Resin sheet application method

Abstract

Resin sheet application method for attaching a resin sheet (4) to a workpiece (2), the method comprising: a molecular weight reduction step for applying vacuum ultraviolet radiation to a front face (4a) of the resin sheet (4), thereby breaking an intermolecular bond in a surface region extending several tens of nanometers from the front face (4a) of the resin sheet (4) in order to reduce the molecular weight of the surface region and generate an adhesive force; and a resin sheet application step for attaching the front side (4a) of the resin sheet (4) to the workpiece (2) after performing the molecular weight reduction step, wherein the resin sheet (4) is formed of polyvinyl chloride, polyethylene terephthalate or polyolefin, wherein the workpiece (2) includes a wafer having several components (22) formed on a front side of the wafer, and the front side (4a) of the resin sheet is applied to the front side or the back side of the wafer in the resin sheet application step.

Description

Field of the invention

[0001] The present invention relates to a resin sheet attaching method for attaching a resin sheet to the front or back of a wafer. Description of the state of the art

[0002] In a semiconductor device manufacturing process, a plurality of intersecting dividing lines are formed on the front side of a substantially disc-shaped semiconductor wafer, thereby dividing a plurality of regions in which a plurality of devices, such as ICs and LSIs, are formed. The back side of the semiconductor wafer is ground with a grinder to reduce the thickness of the semiconductor wafer to a predetermined thickness. The wafer is then separated along the dividing lines using a cutter or a laser processing device, thereby obtaining the separated, individual devices.

[0003] The grinding apparatus for grinding the back surface of a wafer, such as a semiconductor wafer, includes a chuck table having a holding surface for holding the wafer under suction, a grinding means including a grinding wheel with grinding elements for grinding the wafer held on the holding surface of the chuck table, the grinding wheel being mounted on a rotary spindle, and a feeding means for feeding the grinding element in a direction perpendicular to the holding surface of the chuck table. In operation, the front surface of the wafer is held on the holding surface of the chuck table under suction, and the grinding elements of the grinding wheel are brought into contact with the back surface of the wafer and fed by the feeding means, thereby grinding the back surface of the wafer.When grinding the back side of the wafer, a protective tape is applied to the front side of the wafer to protect the components formed on the front side of the wafer (see e.g. JP 2009 - 107 084 A).

[0004] The cutting device for separating a wafer, such as a semiconductor wafer, into individual components along the separation lines includes a chuck table having a holding surface for holding the wafer under suction, a cutting means having a rotatable cutting blade for cutting the wafer held on the holding surface of the chuck table, and a feeding means for relative movement of the chuck table and the cutting means in a feeding direction. In operation, the back side of the wafer is held on the holding surface of the chuck table under suction, and the cutting blade is positioned immediately above each separation line and fed to cut the wafer. Thereafter, the chuck table and the cutting means are moved relative to each other in the feeding direction to thereby cut the wafer along each separation line. Thus, the wafer is separated into individual components.When separating the wafer, a dicing belt is attached to the back of the wafer to prevent scattering of the individual components, and the dicing belt is held on an annular frame at its peripheral portion (see, for example, JP 2005 - 166 969 A).

[0005] The publications US 2004 / 0 211 511 A1, US 2009 / 0 156 016 A1 and JP 2009 - 246 195 A constitute further prior art. SUMMARY OF THE INVENTION

[0006] Both the protective tape and the dicing tape described above have a structure in which an adhesive is applied to the front surface of a resin sheet, such as a polyvinyl chloride sheet. Accordingly, there is a problem in that the adhesive may adhere to the wafer, causing a reduction in device quality.

[0007] Furthermore, there are variations in the thickness of the adhesive layer applied to the front side of the resin sheet, so that the thickness of the resin sheet to be attached to the wafer with the adhesive layer becomes uneven. This causes the following problem. If the back side of the wafer is ground in the state where the resin sheet is attached to the front side of the wafer, the thickness of the wafer cannot be reduced to a uniform thickness by grinding. Furthermore, if the wafer is cut along each parting line formed on the front side of the wafer in the state where the resin sheet is attached to the back side of the wafer, a cutting groove with a uniform depth cannot be formed from the front side of the wafer.

