JP7578451B2 - Wafer processing method - Google Patents

Description

The present invention relates to a wafer processing method for dividing a wafer into individual device chips.

Wafer surfaces are divided into multiple IC, LSI and other devices along planned division lines, and are then divided into individual device chips using a dicing machine or laser processing machine, for use in electronic devices such as mobile phones and personal computers.

As a technique for dividing a wafer into individual device chips using a laser processing device, a technique has been proposed in which a laser beam with a wavelength that is transparent to the wafer is focused on an area inside the wafer that corresponds to the intended dividing line from the rear surface of the wafer, and a continuous modified layer is formed inside the intended dividing line, and then an external force is applied to divide the wafer into individual device chips (see, for example, Patent Document 1).

In addition, in order to facilitate the division of the wafer, the present application proposes a technology for forming a modified layer on the front side of the wafer as well as on the back side (see Patent Document 2).

Patent No. 3408805 JP 2008-131008 A

According to the technology described in the above-mentioned Patent Document 2, by forming a modified layer on the front and back sides, the wafer is prevented from curving, and the wafer can be efficiently divided into individual device chips, making this a recommended processing method.

However, as the size of the device chip becomes smaller, such as 1 mm x 1 mm or less, the internal stress of the modified layer formed on the front side of the wafer can cause unintended cracks to form in the modified layer formed on the back side, resulting in a deterioration in the quality of the separated device chips and making them difficult to remove from the laser processing equipment.

The present invention has been made in consideration of the above facts, and its main technical objective is to provide a wafer processing method that reduces cracks from the modified layer formed on the back side, does not cause a deterioration in the quality of the separated device chips, and makes it easy to remove the device chips from the laser processing equipment.

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 surface on which a plurality of devices are partitioned by planned division lines into individual device chips, the method including a protective member disposing step of disposing a protective member on the surface of the wafer, a light-transmitting film disposing step of disposing a light-transmitting film on the back surface of the wafer, a chuck table holding step of holding the protective member side of the wafer on a chuck table, a first modified layer forming step of irradiating the wafer along the planned division lines with a focused point of a laser beam having a wavelength that is transparent to the wafer, by passing through the light-transmitting film and positioning the focused point on the front surface side of the wafer, thereby forming a modified layer, and The method includes a second modified layer forming step, which is performed after the layer forming step, of positioning the focal point of a laser beam on the back side inside the wafer through the light-transmitting film and irradiating the laser beam along the planned dividing line to form a modified layer, and a dividing step, which removes the light-transmitting film from the back side of the wafer and applies an external force to the modified layer formed along the planned dividing line to divide the wafer into individual device chips . The dividing step includes holding the front side of the wafer via the protective member on a chuck table constituting a grinding apparatus, removing the light-transmitting film from the back side of the wafer, grinding the back side of the wafer to thin it, and dividing the wafer into individual device chips .

The light-transmitting film disposing step is preferably any one of the steps of disposing the light-transmitting film by thermocompression bonding a polyolefin film to the back surface of the wafer, disposing the light-transmitting film by applying a water-soluble liquid resin to the back surface of the wafer and solidifying it, and disposing the light-transmitting film by adhering an adhesive tape to the back surface of the wafer. After carrying out the dividing step , it is preferable to carry out a frame supporting step of positioning the wafer in a frame having an opening for accommodating the wafer divided into individual device chips, adhering a dicing tape to the back surface of the wafer and the frame, and disposing the wafer in the frame via the dicing tape.

The wafer processing method of the present invention is a wafer processing method for dividing a wafer having a surface on which a plurality of devices are partitioned by planned division lines into individual device chips, the method including a protective member disposing step of disposing a protective member on the surface of the wafer, a light-transmitting film disposing step of disposing a light-transmitting film on the back surface of the wafer, a chuck table holding step of holding the protective member side of the wafer on a chuck table, a first modified layer forming step of irradiating a laser beam having a wavelength that is transparent to the wafer along the planned division lines by positioning the focal point of the laser beam on the front surface side of the wafer through the light-transmitting film and forming a modified layer, and after the first modified layer forming step, positioning the focal point of the laser beam on the back surface side of the wafer through the light-transmitting film and irradiating the laser beam along the planned division lines. The method includes a second modified layer forming step of irradiating the wafer with a light beam to form a modified layer, and a dividing step of removing the light-transmitting film from the back surface of the wafer and applying an external force to the modified layer formed along the planned dividing line to divide the wafer into individual device chips, and the dividing step includes holding the front side of the wafer on a chuck table constituting a grinding device via the protective member, removing the light-transmitting film from the back surface of the wafer, grinding the back surface of the wafer to thin it, and dividing the wafer into individual device chips. Therefore, even when the modified layer is formed on both the front side and the back side, the internal stress is suppressed by the light-transmitting film disposed on the back surface, and the occurrence of unintended cracks from the modified layer formed on the back surface can be reduced, and the deterioration of the quality of the device chips generated by the dividing step is prevented. Furthermore, even if the wafer is unintendedly cracked, the wafer is sandwiched between the protective tape and the light-transmitting film, so that the wafer can be easily carried out after the modified layer is formed.

