TWI528431B - 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.

SiC (cerium carbide) is attracting attention as a semiconductor material capable of producing a power element excellent in heat resistance, high voltage resistance, and power saving. However, since SiC is a hard-to-machine material that is second only to diamonds in hardness, it is necessary to perform low-speed processing and frequently replace the blades if the object to be processed having a plate shape including a SiC substrate is cut by a blade. Then, by irradiating the object with the laser light, a modified region is formed inside the SiC substrate along the line to cut, and the object to be processed is cut along the line to cut with the modified region as a starting point. A laser processing method has been proposed (for example, refer to Patent Document 1).

[Patent Literature]

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

However, in the above-described laser processing method, the inventors have found that a plate-shaped object to be processed having a hexagonal SiC substrate (having a main surface deviated from the c-plane) is cut. The following topics are concerned. That is, if extending in a direction parallel to the main surface and the a surface The first modified region is formed in the SiC substrate, and the second modified region is formed in the SiC substrate along the second planned cutting line extending in the direction parallel to the main surface and the m-plane. The cutting accuracy along the first cutting planned line may be worse than the cutting accuracy along the second cutting planned line. As a result of investigation by the inventors of the present invention, it is found that the crack easily spreads from the second modified region toward the thickness direction of the SiC substrate, but the crack does not easily extend from the first modified region toward the thickness of the SiC substrate. .

Accordingly, an object of the present invention is to provide a laser processing method capable of providing a plate-shaped object to be processed having a hexagonal SiC substrate (having a main surface deviated from the c-plane) along a line to be cut. Cut off with high precision.

A laser processing method according to a point of view of the present invention is a plate-shaped object to be processed having a hexagonal SiC substrate (having a main surface deviated from the c-plane), and is parallel to the main surface and the a-plane A laser processing method for cutting a first cutting planned line and a second cutting planned line extending in a direction parallel to the main surface and the m-plane; the laser processing method includes the first step and the second step In the first step, the condensing point of the laser light is aligned with the inside of the SiC substrate, and the laser beam is irradiated onto the object to be processed along the first line to cut, thereby along the first line to cut. The first modified region as the cutting start point is formed inside the SiC substrate, and a plurality of first modified regions are formed in a plurality of first planned cutting lines so as to be aligned in the thickness direction of the SiC substrate. The second step By aligning the condensed spot with the inside of the SiC substrate, the laser beam is irradiated onto the object to be processed along the second line to cut, whereby the second modification is used as the cutting start point along the second line to cut. The region is formed inside the SiC substrate, and a plurality of second modified regions are formed in a plurality of second planned cutting lines so as to be aligned in the thickness direction of the SiC substrate. In the first step, the laser light is separated from the SiC substrate. The first modified region having the second closest incident region is smaller than the first modified region closest to the incident surface of the laser light, and the first modified region is formed from the far side to the near the laser light incident surface; In the second step, the second modified region closest to the incident surface of the laser light is smaller than the second modified region which is closer to the second incident surface of the laser light, and is formed in a sequence from the far side to the near incident surface of the laser light. The second modified area.

In the laser processing method, the first modified region which is second closest to the incident surface of the laser light is formed relatively small along the first planned cutting line. In this manner, even if the a-plane is inclined with respect to the thickness direction of the SiC substrate, it is possible to prevent the crack generated in the first modified region which is closest to the incident surface of the laser light from extending in the a-plane direction, and it is possible to avoid a large deviation from the first one. The state of cutting the predetermined line reaches the laser light incident surface. Further, along the first planned cutting line, the first modified region closest to the incident surface of the laser light is relatively large. In this manner, the crack does not easily extend from the first modified region toward the thickness direction of the SiC substrate, but the crack can be surely made to reach the laser light incident surface from the first modified region closest to the laser light incident surface. Further, along the second planned cutting line, the second modified region which is second closest to the incident surface of the laser light is relatively large. In this way, the crack tends to extend from the second modified region toward the thickness direction of the SiC substrate, and the crack generated in the second modified region near the laser light incident surface can reach the laser light incident surface or Near it. Moreover, along the second cutting line, the closest to the incident surface of the laser light The second modified region is formed relatively small. In this way, it is possible to prevent damage on the incident surface of the laser light, and it is possible to reliably cause the crack to reach the laser light incident surface from the second modified region. As described above, it is possible to surely allow the crack to pass from the first modified region to the laser light incident surface along the first line to cut, and to reliably cause the crack along the second line to cut. The laser light incident surface is reached from the second modified region. Therefore, according to the laser processing method, a plate-shaped object to be processed having a hexagonal SiC substrate (having a main surface which is offset from the c-plane) can be cut with high precision along the line to cut. The off angle is also the case where 0° is included. In this case, the main surface is parallel to the c-plane. Further, the second step may be performed after the first step, or the first step may be performed after the second step.

The laser processing method according to one aspect of the present invention may further include a third step after the first step and the second step, and the third step is to follow the first modified region as a starting point and to follow the first cutting schedule The line cuts the object to be processed, and cuts the object to be processed along the second line to cut along the second modified region. In this way, the object to be processed which is cut with high precision along the line to cut can be obtained. Further, after cutting along the first line to cut, the cutting along the second line to cut can be performed, and the cutting along the second line to cut can be performed along the first line. Cut off the cut of the predetermined line.

