Workpiece processing method

Abstract

To provide a processing method for preventing a metal film of a workpiece from being damaged.SOLUTION: The method for processing a workpiece (wafer W) includes a metal film coating step of coating a surface including a recess with a metal film 10, a protective film forming step of forming a protective film 12 so as to cover the metal film, a first holding step of holding a recess side by a holding surface 2 a of a first holding unit 2 having a diameter smaller than a diameter of the recess and exposing one side surface of the workpiece, a sheet sticking step of sticking one side surface of a protective sheet to one side surface of the workpiece, a second holding step of holding the protective sheet side by a second holding unit and exposing the other side surface of the workpiece, and a ring-shaped reinforcing portion separating step of separating the ring-shaped reinforcing portion from the device region by separation processing.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a technique for protecting a metal film formed on a workpiece such as a semiconductor wafer. [Background technology]

[0002] In recent years, power devices have attracted attention as semiconductor devices that can control higher voltages and currents than ICs, and are used in power supplies and inverter control for electric vehicles, hybrid vehicles, air conditioners, etc.

[0003] Power devices are formed by epitaxially growing a SiC single crystal film (also called an epitaxial film) on the surface of a single crystal substrate (hereinafter simply referred to as the workpiece) made of SiC, which has better electrical properties than a silicon wafer.

[0004] On the other hand, when the thickness of the workpiece becomes thin, there is a problem that the workpiece may break during transportation, so a processing technology (TAIKO (registered trademark)) is known in which a ring-shaped reinforcing portion is formed on the outer periphery (see, for example, Patent Document 1).

[0005] In Patent Document 1, the other side (back side) of a workpiece corresponding to a device region formed on one side (front side) is ground to thin it, forming a recess, and a ring-shaped reinforcing portion is formed on the periphery.The region including the recess is then covered with a metal film that will serve as an electrode, and with the other side of the workpiece exposed upward, the ring-shaped reinforcing portion on the periphery is removed to separate the workpiece into individual devices. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-019461 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, when dividing the workpiece into devices, the outer ring-shaped reinforcing portion is removed while the other side of the workpiece is exposed upward, so it is necessary to attach a protective sheet to one side of the workpiece before the process of removing the ring-shaped reinforcing portion.

[0008] In this case, when the recess on the other surface of the workpiece is held by the holding table of the device for applying the protective sheet, the metal film comes into contact with the holding table, causing damage such as scratches to the metal film.

[0009] In view of the above problems, the present invention proposes a novel technique for preventing damage such as scratches from occurring on the metal film of a workpiece. [Means for solving the problem]

[0010] The problem to be solved by the present invention is as described above, and the means for solving this problem will now be described.

[0011] According to one aspect of the present invention, there is provided a method for processing a workpiece having, on one side thereof, a device region in which devices are formed in multiple regions defined by planned division lines, and a peripheral excess region surrounding the device region, and having, on the other side thereof, a recess formed in an area corresponding to the device region, and a ring-shaped reinforcement portion surrounding the recess, the method including at least a metal film coating step for coating at least the surface of the other side including the recess with a metal film; a protective film forming step for applying a liquid resin to cover the metal film and form a protective film; a first holding step for holding the recess side with a first holding unit having a diameter smaller than the diameter of the recess, thereby exposing the one side of the workpiece; a sheet adhering step for adhering one side of a protective sheet to the one side of the workpiece; a second holding step for holding the protective sheet side with a second holding unit, thereby exposing the other side of the workpiece; and a ring-shaped reinforcement separation step for separating the device region and the ring-shaped reinforcement portion by separation processing.

[0012] According to one aspect of the present invention, the method further includes, after the sheet adhering step, a sheet flattening step of flattening the other side of the protection sheet.

[0013] According to one aspect of the present invention, the method further includes, after the ring-shaped reinforcing portion separating step, a singulating step of singulating the workpiece into individual device chips along the planned dividing lines.

