Wafer processing method

Abstract

A wafer processing method is provided for forming device chips without compromising quality. The wafer processing method separates a wafer having multiple devices formed in respective regions of the front surface defined by a predetermined dividing line into individual device chips. The wafer processing method comprises the following steps: a polyolefin sheet placement step of positioning the wafer within an opening of a frame having an opening for accommodating the wafer, and placing the polyolefin sheet on the back or front surface of the wafer and on the outer periphery of the frame; an integration step of heating the polyolefin sheet and integrating the wafer and the frame via the polyolefin sheet through thermocompression; a separation step of irradiating the wafer along the predetermined dividing line with a laser beam having a wavelength that is transparent to the wafer to form a modified layer in the wafer, thereby separating the wafer into individual device chips; and a pickup step of picking up each device chip 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 No. 3076179

[0009] The adhesive tape consists of a base layer formed, for example, from a vinyl chloride sheet, and a paste layer applied on the base layer. In a laser processing device, a laser beam is focused into the wafer to form a modified layer, which serves as a starting point for separation. However, some of the light from this laser beam leaks into the adhesive tape's paste layer. The heat from the laser beam melts the adhesive tape's paste layer, causing a portion of the paste layer to adhere to the back or front side of the device chip formed from the wafer.

[0010] In this case, even if the adhesive tape is treated by irradiating the tape with ultraviolet light when the device chip is picked up, a portion of the paste layer may remain on the back or front side of the picked device chip, thereby causing a problem of reduced quality of the device chip. Summary of the Invention

[0011] The present invention has been made in view of this problem, and its object is to provide a wafer processing method that does not cause a paste layer to adhere to the back side or the front side of a formed device chip, thereby preventing the quality of the device chip from being degraded due to the adhesion of the paste layer.

[0012] According to one embodiment of the present invention, a method for processing a wafer is provided for dividing a wafer having a plurality of devices formed in respective regions of the front surface divided by a predetermined dividing line into individual device chips, the method comprising the following steps: a polyolefin sheet placement step of positioning the wafer in an opening of a frame having an opening for accommodating the wafer, and placing the polyolefin sheet on the back surface or the front surface of the wafer and on the periphery of the frame; an integration step of heating the polyolefin sheet and integrating the wafer and the frame via the polyolefin sheet by thermocompression bonding; a dividing step of positioning a focal point of a laser beam having a wavelength that is transmissive to the wafer within the wafer, irradiating the wafer with the laser beam along the predetermined dividing line to form a modified layer in the wafer, and dividing the wafer into individual device chips; and a picking step of picking up each of the device chips from the polyolefin sheet.

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

[0014] Furthermore, in the integration step, it is preferred that the polyolefin-based sheet protruding from the outer periphery of the frame be removed after the integration is performed.

[0015] Furthermore, in the pickup step, it is preferred that the polyolefin-based sheet be expanded to increase the intervals between the device chips, and the device chips be lifted from the polyolefin-based sheet side.

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

[0017] In addition, in the integration step, it is preferred that 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.

[0018] In addition, the wafer is preferably made of any material among Si, GaN, GaAs, and glass.

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

[0020] After the integration process, the wafer is irradiated with a laser beam of a wavelength that is transparent to the wafer, forming a modified layer along the predetermined dividing lines within the wafer, thereby dividing the wafer. The device chips are then removed from the polyolefin sheet and mounted on their designated mounting locations.

[0021] When forming the modified layer inside the wafer, leakage of the laser beam reaches the polyolefin sheet. However, since the polyolefin sheet does not have a paste layer, the paste layer does not melt and adhere to the back or front side of the device chip.

[0022] That is, according to one embodiment of the present invention, the frame unit can be formed using a polyolefin-based sheet without a paste layer, thereby eliminating the need for an adhesive tape having a paste layer. As a result, the quality of the device chip does not deteriorate due to adhesion of the paste layer.

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

[0024] 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.

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

[0026] Figure 3 It is a perspective view schematically showing the polyolefin-based sheet disposing step.

