Wafer processing methods

Abstract

[Problem] To provide a wafer processing method that solves the problem of damage to devices caused by cracks extending beyond a predetermined dicing line when processing wafers by irradiating them with laser light. [Solution] A wafer processing method includes the following steps: a shielding via forming step, forming a shielding via consisting of a fine hole and a modified barrel surrounding the fine hole by irradiating the wafer with laser light of a wavelength that has penetrability to the wafer; and a dicing step, applying external force to the wafer to dice it into individual device wafers. The shielding via forming step includes the following steps: a first shielding via forming step, continuously forming shielding vias along a predetermined dicing line with at least one component of the shielding via spaced out; and a second shielding via forming step, continuously forming shielding vias in the area along the predetermined dicing line where the spaced-out portion has been left blank.

Description

[Technical Field]

[0001] This invention relates to a wafer processing method for dividing a wafer into individual device wafers. [Previous Technology]

[0002] A wafer with multiple devices such as ICs and LSIs formed on the front side by multiple intersecting predetermined dividing lines is divided into individual device chips by a dicing device or a laser processing device, and the divided device chips can be used in electrical machines such as mobile phones and personal computers.

[0003] The laser processing apparatus generally consists of a work chuck, an imaging unit, a laser beam irradiation unit, and a processing feed mechanism, and can process wafers with high precision. The aforementioned work chuck holds the wafer, the aforementioned imaging unit images the wafer held on the work chuck and detects the area to be processed, the aforementioned laser beam irradiates the wafer held on the work chuck with laser beams, and the aforementioned processing feed mechanism processes and feeds the work chuck and the laser beam irradiation unit relative to each other (see, for example, Patent Document 1).

[0004] The laser beam irradiation unit has the following configurations: a type that performs ablation processing by irradiating laser light of a wavelength that absorbs the wafer (see, for example, Patent Document 2); a type that performs internal processing by irradiating laser light of a wavelength that penetrates the wafer to form a modified layer internally (see, for example, Patent Document 3); and a type that irradiates laser light of a wavelength that penetrates the wafer and the value of the numerical aperture (NA) of the concentrator divided by the refractive index (N) of the wafer is in the range of 0.05 to 0.2, thereby forming a protective through-hole internally composed of a fine hole and a modified cylinder surrounding the fine hole (see, for example, Patent Document 4). Previous Art Documents Patent Documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2015-085347; Patent Document 2: Japanese Patent Application Publication No. 2004-188475; Patent Document 3: Japanese Patent No. 3408805; Patent Document 4: Japanese Patent Application Publication No. 2014-221483 [Summary of the Invention]

[0006] The problem the invention aims to solve

[0007] Incidentally, due to the crystal structure of the materials that make up the wafer, if laser light is irradiated along the predetermined dividing line by the above-mentioned laser processing equipment to divide into individual device chips, there will be cracks that extend beyond the predetermined dividing line due to the irradiation of the laser light, causing damage to the device.

[0008] Accordingly, the object of the present invention is to provide a wafer processing method that can solve the problem that, during wafer processing by irradiating with laser light, cracks extend beyond the predetermined dicing line, causing damage to the device. Means for solving the problem

[0009] According to the present invention, a wafer processing method is provided, which divides a wafer having a plurality of devices divided by a plurality of intersecting predetermined dividing lines on its front side into individual device wafers. The wafer processing method includes the following steps: a shielding via forming step, wherein laser light of a wavelength having penetrability to the wafer is irradiated to form a shielding via consisting of a fine hole and a modified cylinder surrounding the fine hole; and a dividing step, wherein after performing the shielding via forming step, an external force is applied to the wafer to divide the wafer into individual device wafers. The shielding via forming step includes the following steps: a first shielding via forming step, wherein at least one component of the shielding via is left empty, and the shielding via is continuously formed along the predetermined dividing lines; and a second shielding via forming step, wherein the shielding via is continuously formed in the area of ​​the predetermined dividing lines where the empty interval has been left empty.

