Wafer processing method

Abstract

To provide a wafer processing method with which it is possible to prevent damage to a dicing tape even when irradiating a wafer with a laser beam and forming dividing grooves leading from the surface to the reverse side of the wafer.SOLUTION: The wafer processing method includes: a liquid resin coating step for coating a reverse side 2b of a wafer 2 with a liquid resin that solidifies upon irradiation with an ultraviolet ray; a semi-solidified resin layer formation step for forming a semi-solidified layer 8' by irradiating with an ultraviolet ray to the extent that the liquid resin is semi-solidified; a wafer unit formation step for forming a wafer unit U by fastening a dicing tape 12 to the semi-solidified layer 8' and a frame 10 under pressure; a division step for irradiating a planned division line 4 with a laser beam LB of an ultraviolent wavelength which is absorbable to the wafer 2 and dividing the wafer 2 into individual chips by ablation processing; a resin layer solidification step for irradiating the semi-solidified layer 8' side with an ultraviolet ray and solidifying the semi-solidified layer 8'; and a pickup step for picking up the chips from the solidified resin layer.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for processing a wafer.

Background Art

[0002] A wafer on which a plurality of devices such as ICs and LSIs are partitioned by a dicing line and formed on the surface is divided into individual device chips by a dicing device or a laser processing device, and each divided device chip is used in an electric device such as a mobile phone or a personal computer.

[0003] The laser processing device includes a chuck table for holding a wafer and a laser beam irradiation means for irradiating a laser beam having an absorbable wavelength onto the wafer held on the chuck table along the dicing line to perform ablation processing, and the wafer can be divided into individual device chips (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when the wafer is positioned in the opening of a frame having an opening for accommodating the wafer at the center, and the wafer and the frame are integrated with a dicing tape and the wafer is irradiated with a laser beam to form a dicing groove extending from the front surface to the back surface of the wafer to divide the wafer into individual chips, the dicing tape may be damaged by the irradiation of the laser beam. In such a case, there is a problem that the dicing tape breaks when the dicing tape is extended to pick up the chips.

[0006] In view of the above facts, an object of the present invention is to provide a method for processing a wafer capable of preventing damage to a dicing tape even when a wafer is irradiated with a laser beam to form a dividing groove extending from the front surface to the back surface of the wafer.

Means for Solving the Problems

[0007] According to the present invention, there is provided a method for processing a wafer for solving the above problems. That is, "A method for processing a wafer, comprising: a liquid resin coating step of coating the back surface of the wafer with a liquid resin that cures by irradiation with ultraviolet rays; a semi-cured resin layer forming step of irradiating the liquid resin coated on the back surface of the wafer with ultraviolet rays to the extent that the liquid resin is semi-cured to form a semi-cured resin layer; a wafer unit forming step of positioning the wafer in the opening of a frame having an opening at the center for accommodating the wafer and pressing a dicing tape against the semi-cured resin layer of the wafer and the frame to form a wafer unit; a dividing step of irradiating the wafer with a laser beam having an ultraviolet wavelength that is absorbable by the wafer on a dividing planned line and dividing the wafer into individual chips by ablation processing; a resin layer curing step of irradiating the semi-cured resin layer side of the wafer with ultraviolet rays through the dicing tape to cure the semi-cured resin layer; a pickup step of picking up the chips from the cured resin layer; and a method for processing a wafer including the above steps."

[0008] Preferably, a protective film coating step of coating a protective film on the front surface of the wafer is performed before the dividing step, in which a plurality of devices are partitioned by dividing planned lines and formed on the front surface of the wafer.

Advantages of the Invention

[0009] The method for processing a wafer of the present invention includes a liquid resin coating step of coating the back surface of the wafer with a liquid resin that cures by irradiation with ultraviolet rays; A semi-cured resin layer forming step of irradiating ultraviolet rays to the extent that the liquid resin coated on the back surface of the wafer semi-cures to form a semi-cured resin layer; A wafer unit forming step of positioning the wafer in the opening of a frame having an opening for accommodating the wafer at the center and pressing a dicing tape onto the semi-cured resin layer of the wafer and the frame to form a wafer unit; A dividing step of irradiating a laser beam having an ultraviolet wavelength that is absorbable by the wafer onto a planned dividing line and dividing the wafer into individual chips by ablation processing; A resin layer curing step of irradiating ultraviolet rays to the semi-cured resin layer side of the wafer through the dicing tape to cure the semi-cured resin layer; A pick-up step of picking up the chips from the cured resin layer; Since it includes the above, even if the wafer is irradiated with a laser beam to form a dividing groove from the front surface to the back surface of the wafer, damage to the dicing tape can be prevented.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0011] Hereinafter, a preferred embodiment of the method for processing a wafer according to the present invention will be described with reference to the drawings.

