Next, it will be explained that if the initial facet formation surface 20 has an inclination angle θ of less than 2° in absolute value with respect to the {0001} plane in any direction, a facet is formed directly above the initial facet formation surface 20.

FIG. 4 schematically shows a cross section of a SiC ingot 200 crystal-grown from a SiC seed 100, and also shows an enlarged photograph of the interface between the step-flow growth region 220 and the facet growth region 210. The facet growth region 210 is a shaded area in the drawing, and the step-flow growth region 220 is the other portion.

The SiC ingot 200 is obtained by crystal growth in the +Z direction using the SiC seed 100 as a seed. The facet growth region 210 is different from the step-flow growth region 220 in its growth mechanism and has a different impurity concentration. Therefore, as shown in the enlarged photograph of FIG. 4, the facet growth region 210 and the step-flow growth region 220 can be distinguished from the photograph. In FIG. 4, interfaces with different colors that appear in directions (±X direction) substantially perpendicular to the crystal growth direction (+Z direction) are growth interfaces 210a and 220a at a certain time formed by changing the flow rate of N ₂ , which is an impurity. It is. Generally, the growth interface 210a of the facet growth region is linear, and the growth interface 220a of the step-flow growth region is curved.

Here, attention is paid to the boundary between the growth interface 210a of the facet growth region 210 and the growth interface 220a of the step-flow growth region 220. The growth interface 210a of the facet growth region 210 and the growth interface 220a of the step-flow growth region 220 are bent at the boundary. That is, the extension line of the growth interface 210a of the facet growth region 210 and the growth interface 220a of the step-flow growth region 220 intersect with each other at an angle φ. The facet growth region 210 has a facet on the outermost surface of the SiC ingot during the growth process as described above. That is, the growth interface 210a of the facet growth region 210 corresponds to the outermost surface of the SiC ingot during the growth process, and is therefore parallel to the {0001} plane.

Therefore, it can be said in other words that the growth interface 220a of the step-flow growth region 220 is deviated from the {0001} plane by an angle φ. In other words, in a region deviated from the {0001} plane by an angle φ or more, the crystal growth is step-flow growth. Considering this from the opposite perspective, it shows that a region where the angular deviation from the {0001} plane is less than φ in absolute value grows while forming a facet. As shown in FIG. 4, this angle φ is 2° at the maximum when the cross section of the SiC ingot 200 after crystal growth is checked. Therefore, if the initial facet formation surface 20 has an angular deviation of less than 2 degrees in absolute value from the {0001} plane in any direction, a facet will be formed directly above it. In other words, by providing the initial facet forming surface 20 with an inclination angle θ of less than 2 degrees in absolute value in any direction with respect to the {0001} plane, the initial facet forming surface 20 is Facets can be formed directly above.

The initial facet forming surface 20 is a top surface obtained by cutting out a portion of the top of the SiC single crystal.
FIG. 5 is a schematic plan view and a schematic three-dimensional view before and after producing the initial facet formation surface of the SiC seed according to one embodiment of the present invention. In FIGS. 5(a) to 5(d), the upper side of the figure is a schematic plan view, and the lower side of the figure is a schematic three-dimensional view. The left side of the figure is before the initial facet forming surface is produced, and the right side of the figure is after the initial facet forming surface is produced.

For example, as shown in FIG. 5(a), two adjacent corners of a rectangular SiC seed are cut out, and the top formed by the two sub-growth surfaces 30 and the main surface 10 formed by the cutouts is cut out. The initial facet forming surface 20A may be created by cutting out substantially parallel to the {0001} plane.

Alternatively, the initial facet forming surface 20 may be prepared as shown in FIGS. 5(b) to 5(d). In FIG. 5(b), after processing the SiC seed into a conical shape, the top portion of the seed is further cut out substantially parallel to the {0001} plane, thereby producing an initial facet forming surface 20B.

In FIG. 5(c), a corner of a rectangular SiC seed is cut out, and the corner formed by one sub-growth surface 30 formed by this cut and the main surface 10 is made approximately parallel to the {0001} plane. The initial facet forming surface 20C is created by cutting out.

In FIG. 5(d), the initial facet formation surface 20D is created by cutting out the corner formed by the main surface 10 of a rectangular SiC seed and the seed side surface approximately parallel to the {0001} plane. .

(Screw dislocation generation line)
The screw dislocation generation line 21 means a region where a plurality of screw dislocation generation starting points exist in a line. In FIG. 1, the screw dislocation generation line 21 includes a first screw dislocation generation line 21a extending in a first direction and a second screw dislocation generation line 21a extending in a second direction orthogonal to the first direction. 21b is illustrated.