[0010] Preferably, the via formed in the first via formation step and the via formed in the second via formation step are formed by alternating height differences in the thickness direction. Preferably, the via formation step is to deposit vias in the thickness direction of the wafer. Preferably, the via formation step includes the following steps: a third via formation step, in which a via is formed above the via formed in the first via formation step during the deposition of vias; and a fourth via formation step, in which a via is formed above the via formed in the second via formation step.

[0011] Preferably, in the shielding via formation step, when depositing the shielding via in the thickness direction of the wafer, the upper shielding via is deposited in a manner that does not contact the lower shielding via. Preferably, the wavelength of the laser beam is 532 nm, the power per pulse is 2.0~4.0.10⁻⁵ J, and the spot spacing is 10~15 μm. Effects of the Invention

[0012] According to the present invention, the expansion of the crack into the area beyond the predetermined dividing line can be suppressed. In addition, the effect of heat accumulation caused by the continuous adjacent irradiation of laser light can be avoided, and the problem of the crack expanding into the area where the device is formed and damaging the device can be solved.

Implementation Method

[0014] Form used to implement the invention

[0015] Hereinafter, a wafer processing method according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0016] Hereinafter, a laser processing apparatus suitable for implementing the processing method of the embodiment of the present invention will be described with reference to the accompanying drawings, and a wafer processing method of the present embodiment will be described.

[0017] Figure 1 shows an overall perspective view of the laser processing apparatus 1. The laser processing apparatus 1 includes: a holding unit 3 disposed on a base 2 and holding a wafer 10 (described later) (see Figure 2); a moving mechanism 4 for moving the holding unit 3 in the X-axis and Y-axis directions; an imaging unit 6 for imaging the wafer 10 held in the holding unit 3; a laser beam irradiation unit 7 for irradiating the wafer 10 held in the holding unit 3 with laser beams to perform the desired processing; and a frame 5, which is composed of a vertical wall 5a erected on the side of the moving mechanism 4 and a horizontal wall 5b extending horizontally from the upper end of the vertical wall 5a. Although not shown in the figure, the optical system constituting the imaging unit 6 and the laser beam irradiation unit 7 is housed and held inside the horizontal wall 5b.

[0018] As shown in FIG. 1, the holding unit 3 includes a rectangular X-axis movable plate 31 movably mounted on the base 2 in the X-axis direction, a rectangular Y-axis movable plate 32 movably mounted on the X-axis movable plate 31 in the Y-axis direction, a cylindrical support column 33 fixed to the upper surface of the Y-axis movable plate 32, and a rectangular cover plate 34 fixed to the upper end of the support column 33. A work chuck 35 is provided on the cover plate 34, and the work chuck 35 extends upward through an elongated hole formed in the cover plate 34. The work chuck 35 is an assembly that holds the wafer 10 using the XY plane defined by the X and Y coordinates as the holding surface, and is configured to be rotatable by a rotation drive assembly (not shown) housed in the support column 33. An adsorption chuck 36 is provided on the upper surface of the work chuck 35, and the adsorption chuck 36 is formed of a porous material with air permeability and constitutes the holding surface. The suction chuck 36 is connected to a suction component (not shown) via a flow path through the support column 33, and four clamps 37 are arranged at equal intervals around the suction chuck 36 for use when holding the wafer 10 (described later) on the work chuck 35.

[0019] The moving mechanism 4 includes: an X-axis moving mechanism 4a, which moves the aforementioned worktable 35 in the X-axis direction; and a Y-axis moving mechanism 4b, which moves the worktable 35 in the Y-axis direction. The X-axis moving mechanism 4a converts the rotational motion of the motor 42a into linear motion through the ball screw 42b and transmits it to the movable plate 31 in the X-axis direction, causing the movable plate 31 in the X-axis direction to move along a pair of guide rails 2A, 2A arranged on the base 2 in the X-axis direction. The Y-axis moving mechanism 4b converts the rotational motion of the motor 44a into linear motion through the ball screw 44b and transmits it to the movable plate 32 in the Y-axis direction, causing the movable plate 32 in the Y-axis direction to move along a pair of guide rails 31a, 31a arranged on the movable plate 31 in the X-axis direction in the Y-axis direction.

