Protective film formation method

Abstract

To provide a protection film formation method capable of improving efficiency of protection film formation.SOLUTION: A protection film formation method for forming a protection film on a workpiece includes: a coating step of coating a surface of the workpiece with a protection film agent by holding the workpiece on a holding table, applying a liquid protection film agent to the surface of the workpiece, and rotating the holding table at first rotation speed; and a drying step of drying the protection film agent while applying vibration to the protection film agent by rotating the holding table at second rotation speed slower than the first rotation speed or without rotating the holding table.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for forming a protective film on a workpiece such as a wafer.

Background Art

[0002] In the manufacturing process of device chips, a wafer in which devices are formed in a plurality of regions partitioned by a plurality of intersecting streets (planned division lines) is used. By dividing this wafer along the streets, a plurality of device chips each having a device can be obtained. The device chips are incorporated into various electronic devices such as mobile phones and personal computers.

[0003] For dividing a wafer, a cutting device that cuts a workpiece with an annular cutting blade is used. In recent years, the development of a process for dividing a wafer by laser processing has also been promoted. For example, by irradiating a wafer with a laser beam to perform ablation processing, laser processing grooves extending from the front surface to the back surface of the wafer are formed along the streets, and the wafer is divided into a plurality of device chips.

[0004] When laser processing is performed on a wafer, the melt (debris) generated in the region irradiated with the laser beam scatters, and there is a risk that the wafer and the device are contaminated by the debris. Therefore, a method has been proposed in which a protective film is formed on the wafer and the wafer is irradiated with a laser beam through the protective film (see Patent Documents 1 and 2). When this method is used, the adhesion of debris to the wafer and the device is avoided by the protective film. Thereby, deterioration in the quality of the device chips due to contamination of the wafer or the device is prevented.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] Protective films covering workpieces such as wafers are formed by applying a liquid protective film agent to the surface of the workpiece, followed by drying and curing the protective film agent. However, since it takes time for the protective film agent to dry and cure sufficiently, the drying process of the protective film agent is a factor that reduces the efficiency of protective film formation. In particular, when a thick protective film agent is formed, the drying time is extended significantly, leading to a more serious decrease in productivity.

[0007] This invention has been made in view of the above problems, and aims to provide a method for forming a protective film that can improve the efficiency of protective film formation. [Means for solving the problem]

[0008] According to one aspect of the present invention, a method for forming a protective film on a workpiece includes: a coating step of holding the workpiece with a holding table, applying a liquid protective film agent to the surface of the workpiece, and covering the surface of the workpiece with the protective film agent by rotating the holding table at a first rotational speed; and a drying step of rotating the holding table at a second rotational speed slower than the first rotational speed, or drying the protective film agent while applying vibration to the protective film agent without rotating the holding table. Furthermore, in the drying process, the frequency of the vibrations applied from the vibrator to the protective film agent is changed by controlling the AC voltage applied to the vibrator. A method for forming a protective film is provided.

[0009] Preferably, the vibration is applied to the protective film agent via the workpiece. .Ma Preferably, the vibration is a vibration with a frequency that belongs to the ultrasonic band. Preferably, the vibration is a vibration with a frequency lower than that of vibrations belonging to the ultrasonic band. [Effects of the Invention]

[0010] In a protective film formation method according to one aspect of the present invention, the surface of the workpiece is coated with a protective film agent, and then the protective film agent is dried while vibration is applied to the protective film agent. This accelerates the drying of the protective film agent, shortens the drying time, and improves the efficiency of protective film formation. [Brief explanation of the drawing]

[0011] [Figure 1] This is a perspective view showing the workpiece. [Figure 2] This is a flowchart showing a method for forming a protective film. [Figure 3] Figure 3(A) is a partial cross-sectional front view showing the workpiece during the coating process, and Figure 3(B) is a partial cross-sectional front view showing the workpiece during the drying process. [Figure 4] This is a front view showing the vibration-applying unit. [Figure 5] This is a partial cross-sectional front view showing a workpiece that has undergone a drying acceleration treatment. [Modes for carrying out the invention]

[0012] Hereinafter, an embodiment according to one aspect of the present invention will be described with reference to the attached drawings. First, an example of the configuration of an object on which a protective film is formed by the protective film forming method according to this embodiment will be described. Figure 1 is a perspective view showing the workpiece (object) 11.

[0013] For example, the workpiece 11 is a disc-shaped wafer made of a semiconductor material such as single-crystal silicon, and has a first surface 11a and a second surface 11b that are generally parallel to each other. The workpiece 11 is divided into multiple rectangular regions by multiple streets (division lines) 13 arranged in a grid pattern so as to intersect each other. Furthermore, devices 15 such as ICs (Integrated Circuits), LSIs (Large Scale Integrations), LEDs (Light Emitting Diodes), and MEMS (Micro Electro Mechanical Systems) devices are formed on the first surface 11a side of each of the regions divided by the streets 13.