[0014] According to one aspect of the present invention, the liquid resin is water-soluble.

[0015] According to one aspect of the present invention, the ring-shaped reinforcement separation step is performed by laser processing in which a laser beam is irradiated onto the workpiece from the other side at the boundary between the ring-shaped reinforcement and the device region to cut it.

[0016] According to one aspect of the present invention, the ring-shaped reinforcing portion separating step is performed by cutting the boundary between the ring-shaped reinforcing portion and the device region from the other side surface using a cutting blade.

[0017] Furthermore, according to one aspect of the present invention, the singulation step involves singulating the workpiece into individual device chips along the planned division lines by laser processing, and further includes a protective film removal step of removing the protective film after the singulation step.

[0018] Furthermore, according to one aspect of the present invention, after the ring-shaped reinforcement portion separation step, a protective film removal step is further included in which the protective film is removed, and the singulation step is a step in which the workpiece is singulated into individual device chips along the planned division line by cutting processing. [Effects of the Invention]

[0019] The present invention provides the following effects. That is, according to one aspect of the present invention, it is possible to protect the metal film formed in the recessed portion with the protective film, and to prevent the metal film from being damaged, such as by scratches. [Brief explanation of the drawings]

[0020] [Figure 1] (A) is a diagram showing one side of the wafer, and (B) is a diagram showing the other side of the wafer. [Figure 2] 1 is a flowchart showing steps included in a processing method according to the present invention. [Figure 3] 10A to 10C are diagrams illustrating a metal film coating step. [Figure 4] 5A to 5C are diagrams illustrating a protective film forming step. [Figure 5] FIG. 10 is a diagram illustrating a first holding step. [Figure 6] 1A is a diagram illustrating a sheet adhering step, and FIG. 1B is a diagram illustrating a state in which a protective sheet has been adhered. [Figure 7] 5A to 5C are diagrams illustrating a sheet flattening step. [Figure 8] FIG. 10 is a diagram illustrating a second holding step. [Figure 9] 1A is a diagram illustrating a ring-shaped reinforcing portion separation step, and FIG. 1B is a diagram illustrating a state in which the ring-shaped reinforcing portion has been separated. [Figure 10] FIG. 10 is a diagram illustrating a singulation step. [Figure 11] 10A to 10C are diagrams illustrating an example of performing a singulation step by laser processing. [Figure 12] (A) is a diagram illustrating the protective film removal step, and (B) is a diagram showing the state after cleaning. DETAILED DESCRIPTION OF THE INVENTION

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Figures 1(A) and 1(B) show an example of a wafer W that is a workpiece in a processing method according to the present invention.

[0022] 1(A) shows one side surface Wa of a wafer W, which is configured to have a device region Dr in which devices D are formed in multiple regions defined by planned division lines L. Also, a peripheral surplus region Gr is formed on the side surface Wa, surrounding the device region Dr. In this example, the wafer W is configured as a semiconductor device wafer, and the material of the wafer W is, for example, SiC, silicon, GaN, GaAs, etc.

[0023] 1(B) shows the other side Wb of the wafer W, in which a recess Wk is formed in an area corresponding to the device region Dr. A ring-shaped reinforcing portion Wr is also formed on the other side Wb, surrounding the recess Wk. The recess Wk is formed by grinding and thinning the other side Wb so as to leave the ring-shaped reinforcing portion Wr, and is formed by a well-known method.

[0024] The following description will be given in the order of the flowchart shown in FIG. <Metal film coating step> 3, this is a step of covering the other side surface Wb of the wafer W, including at least the recessed portions Wk, with a metal film 10. The metal film 10 is made of gold, silver, titanium, or the like, and constitutes an electrode.

