Protective film forming method and wafer processing method

Abstract

To provide a protective film forming method that takes into consideration contamination of air bubbles in the protective film formed on the surface of a wafer, and prevents processing defects after forming the protective film.SOLUTION: A protective film forming method includes a holding step of holding a wafer W with a spinner table, a first protective film forming step of supplying a water-soluble resin 12 onto a surface Wa of the held wafer, rotating the spinner table to coat the wafer with the water-soluble resin, and then maintaining the rotation of the spinner table to dry the water-soluble resin with which the wafer is coated, thereby forming a first protective film layer M1, a cleaning and drying step of supplying a cleaning liquid while rotating the wafer W, thereby washing away at least the upper layer of the first protective film layer, and drying it, and a second protective film forming step of supplying the water-soluble resin onto the wafer and rotating the spinner table to cover the wafer with the water-soluble resin, thereby forming a protective film M in which a second protective film layer M2 is laminated.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a protective film forming method for forming a protective film on a wafer, and a wafer processing method. [Background technology]

[0002] Conventionally, as disclosed in Patent Document 1, for example, in laser grooving processing in which a laser is irradiated onto a predetermined region of a wafer such as a semiconductor wafer, it is known that in order to prevent debris generated during processing from adhering to the surface of the wafer, a protective film made of a water-soluble resin is formed on the wafer in advance, and debris adhering to the protective film is washed away together with the protective film after processing.

[0003] Furthermore, as disclosed in Patent Document 2, for example, in plasma dicing of a wafer, it is known that a protective film is formed on the surface of the wafer using a water-soluble resin, an etching mask is formed in a predetermined area, and plasma etching is performed on the unmasked streets.

[0004] As described above, it is known that a protective film is formed on the surface of a wafer using a protective film agent made of a water-soluble resin. However, if air bubbles are mixed into the protective film, the thickness of the protective film in the area where the air bubbles are mixed becomes thinner than in other areas.

[0005] In laser grooving, if a thin area of ​​the protective film peels off locally during laser processing, there is a concern that debris may adhere to the surface of the wafer, resulting in processing defects.

[0006] Furthermore, in plasma dicing, there is a concern that areas where the protective film is thin may be etched and not masked, resulting in processing defects in which areas that should be masked are processed.

[0007] In relation to the above, Patent Document 3 discloses a coating device for degassing a protective film agent made of a water-soluble resin and coating a wafer with the protective film agent without bubbles. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-140311 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-207737 [Patent Document 3] Japanese Patent Publication No. 2020-068323 Summary of the Invention [Problem to be solved by the invention]

[0009] However, as disclosed in Patent Document 3, even when a degassed protective film agent is supplied, bubbles may be generated in the process of the protective film agent being dispensed onto the wafer and coating the wafer surface. In particular, when a thick protective film is formed on the wafer surface, there is a high risk of bubbles being mixed into the formed protective film.

[0010] For example, when forming a protective film on a wafer with large irregularities on its surface, the protective film must be thick enough to fill the irregularities. Also, when forming a protective film as a mask for plasma dicing, the protective film must be thick enough to ensure a sufficient thickness. In such cases, air bubbles are particularly likely to be trapped in the protective film, and measures are required.

[0011] In view of the above problems, the present invention proposes a novel technique for preventing processing defects after forming a protective film, taking into consideration the possibility of bubbles being mixed into the protective film formed on the wafer surface. [Means for solving the problem]

[0012] The problem to be solved by the present invention is as described above, and the means for solving this problem will now be described.

[0013] According to one aspect of the present invention, a protective film formation method for forming a protective film on a wafer includes: a holding step of holding the wafer on a spinner table; a first protective film formation step of supplying a water-soluble resin onto the wafer held on the spinner table and rotating the spinner table to coat the wafer with the water-soluble resin, and then drying the water-soluble resin that has coated the wafer by maintaining the rotation of the spinner table to form a first protective film layer; a cleaning and drying step of, after performing the first protective film formation step, supplying a cleaning liquid onto the wafer while rotating the wafer held on the spinner table to wash away at least the upper layer of the first protective film layer, and then drying the wafer; and a second protective film formation step of, after performing the cleaning and drying step, supplying a water-soluble resin onto the wafer held on the spinner table and rotating the spinner table to coat the wafer with the water-soluble resin to form a protective film having a second protective film layer laminated thereon.

