WORKPIECE MACHINING METHOD AND MANUFACTURING METHOD FOR A COMPONENT CHIP

Abstract

A workpiece machining method for forming chips by dividing a workpiece, the workpiece machining method comprising: a frame unit preparing step of preparing a frame unit including the workpiece on which a planned parting line is set, a stretchable band fixed to an upper surface and a lower surface of the workpiece, and an annular frame having an opening and an annular portion surrounding the opening, wherein an outer peripheral portion of the band is fixed to the annular portion of the annular frame; a protective film forming step of forming a protective film by coating the other of the upper surface and the lower surface of the workpiece with a liquid plastic; a cutting step of completely cutting the workpiece along the designed dividing line by irradiating the workpiece with a laser beam along the designed dividing line so that spaces between the chips are formed, after the protective film forming step; a gap expanding step of expanding gaps between chips formed in the cutting step by expanding the tape outward in a radial direction after the cutting step; and an etching step of removing altered regions formed in cut surfaces of the respective chips by applying the laser beam in the cutting step by wet etching after the pitch expanding step.

Description

BACKGROUND OF THE INVENTIONTechnical field

[0001] The present invention relates to a processing method for processing a workpiece such as a wafer formed of a semiconductor or the like, and a device chip manufacturing method for manufacturing device chips by processing the wafer. DESCRIPTION OF THE STATE OF THE ART

[0002] A plurality of intersecting planned division lines are set on the upper surface of a disk-shaped wafer formed of a semiconductor. A device is formed in each of the regions divided by the planned division lines. Device chips can be formed when the wafer is divided along the planned division lines. For example, a cutting device having an annular cutting blade is used when a wafer formed of a semiconductor material such as Si, GaAs, or the like, which has a plurality of devices formed on an upper surface thereof, is divided into each device (see Japanese Patent Application Laid-Open No. 2001-85365). The cutting device cuts a workpiece by bringing the rotating cutting blade into contact with the workpiece. The wafer can be divided by another method.For example, the wafer can be divided when the wafer is irradiated with a laser beam of a wavelength that can be absorbed by the wafer (wavelength that can be absorbed by the wafer), and dividing grooves are thus formed on the wafer along the planned dividing lines by ablation processing (see Japanese Patent Application Laid-Open No. JP 2013-239591 A).

[0003] Recently, vertical-cavity surface-emitting lasers (VCSELs) have become interesting in technical fields such as optical communications, optical recording, and the like. When manufacturing chips containing VCSEL elements, a metallic film serving as an electrode or the like is formed on the lower surface of the wafer, and the wafer is then divided. US 2017 / 0162521 A1 relates to a wafer processing method. JP 2017-050443 A concerns another Wafer processing methods. US 2013 / 0309844 A1 concerns another wafer processing method. PRESENTATION OF THE INVENTION

[0004] In a case where the cutting device cuts the workpiece so that the wafer has the metallic film or the like formed on the lower surface side, the cutting blade, which is rotated, cuts into the metallic film. When the metallic film is cut by the cutting blade, the metallic film is pulled by the rotation of the cutting blade, and protrusions called burrs originating from the metallic film are formed on a cutting surface of the metallic film, or chipping occurs at an end portion of a formed chip. The formation of burrs or chipping lowers the quality of the chip. In addition, cutting contamination originating from the metallic film adheres to the cutting blade, causing clogging and reducing the life of the cutting blade.Furthermore, in a case where a relatively brittle wafer such as a GaAs wafer or the like is cut, the wafer must be processed under mild processing conditions to prevent damage to the wafer due to cutting. Therefore, cutting the wafer takes time. On the other hand, in a case where the wafer is divided by ablation processing using a laser beam, a deformed region is formed in a cutting surface of a chip due to a thermal effect of the ablation processing. The bending strength of the chip is reduced as the deformed region is formed.

[0005] It is therefore an object of the present invention to provide a workpiece processing method and a device chip manufacturing method which can effectively form chips having high bending strength.

[0006] According to one aspect of the present invention, there is provided a workpiece processing method for forming chips by dividing a workpiece, the workpiece processing method including: a frame unit preparation step of preparing a frame unit including the workpiece on which a planned dividing line is set, a stretchable band fixed to one of the upper surface and the lower surface of the workpiece, and an annular frame having an opening and an annular region surrounding the opening, an outer peripheral portion of the band being fixed to the annular region of the annular frame; a protective film forming step of forming a protective film by coating the other of the upper surface and the lower surface of the workpiece with a liquid resin;a cutting step of cutting the workpiece along the planned dividing line by irradiating the workpiece with a laser along the planned dividing line after the protective film forming step; a pitch expanding step of widening the pitches between the chips formed in the cutting step by expanding the tape in a radially outward direction after the cutting step; and an etching step of removing altered regions formed in cut surfaces of the respective chips by applying the laser beam in the cutting step by wet etching after the pitch expanding step.

[0007] Additionally, according to another aspect of the present invention, there is provided a component chip manufacturing method for manufacturing component chips by dividing a wafer, the component chip manufacturing method including: a frame unit preparation step of preparing a frame unit including the wafer on which a plurality of planned dividing lines crossing each other are set, the wafer having components formed on an upper surface in each of the regions divided by the planned dividing lines, a stretchable band fixed to an upper surface and a lower surface of the wafer, and an annular frame having an opening and an annular region surrounding the opening, an outer peripheral portion of the band being fixed to the annular region of the annular frame;a protective film forming step of forming a protective film by coating the other of the upper surface and the lower surface of the wafer with a liquid plastic; a cutting step of cutting the wafer along the planned dividing lines and forming individual component chips by irradiating the wafer with a laser beam along the planned dividing lines after the protective film forming step; a pitch expanding step of widening the pitches between the component chips formed in the cutting step by expanding the tape outward in a radial direction after the cutting step; and an etching step of removing altered regions formed in cut surfaces of the component chips by applying the laser beam in the cutting step by wet etching after the pitch expanding step.

[0008] Preferably, the wafer has a wet etching-resistant layer on the other of the upper surface and the lower surface, the protective film is applied to the other of the upper surface and the lower surface in the protective film forming step, the protective film formed in the protective film forming step is water-soluble, the laser beam applied to the wafer in the cutting step is a laser beam having a wavelength that can be absorbed by the wafer, the wafer is cut by ablation processing using the laser beam, and in the etching step, the protective film is removed by the wet etching.

[0009] Additionally, preferably, the protective film has resistance to wet etching, and in the etching step, the protective film protects the other of the upper surface and the lower surface of the wafer from wet etching.

[0010] Additionally, preferably, the protective film forming step includes a first coating step of coating the other of the upper surface and the lower surface of the wafer with a first liquid resin serving as a material for a water-soluble protective film, and a second coating step of coating the other of the upper surface and the lower surface of the wafer with a second liquid resin serving as a material for a water-insoluble protective film after the first coating step.

[0011] Further preferably, the wafer contains GaAs.

[0012] Further preferably, the wafer has a metallic film on the lower surface.

[0013] In the workpiece processing method and the device chip manufacturing method according to one mode of the present invention, the wafer is cut by irradiating the workpiece, such as the wafer or the like, with the laser beam along the designed dividing lines in the cutting step. Cutting the wafer by the application of the laser beam can be performed in a relatively short time. On the other hand, altered regions are formed in cutting surfaces of the wafer due to a thermal effect of the application of the laser beam. These altered regions lower the bending strength of the chips. Consequently, the altered regions are removed by wet etching by performing an etching step.

[0014] However, due to the very small gaps between the chips formed by cutting the wafer through the application of the laser beam, an etchant cannot sufficiently penetrate between the chips when the wet etching is performed. Alternatively, it takes a long time to sufficiently perform the wet etching. Accordingly, in the workpiece processing method and the device chip manufacturing method according to one mode of the present invention, a gap expanding step that widens the gaps between chips is performed before the etching step is performed. When the gaps between chips are widened by performing the gap expanding step, the etchant can easily reach the altered regions formed in the cutting surfaces of the respective chips when the etching step is performed, so that the altered regions can be removed with high efficiency.The bending strength of each of the chips is increased if the modified areas formed by applying the laser beam can be removed.