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

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

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

[0030] Figure 7 (A) is a perspective view schematically showing a state where a polyolefin-based 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 segmentation process, Figure 8 (B) is a cross-sectional view schematically showing the dividing step.

[0032] Figure 9 It is a perspective view schematically showing the loading of the frame unit into the pickup device.

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

[0034] Description of labels

[0035] 1: Wafer; 1a: Front side; 1b: Back side; 3: Predetermined dividing 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: Pickup device; 20: Drum; 22: Frame holding unit; 24: Clamp; 26: Frame support platform; 28: Rod; 30: Cylinder; 32: Base; 34: Lifting mechanism; 36: Collet. DETAILED DESCRIPTION

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

[0037] The wafer 1 is a generally disk-shaped substrate made of, for example, Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaAs (gallium arsenide), or other semiconductor materials, or sapphire, glass, quartz, or the like. Examples of the glass include alkali glass, alkali-free glass, soda-lime glass, lead glass, borosilicate glass, and quartz glass.

[0038] The front surface 1a of the wafer 1 is divided by a plurality of predetermined dividing lines 3 arranged in a grid pattern. Furthermore, devices 5, such as ICs, LSIs, and LEDs, are formed within the respective regions of the front surface 1a of the wafer 1 defined by the predetermined dividing lines 3. In the method for processing the wafer 1 of this embodiment, a modified layer is formed within the wafer 1 along the predetermined dividing lines 3, and the wafer 1 is divided starting from this modified layer to form individual device chips.

[0039] When forming a reformed layer in the wafer 1, a laser beam having a wavelength that is transparent to the wafer 1 is irradiated to the wafer 1 along the predetermined dividing line 3, and the laser beam is focused into the interior of the wafer 1. At this time, the laser beam can be Figure 1 The front side 1a shown in (A) is irradiated to the wafer 1, or it can be irradiated from Figure 1 The back surface 1b side shown in (B) is irradiated onto the wafer 1. In addition, when the laser beam is irradiated to the wafer 1 from the back surface 1b side, an alignment unit having an infrared camera is used to detect the predetermined separation line 3 on the front surface 1a side through the wafer 1, and the laser beam is irradiated along the predetermined separation line 3.

[0040] The wafer 1 is loaded into the laser processing apparatus 12 (see FIG. Figure 8 ), 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 device 12 in the state of the frame unit and processed.

[0041] Furthermore, when the polyolefin sheet is expanded, the wafer 1 can be divided, and the individual device chips formed by dividing the wafer 1 are supported on the polyolefin sheet. Then, the polyolefin sheet is further expanded to increase the spacing between the device chips, and the device chips are picked up by a pickup device.

[0042] The annular frame 7 (see Figure 2 The frame 7 is formed of a material such as metal, and has an opening 7a having a diameter larger than that of the wafer 1. When forming the frame unit, the wafer 1 is positioned in the opening 7a of the frame 7 and accommodated in the opening 7a.

[0043] Polyolefin sheet 9 (refer to Figure 3 The polyolefin sheet 9 is a flexible resin sheet with flat front and back surfaces. Furthermore, the polyolefin sheet 9 has a diameter larger than the outer diameter of the frame 7 and does not include a paste layer. The polyolefin sheet 9 is a sheet of a polymer synthesized using an olefin as a monomer, and examples thereof include polyethylene, polypropylene, and polystyrene sheets that are transparent or translucent to visible light. However, the polyolefin sheet 9 is not limited thereto and may also be opaque.

[0044] The polyolefin sheet 9 has no adhesive properties and therefore cannot be attached to the wafer 1 and frame 7 at room temperature. However, the polyolefin sheet 9 has thermoplastic properties. Therefore, when the polyolefin sheet 9 is heated to a temperature near its melting point while being bonded to the wafer 1 and frame 7 under a predetermined pressure, the polyolefin sheet 9 partially melts and becomes 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 thermocompression bonding as described above to form a frame unit.

