Wafer processing method

Abstract

A wafer processing method is provided, wherein the back side of the wafer is ground to thin the wafer, and the wafer can be appropriately divided into individual device chips. The wafer processing method includes the following steps: a division starting point forming step, wherein the focusing point of laser light (LB) having a wavelength that is transparent to the wafer (10) is positioned at a predetermined interior from the back side (10b) of the wafer and the laser light is irradiated to form a division starting point consisting of a modified layer (100) and a crack (102) extending from the modified layer to the front side along a predetermined division line (12); and a division step, wherein the back side of the wafer is ground using a grinding wheel (64) having a plurality of grinding tools (65) in an annular shape to thin the wafer, and the wafer (10) is divided into individual device chips (14'). In the division starting point forming step, a chuck table (24) is heated to a predetermined temperature to grow a crack (102) from the modified layer (100) formed inside the wafer (10) to the front side.

Description

Technical Field

[0001] The present invention relates to a wafer processing method for dividing a wafer having a plurality of devices formed on a front surface thereof by a plurality of intersecting predetermined dividing lines into individual device chips. Background Art

[0002] A wafer having a plurality of devices such as ICs and LSIs formed on the front surface is divided by a plurality of intersecting planned dividing lines and is divided into individual device chips by a dicing device. The device chips are used in electronic devices such as mobile phones and personal computers.

[0003] In addition, the following technology has been proposed: the focal point of a laser beam of a wavelength that is transparent to the wafer is positioned inside the back side of the wafer and irradiated, a modified layer is formed along the predetermined dividing line, the back side of the wafer is then ground to thin the wafer, and cracks are grown from the modified layer to the front side to divide the wafer into individual device chips (for example, refer to patent document 1).

[0004] Furthermore, in order to efficiently form cracks from a reformed layer formed along a planned dividing line to the front surface, the present applicant has proposed a technique of heating a wafer after forming a reformed layer on the wafer (see, for example, Patent Document 2).

[0005] Patent Document 1: Japanese Patent Application Publication No. 2009-290148

[0006] Patent Document 2: Japanese Patent Application Publication No. 2016-213318

[0007] An attempt was made to divide the wafer into individual device chips using the techniques described in the above-mentioned patent documents 1 and 2, but there was a problem: sometimes cracks were not properly formed from the modified layer to the front surface, and even if one wanted to grind the back side of the wafer where cracks were not properly formed and divide the wafer into individual device chips, it would be impossible to obtain device chips of the desired quality. Summary of the invention

[0008] Therefore, an object of the present invention is to provide a wafer processing method capable of grinding the back surface of the wafer to thin the wafer and appropriately dividing the wafer into individual device chips.

[0009] According to the present invention, a wafer processing method is provided, which divides a wafer divided by a plurality of intersecting predetermined dividing lines and having a plurality of devices formed on the front side into individual device chips, wherein the wafer processing method comprises the following steps: a protective tape arrangement step, in which a protective tape is arranged on the front side of the wafer; a wafer holding step, in which the protective tape side is faced to a chuck worktable for holding and heating the wafer, and the wafer is held so that the back side of the wafer is exposed; and a dividing starting point forming step, in which, after the wafer holding step is performed, a laser beam of a wavelength that is transparent to the wafer is emitted to the wafer. The focusing point is positioned at a predetermined interior from the back side of the wafer and the laser beam is irradiated to form a splitting starting point composed of a modified layer and a crack extending from the modified layer to the front side along a predetermined splitting line; and a splitting process, after the splitting starting point forming process is implemented, the back side of the wafer is ground using a grinding wheel having a plurality of grinding tools in an annular shape to thin the wafer, and the wafer is split into individual device chips, in which the chuck worktable is heated to a predetermined temperature to grow the crack from the modified layer formed inside the wafer to the front side.

[0010] In the division starting point forming step, the predetermined temperature is preferably 40°C to 120°C.

[0011] According to the chip processing method of the present invention, in the splitting starting point forming step, the chuck worktable is heated to a specified temperature to grow a crack from a modified layer formed inside the chip to the front surface. Therefore, the contraction force of the protective tape arranged on the front surface of the chip is released due to heating, and when a modified layer is formed by laser light, a crack can be appropriately grown from the modified layer to the front surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is an overall perspective view of the laser processing device.

[0013] Figure 2 It is a perspective view of a wafer and a protective tape to be processed in this embodiment.

[0014] Figure 3 The wafer is held in Figure 1 A perspective view of a chuck table of a laser processing device.

[0015] Figure 4 (a) shows that Figure 1 The laser processing apparatus shown is a three-dimensional diagram of the method of implementing the division starting point forming process, Figure 4 (b) is a partial enlarged cross-sectional view of the wafer held by the chuck table. Figure 4 (c) is a three-dimensional view of the chip after the division starting point forming step is completed.

