Method of processing a wafer

Abstract

A wafer processing method is provided for forming device chips without reducing quality. The wafer processing method divides a wafer in which a plurality of devices are formed in each region of a front surface divided by a division predetermined line into individual device chips, and has: a polyolefin sheet arrangement step of positioning the wafer in an opening of a frame having an opening that receives the wafer, and arranging a polyolefin sheet on the back surface or the front surface of the wafer and on the outer periphery of the frame; an integration step of heating the polyolefin sheet, and integrally joining the wafer and the frame by the polyolefin sheet by heat pressure bonding; a division step of irradiating the wafer with a laser beam of a wavelength that is transmissive to the wafer along the division predetermined line, forming a modified layer in the wafer, and dividing the wafer into individual device chips; and a pickup step of lifting the device chips by blowing air, and picking up the device chips from the polyolefin sheet.

Description

TECHNICAL FIELD

[0001] The present application relates to a wafer processing method for dividing a wafer in which a plurality of devices are formed in each region on a front surface divided by a division predetermined line into individual device chips. BACKGROUND

[0002] In a manufacturing process of a device chip for an electronic device such as a mobile phone or a personal computer, a plurality of division predetermined lines (streets) intersecting each other are set on a front surface of a wafer composed of a material such as a semiconductor. And, a device such as an IC (Integrated Circuit), an LSI (Large-Scale Integration circuit), an LED (Light Emitting Diode) is formed in each region divided by the division predetermined lines.

[0003] Then, an adhesive tape called a dicing tape which is pasted on a frame having a ring shape in a manner of closing an opening of the frame is pasted on the back surface or the front surface of the wafer, and a frame unit in which the wafer, the adhesive tape, and the frame having a ring shape are integrated is formed. And, when the wafer included in the frame unit is processed along the division predetermined lines to be divided, individual device chips are formed.

[0004] A laser processing device is used in the division of the wafer, for example. The laser processing device has a chuck table which holds the wafer through the adhesive tape, and a laser processing unit which converges a laser beam having a wavelength which is permeable to the wafer to the inside of the wafer, and the like.

[0005] In the division of the wafer, the frame unit is placed on the chuck table, and the wafer is held on the chuck table through the adhesive tape. Then, while the chuck table and the laser processing unit are relatively moved in a direction parallel to the upper surface of the chuck table, the laser beam is irradiated to the wafer from the laser processing unit along each division predetermined line. When the laser beam is converged to the inside of the wafer, a modified layer which is a division starting point is formed (refer to Patent Literature 1).

[0006] Then, the frame unit is carried out from the laser processing device, and when the adhesive tape is expanded to the radial outside, the wafer is divided to form individual device chips. In picking up the formed device chips from the adhesive tape, a process of irradiating ultraviolet rays or the like to the adhesive tape is performed in advance to reduce the adhesive force of the adhesive tape. As a processing device in which the production efficiency of the device chips is high, a processing device which can continuously perform the division of the wafer and the ultraviolet irradiation to the adhesive tape by one device is known (refer to Patent Literature 2).

[0007] Patent Literature 1: Japanese Patent No. 3408805

[0008] Patent Document 2: Japanese Patent No. 3076179

[0009] The adhesive tape, for example, comprises a substrate layer formed from a vinyl chloride sheet and a paste layer disposed on the substrate layer. In a laser processing apparatus, in order to form a modified layer as a cleaving starting point inside the wafer, a laser beam is focused into the interior of the wafer; however, a portion of the laser beam leaks into the paste layer of the adhesive tape. Furthermore, due to the heat effect from the laser beam irradiation, the paste layer of the adhesive tape melts, and a portion of the paste layer adheres to the back or front side of the device chip formed from the wafer.

[0010] In this situation, even if the adhesive tape is treated with ultraviolet light or similar methods to pick up the device chip from the adhesive tape, a portion of the paste layer will remain on the back or front side of the picked-up device chip. Therefore, a decrease in the quality of the device chip becomes a problem. Summary of the Invention

[0011] The present invention was made in view of this problem and its object is to provide a wafer processing method that does not attach a paste layer to the back or front side of the formed device chip, and does not cause a quality reduction on the device chip due to the adhesion of the paste layer.

