Wafer processing method

Abstract

To provide a wafer processing method that can remove a chamfered part without generating cracks in a wafer and grind the rear face of the wafer to have a desired finished thickness.SOLUTION: A wafer processing method includes: a removing step of irradiating an area from the boundary between a device area 8 and an outer peripheral excess area 10 up to the outer periphery of a wafer 2 with a laser beam LB with a wavelength having absorbency for the wafer 2 from the side of a front face 2a of the wafer 2, and removing the outer peripheral excess area 10 to a depth corresponding to a finished thickness of the wafer 2; a protective member disposing step of disposing a protective member on the front face 2a of the wafer 2; and a rear face grinding step of holding the side of the protective member on a chuck table, and grinding a rear face 2b of the wafer 2 until the finished thickness is obtained.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a wafer processing method for grinding the back surface of a wafer having, on its front surface, a device region in which a plurality of devices are partitioned by planned division lines and a peripheral excess region surrounding the device region. [Background technology]

[0002] A wafer has, on its surface, a device area where multiple devices such as ICs and LSIs are partitioned by planned division lines, and a peripheral excess area surrounding the device area.The back surface of the wafer is ground to a finished thickness, and then the wafer is divided into individual device chips using a dicing machine and a laser processing machine.Each of the divided device chips is used in electrical equipment such as mobile phones and personal computers.

[0003] When the back surface of a wafer is ground, a knife edge is formed in the chamfered portion formed in the peripheral excess region of the wafer, and there is a risk that the knife edge will cause cracks in the device region and damage the wafer. Therefore, a technique has been proposed in which the chamfered portion is removed with a cutting blade before the back surface of the wafer is ground (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-173961 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in wafers that have a structure in which a semiconductor substrate and a semiconductor layer made of a material different from that of the substrate are stacked on the surface of the semiconductor substrate, there is a problem in that when the chamfered portion of the wafer is removed with a cutting blade, cracks are generated and the device region is damaged.

[0006] Furthermore, the above-mentioned problems can occur even with a general wafer having a passivation film, a low-k film, etc. laminated on the surface of the wafer.

[0007] An object of the present invention is to provide a wafer processing method that can remove a chamfered portion and grind the back surface of the wafer to a desired thickness without generating cracks in the wafer. [Means for solving the problem]

[0008] According to the present invention, there is provided the following wafer processing method that solves the above-mentioned problems. "A wafer processing method for grinding the back surface of a wafer having a device area, in which a plurality of devices are partitioned by planned division lines, and a peripheral excess area surrounding the device area, formed on the front surface, a removing step of irradiating a laser beam having a wavelength absorbed by the wafer from the front surface side of the wafer onto an area extending from the boundary between the device area and the peripheral excess area to the outer periphery of the wafer, thereby removing the peripheral excess area to a depth corresponding to the finished thickness of the wafer; a protective member providing step of providing a protective member on the surface of the wafer; a backside grinding step in which the protective member side of the wafer is held on a chuck table and the backside of the wafer is ground to a finished thickness; Including fruit, In the removal step, when a laser beam is irradiated onto the area from the boundary to the outer periphery of the wafer, a circular motion is given to the focal point of the laser beam. A wafer processing method is provided.

[0009] cormorant The wafer preferably has a two-layer structure in which a gallium nitride layer or a silicon carbide layer is laminated on top of a silicon substrate. [Effects of the Invention]

[0010] In the wafer processing method of the present invention, a removing step of irradiating a laser beam having a wavelength absorbed by the wafer from the front surface side of the wafer onto an area extending from the boundary between the device area and the peripheral excess area to the outer periphery of the wafer, thereby removing the peripheral excess area to a depth corresponding to the finished thickness of the wafer; a protective member providing step of providing a protective member on the surface of the wafer; a backside grinding step in which the protective member side of the wafer is held on a chuck table and the backside of the wafer is ground to a finished thickness; Including fruit, In the removal step, when a laser beam is irradiated onto the area from the boundary to the outer periphery of the wafer, a circular motion is given to the focal point of the laser beam. Therefore, the chamfered portion can be removed and the back surface of the wafer can be ground to a desired thickness without causing cracks in the wafer. [Brief explanation of the drawings]

[0011] [Figure 1] (a) A perspective view of the wafer, (b) A side view of the wafer shown in (a). [Figure 2] FIG. [Figure 3] Schematic diagram showing a groove forming step. [Figure 4] (a) A perspective view of a wafer in which a laser-processed groove is formed at the boundary between the device region and the peripheral excess region, and (b) a cross-sectional view of the wafer shown in (a). [Figure 5] (a) Schematic diagram showing the outer periphery excess region removing step, (b) Plan view of the wafer in the outer periphery excess region removing step, (c) Enlarged view of part C in (b). [Figure 6] FIG. 10 is a perspective view of a wafer from which the peripheral excess region has been removed to a depth corresponding to the finished thickness, and FIG. 10 is a side view of the wafer shown in FIG. [Figure 7] Schematic diagram showing a protective member disposing step. [Figure 8] FIG. 2 is a schematic diagram showing a state in which a wafer is placed on a chuck table. [Figure 9] FIG. [Figure 10] (a) Schematic diagram at the start of the back grinding process, (b) Schematic diagram at the end of the back grinding process. [Figure 11] FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, preferred embodiments of the wafer processing method of the present invention will be described with reference to the drawings.