FIG. 11 is a perspective view showing an embodiment of a protective member disposing step. 1A to 1C are perspective views showing first to third examples of the light-transmitting film disposing step. 1 is an overall perspective view of a laser processing apparatus suitable for this embodiment; FIG. 11 is a perspective view showing an embodiment of a chuck table holding step. 4A and 4B are a perspective view and a partially enlarged cross-sectional view showing an embodiment of a first modified layer forming step. 1A and 1B are a perspective view and a partially enlarged cross-sectional view showing an embodiment of a second modified layer forming step. FIG. 13 is a perspective view showing a mode of carrying a wafer into a grinding device that performs a dividing step. FIG. 13 is a perspective view showing an embodiment of a dividing step. FIG. 13 is a perspective view showing an embodiment of a frame support step.

Below, an embodiment of a wafer processing method according to the present invention will be described in detail with reference to the attached drawings.

When carrying out the wafer processing method of this embodiment, as shown in FIG. 1, a wafer 10 is prepared in which a plurality of devices 12 are partitioned by planned division lines 14 and formed on a surface 10a. The wafer 10 is, for example, a silicon wafer, and the thickness of the wafer 10 before processing is 710 μm, with a target finishing thickness of 50 μm. Furthermore, the devices 12 to be individually divided are set to have dimensions of 1 mm x 1 mm in a plan view. Note that in FIG. 1, for convenience of explanation, the dimensions of the devices 12 are drawn larger than they actually are, and do not correspond to the actual dimensional ratio.

Once the wafer 10 described above is prepared, a protective member disposition process is carried out in which a protective tape T1 is disposed as a protective member on the front surface 10a of the wafer 10, as shown in FIG. 1. More specifically, the protective tape T1 can be, for example, an EVA (ethylene-vinyl acetate copolymer) film with an adhesive layer disposed on its surface, which is attached to the front surface 10a of the wafer 10 to form an integrated unit, as shown in FIG. 1. Once the wafer 10 and the protective tape T1 are integrated, they are flipped over in preparation for the next process, with the back surface 10b of the wafer 10 facing upward. The protective tape T1 is not limited to the EVA film described above, and may be, for example, a PET (polyethylene terephthalate) film.

As described above, once the protective member disposing step has been performed, a light-transmitting film disposing step is performed in which a light-transmitting film is disposed on the back surface 10b of the wafer 10. The light-transmitting film in this embodiment is made of a material that includes transparent and semi-transparent materials and is transparent to the laser beam LB irradiated in the first and second modified layer forming steps described below. With reference to FIG. 2, an embodiment of the light-transmitting film disposing step will be described in more detail.

2(1) shows an embodiment of a first example of the light-transmitting film disposition process. In the first example, for example, a polyolefin film T2 is prepared as the light-transmitting film. The polyolefin film T2 is formed to the same dimensions as the wafer 10 and placed on the back surface 10b of the wafer 10. No adhesive layer is formed on the surface of the polyolefin film T2, and the film is not adhered as it is. Therefore, a thermocompression roller 100 shown by a two-dot chain line on the lower side of FIG. 2(1) is prepared. The thermocompression roller 100 is provided with a heating means for heating the surface of the thermocompression roller 100 to a predetermined temperature inside, and the surface is coated with a fluororesin. The heating means is operated, and the thermocompression roller 100 is pressed from above the polyolefin film T2, rotated in the direction indicated by the arrow R1, and moved in the direction indicated by the arrow R2. The predetermined temperature is preferably set to 120°C to 140°C when a polyethylene sheet is selected as the polyolefin film T2, 160°C to 180°C when a polypropylene sheet is selected, and 220°C to 240°C when a polystyrene sheet is selected. Each of the above temperatures is close to the melting temperature of each sheet, and by setting such a temperature, the polyolefin film T2 exerts its adhesive force without excessive melting, and the polyolefin film T2 is well thermocompressed to the back surface 10b of the wafer 10 as the light-transmitting film TA.