[0008] It is therefore an object of the present invention to provide a resin sheet attachment method capable of attaching a resin sheet to a workpiece so as to obtain a uniform thickness.

[0009] The present invention is defined by the resin sheet attachment method for attaching a resin sheet to a workpiece according to the features of independent claim 1 and the resin sheet attachment method for attaching a resin sheet to a workpiece according to the features of independent claim 3. The dependent claims relate to preferred developments.

[0010] According to one aspect of the present invention, there is provided a resin sheet attachment method for attaching a resin sheet to a workpiece, the method including: a molecular weight reducing step of applying vacuum ultraviolet radiation to the front side of the resin sheet, thereby breaking an intermolecular bond in a surface region having a depth of several tens of nanometers from the front side of the resin sheet, thereby reducing the molecular weight of the surface region and generating an adhesive force; and a resin sheet attachment step of attaching the front side of the resin sheet to the workpiece after performing the molecular weight reducing step.

[0011] Preferably, the molecular weight reduction step is performed by applying vacuum ultraviolet radiation having a wavelength of 200 to 10 nm using an excimer lamp. Preferably, the workpiece includes a wafer having a plurality of devices formed on the front side of the wafer, and the front side of the resin sheet is attached to the front side or the back side of the wafer in the resin sheet attachment step.

[0012] Preferably, the workpiece includes a wafer having a device region in which a plurality of devices are formed on the front side of the wafer and a peripheral edge region surrounding the device region, and the vacuum ultraviolet radiation in the molecular weight reducing step is applied only to a peripheral region on the front side of the resin sheet corresponding to the peripheral edge region of the wafer.

[0013] The resin sheet attachment method according to the present invention includes the molecular weight reduction step of applying vacuum ultraviolet radiation to the front surface of the resin sheet, thereby breaking an intermolecular bond in a surface region having a depth of several tens of nanometers from the front surface of the resin sheet, thereby reducing the molecular weight of the surface region and generating an adhesive force, and the resin sheet attachment step of attaching the front surface of the resin sheet to the workpiece after performing the molecular weight reduction step. Accordingly, it is not necessary to apply an adhesive to the front surface of the resin sheet, and it is possible to solve the problem that the adhesive may adhere to a workpiece such as a wafer, thereby reducing the quality of the components.

[0014] Furthermore, since no adhesive is applied to the front surface of the resin sheet, it is possible to solve the problem that the thickness of a workpiece such as a wafer cannot be reduced to a uniform thickness by grinding due to variations in the thickness of the adhesive layer, or the problem that a cutting groove having a uniform thickness cannot be formed from the front surface of a workpiece such as a wafer due to variations in the thickness of the adhesive layer.

[0015] The above and other objects, features and advantages of the present invention and the mode for carrying them out will become more apparent and the invention itself will be best understood by studying the following description and the appended claims with reference to the accompanying drawings which show some preferred embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a semiconductor wafer as a workpiece; Fig. 2 is a schematic illustration of a molecular weight reduction step in a resin sheet attachment method according to a preferred embodiment of the present invention; Fig. 3 is an enlarged view of an essential part of a device formed by the Fig. 2 shown molecular weight reduction step processed resin sheet; Fig. 4 is a schematic illustration of a resin sheet attaching step in the resin sheet attaching method; Fig. 5A to 5C are schematic illustrations showing another preferred embodiment of the molecular weight reducing step; Fig. 6A is a perspective view of a through the in Fig. 5B shown molecular weight reduction step processed resin sheet; Fig. 6B is an enlarged view of an essential part of the Fig. 6A shown resin sheet; and Fig. 7A to 7C are schematic illustrations showing another preferred embodiment of the resin sheet attaching step. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A preferred embodiment of the resin sheet attaching method according to the present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 is a perspective view of a semiconductor wafer 2 as a workpiece. The Fig. The semiconductor wafer 2 shown in Figure 1 is a circular silicon wafer having a front surface 2a and a back surface 2b. A plurality of intersecting dividing lines 21 are formed on the front surface 2a of the semiconductor wafer 2, thereby defining a plurality of separated regions, each of which houses a plurality of devices 22, such as ICs and LSIs. The front surface 2a of the semiconductor wafer 2 includes a device region 23 in which the devices 22 are formed, and a peripheral edge region 24 surrounding the device region 23. A method for attaching a resin sheet to the front surface 2a or the back surface 2b of the semiconductor wafer 2 will be described below.

