Wafer processing method

Abstract

To provide a wafer processing method capable of solving a problem such that a crack develops in a region protruding from a dividing scheduled line and damages a device when a wafer is processed by irradiating a laser beam.SOLUTION: A method for processing a wafer 10 includes: a shield tunnel formation step of irradiating a laser beam LB of a wavelength having transparency relative to a wafer 10 to form shield tunnels 102, 104 composed of a pore 130 and a modified tube 140 surrounding the pore 130; and a dividing step of applying external force to the wafer 10 to divide the wafer 10 into individual device chips 12. The shield tunnel formation step includes: a first formation step of continuously forming a shield tunnel 102 on a dividing scheduled line 14 at least with an interval of one shield tunnel; and a second formation step of continuously forming a shield tunnel 104 in an area of the dividing scheduled line with the interval.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a wafer processing method for dividing a wafer into individual device chips. [Background technology]

[0002] Wafers with multiple devices such as ICs and LSIs formed on their surfaces, which are divided by planned division lines, are then divided into individual device chips using a dicing machine or laser processing machine, and these are used in electrical devices such as mobile phones and personal computers.

[0003] The laser processing device is generally composed of a chuck table that holds the wafer, an imaging means that images the wafer held on the chuck table and detects the area to be processed, a laser beam application means that applies a laser beam to the wafer held on the chuck table, and a processing feed means that feeds the chuck table and the laser beam application means relative to each other, and is capable of processing wafers with high precision (see, for example, Patent Document 1).

[0004] Laser beam application means include a type that applies a laser beam of a wavelength that is absorbed by the wafer to perform ablation processing (see, for example, Patent Document 2), a type that applies a laser beam of a wavelength that is transparent to the wafer to perform internal processing to form a modified layer inside (see, for example, Patent Document 3), and a type that applies a laser beam of a wavelength that is transparent to the wafer and in which 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 to form a shield tunnel consisting of a pore inside and a modified cylinder surrounding the pore (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-085347 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-188475 [Patent Document 3] Patent No. 3408805 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-221483 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the above-mentioned laser processing apparatus is used to irradiate a laser beam along the planned dividing lines to divide the wafer into individual device chips, there is a problem in that, due to the crystalline structure of the material that constitutes the wafer, the irradiation of the laser beam may cause cracks to grow in areas that extend beyond the planned dividing lines, damaging the devices.

[0007] The present invention has been made in view of the above-mentioned facts, and its main technical object is to provide a wafer processing method that can solve the problem that, when processing a wafer by irradiating it with a laser beam, cracks propagate into areas outside the intended dividing lines, causing damage to devices. [Means for solving the problem]

[0008] In order to solve the above-mentioned main technical problem, according to the present invention, there is provided a wafer processing method for dividing a wafer having a plurality of devices formed on a surface partitioned by a plurality of planned dividing lines into individual device chips, the method comprising: a shield tunnel forming step of irradiating a laser beam having a wavelength that is transparent to the wafer along the planned dividing lines to form shield tunnels each consisting of a small hole and a modified cylinder surrounding the small hole; and a dividing step of applying an external force to the wafer to divide the wafer into individual device chips, the shield tunnel forming step comprising a first forming step of forming successive shield tunnels along the planned dividing lines at intervals of at least one shield tunnel, and a second forming step of forming successive shield tunnels in the spaced-apart areas of the planned dividing lines. , applicableThe shield tunnel formed in the first forming step and the shield tunnel formed in the second forming step are formed so as to overlap by about half their respective lengths by shifting the position of the focal point in the thickness direction, and a wafer processing method is provided in which steps are formed alternately in the thickness direction.

[0009] Applicable In the shield tunnel forming step, it is preferable to stack the shield tunnels in the thickness direction of the wafer. When stacking the shield tunnels in the shield tunnel forming step, it is preferable to include a third forming step of forming a shield tunnel above the shield tunnel formed in the first forming step, and a fourth forming step of forming a shield tunnel above the shield tunnel formed in the second forming step.

