Method of processing a wafer

Abstract

Provided is a wafer processing method 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 includes: 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 a back surface or the front surface of the wafer and on an 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 a laser beam of a wavelength that is transmissive to the wafer along the division predetermined line to form a shield tunnel in the wafer, and dividing the wafer into individual device chips; and a pickup step of picking up the individual 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 a 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 irradiates a laser beam having a wavelength which is transparent to the wafer to the wafer in a state in which a focal point is positioned inside the wafer.

[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 an upper surface of the chuck table, the laser beam is continuously irradiated to the wafer from the laser processing unit along each division predetermined line.

[0006] When the laser beam is irradiated to the wafer, a filament-like region called a shield tunnel is continuously formed along the division predetermined line. The shield tunnel is composed of a fine hole along a thickness direction of the wafer and an amorphous region surrounding the fine hole, and serves as a starting point of the division of the wafer (see Patent Literature 1).

[0007] Then, the frame unit is carried out from the laser processing apparatus, and the wafer is divided to form individual device chips when the adhesive tape is expanded to the radial outside. When the formed device chips are picked up from the adhesive tape, a process of irradiating the adhesive tape with ultraviolet rays or the like is performed in advance to reduce the adhesive force of the adhesive tape. As a processing apparatus that is high in production efficiency of device chips, a processing apparatus capable of continuously performing the division of a wafer and the ultraviolet irradiation of an adhesive tape with one apparatus is known (see Patent Literature 2).

[0008] Patent Literature 1: Japanese Patent No. 6151557

[0009] Patent Literature 2: Japanese Patent No. 3076179

[0010] The adhesive tape contains, for example, a base material layer formed of a vinyl chloride sheet or the like and a paste layer provided on the base material layer. In the laser processing apparatus, a laser beam is irradiated to the inside of the wafer in order to form a shield tunnel as a division starting point in the wafer. At this time, a part of the light leakage of the laser beam reaches the paste layer of the adhesive tape. Also, due to the influence of heat caused by the irradiation of the laser beam, the paste layer of the adhesive tape is melted, and a part of the paste layer is adhered to the back surface side or the front surface side of the device chip formed from the wafer.

[0011] In this case, when the device chips are picked up from the adhesive tape, even if the process of irradiating the adhesive tape with ultraviolet rays or the like is performed, the part of the paste layer remains on the back surface side or the front surface side of the picked-up device chips. Therefore, a decrease in the quality of the device chips becomes a problem. SUMMARY

[0012] The present application was achieved in view of this problem, and an object thereof is to provide a wafer processing method that does not cause the paste layer to adhere to the back surface side or the front surface side of the formed device chips and does not cause a decrease in the quality of the device chips due to the adhesion of the paste layer.

[0013] According to one embodiment of the present application, a wafer processing method that 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 is characterized by comprising: a polyolefin sheet provision step of positioning the wafer in an opening of a frame having the opening to receive the wafer and providing 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 with the polyolefin sheet by thermal compression; 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, continuously forming shield tunnels in the wafer, and dividing the wafer into individual device chips; and a picking-up step of picking up the individual device chips from the polyolefin sheet.

[0014] Preferably, in the integration process, the thermocompression bonding is performed by irradiation of infrared rays.

[0015] Further, preferably, in the integration process, after the integration is performed, the polyolefin sheet that protrudes from the outer periphery of the frame is removed.

[0016] Further, preferably, in the pickup process, the polyolefin sheet is expanded to expand the intervals between the device chips, and the device chips are lifted from the polyolefin sheet side.

[0017] Further, preferably, the polyolefin sheet is any of a polyethylene sheet, a polypropylene sheet, and a polystyrene sheet.

[0018] Further, preferably, in the integration process, in the case where the polyolefin sheet is the polyethylene sheet, the heating temperature is 120°C to 140°C, in the case where the polyolefin sheet is the polypropylene sheet, the heating temperature is 160°C to 180°C, and in the case where the polyolefin sheet is the polystyrene sheet, the heating temperature is 220°C to 240°C.

[0019] Further, preferably, the wafer is composed of any of Si, GaN, GaAs, and glass.

