Patent Publication Number: US-2017355041-A1

Title: METHOD FOR PROCESSING SiC MATERIAL

Description:
TECHNICAL FIELD 
     The present invention relates to a method for processing SiC material. 
     BACKGROUND ART 
     SiC materials are generally cut mechanically using a wire saw or the like. However, since SiC has high hardness, processing using a wire saw or the like has a problem that the processing is performed at a low speed and the throughput decreases. 
     In order to eliminate this problem, a SiC material cutting method in which a pulsed laser beam is irradiated along a cutting scheduled plane of a SiC material to form a altered region inside the SiC material and the SiC material is cut along the cutting scheduled plane is proposed (see Patent Document 1). In the method disclosed in Patent Document 1, the laser beam is moved in relation to the SiC material along a predetermined line in a state in which a focusing point is aligned on the cutting scheduled plane inside the SiC material. In Patent Document 1, it is described that a c-plane crack from the altered region is generated ideally when a pitch between one irradiation point of the laser beam and another irradiation point closes to the irradiation point is equal to or larger than 1 μm and smaller than 10 μm. 
     CITATION LIST 
     Patent Document 
     Patent Document 1: Japanese Patent Application Publication No. 2013-49161 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, when line-shaped altered regions are formed at equal intervals as illustrated in Patent Document 1, if the interval between respective lines exceeds a predetermined pitch, a crack does not progress between the respective lines. The pitch between respective lines may be set to be equal to or smaller than 10 μm as disclosed in Patent Document 1 in order to allow a crack to progress between respective lines reliably. However, in this case, it takes a considerable time to irradiate a laser beam to the cutting scheduled plane and the throughput decreases. 
     The present invention has been made in view of the above-described problem, and an object thereof is to provide a method for processing SiC material capable of allowing a crack to progress between respective lines reliably while shortening a laser beam irradiation time. 
     Solutions to Problems 
     In order to attain the object, the present invention provides a method for processing SiC material, including: allowing a laser beam to be absorbed in a cutting scheduled plane of an SiC material to form an altered pattern including a plurality of line-shaped altered regions; and cutting the SiC material along the cutting scheduled plane, wherein the altered pattern has altered region groups including a plurality of line-shaped main altered regions extending in a predetermined direction and arranged at a first pitch, and a plurality of altered region groups is arranged at a second pitch larger than the first pitch. 
     In the method for processing SiC material, the altered pattern may include a plurality of line-shaped auxiliary altered regions extending in a different direction from the predetermined direction, and the auxiliary altered region may be formed so as to cross at least adjacent two altered region groups. 
     In the method for processing SiC material, the respective auxiliary altered regions may extend in a direction approximately orthogonal to the altered region group, wherein the respective auxiliary altered regions extend in a direction approximately orthogonal to the altered region group. 
     In the method for processing SiC material, the number of main altered regions included in one altered region group may be equal to or larger than 2 and equal to smaller than 10. 
     In the method for processing SiC material, the first pitch may be equal to or larger than 1.0 μm and smaller than 50 μm, and the second pitch may be equal to or larger than 50 μm and equal to smaller than 500 μm. 
     The present invention also provides a method fix processing SiC material including: allowing a laser beam to be absorbed in a cutting scheduled plane of an SiC material to form an altered pattern including a plurality of line-shaped altered regions; and cutting the SiC material along the cutting scheduled plane, wherein the altered pattern has a plurality of line-shaped main altered regions extending in a predetermined direction, and pitches between the respective main altered regions include at least two pitches. 
     Effects of the Invention 
     According to the method for processing SiC material of the present invention, it is possible to allow a crack to progress between respective lines reliably while shortening a laser beam irradiation time. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic perspective view for describing a SiC material illustrating an embodiment of the present invention. 
         FIG. 2  is a schematic view for describing a laser irradiation apparatus. 
         FIG. 3  is a partial plan view of a SiC material illustrating an altered region forming portion. 
         FIG. 4  illustrates a modified example and is a partial plan view of a SiC material illustrating an altered region forming portion. 
