Wafer protective film forming method and wafer grinding device

Abstract

[Problem] To provide a wafer protective film forming method capable of forming a protective film on a surface of a wafer and performing grinding without requiring pasting or releasing of a previously formed thin film-like protective tape. [Solution] A water-soluble protective material 30 is spirally applied to a surface of a wafer 8 by using a dispenser constituting a liquid supply mechanism 30a and is solidified at room temperature, and then the surface is made uniform by using a pressing member 44. After completion of grinding at a grinding part 6, water at 35-100°C which deviates from the temperature for the solidified state is jetted from a lower part of a chuck table 62, or water at 35-100°C is poured from above in a second releasing part 7a, thereby melting the water-soluble protective material 30.

Description

Method for Forming a Protective Film on a Wafer and Wafer Grinding Apparatus

[0001] The present invention relates to a method for forming a protective film on a wafer that enables the formation of a protective film on the surface of the wafer. More specifically, it relates to a method for forming a protective film on a wafer that enables the formation of a protective film on the surface of the wafer without performing an operation of attaching a thin-film protective tape or a peeling operation.

[0002] Generally, when grinding a semiconductor wafer (hereinafter referred to as a wafer) cut out from an ingot, a thin-film protective tape called a BG tape is attached to the surface of the wafer. Then, the protective tape is cut into the shape of the wafer, and thereafter, while grinding the back side of the wafer using a grinding apparatus, after the grinding is completed, the protective tape is peeled off (see Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2011-23612

[0004] However, when attaching such a protective tape, there is a problem that after attaching a large sheet-like protective tape, the surplus portion has to be cut, resulting in waste of materials.

[0005] Further, after the finish grinding is completed, it is necessary to peel off the protective tape. In the peeling process, damage to the wafer becomes a problem, and a method that does not damage the wafer is desired.

[0006] Furthermore, when peeling the protective tape from the wafer, the protective tape has to be peeled off so that a thin wafer is not loaded, and since the peeling has to be performed using a peeling apparatus, there also arises a problem that the cost becomes high.

[0007] Therefore, the present invention has been made by paying attention to the above problems, and an object thereof is to provide a method for forming a protective film on a wafer that enables the formation of a protective film on the surface of the wafer without the need for attaching or peeling a previously formed thin-film protective tape.

[0008] In other words, in order to solve the above problems, the present invention applies a water-soluble protective material to the wafer surface, which is in a solid state at any temperature within the range of 20°C to 70°C and in a liquid state at any temperature within the range of 35°C to 100°C, which is outside the temperature range of the solidification state, to form a protective film.

[0009] This method eliminates the need for applying and removing protective films, and also prevents the generation of large amounts of waste associated with the removal process.

[0010] Furthermore, in such an invention, a step is provided to uniformize the surface by pressing a pressing member onto the applied water-soluble protective material.

[0011] This method allows for a uniform film thickness, making it possible to grind the wafer uniformly during the grinding process.

[0012] Furthermore, after pressing a pressing member onto the coated water-soluble protective material to make the surface uniform, the pressed pressing member is cooled.

[0013] In this way, by contracting the pressing member, it becomes easier to separate the pressing member from the protective film of the water-soluble protective material. Alternatively, by cooling the pressing member, the water-soluble protective material can be cooled and solidified reliably.

[0014] Furthermore, when applying the water-soluble protective material, the water-soluble protective material is applied to the wafer by a liquid supply mechanism.

[0015] This method allows for precise placement and discharge of the water-soluble protective material, thus ensuring its efficient use without waste.

[0016] Furthermore, the film thickness of the applied water-soluble protective material should be measured before the grinding process.

[0017] In this way, only wafers that are judged to have a uniform film thickness can be ground, thus preventing wafers from being ground at an angle due to differences in film thickness.

[0018] Furthermore, when dissolving the water-soluble protective material with water, the holding table that holds the wafer is heated, and then water is poured onto the wafer to dissolve the water-soluble protective material.

[0019] In this way, the water-soluble protective material can be dissolved from both sides of the protective film, allowing for rapid removal of the water-soluble protective material.

