Wafer processing method

Abstract

This invention provides a wafer processing method that prevents scratches on the wafer surface during grinding and solves the problem of a portion of the adhesive layer adhering to the wafer surface and becoming residue, thereby degrading the quality of the device chip. [Solution] The process includes a preparation step of preparing a substrate 20 in which a ring-shaped protrusion 24 is formed in a region corresponding to the excess outer region of the wafer 10 and a recess 22 is formed in a region corresponding to the device region; an adhesion step of positioning the excess outer region of the wafer 10 on the ring-shaped protrusion 24 of the substrate 20 and sealing and bonding the excess outer region and the ring-shaped protrusion 24 together; a holding step of holding the substrate side on a chuck table constituting a grinding device; and a grinding step of grinding the back surface 10b of the wafer 10 bonded to the substrate 20 with a grinding wheel on which grinding wheels are arranged in an annular shape, wherein the grinding device is installed in a depressurized chamber with a pressure slightly below atmospheric pressure.

Description

Technical Field

[0001] The present invention relates to a method for processing a wafer by grinding the back surface of a wafer on which a device region partitioned by a division planned line and an outer peripheral surplus region surrounding the device region are formed on the surface.

Background Art

[0002] A wafer on which a plurality of devices such as ICs and LSIs are partitioned by a division planned line and formed on the surface is ground on the back surface by a grinding device to form a predetermined thickness, and then divided into individual device chips by a dicing device or a laser processing device, and used in electrical devices such as mobile phones and personal computers.

[0003] The grinding device includes a chuck table for holding a wafer, grinding means in which a grinding wheel provided with a grinding stone for grinding the wafer held on the chuck table is rotatably mounted in an annular shape, and feeding means for feeding the grinding means, and can process the wafer to a desired thickness (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the back surface of the wafer is ground and the front surface side of the wafer is directly held by the chuck table, the front surface of the wafer is damaged and the quality of the device chip is deteriorated. Therefore, a protective tape is disposed on the front surface of the wafer.

[0006] However, after grinding, when the protective tape is peeled off the wafer surface, a portion of the adhesive layer of the protective tape adheres to the wafer surface as residue, which degrades the quality of the device chip.

[0007] The present invention has been made in view of the above facts, and its main technical problem is to provide a wafer processing method that can prevent scratches from being made on the wafer surface when grinding is performed, and that can solve the problem of a part of the adhesive layer adhering to the wafer surface and becoming residue, which degrades the quality of the device chip. [Means for solving the problem]

[0008] To solve the main technical problems described above, the present invention provides a wafer processing method for grinding the back surface of a wafer having a device region formed on its surface, partitioned by dividing lines, and an outer peripheral excess region surrounding the device region, comprising: a preparation step of preparing a substrate in which a ring-shaped protrusion is formed in the region corresponding to the outer peripheral excess region of the wafer and a recess is formed in the region corresponding to the device region; an bonding step of positioning the outer peripheral excess region of the wafer on the ring-shaped protrusion of the substrate and sealing and bonding the outer peripheral excess region and the ring-shaped protrusion in close contact; a holding step of holding the substrate side on a chuck table constituting a grinding apparatus; and a grinding step of grinding the back surface of the wafer bonded to the substrate with a grinding wheel in which grinding wheels are arranged in an annular shape, wherein in the grinding step, the grinding apparatus is installed in a reduced pressure chamber at a pressure slightly below atmospheric pressure.

[0009] A pressure slightly below atmospheric pressure is preferably 0.87 to 0.80 atmospheres. Furthermore, in the bonding process, it is preferable to use a thermoplastic polymer or UV-curing resin as the adhesive, and to heat the substrate before removing the wafer from the substrate. The bonding process is preferably carried out at atmospheric pressure. [Effects of the Invention]

