TWI546852B - Laser processing method - Google Patents

Description

Laser processing method

The present invention relates to a laser processing method for cutting a plate-shaped object to be processed having a SiC substrate along a line to cut.

In recent years, as a semiconductor material capable of producing a power element having excellent heat resistance, high voltage resistance, and power saving, SiC (Silicon Carbide) has been attracting attention. However, since the SiC system has a hard-to-machine material that is second only to the hardness of the diamond, it is necessary to perform low-speed processing and frequent cutting of the plate-shaped object to be processed with the SiC substrate by knife cutting. Blade replacement, etc. Therefore, it is proposed to form a modified region in the SiC substrate along the line to cut along the line to be cut, and to cut the object along the line to cut with the modified region as a starting point. Laser processing method (see, for example, Patent Document 1).

[Patent Document 1] Japanese Patent Publication No. 2007-514315

The present inventors have found that a plate-shaped object to be processed having a hexagonal SiC substrate having a c-plane and a principal surface forming an angle of an oblique component is cut by the above-described laser processing method. The following topics. That is, when the first cutting schedule is extended in a direction parallel to the main surface and the a surface In the line, the first modified region is formed inside the SiC substrate, and when the second modified region is formed inside the SiC substrate along the second planned cutting line extending in the direction parallel to the main surface and the m-plane, There is a possibility that the cutting accuracy along the first cutting planned line is deteriorated compared to the cutting accuracy along the second cutting planned line. Further, the inventors of the present invention have found that the crack tends to extend in the thickness direction of the SiC substrate from the second modified region, whereas the crack is less likely to be toward the SiC substrate from the first modified region. Stretch in the thickness direction.

In view of the above, it is an object of the present invention to provide a plate-shaped object to be processed having a hexagonal SiC substrate having a principal surface having an oblique angle component to the c-plane, and to cut it accurately along a line to cut. Laser processing method.

According to a laser processing method of the present invention, a plate-shaped object to be processed having a hexagonal SiC substrate having a principal surface having an oblique angle component to the c-plane is provided along the principal surface and the a-plane A laser processing method in which a first cutting planned line extending in a parallel direction and a second cutting planned line extending in a direction parallel to the main surface and the m-plane are cut, wherein the first processing method is provided. By arranging the light-converging point of the laser light in the inside of the SiC substrate, the object to be processed is irradiated with the laser beam along the first line to cut, and the first line to cut is used as the starting point of the cutting. The first modified region is formed inside the SiC substrate; and the second process is performed after the first process is performed, and the spot is positioned inside the SiC substrate along the second cutting line. , plus The object is irradiated with laser light to form a second modified region as a cutting start point in the inside of the SiC substrate along the second line to cut.

In the laser processing method, the conditions for forming the crack toward the thickness direction of the SiC substrate are severe before forming the second modified region in which the crack is extended in the thickness direction of the SiC substrate. The first modified area. By this, when the first modified region is formed, it is possible to prevent the crack from the first modified region toward the thickness direction of the SiC substrate in the portion where the first planned cutting line intersects with the second planned cutting line. It is caused by the situation that the second modified area is blocked. Therefore, according to the laser processing method, the plate-shaped object to be processed having the hexagonal SiC substrate having the principal surface having an oblique angle component to the c-plane can be accurately cut along the line to be cut. The cutting accuracy is cut off well. Furthermore, the bevel angle includes 0°. In this case, the main surface is parallel to the c-plane.

In the laser processing method of the first aspect of the invention, the first modified region is used as a starting point, and the object to be processed is cut along the first cutting line, and the second modification is performed. The material region serves as a starting point, and the third process of cutting the object to be processed is cut along the second line to cut. Thereby, it is possible to obtain an object to be processed which is accurately cut along the line to cut. Further, after the cutting is performed along the first cutting planned line, the cutting along the second cutting planned line may be performed, or the cutting may be performed along the second cutting planned line. The cutting of the first cutting planned line is performed.

In the laser processing method according to one aspect of the present invention, the first modified region and the second modified region may include a molten processed region.

According to the present invention, the plate-shaped object to be processed having the hexagonal SiC substrate having the principal surface having an oblique angle component to the c-plane can be accurately cut along the line to be cut.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. In the respective drawings, the same reference numerals are given to the phase diagrams or the corresponding portions, and the repeated description thereof is omitted.

In the laser processing method according to the embodiment of the present invention, the object to be processed is irradiated with laser light along the line to be cut, and a modified region is formed inside the object to be processed along the line to be cut. Therefore, first, the formation of this modified region will be described with reference to FIGS. 1 to 6 .

As shown in Fig. 1, the laser processing apparatus 100 includes: a laser light source 101 that pulsates the laser light L, and a beam splitter 103 that is arranged to change the direction of the optical axis (optical path) of the laser light L by 90[deg.] And a collecting lens 105 for collecting the laser light L. Further, the laser processing apparatus 100 includes a support base 107 for supporting the object 1 to be irradiated with the laser light L collected by the collecting lens 105, and a table 111 for moving the support table 107; The laser light source control unit 102 that controls the laser light source 101 to adjust the output of the laser light L, the pulse width, and the like, and the table control unit 115 that controls the movement of the table 111.

In the laser processing apparatus 100, the laser light L emitted from the laser light source 101 is changed by the beam splitter 103 by 90° in the direction of the optical axis. The condensing lens 105 condenses the inside of the object 1 placed on the support table 107. At the same time, the table 111 is moved, and the object 1 is moved relative to the laser beam L along the line to cut 5 . Thereby, the modified region along the line to cut 5 is formed in the object 1 .

As shown in FIG. 2, in the object 1 to be processed, a planned cutting line 5 for cutting the object 1 is set. The line to cut 5 is a virtual line extending in a straight line. When a modified region is formed inside the object 1 as shown in FIG. 3, the laser beam L is placed along the line to cut 5 in a state where the light-converging point P is aligned with the inside of the object 1 ( That is, it moves relatively along the arrow A direction of FIG. 2). As a result, as shown in FIGS. 4 to 6 , the modified region 7 is formed inside the object 1 along the line to cut 5 so that the modified region 7 formed along the line to cut 5 is cut. Break starting point area 8.