[0013] (Wafer 2) Fig. 1 shows a disk-shaped wafer 2 to be processed by the processing method of the present invention. A device region 8, in which a plurality of devices 4 are partitioned by planned division lines 6, and a peripheral surplus region 10 surrounding the device region 8 are formed on the surface 2a of the wafer 2. In Fig. 1(a), for convenience, a boundary 12 between the device region 8 and the peripheral surplus region 10 is shown by a two-dot chain line, but in reality, there is no line indicating the boundary 12. As shown in Fig. 1(b), a chamfered portion 14 is formed in the peripheral surplus region 10 of the wafer 2.

[0014] Although not shown, the wafer 2 has a two-layer structure in which a gallium nitride layer or a silicon carbide layer is laminated on the upper surface of a silicon substrate. However, the wafer 2 may have a passivation film, a low-k film, or the like laminated on the surface 2a.

[0015] (Protective film coating process) In the illustrated embodiment, first, a protective film coating step is performed to coat the front surface 2a of the wafer 2 with a protective film.

[0016] Referring to FIG. 2, in the protective film coating process, the front surface 2a of the wafer 2 is faced upward, and liquid resin 16 is dropped onto the center of the front surface 2a. The liquid resin 16 may be a water-soluble resin (e.g., polyvinyl alcohol) that solidifies over time. Next, the wafer 2 is rotated in the direction indicated by arrow R1, and the liquid resin 16 is caused to flow by centrifugal force. This allows a protective film made of the liquid resin 16 to be coated on the front surface 2a of the wafer 2 with a substantially uniform thickness. In FIG. 4(b), the protective film made of the solidified liquid resin 16 is indicated by the reference symbol 16'.

[0017] (Removal process) After the protective film coating process is performed, a removal process is performed in which a laser beam having a wavelength that is absorbed by the wafer 2 is irradiated from the front surface 2a side of the wafer 2 onto the area from the boundary 12 between the device region 8 and the peripheral excess region 10 to the outer periphery of the wafer 2, thereby removing the peripheral excess region 10 to a depth corresponding to the finished thickness of the wafer 2.

[0018] In the removal process of the illustrated embodiment, first, a groove forming step is performed in which a laser processed groove having a depth corresponding to the finished thickness of the wafer 2 is formed in the boundary 12 .

[0019] The groove forming step can be performed using, for example, a laser processing device 18, a portion of which is shown in Fig. 3. The laser processing device 18 includes a chuck table (not shown) that holds the wafer 2 by suction, and a condenser 20 that irradiates the wafer 2 held by suction on the chuck table with a pulsed laser beam LB.

[0020] In the groove forming step, first, the wafer 2 is suction-held on the upper surface of the chuck table with the front surface 2a (protective film 16' side) of the wafer 2 facing upward. Next, the imaging means (not shown) of the laser processing device 18 images the wafer 2 from above, and the positional relationship between the wafer 2 and the condenser 20 is adjusted based on the image of the wafer 2 captured by the imaging means. At this time, the pulsed laser beam LB is aimed at the boundary 12 between the device region 8 and the outer peripheral surplus region 10, and the height of the focal point of the pulsed laser beam LB is adjusted to the front surface 2a of the wafer 2.

[0021] If the protective film 16' covering the front surface 2a of the wafer 2 is not transparent, an infrared camera can be used to capture an image of the front surface 2a of the wafer 2 through the protective film 16'.

[0022] Next, while the chuck table is rotated at a predetermined rotation speed in the direction indicated by arrow R2 in Fig. 3, a pulsed laser beam LB having a wavelength that is absorbed by the wafer 2 is irradiated from a condenser 20 to perform ablation processing on the wafer 2. As a result, as shown in Fig. 4, a laser-processed groove 22 having a depth corresponding to the finished thickness can be formed in the wafer 2 along the boundary 12 between the device region 8 and the peripheral excess region 10.

[0023] The laser processed grooves 22 are formed by ablation processing, and therefore have walls that are melted and re-solidified, resulting in high strength. Although the ablation processing generates debris, the generated debris is blocked by the protective film 16' and does not adhere to the front surface 2a of the wafer 2.

