Manufacturing method of single-crystal silicon substrate

Abstract

[Problem] To improve the productivity of substrate manufacturing when using a laser beam to remove substrates from workpieces such as crystal ingots. [Solution] After performing a first processing step to form modified portions in multiple first regions, a second processing step is performed to form modified portions and cracks in multiple second regions. Here, the cracks formed in the second processing step tend to extend toward the modified portions formed in the first processing step. Therefore, the direction in which the cracks tend to extend in the second processing step can be arbitrarily set. This makes it easier to thin the release layer formed inside the workpiece. Then, if the release layer is thinner, the amount of workpiece material discarded during substrate cutting from the workpiece and substrate planarization is reduced. As a result, the productivity of substrate manufacturing when using a laser beam to remove substrates from workpieces is improved.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a monocrystalline silicon substrate, wherein the substrate is manufactured from a workpiece made of monocrystalline silicon, the workpiece being manufactured in such a way that specific crystal surfaces included in the crystal surface {100} are exposed on the front and back sides respectively. [Previous Technology]

[0002] Semiconductor wafers are generally manufactured using a disk-shaped monocrystalline silicon substrate (hereinafter also referred to as "substrate"). This substrate is cut, for example, from a cylindrical crystal rod (hereinafter also referred to as "crystal rod") made of monocrystalline silicon using a wire saw (for example, see Patent Document 1).

[0003] However, the cutting allowance when cutting the substrate from the ingot using a wire saw is relatively large, around 300 μm. Furthermore, fine irregularities are formed on the front side of the substrate cut in this way, and the substrate will bend as a whole (warping occurs on the substrate). Therefore, in this substrate, it is necessary to perform wrapping, etching, and / or polishing on its front side to planarize the front side.

[0004] In this case, the amount of monocrystalline silicon material ultimately used as the substrate is about 2 / 3 of the total material of the crystal ingot. That is, about 1 / 3 of the total material of the crystal ingot is discarded when cutting the substrate from the crystal ingot and when planarizing the substrate. Therefore, in the case of manufacturing substrates using a wire saw, productivity will be low.

[0005] In view of this, a method has been proposed in which a release layer comprising a modified portion and cracks extending from the modified portion is formed inside the crystal ingot using a laser beam of wavelength that penetrates monocrystalline silicon, and the substrate is separated from the crystal ingot starting from this release layer (for example, see Patent Document 2). This improves the productivity of the substrate compared to manufacturing the substrate from the crystal ingot using a wire saw. [Preferred Art Documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. Hei 9-262826 [Patent Document 2] Japanese Patent Application Publication No. 2022-25566 [Summary of the Invention]

[0007] [Problem to be Solved by the Invention] Single-crystal silicon is most prone to cracking on specific crystal planes contained in the crystal plane {111}. For example, if a laser beam is irradiated along the specific crystal direction contained in the crystal plane {100}, i.e., the crystal plane (100), which is exposed on the front and back sides respectively, and a modified part is formed inside the crystal rod by means of a laser beam along the specific crystal direction <110>, i.e., the crystal direction

[011] , a large number of cracks will be generated extending along the specific crystal planes contained in the crystal plane {111} that are parallel to the crystal direction

[011] (specifically, the crystal planes shown in (1) below). [Mathematical Formula 1]

[0008] Here, the angle formed by the crystal plane (100) with respect to the specific crystal plane contained in the crystal plane {111} is about 54.7°. Therefore, in the case of irradiating the crystal rod with a laser beam as described above, a large number of cracks will be generated along its thickness direction, which is greater than the amount along the direction parallel to the front and back sides of the crystal rod.

[0009] In this situation, the release layer formed inside the crystal rod becomes thicker, and the amount of discarded crystal rod and substrate material increases during the cutting of the substrate from the crystal rod and the planarization of the substrate. In view of this, the object of the present invention is to provide a method for manufacturing a single-crystal silicon substrate, which can improve the productivity of substrate manufacturing when using a laser beam from a workpiece such as a crystal rod.

[0010] [Technical Means for Solving the Problem] According to the present invention, a method for manufacturing a single-crystal silicon substrate is provided, which manufactures a substrate from a workpiece made of single-crystal silicon, wherein the workpiece is manufactured such that specific crystal surfaces included in the crystal surface {100} are exposed on the front and back sides respectively, and the method for manufacturing the single-crystal silicon substrate includes: a release layer forming step, which forms a release layer including a modified portion and cracks extending from the modified portion inside the workpiece; and a separation step, which separates the substrate from the workpiece starting from the release layer after performing the release layer forming step, and the release layer forming step includes: a first processing step for forming the substrate in a plurality of first regions. The modified portion comprises a plurality of first regions extending along a first direction and separated from each other in a second direction, wherein the first direction is parallel to the specific crystal plane and forms an angle of 5° or less with respect to the specific crystal direction included in the crystal direction <100>, and the second direction is parallel to the specific crystal plane and orthogonal to the first direction; and a second processing step for forming the modified portion and the crack in the plurality of second regions after performing the first processing step, wherein the plurality of second regions extend along the first direction and are separated from each other in the second direction, and any one of the plurality of second regions is positioned adjacent to one of the plurality of first regions. Between the first regions, any one of the plurality of first regions is positioned between one adjacent pair of second regions in the plurality of second regions, and the first processing step is performed by alternately repeating the following steps: a first laser beam irradiation step, in which the focusing point of a laser beam with a wavelength that penetrates the single crystal silicon is positioned inside any of the plurality of first regions and at a first depth from the front surface of the workpiece, and the focusing point and the workpiece are moved relative to each other along the first direction; and a first indexing feed step, in which the position forming the focusing point and the workpiece are moved relative to each other along the second direction, and the second The processing steps are performed by interactively repeating the following steps: a second laser beam irradiation step, in which the focusing point is positioned inside any of the plurality of second regions and at a second depth different from the first depth from the front surface of the workpiece, the focusing point and the workpiece are moved relative to each other along the first direction; and a second indexing feed step, in which the position of the focusing point is moved relative to the workpiece along the second direction, and the power of the laser beam focused at the focusing point during the second laser beam irradiation step is greater than the power of the laser beam focused at the focusing point during the first laser beam irradiation step.