Further, the condensed spot P is a portion where the laser light L is condensed. Further, the line to cut 5 is not limited to a straight line, and may be curved, and is not limited to a virtual line, and may be a line actually drawn on the surface 3 of the object 1 to be processed. Further, the modified region 7 may be formed continuously or intermittently. Further, the modified region 7 may be in a column shape or a dot shape, that is, the modified region 7 may be formed at least inside the object 1 to be processed. Further, the crack may be formed by using the modified region 7 as a starting point, and the crack and the modified region 7 may be exposed on the outer surface (surface, inner surface, or outer peripheral surface) of the object 1 to be processed.

By the way, the laser light L transmitted here passes through the object 1 and is absorbed especially in the vicinity of the spot where the object 1 is processed. Thereby, the modified region 7 is formed in the object 1 (that is, internal absorption type laser processing). Therefore, since the laser light L is hardly absorbed on the surface 3 of the object 1 to be processed, the surface 3 of the object 1 does not melt. In general, in the case where the surface 3 is melted and removed to form a removal portion such as a hole or a groove (surface absorption type laser processing), the processing region gradually proceeds from the surface 3 side toward the back side.

Further, the modified region formed in the present embodiment means a region having a state different from the surroundings such as density, refractive index, mechanical strength, and other physical properties. The modified region includes, for example, a molten processed region, a cracked region, an insulating fracture region, a refractive index change region, and the like, and a region in which these regions are mixed. Further, as the modified region, there is a region in which the density of the modified region is changed, a region in which the lattice defect is formed, and the like in the material of the object to be processed, compared with the density of the non-modified region (the regions are also collectively referred to as high Density transfer area).

Further, in the molten processed region, the refractive index change region, and the density of the non-modified region, the region where the density of the modified region changes, the region in which the lattice defect is formed, and the modified region in the region The interface between the non-modified region and the non-modified region is covered with cracks (fractures, micro-cracks). The crack in the inner package may be formed in a comprehensive state of the modified region, and may be formed only in a part or a plurality of portions.

Further, in the present embodiment, the modified region 7 is formed by forming a plurality of modified spots (machining marks) along the line to cut 5 . The modified point refers to the modified part formed by the pulse of 1 pulse of pulsed laser light (ie, 1 pulse of laser irradiation: laser shooting), which is modified by the aggregation of the modified spots. Area 7. Examples of the modification point include a crack point, a melting treatment point, or a refractive index change point, or a mixture of at least one of these points.

For this modification point, the cutting accuracy required, the required flatness of the cut surface, the thickness, type, and crystal orientation of the object to be processed are appropriately measured, and the size and the length of the crack generated are appropriately controlled. good.

Next, a laser processing method according to an embodiment of the present invention will be described in detail. As shown in FIG. 7, the object 1 is a wafer having a circular plate shape (for example, a diameter of 3 inches and a thickness of 350 μm) including the SiC substrate 12. As shown in FIG. 8, the SiC substrate 12 has a hexagonal crystal structure, and the crystal axis CA is inclined by an angle θ (for example, 4°) with respect to the thickness direction of the SiC substrate 12. That is, the SiC substrate 12 is a hexagonal SiC substrate having an oblique angle of an angle θ. As shown in FIG. 9, the SiC substrate 12 has a surface (main surface) 12a and an inner surface (main surface) 12b having an angle θ which is an oblique component to the c-plane. In the SiC substrate 12, the a-plane is inclined at an angle θ with respect to the thickness direction of the SiC substrate 12 (two-point lock line in the drawing), and the m-plane is not inclined to the thickness direction of the SiC substrate 12.

As shown in FIG. 7 and FIG. 9, in the object 1 to be processed, a plurality of planned cutting lines (first cutting planned lines) 5a and facing surfaces 12a and m extending in a direction parallel to the surface 12a and the a surface are formed. The plurality of predetermined line cutting lines (second cutting planned lines) extending in the parallel direction are set to have a lattice shape (for example, 1 mm × 1 mm). On the surface 12a of the SiC substrate 12, functional elements are formed in each of the regions defined by the cutting planned lines 5a, 5m, and the inside of the SiC substrate 12 12b is cut by each of the predetermined lines 5a, 5m. The area to be zoned is formed with metal wiring. Functional components and The metal wiring is a power element formed by cutting each wafer obtained by cutting the object 1 along the cutting planned lines 5a and 5m. Further, in the SiC substrate 12, the orientation flat surface 6a is formed in a direction parallel to the line to cut 5a, and the orientation flat surface 6m is formed in a direction parallel to the line to cut 5m.

The above-described object 1 is cut along the line to cut 5a, 5m in the following manner. First, as shown in FIG. 10, the extension tape 23 is adhered to the object 1 for covering the metal wiring of the back surface 12b of the SiC substrate 12. Next, as shown in FIG. 11(a), the condensed spot P of the laser light L pulse-oscillated with a pulse width of 20 ns to 100 ns (more preferably, a pulse width of 50 ns to 60 ns) and the inside of the SiC substrate 12 are formed. In the alignment, the object 1 is irradiated with the laser light L along the line to cut 5a so that the pulse pitch is 10 μm to 18 μm (more preferably, the pulse pitch is 12 μm to 14 μm). Thereby, the modified region (first modified region) 7a as the cutting start point is formed inside the SiC substrate 12 along the line to cut 5a. This modified region 7a contains a molten processed region. In addition, the pulse pitch means the value of "the moving speed of the condensed point P of the laser light L to the object 1 to be processed" divided by the "repeating frequency of the pulsed laser light L".