[0012] According to one aspect of the present invention, a wafer processing method is provided, which divides a wafer having multiple devices formed in each region of the front side divided by a predetermined dividing line into individual device chips. The wafer processing method is characterized by comprising the following steps: a polyolefin sheet placement step, in which the wafer is positioned within the opening of a frame having an opening for receiving the wafer, and a polyolefin sheet is placed on the back side or the front side of the wafer and on the outer periphery of the frame; an integration step, in which the polyolefin sheet is heated and the wafer and the frame are integrated by thermoforming using the polyolefin sheet; a slitting step, in which a focusing point of a laser beam of a wavelength transparent to the wafer is positioned inside the wafer, the laser beam is irradiated onto the wafer along the predetermined dividing line, a modified layer is formed in the wafer, and the wafer is divided into individual device chips; and a pick-up step, in which the device chips are picked up one by one from the polyolefin sheet by blowing air from the polyolefin sheet side.

[0013] Preferably, the hot pressing is performed by infrared irradiation in this integrated process.

[0014] In addition, preferably, in this integrated process, after integration is performed, the polyolefin sheets protruding from the periphery of the frame are removed.

[0015] In addition, it is preferable that the polyolefin sheet is expanded during the picking process to increase the spacing between the device chips.

[0016] Further, it is preferable that the polyolefin sheet be any of a polyethylene sheet, a polypropylene sheet, and a polystyrene sheet.

[0017] Further, it is preferable that, in the integrating step, the heating temperature be 120°C to 140°C when the polyolefin sheet is the polyethylene sheet, 160°C to 180°C when the polyolefin sheet is the polypropylene sheet, and 220°C to 240°C when the polyolefin sheet is the polystyrene sheet.

[0018] Further, it is preferable that the wafer be composed of any of Si, GaN, GaAs, and glass.

[0019] In the wafer processing method of one embodiment of the present application, when the frame unit is formed, an adhesive tape having a paste layer is not used, but a polyolefin sheet having no paste layer is used to integrate the frame and the wafer. The integrating step in which the frame and the wafer are integrated by the polyolefin sheet is achieved by heat pressure bonding.

[0020] After the integrating step is performed, the wafer is irradiated with a laser beam having a wavelength that is transmissive through the wafer, a modified layer along the division predetermined line is formed in the wafer, and the wafer is divided. Then, the device chips are individually lifted up by blowing air from the polyolefin sheet side, and the device chips are picked up from the polyolefin sheet. The picked-up device chips are individually mounted on prescribed mounting targets. In this case, when the device chips are lifted up by air at the time of picking up, the load applied to the device chips at the time of peeling from the polyolefin sheet can be reduced.

[0021] When the modified layer is formed in the wafer, the leakage of the laser beam reaches the polyolefin sheet. However, the polyolefin sheet has no paste layer, so the paste layer does not melt and adhere to the back surface or the front surface side of the device chips.

[0022] That is, according to one embodiment of the present application, the polyolefin sheet having no paste layer can be used to form the frame unit, so an adhesive tape having a paste layer is not needed, and as a result, the quality of the device chips is not reduced due to the attachment of the paste layer.

[0023] Thus, according to one embodiment of the present application, the wafer processing method is provided, in which the paste layer is not attached to the back surface or the front surface side of the formed device chips, and the quality of the device chips is not reduced due to the attachment of the paste layer. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 (A) of FIG. 1 is a perspective view schematically showing the front surface of a wafer, Figure 1 (B) of FIG. 1 is a perspective view schematically showing the back surface of the wafer.

[0025] Figure 2 This is a perspective view schematically showing the positioning of the wafer and frame on the holding surface of the chuck stage.

[0026] Figure 3 This is a three-dimensional diagram schematically illustrating the assembly process of polyolefin sheets.

[0027] Figure 4 This is a perspective view schematically illustrating an example of an integrated process.

[0028] Figure 5 This is a perspective view schematically illustrating another example of an integrated process.

[0029] Figure 6 This is a perspective view that schematically illustrates another example of an integrated process.

[0030] Figure 7 (A) is a schematic perspective view showing the cutting of a polyolefin sheet. Figure 7 (B) is a schematic three-dimensional view showing the formed frame unit.

[0031] Figure 8 (A) is a schematic perspective view showing the cutting process. Figure 8 (B) is a schematic cross-sectional view showing the splitting process.

[0032] Figure 9 It is a schematic perspective view showing the frame unit being moved into the pickup device.

[0033] Figure 10 (A) is a schematic cross-sectional view showing a frame unit fixed to a frame support platform. Figure 10 (B) is a schematic cross-sectional view showing the picking process.