[0011] Furthermore, it is preferable that the second depth is deeper than the first depth.

[0012] Furthermore, preferably, the angle formed by the first plane of the first straight line and the second straight line with respect to the front and back surfaces of the workpiece is less than 45°, the first straight line passes through the center of the second region located between the adjacent pair of first regions and along the first direction, the second straight line passes through the center of one of the adjacent pair of first regions and along the first direction, and the angle formed by the second plane of the first straight line and the third straight line with respect to the front and back surfaces of the workpiece is less than 45°, the third straight line passes through the center of the other of the adjacent pair of first regions and along the first direction.

[0013] [Effect of the Invention] In this invention, after performing a first processing step for forming modified parts in a plurality of first regions, a second processing step for forming modified parts and cracks in a plurality of second regions is then performed.

[0014] Here, if the modified part is formed in the first processing step, the volume of the workpiece expands, generating internal stress in the workpiece. Furthermore, cracks formed in the second processing step tend to extend toward the location where internal stress is generated.

[0015] Therefore, the cracks formed in the second processing step tend to extend toward the modified portion formed in the first processing step. Thus, in this invention, the direction in which the cracks tend to extend in the second processing step can be arbitrarily set.

[0016] In this situation, it becomes easier to thin the release layer formed inside the workpiece. Then, if the release layer is thinned, the amount of workpiece material discarded during the cutting of the substrate from the workpiece and the planarization of the substrate is reduced. As a result, in the present invention, the productivity of the substrate when manufacturing the substrate from the workpiece using a laser beam is improved.

Implementation Method

[0018] With reference to the drawings, embodiments of the present invention will be described. FIG1 is a perspective view schematically showing an example of a crystal rod used for manufacturing a substrate, and FIG2 is a top view schematically showing the crystal rod shown in FIG1.

[0019] Furthermore, Figure 1 also shows the crystal plane of the single-crystal silicon exposed in the plane contained in this crystal rod. Also, Figure 2 shows the crystal orientation of the single-crystal silicon constituting this crystal rod.

[0020] In the crystal rod 11 shown in Figures 1 and 2, the specific crystal planes included by the crystal plane {100} (here, for convenience, they are referred to as crystal planes (100)) are exposed on the front side 11a and the back side 11b, respectively. That is, in this crystal rod 11, the vertical lines (crystallization axes) of the front side 11a and the back side 11b are along the crystal direction

[100] .

[0021] In addition, although the crystal rod 11 is manufactured with the crystal surface (100) exposed on the front side 11a and the back side 11b respectively, due to processing errors during manufacturing, it is also possible that the crystal surface (100) is slightly inclined and exposed on the front side 11a and the back side 11b respectively.

[0022] Specifically, the face with an angle of 1° or less relative to the crystal plane (100) can also be exposed on the front side 11a and back side 11b of the crystal rod 11, respectively. That is, the crystal axis of the crystal rod 11 can also be along the direction with an angle of 1° or less relative to the crystal direction

[100] .

[0023] Furthermore, an orientation plane 13 is formed on the side 11c of the crystal rod 11. When viewed from this orientation plane 13, the center C of the crystal rod 11 is located in a specific crystal direction contained in the crystal direction <110> (here, for convenience, it is set as the crystal direction

[011] ). That is, the crystal plane (011) of the single crystal silicon is exposed on this orientation plane 13.

[0024] Figure 3 is a flowchart schematically illustrating an example of a method for manufacturing a monocrystalline silicon substrate from a crystal ingot 11 that becomes the workpiece. In this method, firstly, a release layer comprising a modified portion and cracks extending from the modified portion is formed inside the crystal ingot 11 (release layer formation step: S1).

[0025] In this release layer formation step (S1), release layers are sequentially formed for multiple regions included in the crystal rod 11. Figure 4 is a schematic top view of the multiple regions included in the crystal rod 11. Also, Figure 5 is a flowchart schematically showing an example of the release layer formation step (S1) shown in Figure 3.

[0026] In this stripping layer forming step (S1), firstly, modified parts are formed in a plurality of first regions 11d, the plurality of first regions 11d extending along the crystal direction

[010] and separated from each other in the crystal direction

[001] (first processing step: S11).

[0027] Then, after completing the first processing step (S11), modified parts and cracks are formed in a plurality of second regions 11e, the plurality of second regions 11e extending along the crystal direction

[010] and positioned between an adjacent pair of first regions 11d, and the width of each along the crystal direction

[001] is greater than the width of each of the plurality of first regions 11d (second processing step: S12).

[0028] Furthermore, in the release layer formation step (S1), a release layer containing modified portions and cracks is formed inside the crystal rod 11 using a laser processing apparatus. Figure 6 is a schematic diagram of an example of a laser processing apparatus used to form a release layer inside the crystal rod 11.

[0029] Furthermore, the X-axis direction (first direction) and Y-axis direction (second direction) shown in Figure 6 are mutually orthogonal directions on the horizontal plane, and the Z-axis direction is a direction orthogonal to both the X-axis direction and the Y-axis direction (vertical direction). Also, in Figure 6, functional blocks represent some of the constituent elements of the laser processing apparatus.

[0030] The laser processing apparatus 2 shown in Figure 6 has a disc-shaped holding stage 4. This holding stage 4 has, for example, a circular upper surface (holding surface) that is parallel to the X-axis and Y-axis directions. Furthermore, the holding stage 4 has a disc-shaped perforated plate (not shown) whose upper surface is exposed on this holding surface.

[0031] Furthermore, this porous plate is connected to an attraction source (not shown) such as an ejector through a flow path provided inside the holding platform 4. Then, if this attraction source operates, the attraction force acts on the space near the holding surface of the holding platform 4. In this way, for example, the crystal rod 11 placed on the holding surface can be held by the holding platform 4.