In order to form the modified region 7a, the surface 12a of the SiC substrate 12 is used as a laser light incident surface, and the light collecting point P of the laser light L is positioned inside the SiC substrate 12 along the line to cut 5a. The light collecting point P is relatively moved. Then, the relative movement of the condensed spot P along the line to cut 5a is applied to the one line to cut 5 a plurality of times (for example, eight times). At this time, a plurality of columns (first column) are formed on one planned cutting line 5a so as to be arranged in the thickness direction of the SiC substrate 12 by changing the distance from the surface 12a to the position of the light collecting point P. A modified region 7a of a number, for example, 8 columns). Here, the modified region 7a which is second closest to the surface 12a of the SiC substrate 12 as the laser light incident surface is smaller than the modified region 7a closest to the surface 12a, and is formed from the inner surface 12b of the SiC substrate 12. The modified regions 7a are formed side by side (i.e., in a sequence far from the incident surface of the laser light). Furthermore, the size of the modified region 7a can be adjusted by changing the pulse energy of the laser light L.

Thereby, the cracks generated from the respective modified regions 7a extend toward the thickness direction of the SiC substrate 12 and are connected to each other. In particular, the crack extending from the modified region 7a closest to the surface 12a of the laser light incident surface of the SiC substrate 12 toward the thickness direction of the SiC substrate 12 serves as the reaching surface 12a. In these cases, it is extremely important to accurately cut the SiC substrate 12 composed of a hard-to-machine material having a hardness second only to the diamond along the line to cut 5a.

After the modified region 7a is formed along the line to cut 5a, as shown in FIG. 11(b), the pulse is pulsed with a pulse width of 20 ns to 100 ns (more preferably, a pulse width of 50 ns to 60 ns). The condensed spot P of the illuminating light L is aligned with the inside of the SiC substrate 12, and the object to be processed 1 is irradiated along the line to cut 5m so that the pulse pitch is 10 μm to 18 μm (more preferably, the pulse pitch is 12 μm to 14 μm). Laser light L. Thereby, a modified region (second modified region) 7m as a cutting start point is formed inside the SiC substrate 12 along the line to cut 5m. This change The mass region 7m contains a molten processed region.

In the formation of the modified region 7m, more specifically, the surface 12a of the SiC substrate 12 is used as a laser light incident surface, and the light collecting point P of the laser light L is positioned inside the SiC substrate 12, along the line to cut 5m. The light collecting point P is relatively moved. Then, the relative movement of the condensed spot P along the line to cut 5m is performed for a plurality of predetermined lines 5 (for example, six times). At this time, by dividing the distance from the surface 12a to the position of the light-converging point P in each direction, a plurality of rows are formed on one planned cutting line 5m so as to be arranged in the thickness direction of the SiC substrate 12 (relative to the first The modified region 7m of the second column number (including one column), for example, six columns with a small number of columns. Here, the modified region 7m closest to the surface 12a of the laser light incident surface of the SiC substrate 12 is smaller than the modified region 7m of the second proximity surface 12a, and is formed from the inner surface 12b side of the SiC substrate 12. The modified region 7m is formed sequentially (i.e., in a sequence far from the incident surface of the laser light). Furthermore, the size of the modified region 7m can be adjusted by changing the pulse energy of the laser light L.

Thereby, the cracks generated from the respective modified regions 7m are extended toward the thickness direction of the SiC substrate 12 and are connected to each other. In particular, the crack extending from the modified region 7m closest to the surface 12a of the laser light incident surface of the SiC substrate 12 toward the thickness direction of the SiC substrate 12 serves as the reaching surface 12a. In these cases, it is extremely important to accurately cut the SiC substrate 12 composed of a hard-to-machine material having a hardness second only to the diamond along the line to cut 5m.

After the modified region 7m is formed along the cut line 5m, as shown in FIG. (a), the expansion tape 23 is expanded, and in this state, the blade edge 41 is pressed against the inner surface 12b of the SiC substrate 12 along the respective cutting planned lines 5m via the extension tape 23. Thereby, the object 1 to be processed is cut into a rod shape along the line to cut 5m with the modified region 7m as a starting point. At this time, since the extension belt 23 is in a state of being expanded, as shown in FIG. 12(b), the objects 1 to be cut into a rod shape are separated from each other.

After the object 1 is cut along the line to cut 5m, as shown in FIG. 13(a), the inner side 12b of the SiC substrate 12 is then passed through the extension tape 23 while the extension tape 23 has been expanded. The blade edge 41 is pressed along each of the planned cutting lines 5a. Thereby, the object to be processed 1 is cut into a wafer shape along the line to cut 5a with the modified region 7a as a starting point. At this time, since the extension belt 23 is in a state of being expanded, as shown in FIG. 13(b), the objects 1 to be cut into a wafer shape are separated from each other. As described above, the object 1 is cut into a wafer shape along the line to cut 5a, 5m, and a plurality of power elements are obtained.

According to the above-described laser processing method, the plate-shaped object 1 having the hexagonal SiC substrate 12 having the surface 12a having an angle of an oblique angle to the c-plane can be along the line to be cut. 5a and 5m are cut off with high precision, and as a result, the object 1 (i.e., power element) that is accurately cut along the line to cut 5a, 5m can be obtained.

First, the object 1 is irradiated with the laser light L along the line to cut 5a, 5m so that the pulse pitch is 10 μm to 18 μm. When the object 1 is irradiated with the laser light L under such conditions, cracking can be caused. It is easy to extend from the modified regions 7a and 7m in the thickness direction of the SiC substrate 12, and it is difficult for the crack to extend from the modified regions 7a and 7m toward the c-plane direction. In addition, when the laser beam L is irradiated to the object 1 along the line to cut 5a and 5m so that the pulse pitch is 12 μm to 14 μm, the crack can be further moved from the modified regions 7a and 7m toward the SiC substrate 12. The thickness direction is extended, and the crack is not easily extended from the modified regions 7a, 7m toward the c-plane.