[0020] The laser processing apparatus 1 described above can be controlled by a controller (not shown in the figure). This controller is composed of a computer and includes a central processing unit (CPU) that performs calculations according to a control program, a read-only memory (ROM) that stores the control program, a read-write random access memory (RAM) for temporarily storing detected values ​​and calculation results, an input interface, and an output interface (details omitted in the figure). The following components can be connected to and controlled by this controller: the imaging unit 6, the laser beam irradiation unit 7, the X-axis movement mechanism 4a, the Y-axis movement mechanism 4b, etc., which constitute the movement mechanism 4.

[0021] The wafer processing method according to the present invention can process, for example, the wafer 10 shown in FIG2. The wafer 10 can be a SiC wafer with a thickness of approximately 100 μm, having a front side 10a and a back side 10b, as shown in FIG3(d), and a plurality of devices 12 are divided by a plurality of intersecting predetermined dividing lines 14 and formed on the front side 10a. When the wafer 10 is processed by the laser processing apparatus 1 described above, it is supported by an annular frame F having an opening Fa for accommodating the wafer 10 through adhesive tape T, as shown in FIG, and is fed into the laser processing apparatus as a wafer unit 13. The wafer 10 can be divided into individual device chips by performing the wafer processing method of the present embodiment described below.

[0022] In the wafer processing method of this embodiment, the first step is to perform a shielding via formation step. The aforementioned shielding via formation step involves irradiating the wafer 10 with laser light of a wavelength that has penetrability to form a shielding via consisting of a fine hole and a modified cylinder surrounding the fine hole. Hereinafter, the procedure for performing the shielding via formation step of this embodiment will be described in more detail.

[0023] During the shielding via formation step, after preparing the aforementioned wafer 10, the wafer 10 is placed and held in the suction chuck 36 of the worktable 35 of the laser processing apparatus 1 shown in FIG. 1, and the frame F is clamped and fixed by the clamp 37. Next, the aforementioned moving mechanism 4 is operated to position the wafer 10 directly below the imaging unit 6 for imaging, and the position information of the device 12 and the predetermined dicing line 14 of the wafer 10 is detected and stored in the aforementioned controller. Furthermore, based on the position information, the moving mechanism 4 is operated to align the predetermined dicing line 14 of the wafer 10 with the X-axis direction.

[0024] Next, as shown in FIG3(a), the wafer 10 is positioned directly below the concentrator 71 of the laser beam irradiation unit 7, and based on the position information stored in the controller, the X-axis moving mechanism 4a is operated to feed the wafer 10 in the X-axis direction while irradiating the area where the sizing predetermined line 14 is formed with laser beam LB. As can be understood from FIG3(c), which shows a portion of the sizing predetermined line 14 magnified, a sizing layer 100 having protective vias 102 and 104 is formed inside the central region along the sizing predetermined line 14.

[0025] When irradiating the aforementioned laser beam LB, the numerical aperture (NA) of the focusing lens of the focusing unit 71 constituting the laser beam irradiation unit 7 of this embodiment is set such that, for example, the value divided by the refractive index (N) of the wafer 10 is in the range of 0.05 to 0.2. The wavelength of the laser beam LB is set to, for example, 532 nm, which is penetrable to the wafer 10. The average output is set to 0.2 to 0.4 W. The repetition frequency is set to 10 kHz. The energy per pulse is set to 2.0 to 4.0 × 10⁻⁵ J. The spacing of the light spots is set to 10 to 15 μm. By positioning the focusing point inside the wafer 10 and irradiating the laser beam LB according to such laser processing conditions, as shown in FIG3(d), the shielding vias 102 and 104 can be formed to form a dividing layer 100. The aforementioned dividing layer 100 is the starting point of the division by applying an external force described later. Furthermore, as can be understood from the perspective view enlarged in FIG3(e), the screen through holes 102 and 104 are composed of a fine hole 130 and a modified cylinder 140 surrounding the fine hole 130, and for example, the diameter of the fine hole 130 is about 1 μm and the diameter of the modified cylinder 140 is about 10 μm.