[0032] Furthermore, a laser beam irradiation unit 6 is provided above the holding stage 4. This laser beam irradiation unit 6 has a laser oscillator 8. This laser oscillator 8 has, for example, Nd:YAG as the laser medium.

[0033] Then, the laser oscillator 8 irradiates a pulsed laser beam LB with a wavelength (e.g., 1064 nm or 1342 nm) that penetrates the material (monocrystalline silicon) constituting the crystal rod 11.

[0034] The output (power) of this laser beam LB is adjusted in the attenuator 10 and then supplied to the branch unit 12. This branch unit 12 has, for example, a spatial light modulator containing a liquid crystal phase control element called LCoS (liquid crystal on silicon) and / or a diffraction optical element (DOE).

[0035] Then, the branching unit 12 branches the laser beam LB in such a way that the laser beam LB irradiated from the irradiation head 16 to the holding surface side of the holding table 4 forms a plurality (e.g., more than 4 and less than 16) focusing points arranged along the Y-axis direction.

[0036] The laser beam LB, which is branched in the branching unit 12, is reflected by the reflector 14 and guided to the irradiation head 16. The irradiation head 16 houses a condenser (not shown) for focusing the laser beam LB. The laser beam LB, focused by the condenser, is then irradiated onto the holding surface side of the holding table 4 with the central region of the lower surface of the irradiation head 16 as the emission area; in short, it is irradiated directly below.

[0037] Furthermore, the irradiation head 16 of the laser beam irradiation unit 6 and the optical system (e.g., mirror 14) for guiding the laser beam LB to the irradiation head 16 are connected to a moving mechanism (not shown). This moving mechanism includes, for example, a ball screw. Then, when this moving mechanism is operated, the emission area of ​​the laser beam LB moves along the X-axis, Y-axis, and / or Z-axis directions.

[0038] Then, in the laser processing apparatus 2, by operating this moving mechanism, the position (coordinates) of the focusing point of the laser beam LB that is irradiated from the irradiation head 16 to the holding surface side of the holding table 4 in the X-axis direction, Y-axis direction and Z-axis direction can be adjusted.

[0039] When performing the stripping layer formation step (S1) in the laser processing apparatus 2, firstly, the holding stage 4 holds the crystal rod 11 with the front side 11a facing upward. Figure 7 is a schematic top view showing the state in which the crystal rod 11 is held in the holding stage 4 of the laser processing apparatus 2.

[0040] This crystal rod 11 is held on the holding stage 4 in a state in which the angle formed by the direction from the orientation plane 13 toward the center C of the crystal rod 11 (crystal direction

[011] ) with respect to the X-axis direction and the Y-axis direction respectively is 45°.

[0041] That is, the crystal rod 11 is held on the holding stage 4, for example, with the crystal direction

[010] parallel to the X-axis direction and the crystal direction

[001] parallel to the Y-axis direction. If the crystal rod 11 is held on the holding stage 4 in this way, the first processing step (S11) is performed.

[0042] Figure 8 is a flowchart schematically showing an example of the first processing step (S11) shown in Figure 5. In this first processing step (S11), firstly, with the focusing point of the focused laser beam LB positioned inside any of the plurality of first regions 11d and at a first depth from the front surface 11a of the crystal rod 11, the focusing point and the crystal rod 11 are moved relative to each other along the X-axis direction (crystal direction

[010] ) (first laser beam irradiation step: S111).

[0043] FIG9(A) is a schematic top view showing the state of the first laser beam irradiation step (S111) shown in FIG8, and FIG9(B) is a schematic partial cross-sectional side view showing the state of the first laser beam irradiation step (S111) shown in FIG8. Furthermore, FIG10 is a schematic cross-sectional view showing the peeling layer containing the modified portion and the crack extending from the modified portion formed inside the crystal rod 11 in the first laser beam irradiation step (S111) shown in FIG8.

[0044] In this first laser beam irradiation step (S111), for example, a release layer is first formed in one of the first regions 11d located at one end in the Y-axis direction (crystal direction

[001] ). Specifically, the irradiation head 16 is first positioned such that the first region 11d is positioned in the X-axis direction when viewed from above from the irradiation head 16 of the laser beam irradiation unit 6.

[0045] Next, the irradiation head 16 is raised and lowered in such a way that multiple focusing points formed by focusing the branched laser beams LB are positioned at a height corresponding to the first depth from the front side 11a of the crystal rod 11.

[0046] Next, while irradiating the laser beam LB from the irradiation head 16 toward the holding stage 4, the irradiation head 16 is moved in a manner that, when viewed from above, passes from one end of the crystal rod 11 in the X-axis direction (crystal direction

[010] ) to the other end (see Figures 9(A) and 9(B)).

[0047] If the laser beam LB is irradiated while the irradiation head 16 is moved, then with the multiple focusing points positioned at a first depth from the front side 11a of the crystal rod 11, the multiple focusing points move relative to the crystal rod 11 along the X-axis direction (crystal direction

[010] ).

[0048] Furthermore, the laser beam LB is branched and focused in such a way that multiple (e.g., 5) focusing points are formed at equal intervals in the Y-axis direction (crystal direction

[001] ) (see Figure 10). At this time, the interval between adjacent pairs of focusing points is set to, for example, 5 μm or more and 20 μm or less, typically 10 μm.

[0049] Furthermore, the power obtained by dividing the power of the laser beam LB that is focused at multiple focal points, i.e. the power of the laser beam LB that is adjusted in the attenuator 10, by the number of branches (e.g., 5), is set to a small value, for example, 0.1W or more and 0.3W or less, typically 0.2W.

[0050] Accordingly, a modified portion 15a is formed inside the crystal rod 11, with each of the multiple focusing points as the center, resulting in a disordered crystal structure of single-crystal silicon. Furthermore, if the modified portion 15a is formed inside the crystal rod 11, the volume of the crystal rod 11 will expand, generating internal stress in the crystal rod 11.

[0051] Then, inside the crystal rod 11, cracks 15b extend from the modified portion 15a in a manner that alleviates the internal stress. As a result, a peeling layer 15 is formed inside the crystal rod 11, comprising a plurality of modified portions 15a and cracks 15b extending from the plurality of modified portions 15a respectively.