[0014] According to one aspect of the present invention, there is provided a method for processing a wafer having a plurality of intersecting streets formed on its surface and having devices formed in each of the areas partitioned by the streets, the method comprising: a holding step of holding the wafer on a spinner table to expose the surface; a first protective film forming step of supplying a water-soluble resin to the surface of the wafer held on the spinner table and rotating the spinner table to coat the wafer with the water-soluble resin and form a first protective film layer; and after the first protective film forming step, supplying a cleaning liquid onto the wafer while rotating the wafer held on the spinner table to form a first protective film layer. The wafer processing method includes a cleaning and drying step of washing away an upper layer of a protective film layer and then drying the wafer; a second protective film forming step of supplying a water-soluble resin onto the wafer held by the spinner table after the cleaning and drying step and rotating the spinner table to coat the wafer with the water-soluble resin and form a protective film having a second protective film layer laminated thereon; a groove forming step of removing at least a portion of the protective film along the street after the second protective film forming step; and an etching step of performing plasma etching on the wafer via the protective film after the groove forming step.

[0015] According to one aspect of the present invention, the method further comprises, after the etching step, a protective film removing step of supplying a cleaning liquid to the protective film to remove the protective film. [Effects of the Invention]

[0016] The present invention has the following effects. That is, according to one aspect of the present invention, even if bubbles occur in the first protective film layer, by forming a second protective film layer after removing the bubbles, it is possible to form a protective film M in which the generation of bubbles is suppressed. This effectively prevents processing defects due to insufficient protection against debris during laser processing and processing defects due to insufficient mask effectiveness during plasma dicing. Furthermore, although the thicker the protective film, the more likely bubbles are to occur, according to the present invention, by stacking multiple protective film layers in stages, the generation of bubbles can be suppressed even when a thick protective film is formed overall. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a diagram showing a wafer on which a protective film is formed. [Figure 2] FIG. 2 is a perspective view showing the configuration of a protective film coating and cleaning device. [Figure 3] FIG. 2 is a side cross-sectional view showing the configuration of the protective film coating and cleaning device. [Figure 4] 1 is a flowchart of a method for forming a protective film. [Figure 5] (A) is a diagram explaining the holding step, and (B) is an enlarged cross-sectional view of the wafer. [Figure 6] 1A is a diagram for explaining a first protective film forming step, and FIG. 1B is an enlarged cross-sectional view of the wafer after the first protective film forming step. [Figure 7] (A) is a diagram explaining the cleaning and drying step, (B) is an enlarged cross-sectional view of the wafer after the cleaning and drying step, and (C) is an enlarged cross-sectional view of the wafer after the cleaning and drying step. [Figure 8] 1A is a diagram for explaining the second protective film forming step, and FIG. 1B is an enlarged cross-sectional view of the wafer after the second protective film forming step. [Figure 9] (A) is a diagram for explaining the groove forming step, and (B) is an enlarged cross-sectional view of the wafer after the groove forming step. [Figure 10](A) is a diagram explaining the etching step, and (B) is an enlarged cross-sectional view of the wafer after the etching step. [Figure 11] 1A is a diagram for explaining the protective film removal step, and FIG. 1B is an enlarged cross-sectional view of the wafer after the protective film removal step. DETAILED DESCRIPTION OF THE INVENTION

[0018] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing a wafer on which a protective film is formed.

[0019] The back surface Wb of the wafer W is fixed to an annular frame F via tape T, and the wafer W is handled as a wafer unit U. The wafer W may be handled individually without being fixed to the annular frame F. The material of the wafer W is, for example, silicon, sapphire, SiC, GaAs, etc.

[0020] Devices D are formed in a regular arrangement on the surface Wa of the wafer W, and as will be described in detail later, a protective film is formed on the surface Wa so as to cover the devices D. Mutually perpendicular streets S (planned division lines) are set in a grid pattern on the surface Wa of the wafer W, and devices D are formed in areas defined by each street S. Division starting points are formed by processing such as laser processing, plasma etching, and cutting along the streets S, and the wafer is separated into individual chips by breaking at the division starting points.

