Wafer splitting method

Abstract

To reduce an amount of debris which is derived from a protective film and which adheres to the front surface side of a wafer when the wafer is divided.SOLUTION: There is provided a wafer dividing method of dividing a wafer along each of a plurality of projected dicing lines set in a grid pattern on a front surface of the wafer, each device being formed in each of a plurality of areas sectioned by the projected dicing lines. The wafer dividing method includes steps of: forming a division initiating point serving as an initiating point of division of the wafer along each of the projected dicing lines; adhering a protective film formed of an olefin-based resin and having one surface with no adhesive used therein to the wafer in such a manner that the one surface is brought into close contact with the front surface side of the wafer; supporting the wafer by a support table in such a manner that the front surface side of the wafer and the support table face each other; and applying an external force to the wafer from a back surface side of the wafer to thereby divide the wafer at the division initiating points.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for dividing a wafer having a plurality of planned division lines set in a grid pattern on its surface along each of the planned division lines.

Background Art

[0002] As a method for dividing wafers such as sapphire wafers and silicon wafers into individual chips, it is known to perform a scribing process and a breaking process on the wafer (see, for example, Patent Document 1).

[0003] Specifically, first, along a plurality of planned division lines set on one surface of the wafer, the one surface side of the wafer is scored with a scriber (also referred to as a scribing tool) such as a diamond needle (scribing process).

[0004] Thereafter, the wafer is supported by a support base so that the support base of the breaking device faces the one surface side of the wafer 11, and then an external force is applied to the wafer by pressing the blade of the breaking device against the other surface side of the wafer. By pressing the blade against each planned division line, the wafer is divided into a plurality of chips along each planned division line (breaking process).

[0005] Note that on one surface (front surface) side of the wafer, devices such as LEDs (Light Emitting Diodes) and ICs (Integrated Circuits) may be formed in each of a plurality of regions partitioned by a plurality of planned division lines arranged in a grid pattern.

[0006] In the breaking process, since the front surface of the wafer is disposed on the lower side, in order to reduce damage to the device in the breaking process, it is conceivable to cover the front surface side of the wafer with a resin protection film after the scribing process and before the breaking process. In the subsequent breaking process, the front surface side of the wafer is made to face the support base through the protection film. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2009-148982 [Overview of the project] [Problems that the invention aims to solve]

[0008] During the braking process, fine powdery debris may adhere to the wafer surface due to friction between the wafer surface and the protective film. For example, if the protective film is made of polyethylene terephthalate, friction between the wafer and the protective film can cause debris from the resin that makes up the protective film to adhere to the wafer surface.

[0009] This invention has been made in view of the aforementioned problems, and aims to reduce the amount of debris originating from the protective film that adheres to the surface side of the wafer when the wafer is divided. [Means for solving the problem]

[0010] According to one aspect of the present invention, a wafer is divided along each of the division lines, wherein a wafer has a plurality of division lines arranged in a grid pattern on its surface, and devices are formed in each of the plurality of regions partitioned by the plurality of division lines, the method comprising: a division starting point formation step of forming a division starting point along each division starting line, which has lower mechanical strength than the region in which the devices are formed and serves as the starting point for the division of the wafer; and after the division starting point formation step, the one side of a protective film made of an olefin resin and having one side without adhesive, is made circular boardA wafer splitting method is provided, comprising: a protective film adhesion step of pressing a protective film onto the surface side of the wafer with a shaped pressing body to make it adhere; a support step of supporting the wafer on a support table with the surface side of the wafer facing the support table after the protective film adhesion step; and a splitting step of applying an external force to the wafer from the back side of the wafer with one side of the protective film in close contact with the surface side of the wafer after the support step, thereby splitting the wafer from the splitting starting point.

[0011] Preferably, the support step involves supporting the wafer with an elastic support table.

[0012] Preferably, in the splitting starting point formation step, with the focal point of a pulsed laser beam having a wavelength that penetrates the wafer positioned inside the wafer, the focal point of the laser beam and the wafer are moved relative to each planned splitting line, thereby forming a modified layer that functions as the splitting starting point along each planned splitting line. [Effects of the Invention]

[0013] In a wafer splitting method according to one aspect of the present invention, after the splitting starting point formation step, one side of a protective film made of an olefin resin and having one side without an adhesive is brought into close contact with the surface side of the wafer (protective film adhesion step).

[0014] After the protective film adhesion step, a support step is performed, followed by a splitting step. The splitting step is performed with the protective film and the wafer surface in close contact. Therefore, friction between the protective film and the wafer can be reduced.