[0020] 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 not having a paste layer is used to integrate the frame and the wafer. The integration process in which the frame and the wafer are integrated by the polyolefin sheet is performed by thermocompression bonding.

[0021] After the integration process is performed, a laser beam having a wavelength that is transmissive to the wafer is irradiated to the wafer, and a shield tunnel is continuously formed along the division predetermined line to divide the wafer. Then, the device chips are picked up from the polyolefin sheet. The picked-up device chips are respectively mounted on prescribed mounting targets.

[0022] When the shield tunnel is formed in the wafer, the light leakage of the laser beam reaches the polyolefin sheet. However, the polyolefin sheet does not have a paste layer, and thus the paste layer does not melt and adhere to the back surface or the front surface side of the device chips.

[0023] That is, according to one embodiment of the present application, the polyolefin sheet not having a paste layer can be used to form the frame unit, and thus 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.

[0024] According to one embodiment of the present application, a wafer processing method is provided which does not cause a paste layer to adhere to the back side or the front side of a device chip formed, and does not cause a quality reduction in the device chip due to the adhesion of the paste layer. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 (A) is a perspective view schematically showing the front side of a wafer, Figure 1 (B) is a perspective view schematically showing the back side of the wafer.

[0026] Figure 2 is a perspective view schematically showing a state in which the wafer and the frame are positioned on a holding surface of a chuck table.

[0027] Figure 3 is a perspective view schematically showing a polyolefin sheet providing step.

[0028] Figure 4 is a perspective view schematically showing an example of an integration step.

[0029] Figure 5 is a perspective view schematically showing another example of the integration step.

[0030] Figure 6 is a perspective view schematically showing still another example of the integration step.

[0031] Figure 7 (A) is a perspective view schematically showing a state in which the polyolefin sheet is cut, Figure 7 (B) is a perspective view schematically showing a frame unit formed.

[0032] Figure 8 (A) is a perspective view schematically showing a dividing step, Figure 8 (B) is a cross-sectional view schematically showing the dividing step, Figure 8 (C) is a perspective view schematically showing a shield tunnel.

[0033] Figure 9 is a perspective view schematically showing a state in which the frame unit is carried into a pickup device.

[0034] Figure 10 (A) is a cross-sectional view schematically showing a frame unit fixed to a frame support table, Figure 10 (B) is a cross-sectional view schematically showing a pickup step.

[0035] REFERENCE NUMERALS

[0036] 1: Wafer; 1a: Front side; 1b: Back side; 3: Pre-defined dividing line; 3a: Shield tunnel; 3b: Fine hole; 3c: Amorphous region; 5: Device; 7: Frame; 7a: Opening; 9: Polyolefin sheet; 9a: Cutting mark; 11: Frame unit; 2: Chuck worktable; 2a: Holding surface; 2b, 36a: Suction source; 2c, 36b: Switching part; 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; 36: Collet. Detailed Implementation

[0037] Referring to the accompanying drawings, one embodiment of the present invention will be described. First, a wafer processed using the wafer processing method of this embodiment will be described. Figure 1 (A) is a perspective view schematically showing the front of chip 1. Figure 1 (B) is a perspective view schematically showing the back side of chip 1.

[0038] The wafer 1 is, for example, a generally circular substrate made of materials such as Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaAs (gallium arsenide), or other semiconductor materials, or materials such as sapphire, glass, or quartz. The glass is, for example, alkali glass, alkali-free glass, soda-lime glass, lead glass, borosilicate glass, or quartz glass.

[0039] The front side 1a of wafer 1 is divided by multiple predetermined dividing lines 3 arranged in a grid pattern. Furthermore, devices 5 such as ICs, LSIs, and LEDs are formed in each region defined by the predetermined dividing lines 3 on the front side 1a of wafer 1. In the wafer 1 fabrication method of this embodiment, a shield tunnel is continuously formed in wafer 1 along the predetermined dividing lines 3, and wafer 1 is divided starting from this shield tunnel to form individual device chips.