When the initial facet formation surface 20 has a screw dislocation generation line, when crystal growth is performed using the SiC seed 100, it is possible to suppress the generation of defects inside the crystal due to outflow of different polymorphs and crystal dislocations. I can do it.

Here, we will explain the difference in crystal growth using FIG. 6, and at the same time explain that by having the screw dislocation origin 22, it is possible to suppress the generation of heterogeneous polymorphism and the generation of defects due to the outflow of crystal dislocations. do.

FIG. 6(a) is a diagram schematically showing step flow growth, (b) is a diagram schematically showing facet growth, and (c) is a diagram schematically showing facet growth in the case of having a screw dislocation. FIG. The dotted line in FIG. 6 indicates the {0001} plane. That is, the crystal growth surface (+Z side surface of SiC seed 100) in FIG. 6A has an offset angle with respect to the {0001} plane and corresponds to main surface 10. On the other hand, the crystal growth plane (the +Z side plane of the SiC seed 100) in FIGS. 6(b) and 6(c) is parallel to the {0001} plane and corresponds to the initial facet formation plane 20.

SiC has polymorphisms such as 3C-SiC, 4H-SiC, and 6H-SiC, and these polymorphisms have the same outermost surface structure when viewed from the c-plane direction (<0001> direction). . Therefore, during crystal growth in the c-plane direction, it tends to change into different polymorphs (heterogeneous polymorphs). On the other hand, the outermost surface structure when viewed from the a-plane direction (<11-20> direction) has a difference, and growth in the a-plane direction cannot inherit such polymorphic differences. can.
As shown in FIG. 6A, in the step flow growth, the SiC seed 100 as a whole grows in the +Z direction while the crystal grows in the a-plane direction. That is, since crystal growth is performed while inheriting information from the a-plane, differences in polymorphism can be inherited. On the other hand, as shown in FIG. 6B, when the crystal growth plane is parallel to the {0001} plane, the SiC seed 100 as a whole grows in the +Z direction while the crystal grows in an island shape in the c-plane direction. Since polymorphic information cannot be obtained from the c-plane, differences in polymorphism cannot be inherited, and different polymorphisms occur.

On the other hand, FIG. 6(c) has screw dislocations 23 on the crystal growth plane. In FIG. 6(c), if there is no screw dislocation 23, island-like growth occurs as in FIG. 6(b), so the generation of heterogeneous polymorphism cannot be suppressed. However, when the screw dislocation 23 is present, the spiral portion of the screw dislocation 23 forms a step, which allows growth in the a-plane direction and allows the polymorphism to be inherited. In FIG. 6(c), the explanation was given using the screw dislocation 23 which is an example of the screw dislocation originating point 22, but even if there is a screw dislocation originating point 22 other than the screw dislocation 23, the screw dislocation originating point 22 will be generated immediately after crystal growth. The same can be said for creating a screw dislocation 23. Furthermore, since the screw dislocation generation line is a collection of screw dislocation generation points, the same can be said of the screw dislocation generation line.

Next, it will be explained that the screw dislocation generation starting point is formed into a line shape to form a screw dislocation generation line.

A screw dislocation with a large Burgers vector becomes a micropipe, which is one of the causes of deteriorating the quality of the final device.
Therefore, the facet growth region where crystals are grown from the initial facet formation surface 20 where screw dislocations are normally provided is not used as a semiconductor device.

On the other hand, when crystal growth is performed with the screw dislocation generation starting points arranged in a line, the screw dislocations formed in the SiC ingot and SiC wafer are also aligned in a line. That is, even if some of the screw dislocations are micropipes, the micropipes are arranged in a line. Therefore, in the dicing process for obtaining semiconductor devices from a SiC wafer, cutting along lines where screw dislocations are densely packed can prevent defects such as micropipes from being included in the semiconductor devices. Further, since the occurrence of different polymorphisms due to screw dislocations is also suppressed, it is also possible to suppress the occurrence of different polymorphisms and defects due to different polymorphisms in the semiconductor device.
In other words, the quality of the resulting semiconductor device can be improved by arranging the screw dislocation generation starting point in a line along the dicing line in the semiconductor device manufacturing process instead of arranging it arbitrarily.

Furthermore, aligning a line where screw dislocations are densely packed (hereinafter referred to as a "screw dislocation dense line") with a dicing line also leads to higher quality semiconductor devices when the SiC ingot is lengthened.