[0015] Accordingly, the present invention provides a workpiece processing method and a device chip manufacturing method that can efficiently form device chips having high bending strength.

[0016] The above and other objects, features and advantages of the present invention and the manner of carrying them out will become clearer and the invention itself best understood by studying the following description and appended claims which show a preferred embodiment of the invention. SHORT DESCRIPTION OF THE CHARACTERS Fig. 1A is a perspective view schematically illustrating an upper surface side of a wafer as a workpiece; Fig. 1B is a perspective view schematically illustrating a lower surface side of the wafer as a workpiece; Fig. 2 is a perspective view schematically illustrating a preparation step for a frame; Fig. 3 is a perspective view schematically illustrating a laser processing apparatus; Fig. 4A is a sectional view schematically illustrating a forming step of a protective film; Fig. 4B is a sectional view schematically illustrating the wafer on which a protective film is formed; Fig. 5A is a sectional view schematically illustrating a cutting step; Fig. 5B is a sectional view schematically illustrating the wafer that has been cut; Fig. 6A is a sectional view schematically illustrating a frame unit inserted into an expansion device; Fig. 6B is a sectional view schematically illustrating an expanding step for a gap; Fig. 7A is an enlarged sectional view schematically illustrating a gap between chips before the gap is expanded; Fig. 7B is an enlarged sectional view schematically illustrating the distance between chips after the gap has been extended; Fig. 7C is a sectional view schematically illustrating an etching step; and Fig. 8 is a flowchart for assistance in explaining an example of a workpiece machining process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] An embodiment of the present invention will be described with reference to the accompanying figures. In a workpiece processing method and a device chip manufacturing method according to the present embodiment, chips are formed by dividing a workpiece. The workpiece is, for example, a plate-shaped substrate on which planned dividing lines are set. Chips are formed when the workpiece is divided along the planned dividing lines. The workpiece is, for example, a disc-shaped wafer formed of a semiconductor material. Fig. 1A and Fig. 1B schematically illustrates, as an example of the workpiece, a wafer 1 having a plurality of devices 5 formed on an upper surface 1a thereof. The wafer 1 is formed, for example, from a semiconductor material such as Si (silicon), SiC (silicon carbide), GaAs (gallium arsenide), GaN (gallium nitride), InP (indium phosphide), Ge (germanium), or the like.

[0018] For example, a plurality of planned dividing lines 3 that cross each other are formed on the wafer 1. A component 5 is formed in each of the regions divided by the planned dividing lines 3 on the upper surface 1a of the wafer 1. The component 5 is, for example, an integrated circuit (IC), a large-scale integrated circuit (LSI), or the like. Alternatively, the component 5 is an optical component such as a light-emitting diode (LED), a VCSEL, or the like. A metallic film 7 serving as an electrode or the like is formed on a lower surface 11b of the wafer 1. When the wafer 1 is divided along the planned dividing lines 3, individual component chips including respective components 5 are formed. However, the wafer is not limited to this. There are no restrictions on the material, shape, structure, size, or the like of the wafer 1.The components 5 do not have to be formed on the wafer 1. In the following, a case will be described in which a GaAs wafer having components 5 formed thereon is divided.

[0019] An annular frame, a band attached to the annular frame so that an opening portion of the annular frame is closed, and a wafer 1 are previously integrated so that they simplify the handling of the wafer 1 and the formed chips when the wafer 1 is divided. A lower part of Fig. 2 schematically illustrates a frame 11 and a tape 9. The frame 11 is formed, for example, from a material such as a metal or the like. A circular opening portion 11a having a larger diameter than that of the wafer 1 as a workpiece is formed in the frame 11. The tape 9 includes an expandable base material in the form of a film and an adhesive layer (coupling layer) formed on the surface of the base material. As the base material of the tape 9, for example, polyolefin, polyethylene terephthalate, polyvinyl chloride, polystyrene, or the like is used. In addition, as the adhesive layer of the tape 9, for example, a silicone rubber, an acrylic-based material, an epoxy-based material, or the like is used.

[0020] The wafer 1 is subjected to laser ablation processing, cleaning, and wet etching, as described later. Therefore, the tape 9 attached to the wafer 1 is preferably a material having a certain resistance to this processing. Alternatively, as the tape 9, an ultraviolet type (ultraviolet ray cured) division tape "D-765", "D-181", or "D-510T" and a non-UV type division tape "G-765", "G-967" manufactured by Lintec Corporation, a UV type division tape "DU-300" manufactured by Nitto Denko Corporation, a UV type division tape "UHP-1515M3" manufactured by Denka Company Limited, a UV type division tape "N6801" manufactured by Sumitomo Bakelite Co., Ltd., or the like are suitably used. A UV type graduation band is particularly suitable for use as band 9.In a case where the UV type division tape is used as the tape 9, the tape 9 is cured by irradiating the tape 9 with ultraviolet rays to facilitate peeling when the individual device chips formed from the wafer 1 are peeled from the tape 9.

[0021] The tape 9 has a larger diameter than that of the opening portion 11a of the frame 11. An outer peripheral portion of the frame 9 is fixed to an annular region at the vicinity of the opening portion 11a. At this time, the fixing surface of the tape 9 is exposed in the opening portion 11a of the frame 11. The wafer 1 is fixed to the tape 9 exposed in the opening portion 11a. At this time, the tape 9 is fixed, for example, to the lower surface 11b of the wafer 1. An integral object formed from the wafer 1 as a workpiece, the tape 9, and the frame 11 is called a frame unit. The wafer 1 is supported by the frame 11 through the tape 9.

[0022] The wafer 1 is divided, for example, by applying a laser beam of a wavelength that can be absorbed by the wafer 1 (wavelength absorbable by the wafer 1) along the planned dividing lines 3, thereby forming dividing grooves by ablation processing. A description of the laser processing apparatus that performs the ablation processing is given below. Fig. 3 is a perspective view schematically illustrating a laser processing apparatus 2. The wafer 1 in the state of a frame unit 13 is loaded into the laser processing apparatus 2.

[0023] The laser processing apparatus 2 includes: a chuck table 28 that sucks and holds the wafer in a state of the frame unit 13; a laser processing unit 34 arranged above the chuck table 28. The laser processing apparatus 2 includes a cassette mounting base 6a arranged at a front corner portion of the upper surface of a base 4. A cassette 8 that houses a plurality of wafers 1 is placed on the cassette mounting base 6a. In addition, the laser processing apparatus 2 includes: a conveying unit 10 for conveying a wafer in the state of the frame unit 13 above the base 4; and conveying rails 12.

[0024] An X-axis movement mechanism (processing feed mechanism) includes X-axis guide rails 14, an X-axis movement plate 16, an X-axis ball screw 18, and an X-axis pulse motor 20, which are arranged on the upper surface of the base 4 of the laser processing device 2. A pair of X-axis guide rails 14 parallel to an X-axis direction are arranged on the upper surface of the base 4. The X-axis movement plate 16 is slidably mounted on the X-axis guide rails 14. A nut portion (not shown) is provided on a lower surface side of the X-axis movement plate 16. The X-axis ball screw 18 parallel to the X-axis guide rails 14 is screwed into the nut portion. The X-axis pulse motor 20 is coupled to one end of the X-axis ball screw 18.When the X-axis ball screw 18 is rotated by the X-axis pulse motor 20, the X-axis motion plate 16 moves in the X-axis direction along the X-axis guide rails 14. .

