JP2015201529A - Processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing method of a workpiece capable of forming an appropriate modification layer without generating debris even in the case where a recess is disposed on a predetermined dividing line.SOLUTION: The processing method includes: a first laser beam irradiation step of setting a convergent point (P1) of a laser beam (L1) of a wavelength with permeability on a workpiece (11) at a first position closer to a front surface (11a) of the workpiece than a bottom of a recess (21) from the side of a rear surface (11b) of the workpiece, irradiating the workpiece with the laser beam along the predetermined dividing line, and forming a first modification layer (23); and a second laser beam irradiation step of setting a convergent point (P2) of a laser beam (L2) at a second position closer to the rear surface of the workpiece than the bottom of the recess from the side of the rear surface of the workpiece, irradiating the workpiece with the laser beam along the predetermined dividing line, and forming a second modification layer (25). In the first laser beam irradiation step, the irradiation with the laser beam is stopped in the recess on a predetermined dividing line (17).

Description

  The present invention relates to a processing method for forming a modified layer serving as a starting point of division by irradiating a plate-like workpiece such as a semiconductor wafer with a laser beam.

  In order to divide a plate-like workpiece typified by a semiconductor wafer into a plurality of chips, a processing method for condensing a laser beam inside the workpiece and forming a modified layer as a starting point of the division Has been proposed (see, for example, Patent Document 1).

  In this processing method, a modified layer is formed by irradiating a laser beam having a wavelength that is difficult to be absorbed by the workpiece along a planned division line (street) while condensing the laser beam inside the workpiece. By applying an external force after forming the modified layer, the workpiece can be divided along the planned division line.

JP 2002-192370 A

  By the way, in the case where a structure such as MEMS (Micro Electro Mechanical Systems) is provided on the surface side of the workpiece, a region in which a part of the recess (groove, pore, etc.) constituting the structure overlaps the planned division line. May be placed.

  In order to form a modified layer on such a workpiece, when the laser beam is irradiated with a focusing point positioned at the same depth as the recess, the workpiece is ablated near the recess and debris is formed on the surface side. Will occur. Further, in this case, since an appropriate modified layer cannot be formed in the vicinity of the recess, the work piece becomes poorly divided.

  The present invention has been made in view of such a problem, and an object of the present invention is to form an appropriate modified layer without generating debris even when a concave portion is arranged on a division line. It is to provide a method for processing a workpiece.

  According to the present invention, there is provided a processing method for processing a workpiece by irradiating a workpiece having a plurality of scheduled division lines with a laser beam having a wavelength that is transmissive, on the surface of the workpiece. Has a recess locally formed on the line to be divided, and the condensing point of the laser beam having a wavelength that is transmissive to the workpiece from the back side of the workpiece from the bottom of the recess. A first laser beam irradiation step of forming a first modified layer by irradiating the laser beam along the division line to be positioned at a first position on the surface side of the workpiece; After performing the step, the condensing point of the laser beam from the back surface side of the workpiece is positioned at a second position on the back surface side of the workpiece from the bottom portion of the recess, and the laser beam is aligned along the division line. Second modification by beam irradiation A second laser beam irradiation step for forming a laser beam, and in the first laser beam irradiation step, a laser beam irradiation is stopped at the concave portion on the division line. The

  In the present invention, before performing the first laser beam irradiation step, after performing the expanded sheet adhering step of adhering an expanded sheet to the back surface of the workpiece and the second laser beam irradiation step, the expanded It is preferable to provide a dividing step of applying an external force to the workpiece by expanding the sheet and dividing the workpiece along the planned dividing line.

  In the first laser beam irradiation step of irradiating the laser beam with the condensing point positioned on the surface side of the workpiece from the bottom of the recess, the processing method of the present invention does not irradiate the recess with the laser beam. The workpiece does not ablate in the vicinity of the recess formed in the.

  In addition, a modified layer suitable for division can be formed in the vicinity of the recess. As described above, according to the present invention, it is possible to provide a processing method of a workpiece that can form an appropriate modified layer without generating debris even when a concave portion is arranged on a division line.