Further, the laser light L is pulse-oscillated with a pulse width of 20 ns to 100 ns. Thereby, the crack can be easily and reliably extended from the modified regions 7a and 7m toward the thickness direction of the SiC substrate 12, and the cracks are reliably prevented from extending from the modified regions 7a and 7m toward the c-plane direction. Further, when the laser light L is pulse-oscillated with a pulse width of 50 ns to 60 ns, the crack can be more reliably and easily extended from the modified regions 7a and 7m toward the thickness direction of the SiC substrate 12, and the crack is allowed to be cracked. It is more sure and not easy to extend from the modified regions 7a, 7m toward the c-plane direction.

Further, along the line to cut 5a, the modified region 7a which is second closest to the surface 12a of the SiC substrate 12 as the laser light incident surface is formed to be relatively small. By this, even if a is inclined in the thickness direction of the SiC substrate 12, it is possible to prevent the crack generated from the modified region 7a of the second proximity surface 12a from extending in the a-plane direction and being largely large in the self-cutting line 5a. The situation of reaching the surface 12a in the state of the ground offset occurs. Then, along the line to cut 5a, the modified region 7a closest to the surface 12a of the laser light incident surface of the SiC substrate 12 is formed to be relatively large. Thereby, the crack is hard to extend toward the thickness direction of the SiC substrate 12 from the modified region 7a. In the state, the crack can be surely reached from the modified region 7a closest to the surface 12a to the surface 12a. Moreover, along the line to cut 5m, the modified region 7m which is second closest to the surface 12a of the SiC substrate 12 as the laser light incident surface is formed to face large. Thereby, the modified region 7m is in a state where the crack easily spreads in the thickness direction of the SiC substrate 12, and complements this, and the crack generated from the modified region 7m of the second proximity surface 12a can be brought to the surface 12a. Or nearby. Then, along the line to cut 5m, the modified region 7m closest to the surface 12a of the laser light incident surface of the SiC substrate 12 is formed to be relatively small. Thereby, damage to the surface 12a can be prevented, and the crack can be surely reached from the modified region 7m to the surface 12a. As described above, along the line to cut 5a, the crack can be surely reached from the modified region 7a to the surface 12a, and along the line to cut 5m, the crack can be surely reached from the modified region 7m. Surface 12a. This effect can be achieved irrespective of the formation order of the modified regions 7a and 7m to be described later, the order of formation, and the like, and is more remarkable in the order of formation and formation of the modified regions 7a and 7m to be described later.

In addition, when the modified region 7m is formed along one planned cutting line 5m, the predetermined line 5a is cut along one strip to form a plurality of modified regions 7a. Thereby, even if a is inclined in the thickness direction of the SiC substrate 12, when the modified regions 7a are formed, it is possible to prevent the crack from being greatly extended from the modified region 7a toward the a-plane direction, and all the modifications are performed. Between the regions 7a, the cracks can be easily connected in the thickness direction of the SiC substrate 12. Moreover, compared with the case where the modified region 7a is formed along one planned cutting line 5a, the predetermined line 5m is cut along one strip to form a modified number of fewer rows. Area 7m. Thereby, when each of the modified regions 7m is formed, the crack can be greatly extended from the modified region 7m toward the thickness direction of the SiC substrate 12. As described above, along the line to cut 5a, the crack can be extended from the modified region 7a toward the thickness direction of the SiC substrate 12, and along the line to cut 5m, the crack can be made from the modified region 7m. It extends toward the thickness direction of the SiC substrate 12. This effect can be achieved irrespective of the formation dimensions of the modified regions 7a and 7m described above and the order of formation of the modified regions 7a and 7m to be described later, and the size of the modified regions 7a and 7m can be changed according to the above-described modified regions 7a and 7m. When the order of formation of the prime regions 7a, 7m is achieved, it can be more significantly achieved.

Further, before the conditions for forming the crack to extend in the thickness direction of the SiC substrate 12 are the gentle modified regions 7m, the conditions for stretching the cracks in the thickness direction of the SiC substrate 12 are severely modified. Area 7a. With this, when the modified region 7a is formed, the portion where the planned cutting line 5a intersects the planned cutting line 5m can prevent the crack from extending from the modified region 7a toward the thickness direction of the SiC substrate 12 by the modified region. The situation hindered by 7m. This effect can be achieved irrespective of the formation size, formation of columns, and the like of the modified regions 7a and 7m described above.

In addition, the object 1 is cut along the line to cut 5m as the starting point of the modified region 7m, and then the object 1 is cut along the line to cut 5a with the modified region 7a as a starting point. As a result, the object to be processed 1 is cut along the line 5m to be cut, which is difficult to cut, by the formation of the modified region 7m having a small number of rows, and then the number of columns is changed by a larger number of columns. The formation of the mass region 7a is determined along a cutting premise that is easier to cut. The object 5 is cut and the object 1 is cut. Therefore, it is possible to equalize the force required to cut the object 1 along the line to cut 5m and the force required to cut the object 1 along the line to cut 5a, and it is possible to follow the cutting schedule. The cutting accuracy of the line 5m and the cutting accuracy along the line to cut 5a are further improved. This effect can be achieved irrespective of the formation size, formation of columns, and the like of the modified regions 7a and 7m described above.

Fig. 14 is a view showing a photograph of a cut surface of the SiC substrate 12 cut along the line to cut 5a by the above-described laser processing method. Moreover, FIG. 15 is a view showing a photograph of the cut surface of the SiC substrate 12 cut along the line to cut 5m by the above-described laser processing method. Moreover, FIG. 16 is a plan view showing a cut surface of the cut surface of the SiC substrate 12 cut along the line to cut 5a, 5m by the above-described laser processing method. Here, a hexagonal SiC substrate 12 having a thickness of 4° and a thickness of 350 μm was prepared.

First, as shown in FIG. 14, eight rows of modified regions 7a are formed on one planned cutting line 5a so as to be aligned in the thickness direction of the SiC substrate 12 along the line to cut 5a. Then, the modified region 7a which is second closest to the surface 12a of the SiC substrate 12 as the laser light incident surface becomes smaller than the modified region 7a closest to the surface 12a, and is from the inner surface 12b side of the SiC substrate 12. The modified region 7a is sequentially formed. As can be seen from Fig. 14, the extension of the crack generated from the modified region 7a is stopped by the formation of the modified region 7a with the second proximity surface 12a. As a result, the meandering system that cuts the line to cut 5a is cut as shown in Fig. 16 and is suppressed to ±4 μm or less.