2(2) shows an embodiment of a second example of the light-transmitting film disposing process. In the second example, in order to dispose a light-transmitting film on the back surface 10b of the wafer 10, the wafer 10 is transported to a spin coater (not shown), and the back surface 10b of the wafer 10 is placed on the chuck table of the spin coater with the back surface 10b facing upward and held by suction. Next, as shown in the figure, the nozzle 112 of the water-soluble liquid resin supply means 110 is positioned above the center of the wafer 10, and a predetermined amount of molten water-soluble liquid resin L, for example polyvinyl alcohol (PVA), is dropped from the nozzle 112 while rotating the wafer 10 in the direction indicated by the arrow R3. The dropped water-soluble liquid resin L spreads evenly on the back surface 10b of the wafer 10 by centrifugal force, solidifies after a predetermined time has passed, and a PVA film T3 is disposed as the light-transmitting film TA. The water-soluble liquid resin L is not limited to PVA, but can be selected from other water-soluble liquid resins such as polyvinylpyrrolidone (PVP).

Furthermore, FIG. 2 (3) shows an embodiment of a third example of the light-transmitting film disposing process. In this third example, an EVA film T4 made of adhesive tape, for example, having an adhesive layer on its surface, is used as the light-transmitting film. First, as shown in FIG. 2 (3), the EVA film T4 is placed on the back surface 10b of the wafer 10. Next, as shown on the lower side of the figure, a pressure-applying roller 120 shown by a two-dot chain line is positioned on the EVA film T4 and pressed from above, and while rotating in the direction shown by the arrow R4, it moves in the direction shown by the arrow R5 to attach the EVA film T4 as the light-transmitting film TA to the back surface 10b of the wafer 10 to form an integrated unit. Note that the adhesive tape is not limited to the above-mentioned EVA, and may be PET, as in the case of the above-mentioned protective tape T1.

As described above, once the light-transmitting film disposing step has been carried out and the light-transmitting film TA (either polyolefin film T2, PVA film T3, or EVA film T4) has been disposed on the back surface 10b of the wafer 10, the wafer 10 is transported to the laser processing device 1 shown in FIG. 3. The outline of the laser processing device 1 will be described below with reference to the figure.

Figure 3 shows an overall perspective view of the laser processing device 1 according to this embodiment. The laser processing device 1 includes a base 2, a frame 3, a laser beam application means 4, an imaging means 5, a holding means 20 for holding a wafer 10 as a workpiece, a moving means 30 for moving the holding means 20, and a control means (not shown).

The holding means 20 includes a rectangular X-axis direction movable plate 21 mounted on the base 2 so as to be movable in the X-axis direction indicated by the arrow X in the figure, a rectangular Y-axis direction movable plate 23 mounted on the X-axis direction movable plate 21 so as to be movable in the Y-axis direction indicated by the arrow Y in the figure, a cylindrical support 24 fixed to the upper surface of the Y-axis direction movable plate 23, and a rectangular cover plate 25 fixed to the upper end of the support 24. A disk-shaped chuck table 27 extending upward through a long hole 26 is disposed on the cover plate 25, and the chuck table 27 is configured to be rotatable by a rotation drive means (not shown). The holding surface 28, which is defined by the X-axis coordinate and the Y-axis coordinate constituting the upper surface of the chuck table 27, is made of a porous material and has air permeability, and is connected to a suction means (not shown) by a flow path passing through the inside of the support 24.