[0025] A Y-axis movement mechanism (index feed mechanism) including Y-axis guide rails 22, a Y-axis movement plate 24, a Y-axis ball screw 26, and a Y-axis pulse motor (not shown) is arranged on an upper surface of the X-axis movement plate 16. A pair of Y-axis guide rails 22 parallel to the Y-axis direction are provided on an upper surface of the X-axis movement plate 16. The Y-axis movement plate 14 is slidably attached to the Y-axis guide rails 22. A nut portion (not shown) is provided on a lower surface side of the Y-axis movement plate 24. The Y-axis ball screw 26 parallel to the Y-axis guide rails 22 is screwed into the nut portion. The Y-axis pulse motor is coupled to one end of the Y-axis ball screw 26.When the Y-axis ball screw 26 is rotated by the Y-axis pulse motor, the Y-axis motion plate 24 moves in the Y-axis direction along the Y-axis guide rails 22.

[0026] The chuck table 28 is arranged on the Y-axis moving plate 24. A porous member (not shown) is arranged on an upper surface of the chuck table 28. Alternatively, a plurality of grooves are formed on the upper surface of the chuck table 28. The chuck table 28 is formed, for example, by a stainless steel, a quartz member, or the like. The upper surface of the chuck table 28 forms a holding surface 28a for holding the wafer 1. The chuck table 28 is rotatable about an axis perpendicular to the holding surface 2a. The chuck table 28 has a suction source (not shown) connected to the porous member or the grooves. When the wafer 1 is placed on the holding surface 28a by the belt 9 and a negative pressure generated by the suction source is caused to act on the wafer 1 through holes of the porous member or the grooves, the wafer 1 is sucked and held by the chuck table 28.In addition, clamps 28b that fix the frame 11 constituting the frame unit 13 are provided in the vicinity of the chuck table 28.

[0027] An upright portion 30 supporting the laser processing unit 34 is disposed at a rear portion of the upper surface of the base 4 of the laser processing device 2. A base end side of a support portion 32 extending to a position above the chuck table 28 is connected to an upper portion of the upright portion 30. The laser processing unit 34 and an imaging unit 36 ​​are disposed at a distal end side of the support portion 32. The laser processing unit 34 includes a processing head 34a disposed above the chuck table 28 and an imaging unit 36 ​​disposed at a position adjacent to the processing head 34a.

[0028] The laser processing unit 34 serves to pulse oscillate a laser beam of a wavelength that can be absorbed by the wafer 1 (wavelength absorbable by the wafer 1) and collect the laser beam on the wafer 1 held by the chuck table 28. For example, the laser processing unit 34 oscillates a laser using neodymium-doped yttrium aluminum garnet (Nd:YAG), neodymium-doped yttrium orthovanadate (ND:YVO4), or the like as a laser medium and collects a laser beam of, for example, a wavelength of 532 nm or 355 nm or the like on the wafer 1. The imaging unit 36 ​​has the function of picking up the wafer 1 held by the chuck table 28.The use of the imaging unit 36 ​​enables an alignment to be performed which adjusts the position of the wafer 1 with respect to the processing head 34a so that the laser beam can be applied along the planned dividing lines 3 of the wafer 1.

[0029] The laser processing apparatus 2 includes a protective film coating and cleaning unit 38 on the upper surface of the base 4. The protective film coating and cleaning unit 38 has a function of forming a protective film by coating the upper surface of the wafer 1 with a liquid plastic before processing and a function of cleaning the wafer 1 after processing. The protective film coating and cleaning unit 38 includes a table 42 on which the wafer 1 is placed and a nozzle 40 that ejects a fluid toward the wafer 1 attached to the table 42.

[0030] The table 42 can rotate about an axis along a direction perpendicular to the mounting surface of the wafer 1. The nozzle 40 includes: a shaft portion extending in a Z-axis direction (vertical direction) outside the table 42; an arm portion extending in a horizontal direction perpendicular to the Z-axis direction from an upper portion of the shaft portion; and an exhaust port located at one end of the arm portion and oriented downward in the Z-axis direction. The exhaust port can be moved in the horizontal direction above the chuck table 42 by rotating the shaft portion. The nozzle 40 is formed in the shape of a tube.The nozzle 40 can supply a liquid supplied from a supply source connected to a lower portion of the shaft portion to the outlet port and discharge the liquid from the outlet port to the wafer 1 held on the table 42. The nozzle 40 discharges, for example, a liquid plastic as a material for a protective film for protecting the upper surface 1a of the wafer 1 or a cleaning liquid for cleaning the wafer 1 to the wafer. The nozzle 40 can discharge a mixed fluid of a liquid and a gas to the wafer 1.

[0031] The workpiece processing method and the device chip manufacturing method according to the present embodiment will be described next. Fig. 8 is a flowchart illustrating an example of a sequence of steps in the workpiece processing method and the component chip manufacturing method. The workpiece processing method and the component chip manufacturing method according to the present embodiment first execute a unit frame preparation step S1 for preparing a unit frame 13. Fig. Fig. 2 is a perspective view schematically illustrating the frame unit preparation step S1. In the frame unit preparation step S1 shown in Fig. 2, the outer peripheral portion of a tape 9 is pre-attached to an annular region on the outer periphery of an opening portion 11a of an annular frame 11, and the lower surface side 1b of a wafer 1 as a workpiece is fixed to the bonded layer of the tape 9 exposed in the opening portion 11a of the frame 11. The formed frame unit 13 is housed, for example, in the cassette 8 shown in Fig. 3. The cassette 8 has the function of housing several frame units 13.

[0032] However, the preparation step S1 for a frame unit is not limited to this. For example, in the preparation step S1 for a frame unit, the tape 9 may be fixed to the upper surface 1a of the wafer 1. In addition, the tape 9 may be fixed to the wafer 1 beforehand, and next, the outer peripheral portion of the tape 9 may be fixed to the annular area surrounding the opening portion 11a of the frame 11. The following describes an example of a case where the tape 9 is fixed to the lower surface 1b of the wafer 1.

[0033] The workpiece processing method and the device chip manufacturing method according to the present embodiment next perform the protective film forming step S2. In the protective film forming step S2, a protective film is formed by coating the upper surface 1a of the wafer 1 as a workpiece with a liquid resin. As described later, the protective film has a function of protecting the upper surface 1a of the wafer 1 from an etchant when wet etching the wafer 1. The protective film forming step S2 is performed by the laser processing apparatus 2 shown in Fig. 3, for example. In the protective film forming step S2, the cassette 8 housed in the frame unit 13 is placed on the cassette mounting base 6a of the laser processing apparatus 2, and the conveying unit 10 takes out a frame unit 13 housed in the cassette 8. Then, the conveying unit 10 carries the frame unit 13 onto the table 42 of the protective film coating and cleaning unit 38.

[0034] Next, the wafer 1 is coated with a liquid plastic as a raw material for a protective film. Fig. 4A is a sectional view schematically illustrating the protective film forming step S2. The liquid resin 40a is applied by spin coating, for example. First, the liquid resin 40a is supplied from the outlet port of the nozzle 40 to near a center of the upper surface 1a of the wafer 1 while the table 42 is rotated about an axis along the vertical direction (Z-axis direction). In this case, the liquid resin moves in an outer circumferential direction due to centrifugal force, and the upper surface 1a of the wafer 1 is coated with the liquid resin with a substantially uniform thickness. Fig. 4B is a sectional view schematically illustrating wafer 1 on which a protective film 40b is formed in protective film forming step S2. The protective film 40b may be formed by another method, for example, by spray coating.

[0035] In the protective film forming step S2, the protective film 40b may be cured by heating or drying after the protective film 40b is formed on the upper surface 1a of the wafer 1. Heating the protective film 40b is performed, for example, by pulse irradiation with a xenon lamp, infrared irradiation, baking, or the like. When the protective film 40b is cured, its adhesion to the upper surface of the wafer 1 is improved, thus preventing the protective film from being accidentally peeled off in a subsequent step.