[0012] (Wafer) In FIG. 1(a), a disk-shaped wafer 2 to be processed by the processing method of the present invention is shown. The wafer 2 can be formed from an appropriate semiconductor material such as silicon (Si) or silicon carbide (SiC). The surface 2a of the wafer 2 is partitioned into a plurality of rectangular regions by grid-shaped division planned lines 4, and devices 6 such as ICs and LSIs are formed in each of the plurality of rectangular regions.

[0013] (Liquid resin coating step) In the illustrated embodiment, first, a liquid resin coating step of coating the back surface 2b of the wafer 2 with a liquid resin that cures by ultraviolet irradiation is performed.

[0014] In the liquid resin coating step, as shown in FIG. 1(b), the back surface 2b of the wafer 2 is turned upward, and a liquid resin 8 that cures by ultraviolet irradiation is dropped onto the central portion of the back surface 2b. Next, the wafer 2 is rotated in the direction indicated by the arrow R1, and the liquid resin 8 is caused to flow by centrifugal force. As a result, as shown in FIG. 1(c), the back surface 2b of the wafer 2 can be coated with the liquid resin 8 with a substantially uniform thickness.

[0015] (Semi-cured resin layer forming step) After performing the liquid resin coating step, as shown in FIG. 2(a), ultraviolet rays UV are irradiated onto the liquid resin 8 side to the extent that the liquid resin 8 coated on the back surface 2b of the wafer 2 semi-cures, and a semi-cured resin layer forming step of forming a semi-cured resin layer 8' shown in FIG. 2(b) is performed.

[0016] The semi-cured resin layer 8' refers to a resin layer that has cured more than before the irradiation of the ultraviolet rays UV but has not completely cured and still has adhesiveness. When the liquid resin 8 is completely cured, the adhesiveness of the resin layer is lost.

[0017] (Wafer unit forming step) After performing the semi-cured resin layer forming step, the wafer 2 is positioned in the opening of a frame having an opening for accommodating the wafer 2 at the center, and a dicing tape is pressure-bonded to the semi-cured resin layer 8' of the wafer 2 and the frame to form a wafer unit. The wafer unit forming step is performed.

[0018] In the wafer unit forming step, as shown in FIG. 3, an annular frame 10 having a circular opening 10a for accommodating the wafer 2 at the center and a circular dicing tape 12 that is permeable to ultraviolet rays and has been previously pressure-bonded can be used. Then, the wafer 2 is positioned in the opening 10a, and the semi-cured resin layer 8' of the wafer 2 is pressure-bonded to the dicing tape 12. Thereby, a wafer unit U including the wafer 2, the frame 10, and the dicing tape 12 can be formed.

[0019] The dicing tape 12 used in the wafer unit forming step may be an adhesive tape having an adhesive layer (paste layer) laid on one side of a sheet, or a thermocompression bonding tape having no adhesive layer laid on the sheet. The thermocompression bonding tape is a tape made of a thermoplastic synthetic resin (for example, a polyolefin-based resin), and when heated to a temperature near the melting point, it softens or melts and exhibits adhesive force.

[0020] When using a thermocompression bonding tape as the dicing tape 12, it is necessary to heat the thermocompression bonding tape to a temperature near the melting point when pressure-bonding the thermocompression bonding tape to the frame 10. However, when pressure-bonding the thermocompression bonding tape to the semi-cured resin layer 8' of the wafer 2, since the semi-cured resin layer 8' has adhesiveness, the semi-cured resin layer 8' can be pressure-bonded to the thermocompression bonding tape without heating the thermocompression bonding tape.

[0021] (Protective film coating step) In the illustrated embodiment, after performing the wafer unit forming step, a protective film coating step of coating the surface 2a of the wafer 2 with a protective film is performed.

[0022] Referring to FIG. 4, in the protective film coating step, the surface 2a of the wafer 2 is turned upward, and the liquid resin 14 is dropped onto the central portion of the surface 2a. The liquid resin 14 may be a water-soluble resin (for example, polyvinyl alcohol) that solidifies over time. Next, the wafer unit U is rotated in the direction indicated by the arrow R2, and the liquid resin 14 is caused to flow by centrifugal force. As a result, the protective film made of the liquid resin 14 can be coated on the surface 2a of the wafer 2 with a substantially uniform thickness. In FIG. 5(b), the protective film in which the liquid resin 14 has solidified is indicated by reference numeral 14'.