[0040] When a shield tunnel is formed in wafer 1, a laser beam of wavelength that is transparent to wafer 1 is irradiated along the predetermined dividing line 3, and the laser beam is focused into the interior of wafer 1. At this time, the laser beam can... Figure 1 (A) shows the front side 1a side irradiated onto the wafer 1, or it can also be from... Figure 1 The back side 1b shown in (B) is irradiated onto the wafer 1. In addition, when the laser beam is irradiated onto the wafer 1 from the back side 1b, an alignment unit with an infrared camera is used to detect the pre-defined dividing line 3 on the front side 1a through the wafer 1, and the laser beam is irradiated along the pre-defined dividing line 3.

[0041] Before the wafer 1 is carried into the laser processing apparatus 12 (refer to Figure 8 (A)) that performs laser processing for forming a shield tunnel 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.

[0042] Further, when the polyolefin sheet is expanded, the wafer 1 can be divided, and each device chip formed by dividing the wafer 1 is supported to 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 the pickup apparatus.

[0043] The ring-shaped frame 7 (refer to Figure 2 , etc.) is formed of a material such as metal, for example, and has an opening 7a having a diameter larger than that of the wafer 1. When the frame unit is formed, the wafer 1 is positioned in the opening 7a of the frame 7 and is housed in the opening 7a.

[0044] The polyolefin sheet 9 (refer to Figure 3 , etc.) is a sheet of a resin having flexibility, and the front surface and the back surface are flat. Further, 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 olefin as a monomer, and examples thereof include a polyethylene sheet, a polypropylene sheet, or a polystyrene sheet, or the like, which is transparent or translucent to visible light. However, the polyolefin sheet 9 is not limited thereto and can be opaque.

[0045] The polyolefin sheet 9 does not have adhesiveness and thus cannot be attached to the wafer 1 and the frame 7 at room temperature. However, the polyolefin sheet 9 has thermoplasticity, and thus when the polyolefin sheet 9 is 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 a predetermined pressure is applied to one side, the polyolefin sheet 9 locally melts and can be attached to the wafer 1 and the frame 7. Thus, in the wafer 1 processing method of the present embodiment, the wafer 1, the frame 7, and the polyolefin sheet 9 are integrated by the above-described heat pressure bonding to form the frame unit.

[0046] Next, each process of the wafer 1 processing method of the present embodiment will be described. First, the polyolefin sheet preparation process is performed in order to prepare for integration of the wafer 1, the polyolefin sheet 9, and the frame 7. Figure 2 is a perspective view schematically showing a state where the wafer 1 and the frame 7 are positioned on the holding surface 2a of the chuck table 2. As Figure 2 indicated, the polyolefin sheet preparation process is performed on the chuck table 2 having the holding surface 2a on the upper portion.

[0047] The chuck table 2 has a porous member in the upper center portion with a diameter larger than the outer diameter of the frame 7. The upper surface of the porous member serves as a holding surface 2a of the chuck table 2. The chuck table 2 has, as shown in Figure 3 FIG. 1, an exhaust passage inside thereof communicating with the porous member at one end, and a suction source 2b provided at the other end side of the exhaust passage. A switching portion 2c is provided on the exhaust passage to switch between a communicating state and a cut-off state. When the switching portion 2c is in the communicating state, a negative pressure generated by the suction source 2b is applied to an object placed on the holding surface 2a, thereby attracting and holding the object to the chuck table 2.

[0048] In the polyolefin sheet attaching step, first, as shown in Figure 2 FIG. 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.

[0049] 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 is to be the irradiated surface by the laser beam in the division step 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 wafer processing method of the present embodiment will be described with 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.

[0050] 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 attached to the back surface lb (or the front surface la) of the wafer 1 and the outer periphery of the frame 7. Figure 3 is a perspective view schematically showing the polyolefin sheet attaching step. As shown in Figure 3 , the polyolefin sheet 9 is attached to the wafer 1 and the frame 7 in a manner to cover both of them.

[0051] Also, in the polyolefin sheet attaching step, the 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 is applied to the polyolefin sheet 9 in the integration step to be performed later, if the entire holding surface 2a is not covered with the polyolefin sheet 9, the negative pressure leaks from the gap, and the pressure cannot be properly applied to the polyolefin sheet 9.