[0024] Such a groove forming step can be carried out, for example, under the following processing conditions. Pulse laser beam wavelength: 355nm Average power: 3W Diameter of the focal point: φ10μm Repetition frequency: 50kHz Feed speed: 100mm / s (chuck table rotation speed)

[0025] After the groove forming step, a peripheral excess area removing step is performed in which the peripheral excess area 10 partitioned by the laser processed groove 22 is removed to a depth corresponding to the finished thickness of the wafer 2.

[0026] The peripheral excess region removing step can be performed using, for example, a laser processing device 24, a portion of which is shown in Fig. 5(a) . The laser processing device 24 includes a chuck table (not shown) that suction-holds the wafer 2, an oscillator 26 that oscillates a pulsed laser beam LB having a wavelength that is absorbed by the wafer 2, and a two-dimensional galvano scanner 28 that oscillates the pulsed laser beam LB oscillated by the oscillator 26.

[0027] In the peripheral excess region removal step, first, the wafer 2 is suction-held on the upper surface of the chuck table with the front surface 2a of the wafer 2 facing upward. Next, the imaging means (not shown) of the laser processing device 24 images the wafer 2 from above, and the positional relationship between the wafer 2 and the two-dimensional galvano scanner 28 is adjusted based on the image of the wafer 2 captured by the imaging means. At this time, the pulsed laser beam LB is aimed at the peripheral excess region 10 partitioned by the laser-processed groove 22, and the height of the focal point of the pulsed laser beam LB is adjusted to the front surface 2a of the wafer 2.

[0028] Next, the chuck table is rotated in the direction R3 at a predetermined rotation speed. Then, a pulsed laser beam LB having a wavelength absorbable by the wafer 2 is irradiated onto the region from the boundary 12 between the device region 8 and the peripheral excess region 10 to the outer periphery of the wafer 2 while being oscillated by the two-dimensional galvano scanner 28, thereby performing ablation processing.

[0029] In the outer periphery excess region removing step, when the pulsed laser beam LB is irradiated onto the region extending from the boundary 12 where the laser-processed groove 22 is formed to the outer periphery of the wafer 2, it is preferable to impart a circular motion to the focal point of the pulsed laser beam LB. Examples of laser processing marks 30 in this case are shown in Figures 5(b) and 5(c). By imparting a circular motion to the focal point of the pulsed laser beam LB, the pulsed laser beam LB can be efficiently irradiated onto the above region.

[0030] In this way, ablation is performed on the region from the boundary 12 where the laser-processed groove 22 is formed to the outer periphery of the wafer 2, and the outer periphery excess region 10 can be removed to a depth corresponding to the finished thickness of the wafer 2, as shown in Fig. 6. In the illustrated embodiment, the laser-processed groove 22 has a wall surface with high strength that has been melted and re-solidified, so that even if the outer periphery excess region 10 partitioned by the laser-processed groove 22 is removed, it is possible to prevent cracks from occurring in the device region 8. The processing conditions for the outer periphery excess region removal step may be the same as the processing conditions for the groove formation step.

[0031] The peripheral surplus region removing step is not limited to the above embodiment, and may be performed using the laser processing device 18 used in the groove forming step. That is, the peripheral surplus region 10 may be removed to a depth corresponding to the finished thickness of the wafer 2 by repeating ablation processing in a ring shape along the laser-processed groove 22 using the laser processing device 18.

[0032] (Protective film removal process) After the removal step is performed, a protective film removal step is performed to remove the protective film 16' coated on the front surface 2a of the wafer 2. When the protective film 16' is a water-soluble resin as in the illustrated embodiment, the protective film 16' can be washed away with water. Furthermore, by washing away the protective film 16' with water, debris (debris adhering to the protective film 16') generated during the ablation processing in the removal step can also be washed away.

[0033] (Protective member installation process) After the protective film removing step is performed, a protective member providing step is performed in which a protective member 32 is provided on the front surface 2a of the wafer 2, as shown in FIG.

[0034] The protective member 32 is a circular sheet having a diameter approximately equal to that of the device region 8. The protective member 32 may be an adhesive tape having an adhesive layer (glue layer) on one side of the sheet, or may be a thermocompression tape having no adhesive layer on the sheet. The thermocompression tape is a tape made of a thermoplastic synthetic resin (for example, a polyolefin resin), and when heated to a temperature near its melting point, it softens or melts and exhibits adhesive strength.

[0035] (Back grinding process) After the protective member providing step is performed, the protective member 32 side is held on a chuck table, and a back surface grinding step is performed in which the back surface 2b of the wafer 2 is ground until the wafer 2 has a finished thickness.