[0036] When the ablation processing of the wafer 1 is performed, as described later, the laser beam passing through the protective film 40b melts and vaporizes the wafer 1, and a pressure wave occurs. At this time, the pressure wave occurring from the wafer 1 exerts pressure on the protective film 40b, and there is a risk that the protective film 40b will tear and peel off near a position irradiated with the laser beam. Accordingly, the protective film 40b preferably includes a material (hereinafter referred to as a light absorber) having a property of absorbing the wavelength of the laser beam applied to the wafer 1 when the ablation processing of the wafer 1 is performed, as described later. The protective film 40b including the light absorber is decomposed due to the heat of the laser beam application.Consequently, cracking caused by the pressure wave does not occur, and the protective film 40b does not easily peel off. For example, in a case where the wavelength of the laser beam is 355 nm, ferulic acid, caffeic acid, or the like can be used as the light absorber. Additionally, in a case where the wavelength of the laser beam is 532 nm, Solvent Black 3, phthalocyanine, or the like can be used as the light absorber.

[0037] Additionally, it is preferable that the protective film 40b be resistant to wet etching, which will be described later, and can be easily removed by a predetermined method. For example, the protective film 40b may be a liquid plastic soluble in an organic solvent, a liquid plastic soluble in an alkaline solution, or a liquid plastic soluble in hot water. Specific examples of the protective film 40b are listed below. However, the protective film 40b is not limited to the following.

[0038] Liquid plastics soluble in organic solvents include, for example, polymethyl methacrylate, polyethylene terephthalate, polyvinyl butyral, polyimide, polystyrene, polyethylene, polypropylene, polyurethane, epoxy resin, and the like. Liquid plastics soluble in alkaline solutions include, for example, "UC-3000," "UC-3080," "UC-3510," "UF-5080," and "UC-5022" made from the acrylic polymer "ARUFON (registered trademark)" manufactured by Toagosei Co., Ltd., "8KQ" and "PH" manufactured by Taisei Fine Chemical Co., Ltd. “ZAH-106,” “ZAH-110,” “ZAH-115,” “ZAH-306,” “ZAH-310,” and “ZAH-315” are made from the functional acrylic polymer “PHORET (registered trademark)” manufactured by Soken Chemical & Engineering Co., Ltd., and the like.Further, liquid plastics soluble in alkaline solutions include plastics “CH-9,” “M-5D,” and “M-4” based on a vinyl acetate polymer manufactured by Kagaku Kogyo Kabushiki Kaisha, and reactive polymers “RP-274S” and “RP-310” manufactured by KSM Co., Ltd., and an acrylic-based plastic “BT-9” manufactured by DSM Coating Resins, LLC, and the like.

[0039] Furthermore, a liquid plastic soluble in an alkaline liquid can be prepared by using an additive to produce a liquid plastic soluble in the alkaline solution. Such additives include, for example, alkali-soluble thickeners "VONCOAT (registered trademark) HV-E," "VONCOAT (registered trademark) VE," and "VONCOAT (registered trademark) 3750-E" manufactured by DIC Corporation, an acid anhydride "H-TMAn" manufactured by Mitsubishi Gas Chemical Company, Inc., and the like. In addition, liquid resins that can be dissolved in very warm water include, for example, acrylic-based resins “NW-112B,” “NW-115NH-100S,” “NW-126-100S,” and “NW-128” manufactured by Denki Kagaku Kogyo Kabushiki Kaisha, epoxy coupling agents “U-BOND” and “B-BOND,” and an acrylic-based coupling agent “SKYLOCK RD series” manufactured by Nikka Seiko Co., Ltd., and the like.

[0040] While a case has been described where the tape 9 is fixed to the lower surface 1b of the wafer 1 to form a protective film 40b on the upper surface 1a of the wafer 1, the workpiece processing method and the device chip manufacturing method according to the present embodiment are not limited thereto. The tape 9 may be attached to the upper surface 1a of the wafer 1, and the protective film 40b may be formed on the lower surface 1b of the wafer 1. That is, the tape 9 is fixed to one of the upper surface 1a and the lower surface 1b of the wafer 1, and the protective film 40b is formed on the other of the upper surface 1a and the lower surface 1b of the wafer 1.

[0041] The workpiece processing method and the device chip manufacturing method according to the present invention performs a cutting step S3 after the protective film forming step S2. After the protective film forming step S2 is performed, the conveying unit 10 conveys the frame unit 13 onto the holding surface 28a of the chuck table 28. Then, the wafer 1 as a workpiece is sucked and held by the belt 9 by operating the suction source of the chuck table 28, and the frame 11 is gripped by the clamps 28b. Next, the chuck table 28 is moved to a position below the laser processing unit 34, and information about the position of the planned dividing lines 3 is obtained by capturing the upper surface 1a of the wafer 1 with the imaging unit 36.Then, based on the information, the planned parting line 3 is aligned with the machining feed direction (X-axis direction) by rotating the chuck table 28 about an X-axis along a direction perpendicular to the holding surface 28a. At the same time, the machining head 34a is positioned above an extension of the planned parting line 3 by moving the chuck table 28.

[0042] Fig. 5A is a sectional view schematically illustrating the cutting step S3. The wafer 1 as a workpiece is irradiated with a laser beam 34b along the planned dividing line 3 by moving the chuck table 28 along the machining feed direction while causing the laser machining unit 34 to oscillate a laser. When the laser beam 34b of a wavelength absorbed by the wafer 1 is applied along the planned dividing line 3, a machined groove is formed in the wafer 1 by ablation. The laser beam 34b may be applied to the planned dividing lines 3 multiple times. After ablation machining is performed along a planned dividing line 3, the chuck table 28 is moved along an index feed direction (Y-axis direction), and ablation machining is similarly performed along other planned dividing lines 3.After the ablation machining is performed along all the planned parting lines 3 along the X-axis direction, the chuck table 28 is rotated, and machining is performed similarly along the planned parting lines 3 along a different direction. Then, machined grooves are formed along all the planned parting lines 3.

[0043] Fig. 5B is a sectional view schematically illustrating wafer 1 divided into chips 1d by forming machined grooves 1c penetrating wafer 1 in a thickness direction. When component chips 5 are formed on wafer 1, chips 1d become component chips. When the machined grooves 1c are formed by applying laser beam 34b, a changed area is formed on the cut surfaces of chips 1d (wafer 1) due to a thermal effect accompanying the application of laser beam 34b. Fig. 7A is a sectional view schematically illustrating, in an enlarged scale, chips 1d having a modified region 1e formed in a cut surface. Fine cracks are formed in the modified regions 1e. The chips 1d having the modified region 1e formed in the cut surface thereby have relatively low bending strength. Accordingly, wet etching can be performed to remove the modified regions 1e. However, the machined grooves 1c have a very small width, so it is difficult for an etchant to penetrate into the machined grooves 1c. Therefore, it is not easy to sufficiently remove the modified regions 1e.

[0044] Accordingly, the workpiece processing method and the device chip manufacturing method according to the present embodiment widen the distances between chips 1d by performing a distance expanding step S4 so that an etchant can easily penetrate into the processed grooves 1c. The distance expanding step S4 is performed by an expanding device 44 provided in Fig. 6A and Fig. 6B is shown. Fig. 6A is a sectional view schematically illustrating the frame unit 13 inserted into the expansion device 44. Fig. 6B is a sectional view schematically illustrating the pitch expansion step S4. The expansion device 44 will be described. The expansion device 44 includes a cylindrical expansion drum 54 having a larger diameter than the diameter of the wafer 1; and a frame holding unit 46 including a frame support 48. The frame support 48 of the frame holding unit 46 has an opening having a larger diameter than the diameter of the expansion drum 54. The frame support 48 is supported at a similar height to an upper end portion of the expansion drum 54 and surrounds the upper end portion of the expansion drum 54 from an outer peripheral side.

