Adhesive tape fastening method

Abstract

Adhesive tape fastening method for attaching an adhesive tape (20) to a front face (11a) of a wafer (11) having a setup area (17) in which a plurality of features (15) are formed and a peripheral edge area (19) surrounding the setup area (17), wherein the adhesive tape (20) has an annular adhesive layer (22) corresponding to the peripheral edge area (19), the adhesive tape fastening method comprising: a wafer arrangement step of arranging the wafer (11) on a clamping table (30) in the state in which the front face (11a) of the wafer (11) is exposed;an alignment step of arranging the adhesive strip (20) with the annular adhesive layer (22) corresponding to the peripheral edge region (19) of the wafer (11) arranged opposite the front side (11a) of the wafer (11) arranged on the clamping table (30), and positioning a central section (11C) of the wafer (11) directly below a central section (20C) of the adhesive strip (20), wherein the adhesive strip (20) is formed from a circular base (24) with a diameter identical to that of the wafer (11), and the annular adhesive layer (22) is formed on one side of the circular base (24) along its outer circumference;a partial fastening step of pressing the adhesive strip (20) firmly onto the front (11a) of the wafer (11) using a fastening roller (46) positioned such that it covers the diameter of the adhesive strip (20) passing through the central section (20C) of the adhesive strip (20), thereby fastening a portion of the adhesive strip (20) to the wafer (11) at a position where the central section (20C) of the adhesive strip (20) is superimposed on the central section (11C) of the wafer (11); and a fastening step of moving the fastening roller (46) with a rotational movement from the central section (11C) of the wafer (11) in the direction of the radially opposite outer circumferential sections of the wafer (11), after the partial fastening step has been carried out, thereby fastening the adhesive strip (20) to the wafer (11).

Description

BACKGROUND OF THE INVENTIONTechnical FieldThe present invention relates to an adhesive tape fixing method for fixing an adhesive tape to the front side of a wafer, comprising a device area in which a plurality of devices are formed and a peripheral edge area surrounding the device area, the adhesive tape having an annular adhesive layer corresponding to the peripheral edge area.Description of the Prior ArtIn connection with the high packing density of semiconductor components, elevations made of solder or the like are used for adhering a semiconductor chip to a substrate. For example, in the case of direct adhesion of the semiconductor chip to the substrate, spherical elevations having a respective diameter of approximately 100 μm are frequently used. A wafer having bumps formed on the front side is processed in such a manner that the back side of the wafer is ground to reduce the thickness of the wafer, and the wafer is then divided to produce semiconductor chips each having the bumps on the front side.In grinding the back surface of the wafer to reduce the thickness of the wafer, an adhesive tape (protective tape) is attached to the front surface of the wafer on which the protrusions are provided, and the wafer is held on a suction holding surface or the like by the adhesive tape in the state where the back surface of the wafer is exposed. In this state, the exposed back surface of the wafer is ground. When each bump has a large height (e.g., about 100 μm in diameter), a portion of the front surface of the wafer where no bumps are provided is sucked onto the suction holding surface during the grinding operation, so that irregularities are generated on the back surface of the wafer. In other words, the irregularities on the front side of the wafer due to the protrusion have an influence on the back side of the wafer.When irregularities are generated on the back surface of the wafer as described above, a load applied to the wafer during the grinding operation cannot be sufficiently absorbed by the cushioning property of the adhesive tape, resulting in a problem of damage to the wafer during the grinding operation or a problem of formation of a pit (pit on the back surface of the wafer), resulting in a decrease in the reliability of each device obtained with the wafer. In order to cope with the problem of damage to the wafer, the final thickness of the wafer after grinding is usually set to a relatively high thickness. In the case where a small final thickness of the wafer is required, an adhesive tape having a thick adhesive layer (paste layer) is used to protect the front side of the wafer, and the thickness of the adhesive layer is set to receive the bumps formed on the front side of the wafer. Accordingly, grinding is performed in the state where the protrusions are embedded in the adhesive layer.However, in the case of using such an adhesive tape having a thick adhesive layer in which the bumps are embedded, there occurs a problem that