[0026] In the above-described shielding through-hole forming step, for example, a first shielding through-hole forming step is performed first. This first shielding wall forming step involves continuously forming shielding through-holes 102 along the central region of the predetermined dividing line 14, leaving an interval equal to at least one shielding through-hole component (e.g., 10-15 μm). Next, a second shielding through-hole forming step is performed, whereby shielding through-holes 104 are continuously formed in the central region of the predetermined dividing line 14, where the interval has been left blank. That is, shielding through-holes 102 and 104 are alternately formed along the X-axis direction to form the dividing layer 100. Thus, when forming the partition layer 100, by performing the first and second shielding via forming steps, the expansion of cracks beyond the partition line 14 can be suppressed. Furthermore, the effects of heat accumulation caused by continuous adjacent irradiation of laser beams LB can be avoided, thus preventing the problem of cracks expanding into the area where the device 12 is formed and damaging the device 12. Moreover, in the above embodiment, the method of performing the first and second shielding via forming steps at time intervals is, as mentioned above, to avoid the effects of heat accumulation. This is because when the interval between the shielding vias 102 is shortened while performing the first shielding via forming step, the heat generated during the formation of the shielding vias 102 will not dissipate sufficiently, thus making it impossible to prevent the expansion of cracks into the area where the device 12 is formed. Preferably, the laser processing conditions in the first and second shielding via forming steps are the same, but different laser processing conditions can also be used.

[0027] As described above, after forming the partition layer 100 consisting of shielding vias 102 and 104 along the predetermined partition lines 14, the wafer 10 can be indexed and fed in the Y-axis direction, and the adjacent unprocessed partition lines 14 extending in the first direction along the Y-axis direction can be positioned directly below the condenser 71. Then, as described above, the focusing point of the laser beam LB is positioned inside the central region of the partition lines 14 for irradiation, and the first shielding via forming step and the second shielding via forming step described above are performed sequentially. In this way, shielding vias 102 and 104 are formed to form the partition layer 100. Similarly, the wafer 10 is processed and fed in the X-axis and Y-axis directions, and the same partition layer 100 as described above is formed along all the partition lines 14 extending in the first direction. Next, the wafer 10 is rotated 90 degrees in the direction indicated by arrow R1 in FIG3(a), so that the pre-defined dividing line 14 extending in a second direction orthogonal to the pre-defined dividing line 14 on which the dividing layer 100 has been formed is aligned with the X-axis direction. Then, the laser beam LB is positioned and irradiated in the same manner as above in the central region of the pre-defined dividing line 14 extending in the second direction. As shown in the lower part of FIG3(b), the dividing layer 100 is formed along all the pre-defined dividing lines 14 formed on the front side 10a of the wafer 10, thus completing the shielding via formation step of this embodiment.

[0028] After the above-mentioned screen protection via formation step has been performed, the slitting step can be performed. The aforementioned slitting step is, for example, using the slitting device 50 shown in FIG4 to apply external force to the wafer 10 and slitting the wafer 10 into individual device wafers 12'.

[0029] The dicing apparatus 50 shown in the figure includes a frame holding member 51 that holds an annular frame F holding a wafer 10, a plurality of clamps 52 disposed on the outer periphery of the frame holding member 51 as fixing components, and an expansion cylinder 55 disposed on the inner side of the frame holding member 51. The outer diameter of the expansion cylinder 55 is set to be smaller than the inner diameter of the annular frame F, and the inner diameter of the expansion cylinder 55 is set to be larger than the outer diameter of the wafer 10. Furthermore, a plurality of cylinders 53 are disposed on the outer side of the expansion cylinder 55 to move the frame holding member 51 in a vertical direction, and piston rods 54 that move in a vertical direction by means of the cylinders 53 are connected to the lower surface of the frame holding member 51. The support assembly, consisting of a plurality of cylinders 53 and piston rods 54, is configured to selectively move to a reference position and an expanded position. The reference position is, as shown by the solid line in Figure 4, where the annular frame retaining member 51 is at approximately the same height as the upper end of the expanded cylinder 55. The expanded position is, as shown by the 2-point chain line, where the annular frame retaining member 51 is positioned a predetermined amount below the upper end of the expanded cylinder 55.