         FIG. 5  illustrates a modified example and is a partial plan view of a SiC material illustrating an altered region forming portion. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
       FIGS. 1 to 3  illustrate an embodiment of the present invention and  FIG. 1  is a schematic perspective view for describing a SiC material. 
     As illustrated in  FIG. 1 , a SiC material  1  is formed in a cylindrical aim and is divided into a plurality of SiC substrates  210  by being cut at predetermined cutting scheduled planes  100 . In the present embodiment, the SiC material  1  is formed of 6H-SiC and the diameter thereof may be 3 inches, for example. Moreover, the divided SiC substrates  210  are used as substrates of semiconductor device, for example. 
     Here, the respective cutting scheduled planes  100  are at an angle corresponding to an off-angle with respect to the c-plane orthogonal to the c-axis of the 6H-SiC. Therefore, by cutting the SiC material  1  along the cutting scheduled plane  100 , it is possible to manufacture the SiC substrate  210  having a circumferential surface that is at an angle corresponding to the off-angle with respect to the c-plane. The off-angle is approximately 4°, for example, and may be 0°. When the off-angle is 0°, the interface is parallel to the c-plane. 
       FIG. 2  is a schematic view for describing a laser irradiation apparatus. 
     As illustrated in  FIG. 2 , a laser irradiation apparatus  300  includes a laser oscillator  310  that oscillates a pulsed laser beam, a mirror  320  that changes the direction of the oscillated laser beam, an optical lens  330  that focuses the laser beam, and a stage  340  that supports a SiC stack  1  which is an irradiation target of the laser beam. Although a specific optical system is not illustrated particularly in  FIG. 2 , the laser irradiation apparatus  300  can adjust a focal position, adjust a beam shape, and correct an aberration, for example. Moreover, the laser irradiation apparatus  300  has a housing  350  that maintains the path of the laser beam in a vacuum state. In the present embodiment, a laser beam is irradiated to the SiC material  1  formed of 6H-SiC using the laser irradiation apparatus  300  to form an altered region inside the laser beam to cut the SiC material  1 . 
     The laser oscillator  310  can use second-order harmonics of a YAG laser. A beam emitted from the laser oscillator  310  is reflected by the mirror  320  whereby the direction is changed. A plurality of mirrors  320  is provided to change the direction of the laser beam. Moreover, the optical lens  330  is positioned above the stage  340  to focus the laser beam incident on the SiC material  1 . 
     The stage  340  moves in x and/or y-directions with the aid of a moving mechanism (not illustrated) to move the SiC material  1  placed thereon. Furthermore, the stage  340  may rotate about the z-axis. That is, it is possible to move the SiC material  1  in relation to the laser beam. In this way, it is possible to form a surface machined by the laser beam at a predetermined depth of the SiC material  1 . 
     The laser beam is absorbed at a portion inside the SiC material  1  particularly near the focusing point. As a result, an altered region is formed in the SiC material  1 . In the present embodiment, the laser beam is moved in relation to the SiC material  1  along a predetermined line in a state in which the focusing point is aligned at the respective cutting scheduled planes  100  inside the SiC material  1  whereby an altered pattern formed of a plurality of line-shaped altered regions is formed in the respective cutting scheduled planes  100 . The direction in which the laser beam is moved in relation to the SiC material is not limited to a line shape hut may be moved in a curve shape. 
     In the present embodiment, one shot of pulse is irradiated at predetermined intervals along the respective cutting scheduled planes  100  to form a line-shaped altered region. A machined spot is formed in a portion irradiated with one shot of pulse, and an example of such a machined spot includes a crack spot, a molten spot, a refractive index-altered spot, or a spot in which at least two of these spots are mixed. 
     When the SiC material  1  is cut, first, a focusing point of the laser beam is aligned on the cutting scheduled plane  100  on one end side in the axial direction positioned close to an incidence side of the laser beam so that the laser beam is absorbed. in the cutting scheduled plane  100  to form an altered pattern. In this case, it is preferable to polish an incidence-side surface of the SiC material  1  so that incidence of the laser beam on the SiC material  1  is not interrupted. 