[0045] Clamps 50 are arranged on the outer peripheral side of the frame support 48. When the frame unit 13 is placed on the frame support 48 and the frame unit 13 is gripped by the clamps 50, the frame unit 13 is fixed to the frame support 48. The frame support 48 is supported by a plurality of rods 52 extending along a vertical direction. In a lower end portion of each of the rods 52, an air cylinder (not shown) is arranged that raises and lowers the rod 52. When the rods 52 are lowered by actuating the respective air cylinders, the frame support 48 is lowered with respect to the expansion drum 54.

[0046] When the pitch expansion step S4 is performed, the frame unit 13 is conveyed onto the frame support 48 of the expansion device 44, and the clamps 50 are caused to grip the frame 11. Next, the frame support 48 is lowered by actuating the air cylinders. Then, the belt 9 fixed to the workpiece is stretched outward in a radial direction, thereby widening the pitches between the chips 1d supported by the belt 9. Fig. 7B is a sectional view schematically illustrating, in an enlarged manner, the machined grooves 1c (inter-chip spacing 1d) after the spacing expansion step S4 is performed. For example, the width of the machined grooves 1c immediately after the cutting step S3 is performed is approximately 5 to 15 µm, whereas the spacing between the chips 1d is expanded to approximately 15 to 50 µm by performing the spacing expansion step S4. At the same time, in order to maintain the state in which the spacing between the chips 1d is widened, in the spacing expansion step S4, the annular portion of the tape 9 exposed between the wafer 1 (chips 1d) and the frame 11 may be heated, and the tape 9 may thereby be shrunk in the portion.In addition, before the pitch expanding step S4 is performed, a tape may be replaced by peeling off the tape 9 fixed to the lower surface side 1b of the wafer 1 (chips 1d) as a workpiece and attaching another tape to the lower surface 1b of the wafer 1 (chips 1d).

[0047] The workpiece processing method and the component chip manufacturing method according to the present embodiment perform an etching step S5 after the pitch expansion step S4. In the etching step S5, the altered regions 1e formed in the cut surfaces of the respective chips 1d due to the application of the laser beam 34b in the cutting step S3 are removed by wet etching. The etching step S5 is carried out by a wet etching device 56 provided in Fig. 7C. The wet etching apparatus 56 includes an etching tank 58 having a bottom surface with a larger diameter than the diameter of the frame unit 13. An etchant 60 is contained in the etching tank 58. The etchant 60 is a solution capable of removing the altered regions 1b formed in the cut surfaces of the chips 1d. The etchant 60 is selected according to the material of the wafer 1 and the like. For example, in a case where the wafer 1 is a GaAs wafer, an aqueous solution in which sulfuric acid or an aqueous ammonia solution, a hydrogen peroxide solution, and pure water are mixed together in a predetermined ratio is used as the etchant 60. Further, the etchant 60 can be selected according to the material of the protective film 40b.Alternatively, the material of the protective film 40b may be selected according to a solute of the aqueous solution used as the etchant 60.

[0048] In the etching step S5, the frame unit 13 is placed in the etching tank 58, and the frame unit 13 is immersed in the etchant 60. Thereafter, the frame unit 13 is lifted from the etchant 60 after a predetermined time, and wet etching is stopped by cleaning the frame unit 13 with, for example, pure water or the like. The wet etching is performed for approximately 15 seconds to 3 minutes, for example. In the workpiece processing method and the device chip manufacturing method according to the present embodiment, because the gaps between the chips 1d are widened by performing the gap expanding step S4, the etchant 60 easily penetrates between the chips 1d, and thus, the altered regions 1e are easily removed. Because the altered regions 1e in which small cracks are formed are removed, the bending strength of the chips 1d is increased.

[0049] In a case where the gaps between the chips 1d are not widened using the present embodiment, wet etching must be performed for a relatively long time to sufficiently remove the changed regions 1e by performing wet etching, and manufacturing efficiency of the chips 1d decreases. In addition, if wet etching is performed for a long time, the protective film 40b may peel off, and the chips 1d and the device 5 may be damaged by the etchant 60. On the other hand, the workpiece processing method and the device chip manufacturing method according to the present embodiment can sufficiently perform wet etching in a relatively short time. Furthermore, the protective film 40b does not peel off easily, and therefore, damage to the device chips 1d and the device 5 does not easily occur.Particularly, in a case where the protective member 40b has strong resistance to wet etching, the protective film 40b protects the upper surface 1a of the wafer 1 (chips 1d) from wet etching, and therefore, damage to the chips 1d does not easily occur.

[0050] A protective film removal step for removing the protective film 40b may be performed after the etching step S5 is performed. For example, in a case where the protective film 40b is a liquid plastic soluble in an organic solvent, the protective film 40b may be removed by immersing the chips 1d in an organic solvent such as propylene glycol methyl ether (PGME), isopropyl alcohol (IPA), ethanol, or the like, or a solution obtained by mixing water with such an organic solvent. In addition, in a case where the protective film 40b is a liquid plastic soluble in an alkaline solution, the protective film 40b may be removed, for example, by immersing the chips 1d in an alkaline solution such as a sodium hydroxide solution (aqueous), an aqueous ammonia solution, or the like.Further, in a case where the protective film 40b is a liquid plastic that can be dissolved in warm water, the protective film 40b is removed by immersing the chip 1d in water having a high temperature of approximately 70°C to 90°C.

[0051] When the wafer 1 as a workpiece is subjected to ablation processing by the laser beam 34b in the cutting step S3, a melt of the wafer 1, also referred to as contamination, scatters on the upper surface 1a of the wafer 1 and adheres to the upper surface of the protective film 40b. Part of the contamination can be removed by dry etching. However, if the protective film removal step is performed to remove the protective film 40b, the contamination is surely removed from the chips 1d along with the protective film 40b. Consequently, there is no risk of reduced quality of the chips 1d due to the adhesion of the contamination.

[0052] In the protective film removing step, the removal efficiency of the protective film 40b can be improved by stirring the liquid that can remove the protective film 40b. In addition, in a case of high adhesion between the chips 1d and the protective film 40b, an ultrasonic wave can be applied to the liquid that can remove the protective film 40b. However, the ultrasonic wave must be applied in the liquid under the condition that no damage occurs in the chips 1d. In addition, the protective film removing step can be performed by the protective film coating and cleaning unit 38. In this case, the frame unit 13 is conveyed to the protective film coating and cleaning unit 38, and the frame unit 13 is subjected to high-pressure cleaning using liquid that can remove the protective film 40b, for example.Further, in the protective film coating and cleaning unit 38, two-fluid cleaning may be performed, which supplies a mixture of liquid and air to the frame unit 13.

[0053] After the etching step S5 has been performed, a picking step can be performed which conveys the frame unit 13 to a picking device and receives the individual component chips 1d by detaching the chips 1d from the tape 9.

[0054] In the workpiece processing method and the device chip manufacturing method according to the present embodiment, in a case where the upper surface 1a of the wafer 1 has resistance to the etchant 60, a water-soluble protective film 40b may be formed using a water-soluble liquid resin in the protective film forming step S2. For example, in a case where the wafer 1 is a GaAs wafer and an oxide film serving as a resistance layer having resistance to the etchant 60 is formed on the upper surface 1a, a water-soluble liquid resin may be used as the protective film 40b. Contamination occurring on the wafer 1 due to the ablation processing in the dicing step S3 scatters on the upper surface 1a of the wafer 1, and the contaminant adheres to the protective film 40b.In a case where a water-soluble liquid resin is used as the protective film 40b, the protective film 40b can be removed together with the contamination when altered areas 1e of the wafer 1 (chips 1d) are subsequently removed by the etchant 60. Therefore, the removal step for a protective film does not need to be performed separately.