[0030] The function of the dicing device 50 described above will be explained. An annular frame F supporting a wafer 10 with a dicing layer 100 formed along a predetermined dicing line 14 is placed on the mounting surface of a frame holding member 51 and fixed to the frame holding member 51 by a clamp 52. At this time, the piston rod 54 of the cylinder 53 is extended, and the wafer 10 is positioned at the reference position shown by the solid line in FIG4.

[0031] The frame holding member 51 supporting the wafer 10, which is positioned at the reference position indicated by the solid line in the figure, will descend due to the actuation of the plurality of cylinders 53 constituting the external force applied to the assembly, and the annular frame F will also descend. Thereby, as shown by the two-point chain line in the figure, the adhesive tape T mounted on the annular frame F will abut against the upper edge of the relatively rising expansion cylinder 55 and be expanded. As a result, the radially stretching external force will act on the wafer 10 attached to the adhesive tape T, and starting from the pre-defined dicing line 14, which has been weakened by the dicing layer 100, it will be diced into individual device wafers 12'. Through this, the dicing process is completed.

[0032] The present invention is not limited to the embodiments described above. When forming the screen protection via in the above-described screen protection via forming step, it can also be formed by: when irradiating laser light LB in the thickness direction of wafer 10, the position of the focusing point is staggered in the vertical direction, thereby causing the screen protection via to be deposited. For example, in the shielding via formation step performed on a wafer 10 with a thickness of 500 μm, as can be understood from the cross-sectional view of the wafer 10 shown in FIG5, it can also be configured as follows: performing a first shielding via formation step of continuously forming shielding vias 111 at intervals that leave at least one shielding via component on the pre-defined dividing line 14 aligned with the X-axis direction of the wafer 10; performing a second shielding via formation step of continuously forming shielding vias 112 in the area of ​​the pre-defined dividing line 14 where the interval has been left empty; performing a third shielding via formation step of forming shielding vias 113 above the formed shielding vias 111; and performing a fourth shielding via formation step of forming shielding vias 114 above the shielding vias 112 formed in the second shielding via formation step. In the embodiment shown in Figure 5, in addition to the first to fourth via formation steps described above, a fifth and sixth via formation step is performed to further form vias 115 and 116 by stacking layers on vias 113 and 114, thereby forming a partition layer 110. Furthermore, the focal points of the laser beams LB used to form vias 111 to 116 are positioned so that they are staggered vertically, and height differences are alternately set along the thickness of the wafer 10 to form vias 111 formed in the first via formation step and vias 112 formed in the second via formation step. This allows for more effective avoidance of the effects of heat buildup when performing via formation steps on workpieces with greater thickness, and prevents cracks from extending to the area where devices 12 are formed by the partition layer 110. In this embodiment, when forming the protective through-holes 113-116 in the third to sixth protective through-hole forming steps, the height difference is also alternately set in the thickness direction to form them, and the same effect is achieved. Furthermore, in the aforementioned first to sixth protective through-hole forming steps, when the protective through-holes are stacked in the thickness direction, the upper protective through-holes are stacked in a manner that prevents them from contacting the lower protective through-holes. Therefore, compared to the case where the upper protective through-holes contact the lower protective through-holes, the generation of cracks can be suppressed. [Simplified Explanation of the Diagram]

[0013] FIG1 is an overall perspective view of a laser processing apparatus suitable for implementing the wafer processing method of the present invention. FIG2 is a perspective view of a wafer unit. FIG3(a) is a perspective view of the display screen via forming step, (b) is a perspective view of the wafer unit after the via forming step, (c) is a plan view showing a portion of the wafer that has undergone the via forming step, (d) is a cross-sectional view showing a portion of the wafer after the first and second via forming steps, and (e) is a schematic perspective view of a modified cylinder. FIG4 is a cross-sectional view showing the state of performing a dicing step by applying external force to the wafer by a dicing device. FIG5 is a cross-sectional view showing a portion of the wafer in another embodiment of the via forming step.