       FIG. 3  is a partial plan view of a SiC material illustrating an altered region forming portion. As illustrated in  FIG. 3 , a focusing point of the laser beam is moved linearly to form a main altered region  12  that forms an altered pattern. The main altered region  12  is formed as a set of altered spots formed by one shot of pulse since the laser beam is a pulsed laser beam. Specifically, altered spots are formed continuously so that adjacent altered spots overlap partially with each other whereby respective line-shaped altered regions  12  are formed. The width of each altered region  12  is smaller than 1.0 μm and may be 0.2 μm, for example. 
     Specifically, as illustrated in  FIG. 3 , a plurality of line-shaped main altered regions  12  extending in a predetermined direction is formed at a first pitch P 1  to form an altered region group  13  extending in the predetermined direction. Moreover, a plurality of altered region groups  13  is formed at a second pitch P 2  larger than the first pitch P 1 . When the main altered region  12  is formed in this manner, it is possible to allow a c-plane crack to progress using a small number of main altered regions as compared to when the main altered regions  12  are arranged at equal intervals. Although the dimensions of the first and second pitches P 1  and P 2  are arbitrary, the first pitch P 1  may be equal to or larger than 1 μm and smaller than 50 μm, for example, and the second pitch P 2  may be equal to or larger than 50 μm and equal to or smaller than 500 μm, for example. Although the number of main altered regions  12  included in one altered region group  13  is arbitrary, the number may be equal to or larger than 2 and equal to or smaller than 10, for example. 
     Here, when the SiC material  1  is processed, the respective main altered regions  12  are sequentially formed unless all main altered regions  12  are formed simultaneously. In this case, it is preferable to prevent a c-plane crack from progressing in a forming scheduled portion of a predetermined main altered region  12  as a result of forming of another main altered region  12  before the predetermined main altered region  12  is formed. If the c-plane crack progresses before laser processing is performed, it is difficult to align the focal point of laser at the depth of the cutting scheduled plane  100  and the processing accuracy decreases. 
     After the respective main altered regions  12  are formed in the cutting scheduled plane  100 , the other end side in the axial direction of the SiC material  1  is fixed and force is applied in a direction from the other end side in the axial direction toward one end side in the axial direction whereby the SiC material  1  is cut. After the SiC material  1  is separated, it is preferable to planarize the surface of the separated substrate  210  and a new surface of the SiC material  1  by polishing or the like. Particularly, when the cutting scheduled plane  100  is not parallel to the c-plane, since the separation surface is rough, it is more preferable to planarize the separation surface. 
     After that, the main altered region  12  is formed in the cutting scheduled plane  100  on one end side in the axial direction of the SiC material  1  from which the substrate  210  is separated, and the SiC material  1  is cut. In this manner, the SiC material  1  is sequentially cut from the other end side of all cutting scheduled planes  100  whereby a plurality of SiC substrates  210  is obtained. 
     According to the above-described method for processing the SiC material  1 , since the second pitch P 2  of the respective altered region groups  13  is relatively large, it is possible to shorten the laser beam irradiation time during processing of the cutting scheduled plane  100 . 
     Since the c-plane crack is made easy to progress, it is possible to reduce the power of laser for forming the altered regions and to reduce processing damage per one altered region. In this way, no excessive processing damage is applied to a region other than the cutting scheduled plane  100  in relation to the depth direction of the SiC material  1 , the processing damage near the cutting scheduled plane  100  can be suppressed as much as possible, and the laser processing controllability is improved. Furthermore, since the altered region group  13  includes a plurality of main altered regions  12 , it is possible to apply stress to the SiC material  1 , the stress having a value relatively close to a threshold stress at which a c-plane crack occurs in the SiC material  1 . In this way, the laser processing controllability is also improved. 
     The main altered region  12  may have a curve shape other than the line shape as illustrated in  FIG. 3 . For example, the main altered region may be formed in a spiral form or may be formed in a concentric form at a predetermined interval. In this case, the pitch of the main altered regions adjacent in the radial direction may be changed to a first pitch that is relatively short and a second pitch that is relatively long. 