[0014] However, there are no restrictions on the type, material, shape, structure, size, etc. of the workpiece 11. For example, the workpiece 11 may be a substrate (wafer) made of semiconductors other than silicon (such as GaAs, InP, GaN, SiC, etc.), sapphire, glass, ceramics, resin, metal, etc. Also, there are no restrictions on the type, number, shape, structure, size, arrangement, etc. of the devices 15, and the devices 15 may not be formed on the workpiece 11.

[0015] When various processes (such as formation of a protective film, laser processing, etc.) are performed on the workpiece 11, for the convenience of handling (transportation, holding, etc.) of the workpiece 11, the workpiece 11 is supported by an annular frame 17. The frame 17 is made of a metal such as SUS (stainless steel), and a circular opening 17a penetrating the frame 17 in the thickness direction is provided at the central portion of the frame 17. Note that the diameter of the opening 17a is larger than the diameter of the workpiece 11.

[0016] A circular sheet 19 is fixed to the workpiece 11 and the frame 17. For example, as the sheet 19, a tape including a film-shaped base material formed in a circular shape and an adhesive layer (paste layer) provided on the base material is used. The base material is made of a resin such as polyolefin, polyvinyl chloride, polyethylene terephthalate, etc. Also, the adhesive layer is made of an epoxy-based, acrylic-based, or rubber-based adhesive, etc. Note that the adhesive layer may be an ultraviolet curable resin.

[0017] In a state where the workpiece 11 is disposed inside the opening 17a of the frame 17, the central portion of the sheet 19 is attached to the second surface 11b side of the workpiece 11, and the outer peripheral portion of the sheet 19 is attached to the frame 17. Thereby, the workpiece 11 is supported by the frame 17 via the sheet 19.

[0018] By processing the workpiece 11 with a processing apparatus and dividing it along the street 13, a plurality of device chips each including a device 15 are manufactured. For example, a laser processing apparatus is used for dividing the workpiece 11.

[0019] The laser processing apparatus includes a holding table (chuck table) having a holding surface for holding the workpiece 11, and a laser irradiation unit for irradiating the workpiece 11 with a laser beam. The laser irradiation unit includes a laser oscillator and an optical system for guiding the laser beam emitted from the laser oscillator to the workpiece 11. The optical system is configured to include a plurality of optical elements (such as a condenser lens, a mirror, etc.). By holding the workpiece 11 on the holding surface of the holding table and irradiating the workpiece 11 with a laser beam from the laser irradiation unit, predetermined laser processing is performed on the workpiece 11.

[0020] For example, the irradiation conditions of the laser beam are set so that ablation processing is performed on the workpiece 11. Then, the laser beam is irradiated along the street 13 on the workpiece 11, and the area of the workpiece 11 irradiated with the laser beam is removed by ablation processing. As a result, a laser processing groove extending from the first surface 11a to the second surface 11b of the workpiece 11 is formed along the street 13, and the workpiece 11 is divided along the street 13.

[0021] However, there is no limitation on the content of the laser processing for dividing the workpiece 11. For example, a laser processing groove having a depth less than the thickness of the workpiece 11 may be formed along the street 13 on the first surface 11a side of the workpiece 11. In this case, the second surface 11b side of the workpiece 11 is ground with a grinding wheel, and the laser processing groove is exposed on the second surface 11b of the workpiece 11, so that the workpiece 11 can be divided along the street 13.

[0022] When laser processing is performed on the workpiece 11, the melt (debris) generated in the area irradiated with the laser beam may scatter and adhere to the workpiece 11, contaminating the workpiece 11. Therefore, when laser processing is performed on the workpiece 11, a protective film is formed on the workpiece 11 in advance, and the laser beam is irradiated to the workpiece 11 through the protective film. Thereby, the adhesion of debris to the workpiece 11 is prevented.

[0023] Next, a specific example of a method for forming a protective film on the workpiece 11 will be described. Figure 2 is a flowchart of the protective film formation method. In this embodiment, a protective film is formed on the surface (first surface 11a or second surface 11b) of the workpiece 11 by performing a coating step S1 and a drying step S2. In the following example, an example of forming a protective film on the first surface 11a side of the workpiece 11 will be described, but a protective film can also be formed on the second surface 11b side of the workpiece 11 using the same method.