the adhesive layer may remain as a residue on the bumps on the front side of each device after peeling of the adhesive tape. In order to address this problem, a technique of using an adhesive tape having an annular adhesive layer corresponding to a peripheral edge portion having a device region in which devices are formed on the front surface of the wafer has been proposed. That is, the ring-shaped adhesion layer is disposed only in the peripheral edge portion of the wafer, and the protrusions disposed with a relatively high density are used as a support member instead of the adhesion layer, so that the residue of the adhesion layer does not remain after grinding the wafer (see JP 4 462 997 B2 and JP 4 447 280 B2).JP 2005-109 433 A discloses applying individual protective elements in order to protect a semiconductor wafer in the course of a grinding method.US 2007 / 0 249 146 A1 discloses a protective tape which has to be cut to fit or flush after application.SUMMARY OF THE INVENTIONHowever, in the case where the adhesive tape having the annular adhesive layer is attached to the wafer in the state where the annular adhesive layer is properly disposed only in the peripheral edge portion of the wafer as a specified region without deviation, higher-accuracy alignment is required compared with the case of attaching an adhesive tape having an adhesive layer formed for easy attachment to the entire front side of the wafer.It is therefore an object of the present invention to provide an adhesive tape attaching method which can arrange the annular adhesive layer at an optimum position in the state where the adhesive tape is attached to the wafer.According to an aspect of the present invention, there is provided an adhesive tape attaching method for attaching an adhesive tape to the front side of a wafer having a device area where a plurality of devices are formed and a peripheral edge area surrounding the device area, the adhesive tape having an annular adhesive layer corresponding to the peripheral edge area, the adhesive tape attaching method comprising: a semiconductor arranging step of arranging the wafer on a chuck table in the state where the front side of the wafer is exposed; an alignment step of disposing the adhesive tape having the annular adhesive layer corresponding to the peripheral edge portion of the wafer oppositely to the front side of the wafer disposed on the chuck table and directly below the central portion of the adhesive tape, positioning the central portion of the wafer, wherein the adhesive tape is composed of a circular base having a diameter identical to that of the wafer, and the annular adhesive layer is formed on a side of the circular base along the outer periphery thereof; a partial fixing step of pressing the adhesive tape on the front side of the wafer using a fixing roller positioned to cover the periphery of the adhesive tape passing through the central portion of the adhesive tape, thereby fixing a part of the adhesive tape to the wafer at a position where the central portion of the adhesive tape is superposed on the central portion of the wafer; and a fixing step of rotating the fixing roller from the central portion of the wafer toward the radially opposite outer peripheral portions of the wafer after the partial fixing step is performed, thereby fixing the adhesive tape to the wafer.In the state where the adhesive tape having the annular adhesive layer is attached to the wafer, the annular adhesive layer can be disposed at an optimum position.In the tape attaching method of the present invention, the central portion of the circular tape having the ring-shaped adhesive layer is first aligned with the central portion of the wafer and then superposed thereon. Thereafter, the adhesive tape is pressed onto the wafer using the fixing roller so that the central portion of the adhesive tape is not misaligned with the central portion of the wafer (the partial fixing step). Thereafter, the fixing roller is rotated from the central portion of the wafer (adhesive tape) to one of the radially opposite outer peripheral portions of the wafer (adhesive tape) (the fixing step). Thereafter, the fastening roller is moved in a further rotational movement such that the entire of the adhesive layer of the adhesive tape is fastened to the wafer. Accordingly, as compared with the conventional mounting method in which the mounting roller is moved in a rotational movement from one diametrical end of the wafer (adhesive tape) to the other diametrical end thereof in a tension, the amount of misalignment between the central portion of the adhesive tape and the central portion of the wafer due to an elongation of the adhesive tape is reduced.The above and other objects, features and advantages of the present invention and the manner of realizing the same will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the accompanying drawings showing some preferred embodiments of the invention.