[0034] Label Explanation

[0035] 1: Wafer; 1a: Front side; 1b: Back side; 3: Pre-cut line; 3a: Modified layer; 5: Device; 7: Frame; 7a: Opening; 9: Polyolefin sheet; 9a: Cutting mark; 11: Frame unit; 2: Chuck table; 2a: Holding surface; 2b, 36a: Suction source; 2c, 36b: Switching unit; 4: Hot air gun; 4a: Hot air; 6: Heating roller; 8: Infrared lamp; 8a: Infrared; 10: Cutter; 12: Laser processing device; 14: Laser processing unit; 14a: Processing head; 14b: Focusing point; 16: Laser beam; 18: Pick-up device; 20: Drum; 22: Frame holding unit; 24: Fixture; 26: Frame support platform; 28: Rod; 30: Cylinder; 32: Base; 34: Lifting mechanism; 34a: Air; 36: Collet. Detailed Implementation

[0036] An embodiment of one mode of the present application will be described with reference to the drawings. First, a wafer processed by a wafer processing method using the present embodiment will be described. Figure 1 (A) of FIG. 1 is a perspective view schematically showing a front surface of a wafer 1, Figure 1 (B) of FIG. 1 is a perspective view schematically showing a back surface of the wafer 1.

[0037] The wafer 1 is, for example, a substantially circular plate-like substrate or the like made of a material such as Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaAs (gallium arsenide), or another semiconductor, or a material such as sapphire, glass, quartz, or the like. The glass is, for example, alkali glass, non-alkali glass, soda-lime glass, lead glass, borosilicate glass, quartz glass, or the like.

[0038] The front surface la of the wafer 1 is divided by a plurality of division- scheduled lines 3 arranged in a lattice shape. Further, a device 5 such as an IC, LSI, LED, or the like is formed in each region of the front surface la of the wafer 1 divided by the division-scheduled lines 3. In the wafer processing method of the wafer 1 of the present embodiment, a modified layer along the division-scheduled lines 3 is formed in the inside of the wafer 1, and the wafer 1 is divided from the modified layer as a starting point, thereby forming each device chip.

[0039] When the modified layer is formed in the wafer 1, a laser beam having a wavelength that is transmissive to the wafer 1 is irradiated to the wafer 1 along the division-scheduled lines 3, and the laser beam is converged to the inside of the wafer 1. At this time, the laser beam can be irradiated to the wafer 1 from the front surface la side as shown in (A) of FIG. 1, or can be irradiated to the wafer 1 from the back surface lb side as shown in (B) of FIG. 1. Figure 1 The laser beam can be irradiated to the wafer 1 from the front surface la side as shown in (A) of FIG. 1, or can be irradiated to the wafer 1 from the back surface lb side as shown in (B) of FIG. 1. Figure 1 Further, in a case where the laser beam is irradiated to the wafer 1 from the back surface lb side, an alignment unit having an infrared camera is used, the division-scheduled lines 3 on the front surface la side are detected through the wafer 1, and the laser beam is irradiated along the division-scheduled lines 3.

[0040] Before the wafer 1 is carried into a laser processing apparatus 12 (refer to Figure 8 ) that performs laser processing of forming the modified layer in the wafer 1, the wafer 1, the polyolefin sheet, and the frame are integrated to form a frame unit. The wafer 1 is carried into the laser processing apparatus 12 in the state of the frame unit and is processed.

[0041] Further, when the polyolefin sheet is expanded, the wafer 1 is divided, and each device chip formed by dividing the wafer 1 is supported to the polyolefin sheet. Then, the polyolefin sheet is further expanded, thereby expanding the interval between the device chips, and the device chips are picked up by a pickup device.

[0042] The frame 7 is a frame having a circular shape (refer to Figure 2(e.g., made of materials such as metal), the frame 7 has an opening 7a with a diameter larger than that of the wafer 1. When forming the frame unit, the wafer 1 is positioned within the opening 7a of the frame 7 and housed within the opening 7a.

[0043] Polyolefin series 9 (reference) Figure 3 The polyolefin sheet 9 (etc.) is a flexible resin-based sheet with a flat front and back. Furthermore, the polyolefin sheet 9 has a diameter larger than the outer diameter of the frame 7 and does not have a paste layer. The polyolefin sheet 9 is a sheet of a polymer synthesized using olefins as monomers, such as polyethylene sheets, polypropylene sheets, or polystyrene sheets, which are transparent or translucent to visible light. However, the polyolefin sheet 9 is not limited to these and can also be opaque.

[0044] The polyolefin sheet 9 lacks adhesive properties and therefore cannot be bonded to the wafer 1 and frame 7 at room temperature. However, the polyolefin sheet 9 is thermoplastic, so when heated to a temperature near its melting point while being bonded to the wafer 1 and frame 7 under a specified pressure, the polyolefin sheet 9 partially melts and can be bonded to the wafer 1 and frame 7. Therefore, in the wafer 1 processing method of this embodiment, the wafer 1, frame 7, and polyolefin sheet 9 are integrated by thermoforming as described above to form a frame unit.