The moving means 30 is disposed on the base 2 and includes an X-axis feed means 31 for feeding the holding means 20 in the X-axis direction for processing, and a Y-axis feed means 32 for indexing and feeding the Y-axis movable plate 23 in the Y-axis direction. The X-axis feed means 31 converts the rotational motion of the pulse motor 33 into linear motion via a ball screw 34 and transmits it to the X-axis movable plate 21, and moves the X-axis movable plate 21 forward and backward in the X-axis direction along the guide rails 2a, 2a on the base 2. The Y-axis feed means 32 converts the rotational motion of the pulse motor 35 into linear motion via a ball screw 36 and transmits it to the Y-axis movable plate 23, and moves the Y-axis movable plate 23 forward and backward in the Y-axis direction along the guide rails 22, 22 on the X-axis movable plate 21. Although not shown, the X-axis feed means 31, the Y-axis feed means 32, and the chuck table 27 are provided with position detection means, which accurately detect the X-axis coordinate, the Y-axis coordinate, and the circumferential rotational position of the chuck table 27, and the position information is sent to a control means (not shown). The control means issues an instruction signal based on the position information to drive the X-axis feed means 31, the Y-axis feed means 32, and the rotation drive means of the chuck table 27 (not shown), so that the chuck table 27 can be positioned at the desired position on the base 2.

The frame 3 is erected on the base 2 to the side of the moving means 30. The frame 3 has a vertical wall 3a disposed on the base 2, and a horizontal wall 3b extending horizontally from the upper end of the vertical wall 3a. Inside the horizontal wall 3b of the frame 3, an optical system (not shown) of the laser beam application means 4 is housed, and a condenser 4a constituting part of the optical system is disposed on the underside of the tip of the horizontal wall 3b.

The imaging means 5 is disposed on the underside of the tip of the horizontal wall portion 3b, at a position spaced apart from the collector 4a of the laser beam application means 4 in the X-axis direction. The imaging means 5 includes an infrared irradiation means for irradiating the workpiece with infrared rays, an optical system for capturing the infrared rays irradiated by the infrared irradiation means, an imaging element (infrared CCD) for outputting an electrical signal corresponding to the infrared rays captured by the optical system, and the like. The image captured by the imaging means 5 is sent to the control means and is displayed appropriately on a display means (not shown).

The control means 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, etc., and a readable/writable random access memory (RAM) that stores the calculation results, etc. The control means is electrically connected to the laser beam application means 4, the imaging means 5, the moving means 30, etc., and controls the operation of each means.

The wafer 10 that has been subjected to the above-mentioned light-transmitting film disposing process is transported to the chuck table 27 of the above-mentioned laser processing device 1, and placed on the holding surface 28 of the chuck table 27 with the light-transmitting film TA (either polyolefin film T2, PVA film T3, or EVA film T4) side facing upward and the protective tape T1 side facing downward, as shown in FIG. 4. Next, a suction means (not shown) is operated to supply negative pressure onto the holding surface 28 via the chuck table 27, thereby suction-holding the wafer 10 (chuck table holding process). Note that the light-transmitting film TA shown in FIG. 4 and subsequent figures will be described as a film obtained by thermocompression bonding the polyolefin film T2.

After the chuck table holding process is performed, the first modified layer forming process is performed to form the modified layer 150, which will be described below. More specifically, the moving means 30 is first operated to position the chuck table 27 directly under the imaging means 5, and infrared light is irradiated from the light-transmitting film TA side, i.e., the back surface 10b side of the wafer 10, to take an image, and the planned dividing line 14, which is the laser processing position of the wafer 10, is detected, and the position information is stored in the control means.

Next, the wafer 10 is moved together with the chuck table 27 directly below the condenser 4a of the laser beam application means 4 to align the division line 14 formed in a predetermined direction in the X-axis direction. Once the laser processing start position on the predetermined division line 14 is positioned directly below the condenser 4a, the position of the condenser 4a is adjusted by the condenser 4a as shown in FIG. 5, and the condenser P of the laser beam LB is positioned on the surface 10a side inside the wafer 10 through the light-transmitting film TA. Next, the laser beam application means 4 is operated to irradiate the laser beam LB, and the X-axis direction feed means 31 of the moving means 30 described based on FIG. 3 is operated to move the chuck table 27 in the X-axis direction to form a modified layer 150 along the division line 14. In this embodiment, the modified layer 150 is formed in two layers at different depth positions as shown on the right side of FIG. 5. First, the focal point P is positioned near the surface 10a of the wafer 10 along a predetermined dividing line 14 and irradiated to form the lower layer side of the modified layer 150. Then, the position of the focal point P is slightly raised and the second laser beam LB is irradiated along the same dividing line 14 to form the upper layer side of the modified layer 150 along the dividing line 14 of the wafer 10.

