WAFER DIVISION PROCESS

Abstract

Wafer dividing method for dividing a wafer (11) with a front surface (11a) on which several provided division lines (13) are arranged in a grid pattern and components (15) are formed in respective areas subdivided by the several provided division lines (13) along each of the provided division lines (13), wherein the wafer dividing method comprises: a division start point formation step of forming a division start point along each of the provided division lines (13), wherein the division start point has a lower mechanical strength than that in the areas where the components (15) are formed and serves as a start point for a division of the wafer (11); a protective film adhesion step, following the division start point formation step, of the adhesion of a protective film (25) made of an olefin-based plastic and having a surface (25a) on which no adhesive is used, to which the wafer (11) is brought into close contact with the front surface (11a) of the wafer (11) in such a way that the one surface (25a) is brought into close contact with the front surface (11a) of the wafer (11); a carrying step, following the protective film adhesion step, of carrying the wafer (11) by a carrying table (24) in such a way that the front surface (11a) of the wafer (11) and the carrying table (24) are facing each other; and a division step, after the carrying step, of applying an external force to the wafer (11) from one side of the rear surface (11b) of the wafer (11) in order to divide the wafer (11) at the division start points.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The present invention relates to a wafer dividing method for dividing a wafer having a front surface on which a plurality of intended dividing lines are defined in a grid pattern, along the intended dividing lines. Description of the related art

[0002] As a method for dividing a wafer such as a sapphire wafer or a silicon wafer into individual chips, a technology for performing a scribing step and a breaking step on the wafer is known (see, for example, Japanese Unexamined Patent Application No. JP 2009-148982 A). Specifically, first, a surface of the wafer is scribed along a plurality of predetermined dividing lines defined on one surface of the wafer using a scriber (also called a scribe tool) such as a diamond-tipped scriber (scribing step).

[0003] The wafer is then supported by a support base of a breaking device in such a manner that the support base and one surface of the wafer face each other. After that, a blade of the breaking device is pressed against the other surface of the wafer, thereby applying an external force to the wafer. By pressing the blade against the other surface of the wafer along each of the designated dividing lines, the wafer is divided into a plurality of chips along the designated dividing lines (breaking step). Note that on one surface (front surface) of the wafer, devices such as light-emitting diodes (LEDs) or integrated circuits (ICs) may be formed in respective regions delimited by the plurality of designated dividing lines in a grid pattern.

[0004] In the breaking step, the wafer is placed on the support base with its front surface facing downward. To reduce damage to components during the breaking step, one approach is to cover the front surface of the wafer with a plastic protective film after the scribing step but before the breaking step. In the subsequent breaking step, the front surface of the wafer is made to face the support base, with the protective film sandwiched between them. The breaking step sometimes causes friction between the front surface of the wafer and the protective film, resulting in the adhesion of contaminants in the form of fine powder to the front surface of the wafer.For example, if a protective film made of polyethylene terephthalate is used, the friction between the wafer and the protective film causes dirt particles from the plastic forming the protective film to adhere to the front surface of the wafer.

[0005] Further information helpful for understanding the present invention can be found in the following documents: DE 10 2020 204 897 A1 relates to a machining method for a workpiece comprising a layering step, a thermocompression bonding step, a holding step, an alignment step and a machining step.

[0006] DE 10 2019 208 940 A1 relates to a wafer processing method comprising a foil bonding step, a thermocompression bonding step, a test element group (TEG) cutting step and a modified layer formation step. PRESENTATION OF THE INVENTION

[0007] The present invention has been made in view of the above-described problem, and therefore, an object of the present invention is to reduce an amount of dirt particles originating from the protective film and adhering to the front surface of the wafer when the wafer is divided.

