Method for processing a wafer

Abstract

Provided is a method for processing a wafer to form device chips without reducing the quality. The method for processing the wafer divides a wafer, in which a plurality of devices are formed in respective regions on the front surface divided by dicing lines, into individual device chips. The method for processing the wafer has the following steps: a polyolefin sheet disposing step of positioning the wafer in the opening of a frame having an opening for accommodating the wafer, and disposing a polyolefin sheet on the back surface or the front surface of the wafer and on the outer periphery of the frame; an integrating step of heating the polyolefin sheet and integrally bonding the wafer and the frame with each other through thermocompression bonding by means of the polyolefin sheet; a dicing step of irradiating a laser beam having a wavelength that is transmissive to the wafer along the dicing lines to form a modified layer in the wafer and dividing the wafer into individual device chips; and a picking step of heating the polyolefin sheet, lifting the device chips, and picking up the device chips from the polyolefin sheet.

Description

Technical Field

[0001] The present invention relates to a wafer processing method for dividing a wafer divided by predetermined dividing lines and having a plurality of devices formed in respective regions on the front side into individual device chips. Background Art

[0002] In the manufacturing process of device chips used in electronic devices such as mobile phones and personal computers, multiple intersecting dividing lines (streets) are first set on the front surface of a wafer made of materials such as semiconductors. Devices such as ICs (Integrated Circuits), LSIs (Large-Scale Integration Circuits), and LEDs (Light Emitting Diodes) are then formed in the regions defined by these dividing lines.

[0003] Next, an adhesive tape called a dicing tape, which is attached to an annular frame with an opening to seal the opening, is applied to the back or front side of the wafer, forming a frame unit that integrates the wafer, the adhesive tape, and the annular frame. The wafer contained in the frame unit is then processed and divided along the intended dividing lines to form individual device chips.

[0004] For example, a laser processing device is used to divide the wafer. The laser processing device includes a chuck table that holds the wafer via an adhesive tape, and a laser processing unit that focuses a laser beam of a wavelength that is transparent to the wafer onto the inside of the wafer.

[0005] When dividing a wafer, the frame unit is placed on the chuck table, holding the wafer on the chuck table with adhesive tape interposed therebetween. The chuck table and the laser processing unit are then moved relative to each other in a direction parallel to the upper surface of the chuck table, while the laser processing unit irradiates the wafer along each predetermined dividing line. When this laser beam is focused into the interior of the wafer, a modified layer is formed, which serves as the starting point for dividing (see Patent Document 1).

[0006] The frame unit is then removed from the laser processing apparatus, and as the adhesive tape is radially expanded outward, the wafer is divided into individual device chips. Before the formed device chips are removed from the adhesive tape, the adhesive tape is pre-treated by, for example, ultraviolet light exposure to reduce its adhesive strength. A known processing apparatus for device chip production, which can sequentially perform wafer division and ultraviolet light exposure on the adhesive tape, is known (see Patent Document 2).

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

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

[0009] The adhesive tape includes, for example, a base material layer formed of a vinyl chloride sheet or the like and a paste layer disposed on the base material layer. In a laser processing apparatus, in order to form a modified layer as a starting point for dicing inside a wafer, a laser beam is focused inside the wafer, but a part of the leaked light of the laser beam reaches the paste layer of the adhesive tape. Further, due to the influence of heat caused by the irradiation of the laser beam, the paste layer of the adhesive tape melts, and a part of the paste layer adheres to the back side or the front side of the device chip formed from the wafer.

[0010] In this case, when picking up the device chip from the adhesive tape, even if a process such as irradiating the adhesive tape with ultraviolet rays is performed, this part of the paste layer remains on the back side or the front side of the picked-up device chip. Therefore, a problem arises that the quality of the device chip deteriorates. Summary of the Invention

[0011] The present invention has been completed in view of this problem, and an object thereof is to provide a method for processing a wafer, which does not attach a paste layer to the back side or the front side of the formed device chip and does not cause a deterioration in quality due to the attachment of the paste layer on the device chip.