It is a perspective view which shows a to-be-processed object typically. FIG. 2A is a plan view schematically showing the surface side of the workpiece, and FIG. 2B is a cross-sectional view schematically showing the workpiece. It is a perspective view which shows typically the to-be-processed object after implementing an expand sheet sticking step. FIG. 4A is a cross-sectional view schematically showing the first laser beam irradiation step, and FIG. 4B is a cross-sectional view schematically showing the second laser beam irradiation step. 5A and 5B are partial cross-sectional side views schematically showing the dividing step.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The processing method according to the present embodiment includes an expand sheet attaching step (see FIG. 3), a first laser beam irradiation step (see FIG. 4A), and a second laser beam irradiation step (see FIG. 4B). And a dividing step (see FIG. 5).

  In the expand sheet sticking step, the expand sheet is stuck to the back side of the workpiece in which the concave portion is formed on the division line (street) on the front side. In the first laser beam irradiation step, the first modified layer is formed by irradiating the laser beam from the back surface side of the workpiece with the focusing point positioned on the surface side of the workpiece from the bottom (bottom portion) of the recess. . At this time, the concave portion is not irradiated with a laser beam.

  In the second laser beam irradiation step, the second modified layer is formed by irradiating the laser beam with the focusing point positioned from the bottom surface of the workpiece to the back surface side of the workpiece from the bottom surface of the recess. In the dividing step, the expanded sheet is expanded to apply an external force, and the workpiece is divided along the planned dividing line. Hereinafter, the processing method according to the present embodiment will be described in detail.

  FIG. 1 is a perspective view schematically showing a workpiece to be processed in the present embodiment. As shown in FIG. 1, the workpiece 11 is, for example, a disk-shaped (plate-shaped) semiconductor wafer, and the surface 11 a is divided into a central device region 13 and an outer peripheral surplus region 15 surrounding the device region 13. It is done.

  The device region 13 is further divided into a plurality of regions by division lines (streets) 17 arranged in a lattice pattern, and devices 19 such as MEMS (Micro Electro Mechanical Systems) are formed in each region. The outer periphery 11c of the workpiece 11 is chamfered, and the cross-sectional shape is an arc shape.

  FIG. 2A is a plan view schematically showing the surface 11 a side of the workpiece 11, and FIG. 2B is a cross-sectional view schematically showing the workpiece 11. Note that FIG. 2B shows an AA cross section of FIG. As shown in FIGS. 2A and 2B, the device 19 includes a plurality of recesses 21. Each concave portion 21 is formed in a groove shape parallel to the planned division line 17a extending in the first direction.

  In addition, each recess 21 is formed across two adjacent devices 19 across the planned division line 17b extending in the second direction, and a part of each concave portion 21 is positioned on the planned division line 17b. It has been. That is, the concave portion 21 is locally formed on the planned dividing line 17b. In addition, in this Embodiment, although the groove-shaped recessed part 21 is illustrated, the shape of the recessed part 21 may be a hole shape (pore shape) etc.

  In the processing method of the workpiece of this Embodiment, the expanded sheet sticking step which sticks an expanded sheet on the back surface 11b side of the workpiece 11 mentioned above is implemented first. FIG. 3 is a perspective view schematically showing the workpiece 11 after performing the expand sheet attaching step.

  As shown in FIG. 3, in the expand sheet sticking step, the expand sheet 31 is stuck to the workpiece 11 by bringing the adhesive surface of the expand sheet 31 into contact with the back surface 11 b of the workpiece 11. An annular frame 33 is fixed to the outer peripheral portion of the expand sheet 31.

  After performing the expand sheet sticking step, the first laser beam irradiation step for forming the modified layer (first modified layer) at the first position on the surface 11a side from the bottom (bottom portion) of the recess 21 is performed. FIG. 4A is a cross-sectional view schematically showing the first laser beam irradiation step.

  The first laser beam irradiation step is performed by the laser processing apparatus 2 shown in FIG. The laser processing apparatus 2 includes a holding table (not shown) that holds the workpiece 11. Around the holding table, a clamp (not shown) for holding and fixing the annular frame 33 is provided.

