1. Field of the Invention
The present invention relates to 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 marginal area surrounding the device area, the adhesive tape having an annular adhesive layer corresponding to the peripheral marginal area.
2. Description of the Related Art
In association with high-density packaging of semiconductor devices, bumps formed of solder or the like are used for bonding of a semiconductor chip to a substrate. For example, in the case of directly bonding the semiconductor chip to the substrate, ball-shaped bumps each having a diameter of about 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 next divided to manufacture semiconductor chips each having the bumps on the front side.
In grinding the back side of the wafer to reduce the thickness of the wafer, an adhesive tape (protective tape) is attached to the front side of the wafer on which the bumps are provided, and the wafer is held on a suction holding surface or the like through the adhesive tape in the condition where the back side of the wafer is exposed. In this condition, the exposed back side of the wafer is ground. When each bump has a large height (e.g., about 100 μm in diameter), an area of the front side of the wafer where no bumps are provided is sucked onto the suction holding surface in the grinding operation, so that irregularities are generated on the back side of the wafer. In other words, the irregularities on the front side of the wafer due to the bumps have an effect on the back side of the wafer.
When irregularities are generated on the back side of the wafer as mentioned above, a load applied to the wafer in the grinding operation cannot be sufficiently absorbed by the cushioning property of the adhesive tape, causing a problem of damage to the wafer during the grinding operation or a problem of formation of a dimple (indentation on the back side of the wafer), which causes a reduction in reliability of each device obtained from the wafer. To cope with the problem of damage to the wafer, the finished thickness of the wafer after grinding is conventionally set to a relatively large thickness. In the case that a small finished 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, wherein the thickness of the adhesive layer is set so as to accommodate the bumps formed on the front side of the wafer. Accordingly, grinding is performed in the condition where the bumps 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 is a problem such that the adhesive layer may be left as a residue on the bumps or the front side of each device after peeling the adhesive tape. To cope with this problem, there has been proposed a technique of using an adhesive tape having an annular adhesive layer corresponding to a peripheral marginal area surrounding a device area where devices are formed on the front side of the wafer. That is, the annular adhesive layer is located in only the peripheral marginal area of the wafer, and the bumps arranged at a relatively high density are used as a support member instead of the adhesive layer, so that the residue of the adhesive layer is not left after grinding the wafer (see Japanese Patent Nos. 4462997 and 4447280).
However, in the case of attaching the adhesive tape having the annular adhesive layer to the wafer in the condition where the annular adhesive layer is properly located in only the peripheral marginal area of the wafer as a specified area without deviation, higher-accuracy alignment is required as compared with the case of attaching an adhesive tape having an adhesive layer adapted to be simply attached to the whole front side of the wafer.
It is therefore an object of the present invention to provide an adhesive tape attaching method which can locate the annular adhesive layer at an optimum position in the condition where the adhesive tape is attached to the wafer.
In accordance with 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 marginal area surrounding the device area, the adhesive tape having an annular adhesive layer corresponding to the peripheral marginal area, the adhesive tape attaching method including: a wafer setting step of setting the wafer on a chuck table in the condition where the front side of the wafer is exposed; an aligning step of opposing the adhesive tape having the annular adhesive layer corresponding to the peripheral marginal area of the wafer to the front side of the wafer set on the chuck table and positioning the central portion of the wafer directly below the central portion of the adhesive tape, the adhesive tape being composed of a circular base having a diameter equal to that of the wafer and the annular adhesive layer formed on one side of the circular base along the outer circumference thereof; a partial attaching step of pressing the adhesive tape on the front side of the wafer by using an attaching roller positioned so as to cover the diameter of the adhesive tape passing through the central portion of the adhesive tape, thereby attaching a part of the adhesive tape to the wafer at a position where the central portion of the adhesive tape is superimposed on the central portion of the wafer; and an attaching step of rotationally moving the attaching roller from the central portion of the wafer toward the radially opposite outer circumferential portions of the wafer after performing the partial attaching step, thereby attaching the adhesive tape to the wafer.
In the condition where the adhesive tape having the annular adhesive layer is attached to the wafer, the annular adhesive layer can be located at an optimum position.