[0017] More specifically, a method for attaching a resin sheet to the front surface 2a of the semiconductor wafer 2 so as to protect the components 22 formed on the front surface 2a of the semiconductor wafer 2 while grinding the back surface 2b of the semiconductor wafer 2 to reduce the thickness of the semiconductor wafer 2 to a predetermined thickness will be described below. First, a molecular weight reduction step is performed in such a manner that vacuum ultraviolet radiation is applied to the front surface of the resin sheet to be attached to the front surface 2a of the semiconductor wafer 2, thereby breaking an intermolecular bond in a surface region having a depth of several tens of nanometers from the front surface of the resin sheet, thereby reducing the molecular weight of the surface region and generating an adhesive force. This molecular weight reduction step is carried out by using a Fig. 2. The molecular weight reduction apparatus 3 consists of a treatment housing 31 having an upper opening, a housing cover 32 for closing the upper opening of the treatment housing 31, a workpiece mounting table 33 provided in the treatment housing 31 for mounting the workpiece, and a vacuum ultraviolet lamp 34 provided on the inner surface of the housing cover 32.

[0018] The treatment housing 31 of the molecular weight reduction device 3 is connected to a vacuum means 35. The vacuum ultraviolet lamp 34 is provided, for example, as an excimer lamp for applying vacuum ultraviolet radiation with a wavelength of 172 nm with a power of 100 W. However, any lamp for applying vacuum ultraviolet radiation with a wavelength of 200 to 10 nm can be used as the vacuum ultraviolet lamp 34.

[0019] When performing the molecular weight reduction step by using the molecular weight reduction apparatus 3 described above, the housing cover 32 is first opened to attach a resin sheet 4 to the workpiece attachment table 33. The resin sheet 4 is provided, for example, as a polyvinyl chloride sheet with a thickness of 100 μm. The resin sheet 4 has a circular shape and substantially the same size as the semiconductor wafer 2. However, any resin sheet formed of, for example, polyethylene terephthalate or polyolefin can be used as the resin sheet 4. After the resin sheet 4 is attached to the workpiece attachment table 33 as described above, the housing cover 32 is closed, and next, the vacuuming means 35 is operated to reduce the pressure inside the treatment housing 31 to approximately 100 Pa.Thereafter, the vacuum ultraviolet lamp 34 is operated to apply vacuum ultraviolet radiation to the front surface 4a of the resin sheet 4 attached to the workpiece attachment table 33 (molecular weight reducing step).

[0020] By applying vacuum ultraviolet radiation in the molecular weight reduction step as described above, a material process occurs such that molecules are excited and ambient oxygen is activated. As a result, an intermolecular bond in a surface region having a depth of several tens of nanometers from the front side 4a of the resin sheet 4 is severed, and a polar group is generated, thereby reducing the molecular weight of the surface region and generating an adhesive force.In this preferred embodiment, vacuum ultraviolet ray having a wavelength of 172 nm with a power of 100 W is applied to a polyvinyl chloride sheet having a thickness of 100 µm as the resin sheet 4 for 10 minutes in the state where the pressure inside the treatment case 31 is reduced to 100 Pa, whereby an adhesive layer 41 having a thickness of 30 to 50 nm is formed in the surface region on the front side 4a of the resin sheet 4, as shown in FIG. Fig. 3. This adhesive layer 41 is formed without variations in thickness, that is, it has a uniform thickness.