[0015] Furthermore, since the protective film is made of olefin resin, even if the protective film and the wafer rub against each other to some extent, the amount of debris originating from the protective film that adheres to the wafer surface can be reduced compared to when the protective film is made of relatively brittle polyethylene terephthalate.

Brief Description of the Drawings

[0016] [Figure 1] It is a flowchart showing a method for dividing a wafer. [Figure 2] It is a perspective view of a wafer unit. [Figure 3] It is a view showing a step of forming a division starting point. [Figure 4] It is a view showing a step of adhering a protective film. [Figure 5] It is a view showing a supporting step. [Figure 6] It is a view showing a dividing step.

Modes for Carrying Out the Invention

[0017] Referring to the accompanying drawings, embodiments according to an aspect of the present invention will be described. FIG. 1 is a flowchart showing a method for dividing a wafer 11 (see FIG. 2). First, the disk-shaped wafer 11 to be divided will be described.

[0018] FIG. 2 is a perspective view of a wafer unit 21 including the wafer 11. The wafer 11 is, for example, mainly formed of silicon and has a substantially circular front surface 11a and a back surface 11b, respectively.

[0019] The wafer 11 has, for example, a thickness of 75 μm (i.e., the distance from the front surface 11a to the back surface 11b) and a diameter of about 200 mm (8 inches). On the front surface 11a, a plurality of division planned lines 13 are set in a mutually orthogonal manner (i.e., in a grid pattern).

[0020] In each of the plurality of regions partitioned by the plurality of division planned lines 13, devices 15 such as ICs (Integrated Circuits) and LSIs (Large Scale Integrations) are formed. On the front surface 11a side, slight irregularities are formed due to the structure, shape, etc. of the devices 15.

[0021] Furthermore, the wafer 11 is not limited to silicon, but may be made of other compound semiconductors, sapphire, or glass. There are also no restrictions on the shape, structure, or size of the wafer 11, nor are there any particular restrictions on the type, quantity, shape, structure, size, or arrangement of the devices 15.

[0022] When dividing the wafer 11, a wafer unit 21 is formed in which the wafer 11 is supported by a metal annular frame 19 via a resin dicing tape 17. The dicing tape 17 is a circular tape having a diameter larger than the diameter of the wafer 11.

[0023] The dicing tape 17 has a laminated structure, for example, a base layer and an adhesive layer (glue layer). An adhesive layer made of an adhesive resin, such as an ultraviolet (UV) curing resin or a thermosetting resin, is formed on the entire surface of one side of the base layer.

[0024] A wafer 11 is attached to the approximate center of the dicing tape 17, and one side of the annular frame 19 is attached to the outer periphery of the dicing tape 17. After forming the wafer unit 21 in this manner, a splitting starting point is formed on the wafer 11 using a laser processing device 2 (splitting starting point formation step S10).

[0025] Next, with reference to Figure 3, the laser processing apparatus 2 used in the division starting point formation step S10 will be described. The laser processing apparatus 2 has a disc-shaped chuck table 4 having a substantially flat holding surface 4a. Negative pressure generated by a suction source (not shown), such as an ejector, is transmitted to the holding surface 4a.

[0026] A rotary drive source (not shown) is connected to the lower part of the chuck table 4, and the chuck table 4 is rotatable around a predetermined axis of rotation. A ball screw type machining feed mechanism (not shown) is provided at the lower part of the rotary drive source. The machining feed mechanism moves the chuck table 4 and the rotary drive source along the machining feed direction 6.

[0027] A ball screw type indexing feed mechanism (not shown) is provided at the bottom of the machining feed mechanism. The indexing feed mechanism moves the machining feed mechanism, the chuck table 4, and the rotary drive source together along the indexing feed direction which is perpendicular to the machining feed direction 6 in the horizontal plane.

[0028] Multiple clamping mechanisms 8 are provided on the side of the chuck table 4, along the circumferential direction of the chuck table 4. Each clamping mechanism 8 clamps the annular frame 19 when suction-holding the wafer 11 at the holding surface 4a via the dicing tape 17.

[0029] A head portion 12 of the laser beam irradiation unit 10 is provided above the holding surface 4a. The head portion 12 is equipped with a focusing lens (not shown), and the pulsed laser beam emitted from the laser oscillator (not shown) of the laser beam irradiation unit 10 is irradiated from the head portion 12 toward the holding surface 4a.

[0030] This pulsed laser beam 14 has a wavelength that penetrates the wafer 11. A microscope camera unit (not shown) having a predetermined optical system and image sensor for imaging the surface 11a is provided near the head unit 12.