[0055] Water-soluble plastics include polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, polyacrylamides, poly-N-vinylacetamide, polyethylene oxide, methylcellulose, ethylcellulose, hydroxypropylcellulose, polyacrylic acid, a polyvinylpolyacrylic acid block copolymer, a polyvinylpolyacrylic acid ester block copolymer, and the like. Additionally, a water-soluble protective film material "HOGOMAX (registered trademark)" manufactured by DISCO Corporation is listed.

[0056] Additionally, in the case where a water-soluble liquid resin is used as the protective film 40b, the protective film forming step S2 may coat the wafer 1 with a liquid resin as a material for a water-soluble protective film, and then further coat the wafer 1 with a liquid resin as a material for a water-soluble protective film. In this case, in the protective film forming step S2, a first coating step is first performed, which coats the upper surface 1a of the wafer 1 with a liquid resin as a material for a water-soluble protective film 40b. A water-soluble protective film 40b is formed when the first coating step is performed.Then, after the first coating step, a second coating step is performed, which further coats the upper surface 1a of the wafer 1 with a liquid plastic as a material for a water-insoluble protective film. When the second coating step is performed, a water-insoluble protective film is formed on the water-soluble protective film 40b.

[0057] When the water-insoluble protective film has been formed on the water-soluble protective film 40b, the water-soluble protective film 40b is protected by the water-insoluble protective film in the etching step S5. Therefore, even in a case where the upper surface 1a of the wafer 1 lacks resistance to the etchant 60, the protective film 40b formed of the water-soluble resin can be used. In the workpiece processing method and the device chip manufacturing method according to the present embodiment, wet etching can be completed in a relatively short time, and therefore, damage to the water-soluble protective film 40b can be limited.

[0058] In a case where the liquid resin is supplied to the upper surface 1a of the wafer 1 in the first coating step, in which the liquid resin supplied in the second step is soluble, for example, the water-soluble protective film 40b and the water-insoluble protective film may be mixed with each other at an interface. Even in this case, if an exposed upper portion of the water-insoluble protective film is sufficiently water-insoluble, the water-soluble protective film 40b is protected from the etchant 60.

[0059] At the same time, in the case where the water-insoluble protective film is formed on the protective film 40b formed on the water-soluble liquid resin, if water is used at the time of performing the protective film removing step, the water-insoluble protective film can be removed by removing the water-soluble protective film 40b. A step of peeling the water-insoluble protective film therefore becomes unnecessary. However, in order to remove the water-soluble protective film 40b protected by the water-insoluble protective film, the protective film removing step preferably performs high-force cleaning such as two-fluid cleaning, high-pressure cleaning, or the like, and may perform both two-fluid cleaning and high-pressure cleaning.

[0060] Here, as a plastic material such as hydroxymethylcellulose insoluble in an organic solvent, polyvinyl alcohol having a relatively high saponification value, or the like is used as a liquid plastic in the first coating step. Alternatively, a plastic material such as polyvinylpyrrolidone soluble in an organic solvent, poly-N-vinylacetamide, polyvinyl alcohol having a relatively low saponification value, polyethylene glycol, or the like may be used. Alternatively, a water-soluble protective film material "HOGOMAX" (®) manufactured by DISCO Corporation may be used.In the second coating step, as a liquid plastic, for example, a liquid plastic obtained by dissolving a plastic such as polyvinyl butyral, polymethyl methacrylate, a methacrylate ester copolymer or the like in an organic solvent such as propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, isopropyl alcohol or the like can be used.

[0061] Furthermore, one or both of the liquid resin used in the first coating step and the liquid resin used in the second coating step preferably contain a material (light-absorbing etchant) that has a property of absorbing the wavelength of the laser beam applied to the wafer 1 in the dicing step S3. Including the light-absorbing agent in this liquid resin suppresses peeling of the protective film 40b or the like due to a shock wave caused by the ablation processing in the dicing step S3. In particular, the liquid resin used in the second coating step preferably contains the light-absorbing agent.

[0062] In addition, while the description covers a case where the laser beam 34b of a wavelength that can be absorbed by the wafer 1 is applied in the cutting step S3, and the machined grooves 1c are thus formed by the ablation processing, the cutting step S3 is not limited to this. That is, in the cutting step S3, the wafer 1 may be cut by another method. For example, in the cutting step S3, a laser beam having a wavelength that can be transmitted through the wafer 1 (wavelength passing through the wafer 1) may be collected in the wafer 1 along the planned dividing lines 3, and a modified layer (modified regions) as a division starting point may be formed in the wafer 1 by a multiphoton absorption process.After the modified layer is formed, the wafer 1 can be cut from the modified layer by extending cracks in a thickness direction of the wafer 1. Also in this case, if the modified layer (modified regions 1e) or the like remains in the end surfaces of the formed chips 1d, cracks tend to occur in the chips 1d, so that the bending strength of the chips 1d is reduced. Accordingly, the modified layer (modified regions 1e) or the like is removed by wet etching. At this time, if gaps between the formed chips 1d are previously widened, the etchant 60 easily reaches the modified layer, and thus the modified layer can be effectively removed.

[0063] As described above, according to the workpiece processing method and the device chip manufacturing method according to the present embodiment, chips having high bending strength can be formed by removing the altered portions in the cutting surfaces. [First example]

[0064] In a first example, a case will be described in which a liquid plastic soluble in an organic solvent is used as the protective film 40b. In this first example, a case will be described in which a GaAs wafer 1 is set as a workpiece, the protective film 40b is formed on the upper surface 1a of the wafer 1, and the wafer 1 is sliced. In the first example, the frame unit preparation step S1 was performed to form the frame unit 13 by attaching a division tape "D765" manufactured by Lintec Corporation as the tape 9 to the lower surface side 1b of the wafer 1 having a metallic film on the lower surface side 1b.Next, in protective film formation step S2, the upper surface 1a of the wafer 1 was coated with a liquid resin formed by dissolving polyvinyl butyral (PVB) and propylene glycol methyl ether (PGME). Solvent Black 3, a light absorber capable of absorbing light having a wavelength of 532 nm, was previously added to the liquid resin.

[0065] The protective film forming step S2 and the cutting step S3, described next, were performed in a laser ablation processing apparatus "DFL7161" manufactured by DISCO Corporation. Spin coating was performed for 60 seconds at a rotation speed of 2000 rpm. Thereafter, the protective film 40b, which is soluble in an organic solvent, was formed on the upper surface 1a of the wafer 1 by drying the liquid resin. A pulsed xenon irradiation device was used to dry the liquid resin. The pulsed xenon irradiation device applied pulsed xenon light for 60 seconds.

[0066] Next, in the cutting step S3, a laser oscillated with Nd:YAG as a laser medium was used, and the wafer 1 was irradiated twice (two passes) with the laser beam 34b having a wavelength of 532 nm along each planned dividing line 3. As a result of the application of the laser beam at that time, the shape of an incident point of one pulse was set as an ellipse having a length of 1250 to 1043 μm in a direction along the planned dividing line 3 and a perpendicular length of 12 to 13 μm in a direction perpendicular to the direction along the planned dividing line 3. Ablation processing was performed by applying the laser beam 34b to form the processed grooves 1c on the wafer 1, and the wafer 1 was thereby cut.The laser processing conditions in a first application (first pass) of the laser beam 34b were a power of 5.5 W, a frequency of 5 kHz, a defocus amount (DF) of -0.06 mm, and a processing feed rate of 52 mm / s. The laser processing conditions in a second application (two passes) of the laser beam 34b were a power of 6.0 W, a frequency of 5 kHz, a DF amount of -0.08 mm, and a processing feed rate of 300 mm / s.

[0067] Next, in the pitch expansion step S4, the wafer 1 was placed in an expansion device 44 arranged in Fig. 6A and Fig.6B, and the gaps between the chips 1d of the wafer 1 were expanded. At that time, the gaps between chips 1d were expanded from approximately 10 to 25 μm. Next, etching step S5 was performed. First, the etchant 60 was prepared at room temperature (22°C) by mixing ammonia water with a concentration of 28% to 30% (ammonia water manufactured by Kanto Chemical Co., Inc.), a hydrogen hydroperoxide solution manufactured by Kishida Chemical Co., Ltd., and pure water in a ratio of 1:1:14, and the etchant was prepared in the etching tank 58. Next, the wafer 1 was introduced into the etching tank 58, and the altered regions 1e formed in the cut surfaces of the chips 1d were removed by immersing the wafer 1 in the etchant for 30 seconds.