FIG. 7 is a diagram schematically showing the state before and after the growth of a SiC ingot grown from a SiC seed, and FIG. FIG. 7(b) is a schematic plan view showing an enlarged part of the initial facet forming surface 20, and FIG. 7(c) is a plan view showing an enlarged part of the c-plane facet 210b. It is a schematic diagram.

As shown in FIG. 7(a), as the crystal growth of the SiC single crystal progresses, the screw dislocations generated from the screw dislocation originating point 22 on the initial facet forming surface 20 attract and combine with each other and disappear. or converted into defects in the basal plane. Therefore, if the number of screw dislocation generation points introduced into the initial facet forming surface 20 is not sufficiently large, it will not be possible to maintain a sufficient number of screw dislocations 23 in the latter half of the crystal growth shown in FIG. 7(a). If the number of screw dislocations 23 is not sufficient, a problem arises in that the probability of occurrence of heterogeneous polymorphism increases in the latter half of the growth of the SiC ingot 200. On the other hand, if the number of screw dislocation origin points 22 is increased in order to suppress the occurrence of heterogeneous polymorphism in the latter half of growth, screw dislocations will cause defects such as micropipes that affect the quality of semiconductor devices in the early stage of growth. The problem arises that the possibility increases.

On the other hand, as shown in FIG. 7(b), when the screw dislocation generating points 22 are provided in a line shape as the screw dislocation generating line 21, the screw dislocation generating points 22 are introduced in a high density within the screw dislocation generating line 21. can do. Since the number of screw dislocation originating points 22 is sufficiently large, a sufficient number of screw dislocations 23 can be maintained even in the c-plane facet 210b, as shown in FIG. 7(c). As a result, even if the SiC single crystal is grown into a long length, the generation of different polymorphisms can be continuously suppressed. Further, even if some of the high-density screw dislocations 23 become micropipes, defects will occur in the shape of dicing lines, and this can be avoided from affecting the quality of the semiconductor device.

It is preferable that the screw dislocation occurrence origin 22 exists on the offset upstream side from the main surface 10. That is, it is preferable that the initial facet forming surface 20 is located upstream of the main surface 10 in an offset manner. As shown in FIG. 6A, in the step flow growth, the SiC seed 100 as a whole grows in the +Z direction while the crystal grows in the a-plane direction. Therefore, information on the upstream side of the offset is easily transmitted to the downstream side of the offset. Therefore, if the initial facet formation surface 20 having the screw dislocation origination point 22 is provided on the upstream side of the offset and the generation of heterogeneous polymorphism and the generation of defects due to the outflow of crystal dislocations can be suppressed, the generation on the downstream side of the offset can also be suppressed. At the same time, it leads to suppression. That is, it is possible to suppress the flow of screw dislocations, different polymorphisms, etc. into the high quality region obtained by crystal growth on the main surface 10, and to produce a higher quality SiC ingot.

It is preferable that the first screw dislocation generation line 21a and the second screw dislocation generation line 21b constituting the screw dislocation generation line 22 are orthogonal to each other. When chipping semiconductor devices, SiC wafers are often cut into rectangular shapes. Therefore, if the first screw dislocation generation line 21a and the second screw dislocation generation line are perpendicular to each other, it is possible to increase the number of high-quality semiconductor devices.

The first direction in which the first screw dislocation generation line 21a extends is preferably either a direction parallel to the {1-100} plane or a direction parallel to the {11-20} plane. Preferably perpendicular to the direction.
If the screw dislocation generation line 21 is present in accordance with the surface orientation, it becomes easy to set the dicing line and also facilitate the formation of chips by dicing. Moreover, if the first screw dislocation generation line 21a is arranged perpendicularly to the offset growth direction, generation of different types of polymorphism can be avoided over the entire surface in the growth direction.

The area ratio occupied by the screw dislocation generating line 21 in the SiC seed 100 is preferably 50% or less, more preferably 30% or less. The screw dislocation generation line 21 is a portion that is cut in the dicing process. Therefore, if the area ratio of this part is high with respect to the SiC seed 100, the ratio that can be used as a semiconductor device will decrease, or the characteristics of the produced semiconductor device will deteriorate.