Claims

1. A wafer processing method, comprising dividing a wafer having a plurality of devices divided by a plurality of intersecting predetermined dividing lines on its front side into individual device wafers, the wafer processing method comprising the following steps: a shielding via forming step, wherein laser light of a wavelength having penetrability to the wafer is irradiated to form a shielding via consisting of a fine hole and a modified barrel surrounding the fine hole; and a dividing step, wherein after performing the shielding via forming step, an external force is applied to the wafer to divide the wafer into individual device wafers, the shielding via forming step comprising the following steps: a first shielding via forming step, wherein at least one component of the shielding via is left blank, and the shielding via is continuously formed along the predetermined dividing lines; and a second shielding via forming step, wherein the shielding via is continuously formed in the area of ​​the predetermined dividing lines where the blanked interval is left blank, and approximately half the length of the shielding via formed in the second shielding via forming step overlaps with the shielding via formed in the first shielding via forming step in the thickness direction of the wafer.

2. The wafer processing method of claim 1, wherein the shielding via formed in the first shielding via forming step and the shielding via formed in the second shielding via forming step are formed by alternately setting height differences in the thickness direction.

3. The wafer processing method of claim 1 or 2, wherein the shielding via forming step is to deposit the shielding via in the thickness direction of the wafer.

4. The wafer processing method of claim 3, wherein the shielding via forming step includes the following steps when stacking the shielding via: a third shielding via forming step, forming a shielding via above the shielding via formed in the first shielding via forming step; and a fourth shielding via forming step, forming a shielding via above the shielding via formed in the second shielding via forming step.

5. The wafer processing method of claim 3, wherein in the shielding via forming step, when the shielding via is deposited in the thickness direction of the wafer, the upper shielding via is deposited in a manner that does not contact the lower shielding via.

6. The wafer processing method of claim 4, wherein in the shielding via forming step, when the shielding via is deposited in the thickness direction of the wafer, the upper shielding via is deposited in a manner that does not contact the lower shielding via.

7. The wafer processing method of claim 1, wherein the wavelength of the laser beam is 532 nm, the power of each pulse is 2.0~4.0.10⁻⁵ J, and the spacing of the laser spots is 10~15 μm.

8. A wafer processing method, comprising dividing a wafer having a plurality of devices formed on its front side by a plurality of intersecting predetermined dividing lines into individual device wafers, the wafer processing method comprising the following steps: a shielding via forming step, wherein laser light of a wavelength having penetrability to the wafer is irradiated to form a plurality of shielding vias consisting of a fine hole and a modified barrel surrounding the fine hole; and a dividing step, wherein after performing the shielding via forming step, an external force is applied to the wafer to divide the wafer into individual device wafers, the shielding via forming step comprising the following steps: a first shielding via forming step, wherein at least one component of the shielding via is left blank, and a plurality of first shielding vias are continuously formed along the predetermined dividing lines; and a second shielding via forming step, wherein a plurality of second shielding vias are continuously formed in the area along the predetermined dividing lines where the blanked-out interval is left blank. In the thickness direction of the wafer, the first screen via and the second screen via have the same predetermined length, and the first screen via and the second screen via overlap along the entire predetermined length.

9. The wafer processing method of claim 8, wherein the wavelength of the laser beam is 532 nm, the power of each pulse is 2.0~4.0.10⁻⁵ J, and the spacing of the laser spots is 10~15 μm.

Images