[0025] The metal film 10 can be formed using, for example, a known reduced-pressure film-forming apparatus. In a known method, for example, in a reduced-pressure environment, argon gas is introduced into the wafer W with the other side Wb of the wafer W facing a metal sputtering source to generate plasma. Argon ions in the plasma collide with the sputtering source, ejecting particles that deposit on the other side Wb of the wafer W, forming the metal film 10. The metal film 10 has a thickness of, for example, about 30 to 60 nm, and covers at least the recesses Wk on the other side Wb of the wafer W, thereby forming the metal film 10 at a position corresponding to the backside of the device region Dr (FIG. 1(A)).

[0026] <Protective film formation step> As shown in FIG. 4, this is a step in which a liquid resin is applied so as to cover the metal film 10, thereby forming a protective film 12.

[0027] The protective film 12 can be formed, for example, by holding the wafer W with the metal film 10 exposed on the upper side on a spinner table that rotates around its axis, supplying and applying (spin coating) liquid resin to the surface of the metal film 10, and then drying it.

[0028] The liquid resin may be, for example, a liquid water-soluble resin such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP) (for example, HogoMax (registered trademark) manufactured by Disco Corporation). The thickness of the protective film formed is, for example, 10 to 20 μm.

[0029] <First holding step> As shown in FIG. 5, this is a step in which the recess Wk is held by the first holding unit 21 having a diameter d2 smaller than the diameter d1 of the recess Wk, and one side surface Wa of the wafer W is exposed.

[0030] In this embodiment, the first holding unit 21 is configured as a table having a flat, circular holding surface 21a with a diameter d2, and the wafer W is placed so that a recess Wk formed on the other side Wb of the wafer W is placed over this holding surface 21a. A protective film 12 is formed on the recess Wk, and this protective film 12 abuts against the holding surface 21a, preventing the metal film 10 from coming into contact with the holding surface 21a. This prevents the metal film 10 from coming into contact with the holding surface 21a and causing damage such as scratches to the metal film 10.

[0031] The holding surface 21a of the first holding unit 21 can be configured to be connected to, for example, a suction source (not shown) to generate negative pressure and to hold the wafer W so as not to shift. When held by the first holding unit 21, one side surface Wa of the wafer W is exposed upward.

[0032] <Sheet application steps> As shown in FIGS. 6(A) and 6(B), this is a step of attaching one side surface Sa of the protective sheet S to one side surface Wa of the wafer W.

[0033] Specifically, the protective sheet S is attached with the side surface Sa facing downward to one side surface Wa of the wafer W exposed upward while held by the first holding unit 21. The protective sheet S may be an adhesive sheet having an adhesive layer laminated on a base material, or, for example, a sheet that does not have an adhesive layer laminated on a base material and becomes adhesive when heated.

[0034] In this embodiment, the side of the protective sheet S that is attached to one side Wa of the wafer W is called one side Sa, and the opposite side is called the other side Sb. A metal annular frame F having an inner diameter larger than the outer diameter of the wafer W is attached in advance to one side Sa of the protective sheet S. This annular frame F is integrated with the wafer W via the protective sheet S, and this integration forms a frame unit U (FIG. 6(B)).

[0035] <Sheet flattening step> As shown in FIG. 7, after the sheet adhering step, the other side surface Sb of the protection sheet S is flattened.

[0036] Specifically, the grinding unit 30 is used to grind the protective sheet S attached to the wafer W held by the first holding unit 21 by processing and feeding the first holding unit 21 in the horizontal direction, thereby flattening the other side Sb of the protective sheet S. Flattening the other side Sb of the protective sheet S can eliminate unevenness and thickness variations on the other side Sb.

[0037] Furthermore, this unevenness and thickness variation can be prevented from adversely affecting the subsequent ring-shaped reinforcing portion separation step and singulation step, thereby improving processing accuracy. Specifically, for example, by flattening the other side surface Sb of the protective sheet S, it is possible to suppress variation in the height direction of the focal point of the laser light in the thickness direction of the wafer W.

[0038] The grinding unit 30 can be configured to include, for example, a cutting tool 32, a cutting wheel 34 to which the cutting tool 32 is fixed, and a spindle 36 to which the cutting wheel 34 is rotated. The first holding unit 21 may be the same as that used in the sheet adhering step, or may be another unit.