[0052] Furthermore, in the first laser beam irradiation step (S111), a laser beam LB with a power as low as the following can be irradiated: although a modified portion 15a will be formed inside the crystal rod 11, the crack 15b will not extend from the modified portion 15a. That is, the peeling layer 15 formed in the first laser beam irradiation step (S111) may not contain the crack 15b.

[0053] Then, in the case where the laser beam LB has not been completely irradiated on all of the multiple first regions 11d (step (S112): no), the position of the spotting point is moved relative to the crystal rod 11 along the Y-axis direction (crystal direction

[001] ) (first indexing feed step: S113).

[0054] In this first indexing feed step (S113), for example, the irradiation head 16 is moved along the Y-axis direction (crystal direction

[001] ) until the irradiation head 16 is positioned in the X-axis direction (crystal direction

[010] ) when viewed from the first region 11d adjacent to the first region 11d where the peel layer 15 has been formed and the first region 11d where the peel layer 15 has not been formed.

[0055] Next, the first laser beam irradiation step (S111) described above is performed again. If the first laser beam irradiation step (S111) is performed twice, as shown in FIG11, a release layer 15 (release layer 15-2) is formed inside the crystal rod 11 that is parallel to the already formed release layer 15 (release layer 15-1) and separates from the release layer 15-1 in the Y-axis direction (crystal direction

[001] ).

[0056] Furthermore, the first indexing feed step (S113) and the first laser beam irradiation step (S111) are repeated alternately until a release layer 15 is formed in all of the plurality of first regions 11d contained in the crystal rod 11. Then, if a release layer 15 is formed in all of the plurality of first regions 11d (step (S112): yes), a second processing step (S12) is performed.

[0057] Figure 12 is a flowchart schematically showing an example of the second processing step (S12) shown in Figure 5. In this second processing step (S12), firstly, with the focusing point of the focused laser beam LB positioned inside any of the plurality of second regions 11e and at a second depth from the front surface 11a of the crystal rod 11, the focusing point and the crystal rod 11 are moved relative to each other along the X-axis direction (crystal direction

[010] ) (second laser beam irradiation step: S121).

[0058] Furthermore, the second depth is a depth different from the first depth described above, for example, deeper than the first depth. For example, the difference between the first depth and the second depth is greater than 0 μm and less than 120 μm. Also, this difference is set to be shorter than the interval between the multiple first regions 11d and the multiple second regions 11e.

[0059] Specifically, this difference is set to be shorter than the following two lines when viewed from above: the line located at the center of the second region 11e in the Y-axis direction and along the X-axis direction; and the line located at the center of the first region 11d adjacent to this second region 11e in the Y-axis direction and along the X-axis direction.

[0060] That is, the first depth and the second depth are set such that the angle formed by the plane passing through the two straight lines relative to the front side 11a and the back side 11b of the crystal rod 11 is 45° or less. Furthermore, this angle is preferably 40° or less, more preferably 35° or less, and most preferably 30° or less.

[0061] Furthermore, in the laser processing apparatus 2, by changing the position of the irradiation head 16 in the Z-axis direction, the focusing point of the focusing laser beam LB can be positioned at a second depth from the front side 11a of the crystal rod 11.

[0062] Furthermore, in the second laser beam irradiation step (S121), similarly to the first laser beam irradiation step (S111) described above, while irradiating the laser beam LB from the irradiation head 16 toward the holding stage 4, the irradiation head 16 is moved along the X-axis direction (crystal direction

[010] ) and the Y-axis direction (crystal direction

[001] ).

[0063] If the laser beam LB is irradiated while the irradiation head 16 is moved, then with the multiple focusing points positioned at a second depth from the front side 11a of the crystal rod 11, the multiple focusing points move relative to the crystal rod 11 along the X-axis direction (crystal direction

[010] ).

[0064] Furthermore, during the second laser beam irradiation step (S121), the power of the laser beam LB that is focused at multiple focal points is adjusted to be greater than the power of the laser beam LB that is focused at multiple focal points during the first laser beam irradiation step (S111).

[0065] For example, in the second laser beam irradiation step (S121), the power of the laser beam LB that is focused at multiple focusing points is set to be greater than 0.3W and less than 0.6W.

[0066] Accordingly, as shown in FIG13, a modified portion 15c, which is formed by disordering the crystal structure of single-crystal silicon, is formed inside the crystal rod 11 with each of the multiple focusing points as the center. Furthermore, since the power of the laser beam LB, which is focused at the multiple focusing points in the second laser beam irradiation step (S121), becomes greater than that in the first laser beam irradiation step (S111), the size of the modified portion 15c also becomes larger than that of the modified portion 15a.

[0067] Furthermore, since the volume expansion of the crystal rod 11 accompanying the formation of the modified part 15c is also greater than the volume expansion accompanying the formation of the modified part 15a, the crystal rod 11 will generate internal stress greater than that in the first laser beam irradiation step (S111) during the second laser beam irradiation step (S121).

[0068] Then, inside the crystal rod 11, a crack 15d larger than the crack 15b extends from the modified portion 15c in a manner that alleviates the internal stress. Also, the crack 15d generated inside the crystal rod 11 tends to extend toward the place where internal stress is generated in the crystal rod 11.

[0069] Therefore, the cracks 15d extending from the modified portion 15c tend to extend toward the modified portion 15a and / or cracks 15b contained in the formed release layer 15 (release layer 15-1, 15-2). As a result, a release layer 15 (release layer 15-3) containing a plurality of modified portions 15c and cracks 15d extending from the plurality of modified portions 15c is formed inside the crystal rod 11.

[0070] Then, in the case where the laser beam LB has not been completely irradiated on all of the multiple second regions 11e (step (S122): no), the position of the spotting point is moved relative to the crystal rod 11 along the Y-axis direction (crystal direction

[001] ) (second indexing feed step: S123).