The area ratio occupied by the screw dislocation generation line 21 is defined as "the sum of the width x length of the screw dislocation generation line". Here, in reality, the screw dislocation generation line 21 has a plurality of screw dislocation generation starting points clustered together and looks like a line. Therefore, the "width" and "length" of the screw dislocation generating line cannot actually be measured. Therefore, the "width" and "length" of the screw dislocation generation line are defined as follows in this specification.
First, the "width" is determined from the density distribution of the starting point of screw dislocation. The density distribution of screw dislocation generation points is measured in a direction perpendicular to the extending direction of the screw dislocation generation line, and the width is defined as the width connecting the points that are 1/10 of the maximum screw dislocation generation point density. This width varies depending on the method of providing the screw dislocation generating point, but for example, when the screw dislocation generating point is artificially provided by machining, it is about 100 μm. This width of 100 μm coincides with the width of general dicing, and also coincides with the purpose of setting a preferable area ratio from the viewpoint of semiconductor device removal efficiency.
On the other hand, the "length" is determined by the following procedure. When the distance between adjacent screw dislocation occurrence starting points is 0.25 cm or less, they are connected and it is determined that a screw dislocation occurrence line extends. This is because if the number of screw dislocation starting points is present at a frequency of 4 or more per centimeter, the occurrence of different polymorphisms can be sufficiently suppressed. Then, a perpendicular line parallel to the extending direction of the screw dislocation generation line is drawn from one end of the screw dislocation generation line to the other end, and this length is defined as the length of the screw dislocation generation line.

It is most desirable that the screw dislocation origin 22 is a screw dislocation that is provided in the SiC seed from the beginning. If the screw dislocation origin 22 is a screw dislocation that is provided in the SiC seed 100 from the beginning, it is possible to suppress an increase or decrease in the number of screw dislocations 23 or a change in their position during the growth process. Since one screw dislocation provided in the SiC seed 100 from the beginning is a threading dislocation, it also functions as one screw dislocation during the growth process. On the other hand, if the screw dislocation origination point 22 is caused by distortion of the crystal, for example, multiple screw dislocations may be generated during the growth process, resulting in an increase/decrease in the number of screw dislocations or a change in position. There is a risk. Even when introducing a screw dislocation generation starting point other than the screw dislocation provided in these SiC seeds from the beginning, the number and position of the screw dislocations that occur initially can be manipulated by manipulating the introduction density and introduction intensity. However, by using the screw dislocation itself that is provided in the SiC seed from the beginning, screw dislocation can be reliably introduced even during the growth process without manipulating the introduction density, introduction strength, etc.

(Modified example)
Although the SiC seed according to one aspect of the present invention has been described above with reference to the drawings, various changes can be made to the above structure without departing from the gist of the present invention.

For example, in FIG. 1, a case will be explained in which the first screw dislocation generation line 21a and the second screw dislocation generation line 21b are arranged periodically to form a lattice-like screw dislocation generation line 21. However, the screw dislocation generation line 21 is not limited to this embodiment.

For example, as shown in FIG. 8, the screw dislocation generation line 21 may not include the second screw dislocation generation line 21b and may consist only of the first screw dislocation generation line 21a extending in the first direction. . In this case, dicing in the second direction perpendicular to the first direction can be performed at any position.

Further, as shown in FIG. 9, the screw dislocation generation line 21 may be composed of a first screw dislocation generation line 21a and a second screw dislocation generation line 21b. In this case, the corner of the semiconductor device to be chipped is cut at the intersection of the screw dislocation generation lines 21.

Further, as shown in FIG. 10, when the size of the region 25 surrounded by the screw dislocation generation line 21 is large, a small amount of the screw dislocation generation point 22 may be introduced into the region 25 separately from the screw dislocation generation line 21. good. If the screw dislocation generation point 22 is introduced into the region 25 separately from the screw dislocation generation line 21, the generation of different types of polymorphism can be sufficiently suppressed even if the size of the region 25 is large. On the other hand, if the screw dislocation generation starting point 22 is introduced into the region 25, there is a possibility that a micropipe will be introduced into the semiconductor device. However, if the amount of screw dislocation originating points 22 introduced is small, this possibility can be sufficiently reduced.

In addition to this, the shape of the area surrounded by the screw dislocation generation line 21 may be made into a rectangular shape or the like instead of a square shape.

Furthermore, for example, although a case has been described in which the main surface 20 is provided in FIG. 1, a SiC seed that does not have a main surface having an offset angle and whose entire surface is an initial facet formation surface may be used. Further, a SiC seed may be used in which the initial facet formation surface occupies a large area ratio with respect to the main surface having an offset angle.
Even if there is no main surface or the area ratio of the main surface is small, if sufficient screw dislocation starting points can be provided within the initial facet formation surface, heterogeneous polymorphism can be sufficiently suppressed. Further, by on-growing SiC on the initial facet formation surface, it becomes easier to control the position of the first screw dislocation generation line.