[0039] In one embodiment, the sheet flattening step may be omitted.

[0040] <Second holding step> As shown in FIG. 8, this is a step in which the protective sheet S side is held by the second holding unit 22, and the other side Wb of the wafer W is exposed.

[0041] Specifically, the wafer W (frame unit U) that has undergone the sheet flattening step is turned upside down to expose the other side Wb of the wafer W upward, and the other side Sb of the protective sheet S is held by the second holding unit 22. If the sheet flattening step is omitted, the wafer W (frame unit U) that has undergone the sheet adhering step is held by the second holding unit 22.

[0042] In this embodiment, second holding unit 22 is configured as a table having a flat, circular holding surface 22a, and the other side Sb of protection sheet S is placed on this holding surface 22a.

[0043] The holding surface 22a of the second holding unit 22 is configured to be connected to, for example, a suction source (not shown) to generate negative pressure, and to hold the wafer W by suction via the protective sheet S, thereby preventing the wafer W from shifting. When held by the second holding unit 22, the other side surface Wb of the wafer W is exposed upward.

[0044] <Ring-shaped reinforcement separation step> As shown in FIGS. 9(A) and 9(B), this is a step of separating the device region Dr and the ring-shaped reinforcing portion Wr by separation processing.

[0045] Specifically, for example, as shown in Figure 9(A), a laser processing unit 40 is used to cut the boundary between the device region Dr and the ring-shaped reinforcing portion Wr, thereby separating the ring-shaped reinforcing portion Wr from the wafer W as shown in Figure 9(B).

[0046] The laser processing by the laser processing unit 40 is laser ablation processing using laser light 42, and involves forming a groove at the boundary between the device region Dr and the ring-shaped reinforcing portion Wr. Alternatively, the laser processing by the laser processing unit 40 is performed by setting the focal point of the laser light 42 at the boundary between the device region Dr and the ring-shaped reinforcing portion Wr to form a modified layer and then breaking the modified layer. Alternatively, in addition to performing separation processing by laser processing using the laser processing unit 40, separation may also be performed by forming a cut groove at the boundary between the device region Dr and the ring-shaped reinforcing portion Wr by cutting processing using a rotating cutting blade.

[0047] <Singulation step> As shown in FIG. 10, this is a step of dividing the wafer W into individual device chips along the planned dividing lines L (FIG. 1(A)).

[0048] Specifically, the wafer W (frame unit U) is held on a holding table 60, and the cutting blade 62a of the cutting unit 62 is positioned at a predetermined cutting height. Then, the cutting blade 62a is rotated at high speed while the holding table 60 is moved horizontally for processing, thereby forming cutting grooves along the planned division lines L (FIG. 1(A)) and singulating the wafer into individual device chips. During processing, cutting water (not shown) is supplied to remove the protective film 12 made of a water-soluble resin, thereby exposing the surface 10a of the metal film 10.

[0049] Alternatively, as shown in Fig. 11, in the singulation step, laser processing may be performed along the planned division lines L (Fig. 1(A)) using a laser processing unit 70 to singulate into individual device chips. For the laser processing, well-known applications such as laser ablation processing or a method of forming and breaking a modified layer can be used.

[0050] Furthermore, it is expected that debris will be generated and adhere to the wafer (metal film) during the laser processing shown in FIG. 11, but the protective film 12 can protect the metal film 10.

[0051] <Protection film removal step> As shown in FIG. 12(A), this is a step of removing the protective film 12 after the singulation step.

[0052] Specifically, in this embodiment, the wafer W (frame unit U) is held and rotated on a holding table 50, and cleaning water 54 is supplied from a nozzle 52 to remove the protective film 12 made of a water-soluble resin, thereby exposing the surface 10a of the metal film 10 as shown in Figure 12(B).