[0052] In the wafer processing method of the present embodiment, the integration step is then 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 step. In Figure 4 , members that can be seen through the polyolefin sheet 9 transparent or translucent to visible light are indicated by broken lines.

[0053] In the integration process, first, the switching section 2c of the chuck table 2 is made to operate 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.

[0054] Next, the polyolefin sheet 9 is heated while being sucked by the suction source 2b to perform heat press bonding. The heating of the polyolefin sheet 9 is performed by the hot air gun 4 provided above the chuck table 2, for example, as shown in FIG. 4. Figure 4

[0055] The hot air gun 4 has a heating unit such as an electric heating wire and a blower mechanism such as a fan in the inside, and can jet air heated. The polyolefin sheet 9 is provided with hot air 4a from the upper surface by the hot air gun 4 while the negative pressure is applied to the polyolefin sheet 9, and when the polyolefin sheet 9 is heated to a predetermined temperature, the polyolefin sheet 9 is heat press-bonded to the wafer 1 and the frame 7.

[0056] In addition, 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 by a member heated to a predetermined temperature. Figure 5 FIG. 5 is a perspective view schematically showing another example of the integration process. In FIG. 5, the member that can be seen through the polyolefin sheet 9 that is transparent or translucent to visible light is indicated by a broken line. Figure 5

[0057] In the integration process shown in FIG. 6, for example, a heating roller 6 having a heat source in the inside is used. In the integration process shown in FIG. 6, also, 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 by atmospheric pressure. Figure 5 Figure 5 Then, the heating roller 6 is heated to a predetermined temperature and is placed at one end of the holding surface 2a of the chuck table 2. Then, the heating roller 6 is made to rotate to roll the heating roller 6 on the chuck table 2 from the one end to the other end. Then, the polyolefin sheet 9 is heat press-bonded to the wafer 1 and the frame 7. At this time, when a force is applied in the direction of pressing the polyolefin sheet 9 by the heating roller 6, heat press bonding is performed by a pressure greater than atmospheric pressure. In addition, the surface of the heating roller 6 is preferably coated with a fluororesin.

[0058] Then, the heating roller 6 is heated to a predetermined temperature and is placed at one end of the holding surface 2a of the chuck table 2. Then, the heating roller 6 is made to rotate to roll the heating roller 6 on the chuck table 2 from the one end to the other end. Then, the polyolefin sheet 9 is heat press-bonded to the wafer 1 and the frame 7. At this time, when a force is applied in the direction of pressing the polyolefin sheet 9 by the heating roller 6, heat press bonding is performed by a pressure greater than atmospheric pressure. In addition, the surface of the heating roller 6 is preferably coated with a fluororesin.

[0059] ​​​Alternatively, an iron-shaped pressing member with an internal heat source and a flat bottom plate can be used instead of the heating roller 6 to perform the hot pressing of the polyolefin sheet 9. In this case, the pressing member is heated to a specified temperature to become a hot plate, and the polyolefin sheet 9 held by the chuck table 2 is pressed from above using the pressing member.

[0060] Heating of polyolefin sheet 9 can also be achieved by other methods. Figure 6 This is a perspective view schematically illustrating yet another example of an integrated process. Figure 6 In the diagram, dashed lines represent components that can be seen through the polyolefin sheet 9, which is transparent or translucent to visible light. Figure 6 In the integrated process shown, an infrared lamp 8 disposed above the chuck worktable 2 is used to heat the polyolefin sheet 9. The infrared lamp 8 is capable of irradiating at least infrared light 8a of a wavelength that is absorbed by the material of the polyolefin sheet 9.

[0061] exist Figure 6 In the integrated process shown, the negative pressure of the attraction source 2b is first applied to the polyolefin sheet 9, causing the polyolefin sheet 9 to adhere tightly to the wafer 1 and the frame 7. Next, the infrared lamp 8 is activated to irradiate the polyolefin sheet 9 with infrared rays 8a, thereby heating the polyolefin sheet 9. Then, the polyolefin sheet 9 is hot-pressed onto the wafer 1 and the frame 7.