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, it is possible to cut the object to be processed in a plate shape including a hexagonal SiC substrate (having a main surface which is deviated from the c-plane) The predetermined line is cut off with high precision.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the respective drawings, the same or corresponding components are designated by the same reference numerals, and the description thereof will not be repeated.

In the laser processing method according to the embodiment of the present invention, the object to be processed is irradiated with the laser beam along the line to cut, whereby the modified region is formed inside the object to be processed along the line to cut. Therefore, first, the formation of the 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 applies pulsed laser light to the laser beam 101, and a beam splitter 103 that is arranged to change the optical axis (light path) direction of the laser light L by 90°. 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 (the laser beam L is condensed by the condensing lens 105), and a stage 111 for moving the support table 107, The laser light source control unit 102 of the laser light source 101 and the stage control unit 115 that controls the movement of the stage 111 are controlled to adjust the output of the laser light L and the pulse width.

In the laser processing apparatus 100, the laser beam L emitted from the laser light source 101 is changed in the optical axis direction by the beam splitter 103 by 90 degrees, and then condensed on the support table 107 by the collecting lens 105. The inside of the object 1 to be processed. At the same time, the stage 111 is moved to relatively move the object 1 with respect to the laser beam L along the line to cut 5 . Take this The modified region along the line to cut 5 is formed in the object 1 to be processed.

As shown in FIG. 2, a cutting line 5 for cutting the object 1 is set in the object 1 to be processed. The line to cut 5 is an imaginary line extending linearly. In the case where the modified region is formed inside the object 1 as shown in FIG. 3, the laser light L is placed along the line to cut 5 in a state where the light-converging point P is aligned inside the object 1 (that is, the direction of the arrow A in Fig. 2) relatively moves. As a result, as shown in FIG. 4 to FIG. 6, the modified region 7 is formed inside the object 1 along the line to cut 5, and the modified region 7 formed along the line to cut 5 becomes The starting point area 8 is cut.

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 linear shape but may be a curved shape, and may not be limited to an imaginary line but 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 the form of a column or a dot, and it is important that the modified region 7 is formed at least inside the object 1 to be processed. In addition, a crack may be formed from the modified region 7 as a starting point, and the cracked and modified region 7 may expose the outer surface (surface, back surface, or outer peripheral surface) of the object 1 to be processed.

Incidentally, the laser light L here is such that the object 1 is transmitted and is absorbed particularly in the vicinity of the condensing point inside the object 1 to form the modified region 7 in the object 1 (also That is, internal absorption type laser processing). As described above, 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. 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 processed region gradually progresses from the surface 3 side toward the back surface side.

However, the modified region formed in the present embodiment means a region in which the density, the refractive index, the mechanical strength, and other physical properties are different from the surroundings. 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 may be a region in which the mixture is mixed. Further, the modified region includes: a region in which the density of the modified region in the material of the object to be processed is changed from that in the non-modified region, and a region in which a lattice defect is formed (these can also be collectively referred to as High density difference row area).

Further, the region where the density of the molten processed region, the refractive index change region, and the modified region is changed compared to the density of the non-modified region, and the region where the lattice defect is formed may further be internal to the regions, or may be modified. The interface between the qualitative region and the non-modified region includes cracks (cracks, micro-cracks). The cracks involved may be comprehensive throughout the modified region, formed only in a portion, or formed in 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 spot is a modified portion formed by one pulse of pulsed laser light (that is, a one-shot laser shot: Laser Shot), and the set of modified spots becomes the modified region 7. The modified point includes at least one of a crack point, a melting treatment point, a refractive index change point, or a mixture of the points.

It is preferable to consider the required cutting accuracy and the desired correction point. The flatness of the cut surface, the thickness, the type, the crystal orientation of the object to be processed, and the like are appropriately controlled to control the size and the crack length that occurs.

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 turns and a thickness of 350 μm) of 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 at 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 off angle θ. As shown in Fig. 9, the SiC substrate 12 has a surface (main surface) 12a and a back surface (main surface) 12b which are formed at an angle θ from 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 chain line in the drawing); the m-plane is not inclined with respect to the thickness direction of the SiC substrate 12.

As shown in Fig. 7 and Fig. 9, a plurality of planned cutting lines (first cutting planned lines) 5a extending in a direction parallel to the surface 12a and the a surface are parallel to the surface 12a and the m surface. The cutting line (second cutting planned line) 5 m of a plurality of lines extending in the direction is set in a lattice shape (for example, 1 mm × 1 mm) on the object 1 to be processed. On the surface 12a of the SiC substrate 12, functional elements are formed in the respective regions drawn by the predetermined lines 5a, 5m, and the regions on the back surface 12b of the SiC substrate 12 are cut by the predetermined lines 5a, 5m. Metal wiring is formed. The functional element and the metal wiring constitute a power element in each of the sheet-like bodies obtained by cutting the object 1 along the line to cut 5a, 5m. Further, in the SiC substrate 12, an orientation flat 6a is formed in a direction parallel to the line to cut 5a, and a line to cut is formed. The 5 m parallel direction forms an orientation plane 6 m.