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a perspective view of a wafer and an adhesive tape; FIG. 2 is a perspective view of a tape feeder; FIG. 3 is a side sectional view illustrating a positional relationship between the wafer and the adhesive tape; FIG. 4 is a perspective view showing a positional relationship between a fixing roller and the wafer; FIG. 5A is a partial side sectional view showing a positional relationship between the fixing roller and the wafer; FIG. 5B is a view similar to FIG. 5A, which branches a partial attachment step; FIG. 6 is a perspective view showing a fixing step; and FIG. 7 is a sectional view showing a positional relationship between a peripheral edge portion and an adhesive layer after the fixing step.DETAILED DESCRIPTION OF PREFERRED EMBODIMENTSAs shown in FIG. 1, the present invention relates to an adhesive tape fixing method for fixing an adhesive tape 20 to the front surface 11 aof a wafer 11 having a device area 17 in which a plurality of devices 15 are formed and a peripheral edge area 19 surrounding the device area 17, the adhesive tape 20 having an annular adhesive layer 22 corresponding to the peripheral edge area 19.As shown in FIG. 1, the wafer 11 as a workpiece is, for example, a circular silicon wafer having a thickness of 700 μm. A plurality of crossing division lines (streets) 13 are formed like a lattice on the front surface 11 aof the wafer 11 to thereby partition a plurality of regions where the plurality of devices 15 are each formed. A plurality of bumps 14 as electrodes are provided on the front side of each device 15. As described above, the wafer 11 includes the device region 17 where the devices 15 are formed and the annular peripheral edge region 19 surrounding the device region 17 on the front side 11 a.The shape of the wafer 11 as a workpiece is not limited to a circular shape shown in FIG. 1, but a quadrangular shape such as a rectangular shape and a square shape are also allowed. In the case where the wafer 11 has a quadrangular shape, the peripheral edge portion 19 of the wafer 11 is assumed to have a quadrangular ring shape. Further, the wafer 11 as a workpiece is not limited to a semiconductor wafer, but an optical wafer may be used. Each device 15 of the wafer 11 may be formed without the protrusions 14. Further, irregularities may be formed on the front surface of each device 15 in addition to the protrusions 14 or in place of the protrusions 14.The tape attaching method according to the present invention applied to the wafer 11 will now be described. As shown in FIG. 2, a wafer arranging step is performed in such a manner that the wafer 11 is placed on a chuck table 30 in the state where the front surface 11 aof the wafer 11 is exposed. The upper surface of the chuck table 30 serves as a holding surface for suction-holding the back surface of the wafer 11. the wafer 11 is held on the holding surface of the chuck table in the state where the front surface 11 aof the wafer 11 is oriented or exposed to the top.After the above-mentioned wafer arranging step is performed, an aligning step is carried out, as shown in FIGS. 1-3, in such a manner that the adhesive tape 20 having the annular adhesive layer 22 corresponding to the peripheral edge portion 19 of the wafer 11 is opposed to the front surface 11 aof the wafer 11 placed on the chuck table 30, and that the central portion 11C of the wafer 11 is positioned directly below the central portion 20C of the adhesive tape 20, the adhesive tape 20 is composed of a circular base 24 having a diameter identical to that of the wafer 11, and the annular adhesive layer 22 is formed on one side of the circular base 24 along the outer periphery thereof. In this preferred embodiment, the base 24 has the same shape and size as those of the wafer 11 as viewed in the plane, and the ring-shaped adhesion layer 22 is formed on the back surface 24 b(see FIG. 3 ) of the base 24. The adhesive tape 20 is aligned with the wafer 11 such that the adhesive layer 22 is positioned directly above the peripheral edge region 19 of the wafer 11. The base 24 is not substantially limited. For example, the base 24 may be provided with a base layer formed of a soft resin such as polyolefin and have a thickness of about 70-200 μm. Further, the adhesive layer 22 may be formed by annularly applying an adhesive having a thickness of about 5-100 μm to the back surface 24 bof the base 24.The adhesive tape 20 is supplied with a tape supplying device 40 for continuously supplying a plurality of similar adhesive tapes 20. These plural adhesive tapes 20 are supported on the back surface 41b of a rolled base paper 41 so as to be arranged at intervals in the longitudinal direction of the base paper 41. Each of the plurality of adhesive tapes 20 is supplied by appropriately unrolling the rolled base paper 41 so that the back surface 24 bof the base 24 of the adhesive tape 20 faces the chuck table 30. The tape feeder 40 is positioned such that the center position of the chuck table 30 coincides with the center position of the adhesive tape 20 in