[0053] 10, when the singulation step is performed using a cutting unit 62, the protective film that is not completely removed by the cutting water can be removed in the protective film removal step. Also, when the singulation step is performed using a laser processing unit 70 as shown in FIG. 11, the protective film is completely removed in the protective film removal step.

[0054] As shown in FIG. 12(B), after the protective film 12 is removed, the surface 10a of the metal film 10 is dried by rotating the holding table 50 at high speed, for example.

[0055] In the series of steps described above, in the protective film formation step, as shown in Figure 4, the metal film 10 formed in the recess Wk can be protected by the protective film 12, thereby preventing problems such as scratches from occurring on the metal film 10. [Explanation of symbols]

[0056] 10 Metal Film 10a surface 12 Protective film 21 First holding unit 22 Second holding unit 30 Grinding Unit 32 Tool 34 Bite Wheel 36 Spindle 40 Laser Processing Unit 42 Laser Light 50 holding table 52 nozzles 54 Cleaning water 60 Holding Table 62 Cutting unit 62a Cutting Blade 70 Laser Processing Unit D Device Dr Device Area Front annular frame Gr Surplus outer area L planned division line S Protective Sheet Sa side Sb other side U Frame Unit W wafer One side of Wa Wb other side Wk recess Wr Ring-shaped reinforcement

Claims

1. a device region in which devices are formed in a plurality of regions partitioned by planned division lines; a peripheral excess area surrounding the device area on one side, a recess formed in a range corresponding to the device region; a ring-shaped reinforcing portion surrounding the recess on the other side of the workpiece, a metal film coating step of coating at least the surface of the other side surface including the recess with a metal film; a protective film forming step of applying a liquid resin to cover the metal film to form a protective film; a first holding step of holding the recessed portion side with a first holding unit having a diameter smaller than the diameter of the recessed portion to expose the one side surface of the workpiece; a sheet adhering step of adhering one side of a protective sheet to the one side of the workpiece; a second holding step of holding the protective sheet side with a second holding unit and exposing the other side of the workpiece; a ring-shaped reinforcing portion separating step of separating the device region and the ring-shaped reinforcing portion by a separation process; A method for processing a workpiece comprising at least the steps of:

2. a sheet flattening step of flattening the other side of the protective sheet after the sheet adhering step; 2. The method for processing a workpiece according to claim 1, further comprising:

3. a singulation step of singulating the workpiece into individual device chips along the planned division lines after the ring-shaped reinforcing portion separating step; 3. The method for processing a workpiece according to claim 2, further comprising:

4. The liquid resin is water-soluble.

4. The method for processing a workpiece according to claim 3.

5. the ring-shaped reinforcing portion separating step is performed by laser processing in which a laser beam is applied to the workpiece from the other side surface to cut a boundary between the ring-shaped reinforcing portion and the device region.

5. The method for processing a workpiece according to claim 1.

6. the ring-shaped reinforcing portion separating step is performed by cutting a boundary portion between the ring-shaped reinforcing portion and the device region from the other side surface using a cutting blade.

5. The method for processing a workpiece according to claim 1.

7. the singulation step singulates the workpiece into individual device chips along the planned division lines by laser processing; After the singulation step, the method further includes a protective film removal step of removing the protective film.

6. The method for processing a workpiece according to claim 5.

8. the singulation step singulates the workpiece into individual device chips along the planned division lines by laser processing; After the singulation step, the method further includes a protective film removal step of removing the protective film.

7. The method for processing a workpiece according to claim 6.

9. The method further includes a protective film removing step of removing the protective film after the ring-shaped reinforcing portion separating step, The singulation step involves singulating the workpiece into individual device chips along the planned division lines by cutting.

6. The method for processing a workpiece according to claim 5.

10. The method further includes a protective film removing step of removing the protective film after the ring-shaped reinforcing portion separating step, The singulation step involves singulating the workpiece into individual device chips along the planned division lines by cutting.

7. The method for processing a workpiece according to claim 6.

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