[0010] The present invention relates to a wafer processing method for grinding the back surface of a wafer having a device region formed on its surface, which is demarcated by dividing lines, and an outer peripheral excess region surrounding the device region, comprising: a preparation step of preparing a substrate in which a ring-shaped protrusion is formed in the region corresponding to the outer peripheral excess region of the wafer and a recess is formed in the region corresponding to the device region; an bonding step of positioning the outer peripheral excess region of the wafer on the ring-shaped protrusion of the substrate and sealing and bonding the outer peripheral excess region and the ring-shaped protrusion in close contact; and a grinding apparatus. The process includes a holding step of holding the substrate side on a chuck table, and a grinding step of grinding the back surface of the wafer bonded to the substrate with a grinding wheel on which grinding wheels are arranged in an annular pattern. In the grinding step, the grinding apparatus is installed in a reduced pressure chamber with a pressure slightly below atmospheric pressure. As a result, the back surface of the wafer is ground without the device area on the surface contacting the substrate, preventing damage to the device and eliminating the problem of adhesive residue that can adhere and degrade the quality of the device chip, as can occur when protective tape is used. Furthermore, since the grinding step is performed with the wafer, which is integrated with the substrate, brought into the reduced pressure chamber, the atmospheric pressure sealed between the wafer and the substrate lifts the area of ​​the wafer corresponding to the device area, counteracting the pressing force of the grinding wheels. This allows the back surface of the wafer to be ground in a flat state. [Brief explanation of the drawing]

[0011] [Figure 1] This is a perspective view of the wafer and the substrate prepared by the preparation process of this embodiment. [Figure 2] (a) A perspective view showing an embodiment of the bonding process, and (b) A cross-sectional view of the wafer and substrate joined together by the bonding process shown in (a). [Figure 3] This is an overall perspective view of the grinding machine. [Figure 4] This is a perspective view showing an embodiment of the holding process. [Figure 5](a) A perspective view showing an embodiment of the grinding process, and (b) A perspective view showing a wafer ground by the grinding process shown in (a). [Modes for carrying out the invention]

[0012] Hereinafter, embodiments relating to a wafer processing method constructed according to the present invention will be described in detail with reference to the attached drawings.

[0013] Figure 1 shows a wafer 10 whose back surface is ground by the wafer processing method of this embodiment, and a substrate 20 prepared by the preparation process described later.

[0014] The wafer 10 shown in the figure is a wafer in which, for example, a device region 16 is formed on its surface 10a, which is partitioned by division lines 14, and an outer peripheral excess region 18 surrounds the device region 16. The wafer 10 is, for example, a silicon wafer, with a diameter of 200 mm and a thickness of 700 μm, and the target finished thickness when grinding the back surface 10b by the grinding process described later is 600 μm.

[0015] The wafer processing method of this embodiment involves grinding the back surface 10b of the wafer 10 to a predetermined thickness, and is carried out by the following steps.

[0016] (preparation process) First, a preparation step is performed to prepare the substrate 20 shown in the lower part of Figure 1. The substrate 20 has a ring-shaped protrusion 24 formed in the region corresponding to the excess outer peripheral region 18 of the wafer 10 described above, and a recess 22 formed in the region closer to the center corresponding to the device region 16 of the wafer 10. The diameter of the substrate 20 is, for example, 200 mm, the same as the wafer 10, the thickness of the recess 22 is 1.5 mm, and the height of the ring-shaped protrusion 24 is set to 100 μm relative to the recess 22. The protrusion 24 is formed in a ring shape along the outer peripheral edge of the substrate 20 and has a width of, for example, 3 mm. The substrate 20 described above is made of, for example, silicon, but the material is not particularly limited and may be glass.

[0017] (Adhesion process) Once the substrate 20 is prepared according to the preparation steps described above, an adhesion step is performed in which the excess outer peripheral region 18 of the wafer 10 is positioned on the ring-shaped protrusion 24 of the substrate 20, and the excess outer peripheral region 18 and the ring-shaped protrusion 24 are brought into close contact and sealed to bond. More specifically, as shown in Figure 2(a), adhesive 30 is applied without any gaps to the upper surface of the ring-shaped protrusion 24 of the prepared substrate 20. The adhesive 30 is appropriately selected from, for example, a thermoplastic polymer or a UV-curing resin. Next, as shown in Figure 2(a), the wafer 10 is inverted so that the front surface 10a is facing downwards and the back surface 10b is facing upwards, and the excess outer peripheral region 18 of the wafer 10 is positioned on the ring-shaped protrusion 24 of the substrate 20, bringing the excess outer peripheral region 18 of the wafer 10 into close contact and sealing the ring-shaped protrusion 24 of the substrate 20, and bonding them with the adhesive 30 described above. As a result, as shown in Figure 2(b), a sealed space S is formed by the surface 10a of the wafer 10 and the convex portions 24 and concave portions 22 of the substrate 20. Since the bonding process in this embodiment is carried out under atmospheric pressure, the pressure in the space S is 1 atmosphere. As described above, once the wafer 10 and substrate 20, which are the workpieces, are joined together, they are transported to the grinding apparatus 1 shown in Figure 3.

