Support substrate for thin-sheet work

Abstract

A magnetic tape or magnetized tape is affixed to one side of a sheet-like workpiece, for example, the front surface of a semiconductor wafer. A substrate has a support area, which is at least partially formed of a porous material and is at least partially magnetized or magnetic.

Description

TECHNICAL FIELD

[0001] The present invention relates to a substrate for supporting a sheet-like workpiece such as a semiconductor wafer.

BACKGROUND ART

[0002] As is known to people of ordinary skill in the art, in the production of semiconductor chips, a large number of rectangular areas are defined by streets arranged in a lattice form in the front surface of a semiconductor wafer, and semiconductor circuits are formed in each of the rectangular areas. In general, the back surface of the semiconductor wafer is ground to reduce its thickness and then, the semiconductor wafer is cut along the streets to separate the rectangular areas from one another, thereby forming semiconductor chips. In recent years, prior to the grinding of the back surface of the semiconductor wafer, grooves having a required depth have been formed along the streets from the front surface of the semiconductor wafer and then, the back surface of the semiconductor wafer is ground to reduce the thickness of the semiconductor wafer to a value smaller than the depth of the groove, thus separating the rectangular areas from one another to form semiconductor chips. In either cases, to grind the back surface of the semiconductor wafer, a tape is affixed onto the front surface of the semiconductor wafer to protect the semiconductor circuits, the semiconductor wafer is held on a chuck means in a state of the front surface having the tape affixed thereon facing down, that is, in a state of the front surface and the back being reversed, and a grinding means is caused to act on the back surface of the semiconductor wafer. The semiconductor wafer is held on the chuck means by sucking the semiconductor wafer through the holding area that is formed of a porous material, of the chuck means.

[0003] In recent years, in order to form very small-sized and lightweight semiconductor chips, it has often been desired that the thickness of the semiconductor wafer be made very small, for example, 100 &mgr;m or less, particularly 50 &mgr;m or less. When the thickness of the semiconductor wafer is very small, however, rigidity of the semiconductor wafer greatly lowers, thereby making it extremely difficult to carry the semiconductor wafer, for example, from the chuck means into a cassette container. When a tape having relatively high rigidity, such as a polyethylene terephthalate film or sheet is used as the tape to be affixed onto the front surface of the semiconductor wafer through a suitable adhesive or pressure-sensitive adhesive, the semiconductor wafer can be carried. However, when a tape having relatively high rigidity is affixed onto the front surface of the semiconductor wafer, it is considerably difficult to remove the semiconductor chips that have been separated from one another from the tape, without damaging them.

DISCLOSURE OF THE INVENTION

[0004] It is therefore the principal object of the present invention to provide a substrate for supporting a sheet-like workpiece such as a semiconductor wafer, which makes it possible to carry a semiconductor wafer very easily even when the thickness of the sheet-like workpiece is greatly reduced by grinding without exerting a bad influence upon the grinding of the sheet-like workpiece and without the need of affixing a tape having relatively high rigidity onto the front surface of the sheet-like workpiece.

[0005] The inventor of the present invention has found that the above principal object can be attained by using a magnetic tape or magnetized tape as the tape to be affixed to one surface side of the sheet-like workpiece, for example, the front surface of a semiconductor wafer and by using a substrate having a support area that is at least partially formed of a porous material and at least partially magnetized or magnetic.

[0006] That is, according to one aspect of the present invention, there is provided a substrate for supporting a sheet-like workpiece having a magnetic tape affixed to one surface side thereof, which has a support area that is at least partially formed of a porous material and at least partially magnetized, as a substrate for attaining the above principal object.

[0007] Preferably, the support area is formed of a porous material containing a plurality of magnets dispersed therein or is formed of a magnetized porous material. It is advantageous that the substrate should have a frame for surrounding the support area.

[0008] According to another aspect of the present invention, there is provided a substrate for supporting a sheet-like workpiece having a magnetized tape affixed onto one side thereof, which has a support area that is at least partially formed of a porous material and at least partially magnetic, as a substrate for attaining the above principal object.

