BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are a perspective view and a side view which show a semiconductor wafer onto which a protective tape is applied in an embodiment according to the present invention.
FIG. 2 is a perspective view showing a grinding apparatus which is used for forming a recess by grinding and thinning a portion of a rear surface of semiconductor wafer, which corresponds to the device forming region
FIG. 3 is a side view of the grinding apparatus shown in FIG. 2.
FIGS. 4A and 4B are a perspective view and a cross sectional view which show a semiconductor wafer having a recess formed on a rear surface of semiconductor wafer.
FIGS. 5A to 5D are front views showing a protective tape applying method of the embodiment in process order.
FIGS. 6A to 6C are front views showing a protective tape applying method of the embodiment in process order.
FIGS. 7A to 7C are front views showing a protective tape applying method of another embodiment according to the present invention.
FIG. 8 is a plain view showing the protective tape applying method of the another embodiment.
DETAILED DESCRIPTION OF THE INVENTION
A protective tape applying method of an embodiment according to the present invention will be explained hereinafter with reference to the drawings.
1. Semiconductor Wafer
In FIGS. 1A and 1B, reference numeral 1 denotes a disc-shaped semiconductor wafer 1 (substrate, hereinafter referred to simply as “wafer 1”) onto which a protective tape is applied in the method of the embodiment. The wafer 1 is a silicon wafer or the like. Grid-like predetermined division lines 2 are formed on a surface of the wafer 1, and plural rectangular semiconductor chips (devices) 3 are defined by the predetermined division lines 2 on the surface of the wafer 1. Electronic circuits (for example, Integrated Circuits (ICs) and Large Scale Integrations (LSIs)), which are not shown in FIGS. 1A and 1B, are formed on surfaces of the semiconductor chips 3. The plural semiconductor chips 3 are formed on a device forming region 4 which is almost circular so as to be concentric with the wafer 1. A ring-shaped peripheral extra region 5 (non-device forming region), which has no semiconductor chip 3 formed thereon, is formed around the device forming region 4.
2. Thinning of Wafer
In the wafer 1 shown in FIGS. 1A and 1B, only portion of rear surface of the wafer 1, which corresponds to the device forming region 4, is thinned by grinding. In the grinding, as shown in FIGS. 1A and 1B, a protective tape 6 is applied onto the surface of the wafer 1 beforehand in order to protect the electronic circuits. For example, the protective tape 6 is a tape which has a base film and an adhesive coated on a surface of the base film. For example, the base film of the protective tape 6 is composed of polyolefin and has a thickness of about 70 to 200 μm. The adhesive is composed of acrylic resin and has a thickness of about 5 to 20 μm. A method for applying the protective tape onto the surface of the wafer 1 is freely selected.
A grinding apparatus 10 shown in FIGS. 2 and 3 is desirably used for the grinding of the wafer 1. The grinding apparatus 10 is equipped with a chuck table 11 and a grinding unit 12. The chuck table 11 is a vacuum type one which rotates. The chuck table 11 has a disc-shape which is larger than the wafer 1, and it has an upper surface which is set to be horizontal and on which the wafer 1 is mounted. The wafer 1 is chucked and held on the upper surface of the chuck table 11 by vacuum operation. The chuck table 11 is rotated by a driving mechanism (not shown in the drawings) around an axial center of the chuck table 11.
The grinding unit 12 is equipped with a cylindrical spindle housing 13, a spindle 14, a motor 15, a flange 16, a cup wheel 17, and plural grinding stones 18. The spindle 14 is provided in the spindle housing 13. The cup wheel 17 is secured at an end portion of the spindle 14 via the flange 16. The grinding stones 18 are secured at a whole outer circumferential portion of lower surface of the cup wheel 17 so as to be arranged in a ring-shaped manner. In the grinding unit 12, when the spindle 14 is rotated by the motor 15, the cup wheel 17 is rotated, and the grinding stones 18 grind a work. An outer diameter of circular grinding locus of the grinding stones 18 is almost equal to a radius of the device forming region 4 of the wafer 1. The grinding unit 12 is shifted to be eccentric with the chuck table 11. The detail is shown in FIG. 3. That is, the relative position of the chuck table 11 and the grinding unit 12 is set such that an almost center portion of edge thickness (radius direction length) of the grinding stone 18, which is positioned the most proximate to the center of the chuck table 11 of the plural grinding stones 18, is positioned on a vertical line L on which the center of the chuck table 11 is positioned.