[0018] As shown in FIG. 3, the grinding apparatus 1 includes a chuck table 3 that holds a wafer 10 adhered to a substrate 20, and a grinding means 4 in which a grinding wheel 43 with a grinding wheel 44 for grinding the back surface 10b of the wafer 10 held by the chuck table 3 disposed in an annular shape is rotatably mounted. The grinding apparatus 1 also includes a feeding means 5 that feeds the grinding means 4 in the vertical direction, and is installed in a decompression chamber 52 formed by a cover member 50 (shown by a two-dot chain line) that covers the entire grinding apparatus 1. The decompression chamber 52 is controlled such that its interior is suctioned by a suction pump or the like (not shown) and the internal pressure becomes a predetermined air pressure slightly lower than the atmospheric pressure. The cover member 50 shown in the figure omits the specific shape for convenience of explanation, but is actually composed of a plate-like member made of steel or the like, and appropriate windows and opening / closing doors not shown are provided. The pressure of the decompression chamber 52 will be described more specifically later.

[0019] As can be understood from FIG. 3, the chuck table 3 includes a holding surface 3a that sucks and holds the wafer 10, and a frame body 3b that supports and surrounds the holding surface 3a. The holding surface 3a is composed of a breathable member, and a suction means (not shown) is connected to the frame body 3b. By operating the suction means, a negative pressure is generated on the holding surface 3a, and the wafer 10 can be sucked and held.

[0020] The chuck table 3 is configured to be rotatable by a rotation driving means (not shown), and can be moved to an arbitrary position, for example, a loading / unloading position for loading and unloading the wafer 10 on the front side in the figure, and a grinding position where grinding is performed directly below the grinding means 4, by a moving means (not shown) housed inside the apparatus housing 2.

[0021] The grinding means 4 includes at least a rotating shaft 41, a wheel mount 42 disposed at the lower end of the rotating shaft 41, a grinding wheel 43 mounted on the lower surface side of the wheel mount 42, an electric motor 46 for rotating the rotating shaft 41, a support portion 45 for supporting the grinding means 4, and a moving base 47 supported by the vertical wall portion 2a of the apparatus housing 2 so as to be vertically movable together with the support portion 45. The feeding means 5 converts the rotational motion of the pulse motor 5a into a linear motion via a ball screw 5b rotated by the pulse motor 5a and transmits it to the above-described moving base 47, and can move the grinding means 4 to an arbitrary position in the vertical direction. If the above-described grinding apparatus 1 is prepared, following the above-described preparation process and bonding process, a holding process and a grinding process described below are carried out.

[0022] (Holding Process) The wafer 10 integrated with the substrate 20 by the above-described bonding process is carried in from an opening / closing door (not shown) disposed in a cover member 50 that covers the grinding apparatus 1, and as shown in FIG. 4, is placed on the holding surface 3a of the chuck table 3 constituting the grinding apparatus 1 with the substrate 20 side facing. Next, a suction means (not shown) is operated to generate a negative pressure on the holding surface 3a and suck and hold it. The decompression chamber 52 is blocked from the outside by closing the opening / closing door, and is decompressed to a predetermined air pressure slightly lower than the atmospheric pressure by operating a suction pump (not shown). The air pressure in the decompression chamber 52 is set to be, for example, 0.87 to 0.80 atmospheres.