[0071] In this second indexing feed step (S123), for example, the irradiation head 16 is moved along the Y-axis direction (crystal direction

[001] ) until the irradiation head 16 is positioned in the X-axis direction (crystal direction

[010] ) when viewed from the second region 11e adjacent to the second region 11e where the peel layer 15 has been formed and the second region 11e where the peel layer 15 has not been formed.

[0072] Next, the second laser beam irradiation step (S121) described above is performed again. Furthermore, the second indexing feed step (S123) and the second laser beam irradiation step (S121) are performed alternately until the release layer 15 is formed in all of the plurality of second regions 11e contained in the crystal rod 11.

[0073] Then, if the release layer 15 is formed in all of the multiple second regions 11e (step (S122): yes), the release layer 15 is formed in the entire region inside the crystal rod 11, and the release layer formation step (S1) shown in FIG3 is completed.

[0074] Hereinafter, in this release layer formation step (S1), since the first depth and the second depth are set as described above, the thickness of the release layer 15 formed inside the crystal rod 11 can be reduced. This point will be explained below.

[0075] First, the method for forming the release layer 15 over the entire interior region of the crystal rod 11 is not limited to the method described above. For example, by performing only the second processing step (S12) instead of the first processing step (S11), the release layer 15 can also be formed over the entire interior region of the crystal rod 11. However, in this case, there is a concern that the amount of the crack 15d extending during the second processing step (S12) along the thickness direction of the crystal rod 11 may increase.

[0076] On the other hand, when the first processing step (S11) is performed before the second processing step (S12) and the first depth and the second depth are set as described above, the portion of the crack 15d orthogonal to the thickness direction of the crystal rod 11 tends to become larger than the portion along the thickness direction of the crystal rod 11. As a result, when the first depth and the second depth are set as described above, the thickness of the release layer 15 formed inside the crystal rod 11 becomes thinner.

[0077] Then, if the release layer formation step (S1) shown in FIG3 is completed, the substrate is separated from the crystal rod 11 starting from the release layer 15 (separation step: S2). FIG14(A) and FIG14(B) respectively schematically show partial cross-sectional side views of an example of the separation step (S2) shown in FIG3. This separation step (S2) is performed, for example, in the separation apparatus 18 shown in FIG14(A) and FIG14(B).

[0078] This separation device 18 has a holding stage 20, which holds a crystal rod 11 with a release layer 15 formed thereon. The holding stage 20 has a circular upper surface (holding surface) on which a porous plate (not shown) is exposed.

[0079] Furthermore, this porous plate is connected to a suction source (not shown) such as a vacuum pump through a flow path provided inside the holding stage 20. Then, if this suction source operates, the suction force acts on the space near the holding surface of the holding stage 20. In this way, for example, the crystal rod 11 placed on the holding surface can be held by the holding stage 20.

[0080] Furthermore, a separation unit 22 is provided above the holding platform 20. This separation unit 22 has a cylindrical support member 24. A lifting mechanism (not shown) of, for example, a ball screw type and a rotary drive source such as a motor are connected to the upper part of this support member 24.

[0081] Then, by operating this lifting mechanism, the separation unit 22 is lifted and lowered. Also, by operating this rotation drive source, the support member 24 rotates about a straight line passing through the center of the support member 24 and along a direction perpendicular to the holding surface of the holding platform 20 as a rotation axis.

[0082] Furthermore, the lower end of the support member 24 is fixed to the center of the upper part of the disc-shaped base 26. Then, on the lower side of the outer peripheral region of the base 26, a plurality of movable members 28 are provided at approximately equal intervals along the circumferential direction of the base 26. Each movable member 28 has a plate-shaped upright portion 28a extending downward from the lower surface of the base 26.

[0083] The upper end of this erected part 28a is connected to an actuator such as a cylinder built into the base 26. By operating this actuator, the movable member 28 moves along the radial direction of the base 26. Furthermore, a plate-shaped wedge 28b is provided on the inner side of the lower end of this erected part 28a. The plate-shaped wedge 28b extends toward the center of the base 26 and becomes thinner as it approaches the front end.

[0084] In the separation apparatus 18, the separation step (S2) is performed, for example, in the following sequence. Specifically, firstly, the crystal rod 11 is placed on the holding stage 20 in such a way that the center of the back surface 11b of the crystal rod 11 on which the release layer 15 is formed is aligned with the center of the holding surface of the holding stage 20.

[0085] Next, with the crystal rod 11 held by the holding stage 20, the attraction source communicating with the porous plate exposed on the holding surface is operated. Next, the actuator is operated by positioning the plurality of movable members 28 respectively on the radially outer side of the base 26.

[0086] Next, the lifting mechanism is operated in such a way that the front ends of the wedges 28b of each of the plurality of movable members 28 are positioned at a height corresponding to the peeling layer 15 formed inside the crystal rod 11. Next, the actuator is operated in such a way that the wedges 28b are driven into the side surface 11c of the crystal rod 11 (see Figure 14(A)).

[0087] Next, the rotation drive source is operated by rotating the wedge 28b that is driven into the side 11c of the crystal rod 11. Then, the lifting mechanism is operated by raising the wedge 28b (see Figure 14(B)).

[0088] After the wedge 28b is driven into the side 11c of the crystal ingot 11 as described above and rotated, the cracks 15b and 15d contained in the release layer 15 will further extend by causing the wedge 28b to rise. As a result, the front side 11a and the back side 11b of the crystal ingot 11 are separated. That is, the substrate 17 is manufactured from the crystal ingot 11, starting from the release layer 15.

[0089] Furthermore, in the case where the front 11a side and the back 11b side of the crystal rod 11 are separated at the moment when the wedge 28b is driven into the side 11c of the crystal rod 11, the wedge 28b may not be rotated. Alternatively, the actuator and the rotation drive source may operate simultaneously to drive the rotating wedge 28b into the side 11c of the crystal rod 11.

[0090] In the above-described method for manufacturing a single-crystal silicon substrate, after performing a first processing step (S11) for forming modified portions 15a in a plurality of first regions 11d, a second processing step (S12) for forming modified portions 15c and cracks 15d in a plurality of second regions 11e is then performed.