[0021] After the molecular weight reduction step has been performed as described above, a resin sheet attachment step is performed in such a manner that the front side 4a of the resin sheet 4 processed by the molecular weight reduction step is attached to the front side 2a of the semiconductor 2. More specifically, as shown in Fig. 4, the adhesive layer 41 formed on the front surface 4a of the resin sheet 4 is attached to the front surface 2a of the semiconductor wafer 2. In the state where the resin sheet 4 is attached to the front surface 2a of the semiconductor wafer 2 as described above, the distance between the back surface 2b of the semiconductor wafer 2 and the back surface 4b of the resin sheet 4 is uniform because the thickness of the adhesive layer 41 of the resin sheet 4 is uniform as described above.

[0022] After the resin sheet attachment step as described above is performed, the semiconductor wafer 2 with the resin sheet 4 is transferred to a grinding apparatus (not shown) to perform a back grinding step for grinding the back surface 2b of the semiconductor wafer 2 to reduce the thickness of the semiconductor wafer 2 to a predetermined thickness. In this back grinding step, the resin sheet 4 attached to the front surface 2a of the semiconductor wafer 2 is held under suction on a holding surface of a chuck table included in the grinding apparatus. In this state, grinding elements of a grinding wheel are brought into contact with the back surface 2b of the semiconductor wafer 2 and then fed toward the holding surface of the chuck table, thereby grinding the back surface 2b of the semiconductor wafer 2.As described above, the distance between the back surface 2b of the semiconductor wafer 2 held on the holding surface of the chuck table of the grinding apparatus and the back surface 4b of the resin sheet 4 attached to the front surface 2a of the semiconductor wafer 2 is uniform. Accordingly, the back surface 2b of the semiconductor wafer 2 can be ground uniformly to reduce the thickness of the semiconductor wafer 2 to a uniform thickness.

[0023] A further preferred embodiment of the molecular weight reduction step is described below with reference to the Fig. 5A to 5C. The molecular weight reduction step in this preferred embodiment is carried out if the molecular weights shown on the front side 2a of the Fig. 1, the components 22 formed on the semiconductor wafer 2 are MEMS (microelectromechanical systems) components. If the components 22 are MEMS components, there is a problem that when the resin sheet 4 is attached as a protective member to the front side 2a of the semiconductor wafer 2, the MEMS components may be damaged when peeling off the resin sheet 4. Accordingly, to solve this problem, it is necessary to use a resin sheet that is only in a peripheral region corresponding to the peripheral edge region 24 of the semiconductor wafer 2 shown in Fig. 1, has an adhesion layer, that is to say in a central region corresponding to the component region 23 of the semiconductor wafer 2 shown in Fig. 1, has no adhesion layer.

[0024] The molecular weight reduction step in this preferred embodiment is carried out in the following manner. As in Fig. As shown in Fig. 5A, a mask 5 is provided on the front side 4a of the resin sheet 4 in the central region corresponding to the device region 23 of the semiconductor wafer 2 (covering step). Accordingly, the front side 4a of the resin sheet 4 is partially exposed in an annular region 42 corresponding to the peripheral edge region 24 of the semiconductor wafer 2, as shown in Fig. 5A. After this covering step has been performed, the resin sheet 4 is placed on the workpiece mounting table 33 of the Fig. 2 in the state in which the mask 5 is directed upwards. In this state, the molecular weight reduction step described above is carried out in a similar manner as in Fig. 5B. As a result, vacuum ultraviolet radiation is applied only to the annular region 42 on the front side 4a of the resin sheet 4, which corresponds to the peripheral edge region 24 of the semiconductor wafer 2. Accordingly, as shown in Fig. 5C, an adhesive layer 41 is formed only in the annular region 42 on the front side 4a of the resin sheet 4, which corresponds to the peripheral edge region 24 of the semiconductor wafer 2.