[0021] There are no limitations on the material, shape, structure, size, etc. of the wafer. For example, the wafer may include a substrate formed from other semiconductors, ceramics, resin, or other materials. Similarly, there are no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices. Furthermore, the wafer does not necessarily have to have any devices formed thereon.

[0022] 2 and 3 are diagrams showing the configuration of a protective film coating and cleaning apparatus 50 (also called a spin coater) that has two functions of cleaning and forming a protective film.

[0023] The protective film coating and cleaning device 50 is housed in a housing space 51 a formed in a housing 51 . The protective film coating and cleaning apparatus 50 includes a spinner table 52 that is rotated by a motor 59 (FIG. 3) and holds a wafer W (wafer unit U (FIG. 3)), a support base 53 that supports the lower part of the spinner table 52 and raises and lowers it, a clamp 54 that clamps the wafer unit U (FIG. 3) held on the spinner table 52, a nozzle unit 55 that supplies a cleaning liquid and a protective film agent to the workpiece (wafer W), and a moving unit 58 that moves the nozzle unit 55.

[0024] 2, the spinner table 52 has a suction holder 52a that forms a flat holding surface and a frame holder 52b that surrounds the periphery of the suction holder 52a. The suction holder 52a suction-holds the wafer W of the wafer unit U shown in FIG. 1 from below. The frame holder 52b supports the annular frame F of the wafer unit U.

[0025] As shown in Figures 2 and 3, pendulum-type clamps 54 are provided at four locations on the frame holding portion 52b of the spinner table 52. These clamps tilt due to the centrifugal force generated by the rotation of the spinner table 52, and press down on the annular frame F (Figure 1) from above to clamp it.

[0026] 2 and 3, the nozzle unit 55 has two swing arms 56a and 57a arranged in parallel, and the rear end of each arm is fixed to a rotation shaft 58a of a moving unit 58. The rotation shaft 58a of the moving unit 58 is rotated by a motor 58b (FIG. 3), which causes the swing arms 56a and 57a of the nozzle unit 55 to swing horizontally above the spinner table 52.

[0027] 2 and 3, in the nozzle unit 55, a cleaning liquid nozzle 56 is provided at the tip of one of the swing arms 56a, and a cleaning liquid is supplied from the cleaning liquid nozzle 56. The cleaning liquid may be a single liquid such as pure water, or a mixed fluid (two-fluid) obtained by mixing a liquid such as pure water with a gas such as air. The cleaning liquid nozzle 56 is connected to a cleaning liquid supply source via the swing arm 56a and a control valve (not shown), and the supply and stop of the cleaning liquid is controlled by controlling the control valve.

[0028] 2 and 3, in the nozzle unit 55, a protective film agent nozzle 57 is provided at the tip of the other swing arm 57a, and a water-soluble resin is supplied from the protective film agent nozzle 57 toward the surface of a wafer (not shown). The water-soluble resin is a material for forming a protective film, and examples of this water-soluble resin include PVA (polyvinyl alcohol), PEG (polyethylene glycol), PEO (polyethylene oxide), and PVP (polyvinylpyrrolidone). The protective film agent nozzle 57 is connected to a protective film agent supply source via the swing arm 57a and a control valve (not shown), and the supply and stop of the protective film agent is controlled by controlling the control valve.

[0029] Next, an example of a method for forming a protective film using the above-described apparatus configuration will be described below. Fig. 4 is a flowchart showing steps performed in the method for forming a protective film.

[0030] <Holding step> 5(A), this is a step in which the wafer W is held by the spinner table 52. In this embodiment, the wafer unit U is set on the suction holder 52a of the spinner table 52, and when the spinner table 52 rotates, the annular frame F is held by the clamps 54. It is also possible to suction-hold the wafer W directly on the suction holder 52a without configuring the wafer unit U.

[0031] 5(B) shows a cross section of a wafer W held on a spinner table, with the front surface Wa of the wafer W exposed upward and the back surface Wb of the wafer W superimposed on a tape T. Devices D are arranged at intervals on the front surface Wa of the wafer W, and streets S are formed between each device D. The center of the street S in the width direction is set as the planned division line.