[0045] Next, each step of the wafer 1 processing method of this embodiment will be described. First, a polyolefin sheet arrangement step is performed in order to prepare for the integration of wafer 1, polyolefin sheet 9 and frame 7. Figure 2 This is a perspective view schematically showing the wafer 1 and frame 7 positioned on the holding surface 2a of the chuck stage 2. (See diagram below.) Figure 2 As shown, a polyolefin sheet assembly process is performed on a chuck worktable 2 with a holding surface 2a on the upper part.

[0046] The chuck table 2 has a porous component at its upper center with a diameter larger than the outer diameter of the frame 7. The upper surface of this porous component serves as the holding surface 2a of the chuck table 2. The chuck table 2 is as follows... Figure 3 The device shown has an exhaust passage with one end connected to the porous component, and an attraction source 2b is provided at the other end of the exhaust passage. A switching part 2c is provided on the exhaust passage to switch between a connected state and a disconnected state. When the switching part 2c is in the connected state, a negative pressure generated by the attraction source 2b is applied to the object to be held on the holding surface 2a, thereby attracting and holding the object to be held on the chuck table 2.

[0047] In the polyolefin sheet preparation process, the first step is as follows: Figure 2 As shown, a wafer 1 and a frame 7 are placed on the holding surface 2a of the chuck stage 2, and the wafer 1 is positioned within the opening 7a of the frame 7.

[0048] At this time, the orientation of the wafer 1 is selected in consideration of which one of the front surface la and the back surface lb of the irradiated surface of the laser beam to be irradiated in the division process to be described later. For example, in the case where the irradiated surface is the front surface la, the front surface la side is oriented downward. Also, for example, in the case where the irradiated surface is the back surface lb, the back surface lb side is oriented downward. Hereinafter, the processing method of the wafer of the present embodiment will be described taking the case where the irradiated surface of the laser beam is the front surface la as an example, but the orientation of the wafer 1 is not limited thereto.

[0049] After the wafer 1 and the frame 7 are placed on the holding surface 2a of the chuck table 2, the polyolefin sheet 9 is disposed on the back surface lb (or the front surface la) of the wafer 1 and on the outer periphery of the frame 7. Figure 3 is a perspective view schematically showing the polyolefin sheet disposing process. As shown in Figure 3 , the polyolefin sheet 9 is disposed on the wafer 1 and the frame 7 in a manner to cover them.

[0050] Also, in the polyolefin sheet disposing process, the polyolefin sheet 9 having a larger diameter than the holding surface 2a of the chuck table 2 is used. This is because, when the negative pressure of the chuck table 2 is applied to the polyolefin sheet 9 in the integration process to be performed later, if the entire holding surface 2a is not covered with the polyolefin sheet 9, the negative pressure will leak from the gap, and the pressure cannot be properly applied to the polyolefin sheet 9.

[0051] In the processing method of the wafer 1 of the present embodiment, next, the integration process is performed to heat the polyolefin sheet 9 and integrally bond the wafer 1 and the frame 7 with the polyolefin sheet 9 by heat pressure bonding. Figure 4 is a perspective view schematically showing an example of the integration process. In Figure 4 , components that can be seen through the polyolefin sheet 9 that is transparent or translucent to visible light are indicated by broken lines.

[0052] In the integration process, first, the switching portion 2c of the chuck table 2 is operated to become a communication state in which the suction source 2b is connected to the porous member of the upper portion of the chuck table 2, and the negative pressure of the suction source 2b is applied to the polyolefin sheet 9. Then, the polyolefin sheet 9 is made to adhere to the wafer 1 and the frame 7 by atmospheric pressure.

[0053] Next, heat pressure bonding is performed while the polyolefin sheet 9 is being sucked by the suction source 2b and heated. The heating of the polyolefin sheet 9 is performed, for example, by the hot air gun 4 disposed above the chuck table 2 as shown in Figure 4

[0054] ​The hot air gun 4 has a heating unit such as an electric heating wire and a blower mechanism such as a fan inside, and can inject air heated. The hot air 4a is supplied to the polyolefin sheet 9 from the upper surface by the hot air gun 4 while applying a negative pressure to the polyolefin sheet 9, and when the polyolefin sheet 9 is heated to a predetermined temperature, the polyolefin sheet 9 is thermocompression-bonded to the wafer 1 and the frame 7.

[0055] Further, the heating of the polyolefin sheet 9 can be performed by other methods, for example, by pressing the wafer 1 and the frame 7 from above using a member heated to a predetermined temperature. Figure 5 is a perspective view schematically showing another example of the integration process. In Figure 5 , a member that can be seen through the polyolefin sheet 9 that is transparent or translucent to visible light is indicated by a broken line.