[0012] According to one aspect of the present invention, there is provided a method for processing a wafer, which divides a wafer having a plurality of devices formed in each region of the front surface divided by dicing lines into individual device chips, characterized in that the method for processing the wafer includes the following steps: a polyolefin sheet arranging step of positioning the wafer in the opening of a frame having an opening for accommodating 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 bonding the wafer and the frame through the polyolefin sheet by thermocompression bonding; a dicing step of positioning a focus point of a laser beam having a wavelength transmissive to the wafer inside the wafer, irradiating the laser beam along the dicing line to form a modified layer in the wafer, and dividing the wafer into individual device chips; and a picking-up step of heating the polyolefin sheet in each region corresponding to each device chip, pushing up the device chip from the polyolefin sheet side, and picking up the device chip from the polyolefin sheet.

[0013] Preferably, in the integration step, the thermocompression bonding is performed by irradiation with infrared rays.

[0014] Further, preferably, in the integration step, after the integration, the polyolefin sheet protruding from the outer periphery of the frame is removed.

[0015] Further, preferably, in this picking process, the polyolefin-based sheet is expanded to expand the interval between the device chips.

[0016] Further, preferably, the polyolefin-based sheet is any one of a polyethylene sheet, a polypropylene sheet, and a polystyrene sheet.

[0017] Further, preferably, in this integration process, when the polyolefin-based sheet is the polyethylene sheet, the heating temperature is 120°C to 140°C; when the polyolefin-based sheet is the polypropylene sheet, the heating temperature is 160°C to 180°C; and when the polyolefin-based sheet is the polystyrene sheet, the heating temperature is 220°C to 240°C.

[0018] Further, preferably, the wafer is made of any one of Si, GaN, GaAs, and glass.

[0019] In a method for processing a wafer according to one embodiment of the present invention, when forming a frame unit, instead of using an adhesive tape having a paste layer, a polyolefin-based sheet without a paste layer is used to integrate the frame and the wafer. The integration process of integrating the frame and the wafer by means of the polyolefin-based sheet is achieved by thermocompression bonding.

[0020] After the integration process is performed, a laser beam having a wavelength that is transmissive to the wafer is irradiated onto the wafer, and a modified layer is formed along a dicing predetermined line inside the wafer to dice the wafer. Then, each region of the polyolefin-based sheet corresponding to each device chip is heated, the device chip is lifted from the polyolefin-based sheet side, and the device chip is picked up from the polyolefin-based sheet. The picked-up device chips are respectively mounted on a prescribed mounting object. Among them, when the polyolefin-based sheet is heated during picking, the adhesive force of the polyolefin-based sheet is reduced, and the load applied to the device chip can be reduced.

[0021] When a modified layer is formed inside the wafer, the leakage light of the laser beam reaches the polyolefin-based sheet. However, since the polyolefin-based sheet does not have a paste layer, the situation where the paste layer melts and adheres to the back side or the front side of the device chip does not occur.

[0022] That is, according to one embodiment of the present invention, a polyolefin-based sheet without a paste layer can be used to form a frame unit, so an adhesive tape having a paste layer is not required. As a result, the quality degradation of the device chip caused by the adhesion of the paste layer does not occur.

[0023] Therefore, according to one embodiment of the present invention, there is provided a method for processing a wafer, in which a paste layer does not adhere to the back side or the front side of the formed device chip, and the quality degradation caused by the adhesion of the paste layer does not occur on the device chip. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 2 is a perspective view schematically showing the state where the wafer and the frame are positioned on the holding surface of the chuck table.

[0026] Figure 3 is a perspective view schematically showing the polyolefin sheet disposition process.

[0027] Figure 4 is a perspective view schematically showing an example of the integration process.

[0028] Figure 5 is a perspective view schematically showing another example of the integration process.

[0029] Figure 6 is a perspective view schematically showing still another example of the integration process.

[0030] Figure 7 (A) is a perspective view schematically showing the state where the polyolefin sheet is cut. Figure 7 (B) is a perspective view schematically showing the formed frame unit.

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

[0032] Figure 9 is a perspective view schematically showing the loading of the frame unit into the pick-up device.

[0033] Figure 10 (A) is a cross-sectional view schematically showing the frame unit fixed to the frame support table. Figure 10 (B) is a cross-sectional view schematically showing the pick-up process.