[0020] According to the present invention, a protective film is formed on the surface of a wafer using a water-soluble protective material, and the protective film can be removed with heated water during peeling. This eliminates the generation of large amounts of waste from protective tape as in the past, and also allows for easy removal of the protective film.

[0021] A schematic plan view of a wafer grinding apparatus showing one embodiment of the present invention. A diagram showing the holding table of the transport section in the same form. A diagram showing the coating section in the same form. A diagram showing the operation of the pressing member in the same form. A diagram showing the state of removing the wafer from the holding table in the same form. A diagram showing the action of peeling off the protective film on the chuck table in the same form. A schematic diagram showing the second peeling section in the same form. A flowchart showing the operation in the same form.

[0022] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0023] The wafer grinding apparatus 1 to which the protective film formation method in this embodiment is applied comprises, as shown in Figure 1, a transport unit 2 for transporting wafers 8, a coating unit 3 for applying a water-soluble protective material 30 (see Figure 3) to the transported wafers 8 to form a protective film, a uniformization means 4 for making the applied water-soluble protective material 30 of uniform thickness, a grinding unit 6 for grinding the wafers 8 to which the water-soluble protective material 30 has been uniformly applied, and a peeling unit 7 (and a second peeling unit 7a) for peeling the water-soluble protective material 30 from the ground wafers 8. Characteristically, the water-soluble protective material 30 is applied to the wafers 8, solidified at a temperature between 20°C and 70°C, and after grinding is completed, the water-soluble protective material 30 of the protective film is dissolved by pouring hot water at 35°C to 100°C over it. This eliminates the waste of excess material on the outer periphery as in conventional methods, thus preventing the generation of large amounts of plastic waste. This embodiment will now be described in detail.

[0024] The transport unit 2 transports the wafer 8 in a horizontal position, and is configured to pick up the wafer 8 from below and transport it horizontally. Downstream in the transport direction, it is picked up from above by a multi-joint arm 21 and transferred to the holding table 31 of the coating unit 3.

[0025] The coating unit 3 is configured to form a thin protective film by coating the wafer 8 with a water-soluble protective material 30 using a liquid supply mechanism 30a that can dispense the water-soluble protective material 30 while maintaining its temperature, and is equipped with a holding table 31 as shown in Figures 2 and 3. Air is drawn in through a suction hole provided in the holding table 31 to adsorb and fix the wafer 8, and the water-soluble protective material 30, which has been liquefied by heating, is dispensed from the nozzle of the dispenser constituting the liquid supply mechanism 30a (see Figure 3). A thin protective film is formed by methods such as applying the required amount according to the coating area, or by applying it in a spiral pattern while rotating either the liquid supply mechanism 30a or the holding table 31. In addition, when the material is applied in a spiral pattern as described above, the water-soluble protective material 30 can be applied without overflowing from the wafer 8. However, alternatively, the liquid supply mechanism 30a may be used to dispense the water-soluble protective material 30 from a horizontal rod-shaped member and apply the material by moving the rod-shaped member and the wafer 8 relative to each other, or by spraying the material from above the wafer 8 with a spray, or by using spin coating to spread the water-soluble protective material 30 using the centrifugal force when the wafer 8 is rotated.

[0026] The water-soluble protective material 30 used here is a material that is in a solid state at either room temperature or the grinding temperature of 20°C to 70°C (preferably 20°C to 40°C, more preferably 25°C to 35°C), and is in a fluid liquid state at temperatures outside this solid state, within the range of 35°C to 100°C (preferably 50°C to 90°C), and is capable of clearing wastewater emission regulations. Specifically, polyalkylene glycols such as polyethylene glycol and polypropylene glycol are used, and polyethylene glycol is particularly preferred from the viewpoint of environmental impact. In addition, water-soluble polymers such as polyvinyl alcohol, polyvinylpyrrolidone, and cellulose may be appropriately blended with it, and surface modifiers and fillers may also be added. When polyethylene glycol and polyvinylpyrrolidone are mixed, the freezing point becomes 37°C, resulting in a solid state at room temperature (25°C) and a fluid liquid state at hot water (90°C). Therefore, it is preferable to use a mixture of polyethylene glycol and polyvinylpyrrolidone that has been heated and mixed.