[0032] <First protective film formation step> As shown in Figures 6(A) and (B), this is a step in which water-soluble resin 12 is supplied onto the wafer W held on the spinner table 52, the spinner table 52 is rotated to coat the wafer with the water-soluble resin 12, and then the rotation of the spinner table 52 is maintained to dry the water-soluble resin 12 coating the wafer W, thereby forming a first protective film layer M1.

[0033] Specifically, the water-soluble resin 12 is dropped from the protective film agent nozzle 57 onto the front surface Wa of the wafer W rotating at a predetermined rotation speed, and the water-soluble resin 12 is diffused by centrifugal force to cover the entire front surface Wa of the wafer W. As a result, the entire front surface Wa of the wafer W, including the devices D, is covered with the water-soluble resin 12.

[0034] After a predetermined amount of the water-soluble resin 12 has been dripped, the dripping is stopped and the spinner table 52 is rotated at a predetermined rotation speed to dry and harden the water-soluble resin 12 on the front surface Wa of the wafer W. This forms a first protective film layer M1.

[0035] As shown in Figure 6(B), air bubbles K may be mixed into the first protective film layer M1. At the locations of these air bubbles K, the thickness of the first protective film layer M1 becomes thin, which may result in insufficient protection against debris during laser processing or in insufficient masking effect during plasma dicing. For this reason, a second protective film layer M2 (Figure 8(B)) is formed on the first protective film layer M1, as will be described in detail later.

[0036] <Washing and drying step> As shown in Figure 7(A), after performing the first protective film formation step, the wafer W held by the spinner table 52 is rotated while a cleaning liquid 14 is supplied onto the wafer to wash away at least the upper layer of the first protective film layer M1, and then the wafer W is dried.

[0037] Specifically, cleaning liquid 14 is sprayed from a cleaning liquid nozzle 56 toward the surface Wa of the wafer W rotating at a predetermined rotation speed, washing away thin areas of the upper layer of the first protective film layer M1 and uncured areas.

[0038] 7(B) shows the state after the upper portion of the first protective film layer M1 has been washed away. The surface portion Ka (FIG. 6(B)) where the air bubbles K (FIG. 6(B)) had been formed is removed by washing, and a bubble-free first protective film layer M1 is formed.

[0039] 7(C) shows the state after not only the upper layer portion of the first protective film layer M1 but also a larger portion has been washed away, exposing the device D. In this way, most of the first protective film layer M1 may be removed. Alternatively, the first protective film layer M1 may be removed so that almost no part remains, or may be completely removed, but this is not particularly limited.

[0040] In addition, since air bubbles K (FIG. 6(B)) tend to rise and appear in the upper layer of the first protective film layer M1 during the diffusion and drying process of the water-soluble resin, it is possible to remove the air bubbles K with a high probability by simply washing away only the upper layer in the cleaning and drying step. Therefore, the air bubbles K can be effectively removed without strictly controlling the thickness of the first protective film layer M1 to be removed.

[0041] Furthermore, in the state shown in Figure 7(C), the first protective film layer M1 remains at the position of the street S, so the unevenness formed by the device D, i.e., the step between the street S and the device D, is reduced, and the formation of air bubbles can be prevented when forming the second protective film layer in the subsequent second protective film formation step.

[0042] After cleaning for a predetermined time, the wafer W is rotated at a predetermined rotation speed to remove the cleaning liquid and dry the wafer W. At this time, the upper surface of the remaining first protective film layer M1 becomes nearly flat due to the rotation, so that bubbles are less likely to form when the second protective film layer is formed in the subsequent second protective film formation step.

[0043] <Second protective film formation step> As shown in Figures 8(A) and (B), after performing the cleaning and drying step, water-soluble resin 12 is supplied onto the wafer W held on the spinner table 52, and the spinner table 52 is rotated to coat the wafer W with the water-soluble resin 12, thereby forming a protective film M on which a second protective film layer M2 is laminated.

[0044] Specifically, as shown in Figure 8(A), a water-soluble resin 12 is again dropped onto a wafer W on which a first protective film layer M1 has been formed to coat the wafer W and form a second protective film layer M2.