[0068] In the etching step S5, a similar result was also obtained when the etchant 60 was prepared at room temperature (22°C) by mixing a concentrated sulfuric acid solution, a hydrogen peroxide solution, and pure water in a ratio of 1:10:50, and the wafer 1 was immersed in the etchant for 60 seconds. Next, the protective film 40b formed on the upper surface 1a was removed by cleaning the chips 1d with a PGME solution. At this time, an ultrasonic wave of 46 kHz was generated for 20 seconds using an ultrasonic cleaning device. As a result of the above, chips 1d whose altered regions 1b were removed were manufactured.

[0069] In the present example, the bending strength of the formed chips 1d was evaluated. The bending strength evaluation was performed using a three-point bending method. To evaluate the effect of the pitch expansion step S4, the bending strength of the chips 1d was evaluated according to a comparative example manufactured without performing the pitch expansion step S4. The bending strength evaluation was performed for each of the chips 1d manufactured using the etchant 60 prepared using ammonia water in the etching step S5 and the chips 1d manufactured using the etchant 60 prepared using concentrated sulfuric acid. The bending strength evaluation of the chips 1d was performed using the compact benchtop tester "EZ Graph" manufactured by Shimadzu Corporation.Then, the bending strength σ (MPa) of the chips 1d was evaluated by the following equation (1). In the following equation (1), L denotes the distance between support points, b the width of the chip 1b, and h the thickness of the chip 1d. B denotes the load and was derived by performing a destructive test on a chip 1e using a compact benchtop tester. In the present example, a load cell was set to 100 N and a feed speed was set to 1 mm / s. Additionally, L was set to 2 mm, b to 3.84 mm, and h to 0.1 mm. [Math. 1] δ−3LW2bh2

[0070] An average bending strength of the chips 1d according to the comparative example, which were manufactured using the etchant 60 containing ammonia water, was approximately 222 MPa, whereas the bending strength of the chips 1d according to the example was approximately 327 MPa. In addition, an average bending strength of the chips 1d according to the comparative example, which were manufactured using the etchant 60 containing concentrated sulfuric acid, was 232 MPa, whereas the bending strength of the chips 1d according to the example was approximately 554 MPa. In both cases, using the etchant 60 for the bending strength of the formed chips 1d, the bending strength of the chips 1d according to the example, which were manufactured by performing the pitch expansion step S4, was greater, which was confirmed. That is,that it was confirmed that when the distances between the chips 1b are increased by performing the distance expanding step S4, the etchant 60 easily enters between the chips 1d in the etching step S5 and thus the changed regions 1e in the cut surfaces of the chips 1d can be appropriately removed. [second example]

[0071] In a second example, a case will be described where a water-soluble plastic is used as the protective film 40b. In the second example, a case will be described where GaAs wafer 1 is set as a workpiece, the protective film 40b is formed on the upper surface 1a of the wafer 1, and the wafer 1 is sliced. An oxide film is formed on the upper surface 1a of the wafer 1. In the second example, as in the first example, the frame unit preparation step S1 is performed to form the frame unit 13 by attaching a division tape "D765" manufactured by Lintec Corporation as the tape 9 to the lower surface side 1b of the wafer 1, which has a metallic film formed on the lower surface side 1b.Next, in the protective film forming step S2, the upper surface 1a of the wafer 1 was coated with "HogoMax003," a water-soluble protective film material "HOGOMAX" (registered trademark) manufactured by DISCO Corporate, as the liquid resin. The drying of the liquid resin, the cutting step S3, and the pitch expansion step S4 were performed similarly to the first example.

[0072] Next, etching step S5 was performed. First, the etchant 60 was prepared by mixing ammonia water with a concentration of 28% to 30% (the ammonia water was manufactured by Kanto Chemical Co., Inc.), a hydrogen peroxide solution with a concentration of 30% (the hydrogen peroxide solution was manufactured by Kishida Chemical Co., Ltd.), and pure water in a ratio of 1:1:14, and the etchant 60 was provided in the etching tank 58. Next, the wafer 1 was placed in the etching tank 58, and the modified regions 1e formed with the cut surfaces of the chips 1d were removed by immersing the wafer 1 in the etchant 60 for 60 seconds. When the etching step S5 was performed, the water-soluble protective film 40b was also removed by the etchant 60. Therefore, a step to remove the protective film 40b is not necessary.In the present example, the oxide film having resistance to the etchant 60 was formed on the upper surface 1a of the wafer 1, and therefore, the oxide film protects the wafer 1 (chips 1d) from the etchant 60.

[0073] In this case, the protective film 40b has a function of preventing processing debris generated from the wafer 1 during the ablation processing performed in the dicing step S3 from adhering to the upper surface 1a of the wafer 1. The protective film 40b is removed together with the processing debris when performing the etching step S5 after the processing debris adheres to the protective film 40b due to the ablation processing. As a result of the above, the chips from which the altered regions 1e were removed were manufactured.

[0074] In the present example, the bending strength of the formed chips 1d was evaluated. The evaluation of the bending strength was performed by a three-point bending method as in the first example. In order to evaluate the effect of the pitch expansion step S4, the bending strength of chips 1d according to a comparative example, which were manufactured without the pitch expansion step S4, was also evaluated. As a result, an average bending strength of the chips 1d according to the comparative example was approximately 104 MPa, whereas the bending strength of the chips 1d according to the present example was approximately 341 MPa. That is,that it was confirmed that when the distances between the chips 1d are widened by performing the distance expanding step S4, the etchant 60 easily enters between the chips 1d in the etching step S5 and thus the changed regions 1e formed in the cutting surfaces of the chips 1d can be appropriately removed. [Third example]

[0075] In a third example, a case will be described in which the upper surface 1a of the wafer 1 is coated with a water-soluble liquid resin by performing the first coating step in the protective film forming step S2, and the upper surface 1a of the wafer 1 is next coated with a water-insoluble liquid resin by performing the second coating step. In the third example, a case will be described in which a GaAs wafer 1 is set as a workpiece, the protective film 40b is formed on the upper surface 1a of the wafer 1, and the wafer 1 is sliced.In the third example, as in the first example and the second example, the frame unit preparation step S1 was performed to form the frame unit 13 by attaching a division band “D765” manufactured by Lintec Corporation as the division band 9 to the lower surface side 1b of the wafer 1 having a metallic film formed on the lower surface side 1b.

[0076] Next, protective film forming step S2 was performed. In the first coating step of protective film forming step S2, the upper surface 1a of the wafer 1 was spin-coated with a mixture of "HogoMax003," a water-soluble protective film material "HOGOMAX" (registered trademark) manufactured by DISCO Corporate, which was coated at a ratio of 4:1 as the liquid resin. Spin-coating was performed for 120 seconds at a rotation speed of 2500 rpm. Then, in the second coating step of protective film forming step S2, the upper surface 1a of the wafer 1 was coated with a liquid resin formed by dissolving polyvinyl butyral (PVB) and propylene glycol methyl ether (PGME).Solvent Black 3, a light absorber capable of absorbing light with a wavelength of 532 nm, was pre-added to the liquid plastic. The coating with the liquid plastic was carried out by spin coating. Spin coating was carried out for 60 seconds at a rotation speed of 2000 rpm.