[0031] Next, the division starting point formation step S10 will be described. Figure 3 shows the division starting point formation step S10. In the division starting point formation step S10, first, the back surface 11b side is held by suction on the holding surface 4a via the dicing tape 17, and the annular frame 19 is clamped by each clamping mechanism 8.

[0032] Then, on the surface 11a exposed above, two separate locations of one planned division line 13 are imaged with a microscope camera unit to perform alignment, and the rotation drive source is activated according to the alignment result to make one planned division line 13 approximately parallel to the processing feed direction 6.

[0033] Next, with the focal point 14a of the laser beam 14 positioned at a predetermined depth inside the wafer 11, the chuck table 4 is moved in the processing feed direction 6 relative to the focal point 14a so that the focal point 14a moves along one of the planned division lines 13.

[0034] In this way, by moving the focal point 14a and the wafer 11 relative to each other along a single planned splitting line 13, a modified layer (splitting starting point) 23 is formed on the wafer 11, which has lower mechanical strength than the region where the device 15 is formed and serves as the starting point for splitting the wafer 11. In the splitting starting point formation step S10, for example, the processing conditions are set as follows.

[0035] Laser beam wavelength: 1064nm Average output: 0.3W Pulse repetition frequency: 80kHz Machining feed rate: 300 mm / s Number of passes: 2

[0036] The number of passes refers to the number of times the laser beam 14 is irradiated along one planned division line 13. For example, in the first irradiation (i.e., the first pass), the focusing point 14a is positioned at a depth of approximately 50 μm from the surface 11a to form a modified layer 23 along one planned division line 13.

[0037] Next, in the second irradiation (i.e., the second pass), the focusing point 14a is positioned at a depth of approximately 25 μm from the surface 11a to form a modified layer 23 along the same planned division line 13. In this way, a modified layer 23 is formed at each of the different depths of the wafer 11 along the planned division line 13.

[0038] After forming a number of modified layers 23 corresponding to the number of passes along one planned division line 13, the chuck table 4 is indexed and fed by a predetermined length in the indexing feed direction to similarly form modified layers 23 along other planned division lines 13 adjacent to the said planned division line 13.

[0039] After forming the modified layer 23 along all the planned division lines 13 in one direction, the chuck table 4 is rotated 90 degrees to similarly form the modified layer 23 along all the planned division lines 13 in the other direction perpendicular to the first direction.

[0040] As the modified layer 23 is formed, cracks (not shown) are formed from the modified layer 23 toward the surface 11a and the back surface 11b, but these cracks do not reach the surface 11a and back surface 11b at this point.

[0041] After the division starting point formation step S10, the side 25a of the circular protective film 25, which has one side 25a without adhesive, is brought into close contact with the surface 11a side (protective film adhesion step S20).

[0042] The protective film 25 of this embodiment is formed of an olefin resin. Olefin resins include polyolefins such as polyethylene (PE) and polypropylene (PP), which are polymer compounds synthesized using alkenes as monomers, and copolymers of alkene monomers with other types of monomers, such as ethylene-vinyl acetate copolymers.

[0043] Since the protective film 25 is made of an olefin resin, it generally has a relatively high elongation rate and relatively high flexibility as mechanical properties (compared to, for example, polyethylene terephthalate).

[0044] When the protective film 25 is pressed against the surface 11a, even if there is no adhesive layer on one side 25a of the protective film 25, that side 25a adheres to the surface 11a due to the effects of static electricity, intermolecular forces, and reduced pressure adsorption.

[0045] In this embodiment, by not providing an adhesive that constitutes the adhesive layer on one surface 25a of the protective film 25, there is the advantage that no adhesive remains on the surface 11a after the protective film 25 is peeled off.

[0046] In the protective film adhesion step S20, a protective film 25 of a predetermined size is cut from the roll of protective film 25 (not shown) and pressed against the surface 11a.

[0047] For example, after an operator places a protective film 25 of a predetermined size on the surface 11a, they heat a disc-shaped pressing body (not shown) with a larger diameter than the wafer 11 to a predetermined temperature and press the pressing body onto the protective film 25. However, the same operation may be performed automatically by a predetermined device (not shown).

[0048] The protective film 25 is, for example, circular in shape, and its diameter is larger than the diameter of the wafer 11. When a protective film 25 larger than the diameter of the wafer 11 is brought into close contact with the wafer 11, an annular region of one side 25a of the protective film 25 located on the outer side in the diametrical direction of the wafer 11 adheres to the adhesive layer of the dicing tape 17.