[0045] Next, each step of the method for processing the wafer 1 according to the present embodiment will be described. First, a polyolefin sheet placement step is performed in preparation for integrating the wafer 1, the polyolefin sheet 9, and the frame 7. Figure 2 1 is a perspective view schematically showing the situation where the wafer 1 and the frame 7 are positioned on the holding surface 2a of the chuck table 2. Figure 2 As shown, the polyolefin sheet placement step is performed on a chuck table 2 having a holding surface 2a on its upper portion.

[0046] The chuck table 2 has a porous member at the center of the upper portion thereof, the diameter of which is 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. Figure 3 The chuck 2 is shown as having an internal exhaust passage with one end connected to the porous member. A suction source 2b is provided at the other end of the exhaust passage. A switching portion 2c is provided on the exhaust passage to switch between an open and closed state. When the switching portion 2c is in the open state, 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.

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

[0048] At this time, the orientation of wafer 1 is selected based on whether the surface to be irradiated with the laser beam in the subsequent dividing step is the front surface 1a or the back surface 1b. For example, if the irradiated surface is the front surface 1a, the front surface 1a is oriented downward. Alternatively, if the irradiated surface is the back surface 1b, the back surface 1b is oriented downward. The wafer processing method of this embodiment will be described below using the case where the surface to be irradiated with the laser beam is the front surface 1a, but the orientation of wafer 1 is not limited to this.

[0049] After the wafer 1 and the frame 7 are placed on the holding surface 2 a of the chuck table 2 , a polyolefin sheet 9 is placed on the back surface 1 b (or front surface 1 a ) of the wafer 1 and on the outer periphery of the frame 7 . Figure 3 : is a perspective view schematically showing the polyolefin sheet arrangement process. Figure 3 As shown, a polyolefin-based sheet 9 is provided on the wafer 1 and the frame 7 so as to cover both.

[0050] Furthermore, in the polyolefin sheet placement step, a polyolefin sheet 9 having a larger diameter than the holding surface 2a of the chuck table 2 is used. This is because, when negative pressure from the chuck table 2 is applied to the polyolefin sheet 9 in the subsequent integration step, if the polyolefin sheet 9 does not cover the entire holding surface 2a, the negative pressure will leak through gaps, preventing the polyolefin sheet 9 from being properly pressed.

[0051] In the wafer 1 processing method of the present embodiment, an integration step is then performed in which the polyolefin sheet 9 is heated and integrated with the frame 7 via the polyolefin sheet 9 by thermocompression bonding. Figure 4 This is a perspective view schematically showing an example of the integration process. Figure 4 In FIG. 1 , components that can be viewed through the polyolefin-based sheet 9 that is transparent or translucent to visible light are indicated by dotted lines.

[0052] In the integration step, the switching unit 2c of the chuck table 2 is first operated to establish a communication state between the suction source 2b and the porous member on the upper portion of the chuck table 2. The negative pressure of the suction source 2b is applied to the polyolefin sheet 9. This causes the polyolefin sheet 9 to adhere tightly to the wafer 1 and the frame 7 due to atmospheric pressure.

[0053] Next, the polyolefin sheet 9 is heated while being sucked by the suction source 2b to perform thermocompression bonding. The polyolefin sheet 9 is heated, for example, as follows: Figure 4 As shown, the hot air gun 4 is provided above the chuck table 2 to perform the heat treatment.

[0054] The hot air gun 4 internally includes a heating unit such as a heating wire and an air supply mechanism such as a fan, and is capable of heating and spraying air. While applying negative pressure to the polyolefin sheet 9, the hot air gun 4 supplies hot air 4a to the polyolefin sheet 9 from above. When the polyolefin sheet 9 is heated to a predetermined temperature, the polyolefin sheet 9 is thermally pressed against the wafer 1 and the frame 7.

[0055] The polyolefin-based sheet 9 may be heated 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 This is a perspective view schematically showing another example of the integration process. Figure 5 In FIG. 1 , components that can be viewed through the polyolefin-based sheet 9 that is transparent or translucent to visible light are indicated by dotted lines.