[0024] First, the surface of the workpiece 11 is coated with a protective film agent (coating step S1). Figure 3(A) is a partial cross-sectional front view showing the workpiece 11 in coating step S1. In this embodiment, a protective film is formed on the workpiece 11 by the protective film forming unit 2. The protective film forming unit 2 is, for example, a spin coater and includes a holding table (spinner table) 4 for holding the workpiece 11 and a protective film agent supply unit 6 for supplying the protective film agent, which is the raw material for the protective film.

[0025] The upper surface of the holding table 4 is a flat surface that is generally parallel to the horizontal plane and constitutes a circular holding surface 4a for holding the workpiece 11. The holding surface 4a is connected to a suction source (not shown), such as an ejector, via a flow path (not shown), a valve, etc., formed inside the holding table 4. The holding table 4 is also connected to a rotational drive source (not shown), such as a motor, which rotates the holding table 4 around a rotation axis that is generally parallel to the vertical direction (height direction, up and down direction).

[0026] A protective film supply unit 6 is provided above the holding table 4. The protective film supply unit 6 includes a nozzle 8 that supplies a liquid protective film 10 to the workpiece 11 held by the holding table 4. For example, the nozzle 8 is fixed to the tip of an arm (not shown), and a rotational drive source (not shown), such as a motor that rotates the arm, is connected to the base end of the arm. By rotating the arm with the rotational drive source, the nozzle 8 can be positioned in a position that overlaps the holding surface 4a (supply position) and in a position that does not overlap the holding surface 4a (retracted position).

[0027] The protective film agent 10 is produced by dissolving a solute in a solvent. For example, water can be used as the solvent, and a water-soluble resin can be used as the solute. Specific examples of water-soluble resins include PVP (polyvinylpyrrolidone), PVA (polyvinyl alcohol), PEG (polyethylene glycol), and PEO (polyethylene oxide).

[0028] In the coating process S1, the workpiece 11 is first held by the holding table 4. Specifically, the workpiece 11 is placed on the holding table 4 such that the first surface 11a is exposed upwards and the second surface 11b (sheet 19 side) faces the holding surface 4a. When the suction force (negative pressure) of the suction source is applied to the holding surface 4a in this state, the workpiece 11 is held by the holding table 4 via the sheet 19. Note that the holding table 4 may be surrounded by multiple clamps (not shown) for gripping and fixing the frame 17.

[0029] Next, the nozzle 8 is positioned so that it aligns with the rotation axis of the holding table 4 and the center of the workpiece 11. Then, while rotating the holding table 4, the protective film agent 10 is dripped from the nozzle 8 onto the workpiece 11. This coats the first surface 11a of the central part of the workpiece 11 with the protective film agent 10. The protective film agent 10 supplied to the central part of the workpiece 11 then flows radially toward the outer edge of the workpiece 11 due to the centrifugal force of the rotating holding table 4 and the workpiece 11. As a result, the protective film agent 10 spreads uniformly across the entire first surface 11a of the workpiece 11, and the first surface 11a of the workpiece 11 is covered with the protective film agent 10.

[0030] The rotation speed of the holding table 4 and the amount of protective film agent 10 supplied are set appropriately according to the size of the workpiece 11, the thickness of the protective film agent 10 covering the workpiece 11, the viscosity of the protective film agent 10, etc. For example, the rotation speed of the holding table 4 (first rotation speed) in the coating process S1 is set to 1500 rpm or more and 6000 rpm or less. Also, the amount of protective film agent 10 supplied is set to, for example, 5 ml or more and 30 ml or less.

[0031] There are no restrictions on the timing of the rotation of the holding table 4 and the supply of the protective film agent 10 in the coating process S1. Specifically, the protective film agent 10 may be supplied to the workpiece 11 while the holding table 4 is rotating, or the rotation of the holding table 4 may be started after a predetermined amount of protective film agent 10 has been supplied to the center of the workpiece 11.

[0032] Next, the protective film agent 10 covering the workpiece 11 is dried (drying step S2). Figure 3(B) is a partial cross-sectional front view showing the workpiece 11 during drying step S2.

[0033] In drying step S2, the supply of protective film agent 10 from the protective film agent supply unit 6 to the workpiece 11 is stopped, and the workpiece 11 is left for a certain period of time while the holding table 4 continues to rotate. This allows the protective film agent 10 to dry and harden, forming a protective film 12 made of water-soluble resin. The drying time is set appropriately according to the material and thickness of the protective film agent 10. In this way, a protective film 12 is formed that covers the first surface 11a side of the workpiece 11.