[0010] In the shield tunnel forming step, when the shield tunnels are stacked in the thickness direction of the wafer, it is preferable to stack the upper shield tunnel adjacent to the lower shield tunnel so as not to contact it. The wavelength of the laser beam is 532 nm, and the power per pulse is 2.0 to 4.0·10 -5 J, and the spot interval is preferably 10 to 15 μm. [Effects of the Invention]

[0011] The wafer processing method of the present invention is a wafer processing method for dividing a wafer having a plurality of devices formed on a surface partitioned by a plurality of planned dividing lines into individual device chips, and includes a shield tunnel forming step of irradiating a laser beam having a wavelength that is transparent to the wafer along the planned dividing lines to form shield tunnels consisting of holes and modified cylinders surrounding the holes, and a dividing step of applying an external force to the wafer to divide the wafer into individual device chips, wherein the shield tunnel forming step includes a first forming step of forming consecutive shield tunnels along the planned dividing lines at intervals of at least one shield tunnel, and a second forming step of forming consecutive shield tunnels in the spaced-apart areas of the planned dividing lines. , applicable The shield tunnel formed in the first formation step and the shield tunnel formed in the second formation step are formed so that they overlap by about half their respective lengths by shifting the position of the focal point in the thickness direction, and steps are formed alternately in the thickness direction, which prevents cracks from progressing into areas that extend beyond the planned division line, and furthermore, avoids the effects of heat pools that occur when the laser beam is irradiated in a continuous, adjacent manner, thereby eliminating the problem of cracks progressing into areas where devices are formed and damaging the devices. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an overall perspective view of a laser processing apparatus suitable for the wafer processing method of the present invention. [Figure 2] FIG. 1 is a perspective view of a wafer, which is a workpiece of the present embodiment. [Figure 3] (a) is a perspective view showing an embodiment of a shield tunnel forming process, (b) is an enlarged plan view of a portion of the wafer shown in (a), and (c) is an enlarged cross-sectional view of a portion of the wafer shown in (b). [Figure 4] 10 is a cross-sectional view showing an embodiment in which an external force is applied to a wafer by a dividing device to perform a dividing step. FIG. [Figure 5]FIG. 10 is an enlarged cross-sectional view of a portion of a wafer in another embodiment of the shield tunnel forming step. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a wafer processing method according to the present invention will be described in detail with reference to the accompanying drawings.

[0014] A laser processing apparatus suitable for carrying out a processing method configured based on the present invention will be described below with reference to the accompanying drawings, along with a wafer processing method according to this embodiment.

[0015] Fig. 1 shows an overall perspective view of a laser processing apparatus 1. The laser processing apparatus 1 is disposed on a base 2 and includes a holding means 3 for holding a wafer 10 (see Fig. 2), which will be described later, a moving means 4 for moving the holding means 3 in the X-axis direction and the Y-axis direction, an imaging means 6 for imaging the wafer 10 held by the holding means 3, a laser beam application means 7 for applying a laser beam to the wafer 10 held by the holding means 3 to perform a desired processing, and a frame 5 consisting of a vertical wall 5a erected on the side of the moving means 4 and a horizontal wall 5b extending horizontally from the upper end of the vertical wall 5a. Although not shown, an optical system constituting the imaging means 6 and the laser beam application means 7 is housed and held inside the horizontal wall 5b.

[0016] 1, the holding means 3 includes a rectangular X-axis direction movable plate 31 mounted on the base 2 so as to be movable in the X-axis direction, a rectangular Y-axis direction movable plate 32 mounted on the X-axis direction movable plate 31 so as to be movable in the Y-axis direction, a cylindrical support 33 fixed to the upper surface of the Y-axis direction movable plate 32, and a rectangular cover plate 34 fixed to the upper end of the support 33. A chuck table 35 extending upward through an elongated hole formed in the cover plate 34 is disposed on the cover plate 34. The chuck table 35 is a means for holding the wafer 10 using an XY plane specified by the X and Y coordinates as a holding surface, and is configured to be rotatable by a rotation drive means (not shown) housed in the support 33. A suction chuck 36 formed of a porous material with air permeability as the holding surface is disposed on the upper surface of the chuck table 35. The suction chuck 36 is connected to a suction means (not shown) by a flow path passing through the support 33, and four clamps 37 are arranged at equal intervals around the suction chuck 36 and are used to hold the wafer 10 (described later) on the chuck table 35.