[0008] According to one aspect of the present invention, a wafer dividing method of dividing a wafer having a front surface on which a plurality of provided dividing lines are arranged in a grid pattern and components are formed in respective regions divided by the plurality of provided dividing lines along each of the provided dividing lines is provided. The wafer dividing method includes a dividing start point forming step of forming a dividing start point along each of the provided dividing lines, the dividing start point having a lower mechanical strength than that in the regions where the components are formed and serving as a starting point for dividing the wafer, a protective film adhering step, after the dividing start point forming step, of adhering a protective film made of an olefin-based plastic and having a surface,in which no adhesive is used, to the wafer in such a manner that one surface is brought into close contact with the front surface of the wafer, a supporting step, after the protective film adhering step, of supporting the wafer by a supporting table in such a manner that the front surface of the wafer and the supporting table face each other, and a dividing step, after the supporting step, of applying an external force to the wafer from one side of the rear surface of the wafer to thereby divide the wafer at the division starting points.

[0009] Preferably, in the carrying step, the wafer is carried by the carrying table having elasticity.

[0010] Further preferably, in the division start point forming step, a pulsed laser beam having a wavelength transmissible through the wafer is applied to the wafer, a focused spot of the laser beam is positioned within the wafer, while the focused spot of the laser beam and the wafer are moved relative to each other along each of the intended division lines, thereby forming a modified layer serving as the division start point along each of the intended division lines.

[0011] In the wafer dividing method according to one aspect of the present invention, after the division start point forming step, a protective film made of an olefin-based resin and having one surface without an adhesive used therein is caused to adhere to the wafer in such a manner that one surface is brought into close contact with the front surface of the wafer (protective film adhering step). After the protective film adhering step, the supporting step is performed, and then the dividing step is performed. The dividing step is performed in the state where the protective film and the front surface of the wafer are in close contact with each other. Therefore, friction between the protective film and the wafer can be reduced.In addition, since the protective film is made of an olefin-based plastic, even if some friction occurs between the protective film and the wafer, it is possible to reduce the amount of dirt particles originating from the protective film and adhering to the front surface of the wafer, compared with the case of using a protective film made of polyethylene terephthalate, which is relatively brittle.

[0012] The above and other objects, features and advantages of the present invention, as well as the mode for carrying them into effect, will best become apparent and the invention itself will be best understood by studying the following description and appended claims with reference to the attached drawings which show a preferred embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flowchart for explaining a wafer dividing method; Fig. 2 is a perspective view of a wafer unit; Fig. 3 is a diagram for explaining a division start point forming step; Fig. 4 is a diagram for explaining a protective film adhesion step; Fig. 5 is a diagram for explaining a carrying step; and Fig. Figure 6 is a diagram explaining a division step. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 is a flowchart for explaining a method for dividing a wafer 11 (cf. Fig. 2). First, a description will be given of the dividing wafer 11 in a disc-shaped form. Fig. 2 is a perspective view of a wafer unit 21 including the wafer 11. The wafer 11 is formed mainly of silicon, for example, and has a front surface 11a and a back surface 11b, both of which have a substantially circular shape. The wafer 11 has, for example, a thickness (i.e., a distance from the front surface 11a to the back surface 11b) of 75 µm and a diameter of about 200 mm (eight inches). On the front surface 11a, a plurality of designated dividing lines 13 are defined in an orthogonally intersecting manner (i.e., in a lattice pattern).

[0014] In respective regions divided by the plurality of provided dividing lines 13, components 15 such as ICs and large-scale integration (LSI) circuits are formed, and the front surface 11a therefore has fine irregularities due to configurations, shapes, and the like of the components 15. Note that the material of the wafer 11 is not limited to silicon, and the wafer 11 may be made of another compound semiconductor, sapphire, or glass. Furthermore, the wafer 11 is not limited in its shape, configuration, size, and the like, and the components 15 are not specifically limited in their type, quantity, shape, configuration, size, arrangement, and the like.

[0015] When the wafer 11 is to be divided, a wafer unit 21 is formed in which the wafer 11 is supported on a metallic ring frame 19 by a dividing band 17 made of plastic. The dividing band 17 is a circular band having a diameter larger than that of the wafer 11. The dividing band 17 has a layered structure including, for example, a base material layer and an adhesive layer (adhesive layer). On the entire surface of one side of the base material layer, the adhesive layer is formed from a plastic having adhesiveness, such as an ultraviolet (UV) curable plastic or a thermosetting plastic. The wafer 11 is adhered to a substantially central portion of the dividing band 17, and one surface of the ring frame 19 is adhered to an outer peripheral portion of the dividing band 17.After the wafer unit 21 is formed in this way, division start points are formed in the wafer 11 using a laser processing apparatus 2 (division start point forming step S10).