[0009] Preferably, the support area is formed of a porous and magnetic material. It is advantageous that the substrate should include a frame for surrounding the support area.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a perspective view of a semiconductor wafer as a typical example of a sheet-like workpiece;

[0011] FIG. 2 is a perspective view showing a preferred example of a substrate constituted according to the present invention;

[0012] FIG. 3 is a perspective view showing a state that the semiconductor wafer of FIG. 1 is turned upside down and is adsorbed on the substrate of FIG. 2; and

[0013] FIG. 4 is a sectional view showing a state that the semiconductor wafer adsorbed on the substrate is held on a chuck means of a grinding machine and the back surface of the semiconductor wafer is ground.

BEST MODE FOR CARRYING OUT THE INVENTION

[0014] Preferred embodiments of a substrate constituted according to the present invention will be described in detail with reference to the accompanying drawings.

[0015] FIG. 1 shows a semiconductor wafer 2 as a typical example of a sheet-like workpiece. The illustrated semiconductor wafer 2 is shaped like a disk having a linear edge 4 called “orientation flat” in part thereof and has a large number of rectangular areas 8 defined by streets 6 arranged in a lattice form in its front surface. A semiconductor circuit is formed in each of the rectangular areas 8. When the thickness of the semiconductor wafer 2 is to be reduced by grinding the back surface of the semiconductor wafer 2, a tape 10 is affixed onto the front surface of the semiconductor wafer 2 to protect the semiconductor circuits formed in the rectangular areas 8. In the illustrated embodiment, a magnetic tape provided with magnetism by coating the front surface and/or the back surface of a synthetic resin film or sheet having relatively low rigidity, such as a polyolefin film or sheet, with magnetic powders is used as the tape 10. It is advantageous that this tape 10 be affixed onto the front surface of the semiconductor wafer 2 by a known adhesive whose adhesion is lost or reduced by exposure to ultraviolet radiation or thermal curing. When the semiconductor chips are to be removed from the tape 10 after the semiconductor wafer 2 is cut along the streets 6 to separate a plurality of semiconductor chips from one another, the adhesion of the adhesive can be lost or reduced by exposing the tape 10 to ultraviolet radiation or thermally curing it.

[0016] FIG. 2 shows a preferred embodiment of a substrate constituted according to the present invention. The illustrated substrate 12 is shaped like a disk as a whole and comprises a support area 14 at the center and a frame 16 surrounding this support area 14. The support area 14 has a shape corresponding to the shape of the semiconductor wafer 2 and a linear edge 18 corresponding to the linear edge 4 of the semiconductor wafer 2. It is important that the support area 14 be formed of a porous material. A preferred example of the porous material forming the support area 14 is porous ceramic. In the illustrated embodiment, a plurality of (6 pieces in the figure) magnets 20 are dispersed and buried in the porous material forming the support area 14. Therefore, the support area 14 is partially magnetized due to the existence of magnets 20. The frame 16 of the substrate 12 may be formed of a suitable synthetic resin or suitable metal such as stainless steel. The support area 14 and the frame 16 surrounding the support area 14 are firmly bonded to each other. It is advantageous that the top surface of the support area 14 and the top surface of the frame 16 be flush with each other and that the back surface of the support area 14 and the back surface of the frame 16 be also flush with each other.

[0017] To grind the back surface of the semiconductor wafer 2, as shown in FIG. 3, the semiconductor wafer 2 having the tape 10 affixed onto the front surface thereof is placed on the support area 14 of the substrate 12 in such a state that the front surface faces down, that is, that the front surface and the back surface are reversed. Thereby, as the support area 14 is partially magnetized by the magnets 20 buried therein, the tape 10 having magnetism and affixed onto the front surface of the semiconductor wafer 2, the semiconductor wafer 2 is magnetically adsorbed on the support area 14 of the substrate 12.