As described above, the SiC seed according to one aspect of the present invention has a screw dislocation generation line where screw dislocation generation points are gathered. Therefore, by using the SiC seed according to one embodiment of the present invention, generation of different polymorphisms can be suppressed when growing a SiC single crystal. Furthermore, since the screw dislocation starting points are arranged in a line, defects such as micropipes in the SiC wafer before cutting out semiconductor devices can be arranged in a line. That is, by cutting out a semiconductor device along this line, a high-quality semiconductor device with fewer heterogeneous polymorphisms and fewer defects can be obtained.

(SiC ingot)
FIG. 11 is a diagram schematically showing a cross section of a portion of a SiC ingot according to one embodiment of the present invention. Further, FIG. 12 is a diagram schematically showing the vicinity of the facet growth region of a cut surface of the SiC ingot taken along the BB' plane in FIG.

SiC ingot 200 is grown from SiC seed 100 described above. The SiC ingot 200 has a facet growth region 210 extending from the initial facet formation surface 20 of the SiC seed 100 over the entire region in the SiC growth direction. Here, "the entire area in the growth direction of SiC" means from the initial stage of growth to the end of growth when growing the SiC ingot 200, from the surface of the SiC seed 100 shown in FIG. 11 to the facet growth region. This means that the facet growth region is uninterrupted in the crystal growth direction up to the c-plane facet 210b on the outermost surface of 210.

The initial facet growth region 210 has a screw dislocation dense region 211 . The screw dislocation dense area is a collection of screw dislocations introduced into the initial facet 210 by the screw dislocation generation line 21. Here, densely packed is defined as densely packed if they exist at a frequency of 4 pieces/cm or more.
The screw dislocation dense region 211 extends from the screw dislocation generation line 21 in the SiC seed 100 in the SiC growth direction (direction perpendicular to the c-plane direction). When the screw dislocation generation line 21 is composed of the first screw dislocation generation line 21a and the second screw dislocation generation line 21b, the screw dislocation dense portion 211 also includes the first screw dislocation dense portion 211a and the second screw dislocation dense portion. 211b.

The fact that the initial facet growth region 210 has a screw dislocation dense region 211 extending over the entire SiC growth direction means that the generation of heterogeneous polymorphism is suitably suppressed during the SiC growth process. . That is, the SiC ingot having the screw dislocation dense portion 211 in the initial facet growth region 210 has fewer heterogeneous polymorphisms and crystal defects.

When viewed in plan from a direction perpendicular to the c-plane facet 210b, the initial facet formation surface 20 of the SiC seed 100 and the c-plane facet 210b on the outermost surface of the facet growth region 210 overlap at least in part. It is preferable. When the two surfaces before and after growth satisfy this relationship, the facet growth region 210 is placed at a controlled predetermined position. During the growth process, if the facet growth region 210 moves to the offset downstream side, the shape of the screw dislocation generation line provided on the SiC seed 100 may collapse. Since the screw dislocation generation line is set in accordance with the dicing line when converting the SiC wafer into chips, if the shape is distorted, the number of semiconductor devices that can be obtained will decrease.

The thickness of the portion of the SiC ingot 200 grown from the SiC seed 100 is preferably 30 mm or more, more preferably 50 mm or more. As described above, when increasing the length of the SiC ingot 200, it is extremely difficult to simultaneously suppress heterogeneous polymorphism due to the introduction of screw dislocations and the generation of micropipes due to the introduction of screw dislocations. However, by forming the screw dislocation generating portion 211 along the dicing line, screw dislocations can be introduced at any density, and the SiC ingot 200 can be made longer.

As described above, in the SiC ingot 200 according to one aspect of the present invention, screw dislocations are disposed at predetermined positions that do not affect semiconductor devices. Therefore, a long SiC ingot can be obtained. Moreover, by using this SiC ingot, a high quality semiconductor device can be obtained.

(SiC wafer)
FIG. 13 is a schematic plan view of a SiC wafer according to one embodiment of the present invention. SiC wafer 300 has facet growth marks 310. SiC wafer 300 is obtained by cutting SiC ingot 200 described above.

The facet growth trace 310 corresponds to a cut surface obtained by cutting the facet growth region 210 of the SiC ingot parallel to the c-plane. Therefore, the facet growth trace 310 has a screw dislocation dense line 311. In FIG. 13, the screw dislocation dense line 311 includes a first screw dislocation dense line 311a extending in a first direction, and a second screw dislocation dense line 311a extending in a second direction perpendicular to the first direction. It consists of dense lines 311b.