The above-described object 1 is cut along the line to cut 5a, 5m as follows. First, as shown in FIG. 10, the expanded tape 23 is attached to the object 1 so as to cover 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) is aligned with the SiC substrate 12 In the inside, the laser light L is irradiated onto the object 1 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. The modified region 7a is a molten processed region. The pulse pitch is a value obtained by dividing "the moving speed of the focused spot P of the laser light L with respect to the object 1" by the "repetition frequency of the pulsed laser light L".

The formation of the modified region 7a will be described in more detail. The surface 12a of the SiC substrate 12 serves as a laser light incident surface, and the condensed spot P of the laser light L is positioned inside the SiC substrate 12, and the condensed spot P is relatively moved along the line to cut 5a. Further, the relative movement of the condensed spot P along the line to cut 5a is made plural times (for example, eight times) for one line to cut. At this time, the distance from the surface 12a to the position of the light-converging point P is changed each time, thereby forming a plurality of columns (the number of the first column, for example, 8) for one planned cutting line 5a so as to be aligned in the thickness direction of the SiC substrate 12. The modified region 7a of the column). Here, the modified region 7a which is second closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is closer to the surface 12a. In a manner in which the modified region 7a is smaller, the modified region 7a is formed sequentially from the side of the back surface 12b of the SiC substrate 12 (that is, in order from the far side to the near side of the laser light incident surface). The size of the modified region 7a can be adjusted, for example, by changing the pulse energy of the laser light L.

In this manner, the cracks generated from the respective modified regions 7a are extended toward the thickness direction of the SiC substrate 12 to be connected to each other. In particular, the crack extending from the modified region 7a closest to the laser light incident surface (surface 12a) of the SiC substrate 12 toward the thickness direction of the SiC substrate 12 reaches the surface 12a. In this regard, it is very important that the SiC substrate 12 composed of the hard-to-machine material having a hardness second only to the diamond is cut with high precision 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 width of 20 ns to 100 ns (more preferably, the pulse width of 50 ns to 60 ns) is pulse-oscillated. The condensed spot P of the laser light L is aligned with the inside of the SiC substrate 12, and the laser light L is irradiated along the line 5d to be cut at a pulse pitch of 10 μm to 18 μm (more preferably, the pulse pitch is 12 μm to 14 μm). Processing object 1. In this manner, 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. The modified region 7m is a molten processed region.

The formation of the modified region 7m will be described in more detail. The surface 12a of the SiC substrate 12 is used as a laser light incident surface, and the condensed spot P of the laser light L is placed inside the SiC substrate 12 along the line to cut 5m. Moreover, let the relative movement of the condensed spot P along the cut line 5m, for one The cut line 5 is cut a plurality of times (for example, six times). At this time, the distance from the surface 12a to the position of the light-converging point P is changed every time, whereby a plurality of columns (less than the first column) are formed for one planned cutting line 5m so as to be aligned in the thickness direction of the SiC substrate 12. The modified region 7m of the second column number (including one column), for example, six columns). Here, the modified region 7m closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is made smaller from the back surface 12b side of the SiC substrate 12 so that the modified region 7m closest to the second surface 12a is smaller. The order (i.e., in order from the far side to the near side of the incident surface of the laser light) forms the modified region 7m. The size of the modified region 7m can be adjusted, for example, by changing the pulse energy of the laser light L.

In this manner, the cracks generated from the respective modified regions 7m are extended toward the thickness direction of the SiC substrate 12 to be connected to each other. In particular, the crack extending from the modified region 7m closest to the laser light incident surface (surface 12a) of the SiC substrate 12 toward the thickness direction of the SiC substrate 12 reaches the surface 12a. In this regard, it is very important that the SiC substrate 12 composed of the hard-to-machine material having a hardness second only to the diamond is cut with high precision along the line to cut 5m.

After the modified region 7m is formed along the line to cut 5m, the expanded tape 23 is expanded as shown in Fig. 12(a), and in this state, the blade 41 is passed through the expanded tape along each cut line 5m. 23 is pressed against the back surface 12b of the SiC substrate 12. Thereby, the object 1 is cut into a rod shape along the line to cut 5m from the modified region 7m. At this time, since the expanded tape 23 is in an expanded state, 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), while the expansion tape 23 is continuously expanded, the blade 41 is passed along each line 5a to be cut. The expansion tape 23 is pressed against the back surface 12b of the SiC substrate 12. In this manner, the object 1 is cut into a sheet shape along the line to cut 5a starting from the modified region 7a. At this time, since the expanded tape 23 is in an expanded state, as shown in Fig. 13(b), the objects 1 to be cut into pieces are separated from each other. As described above, the object 1 is cut into a sheet shape along the line to cut 5a, 5m to obtain a plurality of power elements.