In addition, the distance from the surface 12a to the position of the light-converging point P is 314.5 μm, 280.0 μm, 246.0 μm, 212.0 μm, 171.5 μm, and 123.5 in order from the modified region 7a on the inner surface 12b side of the SiC substrate 12. Μm, 79.0 μm, 32.0 μm. Further, the pulse energy of the laser light L is sequentially 25 μJ, 25 μJ, 25 μJ, 25 μJ, 20 μJ, 15 μJ, 6 μJ, and 6 μJ from the modified region 7 a on the back surface 12 b side of the SiC substrate 12 .

In addition, as shown in FIG. 15, the modified region 7m of six rows is formed on one planned cutting line 5m so as to be aligned in the thickness direction of the SiC substrate 12 along the line to cut 5m. Then, the modified region 7m closest to the surface 12a of the laser light incident surface of the SiC substrate 12 is smaller than the modified region 7m of the second proximity surface 12a, and is supported from the inner surface 12b side of the SiC substrate 12. The modified region 7m is sequentially formed. As can be seen from Fig. 15, the crack generated from the modified region 7m extends to the surface 12a or its vicinity by the formation of the modified region 7m with the second proximity surface 12a. As a result, the meandering system that cuts the line 5m to be cut is cut as shown in Fig. 16 and is suppressed to ±2 μm or less.

In addition, the distance from the surface 12a to the position of the light-converging point P is 315.5 μm, 264.5 μm, 213.5 μm, 155.0 μm, 95.5 μm, and 34.5 in order from the modified region 7m on the inner surface 12b side of the SiC substrate 12. Mm. Further, the pulse energy of the laser light L is 25 μJ, 25 μJ, 20 μJ, 20 μJ, 15 μJ, and 7 μJ from the modified region 7 m on the inner surface 12 b side of the SiC substrate 12 .

Next, the cracks on the surface 12a of the laser light incident surface that reaches the SiC substrate 12 from the modified regions 7a and 7m will be described (hereinafter, referred to as "half cut ( The relationship between the half cut) and the crack extending from the modified regions 7a and 7m toward the c-plane direction (hereinafter referred to as "c-plane crack"). Here, as shown in FIG. 17 and FIG. 18, in the case where the crack is to be extended in the thickness direction of the SiC substrate 12, the half-cut is less likely to occur and the c-plane crack is less likely to occur than the modified region 7m. The qualitative region 7a will be described as an object.

Fig. 19 is a table showing the relationship between the pulse width and the ID threshold, the HC threshold, and the processing margin. Here, the pulse width is changed in the range of 1 ns and 10 ns to 120 ns, and the ID threshold, the HC threshold, and the processing margin are evaluated for each pulse width. 20 is a table showing the relationship between the pulse pitch and the ID threshold, the HC threshold, and the machining margin. Here, the pulse pitch was changed in the range of 6 μm to 22 μm, and the ID threshold, the HC threshold, and the processing margin were evaluated for each pulse pitch.

Furthermore, the ID threshold refers to the minimum value of the pulse energy of the laser light L that can cause the c-plane crack, and the one with the highest ID threshold (that is, the one that does not easily generate the c-plane crack) is evaluated as excellent, good, acceptable, and non-existent. . Further, the HC threshold value means the minimum value of the pulse energy of the laser light L which can be generated by half-cutting, and is preferably evaluated as excellent, good, and acceptable from the case where the HC threshold is low (that is, the half-cut is likely to occur). Moreover, the processing margin refers to the difference between the ID threshold and the HC threshold, and is evaluated as excellent, good, acceptable, and incapable from the processing margin. Then, the total system is measured by the priority of the ID threshold, the HC threshold, and the processing margin, and the evaluation is excellent, good, acceptable, and impossible.

As a result, as shown in FIG. 19, it is preferable that the laser light L is pulse-oscillated with a pulse width of 20 ns to 100 ns, and it is more preferable to pulse-raise the laser light L with a pulse width of 50 ns to 60 ns. By doing so, it can suppress The production of c-plane cracks can also promote the production of half-cuts. Further, in the case where the pulse width is 10 ns, the ID threshold value, the machining margin, and the overall evaluation are in a state in which the pulse width is 20 ns.

Further, as shown in FIG. 20, it is preferable that the SiC substrate 12 is irradiated with the laser light L along the line to cut 5a, 5m so that the pulse pitch is 11 μm to 15 μm, and the pulse pitch is 11 μm to 15 μm. It is preferable that the SiC substrate 12 is irradiated with the laser light L along the line to cut 5a, 5m, and the SiC substrate 12 is irradiated with laser light along the line to cut 5a, 5m so that the pulse pitch is 12 μm to 14 μm. L is the best. Thereby, the occurrence of c-plane cracks can be suppressed, and the generation of half-cuts can be promoted. Further, when the pulse pitch is 10 μm, the evaluation of the ID threshold is possible. Therefore, if it is more important to suppress the occurrence of the c-plane crack, the pulse pitch is preferably larger than 10 μm.

21 to 23 are tables showing experimental results of the processing margins of the pulse width and the pulse pitch when the laser light L is condensed by the number of openings 0.8. These experimental results are the basis for the evaluations shown in Figs. 19 and 20. The experimental conditions at the time of obtaining the experimental results of FIGS. 21 to 23 are as follows. . First, the hexagonal SiC substrate 12 having a thickness of 100 μm having an oblique angle of 4° is used as a target, and the laser beam L is concentrated along a line to cut 5a extending in a direction parallel to the surfaces 12a and a. Point P moves. Further, the laser beam L is condensed by the number of openings of 0.8, and the condensed spot P is positioned at a distance of 59 μm from the surface 12a of the laser light incident surface of the SiC substrate 12.