The screw dislocation dense line 311 has grown from the above-described screw dislocation generation line 21, and is obtained by cutting the screw dislocation generation portion 211 along a plane parallel to the c-plane. Therefore, the screw dislocation dense line 311 is not limited to the mode shown in FIG. 13, but can take the same mode as the screw dislocation generation line 21. That is, configurations such as those shown in FIGS. 7 to 10 can be adopted.

The area ratio occupied by the screw dislocation dense lines 311 in the SiC wafer 300 is preferably 50% or less, more preferably 30% or less. In the dicing process, cutting is performed along the screw dislocation dense line 311. Therefore, if the area ratio of this portion is high with respect to the SiC wafer 300, the ratio that can be used as a semiconductor device will decrease, or the characteristics of the manufactured semiconductor device will deteriorate. Here, the area ratio of the screw dislocation dense line can be calculated using the same definition as the above-mentioned screw dislocation generation line.

Dicing when manufacturing a semiconductor device is performed along the screw dislocation dense line 311. Therefore, by using the SiC wafer according to one embodiment of the present invention, a high-quality semiconductor device can be obtained.

Further, FIG. 14 is a schematic plan view showing an enlarged portion of a SiC wafer according to one embodiment of the present invention. As shown in FIG. 14, the SiC wafer 300 includes a dicing area 321, a device fabrication area 323 surrounded by the dicing area 321, and an outer peripheral area 322 sandwiched between the dicing area 321 and the device fabrication area 323. has. The dicing scheduled area 321 is an area having a width centered around the dicing scheduled line 321a.

The widths of the first screw dislocation dense line 311a and the second screw dislocation dense line 311b described above are preferably narrower than the width d2 between adjacent device fabrication regions 323, and more preferably narrower than the width of the dicing scheduled region 321. preferable. The width of the screw dislocation dense line is determined by the same definition as the above-mentioned screw dislocation generation line.
Since the dicing target area 321 is removed in the dicing process, if the width of the screw dislocation dense line is narrower than the width d1 of the dicing target area 321, it is possible to avoid screw dislocations from being included in the chipped semiconductor device. .
Further, if the width of the screw dislocation dense line is narrower than the width d2 between adjacent device fabrication regions 323, screw dislocations will be introduced into a part of the outer peripheral region 322. However, the outer peripheral region is not subjected to a strong electric field when driving the device, and is not an active region that is driven as a device. Therefore, even if screw dislocations are introduced into the outer peripheral region, the resulting semiconductor device can be suitably driven.

That is, it is preferable that the screw dislocation density decreases in the order of device fabrication region 323, outer peripheral region 322, and dicing scheduled region.

The semiconductor device cut out from the SiC wafer shown in FIG. 14 has an active region that is driven as a device and an outer peripheral region surrounding the active region. The active region in the semiconductor device corresponds to the device manufacturing region 323 shown in FIG. 14, and the outer peripheral region in the semiconductor device corresponds to the outer peripheral region 322 shown in FIG. 14. At this time, the screw dislocation density in the outer peripheral region is less than or equal to the screw dislocation density in the active region. By reducing the density of screw dislocations in the active region, it is possible to achieve higher quality and longer life of semiconductor devices.

(Method for manufacturing semiconductor devices)
A method for manufacturing a semiconductor device according to one aspect of the present invention includes the steps of preparing a predetermined SiC wafer, and dividing the SiC wafer along lines with a high concentration of screw dislocations in the SiC wafer.

<SiC wafer preparation process>
SiC wafers can be obtained by cutting SiC ingots grown from SiC seeds. Therefore, first, the manufacturing process of SiC seeds will be explained.

First, a SiC seed is cut out from another SiC single crystal already produced by crystal growth using a wire saw or the like. The SiC single crystal from which this SiC seed is cut out is preferably of high quality with few defects. If the quality of the underlying SiC single crystal is high, the quality of the SiC seed will also be high. If the SiC seed is of high quality, the quality of the SiC ingot and SiC wafer obtained by crystal growth of the SiC seed can be improved.

Here, a high quality SiC single crystal with extremely few defects (including screw dislocations) can be obtained by the RAF method or the like. A high quality SiC seed can be produced by slicing a high quality SiC single crystal obtained by the RAF method. At this time, by adjusting the angle of the SiC seed sliced from the SiC single crystal, a main surface having an offset angle of 2° or more and 20° or less with respect to the {0001} plane can be formed.

Next, a sub-growth surface is formed by further cutting out a part of the sliced SiC seed. The method for forming the sub-growth surface is not particularly limited, and any known method can be used.