[0062] When the polyolefin sheet 9 is heated to a temperature near its melting point by any method, the polyolefin sheet 9 is hot-pressed onto the wafer 1 and the frame 7. After the polyolefin sheet 9 is hot-pressed, the switching unit 2c is activated to disconnect the porous component of the chuck stage 2 from the suction source 2b, thereby releasing the adsorption of the chuck stage 2.

[0063] Next, the polyolefin sheet 9 protruding from the outer periphery of the frame 7 is cut off and removed. Figure 7 (A) is a perspective view schematically showing the cutting of polyolefin sheet 9. Regarding the cutting, as... Figure 7 As shown in (A), a ring-shaped cutter 10 is used. The cutter 10 has a through hole and is able to rotate about a rotation axis passing through the through hole.

[0064] First, the annular cutter 10 is positioned above the frame 7. At this time, the rotation axis of the cutter 10 is aligned radially with the chuck table 2. Next, the cutter 10 is lowered, and the polyolefin sheet 9 is cut by clamping it between the frame 7 and the cutter 10. Thus, a cutting mark 9a is formed on the polyolefin sheet 9.

[0065] In addition, the cutter 10 is made to go around the frame 7 around the opening 7a of the frame 7 by one turn, and the prescribed area of the polyolefin sheet 9 is surrounded by the cut mark 9a. Then, the polyolefin sheet 9 of the area on the outer circumferential side of the cut mark 9a is removed in the manner of the area of the polyolefin sheet 9 remaining. Thus, the unnecessary part of the polyolefin sheet 9 including the area that protrudes from the outer circumference of the frame 7 can be removed.

[0066] In addition, in the cutting of the polyolefin sheet, an ultrasonic cutter can be used, and a vibration source that makes the above-described ring-shaped cutter 10 vibrate at the frequency of the ultrasonic band can be connected to the cutter 10. In addition, in order to make the cutting easy when the polyolefin sheet 9 is cut, 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 the polyolefin sheet 9 is formed. Figure 7 FIG. 2 is a perspective view schematically showing the frame unit 11 formed.

[0067] 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 cannot maintain the shape of the sheet. 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.

[0068] In addition, there are cases where a part of the polyolefin sheet 9 does not have a definite softening point. Therefore, when the heat press bonding is performed, the polyolefin sheet 9 is preferably heated to a temperature above 20°C lower than the melting point thereof and below the melting point thereof.

[0069] 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.

[0070] Here, the heating temperature refers to the temperature of the polyolefin sheet 9 when the integrating process is performed. For example, among heat sources such as the heat 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 prescribed temperature, the output temperature of the heat source can be set to be higher than the melting point of the polyolefin sheet 9.

[0071] Next, in the wafer processing method of the present embodiment, a dicing process is performed to laser process the wafer 1 in a state of the frame unit 11, and continuously form a shield tunnel in the wafer 1 along the dicing intended line 3 to dice the wafer 1. The dicing process is performed, for example, by the laser processing apparatus shown in (A) of FIG. 1. Figure 8 (A) of FIG. 1 is a perspective view schematically showing the dicing process, Figure 8 (A) of FIG. 1 is a perspective view schematically showing the dicing process, Figure 8 (B) of FIG. 1 is a cross-sectional view schematically showing the dicing process.

[0072] The laser processing apparatus 12 has a laser processing unit 14 that irradiates a laser beam 16 to the wafer 1, 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.

[0073] The laser processing unit 14 irradiates the laser beam 16 emitted from the laser oscillator to 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 prescribed height position inside the wafer 1. The processing head 14a has a condenser lens (not shown) inside. The numerical aperture (NA) of the condenser lens is determined in such a manner that the value obtained by dividing the numerical aperture (NA) by the refractive index (N) of the wafer 1 is within the range of 0.05 to 0.2.

[0074] 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 sheet 9 interposed therebetween. Next, the chuck table is rotated to align the dicing intended line 3 of the wafer 1 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 in such a manner that the processing head 14a is disposed above the extension line of the dicing intended line 3. Furthermore, the focal point 14b of the laser beam 16 is positioned at the prescribed height position.