[0016] Next, a description will be given of the laser processing apparatus 2 used in the division start point forming step S10 with reference to Fig. 3. The laser processing apparatus 2 includes a disk-shaped chuck table 4 having a substantially flat support surface 4a. The support surface 4a receives a negative pressure generated and transmitted from a suction source (not shown) such as an ejector. The chuck table 4 is connected at a lower portion thereof to a rotational drive source (not shown) and is rotatable about a predetermined rotational axis. A ball screw-type machining feed mechanism (not shown) is provided below the rotational drive source. The machining feed mechanism moves the chuck table 4 and the rotational drive source in a machining feed direction 6.

[0017] Below the machining feed mechanism, a ball screw type index feed mechanism (not shown) is provided. The index feed mechanism moves the machining feed mechanism, the chuck table 4, and the rotary drive source together in an index feed direction orthogonally intersecting the machining feed direction 6 within a horizontal plane. A plurality of clamping mechanisms 8 are arranged laterally along a circumferential direction of the chuck table 4. The clamping mechanisms 8 each clamp the ring frame 19 when the holding surface 4a holds the wafer 11 under suction by the dividing belt 17.

[0018] Above the holding surface 4a, a head portion 12 of a laser beam application unit 10 is provided. The head portion 12 has a focusing lens (not shown), and a pulsed laser beam emitted from a laser oscillator (not shown) of the laser beam application unit 10 is applied from the head portion 12 to the holding surface 4a. This pulsed laser beam, designated 14, has a wavelength transmissible through the wafer 11. Note that, near the head portion 12, a microscope camera unit (not shown) is provided, which has a predetermined optical system and a predetermined imaging sensor (e.g., a solid-state image sensor) for capturing an image of the front surface 11a.

[0019] Next, the division start point forming step S10 will be described. Fig. 3 is a diagram for explaining the division start point forming step S10. In the division start point forming step S10, first, the back surface 11b of the wafer 11 is suction-held by the holding surface 4a via the division belt 17, and the clamping mechanisms 8 respectively clamp the ring frame 19. The microscope camera unit then captures an image of two separate positions on a designated division line 13 on the front surface 11a exposed upward to perform alignment. According to the alignment results, the rotation drive source is actuated to set the one designated division line 13 and the processing feed direction 6 substantially parallel to each other.

[0020] The chuck table 4 is then moved in the processing feed direction 6 relative to a focused spot 14a of the laser beam 14 such that the focused spot 14a moves along the one designated dividing line 13 while being positioned at a predetermined depth inside the wafer 11. As the focused spot 14a and the wafer 11 are moved relative to each other along the one designated dividing line 13 in this way, a modified layer (division starting point) 23 is formed inside the wafer 11. The modified layer 23 has a lower mechanical strength than that in the regions where the components 15 are formed and serves as a starting point for dividing the wafer 11. In the division starting point forming step S10, processing conditions are set, for example, as follows: Laser beam wavelength: 1064 nm Medium output: 0.3 W Pulse repetition frequency: 80 kHz Machining feed speed: 300 mm / s Number of rounds: 2

[0021] It should be noted that the number of passes means the number of deposition of the laser beam 14 performed along a designated dividing line 13. For example, in a first deposition (i.e., a first pass), the deposition of the laser beam 14 is performed along a designated dividing line 13, with the focused spot 14a positioned at a depth of approximately 50 μm from the front surface 11a to form a modified layer 23.

[0022] Thereafter, in a second deposition (i.e., a second pass), deposition is carried out along the same designated dividing line 13 with the focused spot 14a positioned at a depth of about 25 μm from the front surface 11a to form another modified layer 23. In this way, along a designated dividing line 13, one modified layer 23 is formed at different depths within the wafer 11. After the modified layers 23, the number of which corresponds to the number of passes, are formed along one designated dividing line 13, the chuck table 4 is index-fed by a predetermined length in the index-feed direction. Similar processing is carried out to form modified layers 23 along another designated dividing line 13 beside the one designated dividing line 13.