On the premise of the above experimental conditions, the energy (pulse energy) of the laser light L and the pulse pitch of the laser light L are changed, and the state of the modified region 7a and the half-cut and c-plane cracks are observed. In FIGS. 21 to 23, the pulse width of the laser light L is set to 27 ns, 40 ns, and 57 ns, respectively, and the pulse width (repetition frequency) of the laser light L is set to 10 kHz, 20 kHz, and 35 kHz.

In the experimental results of Figs. 21 to 23, the ST system showed no half cut, and the HC system showed half cut. Further, the ID system showed a c-plane crack, and the LV1 to LV3 system showed the scale of the c-plane crack. In the case where the modified region 7a is formed along the two predetermined lines 5a, the region of 40 mm (20 mm × 2 regions) is set to LV1 when the area where the c-plane crack is generated is less than 150 μm, and the c-plane is used. When the area where the crack is generated is less than 450 μm, LV2 is set, and when the area where the c-plane crack is generated is 450 μm or more, LV3 is used. In LV1, the extension of the c-crack in the direction perpendicular to the line to cut 5a is 10 μm to 20 μm, whereas in the case of LV2, LV3, the extension of the crack in the direction perpendicular to the line to cut 5a becomes The maximum is about 100μm.

Figure 24 is a graph showing the relationship between the pulse pitch and the HC threshold. 25 is a graph showing the relationship between the pulse pitch and the ID threshold. Moreover, Fig. 26 is a graph showing the relationship between the pulse pitch and the machining margin. These charts are based on the experimental results of Figures 21-23. As shown in FIG. 24 and FIG. 25, when the pulse width is increased, both the HC threshold value and the ID threshold value are increased. However, the effect of increasing (rising) the ID threshold value is larger than the deterioration (rise) of the HC threshold value. This is shown in Figure 26, meaning when the pulse When the width becomes larger, the machining margin becomes larger. For example, when focusing on a pulse width of 27 ns and a pulse width of 57 ns, when the pulse pitch is 12 μm, the HC threshold is deteriorated (rised) by 2 μJ from 15 μJ to 17 μJ, and the ID threshold is raised (rised) by 12 μJ from 17 μJ. The formation was 29 μJ. Then, in the case of a pulse width of 40 ns, it was confirmed that the processing margin was greatly improved in the range of the pulse pitch of 10 μm to 16 μm compared to the case where the pulse width was 27 ns. Further, in the case of a pulse width of 57 ns, it was confirmed that the processing margin was greatly improved in the range of the pulse pitch of 6 μm to 20 μm compared to the case where the pulse width was 27 ns.

27 to 29 are tables showing experimental results of the processing margins of the pulse width and the pulse pitch in the case where the laser light L is condensed by the number of openings 0.6. These experimental results are the basis for the evaluations shown in Figs. 19 and 20. The experimental conditions at the experimental results of Figs. 27 to 29 are as follows. First, a hexagonal SiC substrate 12 having a thickness of 350 μm having a surface 12a having an oblique angle component to the c-plane is used as a target along a line to cut 5a extending in a direction parallel to the surfaces 12a and a, The condensing point P of the laser light L is moved. Further, the laser light L is condensed by the number of openings of 0.6, and the condensed spot P is located at a position of 50 μm from the surface 12a of the laser light incident surface of the SiC substrate 12.

On the premise of the above experimental conditions, the energy (pulse energy) of the laser light L and the pulse pitch of the laser light L are changed, and the state of the modified region 7a and the half-cut and c-plane cracks are observed. In FIGS. 27 to 29, the pulse width of the laser light L is set to 27 ns, 40 ns, and 57 ns, respectively, and the pulse width (repetition frequency) of the laser light L is set to 10 kHz, 20 kHz, 35kHz.

In the experimental results of Figs. 27 to 29, the ST system showed no half cut, and the HC system showed half cut. Further, the ID system showed a c-plane crack, and the LV1 to LV3 system showed the scale of the c-plane crack. The reference system of LV1 to LV3 is the same as the experimental results of FIGS. 21 to 23 described above. Further, the OD system shows that when the energy of the laser light L is increased, the modified region 7a also becomes large, because the crack generated for this reason is largely shifted from the line to cut 5a to reach the surface of the SiC substrate 12. 12a. In this case, no evaluation was made for the c-plane crack. However, when the pulse width is 40 ns and the pulse width is 57 ns, and the pulse pitch is 12 μm or more, large-scale c-plane cracks are not generated.

Figure 30 is a graph showing the relationship between the pulse pitch and the HC threshold. This chart is based on the experimental results of Figures 27-29. As shown in FIG. 30, in the case of a pulse width of 57 ns, the HC threshold value is less likely to occur in the case of a pulse width of 40 ns, which is about 2 μJ to 4 μJ. In the case where the number of openings is 0.8, when the number of openings is 0.6, the influence of the difference is small at the condensed point P of the laser light L. Therefore, in the case of a pulse width of 57 ns and a pulse width of 40 ns, Become the same level of HC threshold. Therefore, if the correction is performed, the HC threshold does not deteriorate even if the pulse width is increased (at least 60 ns).

Next, an experimental result regarding the processing margin of the HC quality in the vicinity of the surface 12a of the laser light incident surface of the SiC substrate 12 will be described. The experimental conditions at the experimental results of Figs. 31 to 33 are as follows. First, a hexagonal SiC substrate 12 having a thickness of 100 μm having an oblique angle of 4° was used as The object moves the light-converging point P of the laser light L along the line to cut 5a extending in a direction parallel to the surfaces 12a and a. Further, the laser light L is condensed by the number of openings of 0.8.