[0034] Reference Numeral Explanation

[0035] 1: Wafer; 1a: Front side; 1b: Back side; 3: Dicing predetermined 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 ray; 10: Cutter; 12: Laser processing device; 14: Laser processing unit; 14a: Processing head; 14b: Focus point; 16: Laser beam; 18: Pickup device; 20: Drum; 22: Frame holding unit; 24: Fixture; 26: Frame support table; 28: Rod; 30: Cylinder; 32: Base; 34: Lifting mechanism; 34a: Heating part; 36: Collet. Detailed implementation mode

[0036] With reference to the accompanying drawings, an implementation mode of one aspect of the present invention will be described. First, a wafer processed by the wafer processing method of this implementation mode will be described. Figure 1 (A) of FIG. is a perspective view schematically showing the front side of the wafer 1, Figure 1 and (B) of FIG. is a perspective view schematically showing the back side of the wafer 1.

[0037] The wafer 1 is, for example, a substantially circular plate-shaped substrate made of materials such as Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaAs (gallium arsenide) or other semiconductors, or materials such as sapphire, glass, quartz, etc. This glass is, for example, soda glass, alkali-free glass, soda-lime glass, lead glass, borosilicate glass, fused quartz, etc.

[0038] The front side 1a of the wafer 1 is divided by a plurality of dicing predetermined lines 3 arranged in a grid pattern. In addition, devices 5 such as ICs, LSIs, and LEDs are formed in each region of the front side 1a of the wafer 1 divided by the dicing predetermined lines 3. In the wafer processing method of the wafer 1 in this implementation mode, a modified layer is formed along the dicing predetermined line 3 inside the wafer 1, and the wafer 1 is divided starting from this modified layer to form individual device chips.

[0039] When forming the modified layer 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 dicing predetermined line 3, and the laser beam is focused inside the wafer 1. At this time, this laser beam can be irradiated to the wafer 1 from Figure 1 the front side 1a side shown in (A) of FIG., or can also be irradiated to the wafer 1 from Figure 1 the back side 1b side shown in (B) of FIG. In addition, when irradiating the laser beam to the wafer 1 from the back side 1b side, an alignment unit having an infrared camera is used to detect the dicing predetermined line 3 on the front side 1a side through the wafer 1, and the laser beam is irradiated along the dicing predetermined line 3.

[0040] Before the wafer 1 is transferred into the laser processing apparatus 12 (see Figure 8 ) that performs laser processing for forming a 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 transferred into the laser processing apparatus 12 in the state of the frame unit and processed.

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

[0042] The ring-shaped frame 7 (see Figure 2 etc.) is formed of a material such as metal, and the frame 7 has an opening 7a with a diameter larger than the diameter of the wafer 1. When forming the frame unit, the wafer 1 is positioned within the opening 7a of the frame 7 and received in the opening 7a.

[0043] The polyolefin sheet 9 (see Figure 3 etc.) is a resin sheet with flexibility, and the front and back surfaces are flat. Moreover, 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 an olefin as a monomer, and is, for example, a visible light-transparent or semi-transparent sheet such as a polyethylene sheet, a polypropylene sheet, or a polystyrene sheet. However, the polyolefin sheet 9 is not limited thereto and may also be opaque.

[0044] The polyolefin sheet 9 does not have adhesiveness, and thus cannot be pasted onto the wafer 1 and the frame 7 at room temperature. However, the polyolefin sheet 9 has thermoplasticity, and thus when heated to a temperature near the melting point in a state where the polyolefin sheet 9 is joined to the wafer 1 and the frame 7 while applying a prescribed pressure, the polyolefin sheet 9 locally melts and can be adhered to the wafer 1 and the frame 7. Therefore, in the processing method of the wafer 1 of the present embodiment, the wafer 1, the frame 7, and the polyolefin sheet 9 are integrated by the above-described thermocompression bonding to form a frame unit.

[0045] Next, each process of the processing method of the wafer 1 of the present embodiment will be described. First, a polyolefin sheet disposition process is performed to prepare for integrating the wafer 1, the polyolefin sheet 9, and the frame 7. Figure 2 is a perspective view schematically showing the state where the wafer 1 and the frame 7 are positioned on the holding surface 2a of the chuck table 2. As Figure 2 shown, the polyolefin sheet disposition process is performed on the chuck table 2 having the holding surface 2a at the upper part.

[0046] The chuck table 2 has a porous member at its upper center with a diameter larger than the outer diameter of the frame 7. The upper surface of this porous member serves as the holding surface 2a of the chuck table 2. The chuck table 2 has an exhaust passage inside as shown in Figure 3 which is connected to the porous member at one end, and a suction source 2b is provided on the other end side of this exhaust passage. A switching portion 2c for switching between a connected state and a cut-off state is provided in the exhaust passage. When the switching portion 2c is in the connected state, a negative pressure generated by the suction source 2b acts on the object to be held placed on the holding surface 2a, thereby attracting and holding the object to be held on the chuck table 2.