Next, an initial facet formation surface is formed in which the inclination angle θ with respect to the {0001} plane is less than 2° in absolute value in any direction. Similar to the sub-growth surface, the initial facet formation surface can be formed by cutting out a part of the SiC single crystal. The angular deviation of the initial facet formation surface from the {0001} plane can be adjusted by notching the initial facet formation surface after confirming the crystal plane using X-ray topography. In addition, when it is confirmed by X-ray topography etc. that there are sufficient screw dislocations that serve as the origin of screw dislocation generation in the SiC single crystal, the initial facet formation surface is adjusted to include those screw dislocations. It is preferable to cut out.

Then, a screw dislocation generation line is provided on the initial facet formation surface formed by notching. As a method for providing screw dislocation generation lines, for example, a layer with a disordered crystal structure on the surface can be created by machining, ion implantation, laser marking, or the like. In order to grow a well-ordered crystal structure on a layer with a disordered crystal structure, the disorder must be absorbed in some way. Therefore, the screw dislocation generation starting points forming the screw dislocation generation line become screw dislocations at the stage of crystal growth.

Further, it is preferable to further perform chemical treatment on the initial facet formation surface. When the initial facet formation surface is chemically treated, very minute steps are formed on the initial facet formation surface. When the initial facet formation surface has a step, a part of the initial facet formation surface can undergo step flow growth from the initial stage of crystal growth, which further reduces the generation of heterogeneous polymorphism and the formation of defects due to the outflow of crystal dislocations. The occurrence can be suppressed.

A SiC ingot is produced using a SiC seed in which a screw dislocation generation line is formed. A SiC ingot can be obtained by epitaxially growing SiC on a SiC seed.

When producing a SiC ingot, the crystal is grown so that the isothermal surface at the growth stage has an inclination angle δ of less than 2° in absolute value with respect to a plane parallel to the initial facet formation surface in any direction. It is preferable.

By controlling the isothermal surface so that the inclination angle δ with respect to a plane parallel to the initial facet formation surface is less than 2° in absolute value in any direction, it is possible to control the position of the facet growth region of the SiC ingot. can. This is because the shape of the crystal growth surface of SiC is basically almost the same as the isothermal surface.

Crystal growth of SiC starts from a SiC seed state. Since the SiC seed has an initial facet formation surface, the facets at the very initial stage of growth are formed directly above the initial facet formation surface. If the isothermal surface during crystal growth is controlled so as to be substantially parallel to the initial facet formation surface, the facets obtained at each stage of crystal growth will be formed without greatly deviating from directly above the initial facet formation surface. That is, by controlling the position of the facet at each stage of crystal growth, the position where the facet growth region of the SiC ingot after crystal growth is produced can be limited to a predetermined position. As a result, the c-plane facet on the outermost surface of the SiC ingot and the initial facet overlap when viewed in plan from a direction perpendicular to the c-plane facet.

Here, maintaining an isothermal surface during crystal growth can be achieved, for example, by combining two techniques. One is a technique that creates a slightly convex isothermal surface by adjusting the arrangement of heaters and heat insulators outside the crucible, and the other is a technique that moves the crucible during growth to create an isothermal surface and growth surface height. It is a technology that matches the If a heat insulating material is provided between the high temperature region and the low temperature region, a convex temperature distribution will be created below that position, and the degree of convexity can be adjusted depending on the positional relationship. The height of the growth surface at each time can be inferred from the results of growth under the same conditions, so if you grow while adjusting the height of the growth surface to be the same relative to the above insulation material, , the angle of the isothermal surface can be maintained.

Then, the obtained SiC ingot is cut with a wire saw or the like to form a SiC wafer. Since the SiC wafer has a growth history of SiC seeds and SiC ingots, it has facet growth traces, and screw dislocation dense lines are formed in the facet growth traces.

A semiconductor device is formed using the obtained SiC wafer. A known method can be used for the manufacturing process of the semiconductor device. Generally, a plurality of semiconductor devices are fabricated on a SiC wafer and then formed into chips, but the order may be reversed.

In the dicing process for converting semiconductor devices into chips, the semiconductor devices are divided along lines where screw dislocations are concentrated. There is a high possibility that the screw dislocation dense line contains defects such as micropipes. However, since this portion is separated, the resulting semiconductor device will be of high quality.

Note that if the width of the screw dislocation dense line is wider than the width of the dividing line in the dicing process, the resulting semiconductor device will have a relatively higher defect density at the outer periphery of the device than at the center.