[0049] If the diameter of the protective film 25 is smaller than the diameter of the wafer 11, the protective film 25 may stick to the support table 24 (see Figure 5) used in subsequent processes, and there is a risk that the protective film 25 will peel off from the surface 11a side. In contrast, by making the diameter of the protective film 25 larger than the diameter of the wafer 11, it is possible to prevent the protective film 25 from peeling off from the surface 11a side to the support table 24.

[0050] However, the diameter of the protective film 25 may be larger than the inner diameter of the frame. In this case, a portion of the protective film 25 will adhere to the annular frame 19. This allows the peeling start point to be set in the area where the protective film 25 and the annular frame 19 are in contact when peeling off the protective film 25 in a subsequent process.

[0051] Since the annular frame 19 does not have an adhesive layer, setting the peeling start point in the area where the protective film 25 is in contact with the annular frame 19 makes it easier to peel off the protective film 25 compared to setting the peeling start point in the area where the protective film 25 is in contact with the dicing tape 17.

[0052] After the protective film adhesion step S20, the wafer unit 21 is transported to a braking device 20 (see Figure 5) for dividing the wafer 11 starting from the modified layer 23. As shown in Figure 5, the braking device 20 has a relatively shallow bottomed cylindrical frame 22.

[0053] A disc-shaped support table 24 made of rubber and having elastic properties is positioned in the center of the frame 22. The diameter of the support table 24 is larger than the diameter of the wafer 11 and smaller than the inner diameter of the annular frame 19. In addition, the upper surface 24a of the support table 24 is positioned higher than the upper surface 22a of the frame 22.

[0054] On the inner bottom surface of the frame 22, and on the outer side of the support table 24, there is a projection 22b to prevent horizontal displacement of the annular frame 19. The projection 22b is formed in an annular shape along the circumferential direction of the frame 22, for example.

[0055] After the inner surface of the annular frame 19 is positioned outside the projection 22b, an annular retaining member 26 having an outer diameter approximately the same as the inner diameter of the frame 22 is positioned above the annular frame 19. The annular frame 19 is held between the retaining member 26 and the inner bottom surface of the frame 22.

[0056] When the annular frame 19 is held between the retaining member 26 and the frame 22, a slight tensile stress is applied to the dicing tape 17 in a direction that causes it to expand radially. However, this tensile stress alone is insufficient to divide the wafer 11.

[0057] A cylindrical roller 28 made of stainless steel (see Figure 6) is provided above the support table 24. The longitudinal length of the roller 28 is, for example, greater than or equal to the diameter of the wafer 11 and less than or equal to the inner diameter of the annular frame 19.

[0058] The roller 28 can rotate along a predetermined direction in a horizontal plane. Furthermore, the direction of movement of the roller 28 is configured to allow rotation by 90 degrees relative to the frame 22 in the horizontal plane.

[0059] The height of the lower end of the roller 28 when it rotates is fixed at a predetermined position above the support table 24. However, the height of the lower end of the roller 28 can be adjusted as needed. By adjusting the height of the lower end of the roller 28 from the upper surface 24a, the amount of pressure the roller 28 exerts on the wafer 11 can be adjusted.

[0060] After the protective film adhesion step S20, the wafer 11 is supported by the support table 24 with its surface 11a facing its top surface 24a (support step S30). Figure 5 shows the support step S30.

[0061] Furthermore, in the support step S30, the horizontal position of the annular frame 19 is fixed by the projection 22b, and the vertical position of the annular frame 19 is fixed by the retaining member 26 and the frame 22.

[0062] After the support step S30, the roller 28 is rotated relative to the upper surface 24a, thereby applying an external force to the wafer 11 from the back surface 11b side. This divides the wafer 11 into multiple chips (not shown) (dividing step S40).

[0063] Figure 6 shows the division step S40. In the division step S40, first, the roller 28 is moved so that its direction of travel is approximately parallel to the planned division line 13 in one direction.

[0064] As a result, an external force is applied almost uniformly to each planned division line 13 along one direction, and cracks sequentially extend from the modified layer 23 to the surface 11a and back surface 11b along each planned division line 13 from one end to the other.

[0065] Next, the direction of travel of the roller 28 is rotated 90 degrees relative to the frame 22 in the horizontal plane so that it is approximately parallel to the division lines 13 in the other directions. Then, the roller 28 is rotated. This applies an external force approximately uniformly to each division line 13 along the other directions.