[0075] Next, 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 while continuously irradiating the laser beam 16 to the inside of the wafer 1 from the laser processing unit 14. 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 dicing intended line 3.

[0076] Thus, a filament-like region called a shield tunnel 3a is continuously formed along the dicing intended line 3. In Figure 8In (B) of FIG. 6, a cross-sectional view of the wafer 1 in which the shield tunnels 3a are continuously formed is schematically shown. In addition, Figure 8 (C) of FIG. 6 is a perspective view schematically showing the shield tunnels 3a. The shield tunnels 3a are constituted by the fine holes 3b along the thickness direction of the wafer 1 and the amorphous regions 3c surrounding the fine holes 3b. In addition, in (A) of FIG. 6, the shield tunnels 3a juxtaposed along the division predetermined line 3 are shown by solid lines. Figure 8 (C) of FIG. 6 is a perspective view schematically showing the shield tunnels 3a. The shield tunnels 3a are constituted by the fine holes 3b along the thickness direction of the wafer 1 and the amorphous regions 3c surrounding the fine holes 3b. In addition, in (A) of FIG. 6, the shield tunnels 3a juxtaposed along the division predetermined line 3 are shown by solid lines.

[0077] The irradiation conditions of the laser beam 16 in the division step are set, for example, as follows. However, the irradiation conditions of the laser beam 16 are not limited to this.

[0078] Wavelength: 1030 nm

[0079] Average output: 3 W

[0080] Repetition frequency: 50 kHz

[0081] Pulse width: 10 ps

[0082] Condensing spot diameter:

[0083] Feed rate: 500 mm / sec

[0084] When the laser beam 16 is thus irradiated to the wafer 1, the shield tunnels 3a are formed in the wafer 1 at intervals of 10 μm along the division predetermined line 3. Moreover, each of the shield tunnels 3a formed contains the fine holes 3b on the left and right and the amorphous regions 3c on the left and right. Therefore, the shield tunnels 3a adjacent to each other are connected at the amorphous regions 3c as shown in (B) of FIG. 6. Figure 8

[0085] After the shield tunnels 3a are formed in the wafer 1 along one division predetermined line 3, the chuck table and the laser processing unit 14 are relatively moved in an 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 shield tunnels 3a are formed along all the division predetermined lines 3 in one direction, the chuck table is rotated around 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.

[0086] Here, when the shield tunnels 3a are formed by the laser beam 16 irradiated to the wafer 1 by the laser processing unit 14, the light leakage of the laser beam 16 reaches the polyolefin sheet 9 below the wafer 1.

[0087] ​For example, in the case where the polyolefin sheet 9 is not used in the frame unit 11 but an adhesive tape is used, when the stray light of the laser beam 16 is irradiated to the paste layer of the adhesive tape, the paste layer of the adhesive tape is fused, and a part of the paste layer is fixed to the back surface Ib side of the wafer 1. In this case, the part of the paste layer remains on the back surface side of the device chip formed by dividing the wafer 1. Therefore, a decrease in quality of the device chip becomes a problem.

[0088] On the contrary, in the wafer processing method of the present embodiment, the polyolefin sheet 9 having no paste layer is used in the frame unit 11. Therefore, even if the stray light of the laser beam 16 reaches the polyolefin sheet 9, the paste layer is not fixed to the back surface Ib side of the wafer 1. Therefore, the quality of the device chip formed from the wafer 1 is maintained to be good.

[0089] Next, the wafer 1 is divided to form device chips by expanding the polyolefin sheet 9 to the radial outer side. Then, a pickup 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 pickup device 18 shown in the lower part is used. Figure 9 The pickup device 18 is a device for picking up the device chips from the polyolefin sheet 9. The pickup device 18 is used in the expansion of the polyolefin sheet 9. Figure 9 is a perspective view schematically showing the frame unit 11 carried into the pickup device 18.

[0090] The pickup device 18 has a drum 20 having a larger diameter 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 having a larger diameter than the diameter of the drum 20, and is disposed at the same height as the upper end portion of the drum 20 to surround the upper end portion of the drum 20 from the outer peripheral side.

[0091] A jig 24 is provided 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.