  The holding table is connected to a rotation drive source (not shown) such as a motor, and rotates around a vertical axis. Further, a moving mechanism (not shown) is provided below the holding table, and the holding table moves in the horizontal direction by this moving mechanism.

  A laser processing head 4 is disposed above the holding table. The laser processing head 4 focuses the laser beam L1 oscillated by a laser oscillator (not shown) inside the workpiece 11 held on the holding table.

  In the first laser beam irradiation step, the surface 11a side of the workpiece 11 is held on the holding table. Next, the holding table is moved and rotated to align the laser processing head 4 with the division line 17a to be processed.

  After the alignment, the back surface 11b side of the workpiece 11 is irradiated with the laser beam L1 through the expanded sheet 31, and the holding table and the laser processing head 4 are relatively moved in a direction parallel to the division line 17a to be processed. (Process feed).

  The wavelength of the laser beam L1 is a wavelength that is difficult to be absorbed by the workpiece 11 (wavelength having transparency). For example, when the workpiece 11 is a silicon wafer, a YAG or YVO 4 pulse laser oscillator may be used as a laser oscillator, and the laser beam L1 having a wavelength of 1064 nm may be irradiated.

  Further, the condensing point P1 of the laser beam L1 is positioned at a first position where the distance from the surface 11a is d1. This first position is located closer to the surface 11 a than the bottom (bottom) of the recess 21, and d1 takes a value smaller than the depth of the recess 21.

  When the workpiece 11 is irradiated with such a laser beam L1, the vicinity of the condensing point P1 is modified by multiphoton absorption. Therefore, the modified layer (first modified layer) 23 along the division planned line 17a to be processed can be formed by irradiating the laser beam L1 while relatively moving as described above.

  After forming the modified layer 23 along the division line 17a to be processed, the irradiation of the laser beam L1 is stopped, and the holding table and the laser processing head 4 are moved in a direction perpendicular to the division line 17a to be processed. Move relative (index feed). Thereby, the laser processing head 4 is aligned with the adjacent division planned line 17a.

  After the alignment, a similar modified layer 23 is formed along the adjacent division line 17a. After this operation is repeated and the modified layer 23 is formed along all the planned dividing lines 17a extending in the first direction, the holding table is rotated around the vertical axis to be divided in the second direction. The laser processing head 4 is aligned with the line 17b. And the modified layer 23 along this division | segmentation scheduled line 17b is formed.

  The processing conditions, procedures, and the like when forming the modified layer 23 along the planned division line 17b are substantially the same as those when forming the modified layer 23 along the planned division line 17a. However, as shown in FIG. 4 (A), since the concave portion 21 is formed on the planned division line 17b, when the laser beam L1 is irradiated under exactly the same conditions and procedures, the workpiece is near the concave portion 21. 11 ablate. In addition, an appropriate modified layer 23 cannot be formed in the vicinity of the recess 21.

  Therefore, in the processing method of the present embodiment, the irradiation of the laser beam L1 is stopped during the period in which the laser processing head 4 passes over the recess 21. That is, the recess 21 is not irradiated with the laser beam L1.

  Thereby, the ablation of the workpiece 11 can be prevented in the vicinity of the recess 21. Further, the modified layer 23 suitable for dividing the workpiece 11 can be formed in the vicinity of the recess 21. When the modified layer 23 is formed along all the division lines 17b, the first laser beam irradiation step ends.

  After performing the first laser beam irradiation step, a second laser beam irradiation step for forming a modified layer (second modified layer) at the second position on the back surface 11b side from the bottom of the recess 21 is performed. FIG. 4B is a cross-sectional view schematically showing the second laser beam irradiation step.

  As shown in FIG. 4B, the second laser beam irradiation step is performed by the same laser processing apparatus 2 as the first laser beam irradiation step. In the first laser beam irradiation step, first, the holding table is moved and rotated to align the laser processing head 4 with the scheduled division line 17a to be processed.

  After alignment, the back surface 11b side of the workpiece 11 is irradiated with the laser beam L2 via the expanded sheet 31, and the holding table and the laser processing head 4 are relatively moved in a direction parallel to the division line 17a to be processed. (Process feed).