Once the modified layer 150 has been formed along a given dividing line 14, the Y-axis direction feed means 32 is operated to index and feed the chuck table 27 in the Y-axis direction, and the unprocessed dividing line 14 adjacent to the dividing line 14 on which the modified layer 150 has already been formed is positioned directly under the condenser 4a. Next, in the same manner as described above, the X-axis direction feed means 31 is operated while irradiating the laser beam LB to form two modified layers 150 inside the wafer 10 along the dividing line 14. This laser processing is repeated to form modified layers 150 along all dividing lines 14 along a given direction. Next, the chuck table 27 is rotated 90 degrees, and the unprocessed dividing line 14 perpendicular to the dividing line 14 on which the modified layer 150 has been formed is aligned with the X-axis direction, and modified layers 150 are formed on the front surface 10a side of the wafer 10 along all dividing lines 14 by the same procedure as described above. This completes the first modified layer formation process.

After the first modified layer formation step is performed as described above, the focal point P of the laser beam LB is positioned on the back surface 10b side inside the wafer 10 through the light-transmitting film TA and irradiated along the planned division line 14 to form the modified layer 160 described below, as shown in FIG. 6. More specifically, the moving means 30 is operated to align the planned division line 14 in a predetermined direction, which previously formed the first modified layer 150, with the X-axis direction. Next, the laser processing start position of the planned division line 14 is positioned directly below the condenser 4a, and the condenser 4a is adjusted as shown in FIG. 6 to position the focal point P of the laser beam LB on the back surface 10b side inside the wafer 10 along the planned division line 14 through the light-transmitting film TA. Next, the laser beam application means 4 is operated to apply the laser beam LB, and the X-axis direction feed means 31 of the moving means 30 described based on FIG. 3 is operated to move the chuck table 27 in the X-axis direction to form a modified layer 160 along the planned division line 14. The modified layer 160 formed in this embodiment is also formed in two layers with different depth positions, similar to the modified layer 150 described above. First, the focal point P is positioned on the back surface 10b side of the wafer 10 along a predetermined planned division line 14, and the first layer of laser beam LB is applied, and then the focal point position P is slightly raised and positioned closer to the back surface 10b, and the second layer of laser beam LB is applied along the same planned division line 14 to form two layers of modified layer 160 on the back surface 10b side inside along the planned division line 14 of the wafer 10.

Once the modified layer 160 has been formed along the dividing lines 14 in a predetermined direction, the Y-axis feed means 32 is operated to index and feed the chuck table 27 in the Y-axis direction to position the dividing line 14 adjacent to the dividing line 14 on which the modified layer 160 has already been formed and on which the modified layer 160 has not yet been formed directly under the condenser 4a. Next, in the same manner as described above, the X-axis feed means 31 is operated while irradiating the laser beam LB to form two modified layers 160 inside the wafer 10 along the dividing line 14. This type of laser processing is repeated to form modified layers 160 along all dividing lines 14 along the X-axis direction. Next, the chuck table 27 is rotated 90 degrees, and the unprocessed division lines 14 perpendicular to the division lines 14 on which the modified layers 160 were previously formed are aligned with the X-axis direction, and the modified layers 160 are formed on the back surface 10b of the wafer 10 along all of the division lines 14 in the same manner as described above, completing the second modified layer formation process. Note that, for the sake of convenience, the modified layers 150 and 160 are shown in broken lines in Figures 5 and 6, but the modified layers 150 and 160 are formed inside the wafer 10 and cannot actually be seen.

The laser processing conditions when carrying out the first modified layer forming step and the second modified layer forming step of this embodiment are set, for example, as shown below.
Wavelength: 1342 nm
Repetition frequency: 90kHz
Average output power: 1.2-1.5W
Feed speed in the X-axis direction: 70 mm/sec

After the first modified layer forming process and the second modified layer forming process are performed as described above, the light-transmitting film TA is removed from the back surface 10b of the wafer 10, and an external force is applied to the modified layers 150, 160 formed on the intended dividing lines 14 to divide the wafer 10 into individual device chips 12' as described below. The dividing process will be described below with reference to Figures 7 and 8.

The wafer 10 that has been subjected to the first and second modified layer formation processes is transported to the grinding device 80 (only a portion of which is shown) shown in FIG. 7.