[0023] (Dicing step) After performing the protective film coating step, a dicing step is performed in which the wafer 2 is irradiated with a laser beam having an ultraviolet wavelength and having absorbency on the dicing planned line 4, and the wafer 2 is diced into individual chips by ablation processing.

[0024] The dicing step can be performed, for example, using a laser processing apparatus 16 partially shown in FIG. 5(a). The laser processing apparatus 16 includes a chuck table (not shown) that sucks and holds the wafer 2, and a condenser 18 that irradiates the wafer 2 sucked and held on the chuck table with a pulsed laser beam LB.

[0025] In the dicing step, first, the surface 2a (the side of the protective film 14') of the wafer 2 is turned upward, and the wafer 2 is sucked and held on the upper surface of the chuck table. Next, the wafer 2 is imaged from above by an imaging means (not shown) of the laser processing apparatus 16, and based on the image of the wafer 2 imaged by the imaging means, the dicing planned line 4 is aligned in the X-axis direction. When the protective film 14' coated on the surface 2a of the wafer 2 is not transparent, the dicing planned line 4 can be imaged through the protective film 14' by using an infrared camera. Next, the aiming of the pulsed laser beam LB is aligned with the dicing planned line 4 aligned in the X-axis direction, and the height of the focus point of the pulsed laser beam LB is adjusted to the surface 2a of the wafer 2.

[0026] Note that the X-axis direction is the direction indicated by arrow X in Fig. 5(a). The Y-axis direction indicated by arrow Y in Fig. 5(a) is a direction perpendicular to the X-axis direction. Further, the XY plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.

[0027] Next, while the chuck table is processed and fed in the X-axis direction at a predetermined feed rate with respect to the condenser 18, the wafer 2 is irradiated with a pulsed laser beam LB of ultraviolet light having absorbability from the condenser 18, and the wafer 2 is subjected to ablation processing. Thereby, a dicing groove 20 extending from the front surface 2a to the back surface 2b of the wafer 2 can be formed along the dicing planned line 4.

[0028] In the illustrated embodiment, as shown in Fig. 5(b), since a semi-cured resin layer 8' in which a liquid resin 8 that absorbs ultraviolet rays is semi-cured is formed between the back surface 2b of the wafer 2 and the dicing tape 12, even if the dicing groove 20 extending from the front surface 2a to the back surface 2b of the wafer 2 is formed and the wafer 2 is completely cut, the pulsed laser beam LB having an ultraviolet wavelength is absorbed by the semi-cured resin layer 8', and the pulsed laser beam LB is blocked by the semi-cured resin layer 8'. Therefore, in the illustrated embodiment, the depth of the dicing groove 20 can be suppressed to reach the semi-cured resin layer 8', and the dicing groove 20 can be prevented from reaching the dicing tape 12, and damage to the dicing tape 12 due to irradiation with the pulsed laser beam LB can be prevented.

[0029] Note that debris is generated when ablation processing is performed, but the generated debris is blocked by the protective film 14', so that it does not adhere to the front surface 2a of the wafer 2.

[0030] Next, the chuck table is indexed and fed in the Y-axis direction with respect to the condenser 18 by the interval in the Y-axis direction of the dicing planned line 4. Then, by alternately repeating the irradiation with the pulsed laser beam LB and the indexed feed, ablation processing is performed on all of the dicing planned lines 4 aligned in the X-axis direction.

[0031] Also, after rotating the chuck table by 90 degrees, by alternately repeating the irradiation of the pulsed laser beam LB and the indexing feed, ablation processing is also performed on all of the planned division lines 4 that are orthogonal to the previously ablated planned division line 4. In this way, division grooves 20 are formed along the grid-like planned division lines 4, and the wafer 2 is divided into individual device chips.

[0032] Such a division process can be carried out, for example, under the following processing conditions. Wavelength of pulsed laser beam: 355 nm Repetition frequency: 50 kHz Average output: 3 W Processing feed rate: 100 mm / s

[0033] (Protective film removal process) After performing the division process, a protective film removal process is carried out to remove the protective film 14' coated on the surface 2a of the wafer 2. When the protective film 14' is a water-soluble resin as in the illustrated embodiment, the protective film 14' can be washed away with water. When the protective film 14' is washed away, the debris generated during the ablation process (the debris adhering to the protective film 14') is also washed away together with the protective film 14'. Therefore, no debris remains on the surface 2a of the wafer 2.