First, in the experimental results of FIG. 31, the laser light L is irradiated with respective pulse widths of 27 ns, 40 ns, 50 ns, and 57 ns, and half-cut is generated at a spot position of 40.6 μm and half-cut at a spot position of 40.6 μm. (Pulse energy), the position of the condensed spot was changed in the range of 25.3 μm to 40.6 μm, and the state of the half cut was observed. The pulse pitch of the laser light L is set to a predetermined state of 14 μm. Furthermore, the position of the condensed spot refers to the distance from the surface 12a to the position of the condensed spot P. As a result, deterioration of the quality of the half-cut due to the pulse width hardly occurs, and a high-quality (small cut to small meandering line) half-cut is generated in the pulse width of 27 ns to 57 ns. Further, the machining margin becomes larger as the pulse width increases. When the pulse width is small, branches, cracks (OD), and the like are easily generated in a part of the half cut.

Further, in the experimental results of FIG. 32, the laser light L was irradiated with respective pulse widths of 27 ns, 40 ns, 50 ns, and 57 ns, and the pulse energy was changed in the range of 7 μJ to 12 μJ to observe the half-cut state. The pulse pitch of the laser light L is set to be a certain 14 μm, and the position of the light collecting point is set to be a certain 34.5 μm. As a result, almost no change in the HC threshold due to the pulse width occurs. Moreover, half cuts of the same degree of quality can be produced with the same pulse energy.

Further, in the experimental results of FIG. 33, the laser light L was irradiated at respective pulse intervals of 10 μm, 12 μm, 14 μm, 16 μm, and 18 μm, and the pulse energy was changed in the range of 7 μJ to 12 μJ, and the half-cut state was observed. mine The pulse width of the light beam L is set to be a certain 57 ns, and the position of the light collecting point is set to be a certain 34.5 μm. As a result, almost no change in the HC threshold due to the pulse width occurs. Further, in the case where the condensed spot position is 34.5 μm, half cut of the same degree of quality can be produced with the same pulse energy.

Next, other laser processing methods for suppressing c-plane cracks will be described. First, a plate-shaped object 1 having a hexagonal SiC substrate 12 having a surface 12a having an angle of an oblique angle to the c-plane is prepared, and the planned cutting lines 5a and 5m are set. Next, as shown in FIG. 34(a), the condensed spot P of the laser light L is aligned with the inside of the SiC substrate 12, and is respectively along two preparatory lines set on both sides of the planned cutting line 5a (5 m). 5p, the object 1 is irradiated with the laser light L. Thereby, the preliminary modified region 7p is formed inside the SiC substrate 12 along each of the preliminary lines 5p. This preliminary modified region 7p includes a molten processed region.

The standby line 5p is a line extending in a direction parallel to the line to cut 5a (5m) in a plane parallel to the surface 12a, on both sides of the line to cut 5a (5m). Further, in the case where the functional element is formed on the surface 12a of the SiC substrate 12 in each of the regions defined by the cutting planned lines 5a and 5m, the standby line 5p is set in the phase when viewed from the thickness direction of the SiC substrate 12. It is preferred that the area between adjacent functional elements is good.

When the laser beam L is irradiated to the object 1 along the respective preparatory lines 5p, cracks are less likely to occur from the preliminary modified region 7p toward the SiC substrate 12 than the modified region 7a (7 m) which is the starting point of the cutting. The preliminary modified region 7p can reduce the pulse energy, the pulse pitch, the pulse width, and the like of the laser light L, and can be compared with the modified region 7a (7 m) which is the starting point of the cutting. It is not easy to cause cracks in the SiC substrate 12.

After the preliminary modified region 7p is formed along the preliminary line 5p, the condensed spot P of the laser light L is aligned with the inside of the SiC substrate 12, and the object 1 is irradiated with lightning along the line to cut 5a (5 m). Light L. Thereby, the modified region 7a (7m) as the cutting start point is formed inside the SiC substrate 12 along the line to cut 5a (5 m). This modified region 7a (7m) contains a molten processed region. After the modified region 7a (7m) is formed along the line to cut 5a (5m), the object 1 is cut along the line to cut 5a (5m) with the modified region 7a (7m) as a starting point.

According to the above-described laser processing method, the plate-shaped object 1 having the hexagonal SiC substrate 12 having the surface 12a having an angle of an oblique angle to the c-plane can be along the line to be cut. 5a and 5m are cut off with high precision, and as a result, the object 1 (i.e., power element) that is accurately cut along the line to cut 5a, 5m can be obtained.

In other words, when the modified region 7a (7m) is formed inside the SiC substrate 12 along the line to cut 5a (5 m), the preliminary modified region 7p is formed inside the SiC substrate 12 along each of the preliminary lines 5p. Then, the preparatory line 5p is located in a plane parallel to the surface 12a, is located on both sides of the line to cut 5a (5m), and extends in a direction parallel to the line to cut 5a (5m). Therefore, even if the crack extends from the modified region 7a (7m) toward the c-plane direction, the turtle is not formed as shown in Fig. 34(b), as shown in Fig. 34(a). The extension of the cleft (c-crack) is also inhibited by the preparatory modified region 7p. Therefore, there is no need to consider cracks from the modified area. When the 7a (7m) is easily stretched in the c-plane direction, the object 1 can be irradiated with laser light from the modified region 7a (7m) so as to be easily extended in the thickness direction of the SiC substrate 12. Further, since the preliminary modified region 7p does not need to function as a starting point of the cutting (that is, it is not necessary to promote the crack from the preliminary modified region 7p toward the thickness direction of the SiC substrate 12), the crack is not easily generated by the crack. Since the laser light L of the SiC substrate 12 is irradiated, it is easy to suppress the crack from extending from the preliminary modified region 7p toward the c-plane direction when the preliminary modified region 7p is formed. Therefore, the plate-shaped object to be processed having the hexagonal SiC substrate 12 having the main surface at an angle of the oblique surface of the c-plane can be accurately cut along the line to cut 5a (5 m).

Further, when the modified region 7a (7m) is formed, when the condensed spot P of the laser light L is positioned at a predetermined distance from the surface 12a of the laser light incident surface of the SiC substrate 12, the preparation is changed. At the time of formation of the mass region 7p, the condensed spot P of the laser light L is also positioned at the same distance from the surface 12a. Thereby, it is possible to more reliably suppress the extension of the crack from the modified region 7a (7 m) toward the c-plane direction.