the Y direction. Further, the tape feeder 40 is operated so that the rolled base paper 41 is rolled in an appropriate manner so that the center position of the chuck table 30 coincides with the center position of the adhesive tape 20 in the Y direction. As a modification, an imaging device for detecting the central position of the chuck table 30 and the central position of the adhesive tape 20 may be provided to appropriately perform alignment of the chuck table 30 and the adhesive tape 20 in the case of misalignment between these central positions.In the aforementioned aligning step, the back surface 24 bof the base 24 of the adhesive tape 20 faces the front surface 11 aof the wafer 11 placed on the chuck table 30, and the central portion 11C of the wafer 11 is positioned directly below the central portion 20C of the adhesive tape 20. The phrase "the central portion 20C of the adhesive tape 20" denotes a concept including the central position of the base 24 of the adhesive tape 20, and the phrase "the central portion 11C of the wafer 11" denotes a concept including the central position of the wafer 11. This aligning step is performed to align the adhesive layer 22 of the adhesive tape 20 with the peripheral edge portion 19 of the wafer 11. In this preferred embodiment, the adhesive tape 20 and the wafer 11 have circular shapes with the same diameter.Accordingly, by aligning the central portion 20C of the adhesive tape 20 with the central portion 11C of the wafer 11, the adhesive layer 22 can be aligned with the peripheral edge portion 19 with high accuracy.After performing the above-mentioned alignment step, a partial fixing step is performed, as shown in FIGS. 4, 5A, and 5B, in such a manner that the adhesive tape 20 is fixed and fixed to the wafer 11 at a position 20M at which the central portion 20C of the adhesive tape 20 is superposed on the central portion 11C of the wafer 11 using a fixing roller 46 positioned to press the diameter of the adhesive tape 20 that pulls through the central portion 20C of the adhesive tape 20, whereby a part of the adhesive tape 20 is fixed and fixed to the wafer 11 at a position 20M at which the central portion 20C of the adhesive tape 20 is superposed on the central portion 11C of the wafer 11.The fixing roller 46 is configured to contact the front surface 41 aof the base paper 41 and press the adhesive tape 20 supported on the back surface 41B of the base paper 41 against the wafer 11. The mounting roller 46 is rotatable about its axis 46a. The rotation axis 46 aof the fixing roller 46 is positioned so as to cover the diameter of the adhesive tape 20, i.e., so as to pass through the central portion 20C of the adhesive tape 20 (the central portion 11C of the wafer 11). Accordingly, as shown in FIG. 5A, the rotation axis 46A at the fixing roller 46, the central portion 20C of the adhesive tape 20, and the central portion 11C of the wafer 11 are all arranged in a line as viewed in a side view (at the same position in the X direction).In this state, as shown in FIG. 5B, the fixing roller 46 is lowered to fix a part of the adhesive layer 22 of the adhesive tape 20 to the front surface 11 aof the wafer 11 in the state where the central portion 20C of the adhesive tape 20 is superposed on the central portion 11C of the wafer 11. Since the adhesive layer of the adhesive tape 20 has been aligned with the peripheral edge portion 19 of the wafer 11 in the above-mentioned aligning step, a part of the adhesive layer 22, i.e., a portion of the adhesive layer 22 positioned just below the fixing roller 46, is fixed to a corresponding portion of the peripheral edge portion 19 of the wafer 11.After performing the above-mentioned partial attaching step, an attaching step is performed, as shown in FIG. 6, in such a manner that the attaching roller 46 is rotated from the central portion 1C of the wafer 11 toward the radially opposite outer peripheral portions 11L and 11R of the wafer 11, thereby attaching the adhesive tape 20 to the wafer 11. In the state formed by the foregoing partial fixing step, the adhesive tape 20 is pressed to the wafer 11 by the fixing roller 46 to prevent misalignment between the central portion 20C of the adhesive tape 20 and the central portion 11C of the wafer 11. Accordingly, when moving the fixing roller 46 from the central portion 11C of the wafer 11 toward the outer peripheral portions 11L and 11R in the fixing step, it is possible to suppress occurrence of misalignment between the central portions 20C and 11C due to expansion of the adhesive tape 20 (the base 24).Since the occurrence of misalignment between the central portions 20C and 11C can be suppressed as described above, the occurrence of misalignment between the adhesion layer 22 and the peripheral edge portion 19 can be suppressed. Accordingly, in the state where the adhesive tape 20 having the annular adhesive layer 22 is attached to the wafer 11 as shown in FIG. 7, the annular adhesive layer 22 can be disposed at an optimum position, i.e., at