According to the above-described laser processing method, the object 1 having a plate shape including the hexagonal SiC substrate 12 (having a surface 12a which is deviated from the c-plane) can be along the line to cut 5a. 5 m is cut with high precision, and as a result, the object 1 to be processed (that is, the power element) which is cut with high precision along the line to cut 5a and 5 m 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 these conditions, the crack can be easily extended from the modified regions 7a and 7m toward the thickness direction of the SiC substrate 12, and the crack is not easily changed from the modified region 7a, 7m toward The c-plane extends. In addition, when the laser beam L is irradiated to the object 1 along the line to cut 5a, 5m so that the pulse pitch is 12 μm to 14 μm, the crack can be more easily changed from the modified region 7a, 7m toward the SiC substrate. The thickness direction of 12 is extended, and the crack is less likely to extend from the modified region 7a, 7m toward the c-plane.

In addition, the laser light L is pulsed with a pulse width of 20 ns to 100 ns. oscillation. In this way, it is possible to reliably cause the crack to easily extend from the modified regions 7a and 7m toward the thickness direction of the SiC substrate 12, and it is possible to reliably prevent the crack from extending from the modified regions 7a and 7m toward the c-plane direction. In addition, when the laser beam L is pulse-oscillated with a pulse width of 50 ns to 60 ns, the crack can be more reliably made to extend from the modified region 7a, 7m toward the thickness direction of the SiC substrate 12, and the turtle is more surely made. The crack does not easily extend from the modified region 7a, 7m toward the c-plane.

Further, along the line to cut 5a, the modified region 7a which is second closest to the incident light surface (surface 12a) of the SiC substrate 12 is formed relatively small. In this manner, even if the a-plane is inclined with respect to the thickness direction of the SiC substrate 12, it is possible to prevent the crack generated in the modified region 7a which is second closest to the surface 12a from extending in the a-plane direction, and it is possible to avoid a large deviation from the planned cutting line. The state of 5a reaches the surface 12a. Further, along the line to cut 5a, the modified region 7a closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is formed relatively large. In this manner, the crack does not easily extend from the modified region 7a toward the thickness direction of the SiC substrate 12, but the crack can be surely made to reach the surface 12a from the modified region 7a closest to the surface 12a. Further, along the line to cut 5m, the modified region 7m which is second closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is relatively large. In this way, the crack easily spreads from the modified region 7m toward the thickness direction of the SiC substrate 12, and the crack generated in the modified region 7m which is second from the surface 12a can reach the surface 12a or its vicinity. Further, along the line to cut 5m, the modified region 7m closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is formed relatively small. So, it can be prevented on the surface The damage occurred in 12a, and the crack was surely allowed to reach the surface 12a from the modified region 7m. As described above, along the line to cut 5a, it is possible to surely allow the crack to reach the surface 12a from the modified region 7a, and further, along the line to cut 5m, the crack can be reliably made from the modified region 7m. Reach the surface 12a. This effect can be exhibited irrespective of the number of formation rows and the order of formation of the modified regions 7a and 7m to be described later, and can be more prominently exhibited in accordance with the number of formation rows and the formation order of the modified regions 7a and 7m which will be described later.

Further, in the case where the modified region 7m is formed along one line to be cut 5m, a plurality of modified regions 7a are formed along one planned cutting line 5a. In this manner, even if the a-plane is inclined with respect to the thickness direction of the SiC substrate 12, it is possible to prevent the crack from being greatly extended from the modified region 7a toward the a-plane direction when the modified regions 7a are formed, and to make the between all the modified regions 7a The crack is easily connected to the SiC substrate 12 in the thickness direction. Further, in the case where the modified region 7a is formed along one planned cutting line 5a, the modified region 7m having fewer rows is formed along one planned cutting line 5m. As described above, when each modified region 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, the crack can be extended from the modified region 7a toward the thickness direction of the SiC substrate 12 along the line to cut 5a, and the crack can be made from the modified region 7m along the line 5m to be cut. The SiC substrate 12 is stretched in the thickness direction. This effect can be exerted regardless of the formation size of the modified regions 7a, 7m and the order of formation of the modified regions 7a, 7m described later, and the size of the modified regions 7a, 7m, and the modified regions 7a, 7m, which will be described later. The order of formation can be played more prominently.

In addition, before the modified region 7m in which the crack is stretched in the thickness direction of the SiC substrate 12 is formed, the modified region 7a in which the crack is extended in the thickness direction of the SiC substrate 12 is formed. When the modified region 7a is formed, the portion where the planned cutting line 5a and the planned cutting line 5m intersect with each other can prevent the crack from being extended from the modified region 7a toward the thickness direction of the SiC substrate 12 by the modified region 7m. Obstruction. This effect can be exerted regardless of the formation size and the number of rows of the modified regions 7a and 7m.

In addition, the object 1 is cut along the line to cut 5m from the modified region 7m, and the object 1 is cut along the line to cut 5a starting from the modified region 7a. In this way, the object 1 is cut along the line to cut 5m (the imaginary is difficult to cut due to the formation of the modified region 7m of a small number of rows), and then along the line to cut 5a (due to the formation of a plurality of columns) The object to be processed 1 is cut by changing the region 7a and imagining that it is easier to cut. Therefore, 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 can be made uniform, and the cutting force can be cut along the cutting line 5a. The cutting accuracy of the predetermined line 5m and the cutting accuracy along the line to cut 5a are further improved. This effect can be exerted regardless of the formation size and the number of rows of the modified regions 7a and 7m.