[0047] In the polyolefin sheet disposition process, first, as shown in Figure 2 the wafer 1 and the frame 7 are placed on the holding surface 2a of the chuck table 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 of the front surface 1a and the back surface 1b will be the irradiated surface when irradiated with a laser beam in the subsequent dicing process. For example, when the irradiated surface is the front surface 1a, the front surface 1a side is oriented downward. Additionally, for example, when the irradiated surface is the back surface 1b, the back surface 1b side is oriented downward. Hereinafter, the case where the irradiated surface of the laser beam is the front surface 1a will be taken as an example to describe the processing method of the wafer in the present embodiment, 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, a polyolefin sheet 9 is disposed on the back surface 1b (or the front surface 1a) of the wafer 1 and on the outer periphery of the frame 7. Figure 3 is a perspective view schematically showing the polyolefin sheet disposition process. As shown in Figure 3 the polyolefin sheet 9 is disposed on both of them so as to cover the wafer 1 and the frame 7.

[0050] In addition, in the polyolefin sheet disposition process, a polyolefin sheet 9 having a diameter larger than the holding surface 2a of the chuck table 2 is used. This is because when the negative pressure of the chuck table 2 acts on the polyolefin sheet 9 in the subsequent integration process, if the entire holding surface 2a is not covered by 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 in the present embodiment, then the integration process is carried out, the polyolefin sheet 9 is heated and the wafer 1 and the frame 7 are integrated with each other by thermocompression bonding through the polyolefin sheet 9. Figure 4 is a perspective view schematically showing an example of the integration process. In Figure 4 the components that can be visually recognized through the polyolefin sheet 9 that is transparent or semi-transparent to visible light are shown by dashed lines.

[0052] In the integrated process, first, the switching unit 2c of the chuck table 2 is actuated to establish a communication state in which the suction source 2b is connected to the porous member above the chuck table 2, and the negative pressure of the suction source 2b is applied to the polyolefin sheet 9. Then, due to the atmospheric pressure, the polyolefin sheet 9 is closely attached to the wafer 1 and the frame 7.

[0053] Next, while sucking the polyolefin sheet 9 by the suction source 2b, the polyolefin sheet 9 is heated to perform thermocompression bonding. The heating of the polyolefin sheet 9 is performed, for example, Figure 4 as shown, by a hot air gun 4 disposed above the chuck table 2.

[0054] The hot air gun 4 has a heating unit such as a heating wire and a blowing mechanism such as a fan inside, and can heat and eject air. While applying a negative pressure to the polyolefin sheet 9, hot air 4a is supplied to the polyolefin sheet 9 from the upper surface by the hot air gun 4. When the polyolefin sheet 9 is heated to a specified temperature, the polyolefin sheet 9 is thermocompression bonded to the wafer 1 and the frame 7.

[0055] In addition, the heating of the polyolefin sheet 9 can also be performed by other methods. For example, it can be performed by pressing the wafer 1 and the frame 7 from above with a member heated to a specified temperature. Figure 5 is a perspective view schematically showing another example of the integrated process. In Figure 5 , the components that can be visually recognized through the polyolefin sheet 9 that is transparent or translucent to visible light are shown by dashed lines.

[0056] In Figure 5 the integrated process shown, for example, a heating roller 6 having a heat source inside is used. In Figure 5 the integrated process shown, first, the negative pressure of the suction source 2b is also applied to the polyolefin sheet 9, and due to the atmospheric pressure, the polyolefin sheet 9 is closely attached to the wafer 1 and the frame 7.

[0057] Then, the heating roller 6 is heated to a specified temperature and placed on one end of the holding surface 2a of the chuck table 2. Then, the heating roller 6 is rotated so that the heating roller 6 rolls from this end to the other end on the chuck table 2. Thus, the polyolefin sheet 9 is thermocompression bonded to the wafer 1 and the frame 7. At this time, when a force is applied in the direction of pressing down the polyolefin sheet 9 by the heating roller 6, thermocompression bonding is performed using a pressure greater than the atmospheric pressure. In addition, it is preferable to coat the surface of the heating roller 6 with fluororesin.