[0056] In Figure 5 , a heating roller 6 having a heat source inside is used, for example. In Figure 5 , the polyolefin sheet 9 is first pressed against the wafer 1 and the frame 7 by a negative pressure of the suction source 2b, and then the polyolefin sheet 9 is pressed against the wafer 1 and the frame 7 by atmospheric pressure.

[0057] Then, the heating roller 6 is heated to a predetermined temperature and placed on one end of the holding surface 2a of the chuck table 2. Then, the heating roller 6 is rotated and rolled on the chuck table 2 from the one end to the other end. Thus, the polyolefin sheet 9 is thermocompression-bonded to the wafer 1 and the frame 7. At this time, when a force is applied to the polyolefin sheet 9 in a direction to press it down by the heating roller 6, the thermocompression-bonding is performed by a pressure greater than atmospheric pressure. Further, the surface of the heating roller 6 is preferably coated with a fluororesin.

[0058] Further, instead of the heating roller 6, a pressing member in the shape of an iron having a flat bottom plate with a heat source inside can be used to perform the thermocompression-bonding of the polyolefin sheet 9. In this case, the pressing member is heated to a predetermined temperature to become a hot plate, and the polyolefin sheet 9 held by the chuck table 2 is pressed from above by the pressing member.

[0059] The heating of the polyolefin sheet 9 can also be performed by other methods. Figure 6 is a perspective view schematically showing still another example of the integration process. In Figure 6 , a member that can be seen through the polyolefin sheet 9 that is transparent or translucent to visible light is indicated by a broken line. In Figure 6 , an infrared lamp 8 disposed above the chuck table 2 is used to heat the polyolefin sheet 9. The infrared lamp 8 can at least radiate infrared rays 8a of a wavelength that is absorbable by the material of the polyolefin sheet 9.

[0060] InFigure 6 In the integration process shown, first, the negative pressure of the suction source 2b is applied to the polyolefin sheet 9, and the polyolefin sheet 9 is made to adhere to the wafer 1 and the frame 7. Next, the infrared lamp 8 is made to operate, and the polyolefin sheet 9 is irradiated with infrared rays 8a, and the polyolefin sheet 9 is heated. As a result, the polyolefin sheet 9 is thermocompression-bonded to the wafer 1 and the frame 7.

[0061] When the polyolefin sheet 9 is heated to a temperature near the melting point thereof by any method, the polyolefin sheet 9 is thermocompression-bonded to the wafer 1 and the frame 7. After the polyolefin sheet 9 is thermocompression-bonded, the switching section 2c is made to operate, and the communication state of the porous member of the chuck table 2 with the suction source 2b is released, and the chuck table 2 is released from suction.

[0062] Next, the polyolefin sheet 9 that protrudes from the outer periphery of the frame 7 is cut off and removed. Figure 7 (A) of FIG. 10 is a perspective view that schematically shows the case where the polyolefin sheet 9 is cut off. Regarding the cutting, as shown in (A) of FIG. 10, a circular ring-shaped cutter 10 is used. The cutter 10 has a through-hole, and is rotatable about a rotation axis that passes through the through-hole. Figure 7

[0063] First, the circular ring-shaped cutter 10 is positioned above the frame 7. At this time, the rotation axis of the cutter 10 is aligned with the radial direction of the chuck table 2. Next, the cutter 10 is lowered, and the polyolefin sheet 9 is cut off by sandwiching the polyolefin sheet 9 with the frame 7 and the cutter 10. As a result, a cut mark 9a is formed on the polyolefin sheet 9.

[0064] In addition, the cutter 10 is made to revolve around the opening 7a of the frame 7 along the frame 7, and a prescribed region of the polyolefin sheet 9 is surrounded by the cut mark 9a. Then, the polyolefin sheet 9 of the region on the outer periphery side of the cut mark 9a is removed in such a way that the prescribed region of the polyolefin sheet 9 remains. As a result, the unnecessary part of the polyolefin sheet 9 including the region that protrudes from the outer periphery of the frame 7 can be removed.

[0065] In addition, an ultrasonic cutter can be used in the cutting of the polyolefin sheet, and a vibration source that vibrates the above-described circular ring-shaped cutter 10 at a frequency in the ultrasonic frequency band can be connected to the cutter 10. In addition, in order to make the cutting easy, the polyolefin sheet 9 can be cooled and hardened when the polyolefin sheet 9 is cut. As described above, the frame unit 11 in which the wafer 1 and the frame 7 are integrated by the polyolefin sheet 9 is formed. Figure 7 (B) of FIG. 10 is a perspective view that schematically shows the frame unit 11 that is formed.