Only the portion of the rear surface of the wafer 1, which corresponds to the device forming region 4, is ground by the grinding apparatus 10 in the following manner. First, the wafer 1 is disposed on the upper surface of the chuck table 11, which is under vacuum operation, so as to be almost concentric therewith. In this case, the rear surface of the wafer 1 is exposed upward and the protective tape 6 closely contacts the upper surface of the chuck table 11. Thus, the wafer is held on the chuck table 11. Next, while the cup wheel 17 is rotated in high speed, the grinding unit 12 moves downwardly, and the all grinding stones 18 are pressed on the exposed rear surface of the wafer 1, the chuck table 11 is rotated. As a result, the portion of the rear surface of the wafer 1, which corresponds to the device forming region 4, is ground and thinned.
After the entire portion of the rear surface of the wafer 1, which corresponds to the device forming region 4, is uniformly ground so as to have a predetermined thickness (for example, about 200 to 100 μm or about 50 μm), the grinding unit 12 is moved upwardly, and the rotation of the chuck table 11 is stopped. As shown in FIGS. 4A and 4B, the wafer 1 is processed to have a recessed shape such that a recess 1a is formed at the portion of the rear surface of the wafer 1, which corresponds to the device forming region 4, and a ring-shaped peripheral reinforcing portion 1b is formed at a portion corresponding to the peripheral extra region 5 so as to have an initial thickness of the wafer 1 and project on the rear surface.
3. Applying of Protective Tape
In the wafer 1 in which the recess 1a is formed and the device forming region 4 is thinned, the following processing may be performed with heating. For example, a metal film composed of Au or the like is provided on the rear surface of the wafer 1 by deposition, sputtering, or the like. For example, impurities are diffused in the wafer 1 by ion implantation from the rear surface of the wafer 1. When the above processing is performed, the protective tape 6 is peeled from the surface of the wafer 1 in order to prevent occurrence of problem in which the protective tape 6 is melted and adhered to the surface of the wafer 1 by the heating. Since the peripheral reinforcing portion 1b is not ground in the above grinding, the rigidity of the wafer 1 is maintained even after the peeling of the protective tape 6, and handling (for example, carrying) of the wafer 1 is performed by holding the peripheral reinforcing portion 1b.
In the wafer 1 after the processing with the heating, the peripheral reinforcing portion 1b is finally removed by cutting or grinding. In this case, in order to protect the electronic circuits formed on the wafer 1, a protective tape is applied onto the surface of the wafer 1 again. A protective tape applying method will be explained hereinafter. This protective tape applying method is an embodiment according to the present invention.
FIGS. 5A to 5D show the protective tape applying method of the embodiment in process order. As shown in FIGS. 5A to 5D, reference numeral 21 denotes a protective tape roller having a long transparent protective tape 20 which is wound in a roll form and is stored thereon. The protective tape 20 is wound off from the protective tape roller 21 such that an adhesive surface of the protective tape 21 faces downwardly. The protective tape 20 is wound on a winding roller 24 via pinch rollers 22 and 23, the winding roller 24 being disposed parallel to the protective tape roller 21. The pinch rollers 22 and 23 are disposed at the same height positions. A disc-shaped chuck table 30 is provided directly under the horizontal protective tape 20 strained between the pinch rollers 22 and 23. In this case, the protective tape 20 is the same tape as the above protective tape 6. That is, the protective tape 20 is a tape which has a base film and an adhesive coated on a surface of the base film. For example, the base film of the protective tape 20 is composed of polyolefin and has a thickness of about 70 to 200 μm. The adhesive is composed of acrylic resin and has a thickness of about 5 to 20 μm. The protective tape 20 has a width such that the protective tape 20 can sufficiently cover the entire surface of the wafer 1.