[0058] Alternatively, an iron-shaped pressing member having a flat bottom plate and an internal heat source may be used instead of the heating roller 6 to perform 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 polyolefin-based sheet 9 can also be heated by other methods. Figure 6 This is a perspective view schematically showing another example of the integration process. Figure 6 In FIG, the parts that can be seen through the polyolefin sheet 9 that is transparent or translucent to visible light are indicated by dotted lines. Figure 6 In the integration step shown, the polyolefin sheet 9 is heated using an infrared lamp 8 disposed above the chuck table 2. The infrared lamp 8 can irradiate at least infrared rays 8a having a wavelength that the material of the polyolefin sheet 9 absorbs.

[0060] exist Figure 6 In the illustrated integration step, negative pressure from suction source 2b is first applied to polyolefin sheet 9, causing it to adhere tightly to wafer 1 and frame 7. Next, infrared lamp 8 is activated to irradiate polyolefin sheet 9 with infrared rays 8a, thereby heating polyolefin sheet 9. This results in thermocompression bonding of polyolefin sheet 9 to wafer 1 and frame 7.

[0061] When the polyolefin sheet 9 is heated to a temperature near its melting point by any method, it is thermocompressed and bonded to the wafer 1 and the frame 7. After the polyolefin sheet 9 is thermocompressed, the switching unit 2c is actuated to disconnect the porous member of the chuck table 2 from the suction source 2b, thereby releasing the suction of the chuck table 2.

[0062] Next, the polyolefin-based sheet 9 protruding from the outer periphery of the frame 7 is cut and removed. Figure 7 (A) is a perspective view schematically showing the state of cutting the polyolefin sheet 9. Figure 7 As shown in (A), a circular cutter 10 is used. The cutter 10 has a through hole and can rotate around a rotation axis passing through the through hole.

[0063] First, an annular cutter 10 is positioned above the frame 7. 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 sandwiched between the frame 7 and the cutter 10, thereby cutting the polyolefin sheet 9. This forms a cut mark 9a on the polyolefin sheet 9.

[0064] Further, the cutter 10 is moved along the frame 7 around the opening 7a of the frame 7 for one round, and a predetermined area of the polyolefin sheet 9 is surrounded by the cut mark 9a. Then, the polyolefin sheet 9 in the area on the outer peripheral side of the cut mark 9a is removed in such a manner that the area of the polyolefin sheet 9 remains. Thereby, unnecessary portions of the polyolefin sheet 9 including the area protruding from the outer periphery of the frame 7 can be removed.

[0065] In addition, an ultrasonic cutter can be used for cutting the polyolefin sheet, and a vibration source that vibrates the above-mentioned annular cutter 10 at a frequency in the ultrasonic frequency band can be connected to the cutter 10. In addition, when cutting the polyolefin sheet 9, in order to facilitate cutting, the polyolefin sheet 9 can be cooled to harden it. As described above, the frame unit 11 in which the wafer 1 and the frame 7 are integrated by means of the polyolefin sheet 9 is formed. Figure 7 Fig. (B) is a perspective view schematically showing the formed frame unit 11.

[0066] In addition, when performing thermocompression bonding, the polyolefin sheet 9 is preferably heated to a temperature below its melting point. This is because when the heating temperature exceeds the melting point, the polyolefin sheet 9 may melt and the shape of the sheet cannot be maintained. In addition, the polyolefin sheet 9 is preferably heated to a temperature above its softening point. This is because if the heating temperature does not reach the softening point, thermocompression bonding cannot be properly performed. That is, the polyolefin sheet 9 is preferably heated to a temperature above its softening point and below its melting point.

[0067] In addition, there is also a case where a part of the polyolefin sheet 9 does not have a clear softening point. Therefore, when performing thermocompression bonding, the polyolefin sheet 9 is preferably heated to a temperature above 20°C lower than its melting point and below its melting point.

[0068] In addition, when the polyolefin sheet 9 is a polyethylene sheet, the heating temperature is preferably 120°C to 140°C. In addition, when the polyolefin sheet 9 is a polypropylene sheet, the heating temperature is preferably 160°C to 180°C. In addition, when 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 during the integration process. For example, among heat sources such as the hot air gun 4, the heating roller 6, and the infrared lamp 8, a model capable of setting the output temperature is actually used. However, even when the polyolefin sheet 9 is heated using this 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 specified temperature, the output temperature of the heat source can be set higher than the melting point of the polyolefin sheet 9.