[0023] (Grinding Process) Once the holding process is performed as described above, the back surface 10b of the wafer 10 bonded to the substrate 20 is ground with a grinding wheel 44 arranged in an annular shape on the lower surface of the grinding wheel 43, as shown in Figure 5(a), in a depressurized chamber 52 where the pressure is reduced to slightly below atmospheric pressure. More specifically, the moving means described above is activated to position the chuck table 3, which holds the wafer 10 by suction, at a grinding position where grinding is performed directly below the grinding means 4. Then, as shown in Figure 5(a), the rotation axis 41 of the grinding means 4 is rotated at a predetermined rotational speed (e.g., 6000 rpm) in the direction indicated by arrow R1, and the chuck table 3 is rotated at a predetermined rotational speed (e.g., 300 rpm) in the direction indicated by arrow R2 by activating a rotational drive means (not shown).

[0024] Next, the feed mechanism 5 described above is activated to lower the grinding mechanism 4 in the direction indicated by arrow R3, bringing the grinding wheel 44 into contact with the back surface 10b of the wafer 10. At the same time, a grinding water supply mechanism (not shown) is activated to supply grinding water between the grinding wheel 44 and the back surface 10b of the wafer 10. Then, a contact-type or non-contact-type thickness measuring mechanism (not shown) is activated to measure the thickness of the wafer 10. The grinding mechanism 4 is fed at a predetermined speed (for example, 1.0 μm / second) to grind and thin the wafer 10 to a predetermined thickness (600 μm). With this, the grinding process of this embodiment is completed, and the wafer processing method of this embodiment is completed.

[0025] In this embodiment, as described above, the wafer 10 is sealed and bonded by positioning the outer peripheral excess region 18 on the ring-shaped protrusion 24 of the substrate 20 under atmospheric pressure, thereby forming an atmospheric pressure space S inside. As a result, the back surface 10b of the wafer 10 is ground while the device region 16 on the surface 10a of the wafer 10 is not in contact with the substrate 20, preventing damage to the device 12, and preventing the adhesive layer from adhering and leaving residue that degrades the quality of the device chip, as can happen when protective tape is used. Furthermore, since the grinding process is performed with the wafer 10 transported into the reduced pressure chamber 52 described above, the atmospheric pressure sealed in the space S lifts the area of ​​the wafer 10 corresponding to the device area 16 in response to the pressing force of the grinding wheel 44. As a result, the grinding process is performed with the back surface 10b of the wafer 10 flat, and as shown in Figure 5(b), uniform saw marks 19 are formed across the entire back surface 10b of the wafer 10, allowing the thickness of the wafer 10 to be ground uniformly.

[0026] The atmospheric pressure in the decompression chamber 52 described above can be determined by conducting experiments in advance to find an appropriate value. For example, before performing the grinding process described above, several dummy wafers of the same dimensions and material as the wafer 10 were prepared in advance, and the bonding process described above was performed to integrate the dummy wafers and the substrate 20 under atmospheric pressure. Then, the grinding process described above was performed while changing the atmospheric pressure in the decompression chamber 52 as shown below, so that the thickness of the wafer 10 became 600 μm. The grinding results in this case were as follows.

[0027] Pressure in a decompression chamber; grinding results (1) 0.98 The dummy wafer cracked during grinding. (2) 0.95 The dummy wafer cracked during grinding. (3) 0.92 The dummy wafer did not crack, but the thickness in the center was It was 650 μm. (4) 0.90 The dummy wafer did not crack, but the thickness in the center was It was 630 μm. (5) 0.87 Grinding was performed well, and the thickness in the center was 610 μm That was the case. (6) 0.84 Grinding was performed well, and the thickness in the center was 600 μm That was the case. (7) 0.80 Grinding was performed well, and the thickness in the center was 590 μm That was the case. (8) 0.78 The dummy wafer did not crack, but the thickness in the center was It was 580 μm. (9) 0.75 The dummy wafer cracked during grinding.

[0028] The experiments described above confirmed that the wafer 10 falls within the acceptable range of 600 μm ± 10 μm relative to its target thickness of 600 μm, specifically when the atmospheric pressure in the decompression chamber 52 is controlled to 0.87 to 0.80 atmospheres, as shown in experimental results (5) to (7) above. The thickness of the center of the wafer 10 in the grinding process depends on the atmospheric pressure in the decompression chamber 52, that is, the amount by which the center of the back surface 10b of the wafer 10 is lifted in the decompression chamber 52. Therefore, based on the experimental results described above, the operator set the atmospheric pressure in the decompression chamber 52 to be controlled within the range of 0.87 to 0.80 atmospheres so that grinding in the grinding process described above is carried out uniformly across the entire back surface 10b of the wafer 10.