The chuck table 30 is a vacuum chuck type table and is provided on a table base 31 such that an upper surface of the chuck table 30 is horizontal. A porous vacuum chucking portion 30a is formed at an area of upper portion of the chuck table 30, the area being other than a circumferential edge thereof. The chuck table 30 has an outer diameter which is slightly smaller than an inner diameter of the recess 1a of the wafer 1. As shown in FIGS. 5A to 5D, the wafer 1 is set on the chuck table 30 such that the surface of the wafer 1 is exposed upward and the recess 1a of the wafer 1 is fitted to the upper portion of the chuck table 30. While the chuck table 30 is under vacuum operation, the wafer 1 is set on the chuck table 30 such that the recess 1a is fitted to the upper portion in the above manner and the air is absorbed from the vacuum chucking portion 30a, so that a bottom surface of the recess 1a is chucked on the upper surface of the chuck table 30. The surface of the wafer 1 held on the chuck table 30 in the above manner is horizontal. The protective tape 20 between the pinch rollers 22 and 23 horizontally faces the surface of the wafer 1, which is disposed on the chuck table 30, so to be slightly spaced from the surface of the wafer 1.
As shown in FIG. 5A, a pressing roller 40 is provided above the protective tape 20 disposed above the chuck table 30, and it has a rotational axis parallel to those of the rollers 21 to 24. The pressing roller 40 is elevatable and parallel movable between the left pinch roller 22 and the right pinch roller 23. The pressing roller 40 is a driven rotation roller. The pressing roller 40 rolls right or left while pressing the protective tape 20 onto the wafer 1 from the upside, so that the protective tape 20 is applied onto the wafer 1 by the pressing roller 40. The pressing roller 40 has at least a surface which is appropriately elastic so as to have affinity to the protective tape 20 and facilitate easily applying of the protective tape 20 onto the wafer 1. The pressing roller 40 has a pressing width (in this case, axial direction length) which is almost wider than a diameter of the wafer 1. The pressing roller 40 is disposed above the chuck table 30 so as be sufficiently rollable on the entire surface of the wafer 1.
In order to apply the protective tape 20 on the surface of the wafer 1, first, vacuum operation of the chuck table 30 starts, the recess 1a of the wafer 1 is fitted to the chuck table 30, and the wafer 1 is chucked and held. Next, the winding roller 24 is rotated, the protective tape 20 is wound off from the protective tape roller 21. A lower surface of the protective tape 20, which is a fresh adhesive surface, faces the surface of the wafer 1 disposed on the chuck table 30. As shown in FIGS. 5B and 6A, the pressing roller 40 moves downwardly to a center portion of the wafer 1, and it presses the protective tape 20 onto the surface of the wafer 1 at a predetermined load.
As shown in FIGS. 5C and 6B, the pressing roller 40 rolls from the center portion of the wafer 1 to one end portion (right end portion in these drawings) of the wafer 1, so that the protective tape 20 is applied onto the almost half of the surface of the wafer 1. As shown in FIGS. 5D and 6C, while the pressing load is maintained to be constant, the pressing roller 40 moves in an opposite direction, and it rolls to the other end portion (left end portion in these drawings) of the wafer 1. Thus, the protective tape 20 is applied onto the entire surface of the wafer 1. After that, the pressing roller 40 moves upwardly from the wafer 1, and a cutter (not shown in the drawings) cuts the protective tape 20 circularly along a circumferential edge of the wafer 1. Thus, the applying of the protective tape 20 onto one wafer 1 is completed. The protective tape 20 is wound onto the winding roller 24 by a predetermined length approximately corresponding to a diameter of one wafer, a next new portion is disposed on the chuck table 30, and a next wafer 1 is set on the chuck table 30.
In the above method, since in the initial applying of the protective tape 20, the load is not provided on the end portion of the wafer 1 but is provided on the center portion of the wafer 1, the load is widely dispersed and becomes minimal. As a result, breakage of the end portion of the wafer 1, which is caused by locally providing the load thereto by the pressing roller 40, can be prevented, and the protective tape 20 can be reliably applied thereon. In the initial applying of the protective tape 20, providing of excessive load to the end portion of the wafer 1 is avoided, so that the load of the pressing roller 40 onto the wafer 1 can be constant in the rolling of the pressing roller 40. That is, while the load, which is not changed depending on applying width but is constant, is provided to the wafer 1 by the pressing roller 40, the applying of the protective tape 20 onto the wafer 1 can be easily performed by simply rolling the pressing roller 40. It is advantageous that the position of the wafer 1 pressed by the pressing roller be the center portion of the wafer 1 described above. Alternatively, even when the position is a position which is slightly away from the center portion of the wafer 1, that is, which is proximate to the center portion of the wafer 1, the same actions and effects described above can be obtained.
Next, another embodiment according to the present invention will be explained with reference to FIGS. 7A to 8.