[0023] After the modified layers 23 are formed along all the designated dividing lines 13 extending in one direction, the chuck table 4 is rotated 90 degrees, and similar processing is performed to form the modified layers 23 along all the designated dividing lines 13 extending in another direction orthogonally intersecting the one direction. Note that, although cracks (not shown) are formed extending from the modified layers 23 toward the front surface 11a and the back surface 11b during the formation of the modified layers 23, the cracks do not reach the front surface 11a and the back surface 11b at this point.

[0024] After the division start point forming step S10, a circular protective film 25 having one surface 25a in which no adhesive is used is caused to adhere to the front surface 11a of the wafer 11 in such a manner that the one surface 25a is brought into close contact with the front surface 11a (protective film adhering step S20). Fig. 4 is a diagram for explaining the protective film adhesion step S20. The protective film 25 in the present embodiment is made of an olefin-based resin. The olefin-based resin includes polyolefin such as polyethylene (PE) or polypropylene (PP), each of which is a high-molecular compound synthesized using alkenes as a monomer, and also includes a copolymer of an alkene monomer and another type of monomer, such as an ethylene-vinyl acetate copolymer. The protective film 25 made of the olefin-based resin essentially has a relatively high elongation rate and a relatively high flexibility as mechanical properties (compared, for example, with a protective film made of polyethylene terephthalate).

[0025] When the protective film 25 is pressed against the front surface 11a of the wafer 11, an electrostatic force, an intermolecular force, a negative pressure suction, or the like acts to bring one surface 25a of the protective film 25 into close contact with the front surface 11a, even though the one surface 25a does not have an adhesive layer. Note that the present embodiment offers the advantageous effect that, by not using an adhesive to form an adhesive layer on the one surface 25a of the protective film 25, no adhesive remains on the front surface 11a of the wafer 11 after the protective film 25 is peeled off from the wafer 11.

[0026] In the protective film adhesion step S20, a protective film 25 having a predetermined size is cut out from a film roll (not shown) obtained by winding the protective film 25 into a roll shape, and the cut-out protective film 25 is pressed against the front surface 11a. For example, after an operator places the protective film 25 in the predetermined shape on the front surface 11a, a disk-shaped pressing body (not shown) whose diameter is larger than that of the wafer 11 is heated to a predetermined temperature, and the heated pressing body is pressed against the protective film 25. Note that similar processing could also be performed automatically by a predetermined device (not shown).

[0027] The protective film 25 has, for example, a circular shape and a diameter that is larger than that of the wafer 11. When the protective film 25, whose diameter is larger than that of the wafer 11, is brought into close contact with the wafer 11, an annular region on one surface 25a of the protective film 25, which is positioned outwardly with respect to the wafer 11 in its radial direction, adheres to the adhesive layer of the dividing band 17. If the diameter of the protective film 25 were smaller than that of the wafer 11, the protective film 25 would be supported on a support table 24 (see Fig. 5) to be used in a subsequent step, which could result in the protective film 25 being inadvertently peeled off from the front surface 11a. However, since the protective film 25 in the present embodiment has a larger diameter than the wafer 11, such inadvertent peeling off of the protective film 25 from the front surface 11a and inadvertent adhesion of the protective film 25 to the support table 24 can be prevented.

[0028] It should be noted that the diameter of the protective film 25 may be larger than an inner diameter of the ring frame 19. In this case, a part of the protective film 25 is brought into close contact with the ring frame 19. Thereby, a peeling start point to be used when peeling the protective film 25 in a subsequent step can be set in the region of close contact between the protective film 25 and the ring frame 19. Since no adhesive layer is provided on the ring frame 19, it is easier to peel off the protective film 25 due to the peeling start point set in the region of close contact between the protective film 25 and the ring frame 19 than in a case where a peeling start point is set in a region where the protective film 25 and the division band 17 are bonded to each other.