[0027] Furthermore, if the water-soluble protective material 30 is applied with an uneven film thickness, the wafer 8 will be ground at an angle when it is ground in the grinding section 6. Therefore, a uniformization means 4 (see Figures 1 and 4) is provided to make the thickness of the water-soluble protective material 30 uniform.

[0028] Various methods can be used for this uniformization means 4, but here, as shown in Figure 4, a configuration is used in which a pressing member 44 is pressed onto the wafer 8 to make the thickness of the protective film uniform. Then, by pressing while heating with a heater 44a provided on the pressing member 44, the surface of the water-soluble protective material 30 is uniformly melted, and then by controlling the temperature, such as by cooling the pressing member 44 (forced cooling or natural cooling), the pressing member 44 can be peeled off the protective film. By controlling the cooling of the pressing member 44 in this way, the pressing member 44 shrinks due to the cooling, making it easier to peel the pressing member 44 off the surface of the protective film, and making it possible to lift the pressing member 44. Alternatively, although the pressing member 44 is separated by temperature control in this way, the pressing member 44 may also be separated from the protective film by sandwiching a sheet between the pressing member 44 and the water-soluble protective material 30.

[0029] Another example of the homogenization means 4 is that when applying the water-soluble protective material 30, heaters may be provided on both the holding table 31 and the dispenser to control the solidification time of the water-soluble protective material 30 and homogenize the surface. Specifically, the holding table 31 may be heated to the temperature at which the water-soluble protective material 30 melts, thereby melting the water-soluble protective material 30 applied to the wafer 8 and homogenizing the surface.

[0030] Furthermore, as another example of the homogenization means 4, a method may be used in which the wafer 8 coated with the water-soluble protective material 30 is rotated, and the surface is uniformly scraped off by a scraper provided above it.

[0031] The wafer 8, whose surface has been made uniform in this way, has its thickness of the water-soluble protective material 30 inspected by the thickness inspection unit 5 (see Figure 1). When inspecting with this thickness inspection unit 5, the protective film can be photographed with a camera, or inspected using a probe-type thickness gauge or an ultrasonic thickness gauge.

[0032] Then, wafers 8 that are determined to have a uniform thickness are transferred from the holding table 31 to the chuck table 62 of the grinding unit 6 using a multi-joint arm 21 (see Figure 1). When transferring wafers 8 to the grinding unit 6, it is necessary to flip the wafers 8 so that the protective film is on the bottom. Here, as shown in Figure 5, a pin 32 is made to protrude from below the holding table 31 to lift the wafers 8, and a fork 22 provided at the tip of the arm 21 is inserted between the holding table 31 and the wafers 8, and the wafers 8 are held by suction from below. The wafers 8 are then flipped over with the fork 22 so that the coated film is on the bottom, and then transferred to the grinding unit 6.

[0033] The grinding unit 6 (see Figure 1) is configured with a rotatable index table 61, a plurality of chuck tables 62 rotatably mounted within the index table 61, and a rotatable grinding wheel device 63 for grinding the wafer 8 held by the chuck tables 62. When grinding, the wafer 8 is held by suction on the chuck tables 62, and the wafer 8 is moved to the rough grinding position (area A) by the rotation of the index table 61. Rough grinding is performed by rotating the chuck tables 62 and the grinding wheel device 63 while applying water. After rough grinding is completed, the index table 61 is rotated to perform finish grinding at the finish grinding position (area B). If necessary, the thickness is measured after the finish grinding to inspect the grinding condition.

[0034] Then, the protective film is removed from the wafer 8, which has been finished grinding in this manner, using the peeling section 7.

[0035] When removing the protective film at this peeling section 7, as shown in Figure 6, a heater 62a located below the chuck table 62 is heated to melt the protective film in close contact with the chuck table 62, and heated hot water (hot water in the range of 35°C to 100°C, preferably 50°C to 90°C, outside the solidification temperature range) is discharged from a hole 62b provided in the chuck table 62 to melt the water-soluble protective material 30. This melts the water-soluble protective material 30 from both sides of the protective film, allowing for quick removal of the peel. Alternatively, instead of melting and removing by heating the chuck table 62, the protective film may be removed at a separately provided second peeling section 7a (see Figure 1). In the second peeling section 7a, the wafer 8 is flipped over by the arm 21 and transferred to the holding table 70 of the second peeling section 7a. While rotating the wafer 8, hot water at the above temperature is sprayed from a nozzle 70a located above the protective film of the wafer 8 to completely remove the water-soluble protective material 30, and then air is sprayed from the drying section 70b to dry it. The residual inspection section 71 allows for inspection of the remaining state of the water-soluble protective material 30.