[0016] Figure 5(a) is a perspective view showing a method of performing a wafer splitting process. Figure 5 (b) is a perspective view showing a state where a wafer is divided into individual device chips through a dividing step. Figure 5 (c) is a perspective view of the wafer after the dividing step is completed.

[0017] Description of symbols

[0018] 1: laser processing device; 2: base; 4: frame; 6: grinding device; 10: wafer; 12: predetermined dividing line; 14: device; 14': device chip; 20: holding unit; 24: chuck table; 26: suction chuck; 30: moving mechanism; 31: X-axis feeding mechanism; 32: Y-axis feeding mechanism; 50: laser beam irradiation unit; 52: condenser; 55: shooting unit; 60: grinding unit; 64: grinding wheel; 65: grinding tool; 100: modified layer; 102: crack; 110: dividing line. DETAILED DESCRIPTION

[0019] Hereinafter, an embodiment of a wafer processing method according to the present invention will be described in more detail with reference to the accompanying drawings.

[0020] exist Figure 1 1 is an overall perspective view of a laser processing apparatus 1 which is suitable for the wafer processing method according to the present embodiment.

[0021] Figure 1 The laser processing device 1 shown comprises: a holding unit 20, which holds a circular workpiece (wafer); a moving mechanism 30, which moves the holding unit 20; a laser beam irradiation unit 50, which irradiates the workpiece held by the holding unit 20 with laser beam; a shooting unit 55, which shoots the workpiece held by the holding unit 20; and a display device M.

[0022] The holding unit 20 is arranged on the base 2 as a base of the laser processing device 1, and the holding unit 20 has: a rectangular X-axis movable plate 21, which is mounted in a manner that it can move freely in the X-axis direction indicated by the arrow X in the figure; a rectangular Y-axis movable plate 22, which is mounted on the X-axis movable plate 21 in a manner that it can move freely in the Y-axis direction indicated by the arrow Y in the figure; a chuck table 24, which is arranged on the upper surface of the Y-axis movable plate 22 and is configured to be rotatable by a driving unit not shown; and an adsorption chuck 26, which constitutes the upper surface of the chuck table 24 and is formed of a porous material such as porous ceramics with air permeability. A heating unit such as a heater described later is built into the chuck table 24, which has the function of heating the front surface of the adsorption chuck 26 to a predetermined temperature.

[0023] The moving mechanism 30 includes an X-axis feed mechanism 31 that feeds the holding unit 20 in the X-axis direction for processing, and a Y-axis feed mechanism 32 that indexes the holding unit 20 in the Y-axis direction. The X-axis feed mechanism 31 converts the rotational motion of the pulse motor 33 into linear motion by means of a ball screw 34 and transmits it to the X-axis movable plate 21, so that the X-axis movable plate 21 moves forward and backward in the X-axis direction along the guide rails 2a, 2a on the base 2. The Y-axis feed mechanism 32 converts the rotational motion of the pulse motor 35 into linear motion by means of a ball screw 36 and transmits it to the Y-axis movable plate 22, so that the Y-axis movable plate 22 moves forward and backward in the Y-axis direction along the guide rails 21a, 21a on the X-axis movable plate 21. The moving mechanism 30 is provided with a position detection unit (not shown) to detect the position of the chuck table 24 in the X-axis direction, the Y-axis direction, and the rotational direction and feed back to a control unit (not shown), thereby moving the chuck table 24 to a desired position.

[0024] A frame 4 is erected on the side of the moving mechanism 30. The frame 4 has a vertical wall portion 4a disposed on the base 2 and a horizontal wall portion 4b extending in the horizontal direction from the upper end portion of the vertical wall portion 4a. An optical system (not shown) including a laser oscillator of the laser beam irradiation unit 50 is built in the horizontal wall portion 4b of the frame 4. A condenser 52 constituting a part of the laser beam irradiation unit 50 is disposed on the lower surface of the front end portion of the horizontal wall portion 4b, and a condenser lens (not shown) for converging the laser beam is built in the condenser 52. The laser beam emitted from the laser oscillator of the laser beam irradiation unit 50 is condensed by the condenser 52 through the optical system (not shown), and a condensed spot is formed at a desired position of the workpiece held by the chuck table 24 of the holding unit 20.

[0025] The imaging unit 55 is disposed on the lower surface of the front end of the horizontal wall portion 4b at a position adjacent to the condenser 52 in the X-axis direction, and images the workpiece held by the holding unit 20 from a direction opposite to the holding unit 20. The imaging unit 55 includes an infrared imaging element (infrared CCD) that images with infrared rays (not shown) and an infrared irradiation unit (not shown) that irradiates the workpiece with infrared rays, and is connected to a control unit (not shown) that controls each operating unit of the laser processing device 1. The signal of the image captured by the imaging unit 55 is sent to the control unit. In addition, depending on the type of the workpiece, the imaging unit 55 may include a visible light irradiation unit and a normal imaging element (CCD) that images visible light.