Further, even if the preliminary modified region 7p is formed inside the SiC substrate 12 along each of the preliminary lines 5p, the SiC substrate 12 is formed along the planned cutting line 5a (5 m) set between the preliminary lines 5p. The inside of the modified region 7a (7m) is formed, and the extension of the c-plane crack is also suppressed by the preliminary modified region 7p. In this case, the formation of the modified region 7a (7m) along the line to cut 5a (5m) is excellent in the formation of the preliminary modified region 7p along the preliminary line 5p.

[Industry use possibility]

According to the present invention, the plate-shaped object to be processed having the hexagonal SiC substrate having the principal surface having an oblique angle component to the c-plane can be accurately cut along the line to be cut.

1‧‧‧Processing objects

5a, 5m‧‧‧ cut-off line

5p‧‧‧Preparation line

7a, 7m‧‧‧ modified areas

7p‧‧‧Prepared modified area

12‧‧‧ SiC substrate

12a‧‧‧Surface (main surface)

12b‧‧‧ inside (main face)

L‧‧‧Laser light

P‧‧‧ spotlight

Fig. 1 is a configuration diagram of a laser processing apparatus for forming a modified region.

Fig. 2 is a plan view of an object to be processed before laser processing.

Fig. 3 is a cross-sectional view taken along line III-III of the object of Fig. 2;

Fig. 4 is a plan view showing an object to be processed after laser processing.

Fig. 5 is a cross-sectional view taken along line V-V of the object of Fig. 4;

Fig. 6 is a cross-sectional view taken along line VI-VI of the object of Fig. 4;

Fig. 7 is a plan view showing an object to be processed which is a target of the laser processing method according to the embodiment of the present invention.

Fig. 8 is a view showing a crystal structure of the object to be processed of Fig. 7;

Fig. 9 is a partial cross-sectional view showing the object to be processed of Fig. 7;

Fig. 10 is a partial cross-sectional view showing an object to be processed in a laser processing method according to an embodiment of the present invention.

Fig. 11 is a partial cross-sectional view showing an object to be processed in a laser processing method according to an embodiment of the present invention.

Fig. 12 is a partial cross-sectional view showing an object to be processed in a laser processing method according to an embodiment of the present invention.

Fig. 13 is a partial cross-sectional view showing an object to be processed in a laser processing method according to an embodiment of the present invention.

Fig. 14 is a view showing a photograph of a cut surface of a SiC substrate cut by a laser processing method according to an embodiment of the present invention.

Fig. 15 is a view showing a photograph of a cut surface of a SiC substrate cut by a laser processing method according to an embodiment of the present invention.

Fig. 16 is a plan view showing a plan view of a SiC substrate cut by a laser processing method according to an embodiment of the present invention.

Fig. 17 is a perspective view for explaining a c-plane crack generated inside the SiC substrate.

Fig. 18 is a view showing a photograph of a cut surface of a SiC substrate in which a c-plane crack is generated.

Fig. 19 is a table showing the relationship between the pulse width and the ID threshold, the HC threshold, and the processing margin.

Fig. 20 is a table showing the relationship between the pulse pitch and the ID threshold, the HC threshold, and the processing margin.

Fig. 21 is a table showing experimental results of processing margins of pulse width and pulse pitch.

Fig. 22 is a table showing experimental results of processing margins of pulse width and pulse pitch.

Fig. 23 is a table showing experimental results of processing margins of pulse width and pulse pitch.

Figure 24 is a graph showing the relationship between the pulse pitch and the HC threshold.

Figure 25 is a graph showing the relationship between pulse pitch and ID threshold.

Fig. 26 is a graph showing the relationship between the pulse pitch and the machining margin.

Fig. 27 is a table showing experimental results of processing margins of pulse width and pulse pitch.

Fig. 28 is a table showing experimental results of processing margins of pulse width and pulse pitch.

Fig. 29 is a table showing experimental results of processing margins of pulse width and pulse pitch.

Figure 30 is a graph showing the relationship between the pulse pitch and the HC threshold.

Fig. 31 is a table showing the experimental results of the processing margin of HC quality in the vicinity of the laser light incident surface.

Fig. 32 is a table showing experimental results of processing margin of HC quality in the vicinity of the laser light incident surface.

Fig. 33 is a table showing the experimental results of the processing margin of HC quality in the vicinity of the laser light incident surface.

Figure 34 is a plan view for explaining a laser processing method according to another embodiment of the present invention.

1‧‧‧Processing objects

5a, 5m‧‧‧ cut-off line

7a, 7m‧‧‧ modified areas

12‧‧‧ SiC substrate

12a‧‧‧Surface (main surface)

12b‧‧‧ inside (main face)

23‧‧‧Expansion belt

L‧‧‧Laser light

P‧‧‧ spotlight

Claims (2)

A laser processing method for forming a plate-shaped object to be processed having a hexagonal SiC substrate having a principal surface having an oblique angle component to a c-plane, respectively, along a direction parallel to the main surface and the a-plane A laser processing method in which a first cutting planned line extending in a direction and a second cutting planned line extending in a direction parallel to the main surface and the m-plane are cut is characterized in that: a first process is provided By concentrating the condensing point of the laser light in the inside of the SiC substrate, the laser beam is irradiated onto the object to be processed along the first line to cut, and the first line is cut along the first line to be cut. a first modified region in which the starting point is cut is formed inside the SiC substrate; and a second process is performed after the first process, and the condensed spot is located inside the SiC substrate, along the first (2) cutting the predetermined line, irradiating the target object with the laser beam, and forming a second modified region as a cutting start point in the inside of the SiC substrate along the second cutting planned line; After the 2 process, the first modified area is used as the The starting point is that the object to be processed is cut along the first line to be cut, and the third process of cutting the object to be processed along the second line to cut is started with the second modified region as a starting point. The laser processing method according to claim 1, wherein the first modified region and the second modified region comprise a molten processed region.