[0077] The water-soluble protective film 40b was formed in the first coating step, and the water-insoluble protective film was formed on the water-soluble protective film 40b in the second coating step. The drying of the liquid resin applied in the protective film forming step S2, the cutting step S3, and the spacing expansion step S4 were performed similarly to the first example and the second example. Next, the etching step S5 was performed. First, the etchant 60 was prepared by mixing ammonia water with a concentration of 28% to 30% (the ammonia water was manufactured by Kanto Chemical Co. Inc.), a hydrogen peroxide solution with a concentration of 30% (the hydrogen peroxide solution was manufactured by Kishida Chemical Co., Ltd.), and pure water in a ratio of 1:1:14, and the etchant was prepared in the etching tank 58.Next, the wafer 1 was placed in the etching tank 58, and the modified regions 1e formed in the cut surfaces of the chips 1d were formed by immersing the wafer 1 in the etchant 60 for 120 seconds. While the upper surface 1a of the wafer 1 was protected by the water-insoluble protective film during the etching step S5, no unexpected damage occurred to the water-soluble protective film 40b and the upper surface 1a of the wafer 1.

[0078] After the etching step S5 was performed, the protective film removal step was performed. In the protective film removal step, first, two-fluid cleaning was performed in which a mixture of pure water and air was supplied to the upper surface 1a of the wafer 1. Next, high-pressure cleaning was performed in which the upper surface 1a of the wafer was supplied with pure water under high pressure. In the protective film removal step, strong cleaning was performed, and thus, the water-soluble protective film 40b protected by the water-insoluble protective film could be removed together with the water-insoluble protective film. A step for removing the water-insoluble protective film using an organic solvent or the like is therefore unnecessary.

[0079] In the present example, the water-insoluble protective film was formed on the water-soluble protective film 40b, and thus, wet etching could be performed even on the wafer 1 having no layer resistant to the etchant 60 as the upper surface 1a. In addition, the water-insoluble protective film is capable of being removed together with the water-soluble protective film 40b without the need to use an organic solvent. In addition, it was confirmed that even in a case of performing only high-pressure cleaning in the protective film removing step as a modification of the present example, the water-soluble protective film 40b protected by the water-insoluble protective film can be suitably removed together with the water-insoluble protective film.

[0080] It should be noted that the present invention is not limited to the description of the foregoing embodiment, but can be modified and embodied in various ways. For example, while a description was given of a case in which the protective film forming step S2 and the cutting step S3 were performed after the frame unit preparing step S1 in the foregoing embodiment, a mode of the present invention is not limited thereto. That is, the frame unit preparing step S1 may be performed immediately before the pitch expanding step S4. That is, the tape 9 may be exchanged between the cutting step S3 and the pitch expanding step S4.In this case, before performing the protective film forming step S2, a frame unit different from the frame unit 13 is formed using a frame and a tape different from the frame 11 and the tape 9 used in the frame unit preparation step S1. After that, the tape is peeled off from the wafer 1 (chips 1d) after performing the protective film forming step S2 and the dicing step S3, and the frame 11 and the tape 9 are integrated with the wafer 1 (chips 1d) by performing the frame unit preparation step S1.

[0081] In addition, while a case was described in which the tape 9 is fixed to the lower surface 1b of the wafer 1 having the metallic film 7 formed on the lower surface 1b side in the foregoing embodiment, a mode of the present invention is not limited to this. That is, the metallic film 7 may be formed on the upper surface 1a side of the wafer 1. Alternatively, the upper surface 1a side of the wafer 1 may be oriented downward, and the tape 9 may be fixed to the upper surface 1a side.

[0082] In addition, while a description was given of a case where the ablation processing along the planned dividing lines 3 was performed by applying the laser beam 34b that can be absorbed by the wafer 1 in the cutting step S3 in the foregoing embodiment, a mode of the present invention is not limited to this. That is, the wafer 1 may be cut by another method in the cutting step S3. For example, the frame unit 13 is formed by attaching the tape 9 to the lower surface 1b of the wafer 1 having the metallic film 7 formed on the upper surface 1a, the protective film 40b is formed on the upper surface 1a, and ablation processing is performed by the laser beam 34b.At this time, a machined groove having a depth that does not reach the lower surface 1b of the wafer 1 is formed along the planned dividing line 3. Next, the wafer is cut by advancing a cutting blade having a width smaller than the width of the machined grooves into the machined groove while rotating the cutting blade, thereby forming a cut groove that reaches the lower surface 1b of the wafer 1 from a lower surface of the machined grooves. Also in this case, the bending strength of the chips 1d can be improved by removing the altered regions that appear in the cut surfaces of the wafer 1 (chips 1d) due to the ablation processing by wet etching.In addition, because the cutting blade is not used for the metallic film 7, a burr or the like does not occur from the cut surfaces, so that the quality of the chips 1d is not reduced.

Claims

[1] A workpiece machining method for forming chips by dividing a workpiece, the workpiece machining method comprising: a frame unit preparing step of preparing a frame unit including the workpiece on which a planned parting line is set, a stretchable band fixed to an upper surface and a lower surface of the workpiece, and an annular frame having an opening and an annular portion surrounding the opening, wherein an outer peripheral portion of the band is fixed to the annular portion of the annular frame; a protective film forming step of forming a protective film by coating the other of the upper surface and the lower surface of the workpiece with a liquid plastic; a cutting step of completely cutting the workpiece along the designed dividing line by irradiating the workpiece with a laser beam along the designed dividing line so that spaces between the chips are formed, after the protective film forming step; a gap expanding step of expanding gaps between chips formed in the cutting step by expanding the tape outward in a radial direction after the cutting step; and an etching step of removing altered regions formed in cut surfaces of the respective chips by applying the laser beam in the cutting step by wet etching after the pitch expanding step. [2] A device chip manufacturing method for manufacturing device chips by dividing a wafer, the device chip manufacturing method comprising: a frame unit preparation step of preparing a frame unit including the wafer on which a plurality of planned dividing lines are set that cross each other, the wafer having a component formed on an upper surface in each of the regions divided by the planned dividing lines, a stretchable band attached to one of the upper surface and the lower surface of the wafer, and an annular frame having an opening and an annular region surrounding the opening, an outer peripheral portion of the band being fixed to the annular region of the annular frame; a protective film forming step of forming a protective film by coating the other of the upper surface and the lower surface of the wafer with a liquid plastic; a cutting step of cutting the wafer along the planned dividing lines and forming individual device chips by irradiating the wafer with a laser beam along the planned dividing lines after the protective film forming step; a pitch expanding step of expanding the pitches between belly element chips formed in the cutting step by expanding the strip outward in a radial direction after the cutting step; and an etching step of removing altered regions formed in cut surfaces of the device chips by applying the laser beam in the cutting step by wet etching after the pitch expanding step. [3] A manufacturing method for a component chip according to claim 2, wherein the wafer has a resistant layer having resistance to wet etching on the other of the upper surface and the lower surface, wherein the protective film has been formed on the other of the upper surface and the lower surface in the protective film forming step, the protective film formed in the protective film forming step is water-soluble, the laser beam applied to the wafer in the cutting step is a laser beam whose wavelength can be absorbed by the wafer, in the cutting step, the wafer is cut by ablation processing using the laser beam, and in the etching step the protective film is removed by wet etching. [4] A manufacturing method for a component chip according to claim 2, wherein the protective film is resistant to wet etching, and In the etching step, the protective film protects the other of the top surface and the bottom surface of the wafer from wet etching. [5] The manufacturing method for a component chip according to any one of claims 2 to 4, wherein the protective film forming step includes: a first coating step of coating the other of the upper surface and the lower surface of the wafer with a first liquid plastic serving as a material for a water-soluble protective film, and a second coating step of coating the other of the upper surface and the lower surface of the wafer with a second liquid plastic serving as a material for a water-insoluble protective film after the first coating step. [6] A manufacturing method for a device chip according to any one of claims 2 to 5, wherein the wafer includes GaAs. [7] A manufacturing method for a device chip according to any one of claims 2 to 6, wherein the wafer has a metallic film formed on the lower surface.

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