[0092] The frame support table 26 is supported by a plurality of rods 28 extending in the vertical direction, and a cylinder 30 that raises and lowers the rod 28 is provided at the lower end portion of each rod 28. The plurality of cylinders 30 are supported by a circular plate-shaped base 32. When each cylinder 30 is operated, the frame support table 26 is lowered with respect to the drum 20.

[0093] A lifting mechanism 34 that lifts the device chips supported by the polyolefin sheet 9 from below is provided inside the drum 20. In addition, a collet 36 that can suction-hold the device chips is provided above the drum 20 (see (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 the lifting mechanism 34 via a switching portion 36b (see (A) of Figure 10(B) is a cross-sectional view schematically showing the frame unit 11 fixed to the frame support table 26. The shield tunnels 3a are formed in the wafer 1 in parallel along the division predetermined lines 3. Figure 10

[0094] When the polyolefin sheet 9 is expanded, first, the height of the frame support table 26 is adjusted in such a manner that the height of the upper end of the drum 20 of the pickup device 18 coincides with the height of the upper surface of the frame support table 26 by causing the cylinder 30 to act. 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.

[0095] 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 shield tunnels 3a are formed in the wafer 1 in parallel along the division predetermined lines 3.

[0096] 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 (B) of FIG. 6, the polyolefin sheet 9 is expanded to the radial outside. Figure 10 Figure 10 (B) is a cross-sectional view schematically showing the expanded polyolefin sheet 9.

[0097] 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 shield tunnels 3a as a starting point to form individual device chips 1c. When the polyolefin sheet 9 is further expanded, the interval between the individual device chips 1c supported by the polyolefin sheet 9 is expanded, and the pickup of the individual device chips 1c becomes easy.

[0098] In the wafer processing method of the present embodiment, after the wafer 1 is divided to form individual device chips 1c, a pickup process is performed to pick up the device chips 1c from the polyolefin sheet 9. In the pickup process, the device chip 1c that is the pickup target is determined, and the jacking mechanism 34 is moved to below the device chip 1c and the collet 36 is moved to above the device chip 1c.

[0099] Then, the jacking mechanism 34 is caused to act to jack up the device chip 1c from the polyolefin sheet 9 side. Then, the switching portion 36b is caused to act to cause the collet 36 to communicate with the suction source 36a. Thus, 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 individual device chips 1c are used after being mounted on a prescribed wiring substrate or the like.

[0100] ​​For example, in the case where the frame units 11 are formed using the 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 is fixed to the back surface side of the device chip. Also, the quality reduction of the device chip due to the attachment of the paste layer becomes a problem.

[0101] On the other hand, according to the wafer processing method of the present embodiment, the frame units 11 using the polyolefin sheet 9 not having a paste layer can be formed by heat pressure bonding, and thus the adhesive tape having a paste layer is not required. As a result, the quality reduction of the device chip due to the attachment of the paste layer to the back surface side does not occur.

[0102] In addition, the present application is not limited to the description of the above-described embodiments, and various modifications can be made and implemented. 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.

[0103] 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 arranging step of positioning the wafer in an opening of a frame having an opening that receives the wafer, and arranging a polyolefin sheet that does not include a paste layer on the back surface or the front surface of the wafer and on the outer periphery of the frame so that the polyolefin sheet directly contacts the wafer and the frame; an integration step of heating the polyolefin sheet and integrally joining the wafer and the frame by heat pressure bonding 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, continuously forming a shield tunnel in the wafer, and dividing the wafer into individual device chips; and a pickup step of picking up each of the device chips from the polyolefin sheet.

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

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

4. The wafer processing method according to claim 1, characterized in that: in the pickup step, the polyolefin sheet is expanded to expand the interval between the device chips, and the device chips are lifted from the polyolefin sheet side.

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, in the case where the polyolefin sheet is the polyethylene sheet, the heating temperature is 120°C to 140°C, in the case where the polyolefin sheet is the polypropylene sheet, the heating temperature is 160°C to 180°C, and in the case where the polyolefin sheet is the polystyrene sheet, the heating temperature is 220°C to 240°C.

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

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