[0045] The amount of water-soluble resin 12 dispensed and the rotation speed of spinner table 52 may be the same as or different from those in the first protective film forming step, or may be set by an operator so that a second protective film layer M2 of a desired thickness is formed.

[0046] 8(B) shows the state in which a second protective film layer M2 is formed on a first protective film layer M1, thereby forming a protective film M consisting of a plurality of laminated protective film layers. In this protective film M, the air bubbles K (FIG. 6(B)) formed in the first protective film layer M1 have been removed, and the protective film M can have a uniform thickness.

[0047] Furthermore, when the second protective film layer M2 is formed, for example, if the first protective film layer M1 is present as shown in FIG. 7(B), the surface irregularities of the first protective film layer M1 are small, making it difficult for new bubbles to form. Furthermore, even if part of the device D is exposed as shown in FIG. 7(C), the difference in level between the street S and the device D is small, making it difficult for new bubbles to form. In this way, by forming the first protective film layer M1, it is possible to prevent the generation of bubbles when the second protective film layer M2 is formed.

[0048] Furthermore, by forming the second protective film layer M2 using the same protective film agent as that used to form the first protective film layer M1, the affinity between the first protective film layer M1 and the second protective film layer M2 is increased, making it less likely that air bubbles will occur when forming the second protective film layer M2.

[0049] Furthermore, even if air bubbles occur in the second protective film layer M2, the surface Wa of the wafer W is protected by the first protective film layer M1, so that more reliable protection can be achieved compared to when the surface Wa of the wafer W is protected by only the first protective film layer M1.

[0050] <Groove formation step> As shown in FIGS. 9(A) and 9(B), this is a step of removing at least a part of the protective film M along the street S after the second protective film forming step is performed.

[0051] As shown in Figure 9(A), a protective film M is formed on the surface of the wafer W, and by irradiating a laser beam from the laser processing head 40, laser grooving is performed along the street S, removing the protective film M and forming a groove 44.

[0052] 9(B) shows a cross section of the wafer W, illustrating how the protective film M is removed by the laser beam L to form grooves 44 at the locations of the streets S. The grooves 44 are configured to reach the surface Wa of the wafer W, and a predetermined thickness of the protective film M can be left behind.

[0053] <Etching step> As shown in FIGS. 10(A) and 10(B), this is a step in which plasma etching is performed on the wafer W via the protective film M after the groove forming step is performed.

[0054] Specifically, as shown in FIG. 10(A), a holding table 92 is provided in a chamber 91 of a plasma etching apparatus 90, and a wafer unit U is placed on the holding table 92, with the surface Wa of the wafer W on which a protective film M is formed being exposed upward.

[0055] An exhaust port 93 is provided at the bottom of the chamber 91, and the pressure inside the chamber 91 is reduced to create a vacuum atmosphere through the exhaust port 93. A gas jet head 94 supplies plasmatized fluorine-based gas to the top of the chamber 91.

[0056] 10(B), plasma etching is performed to form etched grooves 46 in the locations of the grooves 44 formed by removing the protective film M. One cycle of plasma etching consists of, for example, isotropic etching with plasmatized SF6 gas, formation of a protective film on the sidewalls and bottom of the etched grooves 46 with plasmatized C4F8 gas, and anisotropic etching with plasmatized SF6 gas to remove the bottom portion of the protective film, and this cycle is repeated several dozen times until the etched grooves 46 reach the back surface Wb of the wafer W. This allows the wafer W to be divided into chips along the streets S (plasma dicing).

[0057] When plasma dicing is performed by such plasma etching, a sufficient thickness is ensured in the protective film M, so that the protective film M can reliably function as a mask for forming etching grooves 46 in the depth direction of the grooves 44. Note that the apparatus configuration and method for plasma etching are not limited to those shown in FIG. 10(A) and the above description.

[0058] <Protection film removal step> As shown in FIGS. 11(A) and 11(B), this is a step in which, after the etching step has been performed, a cleaning liquid 14 is supplied to the protective film M to remove the protective film M.

[0059] Specifically, as shown in FIG. 11(A), the wafer unit U is again held by the spinner table 52, and while the wafer W is being rotated, cleaning liquid 14 is supplied onto the wafer, washing away all of the protective film M, and then drying the wafer.