[0029] In the wafer processing method of this embodiment, based on the results of the above-described experiment, by setting the pressure of the decompression chamber 52 to 0.87 to 0.80 atmospheres, it was possible to appropriately lift the back surface 10b of the wafer 10 during the grinding process and uniformly grind the back surface 10b. Thus, it is preferable that the atmospheric pressure of the decompression chamber 52 in the wafer processing method of the present invention be appropriately adjusted according to the type and shape of the wafer. For example, although the diameter of the wafer 10 in this embodiment was 200 mm, when processing a larger wafer, for example a wafer with a diameter of 300 mm, it is preferable to adjust the atmospheric pressure of the decompression chamber 52 in a direction that further reduces the pressure. Furthermore, the appropriate atmospheric pressure of the decompression chamber 52 also changes depending on the thickness of the wafer to be processed, the hardness according to the material, etc., so in any case, it is preferable to determine the appropriate atmospheric pressure of the decompression chamber 52 in response to changes in the shape of the wafer of the workpiece.

[0030] Once the grinding process described above is complete, the substrate 20 can be heated to melt the thermoplastic polymer or UV-effect resin that was functioning as the adhesive 30, thereby allowing the wafer 10 to be removed from the substrate 20.

[0031] In the embodiment described above, an example was shown in which the back surface 10b of the wafer 10 was ground by infeed grinding. However, the present invention is not limited to this and can also be applied when the back surface 10b of the wafer 10 is ground by creep-feed grinding.

[0032] In the embodiments described above, the bonding process was carried out under atmospheric pressure, and the pressure in the space S formed by sealing the wafer 10 and the substrate 20 was set to atmospheric pressure. However, the present invention is not limited to carrying out the bonding process in a space strictly adjusted to atmospheric pressure. The bonding process of the present invention only needs to be carried out in an environment set to a pressure higher than the pressure in the decompression chamber 52, which is set to a pressure slightly below atmospheric pressure as described above. In other words, it is sufficient to carry out the bonding process in an environment where the back surface 10b of the wafer 10 is lifted during the grinding process, and a space S is formed between the wafer 10 and the substrate 20, which is uniformly ground by the grinding wheel 44. [Explanation of Symbols]

[0033] 1: Grinding device 2: Device housing 3: Chuck Table 4: Grinding method 41: Rotation axis 42: Wheel Mount 43: Grinding Wheel 44: Grinding Wheel 45: Support part 46: Electric motor 47: Mobile base 5: Feeding method 10: Wafer 10a: surface 10b: Back side 12: Devices 14: Planned division line 16: Device Area 18: Peripheral surplus area 19: Somark 20: Substrate 22: Recess 24: Convex part 50: Cover component 52: Decompression chamber S: Space

Claims

1. A wafer processing method for grinding the back surface of a wafer having a device region formed on its surface by dividing lines and an outer peripheral surplus region surrounding the device region, wherein A preparation step of preparing a substrate in which a ring-shaped protrusion is formed in the region corresponding to the excess outer region of the wafer and a recess is formed in the region corresponding to the device region, A bonding process in which the excess outer region of the wafer is positioned on the ring-shaped protrusion of the substrate, and the excess outer region and the ring-shaped protrusion are brought into close contact and sealed to bond them together, A holding step in which the substrate side is held in the chuck table that constitutes the grinding device, The process includes a grinding step in which the back surface of a wafer bonded to the substrate is ground with a grinding wheel having grinding wheels arranged in an annular pattern, A method for processing wafers, wherein the grinding apparatus is installed in a depressurized chamber with a pressure slightly below atmospheric pressure during the grinding process.

2. A pressure slightly below atmospheric pressure is defined as 0.87 to 0.80 atmospheres. The wafer processing method according to claim 1.

3. In the bonding process, a thermoplastic polymer or UV-curing resin is used as the adhesive. The wafer processing method according to claim 1, wherein when removing the wafer from the substrate, the substrate is heated and the wafer is removed.

4. The wafer processing method according to claim 1, wherein the bonding step is carried out at atmospheric pressure.

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