[0066] ​In addition, when the heat press bonding is performed, the polyolefin sheet 9 is preferably heated to a temperature below the melting point thereof. This is because, when the heating temperature exceeds the melting point, the polyolefin sheet 9 sometimes melts and the shape of the sheet cannot be maintained. In addition, the polyolefin sheet 9 is preferably heated to a temperature above the softening point thereof. This is because, if the heating temperature does not reach the softening point, the heat press bonding cannot be properly performed. That is, the polyolefin sheet 9 is preferably heated to a temperature above the softening point thereof and below the melting point thereof.

[0067] In addition, there are cases where a part of the polyolefin sheet 9 does not have a clear softening point. Therefore, when the heat press bonding is performed, the polyolefin sheet 9 is preferably heated to a temperature above 20°C below the melting point thereof and below the melting point thereof.

[0068] In addition, in the case where the polyolefin sheet 9 is a polyethylene sheet, the heating temperature is preferably 120°C to 140°C. In addition, in the case where the polyolefin sheet 9 is a polypropylene sheet, the heating temperature is preferably 160°C to 180°C. In addition, in the case where the polyolefin sheet 9 is a polystyrene sheet, the heating temperature is preferably 220°C to 240°C.

[0069] Here, the heating temperature refers to the temperature of the polyolefin sheet 9 when the integration process is performed. For example, among heat sources such as the hot air gun 4, the heating roller 6, and the infrared lamp 8, there are models in which the output temperature can be set, but even if the polyolefin sheet 9 is heated using such a heat source, the temperature of the polyolefin sheet 9 sometimes does not reach the set output temperature. Therefore, in order to heat the polyolefin sheet 9 to a predetermined temperature, the output temperature of the heat source can be set to be higher than the melting point of the polyolefin sheet 9.

[0070] Next, in the wafer processing method of the present embodiment, a dividing process is performed to laser process the wafer 1 in a state of the frame unit 11 to form a modified layer along the division intended line 3 in the inside of the wafer 1 and divide the wafer 1. The dividing process is performed, for example, using the laser processing apparatus shown in (A) of FIG. 10. Figure 8 (A) of FIG. 10 is a perspective view schematically showing the dividing process, Figure 8 (A) of FIG. 10 is a perspective view schematically showing the dividing process, Figure 8 (B) of FIG. 10 is a cross-sectional view schematically showing the dividing process.

[0071] The laser processing apparatus 12 has a laser processing unit 14 that irradiates the wafer 1 with a laser beam 16, and a chuck table (not shown) that holds the wafer 1. The laser processing unit 14 has a laser oscillator (not shown) that can oscillate a laser, and can emit the laser beam 16 having a wavelength that is transparent to the wafer 1 (a wavelength that can pass through the wafer 1). The chuck table can move (processing feed) in a direction parallel to the upper surface.

[0072] The laser processing unit 14 irradiates the laser beam 16 emitted from the laser oscillator to the wafer 1 held on the chuck table. The processing head 14a of the laser processing unit 14 has a function of positioning the focal point 14b of the laser beam 16 at a prescribed height position inside the wafer 1.

[0073] When the wafer 1 is subjected to laser processing, the frame unit 11 is placed on the chuck table, and the wafer 1 is held on the chuck table through the polyolefin sheet 9. Next, the chuck table is rotated so that the division predetermined line 3 of the wafer 1 is aligned with the processing feed direction of the laser processing device 12. In addition, the relative positions of the chuck table and the laser processing unit 14 are adjusted in such a manner that the processing head 14a is disposed above the extension line of the division predetermined line 3. Further, the focal point 14b of the laser beam 16 is positioned at a prescribed height position.

[0074] Next, the chuck table and the laser processing unit 14 are relatively moved along the processing feed direction parallel to the upper surface of the chuck table while the laser beam 16 is irradiated from the laser processing unit 14 to the inside of the wafer 1. That is, the focal point 14b of the laser beam 16 is positioned inside the wafer 1, and the laser beam 16 is irradiated to the wafer 1 along the division predetermined line 3. Thus, the modified layer 3a is formed inside the wafer 1. In addition, in the case where the wafer 1 is held on the chuck table through the polyolefin sheet 9, the modified layer 3a is formed inside the wafer 1 through the polyolefin sheet 9. Figure 8 In (A) of FIG. 19, the modified layer 3a formed inside the wafer 1 is shown by a broken line.

[0075] The irradiation conditions of the laser beam 16 in the division process are set as follows, for example. However, the irradiation conditions of the laser beam 16 are not limited to this.