[0018] Continuing a description with reference to FIG. 4 together with FIGS. 1 to 3, a grinding machine used for grinding the back surface of the semiconductor wafer 2, for example, a grinding machine marketed under the trade name of DFG841 from DISCO CORPORATION has a chuck means 22. The chuck means 22 has a disk-like porous central member 24 and an annular casing 26 surrounding the central member 24. The outer diameter of the central member 24 fixed in the annular casing 26 corresponds to the outer diameter of the support area 14, that is, to the outer diameter of the semiconductor wafer 2, and the outer diameter of the annular casing 26 is made to correspond to the outer diameter of the frame 16 of the substrate 12. The top surface of the central member 24 and the top surface of the annular casing 26 are flush with each other. As clearly shown in FIG. 4, the substrate 12 which magnetically adsorbs the semiconductor wafer 2 on the support area 14 is placed on the chuck means 22 by aligning the support area 14 with the central member 24. The central member 24 of the chuck means 22 is communicated with a vacuum source (not shown) through a suitable suction path so that when the vacuum source is activated, air is sucked in through the central member 24 of the chuck means 22 and the support area 14 of the substrate 12 to adsorb the semiconductor wafer 2 on the central member 24 of the chuck means 22 fully firmly. The exposed back surface of the semiconductor wafer 2 is ground by the function of a grinding means 28. The grinding means 28 is constituted by an annular grinding tool having an abrasive means containing diamond abrasive grains in the under surface. To grind the back surface of the semiconductor wafer 2, the chuck means 22 holding the semiconductor wafer 2 is turned on its center axis, and the grinding means 28 is turned on its center axis and pressed against the back surface of the semiconductor wafer 2.

[0019] After the back surface of the semiconductor wafer 2 is ground as required, the operation of the vacuum source is stopped to release the suction operation of the chuck means 22, the substrate 12 and the semiconductor wafer 2 magnetically adsorbed on the substrate 12 are disengaged from the chuck means 22, and the semiconductor wafer 2 is carried to a required position, for example, in a cassette container. When the semiconductor 2 is adsorbed on the substrate 12, the substrate 12 and the semiconductor wafer 2 adsorbed on the substrate 12 can be carried by holding a suitable portion, for example, the frame 16 of the substrate 12. Therefore, even when the thickness of the semiconductor wafer is greatly reduced and the rigidity of the semiconductor wafer 2 is thereby greatly reduced, the semiconductor wafer 2 can be carried as required without being damaged. Since the semiconductor wafer 2 is adsorbed on the substrate 14 by the magnetic adsorption of the tape 10 affixed onto the front surface of the semiconductor wafer 2, when the semiconductor wafer 2 is to be removed from the substrate 12, it can be easily removed from the substrate 12 with relatively small force.

[0020] In the illustrated embodiment, the support area 14 is partially magnetized by dispersing a plurality of magnets 20 in the porous material forming the support area 14 of the substrate 12. As desired, magnetic powders may be contained in the entire porous material forming the support area 14 to entirely magnetize the support area 14, or the entire support area 14 may be formed of a magnetized porous material to entirely magnetize the support area 14.

[0021] Further, if desired, as the tape 10 affixed onto the front surface of the semiconductor wafer 2 may be used a magnetized tape which has been at least partially magnetized. A typical example of the magnetized tape is a tape prepared by coating the front surface and/or the back surface of a synthetic resin film or sheet having relatively low rigidity, such as a polyolefin film or sheet, with magnetic powders. When the tape 10 affixed onto the front surface of the semiconductor wafer 2 is a magnetized tape, the support area 14 of the substrate 12 does not need to be magnetized. When the support area 14 is at least partially formed of a magnetic material, the magnetized tape 10, that is, the semiconductor wafer 2 having the magnetized tape on the front surface can be magnetically adsorbed on the support area 14 of the substrate 12.

Claims

1. A substrate for supporting a sheet-like workpiece having a magnetic tape affixed onto one side thereof, which has a support area that is at least partially formed of a porous material and at least partially magnetized.

2. The substrate of claim 1, wherein the support area is formed of a porous material containing a plurality of magnets dispersed therein.

3. The substrate of claim 1., wherein the support area is formed of a magnetized porous material.

4. The substrate of claim 1 which has a frame surrounding the support area.

5. A substrate for supporting a sheet-like workpiece having a magnetized tape affixed to one side thereof, which has a support area that is at least partially formed of a porous material and at least partially magnetic.

6. The substrate of claim 5, wherein the support area is formed of a porous and magnetic material.

7. The substrate of claim 5 which has a frame surrounding the support area.