[0056] exist Figure 5 In the integration process shown, for example, a heating roller 6 having a heat source inside is used. Figure 5 In the integration step shown, negative pressure from the suction source 2b is first applied to the polyolefin sheet 9, and the polyolefin sheet 9 is brought into close contact with the wafer 1 and the frame 7 by atmospheric pressure.

[0057] Next, 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. The heating roller 6 is then rotated, rolling from one end to the other end on the chuck table 2. This allows the polyolefin sheet 9 to be thermocompressed onto the wafer 1 and the frame 7. At this time, when the heating roller 6 applies a force in a direction that presses down the polyolefin sheet 9, thermocompression bonding is achieved using a pressure greater than atmospheric pressure. The surface of the heating roller 6 is preferably coated with a 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] Furthermore, the cutter 10 is moved along the frame 7 around the opening 7a of the frame 7, enclosing a predetermined area of ​​the polyolefin sheet 9 via the cut mark 9a. The polyolefin sheet 9 is then removed from the area surrounding the cut mark 9a, leaving the remaining area of ​​the polyolefin sheet 9. Thus, the unnecessary portion of the polyolefin sheet 9, including the area protruding from the outer periphery of the frame 7, can be removed.

[0065] Furthermore, an ultrasonic cutter can be used to cut the polyolefin sheet, and a vibration source that causes the annular cutter 10 to vibrate at a frequency within the ultrasonic frequency band can be connected to the cutter 10. Furthermore, to facilitate cutting, the polyolefin sheet 9 can be cooled and hardened. As described above, the frame unit 11 is formed, in which the wafer 1 and the frame 7 are integrated via the polyolefin sheet 9. Figure 7 (B) is a perspective view schematically showing the formed frame unit 11 .

[0066] Furthermore, when performing heat compression bonding, the polyolefin sheet 9 is preferably heated to a temperature below its melting point. This is because, if the heating temperature exceeds the melting point, the polyolefin sheet 9 may melt and lose its shape. Furthermore, 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, heat compression bonding cannot be performed properly. In other words, the polyolefin sheet 9 is preferably heated to a temperature above its softening point and below its melting point.

[0067] In addition, some polyolefin sheets 9 may not have a clear softening point. Therefore, when performing thermocompression bonding, the polyolefin sheet 9 is preferably heated to a temperature that is 20° C. lower than its melting point and below its melting point.

[0068] When the polyolefin sheet 9 is a polyethylene sheet, the heating temperature is preferably 120° C. to 140° C. When the polyolefin sheet 9 is a polypropylene sheet, the heating temperature is preferably 160° C. to 180° C. 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, although heat sources such as the heat gun 4, the heating roller 6, and the infrared lamp 8 are typically configured with a set output temperature, even when the polyolefin sheet 9 is heated using such a heat source, the temperature of the polyolefin sheet 9 may not reach the set output temperature. Therefore, to heat the polyolefin sheet 9 to a predetermined temperature, the output temperature of the heat source may be set to a value higher than the melting point of the polyolefin sheet 9.

[0070] Next, in the wafer processing method of this embodiment, a dividing step is performed to laser process the wafer 1 in the state of the frame unit 11, thereby forming a modified layer along the predetermined dividing line 3 inside the wafer 1 and dividing the wafer 1. The dividing step is performed, for example, by Figure 8 It is implemented by the laser processing device shown in (A). Figure 8 (A) is a perspective view schematically showing the segmentation process, Figure 8 (B) is a cross-sectional view schematically showing the dividing step.

[0071] The laser processing apparatus 12 includes a laser processing unit 14 for irradiating a laser beam 16 onto the wafer 1, and a chuck table (not shown) for holding the wafer 1. The laser processing unit 14 includes a laser oscillator (not shown) capable of oscillating laser light, and is capable of emitting a laser beam 16 having a wavelength that is transmissive to the wafer 1 (a wavelength that can transmit the wafer 1). The chuck table is movable (processing feed) in a direction parallel to the upper surface.