[0029] After the protective film adhesion step S20, the wafer unit 21 is subjected to a breaking device 20 (see Fig. 5) for dividing the wafer 11, using the modified layers 23 as the division starting points. As shown in Fig. As shown in Figure 5, the breaking device 20 includes a frame body 22 in a relatively flat, bottomed cylindrical shape. Disposed in a central portion of the frame body 22 is the disc-shaped support table 24, which is made of rubber and has elasticity. A diameter of the support table 24 is larger than that of the wafer 11, but smaller than the inner diameter of the ring frame 19. Furthermore, the support table 24 includes an upper surface 24a of the support table 24 positioned higher than an upper surface 22a of the frame body 22.

[0030] A protrusion 22b for preventing positional deviation of the ring frame 19 in a horizontal direction is provided on a portion of an inner surface of the frame body 22, the portion being positioned outward with respect to the support table 24. The protrusion 22b is formed, for example, in an annular shape along a circumferential direction of the frame body 22. After the ring frame 19 is arranged so that its inner side contacts an outer side of the protrusion 22b, an annular pressing member 26 whose outer diameter substantially corresponds to the inner diameter of the frame body 22 is arranged above the ring frame 19. The ring frame 19 is clamped by the pressing member 26 and the inner bottom surface of the lower surface of the frame body 22.It should be noted that although a certain tensile stress acts on the dividing band 17 in a radially expanding direction when the ring frame 19 is clamped by the pressing member 26 and the frame body 22, this tensile stress alone is not sufficient to divide the wafer 11.

[0031] Above the support table 24 there is a cylindrical roller 28 (cf. Fig. 6) made of stainless steel. The length of the roller 28 in its longitudinal direction is, for example, equal to or greater than the diameter of the wafer 11, but equal to or smaller than the inner diameter of the ring frame 19. The roller 28 is capable of rolling movement in a predetermined direction within a horizontal plane. Furthermore, the direction of movement of the roller 28 can be rotated by 90 degrees relative to the frame body 22 within the horizontal plane.

[0032] A height of a lower end of the roller 28 is fixed at a predetermined position above the support table 24, while the roller 28 is moved in a rolling manner. Note that 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 with respect to the upper surface 24a, it is possible to adjust the amount of pressure of the roller 28 against the wafer 11. The wafer 11, which has undergone the protective film adhesion step S20, is supported by the support table 24 such that the front surface 11a and the upper surface 24a face each other (supporting step S30). Fig. 5 is a diagram for explaining the carrying step S30.

[0033] In the supporting step S30, the ring frame 19 is fixed in a horizontal position by the projection 22b and positioned in a vertical position by the pressing member 26 and the frame body 22. After the supporting step S30, the roller 28 is moved in a rolling manner with respect to the upper surface 24a, so that an external force is applied to the wafer 11 from the rear surface 11b side. Accordingly, the wafer 11 is divided into a plurality of chips (not shown) (dividing step S40).

[0034] Fig.6 is a diagram for explaining the dividing step S40. In the dividing step S40, first, the roller 28 is rolled with its moving direction set parallel to the provided dividing lines 13 extending in the one direction. As a result, an external force is applied to each of the provided dividing lines 13 extending in the one direction in a substantially uniform manner, so that cracks sequentially extend from the respective modified layers 23 toward the front surface 11a and the back surface 11b over the entire provided dividing lines 13 extending in the one direction from one end to the other end thereof.

[0035] The moving direction of the roller 28 is then rotated 90 degrees in the horizontal plane relative to the frame body 22, so that the moving direction is set substantially parallel to the provided parting lines 13 extending in the other direction orthogonal to the one direction. The roller 28 is moved in a rolling manner in this state. As a result, an external force is applied to each of the provided parting lines 13 extending in the other direction in a substantially uniform manner. When such external forces are applied, cracks progressively extend from the respective modified layers 23 toward the front surface 11a and the back surface 11b over the entire provided parting lines 13 extending in the other direction from one end to the other end thereof.The cracks formed along the respective provided dividing lines 13 thus reach the front surface 11a and the back surface 11b, and accordingly the wafer 11 is divided into a plurality of chips.