[0034] (Resin layer curing process) After performing the protective film removal process, as shown in FIG. 6, a resin layer curing process is carried out by irradiating ultraviolet rays UV onto the semi-cured resin layer 8' side of the wafer 2 through the dicing tape 12 to cure the semi-cured resin layer 8'. As described above, when the semi-cured resin layer 8' is completely cured, the adhesiveness is lost, so it becomes easier to pick up the individual device chips 6' from the cured resin layer.

[0035] (Pick-up process) After performing the resin layer curing process, a pick-up process is carried out to pick up the device chips 6' from the cured resin layer.

[0036] The picking-up process can be carried out, for example, using the picking-up device 22 shown in FIG. 7. The picking-up device 22 includes an expanding means 24 for expanding the dicing tape 12 to increase the spacing between adjacent device chips 6', and a collet 26 for adsorbing and transporting the device chips 6'. The collet 26 is connected to a suction means (not shown) and is adapted to adsorb the device chip 6' on the lower surface of its tip.

[0037] The expanding means 24 includes a cylindrical drum 28, a pushing-up means 30 disposed inside the drum 28 for pushing up the device chip 6', and an annular holding member 32 disposed on the outer periphery of the drum 28. A plurality of clamps 34 are arranged at intervals in the circumferential direction on the outer peripheral edge of the holding member 32.

[0038] In the picking-up process, first, the divided wafer 2 is placed upward, and the frame 10 is placed on the upper surface of the holding member 32. Next, the frame 10 is fixed by a plurality of clamps 34. Then, the holding member 32 is lowered to apply a radial tension to the dicing tape 12. Then, as shown by the two-dot chain line in FIG. 7, the spacing between the device chips 6' on the dicing tape 12 is increased. As described above, since the dividing groove 20 formed in the dividing process does not reach the dicing tape 12, the dicing tape 12 will not break even when it is expanded.

[0039] Next, the collet 26 is positioned above the device chip 6' to be picked up, and the pushing-up means 30 is positioned below the device chip 6' to be picked up. Then, the device chip 6' is pushed up by the pushing-up means 30, and the collet 26 is lowered to adsorb the device chip 6' on the lower surface of the tip of the collet 26. Then, the collet 26 is raised to pick up the device chip 6'. Next, the picked-up device chip 6' is transported to a predetermined transport position such as a tray. And such picking-up operations are sequentially performed for all the device chips 6'.

[0040] As described above, in the method for processing a wafer according to the illustrated embodiment, even if the wafer 2 is irradiated with the pulsed laser beam LB to form the dividing groove 20 extending from the front surface 2a to the back surface 2b of the wafer 2, the depth of the dividing groove 20 can be suppressed to reach the semi-cured resin layer 8', and the dividing groove 20 can be prevented from reaching the dicing tape 12. Therefore, in the illustrated embodiment, even if the dividing groove 20 is formed by irradiating the pulsed laser beam LB, damage to the dicing tape 12 can be prevented. For this reason, in the pickup process, even if the dicing tape 12 is expanded, the dicing tape 12 will not break.

Explanation of Signs

[0041] 2: Wafer 2a: Front surface of the wafer 2b: Back surface of the wafer 4: Predetermined dividing line 6: Device 6’: Device chip 8: Liquid resin 8’: Semi-cured resin layer 10: Frame 10a: Opening of the frame 12: Dicing tape 14’: Protective film U: Wafer unit LB: Laser beam

Claims

1. A method for processing a wafer, comprising: a liquid resin coating step of coating the back surface of the wafer with a liquid resin that solidifies upon irradiation with ultraviolet light; a semi-cured resin layer forming step of irradiating the liquid resin coated on the back surface of the wafer with ultraviolet light to such an extent that the liquid resin is semi-cured to form a semi-cured resin layer; a wafer unit forming step of positioning the wafer in the opening of a frame having an opening for accommodating the wafer at the center and pressing a dicing tape onto the semi-cured resin layer of the wafer and the frame to form a wafer unit; a dividing step of irradiating a laser beam having an ultraviolet wavelength that is absorbable by the wafer onto a planned dividing line and dividing the wafer into individual chips by ablation processing; a resin layer curing step of irradiating the semi-cured resin layer side of the wafer with ultraviolet light through the dicing tape to cure the semi-cured resin layer; a pick-up step of picking up the chips from the cured resin layer; A method for processing a wafer, including the above steps.

2. The method for processing a wafer according to claim 1, wherein a plurality of devices are formed on the surface of the wafer partitioned by planned dividing lines, and before the dividing step, a protective film coating step of coating a protective film on the surface of the wafer is performed.

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