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

[0073] When laser processing wafer 1, frame unit 11 is placed on the chuck table, holding wafer 1 on the chuck table via polyolefin sheet 9. Next, the chuck table is rotated to align the intended dividing line 3 of wafer 1 with the processing feed direction of laser processing device 12. Furthermore, the relative positions of the chuck table and laser processing unit 14 are adjusted so that processing head 14a is positioned above an extension of intended dividing line 3. Furthermore, focal point 14b of laser beam 16 is positioned at a predetermined height.

[0074] Next, while the laser processing unit 14 irradiates the interior of the wafer 1 with a laser beam 16, the chuck table and the laser processing unit 14 are relatively moved in a 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 predetermined dividing line 3. Thus, a modified layer 3a is formed inside the wafer 1. Figure 8 In (A), the reformed layer 3 a formed inside the wafer 1 is indicated by a dotted line.

[0075] The irradiation conditions of the laser beam 16 in the dividing step are set, for example, as follows. However, the irradiation conditions of the laser beam 16 are not limited thereto.

[0076] Wavelength: 1064nm

[0077] Repetition frequency: 50kHz

[0078] Average output: 1W

[0079] Feed speed: 200mm / s

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

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

[0082] For example, if an adhesive tape is used instead of the polyolefin sheet 9 in the frame unit 11, when the leaked light from the laser beam 16 hits the paste layer of the adhesive tape, the paste layer of the adhesive tape melts, and a portion of the paste layer adheres to the back surface 1b of the wafer 1. In this case, this portion of the paste layer remains on the back surface of the device chips formed by dividing the wafer 1. This can lead to a decrease in the quality of the device chips.

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

[0084] Next, the polyolefin sheet 9 is expanded radially outward to divide the wafer 1 into device chips. Then, a picking process is performed to pick up each device chip from the polyolefin sheet 9. Figure 9 The pickup device 18 is shown at the bottom. Figure 9 It is a perspective view schematically showing the loading 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 base 26. The frame support base 26 of the frame holding unit 22 has an opening having a diameter larger than that of the drum 20, is arranged at the same height as the upper end of the drum 20, and surrounds the upper end of the drum 20 from the outer circumference.

[0086] The jig 24 is disposed on the outer peripheral side of the frame support base 26 . When the frame unit 11 is placed on the frame support base 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 base 26 .

[0087] The frame support 26 is supported by a plurality of rods 28 extending in the vertical direction. A cylinder 30 is provided at the lower end of each rod 28 to raise and lower the rod 28. The cylinders 30 are supported on a disk-shaped base 32. When the cylinders 30 are actuated, the frame support 26 is lowered relative to the drum 20.

[0088] A lifting mechanism 34 is provided inside the drum 20 to lift the device chip supported by the polyolefin sheet 9 from below. In addition, a collet 36 (see FIG. 1 ) is provided above the drum 20 to attract and hold the device chip. Figure 10(B)). The lifting mechanism 34 and the collet 36 can move in the horizontal direction along the upper surface of the frame support 26. In addition, the collet 36 is connected to the switching portion 36b (see Figure 10 (B)) and the suction source 36a (refer to Figure 10 (B)) connection.

[0089] When expanding the polyolefin sheet 9, the air cylinder 30 is first operated to adjust the height of the frame support table 26 so that the height of the upper end of the drum 20 of the pickup device 18 is consistent with the height of the upper surface of the frame support table 26. Next, the frame unit 11 unloaded 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 stand 26 by the clamps 24 . Figure 10 (A) is a cross-sectional view schematically showing the frame unit 11 fixed to the frame support 26. A reformed layer 3a is formed along the planned dividing lines 3 inside the wafer 1.

[0091] Next, the air cylinder 30 is operated to lower the frame support 26 of the frame holding unit 22 relative to the drum 20. Figure 10 As shown in (B), the polyolefin-based sheet 9 expands radially outward. Figure 10 (B) is a cross-sectional view schematically showing the expanded polyolefin-based sheet 9 .