[0091] Here, if the modified portion 15a is formed in the first processing step (S11), the volume of the crystal rod 11 will expand and internal stress will be generated in the crystal rod 11. Furthermore, the crack 15d formed in the second processing step (S12) tends to extend toward the place where internal stress is generated.

[0092] Therefore, the crack 15d formed in the second processing step (S12) tends to extend toward the modified portion 15a formed in the first processing step (S11). Thus, in this method, the direction in which the crack 15d tends to extend in the second processing step (S12) can be arbitrarily set.

[0093] In this situation, it becomes easier to thin the release layer 15 formed inside the crystal ingot 11. Then, if the release layer 15 is thinned, the amount of crystal ingot material discarded during the cutting of the substrate 17 from the crystal ingot 11 and the planarization of the substrate 17 is reduced. As a result, in this method, the productivity of the substrate 17 when manufacturing the substrate 17 from the crystal ingot 11 using a laser beam LB is improved.

[0094] Furthermore, in this method, a laser beam LB is irradiated along the crystal direction

[010] onto a crystal rod 11 made of monocrystalline silicon, wherein the crystal rod 11 is manufactured such that the crystal surfaces (100) are exposed on the front side 11a and the back side 11b respectively.

[0095] Here, the crystal direction

[010] is a direction with a larger angle (e.g., 45°) relative to the specific crystal direction (e.g., crystal direction

[011] ) contained in the crystal direction <110>. Therefore, in this method, it is less likely to produce cracks extending from the modified portions 15a, 15c formed inside the crystal rod 11 by irradiating the laser beam LB along the specific crystal surface (e.g., the crystal surface shown in (2) below) contained in the crystal surface {111}. [Mathematical Formula 2]

[0096] Furthermore, in this method, a large number of cracks are generated extending from the modified portions 15a and 15c formed inside the crystal rod 11 by irradiating the laser beam LB along a specific crystal plane included in the crystal plane {110} that is parallel to the crystal direction

[010] (specifically, the crystal plane shown in (3) below). [Mathematical Formula 3]

[0097] Then, the angle formed by a particular crystal plane contained in the crystal plane {111} relative to the crystal plane (100) is about 54.7°, and in contrast, the angle formed by a crystal plane (e.g., crystal plane (101)) that is parallel to the crystal direction

[010] in the particular crystal plane contained in the crystal plane {110} relative to the crystal plane (100) is 45°.

[0098] Therefore, in this method, the generation of cracks in the thickness direction of the crystal rod 11 can be suppressed, which is greater than the amount in the direction parallel to the front side 11a and back side 11b of the crystal rod 11.

[0099] In this case, the thickness of the release layer 15 formed inside the crystal ingot 11 is suppressed, and the amount of material of the crystal ingot 11 and the substrate 17 discarded during the cutting of the substrate 17 from the crystal ingot 11 and the planarization of the substrate 17 is reduced. As a result, in this method, the productivity of the substrate 17 when manufacturing the substrate 17 from the crystal ingot 11 using a laser beam LB is further improved.

[0100] Furthermore, the above-described method for manufacturing a single-crystal silicon substrate is one aspect of the present invention, and the present invention is not limited to the above method. For example, in the present invention, the crystal rod used to manufacture the substrate is not limited to the crystal rod 11 shown in FIG1 and FIG2.

[0101] Specifically, in this invention, a crystal rod manufacturing substrate with a notch formed on its side can also be used. Alternatively, in this invention, a crystal rod manufacturing substrate without either an orientation plane or a notch formed on its side can also be used.

[0102] Furthermore, the structure of the laser processing apparatus used in this invention is not limited to the structure of the laser processing apparatus 2 described above. For example, this invention can also be implemented using a laser processing apparatus equipped with a moving mechanism, which moves the holding stage 4 along the X-axis, Y-axis and / or Z-axis directions respectively.

[0103] Alternatively, the present invention can also be implemented using a laser processing apparatus with a scanning optical system provided in the laser beam irradiation unit 6, wherein the scanning optical system can change the direction of the laser beam LB irradiated from the irradiation head 16. In addition, this scanning optical system includes, for example, a galvano scanner, an acousto-optic modulator (AOD), and / or a polygonal reflector.

[0104] That is, in this invention, as long as the crystal rod 11 held by the holding stage 4 and the focusing point of the laser beam LB irradiated from the irradiation head 16 can move relative to each other along the X-axis, Y-axis and Z-axis directions respectively, there is no limitation on the structure used to achieve it.

[0105] Furthermore, in the stripping layer formation step (S1) of the present invention, the plurality of first regions and the plurality of second regions included in the crystal rod 11 irradiated with the laser beam LB are not limited to the region along the crystal direction

[010] . For example, in the present invention, the region along the crystal direction

[001] may also be irradiated with the laser beam LB.

[0106] Furthermore, when the crystal rod 11 is irradiated with a laser beam LB, the cracks become more prone to propagate at the crystal surface shown in (4) below. [Mathematical Formula 4]

[0107] Furthermore, in this invention, a laser beam LB can also be irradiated along a direction that is slightly inclined from the crystal direction

[010] or the crystal direction

[001] when viewed from above. This point will be explained with reference to FIG15.

[0108] Figure 15 is a graph showing the width of the lift-off layer formed inside a workpiece made of monocrystalline silicon when a laser beam LB is irradiated on regions along different crystal directions. In addition, the horizontal axis of this graph represents the angle formed by the direction of extension of the region orthogonal to the crystal direction

[011] (reference region) and the direction of extension of the region being measured (measurement region) when viewed from above.

[0109] That is, when the horizontal axis value of this chart is 45°, the area along the crystal direction

[001] becomes the measurement object. Similarly, when the horizontal axis value of this chart is 135°, the area along the crystal direction

[010] becomes the measurement object.

[0110] Furthermore, the vertical axis of this chart represents the value when the width of the stripping layer formed in the measurement area by irradiating the measurement area with a laser beam LB is divided by the width of the stripping layer formed in the reference area by irradiating the reference area with a laser beam LB.