[0066] By applying such external force, cracks sequentially extend from the modified layer 23 to the surface 11a and back surface 11b along each planned division line 13 in the opposite direction. As the cracks formed along each planned division line 13 reach the surface 11a and back surface 11b, the wafer 11 is divided into multiple chips.

[0067] In the splitting step S40 of this embodiment, one side 25a of the protective film 25 and the surface 11a of the wafer 11 are in close contact, thus reducing friction between the protective film 25 and the wafer 11.

[0068] Furthermore, since the protective film 25 is made of an olefin resin, even if the protective film 25 and the wafer 11 rub against each other to some extent, the amount of debris originating from the protective film 25 that adheres to the surface 11a of the wafer 11 can be reduced compared to the case where the protective film 25 is made of relatively brittle polyethylene terephthalate.

[0069] After the splitting step S40, the wafer unit 21 is removed from the braking device 20, and the protective film 25 is peeled off the wafer 11 (protective film peeling step S50). The peeling off of the protective film 25 may be done manually by an operator, or it may be done automatically by a peeling device (not shown).

[0070] After the protective film peeling step S50, the tackiness of the dicing tape 17 is reduced (tackiness reduction step S60). For example, if the adhesive layer is a UV-curing resin, the dicing tape 17 is irradiated with UV light. If the adhesive layer is a thermosetting resin, the tackiness is reduced by heating the dicing tape 17 to a predetermined temperature.

[0071] After the adhesion reduction step S60, the dicing tape 17 is expanded using an expander (not shown) to widen the spacing between the chips (expand step S70). Then, each chip is picked up using a collet or the like (pickup step S80).

[0072] Furthermore, the structures, methods, etc., according to the above embodiments can be modified as appropriate without departing from the scope of the object of the present invention. For example, in the division starting point formation step S10, instead of forming the modified layer 23, the surface 11a side can be formed by scribing along each planned division line 13 with a diamond scriber or the like to form a division starting point on the surface 11a side.

[0073] Furthermore, if the protective film 25 is relatively thick (for example, more than 50 μm), the support table 24 does not necessarily have to be made entirely of rubber. For example, part of the support table 24 may be made of a metal such as stainless steel.

[0074] However, even if a portion of the support table 24 is made of metal, it is preferable to provide a circular elastic layer made of rubber on the top of the support table 24 in order to more reliably prevent damage to the device 15.

[0075] In addition, in the splitting step S40, instead of the rollers 28, an external force may be applied to the wafer 11 by sequentially pressing a straight blade or break bar against the back surface 11b corresponding to each planned splitting line 13. [Explanation of Symbols]

[0076] 2: Laser processing device, 4: Chuck table, 4a: Holding surface 6: Machining feed direction, 8: Clamping mechanism, 10: Laser beam irradiation unit 11: Wafer, 11a: Front side, 11b: Back side, 13: Planned division line, 15: Device 12: Head unit, 14: Laser beam, 14a: Focusing point 17: Dicing tape, 19: Ring frame, 21: Wafer unit 20: Braking device, 22: Frame, 22a: Top surface, 22b: Protrusion 23: Modified layer (starting point of splitting), 25: Protective film, 25a: One side 24: Support table, 24a: Top surface, 26: Pressing member, 28: Roller

Claims

1. A wafer splitting method for a wafer in which a plurality of division lines are set in a grid pattern on the surface, and a device is formed in each of a plurality of regions partitioned by the plurality of division lines, wherein the wafer is split along each division line, A division starting point formation step, which involves forming a division starting point along each planned division line, having lower mechanical strength compared to the region where the device is formed, and which serves as the starting point for the division of the wafer, After the division starting point formation step, a protective film adhesion step is performed, in which a protective film made of an olefin resin, having one side without adhesive, is pressed against the surface of the wafer with a disc-shaped pressing body to adhere it to the wafer. After the protective film adhesion step, the wafer is supported by the support table with the wafer surface facing the support table, in a support step, Following the support step, a splitting step is performed in which, with one side of the protective film in close contact with the surface side of the wafer, an external force is applied to the wafer from the back side of the wafer to split the wafer from the splitting starting point. A method for dividing a wafer, characterized by comprising the following:

2. The wafer splitting method according to claim 1, characterized in that the wafer is supported by an elastic support table in the support step.

3. The wafer splitting method according to claim 1 or 2, characterized in that, in the splitting starting point formation step, the focal point of a pulsed laser beam having a wavelength that penetrates the wafer is positioned inside the wafer, and the focal point of the laser beam and the wafer are moved relative to each planned splitting line, thereby forming a modified layer that functions as the splitting starting point along each planned splitting line.

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