[0092] As the polyolefin sheet 9 expands, it exerts a radially outward force on the wafer 1, dividing the wafer 1 with the modified layer 3a as the starting point to form individual device chips 1c. Further expansion of the polyolefin sheet 9 increases the spacing between the device chips 1c supported by the polyolefin sheet 9, making it easier to pick up the individual device chips 1c.

[0093] In the wafer processing method of this embodiment, after the wafer 1 is divided into individual device chips 1c, a pickup step is performed to pick up the device chips 1c from the polyolefin sheet 9. In the pickup step, the device chip 1c to be picked up is identified, the lift mechanism 34 is moved below the device chip 1c, and the collet 36 is moved above the device chip 1c.

[0094] Next, the lifting mechanism 34 is activated to lift the device chip 1c from the polyolefin sheet 9. The switching unit 36b is then activated to connect the collet 36 to the suction source 36a. The collet 36 then suctions and holds the device chip 1c, picking up the device chip 1c from the polyolefin sheet 9. Each picked device chip 1c is then mounted on a predetermined wiring board or the like for use.

[0095] For example, when using adhesive tape to form the frame unit 11, during the dicing process, light leakage from the laser beam 16 irradiating the wafer 1 reaches the adhesive tape, causing the adhesive layer of the adhesive tape to adhere to the back side of the device chip. This adhesion of the adhesive layer can lead to a decrease in the quality of the device chip, which can be problematic.

[0096] In contrast, the wafer processing method of this embodiment enables the formation of frame units 11 using polyolefin sheets 9 without a paste layer by thermocompression bonding, eliminating the need for adhesive tape with a paste layer. Consequently, the quality of the device chips, which would otherwise be degraded due to the paste layer adhering to the back surface, is eliminated.

[0097] The present invention is not limited to the above-described embodiment and can be implemented with various modifications. For example, in the above-described embodiment, the polyolefin sheet 9 is described as a polyethylene sheet, a polypropylene sheet, or a polystyrene sheet, but one embodiment of the present invention is not limited thereto. For example, the polyolefin sheet can be made of other materials, such as a copolymer of propylene and ethylene, an olefin-based elastomer, or the like.

[0098] In addition, the structure, method, etc. of the above-mentioned embodiment can be appropriately modified and implemented without departing from the scope of the purpose of the present invention.

Claims

1. A wafer processing method for dividing a wafer having a plurality of devices formed in respective regions of a front surface divided by predetermined dividing lines into individual device chips, characterized in that: The wafer processing method has the following steps: a polyolefin sheet placement step of positioning a wafer in an opening of a frame having an opening for accommodating the wafer, and placing a polyolefin sheet having no paste layer on the back side or the front side of the wafer and on the outer periphery of the frame such that the polyolefin sheet is in direct contact with the wafer and the back side of the frame; an integration step, after the polyolefin sheet disposing step, heating and applying pressure to the polyolefin sheet without the paste layer, integrating the wafer and the frame via the polyolefin sheet by thermocompression bonding, thereby forming a frame unit; a dividing step of positioning a focal point of a laser beam of a wavelength that is transparent to the wafer inside the wafer, irradiating the wafer with the laser beam along the planned dividing line to form a modified layer in the wafer, and dividing the wafer into individual device chips; and The picking-up step is to pick up each device chip from the polyolefin-based sheet.

2. The wafer processing method according to claim 1, wherein: In this integration step, the thermocompression bonding is performed by irradiation with infrared rays.

3. The wafer processing method according to claim 1, wherein: In the integration step, after the integration is performed, the polyolefin-based sheet protruding from the outer periphery of the frame is removed.

4. The wafer processing method according to claim 1, wherein: In the pickup step, the polyolefin-based sheet is expanded to widen the intervals between the device chips, and the device chips are lifted up from the polyolefin-based sheet side.

5. The wafer processing method according to claim 1, wherein: The polyolefin-based sheet is any of a polyethylene sheet, a polypropylene sheet, and a polystyrene sheet.

6. The wafer processing method according to claim 5, wherein: In the integration process, 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 wafer processing method according to claim 1, wherein: The wafer is made of any material among Si, GaN, GaAs, and glass.

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