In an applying method of this embodiment, a supporting plate (supporting member) 50 is disposed around the wafer 1 held on the chuck table 30 such that an upper surface of the supporting plate 50 has the same height as the surface of the wafer 1. The pressing roller 40 rolls on the supporting plate 50 too. The supporting plate 50 has a rectangular shape having a width equal to or wider than that of the protective tape 20. The supporting plate 50 has a circular hole 51 formed at a center portion thereof. The hole 51 is slightly larger than the outer diameter of the wafer 1, and the wafer 1 is provided in the hole 51. In order to easily peel the adhesive surface of the protective tape 20 from the supporting plate 50, fine convexoconcaves or fine grooves are formed by processing on the upper surface of the supporting plate 50.
As shown in FIGS. 7A to 7C, the supporting plate 50 is supported by an upper end of extensible rods 53 such that the upper surface of the supporting plate 50 is horizontal. The extensible rods 53 are provided on plural actuators 52 so as to be extensible upwardly, the actuators 52 being provided on the table base 31. The extensible rods 53 extend or contract together with each other, so that the supporting plate 50 moves vertically around the wafer 1 while the upper surface of the supporting plate 50 is maintained to be horizontal.
In the applying method for the protective tape 20 which uses the supporting plate 50, first, the extensible rods 53 appropriately extend or contract, so that as shown in FIG. 7A, the upper surface of the supporting plate 50 is set to be flush with the surface (upper surface) of the wafer 1 held on the chuck table 30. In the same manner as the above embodiment, the wafer 1 is held on the chuck table 30, and the protective tape 20 faces the wafer 1. Next, as shown in FIG. 7B, the pressing roller 40, which moved above one end portion (left end portion shown in FIGS. 7A to 8) of the wafer 1, moves downwardly, and it presses the protective tape 20 onto the end portion of the wafer 1. In this initial applying of the protective tape 20, both end portions of the pressing roller 40 are also disposed on the upper surface of the supporting plate 50, so that the pressing roller 40 presses the supporting plate 50 at the same load as that on the wafer 1.
Next, while the pressing load of the pressing roller 40 is maintained to be constant, as shown in FIG. 7C, the pressing roller 40 rolls to the other end portion (right end portion shown in FIGS. 7A to 8) of the wafer 1. In the rolling of the pressing roller 40, both end portions of the pressing roller 40 are always positioned on the supporting plate 50. The pressing roller 40 for pressing the protective tape 20 rolls on the entire surface of the wafer 1, so that the protective tape 20 is applied onto the surface of the wafer 1. After that, in the same manner as the above embodiment, the pressing roller 40 moves upwardly from the wafer 1, a cutter (not shown in the drawings) cuts the protective tape 20 circularly along a circumferential edge of the wafer 1, and the applying of the protective tape 20 onto one wafer 1 is completed. Since unnecessary portion of the protective tape 20 remains on the upper surface of the supporting plate 50 after the cutting of the protective tape 20, the portion thereof is peeled and removed therefrom. In this case, since the fine convexoconcaves or the fine grooves are formed on the upper surface of the supporting plate 50 by the processing as described above, even when the protective tape 20 is pressed onto the upper surface of the supporting plate 50, the protective tape 20 is not easily adhered thereto, and is thereby easily peeled therefrom.
In the applying method of the embodiment, from the initial applying to the end applying of the protective tape 20 onto the entire surface of the wafer 1, the pressing roller 40 rolls on the surface of the wafer 1 and the surface of the supporting plate 50 which is around the wafer 1. Since the pressing roller 40 rolls on the surfaces of the wafer 1 and the supporting plate 50 which are flush with each other, the load provided from the pressing roller 40 to the wafer 1 is dispersed. Therefore, the load provided to the wafer 1 is not excessive. As a result, the breakage of the wafer 1 can be prevented, so that the pressing roller 40 can roll at a constant pressing load.
The rolling pattern of the pressing roller 40 is not limited to the above action in which the pressing roller 40 rolls from the end portion of the wafer 1 to the other end portion thereof. That is, the position of the wafer 1, onto which the pressing roller 40 initially presses the protective tape 20 by moving downwardly, is freely selected. In this case, the pressing roller rolls on the entire surface of the wafer 1 from the initial pressing position in order that the supporting plate 50 receive and disperse the initial pressing load of the pressing roller and this pressing load to the wafer 1 be not excessive.
Patent Application
20070249146