     In the embodiment, although the main altered regions  13  are formed at the first and second pitches P 1  and P 2 , the main altered regions may be formed at three or more pitches. In this case, it is sufficient that the main altered regions  13  are formed at least at two pitches. 
     In the embodiment, although a plurality of main altered regions  12  extending in the same direction are formed, a plurality of line-shaped auxiliary altered regions  22  extending in a different direction from the main altered region  12  may be formed as illustrated in  FIG. 4 , for example. When the respective auxiliary altered regions  22  are formed so as to cross at least adjacent two altered region groups  13 , it is possible to effectively allow a crack to progress in a region surrounded by each altered region group  13  and each auxiliary altered region  22 . Moreover, as illustrated in  FIG. 4 , the auxiliary altered regions  22  are preferably formed so as to extend in a direction approximately orthogonal to the main altered regions  12 . In this case, a third pitch P 3  of the auxiliary altered regions  22  may be larger than the second pitch P 2  of the altered region groups  13 . When the main altered regions extend in a circumferential direction like a spiral form or a concentric form, the auxiliary altered regions are preferably formed so as to extend in a radial direction. 
     As illustrated in  FIG. 5 , a plurality of line-shaped auxiliary altered regions  22  may be formed at a fourth pitch P 4  that is relatively short to form auxiliary altered region groups  23 , and a plurality of auxiliary altered region groups  23  may be formed at the third pitch P 3  larger than the fourth pitch P 3 . In this case, the third pitch P 3  of the auxiliary altered regions  22  may be larger than the first pitch P 1  of the main altered regions  12 , and the fourth pitch P 4  of the auxiliary altered region groups  23  may be larger than the second pitch P 2  of the altered region groups  13 . Moreover, although the number of auxiliary altered regions  22  included in one auxiliary altered region group  23  is arbitrary, the number may be equal to or larger than 2 and equal to or smaller than 10, for example. 
     As illustrated in  FIGS. 4 and 5 , even when the auxiliary altered regions  22  are formed as well as the main altered regions  12 , the main altered regions  12  and the auxiliary altered regions  22  are sequentially formed unless all main altered regions  12  and all auxiliary altered regions  22  are formed simultaneously. In this case, it is preferable to prevent a c-plane crack from progressing in a forming scheduled portion of a predetermined main altered region  12  or a predetermined auxiliary altered region  22  as a result of forming of another main altered region  12  or another auxiliary altered region  22  before the predetermined main altered region  12  or the predetermined auxiliary altered region  22  is formed. 
     In the embodiment, although the present invention is applied to the SiC material  1  formed of 6H-SiC, the present invention can be applied to other poly SiC materials such as 3C-SiC or 4H-SiC, for example. Furthermore, the present invention can be applied to materials other than SiC in which a progress direction of cracks in the material is approximately parallel to a cutting scheduled plane. Examples of such materials include GaN, AlN, ZnO, and the like. In the present embodiment, although a plane orientation in which a progress direction of cracks in the material is approximately parallel to a cutting scheduled plane is the c-plane, the plane orientation may be the m-plane or the a-plane. 
     Although the embodiment of the present invention has been described above, the invention according to the claims is not limited to the above-mentioned embodiment. Moreover, it should be noted that all combinations of the features described in the embodiment are not essential for solving the problem of the invention. 
     INDUSTRIAL APPLICABILITY 
     As described above, the method for processing SiC material according to the present invention is industrially useful in that it is possible to allow a crack to progress between respective lines reliably while shortening a laser beam irradiation time. 
     REFERENCE SIGNS LIST 
       1 : SiC material 
       11 : Non-altered region 
       12 : Main altered region 
       13 : Altered region group 
       22 : Auxiliary altered region 
       23 : Auxiliary altered region group 
       100 : Cutting scheduled plane 
       210 : SiC substrate 
       300 : Laser irradiation apparatus 
       310 : Laser oscillator 
       320 : Mirror 
       330 : Optical lens 
       340 : Stage 
       350 : Housing