  The condensing point P2 of the laser beam L2 is positioned at a second position where the distance from the surface 11a is d2. This second position is located on the back surface 11 b side from the bottom of the recess 21, and d2 takes a value larger than the depth of the recess 21. The wavelength of the laser beam L2 may be the same as that of the laser beam L1.

  When the workpiece 11 is irradiated with such a laser beam L2, the vicinity of the focal point P2 is modified by multiphoton absorption. Therefore, the modified layer (second modified layer) 25 along the division planned line 17a to be processed can be formed by irradiating the laser beam L2 while relatively moving as described above.

  After forming the modified layer 25 along the division line 17a to be processed, the irradiation of the laser beam L2 is stopped, and the holding table and the laser processing head 4 are moved in a direction perpendicular to the division line 17a to be processed. Move relative (index feed). Thereby, the laser processing head 4 is aligned with the adjacent division planned line 17a.

  After the alignment, a similar modified layer 25 is formed along the adjacent division planned line 17a. After this operation is repeated and the modified layer 25 is formed along all the planned dividing lines 17a extending in the first direction, the holding table is rotated around the vertical axis to be divided in the second direction. The laser processing head 4 is aligned with the line 17b. And the modified layer 25 along this division | segmentation scheduled line 17b is formed.

  The processing conditions, procedures, and the like when forming the modified layer 25 along the planned division line 17b may be the same as those when forming the modified layer 25 along the planned division line 17a. When the modified layer 25 is formed along all the planned division lines 17b, the second laser beam irradiation step ends.

  After carrying out the second laser beam irradiation step, a dividing step of dividing the workpiece 11 by expanding the expanded sheet 31 attached to the back surface 11b side is carried out. 5A and 5B are partial cross-sectional side views schematically showing the dividing step.

  As shown in FIG. 5A, the dividing step is performed by the expanding device 10. The expanding apparatus 10 includes a workpiece support mechanism 12 that supports the workpiece 11, and a cylindrical expansion drum 14 that expands the expanded sheet 31 attached to the back surface 11 b side of the workpiece 11. . The inner diameter of the expansion drum 14 is larger than the diameter of the workpiece 11, and the outer diameter of the expansion drum is smaller than the inner diameter of the frame 33.

  The workpiece support mechanism 12 includes an annular frame support table 16 that supports the frame 33. The upper surface of the frame support table 16 is a mounting surface on which the frame 33 is mounted. A plurality of clamps 18 that sandwich and fix the frame 33 are provided on the outer peripheral portion of the frame support table 16.

  Below the workpiece support mechanism 12, an elevating mechanism 20 is provided. The lifting mechanism 20 includes a cylinder case 22 fixed to a base (not shown) and a piston rod 24 inserted through the cylinder case 22. A frame support table 16 is fixed to the upper end portion of the piston rod 24.

  The elevating mechanism 20 moves the upper surface (mounting surface) of the frame support table 16 between a reference position having a height substantially equal to the upper end of the expansion drum 14 and an expansion position below the upper end of the expansion drum 14. As described above, the workpiece support mechanism 12 is moved up and down.

  In the dividing step, first, as shown in FIG. 5A, the frame 33 holding the workpiece 11 is placed on the upper surface of the frame support table 16 positioned at the reference position, and the frame 33 is held by the clamp 18. Fix it. As a result, the upper end of the expansion drum 14 comes into contact with the expanded sheet 31 positioned between the outer periphery of the workpiece 11 and the inner periphery of the frame 33.

  Next, the workpiece support mechanism 12 is lowered by the elevating mechanism 20, and the upper surface of the frame support table 16 is positioned at the extended position below the upper end of the expansion drum 14, as shown in FIG. As a result, the expansion drum 14 is raised relative to the frame support table 16, and the expanded sheet 31 is pushed up by the expansion drum 14 to expand.

  As described above, on the workpiece 11, the modified layers 23 and 25 that are the starting points of the break are formed along the planned dividing line 17. Therefore, when the expand sheet 33 is expanded and an external force is applied, the workpiece 11 is divided into a plurality of chips starting from the modified layers 23 and 25.