Fig. 14 is a photograph of the cut surface of the SiC substrate 12 cut along the line to cut 5a by the above-described laser processing method. Further, Fig. 15 is 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. Furthermore, Figure 16 is performed by the above laser processing. The method cuts the planar photograph of the SiC substrate 12 along the cut line 5a, 5m. Here, a hexagonal SiC substrate 12 having a thickness of 350 μm having an off angle of 4° is prepared.

First, as shown in Fig. 14, eight rows of modified regions 7a are formed for one planned cutting line 5a so as to be aligned along the thickness direction of the SiC substrate 12 along the line to cut 5a. Further, the modified region 7a which is second closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is smaller than the modified region 7a closest to the surface 12a, and is formed in accordance with the order of the back surface 12b side of the SiC substrate 12. Quality area 7a. As is apparent from Fig. 14, by forming the modified region 7a which is second closest to the surface 12a, the stretching of the crack generated from the modified region 7a can be stopped. As a result, as shown in Fig. 16, the meandering of the cut surface of the cutting planned line 5a can be suppressed to ±4 μm or less.

Further, the distance from the surface 12a to the position of the condensed spot P is 314.5 μm, 280.0 μm, 246.0 μm, 212.0 μm, 171.5 μm, 123.5 μm, and 79.0 μm in accordance with the order of the modified region 7a on the back surface 12b side of the SiC substrate 12. 32.0 μm. Further, the pulse energy of the laser light L is 25 μJ, 25 μJ, 25 μJ, 25 μJ, 20 μJ, 15 μJ, 6 μJ, and 6 μJ in accordance with the order of the modified region 7 a on the back surface 12 b side of the SiC substrate 12 .

Further, as shown in Fig. 15, six rows of modified regions 7m are formed for one planned cutting line 5m so as to be aligned along the cutting line 5m so as to be aligned in the thickness direction of the SiC substrate 12. Further, the modified region 7m closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is smaller than the second modified region 7m from the surface 12a, and the order of the back surface 12b of the SiC substrate 12 is changed. The quality area is 7m. As can be seen from Figure 15, by shape The modified region 7m which is second to the second surface 12a can extend the crack generated from the modified region 7m to the surface 12a or its vicinity. As a result, as shown in Fig. 16, the meandering of the cut surface with respect to the cutting line of 5 m can be suppressed to ±2 μm or less.

Further, 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 μm in accordance with the order of the modified region 7m on the back surface 12b side of the SiC substrate 12. Further, the pulse energy of the laser light L is 25 μJ, 25 μJ, 20 μJ, 20 μJ, 15 μJ, and 7 μJ in accordance with the order of the modified region 7 m on the back surface 12 b side of the SiC substrate 12 .

Next, the cracks (hereinafter referred to as "half-cut") of the laser light incident surface (surface 12a) of the SiC substrate 12 from the modified regions 7a, 7m and the extension from the modified regions 7a, 7m toward the c-plane are described. The relationship between cracks (hereinafter referred to as "c-plane cracks"). Here, as shown in FIGS. 17 and 18, the modified region 7a is described as an object; the modified region 7a is formed by causing the crack to extend in the thickness direction of the SiC substrate 12, as compared with the case of the modified region 7a. It is more difficult for the modified region 7m to be half-cut and the c-plane crack is more likely to occur.

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

Further, the ID threshold value refers to the minimum value of the laser light L pulse energy at which the c-plane crack can occur, and the order in which the ID threshold is high (that is, the c-plane crack is unlikely to occur) is evaluated as excellent, good, and acceptable. No. In addition, the HC threshold value refers to the minimum value of the pulse energy of the laser light L which can be half-cut, and the order of the HC threshold is low (that is, the half cut is easy to occur), and the evaluation is excellent, good, OK, and not . Furthermore, the processing margin is the difference between the ID threshold and the HC threshold, and is evaluated as excellent, good, acceptable, and not in accordance with the order of the processing margin. Moreover, the integration is weighted according to 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 that the laser light L is pulse-oscillated with a pulse width of 50 ns to 60 ns. In this way, the occurrence of c-plane cracks can be suppressed and the occurrence of half-cutting can be promoted. Further, in the case where the pulse width is 10 ns, the ID threshold, the processing margin, and the comprehensive evaluation are closer to the case where 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 with a pulse pitch of 10 μm to 18 μm; more preferably, the pulse pitch is 11 μm. The SiC substrate 12 is irradiated with the laser light L along the line to cut 5a, 5m in a 15 μm manner; it is particularly preferable to irradiate the SiC substrate 12 with laser light along the line to cut 5a, 5 m with a pulse pitch of 12 μm to 14 μm. L. In this way, the occurrence of c-plane cracks can be suppressed and the occurrence of half-cutting can be promoted. Also, because the pulse threshold is 10 μm, the evaluation of the ID threshold is acceptable. If it is more important to suppress the occurrence of c-plane cracks, it is better. In order to make the pulse pitch larger than 10 μm.