[0017] The moving means 4 includes an X-axis moving means 4a that moves the chuck table 35 in the X-axis direction, and a Y-axis moving means 4b that moves the chuck table 35 in the Y-axis direction. The X-axis moving means 4a converts the rotational motion of the motor 42a into linear motion via a ball screw 42b and transmits the linear motion to the X-axis movable plate 31, moving the X-axis movable plate 31 in the X-axis direction along a pair of guide rails 2A, 2A that are arranged on the base 2 along the X-axis direction. The Y-axis moving means 4b converts the rotational motion of the motor 44a into linear motion via a ball screw 44b and transmits the linear motion to the Y-axis movable plate 32, moving the Y-axis movable plate 32 in the Y-axis direction along a pair of guide rails 31a, 31a that are arranged on the X-axis movable plate 31 along the Y-axis direction.

[0018] The above-described laser processing apparatus 1 is controlled by a control means (not shown). The control means is configured by 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, etc., a readable / writable random access memory (RAM) that temporarily stores detected values, calculation results, etc., an input interface, and an output interface (details not shown). The image capturing means 6, the laser beam application means 7, the X-axis moving means 4a, the Y-axis moving means 4b, etc. that constitute the moving means 4 are connected to and controlled by the control means.

[0019] A wafer 10 shown in Fig. 2, for example, is processed by a wafer processing method configured according to the present invention. The wafer 10 is, for example, a SiC wafer having a thickness of about 100 µm, and a plurality of devices 12 are formed on a surface 10a defined by division lines 14. When the wafer 10 is processed by the laser processing apparatus 1, as shown in the figure, the wafer 10 is supported via adhesive tape T by an annular frame F having an opening Fa capable of accommodating the wafer 10. By carrying out the wafer processing method of this embodiment described below, the wafer 10 is divided into individual device chips.

[0020] In the wafer processing method of this embodiment, first, a shield tunnel forming step is carried out in which a laser beam having a wavelength that allows transmission through the wafer 10 is irradiated to form a shield tunnel consisting of a pore and a transformation tube surrounding the pore. The procedure for carrying out the shield tunnel forming step of this embodiment will be described in more detail below.

[0021] When the shield tunnel forming step is performed, once the wafer 10 described above is prepared, the wafer 10 is placed on the suction chuck 36 of the chuck table 35 of the laser processing apparatus 1 shown in FIG. 1 and held by suction, and the frame F is clamped and fixed by the clamps 37. Next, the moving means 4 described above is operated to position the wafer 10 directly below the imaging means 6 and capture an image, and positional information of the devices 12 and the planned dividing lines 14 on the wafer 10 is detected and stored in the control means described above. Furthermore, based on the positional information, the moving means 4 and the like are operated to align the predetermined planned dividing lines 14 on the wafer 10 in the X-axis direction.

[0022] 3(a), the wafer 10 is positioned directly below the condenser 71 of the laser beam application means 7, and the X-axis moving means 4a is operated to feed the wafer 10 in the X-axis direction based on the position information stored in the control means, while the laser beam LB is applied to the area where the dividing lines 14 have been formed. As can be seen from FIG. 3(b), which shows an enlarged portion of the dividing lines 14, a dividing layer 100 having shield tunnels 102, 104 inside is formed along the central area of ​​the dividing lines 14.

[0023] When irradiating the laser beam LB, the numerical aperture (NA) of the condenser lens constituting the condenser 71 of the laser beam application means 7 of this embodiment is set so that the value divided by the refractive index (N) of the wafer 10 is in the range of 0.05 to 0.2, for example, and the wavelength of the laser beam LB is set to, for example, 532 nm which is transparent to the wafer 10, the average output is set to 0.2 to 0.4 W, the repetition frequency is set to 10 kHz, and the energy per pulse is set to 2.0 to 4.0·10 -5The spot spacing is set to J, and the spot interval is set to 10 to 15 μm. By positioning the focal point inside the wafer 10 and irradiating the wafer with the laser beam LB based on these laser processing conditions, shield tunnels 102 and 104 are formed as shown in FIG. 3(c), and a division layer 100, which serves as the starting point for division, is formed by applying an external force described below. As can be seen from the enlarged perspective view shown at the bottom of FIG. 3(c), the shield tunnels 102 and 104 consist of a fine hole 130 and a transformation tube 140 surrounding the fine hole 130. For example, the diameter of the fine hole 130 is approximately 1 μm, and the diameter of the transformation tube 140 is approximately 10 μm.