[0025] After the adhesive layer 41 has been formed as described above, the mask 5 is removed from the central region of the front side 4a of the resin sheet 4, which corresponds to the device region 23 of the semiconductor wafer 2, as shown in Fig. 6A, whereby the resin sheet 4 is obtained with the adhesive layer 41 formed only in the annular region 42 on the front side 4a of the resin sheet 4, which corresponds to the peripheral edge region 24 of the semiconductor wafer 2. As shown in Fig. 6B, the adhesive layer 41 formed only in the annular region 42 on the front surface 4a of the resin sheet 4, which corresponds to the peripheral edge region 24 of the semiconductor wafer 2, is flush with the central region on the front surface 4a of the resin sheet 4. Accordingly, the overall flatness of the front surface 4a of the resin sheet 4 can be maintained.

[0026] Next, when the front surface 4a of the resin sheet 4 is attached to the front surface 2a of the semiconductor wafer 2, the adhesive layer 41 formed only in the annular region 42 of the resin sheet 4 adheres only to the peripheral edge region 24 of the semiconductor wafer 2. That is, the adhesive layer 41 of the resin sheet 4 does not adhere to the device region 23 where the MEMS devices are formed. Accordingly, even if the resin sheet 4 is peeled off from the front surface 2a of the semiconductor wafer 2 after a back surface grinding step for grinding the back surface 2b of the semiconductor wafer 2 is performed, there is no possibility that the MEMS devices may be damaged.

[0027] Another preferred embodiment of the resin sheet attaching step will be described below with reference to the Fig. 7A to 7C. In this preferred embodiment, the resin sheet 4 is used as a dicing tape in such a manner that a central portion of the resin sheet 4 is attached to the back surface 2b of the semiconductor wafer 2 and a peripheral portion of the resin sheet 4 is held on an annular frame 6. As shown in FIGS. Fig. 7A to 7C, the resin sheet 4 has a diameter larger than the diameter of the semiconductor wafer 2 and an outer diameter larger than the inner diameter of the annular frame 6. The resin sheet 4 has an adhesive layer 41 formed by performing the molecular weight reduction step using the method shown in Fig. 2 is formed entirely on the front side 4a.

[0028] Next, the resin sheet attaching step for attaching the central portion of the resin sheet 4 having the adhesive layer 41 on the front side 4a to the back side 2b of the semiconductor wafer 2 and for holding the peripheral portion of the resin sheet 4 to the annular frame 6 will be described. As shown in Fig. 7A and Fig. As shown in Fig. 7B, the annular frame 6 is attached to a holding table 7, and the semiconductor wafer 2 is also attached to the holding table 7 so as to be located at a central portion of the annular frame 6. At this time, the semiconductor wafer 2 is attached to the holding table 7 in the state where the back surface 2b is facing upward, that is, the front surface 2a is in contact with the upper surface of the holding table 7. Thereafter, the central portion of the adhesive layer 41 formed on the front surface 4a of the resin sheet 4 processed by the molecular weight reduction step is attached to the back surface 2b of the semiconductor wafer 2, and the peripheral portion of the adhesive layer 41 is attached to the annular frame 6, as shown in Fig. Fig. 7B. In this way, the semiconductor wafer 2 is held by the resin sheet 4 on the annular frame 6 in the state in which the front side 2a of the semiconductor wafer 2 is exposed, as shown in Fig.7C is shown.