[0111] As shown in Figure 15, the width of the release layer increases when the angle formed by the direction of extension of the reference region and the direction of extension of the measurement region is 40° or more and 50° or less, or 130° or more and 140° or less. That is, the width of the release layer increases not only in the crystal direction

[001] or the crystal direction

[010] , but also when a laser beam LB is irradiated in a region along a direction with an angle of 5° or less relative to such crystal directions.

[0112] Therefore, in the stripping layer forming step (S1) of the present invention, a laser beam LB may also be irradiated on the area that is tilted at less than 5° from the crystal direction

[001] or the crystal direction

[010] when viewed from above.

[0113] That is, in the peeling layer forming step (S1) of the present invention, a laser beam LB can also be irradiated in the region along the following direction (first direction): parallel to the crystal surface exposed on the front side 11a and back side 11b of the crystal rod 11 (here crystal surface (100)) of the specific crystal surface included in the crystal surface {100}, and the angle formed with respect to the specific crystal direction included in the crystal direction <100> (here crystal direction

[001] or crystal direction

[010] ) is 5° or less.

[0114] Furthermore, in this invention, forming a release layer 15 over the entire interior region of the crystal rod 11 in the release layer formation step (S1) is not an indispensable feature. For example, in the case where cracks 15b and 15d extend in the region near the side surface 11c of the crystal rod 11 in the separation step (S2), a portion or all of the region near the side surface 11c of the crystal rod 11 may not have a release layer 15 formed in the release layer formation step (S1).

[0115] Furthermore, in the present invention, in the second laser beam irradiation step (S121), the focusing point of the focusing laser beam LB can be positioned at a second depth that is shallower than the first depth, and the focusing point can be moved relative to the crystal rod 11.

[0116] Furthermore, the separation step (S2) of the present invention can also be implemented using a device other than the separation device 18 shown in FIG14(A) and FIG14(B). For example, in the separation step (S2) of the present invention, the substrate 17 can also be separated from the crystal rod 11 by attracting the front side 11a side of the crystal rod 11.

[0117] Figures 16(A) and 16(B) are partial cross-sectional side views schematically showing the state of the separation step (S2) thus performed. The separation device 30 shown in Figures 16(A) and 16(B) has a holding stage 32 that holds the crystal rod 11 on which the peeling layer 15 is formed.

[0118] This holding stage 32 has a circular upper surface (holding surface) on which a perforated plate (not shown) is exposed. Furthermore, this perforated plate is connected to a suction source (not shown) such as a vacuum pump through a flow path provided inside the holding stage 32.

[0119] Therefore, if this attraction source operates, the attraction force acts on the space near the holding surface of the holding platform 32. In this way, for example, the crystal rod 11 placed on the holding surface can be held by the holding platform 32.

[0120] Furthermore, a separation unit 34 is provided above the holding platform 32. This separation unit 34 has a cylindrical support member 36. A lifting mechanism (not shown), such as a ball screw, is connected to the upper part of this support member 36, and the separation unit 34 is raised and lowered by operating this lifting mechanism.

[0121] Furthermore, the lower end of the support member 36 is fixed to the center of the upper part of the disc-shaped suction plate 38. Then, a plurality of suction ports are formed on the lower surface of the suction plate 38, and the plurality of suction ports are respectively connected to a suction source (not shown) such as a vacuum pump through a flow path provided inside the suction plate 38.

[0122] Therefore, if this attraction source is operational, the attraction force acts on the space near the lower surface of the attraction plate 38. In this way, for example, a crystal rod 11 close to the lower surface of the attraction plate 38 can be attracted in a way that pulls it upward.

[0123] In the separation apparatus 30, the separation step (S2) is performed, for example, in the following sequence. Specifically, firstly, the crystal rod 11 is placed on the holding stage 32 in such a way that the center of the back surface 11b of the crystal rod 11 on which the release layer 15 is formed is aligned with the center of the holding surface of the holding stage 32.

[0124] Next, with the crystal rod 11 held by the holding stage 32, the attraction source communicating with the perforated plate exposed on the holding surface is activated. Next, the lifting mechanism is activated to lower the separation unit 34 so that the lower surface of the attraction plate 38 contacts the front surface 11a of the crystal rod 11.

[0125] Next, the attraction source connected to the plurality of attraction ports is operated in such a way that the front side 11a of the crystal rod 11 is attracted through the plurality of attraction ports formed on the attraction plate 38 (see Figure 16(A)). Next, the lifting mechanism is operated to raise the separation unit 34 in such a way that the attraction plate 38 is separated from the holding platform 32 (see Figure 16(B)).

[0126] At this time, an upward force acts on the front 11a side of the crystal ingot 11, which is attracted through the plurality of suction ports formed on the suction plate 38. As a result, the cracks 15b and 15d contained in the release layer 15 extend further, and the front 11a side and the back 11b side of the crystal ingot 11 are separated. That is, the substrate 17 is manufactured from the crystal ingot 11, starting from the release layer 15.

[0127] Furthermore, in the separation step (S2) of the present invention, ultrasound may also be applied to the front side 11a side of the crystal rod 11 before the separation of the front side 11a side and the back side 11b side. In this case, because the cracks 15b and 15d contained in the peeling layer 15 extend further, it becomes easier to separate the front side 11a side and the back side 11b side of the crystal rod 11.

[0128] Furthermore, in this invention, the front side 11a of the crystal rod 11 can also be planarized (planarization step) by grinding or polishing before the release layer formation step (S1). For example, this planarization can also be performed when manufacturing multiple substrates from the crystal rod 11.

[0129] Specifically, if the crystal ingot 11 is separated from the release layer 15 to manufacture the substrate 17, an uneven surface will be formed on the newly exposed surface of the crystal ingot 11. The uneven surface reflects the distribution of the modified portions 15a, 15c and cracks 15b, 15d included in the release layer 15. Therefore, in the case of manufacturing a new substrate from this crystal ingot 11, it is preferable to planarize the surface of the crystal ingot 11 before the release layer formation step (S1).