[0034] In addition, the rotation speed of the holding table 4 in the drying process S2 (second rotation speed) is preferably slower than the rotation speed of the holding table 4 in the coating process S1 (first rotation speed). Specifically, the second rotation speed is preferably 85% or less of the first rotation speed, and more preferably 70% or less. This suppresses the scattering of the protective film agent 10 due to the centrifugal force of the workpiece 11, and prevents the protective film 12 from becoming unintentionally thin. For example, the second rotation speed is set to 1000 rpm or more and 5000 rpm or less. Furthermore, in the drying process S2, the workpiece 11 may be left for a certain period of time with the holding table 4 stopped without rotating in order to further reduce the scattering of the protective film agent 10.

[0035] In order for the protective film agent 10 to dry and harden sufficiently, the workpiece 11 must remain on the holding table 4 for an extended period, which prolongs the formation process of the protective film 12. In particular, when the protective film agent 10 is formed thickly, the drying time is significantly extended, leading to a more serious decrease in productivity.

[0036] Specifically, when the protective film agent 10 is applied to the workpiece 11, solvent detachment is likely to occur on the exposed side of the protective film agent 10 that is not in contact with the workpiece 11 (the upper side of the protective film agent 10 in Figure 3(B)). Therefore, if the workpiece 11 is left stationary, the exposed side of the protective film agent 10 dries preferentially, and a thin film of solute is formed on the exposed side of the protective film agent 10 (skinning). As a result, the solvent inside the protective film agent 10 is covered by the thin film of solute, making it difficult for the solvent to detach from inside the protective film agent 10. It is presumed that this condition is one of the factors that increases the time required to dry and harden the entire protective film agent 10.

[0037] Therefore, in this embodiment, the protective film agent 10 is dried while vibration is applied to it. This suppresses the formation of a thin film (skinning) on ​​the exposed side of the protective film agent 10, and makes it easier for the solvent to detach from the entire protective film agent 10. As a result, the drying time of the protective film agent 10 is shortened.

[0038] Figure 4 is a front view showing the vibration application unit 20. For example, the vibration application unit 20, which applies vibration to the protective film agent 10, is connected to the holding table 4. The vibration application unit 20 applies vibration to the protective film agent 10 via the holding table 4 and the workpiece 11.

[0039] Specifically, the vibration unit 20 includes a rotational drive source 22 such as a motor. A cylindrical spindle 24, positioned vertically, is connected to the output shaft of the rotational drive source 22. A vibrator 26 is fixed to the upper end of the spindle 24, and the vibrator 26 is connected to the central part of the lower surface of the holding table 4.

[0040] For example, a Langevin-type transducer is used as the transducer 26. In this case, by applying a predetermined AC voltage to the transducer 26, the transducer 26 vibrates at a predetermined frequency, and vibration is applied to the holding table 4. For example, the transducer 26 vibrates at a frequency belonging to the ultrasonic band, and vibrations of a frequency belonging to the ultrasonic band (ultrasonic vibrations) are applied to the holding table 4.

[0041] When the transducer 26 is activated while the protective film agent 10 is drying (see Figure 3(B)), ultrasonic vibrations applied from the transducer 26 to the holding table 4 are transmitted to the protective film agent 10 via the sheet 19 and the workpiece 11. When ultrasonic vibrations are applied to the protective film agent 10, the drying protective film agent 10 is agitated, the solute is uniformly dispersed, and skin formation on the exposed surface of the protective film agent 10 is suppressed. As a result, the solvent is more easily released from inside the protective film agent 10, and the drying and curing of the protective film agent 10 are accelerated.

[0042] Furthermore, if vibration is continuously applied to the protective film agent 10 at a constant frequency, undulation will occur on the surface of the protective film agent 10, making it easier for variations in the thickness of the protective film agent 10 (protective film 12) after drying to occur. For this reason, during the drying of the protective film agent 10, vibrations with varying frequencies may be applied to the protective film agent 10. Specifically, by controlling the AC voltage applied to the vibrator 26, the frequency of the vibrations applied from the vibrator 26 to the protective film agent 10 via the holding table 4, sheet 19, and workpiece 11 is increased or decreased. This suppresses undulation on the surface of the protective film agent 10 and reduces variations in the thickness of the protective film 12.

[0043] The frequency of the vibrations applied to the protective film agent 10 can be appropriately set according to the material, thickness, etc., of the protective film agent 10. For example, if it is possible to suppress the skinning of the protective film agent 10, vibrations with a frequency lower than ultrasonic vibrations may be applied to the protective film agent 10. Also, when the frequency is varied, both the upper and lower limits of the frequency may belong to the ultrasonic band, or one or both of the upper and lower limits of the frequency may be outside the ultrasonic band.