[0026] The display device M is arranged on the horizontal wall portion 4b and is connected to a control unit not shown in the figure. It displays various processing information output from the control unit, such as the wavelength, repetition frequency, focal point position, spot diameter of the laser light, and image information of the chip captured by the imaging unit 55, and has a touch panel function that receives the operator's operation and sends it to the control unit.

[0027] The laser processing apparatus 1 roughly has the above-described structure. Hereinafter, a wafer processing method according to an embodiment of the present invention performed using the laser processing apparatus 1 will be described.

[0028] (Protective tape installation process)

[0029] First, when implementing the wafer processing method of this embodiment, Figure 2 As shown, a wafer 10 made of a semiconductor such as silicon (Si) is prepared, which is divided by a plurality of mutually intersecting predetermined dividing lines 12 and has a plurality of devices 14 formed on the front side 10a. If the wafer 10 is prepared, a protective tape 16 is provided on the front side 10a. The protective tape 16 is composed of a flexible film-like substrate and a paste layer formed on one surface of the substrate, and is adhered to the front side 10a of the wafer 10 by means of the paste layer. The substrate is, for example, PO (polyolefin), but is not limited to PO, and PET (polyethylene terephthalate), polyvinyl chloride, polystyrene, etc. may also be used. The paste layer is, for example, silicone rubber, acrylic material, epoxy material, etc. In addition, the protective tape 16 is not limited to the above-mentioned protective tape composed of the substrate and the paste layer, and a sheet composed of a polyolefin raw material or a sheet composed of a polyester raw material that exerts adhesive force by heating to near the melting temperature may also be used. When a sheet made of a polyolefin-based material or a sheet made of a polyester-based material is used as the protective tape 16, the paste layer can be omitted. The protective tape disposing step is completed as described above.

[0030] (Wafer holding process)

[0031] Once the protective tape installation process is completed as described above, Figure 3 As shown, the protective tape 16 is placed opposite to the chuck table 24 of the laser processing device 1, and a suction unit (not shown) is operated to suck and hold the wafer so that the back side 10b of the wafer is exposed upward. The wafer holding step is completed as described above.

[0032] (Division starting point forming step)

[0033] If the wafer holding process is completed, Figure 4As shown in (a) of FIG. 1 , a splitting starting point forming step is performed, whereby a laser beam LB is irradiated from a laser beam irradiation unit 50 of the laser processing device 1 to form a modified layer serving as a splitting starting point along the splitting predetermined line 12 inside the wafer 10. More specifically, infrared rays are first irradiated from an imaging unit 55 to the back side 10b of the wafer 10 to perform imaging, thereby performing alignment, and aligning the position irradiated with the laser beam LB with the splitting predetermined line 12 of the wafer 10. Once this alignment is performed, Figure 4 The heating unit 40 shown in (b) of FIG. 1 and built into the chuck table 24 is operated. The heating unit 40 has an electric heater and a temperature sensor, and heats the adsorption chuck 26 constituting the upper surface of the chuck table 24 to a specified temperature (for example, 80° C.) set by a control unit not shown in the figure and maintains the temperature. When the chuck table 24 is heated to this temperature, the laser beam irradiation unit 50 of the laser processing device 1 is started, and a laser beam LB having a wavelength that is transparent to the wafer 10 is emitted from a laser oscillator (not shown) provided in the laser beam irradiation unit 50 from the back side 10b of the wafer 10, and the focal point is positioned at a specified height position inside the wafer 10 via the condenser 52, and the laser beam LB is irradiated along the predetermined dividing line 12, so that the chuck table 24 moves in the X-axis direction indicated by the arrow X at a specified processing feed speed. In addition, the laser beam irradiation unit 50, the X-axis feed mechanism 31 for moving the chuck table 24, the Y-axis feed mechanism 32, the rotation unit (not shown) for rotating the chuck table 24, etc. are controlled, such as Figure 4 As shown in (b) and (c) of FIG. 1 , the reformed layer 100 and the crack 102 serving as the starting point of division are formed along all the planned division lines 12 on the wafer 10. The division starting point forming step is completed as described above.

[0034] In addition, the laser processing conditions performed in the above-mentioned division starting point forming step are set as follows, for example.

[0035]

[0036]

[0037] (Separation process)

[0038] After the division starting point forming step is completed as described above, a division step is performed to grind the back surface of the wafer 10 to thin the wafer 10 and to divide the wafer 10 into individual device chips 14 ′. Figure 5 A more specific description will be given.