[0024] In the above shield tunnel forming process, for example, a first forming step is performed in which shield tunnels 102 are formed consecutively along the central region of the division line 14, with an interval (e.g., 10 to 15 μm) for at least one shield tunnel. Next, a second forming step is performed in which shield tunnels 104 are formed consecutively in the central region of the division line 14 with the interval. That is, the shield tunnels 102 and the shield tunnels 104 are formed alternately along the X-axis direction to form the division layer 100. By performing the first forming step and the second forming step in this manner when forming the division layer 100, it is possible to prevent cracks from progressing in regions extending beyond the division line 14, and further, it is possible to avoid the effect of heat accumulation that occurs when the laser beam LB is irradiated consecutively adjacent to each other, thereby avoiding the problem of cracks progressing to regions where the devices 12 are formed and damaging the devices 12.

[0025] As described above, after forming the dividing layer 100 consisting of the shield tunnels 102 and 104 along a predetermined dividing line 14, the wafer 10 is indexed and fed in the Y-axis direction to position the unprocessed dividing line 14 adjacent in the Y-axis direction directly below the condenser 71. Then, in the same manner as described above, the focal point of the laser beam LB is positioned within the central region of the dividing line 14 and irradiated, thereby sequentially performing the first and second forming steps described above. This forms the shield tunnels 102 and 104 and the dividing layer 100. In the same manner, the wafer 10 is fed in the X-axis direction and the Y-axis direction to form the same dividing layer 100 along all the dividing lines 14 along the X-axis direction. Next, the wafer 10 is rotated 90 degrees in the direction indicated by the arrow R1 in FIG. 3( a) to align the unprocessed dividing line 14 perpendicular to the dividing line 14 along which the dividing layer 100 has already been formed in the X-axis direction. Then, the focal point of the laser beam LB is positioned and irradiated in the same manner as described above inside the central regions of the remaining planned dividing lines 14, forming dividing layers 100 along all of the planned dividing lines 14 formed on the surface 10a of the wafer 10, as shown in the lower part of Figure 3(a), and the shield tunnel forming process of this embodiment is completed.

[0026] After the above-described shield tunnel forming step is performed, a dividing step is performed in which an external force is applied to the wafer 10 to divide the wafer 10 into individual device chips 12′, for example, using a dividing device 50 shown in FIG. 4.

[0027] The illustrated dividing device 50 includes a frame holding member 51 that holds an annular frame F that holds wafers 10, a plurality of clamps 52 as fixing means disposed on the outer periphery of the frame holding member 51, and an expansion drum 55 disposed inside the frame holding member 51. The outer diameter of this expansion drum 55 is smaller than the inner diameter of the annular frame F, and the inner diameter of the expansion drum 55 is set larger than the outer diameter of the wafers 10. In addition, a plurality of air cylinders 53 that move the frame holding member 51 up and down are disposed outside the expansion drum 55, and a piston rod 54 that is moved up and down by the air cylinders 53 is connected to the underside of the frame holding member 51. In this way, the support means consisting of multiple air cylinders 53 and piston rods 54 is configured to selectively move the annular frame holding member 51 to a reference position at approximately the same height as the upper end of the expansion drum 55, as shown by the solid line in Figure 4, and to an expanded position a predetermined amount below the upper end of the expansion drum 55, as shown by the dotted line.

[0028] The operation of the above-mentioned dividing device 50 will be described. The annular frame F supporting the wafer 10 on which the divided layers 100 are formed along the intended dividing lines 14 is placed on the mounting surface of the frame holding member 51 and fixed to the frame holding member 51 by the clamps 52. At this time, the piston rod 54 of the air cylinder 53 is extended, and the wafer 10 is positioned at the reference position shown by the solid line in FIG. 4.

[0029] The frame holding member 51 supporting the wafer 10 positioned at the reference position indicated by the solid line in the figure is lowered by the operation of multiple air cylinders 53 constituting the external force application means, and the annular frame F also descends. As a result, the adhesive tape T attached to the annular frame F comes into contact with the upper edge of the expanding drum 55, which is rising relatively, as indicated by the two-dot chain line in the figure, and is expanded. As a result, a radially pulling external force acts on the wafer 10 attached to the adhesive tape T, and the planned division lines 14 weakened by the dividing layer 100 become the division starting points, and the wafer is divided into individual device chips 12'. This completes the division process.