[0036] In the present embodiment, since the dividing step S40 is performed in the state where one surface 25a of the protective film 25 and the front surface 11a of the wafer 11 are in close contact with each other, friction between the protective film 25 and the wafer 11 can be reduced. In addition, since the protective film 25 is made of an olefin-based resin, even if some friction occurs between the protective film 25 and the wafer 11, it is possible to reduce the amount of dirt particles originating from the protective film 25 and adhering to the front surface 11a of the wafer 11, compared to the case of using a protective film made of polyethylene terephthalate, which is relatively brittle. After the dividing step S40, the wafer unit 21 is removed from the breaking device 20, and the protective film 25 is peeled off the wafer 11 (protective film peeling step S50).The removal of the protective film 25 could be carried out manually by an operator or automatically by a peeling device (not shown).

[0037] After the protective film peeling step S50, the adhesiveness of the dividing band 17 is reduced (adhesion reducing step S60). For example, in the case of using a UV-curable resin as the adhesive layer of the dividing band 17, UV rays are applied to the dividing band 17. Alternatively, in the case of using a thermosetting resin as the adhesive layer, the adhesiveness is reduced by heating the dividing band 17 to a predetermined temperature. After the adhesiveness reducing step S60, the dividing band 17 is expanded using an expanding device (not shown) to enlarge gaps between the chips (expanding step S70). Thereafter, each of the chips is picked up using a gripper or the like (picking step S80).

[0038] The configurations and methods relating to the above-described embodiment can be appropriately modified without departing from the scope of the present invention. For example, in the division start point formation step S10, instead of forming the modified layers 23, the front surface 11a could be scribed along each of the intended division lines 13 using a scriber, such as a diamond-tipped scriber, to thereby form division start points on the front surface 11a.

[0039] It should be noted that when using a protective film 25 having a relatively large thickness (e.g., 50 μm or more), the entire support table 24 does not necessarily have to be made of rubber. For example, the support table 24 could be partially made of metal, such as stainless steel. However, even when using the support table 24 partially made of metal, it is advantageous to arrange a circular elastic layer of rubber on an uppermost portion of the support table 24 to more reliably prevent damage to the components 15.

[0040] Furthermore, in the dividing step S40, instead of using the roller 28, a linear blade or a crowbar may be pressed sequentially against the rear side of the rear surface 11b along the positions corresponding to the intended dividing lines 13, thereby applying external forces to the wafer 11.

Claims

[1] A wafer dividing method for dividing a wafer (11) having a front surface (11a) on which a plurality of provided dividing lines (13) are arranged in a lattice pattern and components (15) are formed in respective regions divided by the plurality of provided dividing lines (13) along each of the provided dividing lines (13), the wafer dividing method comprising: a division start point forming step of forming a division start point along each of the provided division lines (13), the division start point having a lower mechanical strength than that in the regions where the components (15) are formed and serving as a start point for dividing the wafer (11); a protective film adhering step, after the division start point forming step, of adhering a protective film (25) made of an olefin-based plastic and having a surface (25a) on which no adhesive is used, to the wafer (11) in such a manner that the one surface (25a) is brought into close contact with the front surface (11a) of the wafer (11); a supporting step, after the protective film adhering step, of supporting the wafer (11) by a supporting table (24) in such a manner that the front surface (11a) of the wafer (11) and the supporting table (24) face each other; and a dividing step, after the supporting step, of applying an external force to the wafer (11) from a side of the rear surface (11b) of the wafer (11), to thereby divide the wafer (11) at the division starting points. [2] A wafer dividing method according to claim 1, wherein in said supporting step, said wafer (11) is supported by said supporting table (24) having elasticity. [3] A wafer dividing method according to claim 1 or 2, wherein, in the dividing start point forming step, a pulsed laser beam (14) having a wavelength transmissible through the wafer (11) is applied to the wafer (11), a focused spot (14a) of the laser beam (14) is positioned inside the wafer (11), while the focused spot (14a) of the laser beam (14) and the wafer (11) are moved relative to each other along each of the provided dividing lines (13), to thereby form a modified layer (23) serving as the dividing start point along each of the provided dividing lines (13).

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