[0029] The semiconductor wafer 2 held on the annular frame 6 by the resin sheet 4 is next transferred to a cutting device (not shown) to cut the semiconductor wafer 2 along the dividing lines 21 to separate it into the individual components 22 (separating step). This separating step using the cutting device is performed by holding the semiconductor wafer 2 on a chuck table in the state where the resin sheet 4 is in contact with the upper surface of the chuck table, and rotating a cutting blade to cut the semiconductor wafer 2 along the dividing lines 21. Since the thickness of the adhesive layer 41 of the resin sheet 4 is uniform as described above, the distance between the front surface 2a of the semiconductor wafer 2 and the back surface 4b of the resin sheet 4 is uniform.Accordingly, in this dicing step, a cutting groove with a uniform depth can be formed from the front surface 2a of the semiconductor wafer 2 along each dicing line 21. Furthermore, since the resin sheet 4 has the adhesive layer 41 formed by performing the above-described molecular weight reduction step, it is not necessary to apply an adhesive to the front surface 4a of the resin sheet 4. Accordingly, it is possible to solve the problem that the adhesive may adhere to a workpiece such as a wafer, thereby reducing the quality of the devices.

[0030] Having thus described specific preferred embodiments of the present invention, it should be noted that the present invention is not limited to the above preferred embodiments, but various modifications can be made within the scope of the present invention. For example, although the molecular weight reduction step is performed for a resin sheet having a predetermined shape in the above preferred embodiments, the molecular weight reduction step may be performed for a ribbon-shaped resin sheet, and this ribbon-shaped resin sheet processed through the molecular weight reduction step may be cut into a predetermined shape.

[0031] The present invention is not limited to the details of the preferred embodiments described above. The scope of the invention is defined by the appended claims.

Claims

[1] A resin sheet attachment method for attaching a resin sheet (4) to a workpiece (2), the method comprising: a molecular weight reduction step of applying vacuum ultraviolet radiation to a front surface (4a) of the resin sheet (4), thereby breaking an intermolecular bond in a surface region having a depth of several tens of nanometers from the front surface (4a) of the resin sheet (4), thereby reducing the molecular weight of the surface region and generating an adhesive force; and a resin sheet attaching step for attaching the front side (4a) of the resin sheet (4) to the workpiece (2) after performing the molecular weight reduction step, wherein the resin sheet (4) is formed of polyvinyl chloride, polyethylene terephthalate or polyolefin, wherein the workpiece (2) includes a wafer having a plurality of components (22) formed on a front side of the wafer, and the front side (4a) of the resin sheet is attached to the front side or the back side of the wafer in the resin sheet attaching step. [2] The resin sheet attaching method according to claim 1, wherein the molecular weight reducing step is carried out by using an excimer lamp to apply vacuum ultraviolet rays having a wavelength of 200 to 10 nm. [3] A resin sheet attachment method for attaching a resin sheet (4) to a workpiece (2), the method comprising: a molecular weight reduction step of applying vacuum ultraviolet radiation to a front surface (4a) of the resin sheet (4), thereby breaking an intermolecular bond in a surface region having a depth of several tens of nanometers from the front surface (4a) of the resin sheet (4), thereby reducing the molecular weight of the surface region and generating an adhesive force; and a resin sheet attaching step for attaching the front side (4a) of the resin sheet (4) to the workpiece (2) after performing the molecular weight reduction step, wherein the resin sheet (4) is formed of polyvinyl chloride, polyethylene terephthalate or polyolefin, wherein the workpiece (2) includes a wafer having a device region (23) in which a plurality of devices (22) are formed on a front side of the wafer, and a peripheral edge region (24) surrounding the device region, and the vacuum ultraviolet radiation in the molecular weight reducing step is applied only to a peripheral region (42) on the front side (4a) of the resin sheet corresponding to the peripheral edge region of the wafer. [4] The resin sheet mounting method according to claim 1 or 2, wherein the workpiece (2) includes a wafer having a device region (23) in which a plurality of devices (22) are formed on a front side of the wafer, and a peripheral edge region (24) surrounding the device region, and the vacuum ultraviolet radiation in the molecular weight reducing step is applied only to a peripheral region (42) on the front side (4a) of the resin sheet corresponding to the peripheral edge region of the wafer.

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