[0130] This can suppress the diffusion of the laser beam LB irradiated to the crystal rod 11 on the front side of the crystal rod 11 during the release layer formation step (S1). Similarly, in the present invention, the surface of the release layer 15 side of the substrate 17 that has been separated from the crystal rod 11 can also be planarized by grinding or polishing.

[0131] Furthermore, in this invention, a bare wafer made of monocrystalline silicon can also be used as a workpiece to manufacture a substrate, wherein the bare wafer is manufactured in such a way that specific crystal surfaces included in the crystal surface {100} are exposed on the front and back sides respectively.

[0132] Furthermore, this bare wafer has, for example, a thickness of more than 2 and less than 5 times that of the substrate being manufactured. Also, this bare wafer is manufactured, for example, by being separated from the ingot 11 using the same method as described above. In this case, it may also be that the substrate is manufactured by repeating the above method twice.

[0133] Furthermore, in this invention, a substrate can also be manufactured by using a device wafer, which is formed by forming semiconductor elements on one side of the bare wafer, as a workpiece. In this case, in order to prevent adverse effects on the semiconductor elements, it is preferable to irradiate the device wafer with a laser beam LB from the side of the device wafer where no semiconductor elements are formed.

[0134] Furthermore, the structure and method of the above embodiments can be appropriately modified and implemented as long as they do not depart from the scope of the purpose of the present invention. [Simplified Explanation of the Diagram]

[0017] Figure 1 is a perspective view schematically showing an example of a crystal ingot used to manufacture a substrate. Figure 2 is a top view schematically showing the crystal ingot shown in Figure 1. Figure 3 is a flowchart schematically showing an example of a method for manufacturing a single-crystal silicon substrate from a crystal ingot that becomes a workpiece. Figure 4 is a top view schematically showing multiple regions included in the crystal ingot. Figure 5 is a flowchart schematically showing an example of a release layer formation step shown in Figure 3. Figure 6 is a diagram schematically showing an example of a laser processing apparatus used to form a release layer inside the crystal ingot. Figure 7 is a top view schematically showing the state of the crystal ingot held on the holding stage of the laser processing apparatus. Figure 8 is a flowchart schematically showing an example of the first processing step shown in Figure 5. Figure 9(A) is a top view schematically showing the state of the first laser beam irradiation step shown in Figure 8, and Figure 9(B) is a partial cross-sectional side view schematically showing the state of the first laser beam irradiation step shown in Figure 8. Figure 10 is a schematic cross-sectional view of a peeling layer, including the modified portion and the crack extending from the modified portion, formed inside the crystal rod during the first laser beam irradiation step shown in Figure 8. Figure 11 is a schematic cross-sectional view of a peeling layer formed inside the crystal rod by performing the first laser beam irradiation step shown in Figure 8 twice. Figure 12 is a flowchart schematically showing an example of the second processing step shown in Figure 5. Figure 13 is a schematic cross-sectional view of a peeling layer formed inside the crystal rod by performing the second laser beam irradiation step shown in Figure 12. Figures 14(A) and 14(B) are partial cross-sectional side views schematically showing an example of the separation step shown in Figure 3. Figure 15 is a graph showing the width of the peeling layer formed inside the workpiece made of monocrystalline silicon when irradiating regions along different crystal orientations with laser beams. Figures 16(A) and 16(B) are partial cross-sectional side views schematically illustrating another example of the separation step shown in Figure 3.

Claims

1. A method for manufacturing a single-crystal silicon substrate, comprising manufacturing a substrate from a workpiece made of single-crystal silicon, the workpiece being manufactured such that specific crystal planes included in a crystal plane {100} are exposed on a front side and a back side respectively, the method comprising: a release layer forming step, wherein a release layer including a modified portion and cracks extending from the modified portion is formed inside the workpiece; and a separation step, wherein after performing the release layer forming step, the substrate is separated from the workpiece starting from the release layer, the release layer forming step comprising: A first processing step is used to form the modified portion in a plurality of first regions, the plurality of first regions extending along a first direction and separated from each other in a second direction, the first direction being parallel to the specific crystal plane and forming an angle of less than 5° with respect to the specific crystal direction included in the crystal direction <100>, the second direction being parallel to the specific crystal plane and orthogonal to the first direction; and a second processing step is used to form the modified portion and the crack in a plurality of second regions after performing the first processing step, the plurality of second regions extending along the first direction and separated from each other in the second direction, any one of the plurality of second regions being positioned between an adjacent pair of first regions in the plurality of first regions, any one of the plurality of first regions being positioned between an adjacent pair of second regions in the plurality of second regions, the first processing step being performed by alternately repeating the following steps: The first laser beam irradiation step involves positioning the focal point of a laser beam with a wavelength capable of penetrating the single-crystal silicon inside any of the plurality of first regions at a first depth from the front surface of the workpiece, and moving the focal point relative to the workpiece along the first direction; and the first indexing feed step involves moving the position of the focal point relative to the workpiece along the second direction. The second processing step is performed by alternately repeating the following steps: the second laser beam irradiation step involves positioning the focal point inside any of the plurality of second regions at a second depth different from the first depth from the front surface of the workpiece, and moving the focal point relative to the workpiece along the first direction; and the second indexing feed step involves moving the position of the focal point relative to the workpiece along the second direction. During the second laser beam irradiation step, the power of the laser beam focused at the focal point is greater than the power of the laser beam focused at the focal point during the first laser beam irradiation step.

2. A method for manufacturing a single-crystal silicon substrate as claimed in claim 1, wherein, The second depth is deeper than the first depth.

3. A method for manufacturing a single-crystal silicon substrate as claimed in claim 1 or 2, wherein, The angle formed by the first plane of the first straight line and the second straight line relative to the front and back surfaces of the workpiece is less than 45°. The first straight line passes through the center of the second region located between the adjacent pair of first regions and along the first direction. The second straight line passes through the center of one of the adjacent pair of first regions and along the first direction. The angle formed by the second plane of the first straight line and the third straight line relative to the front and back surfaces of the workpiece is less than 45°. The third straight line passes through the center of the other of the adjacent pair of first regions and along the first direction.

Images