[0036] The backside grinding step can be performed using, for example, a grinding device 34, a portion of which is shown in Figures 8 and 9. The grinding device 34 includes a chuck table 36 that holds the wafer 2 by suction, and a grinding means 38 that grinds the wafer 2 held by suction on the chuck table 36.

[0037] 8, a circular porous suction chuck 40 connected to a suction means (not shown) is disposed on the upper end portion of the chuck table 36. The suction means generates a suction force on the upper surface of the suction chuck 40, so that the chuck table 36 suction-holds the wafer 2 placed on the upper surface of the suction chuck 40. The chuck table 36 is configured to be rotatable about an axis extending in the vertical direction.

[0038] 9, the grinding means 38 includes a spindle 42 configured to be rotatable about an axis extending in the vertical direction, and a disk-shaped wheel mount 44 fixed to the lower end of the spindle 42. An annular grinding wheel 48 is fastened to the lower surface of the wheel mount 44 by bolts 46. A plurality of grinding stones 50 are fixed to the outer periphery of the lower surface of the grinding wheel 48, and are arranged in an annular shape at intervals in the circumferential direction.

[0039] In the backside grinding process, first, as shown in Fig. 8, the wafer 2 is suction-held on the upper surface of the chuck table 36 with the backside 2b of the wafer 2 facing upward. Next, as shown in Fig. 9, the chuck table 36 is rotated in the R5 direction at a predetermined rotational speed (e.g., 300 rpm). Also, the spindle 42 is rotated in the R6 direction at a predetermined rotational speed (e.g., 6000 rpm).

[0040] 10(a), the spindle 42 is lowered by the lifting means (not shown) of the grinding device 34, and the grinding wheel 50 is brought into contact with the back surface 2b of the wafer 2, and grinding water is supplied to the portion of the back surface 2b of the wafer 2 where the grinding wheel 50 is to be brought into contact. After the grinding wheel 50 has been brought into contact with the back surface 2b of the wafer 2, the spindle 42 is lowered at a predetermined grinding feed rate (for example, 1.0 μm / s). This allows the back surface 2b of the wafer 2 to be ground down to the finished thickness, as shown in FIG. 10(b).

[0041] As described above, in the outer circumferential surplus region removing step, the outer circumferential surplus region 10 is removed to a depth corresponding to the finished thickness of the wafer 2, and therefore, in the back surface grinding step, the back surface 2b of the wafer 2 is ground down to the finished thickness, thereby removing the chamfered portion 14 formed in the outer circumferential surplus region 10. In the illustrated embodiment, the outer periphery of the device region 8 becomes a wall surface with high strength when the laser processed grooves 22 are formed, and therefore, the occurrence of cracks in the device region 8 can be prevented even in the back surface grinding step.

[0042] After the back surface grinding step is performed in this manner, the protective member 32 is peeled off from the front surface 2a of the wafer 2, as shown in FIG.

[0043] As described above, in the illustrated embodiment, the laser-processed grooves 22 having strong wall surfaces are formed by ablation processing, so that even if the peripheral excess region 10 partitioned by the laser-processed grooves 22 is removed and the back surface 2b of the wafer 2 is ground, it is possible to prevent cracks from occurring in the device region 8. Therefore, in the illustrated embodiment, the chamfered portion 14 can be removed and the back surface 2b of the wafer 2 can be ground to a desired thickness without causing cracks in the wafer 2. [Explanation of symbols]

[0044] 2: Wafer 2a: Surface of wafer 2b: Backside of wafer 4: Device 6: Planned division line 8: Device area 10: Surplus outer area 12: Boundary 22: Laser processed groove 32: Protective material 36: Chuck table LB: Laser beam

Claims

1. A wafer processing method for grinding a back surface of a wafer having a device region, in which a plurality of devices are partitioned by planned division lines, and a peripheral excess region surrounding the device region, formed on the front surface, comprising: a removing step of irradiating a laser beam having a wavelength absorbed by the wafer from the front surface side of the wafer onto an area extending from the boundary between the device area and the peripheral excess area to the outer periphery of the wafer, thereby removing the peripheral excess area to a depth corresponding to the finished thickness of the wafer; a protective member providing step of providing a protective member on the surface of the wafer; a backside grinding step in which the protective member side of the wafer is held on a chuck table and the backside of the wafer is ground to a finished thickness; Including, In the removing step, when a laser beam is irradiated onto the region from the boundary to the outer periphery of the wafer, a circular motion is imparted to the focal point of the laser beam.

2. 2. The wafer processing method according to claim 1, wherein the wafer has a two-layer structure in which a gallium nitride layer or a silicon carbide layer is laminated on the upper surface of a silicon substrate.

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