[0076] Wavelength: 1064 nm

[0077] Repetition frequency: 50 kHz

[0078] Average output: 1 W

[0079] Feed rate: 200 mm / sec

[0080] After the modified layer 3a is formed inside the wafer 1 along one division predetermined line 3, the chuck table and the laser processing unit 14 are relatively moved in the indexing feed direction perpendicular to the processing feed direction, and the wafer 1 is subjected to laser processing along other division predetermined lines 3 as well. After the modified layer 3a is formed along all the division predetermined lines 3 in one direction, the chuck table is rotated about the axis perpendicular to the holding surface, and the wafer 1 is subjected to laser processing along the division predetermined lines 3 in the other direction as well.

[0081] When the laser beam 16 is converged by the laser processing unit 14 to form the modified layer 3a inside the wafer 1, the light leakage of the laser beam 16 reaches the polyolefin sheet 9 below the wafer 1.

[0082] For example, if an adhesive tape is used instead of a polyolefin sheet 9 in the frame unit 11, when the leaked light from the laser beam 16 irradiates the paste layer of the adhesive tape, the paste layer melts, and a portion of the paste layer adheres to the back side 1b of the wafer 1. In this case, this portion of the paste layer remains on the back side of the device chip formed by dividing the wafer 1. Therefore, a reduction in the quality of the device chip becomes a problem.

[0083] In contrast, in the wafer fabrication method of this embodiment, a polyolefin sheet 9 without a paste layer is used in the frame unit 11. Therefore, even if light leakage from the laser beam 16 reaches the polyolefin sheet 9, the paste layer will not adhere to the back side 1b of the wafer 1. As a result, the quality of the device chip formed from the wafer 1 remains good.

[0084] Next, the wafer 1 is diced to form device chips by extending the polyolefin substrate 9 radially outward. Then, a pick-up process is performed to pick up each device chip from the polyolefin substrate 9. In the extension of the polyolefin substrate 9, [the following process is used]. Figure 9 The pickup device 18 is shown at the bottom. Figure 9 This is a perspective view schematically showing the transfer of the frame unit 11 into the pickup device 18.

[0085] The pickup device 18 includes: a cylindrical drum 20 having a diameter larger than that of the wafer 1; and a frame holding unit 22 including a frame support 26. The frame support 26 of the frame holding unit 22 has an opening with a diameter larger than that of the drum 20, and is positioned at the same height as the upper end of the drum 20, surrounding the upper end of the drum 20 from the outer periphery.

[0086] A clamp 24 is provided on the outer periphery of the frame support platform 26. When the frame unit 11 is placed on the frame support platform 26 and the frame 7 of the frame unit 11 is held by the clamp 24, the frame unit 11 is fixed to the frame support platform 26.

[0087] The frame support platform 26 is supported by a plurality of rods 28 extending vertically, and each rod 28 is equipped with a cylinder 30 at its lower end to raise or lower it. The plurality of cylinders 30 are supported on a circular plate-shaped base 32. When the cylinders 30 are actuated, the frame support platform 26 is lowered relative to the drum 20.

[0088] Inside the drum 20 is a lifting mechanism 34 that lifts the device chip supported by the polyolefin sheet 9 from below. The lifting mechanism 34 has the function of blowing air 34a upwards. In addition, a collet 36 (see reference) is provided above the drum 20 to attract and hold the device chip. Figure 10The jacking mechanism 34 and the collet 36 are movable in the horizontal direction along the upper surface of the frame support table 26. In addition, the collet 36 is connected to the suction source 36a (refer to Figure 10 (B)) via the switching section 36b (refer to Figure 10 (B)).

[0089] When the polyolefin sheet 9 is expanded, first, the height of the upper end of the drum 20 of the pickup device 18 is made to coincide with the height of the upper surface of the frame support table 26 by causing the cylinder 30 to act to adjust the height of the frame support table 26. Next, the frame unit 11 carried out from the laser processing device 12 is placed on the drum 20 of the pickup device 18 and the frame support table 26.

[0090] Then, the frame 7 of the frame unit 11 is fixed to the frame support table 26 by the jig 24. Figure 10 (A) is a cross-sectional view schematically showing the frame unit 11 fixed to the frame support table 26. The modification layer 3a is formed inside the wafer 1 along the division predetermined line 3.

[0091] Next, the frame support table 26 of the frame holding unit 22 is lowered with respect to the drum 20 by causing the cylinder 30 to act. Then, as shown in Figure 10 (B), the polyolefin sheet 9 is expanded to the radial outside. Figure 10 (B) is a cross-sectional view schematically showing the expanded polyolefin sheet 9.

[0092] When the polyolefin sheet 9 is expanded, a force toward the radial outside is applied to the wafer 1, and the wafer 1 is divided from the modification layer 3a, and each device chip 1c is formed. When the polyolefin sheet 9 is further expanded, the interval between each device chip 1c supported by the polyolefin sheet 9 is expanded, and the pickup of each device chip 1c becomes easy.