[0070] Next, in the method for processing a wafer according to the present embodiment, a dicing process is performed. The wafer 1 in the state of the frame unit 11 is laser processed to form a modified layer along the dicing line 3 inside the wafer 1, and the wafer 1 is diced. The dicing process is performed, for example, using Figure 8 the laser processing apparatus shown in (A) of Figure 8 . (A) of Figure 8 is a perspective view schematically showing the dicing process, and

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

[0072] The laser processing unit 14 irradiates the laser beam 16 emitted from the laser oscillator onto the wafer 1 held by 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 predetermined height position inside the wafer 1.

[0073] When laser processing the wafer 1, the frame unit 11 is placed on the chuck table, and the wafer 1 is held on the chuck table with the polyolefin-based sheet 9 interposed therebetween. Next, the chuck table is rotated so that the dicing line 3 of the wafer 1 is aligned with the processing feed direction of the laser processing apparatus 12. In addition, the relative positions of the chuck table and the laser processing unit 14 are adjusted so that the processing head 14a is disposed above the extension line of the dicing line 3. And the focal point 14b of the laser beam 16 is positioned at a predetermined height position.

[0074] Next, while irradiating the laser beam 16 into the wafer 1 from the laser processing unit 14, the chuck table and the laser processing unit 14 are relatively moved in the processing feed direction parallel to the upper surface of the chuck table. That is, the focal point 14b of the laser beam 16 is positioned inside the wafer 1, and the laser beam 16 is irradiated onto the wafer 1 along the dicing line 3. Then, a modified layer 3a is formed inside the wafer 1. In addition, in Figure 8 (A) of

[0075] the modified layer 3a formed inside the wafer 1 is shown by a dotted line.

[0076] Wavelength: 1064 nm

[0077] Repetition frequency: 50 kHz

[0078] Average output: 1 W

[0079] Feed rate: 200 mm / second

[0080] After a modified layer 3a is formed inside the wafer 1 along a 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 similarly laser processed along other division predetermined lines 3. After the modified layer 3a is formed along all the division predetermined lines 3 in one direction, the chuck table is rotated about an axis perpendicular to the holding surface, and the wafer 1 is similarly laser processed along the division predetermined lines 3 in the other direction.

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

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

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

[0084] Next, the wafer 1 is divided to form device chips by expanding the polyolefin sheet 9 radially outward. Then, a pick-up process is performed to pick up each of the device chips from the polyolefin sheet 9. In the expansion of the polyolefin sheet 9, the pick-up device 18 shown in the Figure 9 lower part is used. Figure 9 is a perspective view schematically showing the loading of the frame unit 11 into the pick-up device 18.

[0085] The pick-up device 18 includes: a cylindrical drum 20 having a diameter larger than the diameter of the wafer 1; and a frame holding unit 22 including a frame support table 26. The frame support table 26 of the frame holding unit 22 has an opening with a diameter larger than the diameter of the drum 20, is arranged at the same height as the upper end portion of the drum 20, and surrounds the upper end portion of the drum 20 from the outer peripheral side.

[0086] A jig 24 is disposed on the outer peripheral side of the frame support table 26. When the frame unit 11 is placed on the frame support table 26 and the frame 7 of the frame unit 11 is gripped by the jig 24, the frame unit 11 is fixed to the frame support table 26.

[0087] The frame support table 26 is supported by a plurality of rods 28 extending in the vertical direction, and cylinders 30 for raising and lowering the rods 28 are disposed at the lower ends of the respective rods 28. The plurality of cylinders 30 are supported by a disk-shaped base 32. When the respective cylinders 30 are actuated, the frame support table 26 is lowered relative to the drum 20.

[0088] A lifting mechanism 34 for lifting the device chip supported by the polyolefin-based sheet 9 from below is disposed inside the drum 20. The lifting mechanism 34 has a heating portion 34a at the upper end, and heat sources such as a Peltier element and a heating wire are built in the heating portion 34a. In addition, a collet 36 capable of attracting and holding the device chip is disposed above the drum 20 (see Figure 10 (B) of Figure 10 . The lifting mechanism 34 and the collet 36 can move in the horizontal direction along the upper surface of the frame support table 26. In addition, the collet 36 is connected to an attracting source 36a (see Figure 10 (B) of

[0089] via a switching portion 36b (see

[0090] (B) of Figure 10 (A) of is a cross-sectional view schematically showing the frame unit 11 fixed to the frame support table 26. A modified layer 3a is formed along the dicing line 3 inside the wafer 1.