[0044] Furthermore, there are no restrictions on the method of applying vibration to the protective film agent 10. For example, the protective film forming unit 2 may include a vibration-applying unit that directly applies vibration to the protective film agent 10 instead of the vibration-applying unit 20.

[0045] As described above, after the protective film 12 is formed on the first surface 11a side of the workpiece 11, the workpiece 11 is subjected to a predetermined process. For example, the protective film forming unit 2 is mounted on a laser processing device. The laser processing device then forms the protective film 12 on the workpiece 11 using the protective film forming unit 2, and then irradiates the workpiece 11 with a laser beam to perform laser processing.

[0046] For example, a laser beam with a wavelength that is absorbed by the workpiece 11 is irradiated onto the first surface 11a of the workpiece 11 through the protective film 12. This causes ablation processing on the workpiece 11. At this time, debris is generated in the area irradiated by the laser beam, but because the protective film 12 is formed on the first surface 11a of the workpiece 11, the adhesion of the debris to the workpiece 11 is prevented by the protective film 12.

[0047] Once laser processing is complete, the protective film 12 is removed from the workpiece 11. At this time, any debris adhering to the protective film 12 is also removed along with the protective film 12. If the protective film 12 is made of a water-soluble resin, it can be easily removed by simply supplying a cleaning solution such as pure water to the workpiece 11. This simplifies the process of removing the protective film 12.

[0048] As described above, in the protective film formation method according to this embodiment, the surface of the workpiece 11 is coated with the protective film agent 10, and then the protective film agent 10 is dried while vibration is applied to the protective film agent 10. This promotes the drying of the protective film agent 10, shortens the drying time, and improves the efficiency of protective film formation.

[0049] In addition to applying vibration to the protective film agent 10 in the drying process S2, a drying acceleration treatment may be applied to the protective film agent 10 to promote drying. For example, the protective film agent 10 may be dried while being heated by applying hot air, microwaves, infrared rays, etc.

[0050] Figure 5 is a partial cross-sectional front view showing a workpiece 11 subjected to a drying acceleration treatment. The protective film forming unit 2 may also include a drying acceleration unit 30 that accelerates the drying of the protective film agent 10. For example, the drying acceleration unit 30 is composed of a heat gun and includes a nozzle 32 that sprays hot air 34. The heat gun includes a heat source (heating mechanism) such as an electric heating wire and a blowing mechanism such as a fan, which heats the air and sprays it from the nozzle 32. By spraying hot air 34 toward the protective film agent 10 while the protective film agent 10 is drying, the drying of the protective film agent 10 is accelerated and the time required for the drying of the protective film agent 10 is shortened.

[0051] However, there are no restrictions on the configuration of the drying acceleration unit 30. For example, the drying acceleration unit 30 may include a microwave irradiation unit that irradiates the protective film agent 10 with microwaves, or an infrared lamp that irradiates the protective film agent 10 with infrared rays. By irradiating the protective film agent 10 with microwaves or infrared rays during the drying of the protective film agent 10, the drying of the protective film agent 10 is accelerated.

[0052] Furthermore, the structures, methods, etc., according to the above embodiments can be modified as appropriate without departing from the scope of the objectives of the present invention. [Explanation of symbols]

[0053] 11 Workpiece (object) 11a 1st page 11b Side 2 13th Street (planned division line) 15 devices 17 frames 17a aperture 19 seats 2. Protective film forming unit 4. Holding table (spinner table) 4a Holding surface 6. Protective film supply unit 8 nozzles 10 Protective film agent 12 Protective film 20 Vibration Unit 22 Rotary drive source 24 spindles 26. Transducer 30 Drying acceleration unit 32 nozzles 34. Warm air

Claims

1. A method for forming a protective film on a workpiece, A coating step in which the workpiece is held in a holding table, a liquid protective film agent is applied to the surface of the workpiece, and the surface of the workpiece is covered with the protective film agent by rotating the holding table at a first rotational speed, The process includes a drying step of rotating the holding table at a second rotational speed slower than the first rotational speed, or drying the protective film agent while applying vibration to the protective film agent without rotating the holding table, A method for forming a protective film, characterized in that, in the drying step, the frequency of the vibrations applied from the vibrator to the protective film agent is changed by controlling the AC voltage applied to the vibrator.

2. The method for forming a protective film according to claim 1, characterized in that the vibration is applied to the protective film agent via the workpiece.

3. The method for forming a protective film according to claim 1, characterized in that the vibration is a vibration with a frequency belonging to the ultrasonic band.

4. The method for forming a protective film according to claim 1, characterized in that the vibration is a vibration with a frequency lower than that of a vibration with a frequency belonging to the ultrasonic band.

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