[0036] The residual inspection unit 71 is designed to inspect whether the water-soluble protective material 30 has been completely removed from the wafer 8. It uses a wide-angle camera 72a to photograph the surface of the wafer 8 and confirm the remaining state of the water-soluble protective material 30. Alternatively, a method of inspecting the surface state using a line sensor may be used. If the water-soluble protective material 30 is still present, hot water is sprayed again to remove the water-soluble protective material 30.

[0037] Then, the wafer 8, from which the water-soluble protective material 30 has been completely removed, is returned to the transport unit 2, where it is cleaned and dried on the grinding surface before being recovered.

[0038] Next, the method for forming the protective film and the grinding process in the grinding apparatus 1 configured in this way will be explained using the flowchart in Figure 8.

[0039] First, the wafer 8 is removed from a cassette (not shown) and placed on the transport unit 2 by the arm 21 for transport.

[0040] Then, the arm 21 uses suction to pick up the wafer 8 from above and transfer it to the holding table 31 of the coating unit 3, where the holding table 31 holds the wafer 8 (step S1). At this time, air is sucked in from micro-holes (not shown) provided in the holding table 31 to pick up and fix the wafer 8.

[0041] Then, the liquid supply mechanism 30a is lowered from above onto the fixed wafer 8 (see Figure 3), and the water-soluble protective material 30 is applied in a spiral pattern while the nozzle of the dispenser constituting the liquid supply mechanism 30a and the wafer 8 are rotated relative to each other (step S2). At this time, when the water-soluble protective material 30, which has been liquefied by heating, is discharged from the nozzle, the water-soluble protective material 30 solidifies instantly within the range of room temperature, which may create a step on the surface, but it has the advantage that the water-soluble protective material 30 will not overflow from the outside of the wafer 8.

[0042] After applying the water-soluble protective material 30 in this manner, the nozzle is retracted to its retracted position, the pressing member 44 is moved above the wafer 8, and then lowered from there (see Figure 4). The pressing member 44 is then heated, and the holding table 31 is also heated as needed to make the thickness of the applied water-soluble protective material 30 uniform (step S3). The pressing member 44 is then cooled to shrink it and separate it from the protective film. If necessary, the surface is uniformly scraped off with a scraper or the like. Here, the characteristic of the material of the pressing member 44 to shrink when cooled (for example, the temperature characteristics of metal) is utilized, but a method may be used to more reliably solidify the water-soluble protective material 30 by cooling the water-soluble protective material 30 that is in contact with the pressing member 44, or the surface of the pressing member 44 may be made of silicone so that the pressing member 44 can be easily peeled off.

[0043] Then, the pressing member 44 is retracted to the retracted position, and the camera and other components of the thickness inspection unit 5 are used to inspect whether the thickness of the protective film is uniform (step S4). If the thickness is not uniform at this time, the pressing member 44 is lowered again to uniformize the thickness by melting the surface.

[0044] Then, the wafer 8 with a uniform surface is transferred to the grinding section 6. When performing this transfer, the pins 32 are protruded from the holding table 31 to lift the wafer 8, and the fork 22 of the arm 21 is sandwiched and adsorbed in the gap between the holding table 31 and the wafer 8 (see FIG. 5). Then, the arm 21 is rotated so that the protective film faces downward, and it is placed on the chuck table 62 of the grinding section 6 (see FIG. 1) (step S5).

[0045] Then, the index table 61 is rotated to perform rough grinding at the position of region A, and further, the index table 61 is rotated to perform finish grinding at the position of region B (step S6).

[0046] Next, the protective film is removed from the wafer 8 thus finish - ground (step S7).

[0047] When removing this protective film, as shown in FIG. 6, the chuck table 62 is heated, warm water is discharged from below the chuck table 62, and the protective film is melted and removed.