In the adhesive tape attaching method of the present invention, the central portion of the circular adhesive tape having the annular adhesive layer is first aligned to the central portion of the wafer and then superimposed thereon. Thereafter, the adhesive tape is pressed on the wafer by using the attaching roller so that the central portion of the adhesive tape is not misaligned to the central portion of the wafer (the partial attaching step). Thereafter, the attaching roller is rotationally moved from the central portion of the wafer (adhesive tape) to one of the radially opposite outer circumferential portions of the wafer (adhesive tape) (the attaching step). Thereafter, the attaching roller is further rotationally moved so as to attach the whole of the adhesive layer of the adhesive tape to the wafer. Accordingly, as compared with the conventional attaching method that the attaching roller is rotationally moved from one diametrical end of the wafer (adhesive tape) to the other diametrical end thereof in one stroke, the amount of misalignment between the central portion of the adhesive tape and the central portion of the wafer due to elongation of the adhesive tape can be reduced.
The above and other objects, features and advantages of the present invention and the manner of realizing them 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 attached drawings showing some preferred embodiments of the invention.
As shown in
As shown in
The shape of the wafer 11 as a workpiece is not limited to a circular shape shown in
The adhesive tape attaching method according to the present invention as applied to the wafer 11 will now be described. As shown in
After performing the wafer setting step mentioned above, an aligning step is performed as shown in
The adhesive tape 20 is supplied by a tape supplying apparatus 40 for continuously supplying a plurality of similar adhesive tapes 20. These plural adhesive tapes 20 are supported on the back side 41b of a rolled release paper 41 so as to be arranged at intervals in the longitudinal direction of the release paper 41. Any one of the plural adhesive tapes 20 is supplied by suitably unwinding the rolled release paper 41 so that the back side 24b of the base 24 of the adhesive tape 20 is opposed to the chuck table 30. The tape supplying apparatus 40 is positioned so 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 supplying apparatus 40 is operated to suitably unwind the rolled release paper 41 so that the center position of the chuck table 30 coincides with the center position of the adhesive tape 20 in the X direction. As a modification, an imaging apparatus for detecting the center position of the chuck table 30 and the center position of the adhesive tape 20 may be provided to suitably perform alignment of the chuck table 30 and the adhesive tape 20 in the case of misalignment between these center positions.
In the aligning step mentioned above, the back side 24b of the base 24 of the adhesive tape 20 is opposed to the front side 11a of the wafer 11 set 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 wording of “the central portion 20C of the adhesive tape 20” means a concept including the center position of the base 24 of the adhesive tape 20, and the wording of “the central portion 11C of the wafer 11” means a concept including the center position of the wafer 11. This aligning step is performed in order to align the adhesive layer 22 of the adhesive tape 20 with the peripheral marginal area 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 marginal area 19 with high accuracy.
After performing the aligning step mentioned above, a partial attaching step is performed as shown in
The attaching roller 46 is arranged so as to come into contact with the front side 41a of the release paper 41 and press the adhesive tape 20 supported on the back side 41b of the release paper 41 against the wafer 11. The attaching roller 46 is rotatable about its axis 46a. The rotation axis 46a of the attaching 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
In this condition, the attaching roller 46 is lowered as shown in
After performing the partial attaching step mentioned above, an attaching step is performed as shown in
Since the occurrence of misalignment between the central portions 20C and 11C can be suppressed as mentioned above, the occurrence of misalignment between the adhesive layer 22 and the peripheral marginal area 19 can be suppressed. Accordingly, in the condition where the adhesive tape 20 having the annular adhesive layer 22 is attached to the wafer 11 as shown in
The path of the rotational movement of the attaching roller 46 is not especially limited, but it is essential that the attaching roller 46 is moved from a position corresponding to the central portion 11C of the wafer 11 toward the outer circumferential portions 11L and 11R. For example, a path 1A shown in
By adopting such a path to move the attaching roller 46 from the central portion 11C toward the outer circumferential portions 11L and 11R, the misalignment between the central portions 20C and 11C can be suppressed to the half or less as compared with the case that the attaching roller 46 is moved from the outer circumferential portion 11R to the outer circumferential portion 11L in one stroke. Accordingly, the misalignment between the adhesive layer 22 and the peripheral marginal area 19 can be suppressed.
Further, as shown in
If the misalignment between the central portions 20C and 11C is large, there arises a problem that the adhesive layer 22 may be located in the device area 17 and come into contact with the bumps 14 in the configuration shown in
The present invention is not limited to the details of the above described preferred embodiments. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.
Number | Date | Country | Kind |
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2012-111411 | May 2012 | JP | national |