[0039] When the division starting point forming step is completed, the wafer 10 is unloaded from the chuck table 24 of the laser processing device 1 and transported to the Figure 5The grinding device 6 shown in (a) (the whole view is omitted) places the chip 10 on a chuck table 61 of the grinding device 6 with the back side 10b of the chip 10 exposed upward, and the suction force of the suction unit (not shown) acts on the holding surface of the chuck table 61 to attract and hold the chip 10.

[0040] like Figure 5 As shown in (a), the grinding device 6 has a grinding unit 60 for grinding and thinning the wafer 10 placed on a chuck table 61. The grinding unit 60 has: a rotating spindle 62, which is rotated by a rotating drive mechanism (not shown); a mounting seat 63, which is mounted on the lower end of the rotating spindle 62; and a grinding wheel 64, which is mounted on the lower surface of the mounting seat 63, and a plurality of grinding tools 65 are arranged in an annular shape on the lower surface of the grinding wheel 64.

[0041] When the wafer 10 is held by suction on the chuck table 61 as described above, the rotating spindle 62 is rotated in the Figure 5 The chuck table 61 is rotated in the direction indicated by the arrow R1 in (a), for example, at 3000 rpm, and the chuck table 61 is rotated in the direction indicated by the arrow R1 in (a). Figure 5 The grinding tool 65 is rotated in the direction indicated by the arrow R2 in (a) at, for example, 300 rpm. Then, the grinding tool 65 is brought into contact with the back surface 10b of the wafer 10 and is fed downward, i.e., perpendicularly to the chuck table 61, at a grinding feed rate of, for example, 1 μm / sec. At this time, the thickness of the wafer 10 can be measured by a measuring instrument (not shown) while grinding. Figure 5 As shown in (b), the back side 10b of the wafer 10 is ground until the modified layer 100 is removed (for example, the thickness of the wafer 10 becomes 60 μm), forming a dividing line 110 that completely divides the wafer 10 into individual device chips 14'. As described above, the wafer 10 is ground in a state where the modified layer 100 and the cracks 102 are formed along all the predetermined dividing lines 12. Therefore, the result of grinding until the thickness reaches the above-mentioned thickness is that the wafer 10 can be appropriately divided into individual device chips 14' without damaging the quality, and the dividing process is completed (refer to Figure 5 (c)). When the separation step is completed, the wafer 10 is transported to a step of picking up individual device chips 14' while being held by the protective tape 16.

[0042] In this embodiment, if Figure 4As shown in (b), the chuck table 24 is provided with a heating unit 30, and the adsorption chuck 26 is heated to 80°C, so that the crack 102 is well formed from the modified layer 100 formed by irradiation with the laser beam LB to the bottom. It is presumed that this is because the wafer 10 and the protective tape 16 are heated by the chuck table 24, so that the contraction force of the protective tape 16 is released by heating, and an environment is formed in which the crack 102 is easily grown from the modified layer 100 to the front surface 10a side when the modified layer 100 is formed inside the wafer 10 by the laser beam LB. In this way, according to the method of heating the protective tape 16 attached to the wafer 10 in coordination with the irradiation with the laser beam LB, the crack 102 can be well grown compared with the case where the wafer 10 is heated after the modified layer 100 is formed in the wafer 10 in an unheated state. In addition, the temperature when the chuck table 24 is heated is not limited to the above-mentioned 80°C, and can be appropriately adjusted in consideration of the raw materials or thickness of the wafer 10 and the protective tape 16. The temperature at this time is preferably set between 40°C and 120°C.

Claims

1. A method for processing a wafer, wherein a wafer having a plurality of devices formed on a front surface thereof is divided by a plurality of intersecting predetermined dividing lines into individual device chips, wherein: The wafer processing method has the following steps: A protective tape placement step of placing a protective tape on the front side of the wafer; A wafer holding step of holding the wafer with the protective tape side facing a chuck table for holding and heating the wafer, so that the back side of the wafer is exposed; a splitting starting point forming step, after the wafer holding step is performed, positioning a focal point of a laser beam having a wavelength that is transparent to the wafer from the back side of the wafer to a predetermined interior and irradiating the wafer with the laser beam, thereby forming a splitting starting point consisting of a modified layer and a crack extending from the modified layer to the front side along a predetermined splitting line; as well as A dividing step, after the dividing starting point forming step is performed, the back side of the wafer is ground by a grinding wheel having a plurality of grinding tools in an annular shape to thin the wafer and divide the wafer into individual device chips. In the splitting starting point forming process, before irradiating the laser light, the chip and the protective tape are heated to a specified temperature by heating the chuck worktable, so that the contraction force of the protective tape is released due to the heating, forming an environment in which it is easy for the crack to grow from the modified layer formed inside the chip to the front side when the modified layer is formed inside the chip by the laser light.

2. The wafer processing method according to claim 1, wherein: In the division starting point forming step, the predetermined temperature is 40°C to 120°C.

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