The grinding device 80 includes a chuck table 82 shown in FIG. 7 and a grinding means 84 shown in FIG. 8. The chuck table 82 includes a porous, breathable suction chuck 82a that suctions the wafer 10. The suction chuck 82a is connected to a suction means (not shown), and a negative suction pressure is supplied to the upper surface of the suction chuck 82a by the action of the suction means. The chuck table 82 includes a rotating means (not shown) and a moving means (not shown), and is configured to be rotatable by the action of the rotating means. The chuck table 82 is moved by the action of the moving means between a loading/unloading area where the wafer 10 is loaded and unloaded onto the chuck table 82 and a grinding area where the wafer 10 is ground by the grinding means 84. The grinding means 84 shown in FIG. 8 includes a rotating spindle 842 rotated by an electric motor (not shown), a wheel mount 844 disposed at the lower end of the rotating spindle 842, a grinding wheel 846 attached to the underside of the wheel mount 844, and a plurality of grinding stones 848 arranged in a ring shape on the underside of the grinding wheel 846.

As shown in FIG. 7, the wafer 10 transported to the grinding device 80 is placed on the suction chuck 82a of the chuck table 82 with the protective tape T1 side (front surface 10a side) facing downward, and is held by suction by supplying negative suction pressure to the suction chuck 82a by the action of a suction means (not shown). In conjunction with this, the translucent film TA is heated or cooled to reduce its adhesive force, and the translucent film TA is removed from the back surface 10b of the wafer 10. If the translucent film TA is a PVA film T3 formed by solidifying a water-soluble liquid resin L, cleaning water can be supplied from above the chuck table 22 to melt and remove the PVA film T3. If the translucent film TA is, for example, an EVA film T4 similar to the protective tape T1, it can be peeled off by reducing its adhesive force by irradiating it with ultraviolet light, etc.

Next, the chuck table 32 is moved by the moving means to a position directly below the grinding means 84 shown in FIG. 8, that is, to the grinding processing area, and the center O of the wafer 10 held on the chuck table 82 is positioned at a position where the grinding stone 848 arranged in a ring shape on the lower surface of the grinding wheel 846 passes when viewed from above. When the wafer 10 is positioned in the grinding processing area in this manner, the chuck table 82 is rotated in the direction shown by the arrow R6 in FIG. 8 at, for example, 300 rpm, and at the same time, the grinding wheel 846 of the grinding means 84 is rotated in the direction shown by the arrow R7 in FIG. 8 at, for example, 6000 rpm. Then, the grinding feed means (not shown) is operated to lower the grinding means 84 in the direction shown by the arrow R8, so that it comes into contact with the back surface 10b of the wafer 10 on the chuck table 82 from above, and is ground at a grinding feed speed of, for example, 1.0 μm/sec. At this time, the thickness of the wafer 10 is measured using a measuring gauge (not shown) while the grinding process is continued until the desired thickness (e.g., 50 μm) is reached.

As described above, by performing a grinding process to grind off a predetermined amount of the back surface 10b of the wafer 10, an external force is applied to the modified layers 150, 160 formed on the intended dividing line 14. As a result, as shown in FIG. 8, the wafer 10 is divided along the modified layers 150, 160 formed inside the wafer 10, and the wafer 10 is divided into individual device chips 12'. This completes the dividing process.

After the above-mentioned division step is performed, a frame holding step shown in FIG. 9 may be performed as necessary. More specifically, first, as shown in FIG. 9, a ring-shaped frame F having an opening Fa large enough to accommodate the wafer 10 is prepared. Next, the wafer 10 divided into individual device chips 12' by performing the above-mentioned division step is positioned in the center of the opening Fa of the frame F with the back surface 10b side facing downward, and a dicing tape T5 is attached to the back surface 10b of the wafer 10 and the frame F. As a result, the wafer 10 is held and integrated by the frame F via the dicing tape T5. The dicing tape T5 can be a tape similar to the protective tape T1 described above. As a result, the device chips 12' individually divided from the wafer 10 can be easily transported to the next step, for example, a pick-up step can be performed. It is preferable that the protective tape T1 attached to the front surface 10a side of the wafer 10 is peeled off at the same time as performing this frame arrangement step.