[0093] In the wafer processing method of the present embodiment, after the wafer 1 is divided to form each device chip 1c, a pickup process is performed to pick up the device chip 1c from the polyolefin sheet 9. In the pickup process, the device chip 1c that is the pickup target is determined, the jacking mechanism 34 is moved to below the device chip 1c, and the collet 36 is moved to above the device chip 1c.

[0094] Then, the jacking mechanism 34 is caused to act to blow air 34a from the polyolefin sheet 9 side to jack up the device chip 1c. Then, the switching section 36b is caused to act to make the collet 36 communicate with the suction source 36a. Then, the device chip 1c is suction-held by the collet 36, and the device chip 1c is picked up from the polyolefin sheet 9. The picked-up each device chip 1c is used after being mounted on a prescribed wiring substrate or the like.

[0095] In addition, when the device chip 1c is lifted by blowing air 34a from the polyolefin sheet 9 side against the device chip 1c at the time of pickup of the device chip 1c, the load applied to the device chip 1c at the time of peeling the device chip 1c from the polyolefin sheet 9 can be reduced.

[0096] For example, in the case of using an adhesive tape to form the frame unit 11, in the dividing process, the light leakage of the laser beam 16 irradiated to the wafer 1 reaches the adhesive tape, and the paste layer of the adhesive tape is fixed to the back surface side of the device chip. Also, the reduction in the quality of the device chip due to the attachment of the paste layer becomes a problem.

[0097] On the contrary, according to the wafer processing method of the present embodiment, the frame unit 11 using the polyolefin sheet 9 not having a paste layer can be formed by heat pressure bonding, and therefore, an adhesive tape having a paste layer is not required. As a result, the reduction in the quality of the device chip due to the attachment of the paste layer to the back surface side does not occur.

[0098] In addition, the present application is not limited to the description of the above-described embodiments, and various modifications and implementations can be made. For example, in the above-described embodiments, the case where the polyolefin sheet 9 is, for example, a polyethylene sheet, a polypropylene sheet, or a polystyrene sheet is described, but one embodiment of the present application is not limited thereto. For example, the polyolefin sheet can use other materials, and can be a copolymer of propylene and ethylene, an olefin-based elastomer, or the like.

[0099] In addition to the above, the configuration, method, and the like of the above-described embodiments can be appropriately changed and implemented as long as the scope of the object of the present application is not deviated.

Claims

1. A wafer processing method of dividing a wafer in which a plurality of devices are formed in each region of a front surface divided by a division predetermined line into individual device chips, characterized by comprising: the wafer processing method comprising: a polyolefin sheet arrangement step of positioning the wafer in an opening of a frame having an opening that receives the wafer, arranging a polyolefin sheet that does not have a paste layer on the back surface of the wafer or the front surface and the outer periphery of the frame in a manner that covers the entire wafer and frame, and covering the entire holding surface of a chuck table on which the wafer and frame are placed with the polyolefin sheet; an integration step of heating the polyolefin sheet and integrally joining the wafer and the frame by thermal compression via the polyolefin sheet; a division step of positioning a focal point of a laser beam having a wavelength that is transmissive through the wafer inside the wafer, irradiating the wafer with the laser beam along the division predetermined line, forming a modified layer in the wafer, and dividing the wafer into individual device chips; and a pickup step of picking up the device chips one by one from the polyolefin sheet by blowing air from the polyolefin sheet side to lift the device chips one by one.

2. The wafer processing method according to claim 1, characterized in that: in the integration step, the thermal compression is performed by irradiation of infrared rays.

3. The wafer processing method according to claim 1, characterized in that: in the integration step, the polyolefin sheet that protrudes from the outer periphery of the frame is removed after integration is performed.

4. The wafer processing method according to claim 1, characterized in that: in the pickup step, the polyolefin sheet is expanded to expand the intervals between the individual device chips.

5. The wafer processing method according to claim 1, characterized in that: the polyolefin sheet is any of a polyethylene sheet, a polypropylene sheet, and a polystyrene sheet.

6. The wafer processing method according to claim 5, characterized in that: in the integration step, the heating temperature is 120°C to 140°C when the polyolefin sheet is the polyethylene sheet, the heating temperature is 160°C to 180°C when the polyolefin sheet is the polypropylene sheet, and the heating temperature is 220°C to 240°C when the polyolefin sheet is the polystyrene sheet.

7. The wafer processing method according to claim 1, characterized in that: the wafer is composed of any of Si, GaN, GaAs, and glass.

Images