Fig. 21 to Fig. 23 show the experimental results of the processing margins of the pulse width and the pulse pitch of the laser light L with a numerical aperture of 0.8. These experimental results are based on the evaluations shown in Figs. 19 and 20. The experimental conditions for 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 off angle of 4° is moved, and the light-converging point P of the laser light L is moved along the line to cut 5a extending in a direction parallel to the surfaces 12a and a. . Further, the laser light L was condensed at a numerical aperture of 0.8, and the condensed spot P was aligned at a position separated from the laser light incident surface (surface 12a) of the SiC substrate 12 by a distance of 59 μm.

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

In the experimental results of Figs. 21 to 23, ST indicates that half cut did not occur, and HC indicates that half cut occurred. In addition, ID indicates that c-plane cracks have occurred, and LV1 to LV3 indicate the occurrence scale of c-plane cracks. In the case where the modified region 7a is formed along the two planned cutting lines 5a, for the region of 40 mm (the region of 20 mm × 2), when the region where the c-plane crack occurs is less than 150 μm, it is represented by LV1, and the c-plane is When the area where the crack occurs is less than 450 μm, it is expressed by LV2, and when the area where the crack of c-plane is generated is 450 μm or more. Expressed in LV3. In LV1, the extension of the c-plane crack in the direction perpendicular to the line to cut 5a is 10 μm to 20 μm, whereas in LV2, LV3, the extension of the c-plane crack in the direction perpendicular to the line to cut 5a is the largest. Up to about 100μm.

Figure 24 shows the relationship between pulse pitch and HC threshold. In addition, Fig. 25 shows the relationship between the pulse pitch and the ID threshold. Furthermore, Figure 26 shows the relationship between pulse pitch and processing margin. These figures are based on the experimental results of Figures 21 to 23. As shown in Fig. 24 and Fig. 25, if the pulse width becomes larger, both the HC threshold and the ID threshold increase, and the ID threshold is increased compared to the deterioration (rise) of the HC threshold ( Rise) is more effective. This means that as shown in Fig. 26, as the pulse width becomes larger, the processing margin becomes larger. For example, when the pulse width is 27 ns and the pulse width is 57 ns, when the pulse pitch is 12 μm, the HC threshold is from 15 μJ to 17 μJ and deteriorates (rises) by 2 μJ. In contrast, the ID threshold is from 17 μJ to 29 μJ. And increase (rise) 12μJ. Further, in the case where the pulse width is 40 ns, the processing margin is greatly improved in the range of the pulse pitch of 10 μm to 16 μm compared to the case where the pulse width is 27 ns. Further, in the case where the pulse width is 57 ns, the processing margin is greatly improved in the range of the pulse pitch of 6 μm to 20 μm compared to the case where the pulse width is 27 ns.

Fig. 27 to Fig. 29 show the 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 numerical aperture 0.6. These experimental results are the basis for the evaluation shown in Figs. 19 and 20. The experimental conditions for obtaining the experimental results of Figs. 27 to 29 are as follows. First, use a thick surface 12a (deviating from the c-plane) The hexagonal SiC substrate 12 having a degree of 350 μm is moved toward 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 was condensed at a numerical aperture of 0.6, and the condensed spot P was aligned at a position separated from the laser light incident surface (surface 12a) of the SiC substrate 12 by a distance of 50 μm.

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

In the experimental results of Figs. 27 to 29, ST indicates that half cut did not occur, and HC indicates that half cut occurred. In addition, ID indicates that c-plane cracks occur, and LV1 to LV3 indicate the occurrence scale of c-plane cracks. The reference of LV1 to LV3 is the same as the experimental results of the above 21st to 23rd. In addition, OD indicates that when the energy of the laser light L is increased, the modified region 7a also becomes large, and the crack that has migrated due to this greatly deviates from the line to cut 5a and reaches the surface 12a of the SiC substrate 12. In this case, the c-plane crack is not evaluated. However, in the case of a pulse width of 40 ns and a pulse width of 57 ns, large-scale c-plane cracks did not occur at a pulse pitch of 12 μm or more.

Figure 30 shows the relationship between pulse pitch and HC threshold. This figure is based on the experimental results of Figs. 27 to 29. As shown in Fig. 30, in the case where the pulse width is 57 ns, the HC threshold value is degraded by about 2 μJ to 4 μJ compared to the case where the pulse width is 40 ns. Compared to the above numerical aperture 0.8 In the case where the numerical aperture is 0.6, the converging point P of the laser light L is less affected by the aberration, and the HC threshold is the same level in the case where the pulse width is 57 ns and the case where the pulse width is 40 ns. In this way, if the aberration correction is performed, the HC threshold value does not deteriorate even if the pulse width becomes large (at least until 60 ns).

Next, an experimental result of the processing margin of the HC quality in the vicinity of the laser light incident surface (surface 12a) of the SiC substrate 12 will be described. The experimental conditions for obtaining 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 off angle of 4° is used as a target, and the light-converging point P of the laser light L is moved along a line to cut 5a extending in a direction parallel to the surfaces 12a and a. . Further, the laser light L is condensed at a numerical aperture of 0.8.