a position corresponding to the peripheral edge portion 19. In the case where the fixing roller 46 is moved from one diametrical end (the outer peripheral portion 11L) of the wafer 11 (the adhesive tape 20) to the other diametrical end (the outer peripheral portion 11R) of the wafer 11 in tension, the distance travelled by the fixing roller 46 is large, so that when the adhesive tape 20 (the base 24) is stretched during the movement of the fixing roller 46, misalignment may occur between the central portions 20C and 11C. As a result, the adhesive layer 22 can be disposed at a position deviating from the peripheral edge portion 19.The path of the rotational movement of the fixing roller 46 is not particularly limited, but it is essential that the fixing roller 46 is moved from a position corresponding to the central portion of the wafer 11 toward the outer peripheral portions 11L and 11R. For example, a path 1A shown in FIG. 6 may be adopted. That is, the path 1A is a path in which the fixing roller 46 is moved from the central portion 11C through the outer peripheral portion 11L to the outer peripheral portion 11R. Further, a path 11B shown in FIG. 6 may also be adopted. That is, the path 11B is a path in which the fixing roller 46 is once moved from the central portion 11C to the outer peripheral portion 11L, then returned to the central portion 11C, and thereafter again moved from the central portion 11C to the outer peripheral portion 11R.By realizing such a path as to move the fixing roller 46 from the central portion 11C toward the outer peripheral portions 11L and 11R, the misalignment between the central portions 20C and 11C can be suppressed to half or less as compared with the case that the fixing roller 46 is moved from the outer peripheral portion 11R toward the outer peripheral portion 11L in one stroke. Accordingly, the misalignment between the adhesion layer 22 and the peripheral edge portion 19 can be suppressed.Further, as shown in FIG. 7, the device area of the wafer 11 is surrounded by the annular adhesion layer 20, and the bumps 14 formed on the front side of each device 15 are accommodated in a space 23 defined inside the annular adhesion layer 22. Accordingly, there is no possibility that the adhesive layer 22 adheres to the protrusions 14, and the residue of the adhesive layer 22 may remain on the front surface of each device 15 after the adhesive tape 20 is peeled off.When the misalignment between the central portions 20C and 11C is large, there occurs a problem that the adhesive layer 22 may be disposed in the device region 17 and come into contact with the protrusions 14 in the configuration shown in FIG. 7, so that the residue of the adhesive layer 22 may remain on the front side of each device 15 after the peeling of the adhesive tape 20. In the case where the protrusions 14 formed on the front surface of each device 15 are arranged at a relatively high density, as shown in FIG. 7, the protrusions 14 may be employed as a support member in a subsequent step of grinding the back surface of the wafer 11.

Claims

An adhesive tape fixing method for fixing an adhesive tape (20) to a front side (11a) of a wafer (11) having a device area (17) in which a plurality of devices (15) are formed and a peripheral edge area (19) surrounding the device area (17), the adhesive tape (20) having an annular adhesive layer (22) corresponding to the peripheral edge area (19), the adhesive tape fixing method comprising: a wafer arranging step of arranging the wafer (11) on a chuck table (30) in the state where the front side (11a) of the wafer (11) is exposed; an aligning step of disposing the adhesive tape (20) having the annular adhesive layer (22) corresponding to the peripheral edge region (19) of the wafer (11) opposed to the front side (11a) of the wafer (11) placed on the chuck table (30) and directly below a central portion (20C) of the adhesive tape (20), positioning a central portion (11C) of the wafer (11), wherein the adhesive tape (20) is formed of a circular base (24) having a diameter identical to that of the wafer (11), and the annular adhesive layer (22) is formed on a side of the circular base (24) along the outer periphery thereof; a partial fixing step of fixing the adhesive tape (20) on the front surface (11a) of the wafer (11) using a fixing roller (46) positioned to cover the diameter of the adhesive tape (20) passing through the central portion (20C) of the adhesive tape (20), thereby fixing a part of the adhesive tape (20) to the wafer (11) at a position where the central portion (20C) of the adhesive tape (20) is superposed on the central portion (11C) of the wafer (11); and a fixing step of, with a rotational movement from the central portion (11C) of the wafer (11) toward the radially opposite outer circumferential portions of the wafer (11), moving the fixing roller (46) after performing the partial fixing step, thereby fixing the adhesive tape (20) to the wafer (11).

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