[0060] As a result, the surface Wa of the wafer W and the surfaces of the devices D can be exposed, as shown in FIG. 11(B).

[0061] Since the surface Wa of the wafer W and the device D are protected by the protective film M, the occurrence of defects such as adhesion of debris generated by laser processing and mask defects during plasma etching is suppressed.

[0062] <Laser processing steps> Instead of the above-mentioned plasma etching, a laser processing step may be performed. In this case, in the groove forming step shown in Figures 9(A) and 9(B), laser grooving is performed to reach the back surface Wb of the wafer W.

[0063] According to the embodiment described above, even if bubbles K (FIG. 6(B)) occur in the first protective film layer M1, by forming the second protective film layer M2 (FIG. 8(B)) after removing the bubbles K, it is possible to form a protective film M (FIG. 8(B)) in which the generation of bubbles is suppressed. This makes it possible to effectively prevent processing defects caused by insufficient protection against debris when performing laser processing, and processing defects caused by insufficient mask effectiveness in plasma dicing. Furthermore, although the thicker the protective film, the more likely bubbles are to occur, according to the present invention, by stacking multiple protective film layers in stages, the generation of bubbles can be suppressed even when a thick protective film is formed overall. [Explanation of symbols]

[0064] D Device Front annular frame K bubbles L laser beam M Protective film M1 1st protective film layer M2 2nd protective film layer S Street T-tape U Wafer Unit W wafer Wa surface Wb back side 12 Water-soluble resin 14 Cleaning Solution 40 Laser processing head 44 Groove 46 Etching groove 50 Protective film coating and cleaning equipment 51 Case 51a Containment space 52 Spinner Table 52a Suction holding part 52b Frame holder 53 Support stand 54 Clamp 55 Nozzle unit 56 Cleaning liquid nozzle 56a Swing arm 57 Protective film nozzle 57a Swing arm 58 Mobile Unit 58a Rotating shaft 58b motor 59 Motor 90 Plasma etching equipment 91 Chamber 92 Holding table 93 Exhaust port 94 Gas Ejection Head

Claims

1. A protective film forming method for forming a protective film on a wafer, comprising: a holding step of holding the wafer on a spinner table; a first protective film forming step of supplying a water-soluble resin onto the wafer held by the spinner table while rotating the spinner table to coat the wafer with the water-soluble resin, and then continuing to rotate the spinner table to dry the water-soluble resin that has coated the wafer, thereby forming a first protective film layer; a cleaning and drying step of, after the first protective film forming step, supplying a cleaning liquid onto the wafer while rotating the wafer held by the spinner table to wash away at least an upper layer of the first protective film layer, and then drying the wafer; a second protective film forming step of supplying a water-soluble resin onto the wafer held by the spinner table and rotating the spinner table to coat the wafer with the water-soluble resin, thereby forming a protective film having a second protective film layer laminated thereon, after the cleaning and drying step; A protective film forming method comprising:

2. A method for processing a wafer having a plurality of intersecting streets defined on its surface and having devices formed in each of areas partitioned by the streets, comprising the steps of: a holding step of holding the wafer on a spinner table to expose the surface; a first protective film forming step of supplying a water-soluble resin onto the surface of the wafer held by the spinner table and rotating the spinner table to coat the wafer with the water-soluble resin and form a first protective film layer; a cleaning and drying step of, after the first protective film forming step, supplying a cleaning liquid onto the wafer while rotating the wafer held by the spinner table to wash away at least an upper layer of the first protective film layer, and then drying the wafer; a second protective film forming step of supplying a water-soluble resin onto the wafer held by the spinner table and rotating the spinner table to coat the wafer with the water-soluble resin, thereby forming a protective film having a second protective film layer laminated thereon, after the cleaning and drying step; a groove forming step of removing at least a portion of the protective film along the street after the second protective film forming step is performed; a step of performing plasma etching on the wafer through the protective film after the groove forming step is performed.

3. 3. The wafer processing method according to claim 2, further comprising a protective film removing step of supplying a cleaning liquid to the protective film to remove the protective film after the etching step is performed.

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