First, the experimental result in Fig. 31 is that the laser light L is irradiated with a pulse width of 27 ns, 40 ns, 50 ns, and 57 ns, respectively, and half cut is performed at a position of 25.3 μm at the spot position and 40.6 μm at the spot position. The half-cut energy (pulse energy) is generated, and the position of the light-converging point is changed in the range of 25.3 μm to 40.6 μm to observe the state of the half-cut. The pulse pitch of the laser light L is 14 μm and is kept constant. The position of the condensed spot is the distance from the surface 12a to the position of the condensed spot P. As a result, the deterioration of the quality of the half cut caused by the pulse width hardly occurs, and a half cut of a high quality (small cut of the half cut with respect to the line to cut) can be formed at a pulse width of 27 ns to 57 ns. Further, regarding the processing margin, the larger the pulse width, the larger. When the pulse width is small, a part of the half cut is prone to splitting or cracking (OD).

Further, in the experimental result of Fig. 32, the laser light L was irradiated with a pulse width of 27 ns, 40 ns, 50 ns, and 57 ns, respectively, and the pulse energy was changed in the range of 7 μJ to 12 μJ to observe the state of the half cut. The pulse pitch of the laser light L is 14 μm and is kept constant, and the position of the light-converging point is 34.5 μm and is kept constant. As a result, the change in the HC threshold caused by the pulse width hardly occurs. In addition, the same pulse energy can produce a half cut of the same degree of quality.

Furthermore, in the experimental result of Fig. 33, the laser light L is irradiated with pulse pitches of 10 μm, 12 μm, 14 μm, 16 μm, and 18 μm, respectively, and the pulse energy is changed in the range of 7 μJ to 12 μJ to observe the state of the half cut. . The pulse width of the laser light L is kept constant for 57 ns, and the position of the light-converging point is 34.5 μm and is kept constant. As a result, changes in the HC threshold caused by the pulse pitch hardly occur. Further, in the case where the position of the condensed spot is 34.5 μm, the same pulse energy can be subjected to the half cut of the same quality.

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 deviated from 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 inside the SiC substrate 12, along two preparatory lines 5p set on both sides of the planned cutting line 5a (5 m). The laser light L is irradiated onto the object 1 to be processed. Thereby, the preliminary modified region 7p is formed inside the SiC substrate 12 along each of the preliminary lines 5p. The preliminary modified region 7p includes a molten processed region.

The preparatory line 5p is located on both sides of the planned cutting line 5a (5m) in a plane parallel to the surface 12a and faces the line parallel to the planned cutting line 5a (5m). Extend. Further, when the functional elements are formed on the surface 12a of the SiC substrate 12 by cutting the respective regions drawn by the predetermined lines 5a, 5m, it is preferable to set the standby line 5p when viewed from the thickness direction of the SiC substrate 12. Within the area between adjacent functional components.

When the laser light L is irradiated onto the object 1 along each of the preparatory lines 5p, the SiC substrate 12 is less likely to be cracked from the preliminary modified region 7p than the modified region 7a (7m) which is the starting point of the cutting. By preparing the modified region 7p, it is possible to reduce the pulse energy, the pulse pitch, the pulse width, and the like of the laser light L, and it is less likely to cause a turtle on the SiC substrate 12 than the modified region 7a (7m) which is the starting point of the cutting. crack.

After the preliminary modified region 7p is formed along the preliminary line 5p, the light-converging point P of the laser light L is aligned with the inside of the SiC substrate 12, and the laser beam L is irradiated onto the object 1 along the line to cut 5a (5 m). 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). The modified region 7a (7m) is 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 deviated from the c-plane) can be along the line to cut 5a. 5 m is cut with high precision, and as a result, the object 1 to be processed (that is, the power element) which is cut with high precision along the line to cut 5a and 5 m can be obtained.

That is, it is to be in the SiC substrate 12 along the cutting planned line 5a (5 m). When the modified region 7a (7 m) is formed in the portion, the preliminary modified region 7p is formed inside the SiC substrate 12 along each of the preliminary lines 5p. Further, the preliminary line 5p is located on both sides of the planned cutting line 5a (5m) in a plane parallel to the surface 12a and extends in a direction parallel to the planned cutting line 5a (5m). Therefore, even if the crack extends from the modified region 7a (7m) in the c-plane direction, the case where the preliminary modified region 7p is not formed as shown in Fig. 34(b) is as shown in Fig. 34(a). The extension of the crack (c-crack) is suppressed by the preparatory modified region 7p. In this way, it is possible to make the crack easily extend from the modified region 7a (7 m) toward the thickness direction of the SiC substrate 12 without considering whether the crack is easily extended from the modified region 7a (7 m) toward the c-plane direction. The emitted light is irradiated onto the object 1 to be processed. Further, since the modified region 7p is not required to function as a cutting start point (that is, it promotes crack propagation from the preliminary modified region 7p toward the thickness direction of the SiC substrate 12), it is not easy to occur on the SiC substrate 12. Since the crack is formed by irradiating the laser light L, it is easy to suppress the crack extension from the preliminary modified region 7p toward the c-plane direction when the preliminary modified region 7p is formed. In this way, the object to be processed having a plate-like shape of the hexagonal SiC substrate 12 (having a main surface that is offset from the c-plane) can be cut with high precision along the line to cut 5a (5 m).