[0030] The present invention is not limited to the above-described embodiment. When forming the shield tunnels in the above-described shield tunnel forming process, the position of the focal point may be shifted vertically when irradiating the wafer 10 with the laser beam LB in the thickness direction, thereby forming stacked shield tunnels. For example, in the shield tunnel forming process performed on a wafer 10 having a thickness of 500 μm, as can be seen from the cross-sectional view of the wafer 10 shown in FIG. 5 , the following steps may be performed: a first forming step of forming successive shield tunnels 111 along the dividing line 14 aligned in the X-axis direction of the wafer 10 with a spacing of at least one shield tunnel; a second forming step of forming successive shield tunnels 112 in the region of the dividing line 14 with the spacing; a third forming step of forming a shield tunnel 113 above the formed shield tunnel 111; and a fourth forming step of forming a shield tunnel 114 above the shield tunnel 112 formed in the second forming step. In the embodiment shown in FIG. 6 , in addition to the first to fourth forming steps described above, fifth and sixth forming steps are performed to form shield tunnels 115 and 116 so as to be stacked on top of shield tunnels 113 and 114, thereby forming division layer 110. The positions of the focal points when irradiating laser beams LB to form shield tunnels 111 to 116 are positioned so as to be vertically offset from each other, and shield tunnel 111 formed in the first forming step and shield tunnel 112 formed in the second forming step are formed with alternating steps in the thickness direction of wafer 10. This more effectively avoids the effects of heat accumulation when performing the shield tunnel forming process on a thick workpiece, and division layer 110 prevents cracks from progressing in the region where device 12 is formed. In this embodiment, when shield tunnels 113 to 116 are formed in the third to sixth forming steps, they are also formed with alternating steps in the thickness direction, achieving the same effect.In the first to sixth forming steps, when the shield tunnels are stacked in the thickness direction, the upper shield tunnels are stacked so as not to come into contact with the lower shield tunnels. This makes it possible to suppress the occurrence of cracks compared to when the upper shield tunnels are formed so as to come into contact with the lower shield tunnels. [Explanation of symbols]

[0031] 1: Laser processing equipment 2: Base 2A: Guide rail 3: Holding means 31:X-axis movable plate 32: Y-axis direction movable plate 33: Post 34: Cover plate 35: Chuck table 36: Vacuum chuck 37: Clamp 4. Transportation 4a:X-axis movement means 4b: Y-axis movement means 5:Frame body 5a: Vertical wall 5b:Horizontal wall part 6: Imaging means 7: Laser beam irradiation means 71: Concentrator 10: Wafer 10a: surface 12: Device 14: Planned division line 50: Splitting device 51: Frame holding member 52: Clamp 53: Air cylinder 54: Piston rod 55: Extended Drum 100, 110: Split layer 102, 104: Shield tunnel 111~116: Shield Tunnel LB: Laser beam

Claims

1. A wafer processing method for dividing a wafer having a plurality of devices formed on a surface defined by a plurality of dividing lines into individual device chips, comprising: a shield tunnel forming step of irradiating a laser beam having a wavelength that is transparent to the wafer along the intended dividing line to form a shield tunnel consisting of a hole and a modified cylinder surrounding the hole; a dividing step of dividing the wafer into individual device chips by applying an external force to the wafer, the shield tunnel forming step includes a first forming step of forming successive shield tunnels along the planned division line at intervals of at least one shield tunnel; a second forming step of continuously forming shield tunnels in the spaced apart regions of the planned dividing lines, A wafer processing method in which the shield tunnel formed in the first formation step and the shield tunnel formed in the second formation step are formed so that they overlap by about half their respective lengths by shifting the position of the focal point in the thickness direction, and steps are formed alternately in the thickness direction.

2. A wafer processing method as described in claim 1, wherein in the shield tunnel forming process, shield tunnels are stacked in the thickness direction of the wafer.

3. 3. The wafer processing method according to claim 2, wherein the shield tunnel forming step includes, when stacking the shield tunnels, a third forming step of forming a shield tunnel above the shield tunnel formed in the first forming step, and a fourth forming step of forming a shield tunnel above the shield tunnel formed in the second forming step.

4. 4. The wafer processing method according to claim 3, wherein in the shield tunnel forming step, when stacking the shield tunnels in the thickness direction of the wafer, the upper shield tunnels are stacked adjacent to the lower shield tunnels so as not to come into contact with each other.

5. A wafer processing method according to any one of claims 1 to 4, wherein the wavelength of the laser beam is 532 nm, the power per pulse is 2.0 to 4.0·10-5 J, and the spot spacing is 10 to 15 μm.

Images