According to this embodiment, as described above, the protective tape T1 is disposed as a protective member on the front surface 10a side of the wafer 10, and the light-transmitting film TA (for example, any one of the polyolefin film T2, PVA film T3, and EVA film T4) is disposed on the back surface 10b side, and the first modified layer forming process and the second modified layer forming process are performed. As a result, even when the modified layers 150 and 160 are formed inside the wafer 10, the light-transmitting film TA disposed on the back surface 10b side prevents the internal stress caused by the modified layer 150 formed on the front surface 10a side from reaching the back surface 10b side, and the occurrence of unintended cracks from the modified layer 160 formed on the back surface 10b side can be reduced, and the deterioration of the quality of the device chip 12' generated by the division process is prevented. Furthermore, even if the wafer 10 is unintendedly cracked, the wafer 10 is sandwiched between the protective tape T1 and the light-transmitting film TA, which has the effect of making it easy to carry out from the laser processing device 1.

In the above embodiment, when dividing the wafer 10 into individual device chips 12' along the modified layers 150, 160 formed on the division line 14 in the division process, an external force is applied using a grinding device 80, but the present invention is not limited to this. For example, the wafer 10 before the division process can be supported by an annular frame F as shown in FIG. 9 via an elastic tape, and the tape can be expanded to apply an external force to the modified layers 150, 160, thereby dividing the wafer 10 into individual device chips 12'. In addition, the wafer 10 before the division process can be placed on a soft urethane mat or the like, and a roller can be pressed against the entire wafer 10 from the back surface 10b side of the wafer 10 to apply an external force, and the wafer 10 can be divided into individual device chips 12' along the modified layers 150, 160.

In addition, in the above embodiment, the modified layer 150 and the modified layer 160 formed by carrying out the first and second modified layer formation processes each have two layers, but the present invention is not limited to this, and they can also be configured with one layer or three or more layers.

1: Laser processing device 2: Base 3: Frame 3a: Vertical wall 3b: Horizontal wall 4: Laser beam irradiation means 4a: Condenser 5: Imaging means 10: Wafer 10a: Front surface 10b: Back surface 12: Device 12': Device chip 14: Planned division line 20: Holding means 27: Chuck table 28: Holding surface 30: Moving means 31: X-axis direction feed means 32: Y-axis direction feed means 80: Grinding device 82: Chuck table 82a: Suction chuck 84: Grinding means 846: Grinding wheel 848: Grinding stone 100: Thermocompression roller 110: Water-soluble resin supply means 112: Nozzle 120: Compression roller TA: Light-transmitting film T1: Protective tape T2: Polyolefin film T3: PVA film T4: EVA film L: Water-soluble liquid resin LB: Laser beam

Claims (3)

A wafer processing method for dividing a wafer having a surface on which a plurality of devices are formed by dividing lines into individual device chips, comprising the steps of:
a protective member providing step of providing a protective member on a front surface of the wafer;
a light-transmitting film providing step of providing a light-transmitting film on the back surface of the wafer;
a chuck table holding step of holding the protective member side of the wafer on a chuck table;
a first modified layer forming step of irradiating a laser beam having a wavelength that is transparent to the wafer with a focal point located on the front side of the wafer through the light-transmitting film along the intended dividing lines to form a modified layer;
a second modified layer forming step of forming a modified layer by irradiating a laser beam along a planned dividing line through the light-transmitting film at a focal point on the back side of the wafer inside the wafer after the first modified layer forming step;
a dividing step of removing the light-transmitting film from the back surface of the wafer and dividing the wafer into individual device chips by applying an external force to the modified layer formed along the dividing lines;
The present invention includes :
The dividing step is a wafer processing method in which the front side of the wafer is held via the protective member on a chuck table constituting a grinding device, the light-transmitting film is removed from the back side of the wafer, the back side of the wafer is ground to thin it, and the wafer is divided into individual device chips . The wafer processing method according to claim 1, wherein the light-transmitting film disposing step is any one of the steps of disposing the light-transmitting film by thermocompression bonding a polyolefin film to the back surface of the wafer, disposing the light-transmitting film by applying a water-soluble liquid resin to the back surface of the wafer and solidifying it, and disposing the light-transmitting film by adhering an adhesive tape to the back surface of the wafer. 3. The wafer processing method according to claim 1 or 2, further comprising the steps of: after carrying out the dividing step, positioning the wafer in a frame having openings for accommodating the wafer divided into individual device chips; attaching a dicing tape to the back surface of the wafer and the frame; and mounting the wafer in the frame via the dicing tape .