[0091] Next, the cylinders 30 are actuated to lower the frame support table 26 of the frame holding unit 22 relative to the drum 20. Then, as shown in Figure 10 (B) of Figure 10 (B) of is a cross-sectional view schematically showing the expanded polyolefin-based sheet 9.

[0092] When the polyolefin-based sheet 9 expands, a force acting radially outward is applied to the wafer 1, and the wafer 1 is divided starting from the modified layer 3a to form individual device chips 1c. When the polyolefin-based sheet 9 is further expanded, the interval between the individual device chips 1c supported by the polyolefin-based sheet 9 is expanded, and it becomes easier to pick up each device chip 1c.

[0093] In the method for processing a wafer according to the present embodiment, after dividing the wafer 1 to form individual device chips 1c, a picking-up process is performed to pick up the device chips 1c from the polyolefin-based sheet 9. In the picking-up process, the device chip 1c to be picked up is determined, the jacking mechanism 34 is moved below the device chip 1c, and the collet 36 is moved above the device chip 1c.

[0094] Then, the heating unit 34a is operated to raise the temperature, and the heating unit 34a contacts the region of the polyolefin-based sheet 9 corresponding to the device chip 1c to heat the region. And the jacking mechanism 34 operates to jack up the device chip 1c from the side of the polyolefin-based sheet 9. Then, the switching unit 36b is operated to connect the collet 36 to the suction source 36a. Thus, the device chip 1c is attracted and held by the collet 36, and the device chip 1c is picked up from the polyolefin-based sheet 9. Each of the picked-up device chips 1c is then mounted on a predetermined wiring board or the like for use.

[0095] In addition, when heating this region of the polyolefin-based sheet 9 by the heating unit 34a, for example, this region is heated to a temperature near the melting point of the polyolefin-based sheet 9. Since the adhesive force decreases during the period when the polyolefin-based sheet 9 is at a temperature near the melting point, the load applied to the device chip when peeling from the polyolefin-based sheet 9 can be reduced.

[0096] For example, in the case of forming the frame unit 11 using an adhesive tape, 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 adheres to the back side of the device chip. And the reduction in the quality of the device chip due to the adhesion of the paste layer becomes a problem.

[0097] In contrast, according to the method for processing a wafer of the present embodiment, the frame unit 11 using the polyolefin-based sheet 9 without a paste layer can be formed by thermocompression bonding, so 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 paste layer adhering to the back side does not occur.

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

[0099] In addition to this, as long as the structures, methods, etc. of the above embodiments do not deviate from the scope of the object of the present invention, they can be appropriately modified and implemented.

Claims

1. A method for processing a wafer, which divides a wafer having a plurality of devices formed in respective regions on the front surface divided by dicing predetermined lines into individual device chips, characterized in that the method for processing the wafer has the following steps: A polyolefin sheet disposing step of positioning the wafer in the opening of a frame having an opening for accommodating the wafer, disposing a polyolefin sheet not including a paste layer on the back surface or the front surface of the wafer and on the outer periphery of the frame, and bringing the polyolefin sheet into direct contact with the back surface or the front surface of the wafer and the back surface of the frame; An integration step of heating the polyolefin sheet and integrally forming the wafer and the frame by thermocompression bonding through the polyolefin sheet to form a frame unit by integrating the wafer, the polyolefin sheet, and the frame; A dicing step of positioning the focal point of a laser beam having a wavelength transmissive to the wafer inside the wafer, irradiating the laser beam along the dicing predetermined line to form a modified layer in the wafer, and dividing the wafer into individual device chips; and A picking step of heating the polyolefin sheet in respective regions corresponding to the device chips, pushing up the device chips from the side of the polyolefin sheet, and picking up the device chips from the polyolefin sheet.

2. The method for processing a wafer according to claim 1, characterized in that in the integration step, the thermocompression bonding is performed by irradiation with infrared rays.

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

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

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

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

7. The method for processing a wafer according to claim 1, characterized in that the wafer is made of any one of Si, GaN, GaAs, and glass.

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