Further, when the modified region 7a (7m) is formed, the condensed spot P of the laser light L is aligned with a predetermined distance from the laser light incident surface (surface 12a) of the SiC substrate 12, and when the preliminary modified region 7p is formed Also, it is preferable that the condensed spot P of the laser light L is aligned at the same distance from the surface 12a. In this way, it is possible to more reliably suppress the direction from the modified region 7a (7m) toward the c-plane. Cracks stretch.

Further, when the preliminary modified region 7p is formed inside the SiC substrate 12 along each of the standby lines 5p, the cut line 5a (5 m) set between the preliminary lines 5p is also formed inside the SiC substrate 12. In the case of the mass region 7a (7 m), the pre-modified region 7p can still be used to suppress the stretching of the c-plane crack. In this case, it is preferable to form the preliminary modified region 7p along the preliminary line 5p first in comparison with the formation of the modified region 7a (7m) along the line to cut 5a (5 m).

According to the present invention, it is possible to cut the object to be processed in a plate shape having a hexagonal SiC substrate (having a main surface which is offset from the c-plane) along the line to cut with high precision.

1‧‧‧Processing objects

5a, 5m‧‧‧ cut-off line

5p‧‧‧Preparation line

7a, 7m‧‧‧ modified area

7p‧‧‧Prepared modified area

12‧‧‧ SiC substrate

12a‧‧‧Surface (main surface)

12b‧‧‧Back (main side)

L‧‧‧Laser light

P‧‧‧ spotlight

Fig. 1 is a structural view of a laser processing apparatus used to form a modified region.

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

Fig. 3 is a cross-sectional view taken along line III-III of the object to be processed in Fig. 2 .

Fig. 4 is a plan view of the 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;

Figure 7 is a pair of laser processing methods as an embodiment of the present invention. A top view of the object to be processed.

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

Fig. 9(a)(b) is a partial cross-sectional view of the object to be processed in Fig. 7.

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

11(a) and (b) are partial cross-sectional views of the object to be processed which is subjected to the laser processing method according to the embodiment of the present invention.

Fig. 12 (a) and (b) are partial cross-sectional views showing an object to be processed which is subjected to the laser processing method according to the embodiment of the present invention.

Fig. 13 (a) and (b) are partial cross-sectional views of the object to be processed which is subjected to the laser processing method according to the embodiment of the present invention.

Fig. 14 is a photograph showing 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 photograph showing 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 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 occurring inside the SiC substrate.

Figure 18 is a photograph of the cut surface of the SiC substrate on which the c-plane crack occurred.

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

Figure 20 shows the relationship between pulse pitch, ID threshold, HC threshold, and machining margin.

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

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

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

Figure 24 shows the relationship between pulse pitch and HC threshold.

Figure 25 shows the relationship between pulse pitch and ID threshold.

Figure 26 shows the relationship between pulse pitch and machining margin.

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

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

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

Figure 30 shows the relationship between pulse pitch and HC threshold.

Figure 31 is a table showing experimental results of processing margins of HC quality near the incident surface of the laser light.

Figure 32 is a table showing experimental results of processing margins of HC quality near the incident surface of the laser light.

Figure 33 is a table showing experimental results of processing margins of HC quality near the incident surface of the laser light.

Fig. 34 (a) and (b) are plan views 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 area

12‧‧‧ SiC substrate

12a‧‧‧Surface (main surface)

12b‧‧‧Back (main side)

23‧‧‧Expansion tape

L‧‧‧Laser light

P‧‧‧ spotlight

Claims (3)

A laser processing method is a plate-shaped object to be processed having a hexagonal SiC substrate (having a main surface that is offset from the c-plane), and extends in a direction parallel to the main surface and the a-plane. a laser cutting method for cutting a first cutting planned line and a second cutting planned line extending in a direction parallel to the main surface and the m-plane; the laser processing method includes a first step and a second step; In the first step, the light-converging point of the laser light is aligned with the inside of the SiC substrate, and the laser beam is irradiated onto the object to be processed along the first line to cut, thereby following the first cutting schedule. The first modified region which is the starting point of the cutting is formed in the inside of the SiC substrate, and the first modified first plurality of rows are formed on one of the first planned cutting lines so as to be aligned in the thickness direction of the SiC substrate. In the second step, the condensing point is aligned with the inside of the SiC substrate, and the laser light is irradiated onto the object to be processed along the second line to cut, thereby cutting along the second cutting line. The scheduled line will serve as the second modification of the starting point The second modified region is formed in a plurality of rows in the first SiC substrate so as to be aligned in the thickness direction of the SiC substrate; and in the first step, The first modified region in which the laser light incident surface of the SiC substrate is second is smaller than the first modified region closest to the incident surface of the laser light, and is distant from the far side to the incident surface of the laser light. Forming the first modified region in sequence; in the second step, the front is the closest to the incident surface of the laser light The second modified region is formed such that the second modified region is smaller than the second modified region that is closer to the second incident light incident surface, and the second modified region is formed from the far side to the near side of the laser light incident surface. The laser processing method according to claim 1, further comprising a third step after the first step and the second step; wherein the third step is based on the first modified region The object to be processed is cut along the first line to be cut, and the object to be processed is cut along the second line to cut along the second modified region as a starting point. The laser processing method according to claim 1 or 2, wherein the first modified region and the second modified region include a molten processed region.