[0048] Alternatively, the wafer 8 is taken out from the chuck table 62, turned over by the arm 21, placed on the holding table 70 of the separately provided second peeling section 7a (see FIGS. 1 and 7), and water at a temperature capable of melting is discharged from above. Then, by rotating, the water - soluble protective material 30 is removed and the moisture on the surface is also removed.

[0049] Then, after removing the moisture in this way, the residual state of the water - soluble protective material 30 is inspected by the residual inspection section 72 (step S8). If the water - soluble protective material 30 still remains, warm water is applied again to remove the water - soluble protective material 30.

[0050] Then, after completely removing the water - soluble protective material 30 in this way, the wafer 8 is returned to the transfer section 2 by the arm 21, and the grinding surface is washed and dried and then recovered. Note that the washing and drying of this grinding surface may be performed simultaneously in the second peeling section 7a.

[0051] As described above, according to this embodiment, a protective film is formed on the surface of the wafer 8 by applying a water-soluble protective material such as polyethylene glycol, which is in a solid state at a temperature within the range of 20°C to 70°C and in a liquid state at a temperature outside this solidification temperature range of 35°C to 100°C. This eliminates the need for the work of applying and peeling off the protective film, and also eliminates the problem of generating a large amount of waste during peeling.

[0052] The present invention is not limited to the embodiments described above and can be implemented in various ways.

[0053] For example, in the above embodiment, the protective film is formed during transport in the transport unit 2, but the protective film may be formed before storing the wafer 8 in the cassette. In this case, after applying the water-soluble protective material 30 in the coating unit 3, the surface may be made uniform using the uniformization means 4, and it may be checked whether the film thickness is uniform.

[0054] Furthermore, in the above embodiment, the water-soluble protective material 30 was removed using the chuck table 62 or the second peeling section 7a after grinding was completed. However, the wafers 8 may be collected in a cassette with the protective film still attached, and the protective film may be removed by pouring hot water over multiple wafers 8 at once.

[0055] Furthermore, while the water-soluble protective material 30 is designed to meet wastewater discharge standards, it may also be recycled and reused without being discharged.

[0056] 1...Grinding device 2...Transportation unit 21...Arm 22...Fork 3...Coating unit 30.Water-soluble protective material 30a...Liquid supply mechanism (dispenser) 31...Holding table 32...Pin 4...Uniformization means 44...Pressing member 5...Thickness inspection unit 6...Grinding unit 61...Indexing table 62...Chuck table (heater 62a, hole 62b) 63...Grinding wheel device 7...Peeling unit (7a Second peeling unit) 71...Residual inspection unit 70...Holding table 70a...Nozzle 70b...Drying unit 8...Wafer

Claims

1. A method for forming a protective film on a wafer, characterized in that a water-soluble protective material is applied to the surface of the wafer, which is in a solid state at any temperature within the range of 20°C to 70°C and in a liquid state at any temperature within the range of 35°C to 100°C, outside of the temperature range of the solidification state, thereby forming a protective film.

2. The method for forming a protective film on a wafer according to claim 1, further comprising a step of pressing a pressing member onto the applied water-soluble protective material to homogenize the surface.

3. The method for forming a protective film on a wafer according to claim 1, further comprising: a step of pressing a pressing member onto the applied water-soluble protective material to make the surface uniform; and a step of cooling the pressed pressing member.

4. The method for forming a protective film on a wafer according to claim 1, wherein the step of applying the water-soluble protective material is to apply the water-soluble protective material to the wafer surface using a liquid supply mechanism that dispenses the water-soluble protective material.

5. The method for forming a protective film on a wafer according to claim 1, further comprising measuring the thickness of the applied water-soluble protective material before the grinding step.

6. The wafer protective film forming method according to claim 1, wherein the step of dissolving the water-soluble protective material with water is performed by heating the holding table and then pouring water onto the wafer to dissolve the water-soluble protective material.

7. A wafer grinding apparatus comprising: a coating unit for applying a water-soluble protective material to the surface of a wafer; a holding table for adsorbing the side of the wafer to which the water-soluble protective material has been applied; a grinding unit for grinding the opposite side of the wafer adsorbed on the holding table; and a peeling unit for dissolving and peeling off the water-soluble protective material from the ground wafer with water.

Images