  As described above, in the processing method of the present embodiment, the first laser beam irradiation is performed in which the focusing point P1 is positioned closer to the surface 11a side of the workpiece 11 than the bottom (bottom portion) of the recess 21 and the laser beam L1 is irradiated. In the step, since the concave portion 21 is not irradiated with the laser beam L1, the workpiece 11 is not ablated in the vicinity of the concave portion 21 formed in the division line 17b.

  In addition, a modified layer (first modified layer) 23 suitable for division can be formed in the vicinity of the recess 21. As described above, according to the processing method of the present embodiment, even when the concave portion 21 is arranged on the planned dividing line 17, the workpiece capable of forming an appropriate modified layer 23 without generating debris. Eleven processing methods can be provided.

  In addition, this invention is not limited to description of the said embodiment, A various change can be implemented. For example, in the workpiece 11 of the above embodiment, the concave portion 21 is formed on the planned division line 17b extending in the second direction, but the concave portion 21 is on the planned division line 17a extending in the first direction. May be formed.

  In the above embodiment, in the first laser beam irradiation step and the second laser beam irradiation step, the modified layers 23 and 25 are formed on the planned division lines 17a extending in the first direction, and then in the second direction. Although the modified layers 23 and 25 are formed in the extending division line 17b, the present invention is not limited to this. After forming the modified layers 23 and 25 on the planned division line 17b extending in the second direction, the modified layers 23 and 25 may be formed on the planned division line 17a extending in the first direction.

  Further, in the above embodiment, the expand sheet 31 is expanded to apply an external force, and the workpiece 11 is divided into a plurality of chips. However, the external force is applied to the workpiece 11 by other methods and divided. You can also In that case, the expand sheet sticking step and the dividing step can be omitted or changed.

  For example, the first laser beam irradiation step and the second laser beam irradiation step are performed without performing the expand sheet attaching step, and then the grinding step for grinding the back surface 11b side of the workpiece 11 is performed. You can also. In this case, the workpiece 11 can be thinly processed in the grinding step, and the workpiece 11 can be divided into a plurality of chips by applying an external force. In this case, if the tape is attached to the surface 11a side of the workpiece 11 before and after the first laser beam irradiation step and the second laser beam irradiation step, the divided chips can be easily handled. it can.

  In addition, the configurations, methods, and the like according to the above-described embodiments can be changed as appropriate without departing from the scope of the object of the present invention.

DESCRIPTION OF SYMBOLS 11 Workpiece 11a Front surface 11b Back surface 11c Outer periphery 13 Device region 15 Outer peripheral surplus region 17, 17a, 17b Scheduled division line (street)
19 Device 21 Recess 23 Modified layer (first modified layer)
25 Modified layer (second modified layer)
31 Expanding sheet 33 Frame 2 Laser processing device 4 Laser processing head 10 Expanding device 12 Workpiece support mechanism 14 Expansion drum 16 Frame support table 18 Clamp 20 Lifting mechanism 22 Cylinder case 24 Piston rod L1, L2 Laser beam P1, P2 Condensing point

Claims (2)

A processing method for processing a workpiece by irradiating a workpiece having a plurality of division lines with a laser beam having a wavelength having transparency,
On the surface of the workpiece, a concave portion is locally formed on the planned division line,
The focusing point of the laser beam having a wavelength that is transparent to the workpiece from the back side of the workpiece is positioned at the first position on the surface side of the workpiece relative to the bottom of the recess, Irradiating the laser beam along the first laser beam irradiation step of forming a first modified layer,
After performing the first laser beam irradiation step, the condensing point of the laser beam from the back side of the workpiece is positioned at a second position on the back side of the workpiece from the bottom of the recess, and the division is scheduled A second laser beam irradiation step of irradiating the laser beam along a line to form a second modified layer,
In the first laser beam irradiation step, the laser beam irradiation is stopped at the concave portion on the division line. Before carrying out the first laser beam irradiation step, an expand sheet attaching step for attaching an expand sheet to the back surface of the workpiece;
After performing the second laser beam irradiation step, it was provided with a dividing step of extending the expanded sheet to apply an external force to the workpiece to divide the workpiece along the division line. The processing method according to claim 1.

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