Although the present invention has been described in detail above, the present invention is not limited to the embodiments, and various modifications can be made without departing from the gist of the present invention. For example, although the present invention mainly describes the (000-1) plane (C plane) among the {0001} planes, the present invention is not limited thereto, and describes the (0001) plane (Si plane). can be similarly applied.
Note that, crystallographically, (0001) and {0001} indicate crystal planes. The difference between these is that since the {0001} plane includes planes with equivalent symmetry, it includes both the (0001) plane and the (000-1) plane. On the other hand, <0001> indicates the crystal direction.

DESCRIPTION OF SYMBOLS 10... Main surface, 20, 20A, 20B, 20C, 20D... Initial facet formation surface, 21... Screw dislocation generation line, 21a... First screw dislocation generation line, 21b... Second screw dislocation generation line, 22... Spiral Dislocation origin, 23... Screw dislocation, 30... Sub-growth surface, 100... SiC seed, 200... SiC ingot, 210... Facet growth region, 210a... Growth interface, 210b... C-plane facet, 211... Screw dislocation dense area, 211a ...First screw dislocation dense area, 211b... Second screw dislocation dense area, 220... Step flow growth region, 220a... Growth interface, 300... SiC wafer, 311... Screw dislocation dense line, 311a... First screw dislocation Dense line, 311b...Second screw dislocation dense line, 321...Dicing planned area, 321a...Dicing planned line, 322...Outer peripheral area, 323...Device fabrication area

Claims (13)

comprising an initial facet forming surface whose inclination angle θ with respect to the {0001} plane is less than 2° in any direction,
having a first screw dislocation generation line extending in a first direction at least on the initial facet formation surface;
The first screw dislocation generation line is a region where a plurality of screw dislocation generation starting points exist in a line shape,
The first screw dislocation generation line has a width of 100 μm or less,
In the first screw dislocation generation line, the distance between adjacent screw dislocation generation points is 0.25 cm or less,
In a region other than the first screw dislocation generation line, the distance between adjacent screw dislocation generation points is greater than 0.25 cm. The SiC seed. The SiC seed according to claim 1, further comprising a main surface having an offset angle of 2° or more and 20° or less with respect to the {0001} plane. There are a plurality of first screw dislocation generation lines,
3. The SiC seed according to claim 1, wherein the plurality of first screw dislocation generation lines are arranged periodically at predetermined intervals. The SiC seed according to any one of claims 1 to 3, wherein the first direction is either a direction parallel to the {1-100} plane or a direction parallel to the {11-20} plane. Further having a second screw dislocation generation line extending in a second direction intersecting the first direction on the initial facet formation surface,
The second screw dislocation generation line is a region where a plurality of screw dislocation generation starting points exist in a line shape,
The second screw dislocation generation line has a width of 100 μm or less,
In the second screw dislocation generation line, the distance between adjacent screw dislocation generation points is 0.25 cm or less,
The SiC seed according to any one of claims 1 to 4 , wherein in a region other than the second screw dislocation generation line, a distance between adjacent screw dislocation generation points is greater than 0.25 cm . The SiC seed according to claim 5, wherein the second direction is orthogonal to the first direction. There are a plurality of second screw dislocation generation lines,
The SiC seed according to claim 5 or 6, wherein the plurality of second screw dislocation generation lines are arranged periodically at predetermined intervals. The SiC seed according to any one of claims 1 to 7, wherein the area ratio occupied by the first screw dislocation generating line in the SiC seed is 50% or less. The SiC seed according to any one of claims 5 to 7, wherein the area ratio occupied by the second screw dislocation generating line in the SiC seed is 50% or less. SiC seed according to any one of claims 1 to 9,
a growth part grown on the SiC single crystal sheet,
The growth part has a facet growth region over the entire growth direction from the initial facet formation surface of the SiC seed,
An SiC ingot in which the facet growth region has a first screw dislocation dense region extending from the first screw dislocation generation line in the SiC growth direction. The SiC seed has a second screw dislocation generation line extending in a second direction intersecting the first direction,
The SiC ingot according to claim 10, wherein the facet growth region has a second screw dislocation dense region extending from the second screw dislocation generation line in the SiC growth direction. The c-plane facet on the outermost surface of the facet growth region and the initial facet formation surface of the SiC seed,
The SiC ingot according to claim 10 or 11, wherein the c-plane facets overlap at least in part when viewed in plan from a direction perpendicular to the c-plane facets. The SiC ingot according to any one of claims 10 to 12, wherein the thickness of the growth portion in the c-axis direction is 30 mm or more.

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