JP2022049945A - Polishing method - Google Patents

Abstract

To provide a polishing method which can polish a workpiece without making an area near an outer edge of a workpiece excessively thinner than the other areas.SOLUTION: A workpiece is polished while an area of the workpiece excluding an outer edge of thereof is held by a chuck table having a holding surface smaller in diameter than the workpiece. In this case, the workpiece is polished while an area near the outer edge of the workpiece not held by the chuck table is kept pressed against a polishing pad and slightly bent. As a result, the area near the outer edge of the workpiece is prevented from being excessively thinned.SELECTED DRAWING: Figure 4

Description

The present invention relates to a polishing method.

Chips of semiconductor devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integration) are indispensable configurations in various electronic devices such as mobile phones and personal computers. Such a chip is generally manufactured by dividing a wafer having a large number of semiconductor devices formed on its surface into regions including individual semiconductor devices.

The wafer is divided by, for example, grinding the back surface side to a predetermined thickness and then cutting the wafer. However, when grinding a wafer, grinding marks may remain on the surface to be ground of the wafer and fine cracks may be formed. Therefore, when a chip is manufactured by grinding a wafer and then cutting and dividing the wafer, the bending strength of the obtained chip may decrease.

Grinding marks and cracks formed on the surface to be ground of the wafer can be removed, for example, by polishing the surface to be ground (see, for example, Patent Document 1). Therefore, by polishing the surface to be ground of the wafer, it is possible to suppress a decrease in the bending strength of the chip obtained by cutting and dividing the wafer.

Japanese Unexamined Patent Publication No. 8-99265

Polishing of a workpiece such as a wafer is generally performed by pressing the workpiece and the polishing pad against each other while rotating them relatively. Here, the polishing pad used for polishing the workpiece is often flexible. Therefore, the polishing of the workpiece may be performed in a state where the polishing pad is slightly deformed, that is, a state in which the polishing pad is slightly contracted in a direction orthogonal to the contact surface between the workpiece and the polishing pad.

Further, the polished surface of the polishing pad is generally designed to be larger than the surface to be polished of the workpiece so that the surface to be polished of the workpiece is uniformly polished. Here, the external force applied to the region of the polishing pad (the former region) pressed against the region near the outer edge of the workpiece is a region other than the region near the outer edge of the workpiece because the workpiece does not exist outside the region. It may be smaller than the external force applied to the area of the polishing pad pressed against (the latter area).

Therefore, the amount of deformation in the former region of the polishing pad may be smaller than the amount of deformation in the latter region of the polishing pad. Alternatively, the polishing pad may be pushed by the workpiece in the latter region and slightly shrink, and in the former region may be slightly raised toward the workpiece.

In this case, the region near the outer edge of the workpiece may be thinner than the other regions of the workpiece after polishing. In view of the above points, an object of the present invention is to provide a polishing method capable of polishing a work piece without making a region near the outer edge of the work piece excessively thinner than other regions.

According to the present invention, there is a polishing method for polishing a work piece, which comprises a holding step of holding a region excluding the outer edge of the work piece on a chuck table having a holding surface having a diameter smaller than that of the work piece. Provided is a polishing method comprising a polishing step of pressing a polishing pad against the workpiece held on the chuck table to polish the workpiece while rotating a polishing pad having a diameter larger than that of the workpiece. Will be done.

In the present invention, the workpiece is polished while holding the region excluding the outer edge of the workpiece with a chuck table having a holding surface having a diameter smaller than that of the workpiece. In this case, the work piece is polished in a state where the region near the outer edge of the work piece, which is not held by the chuck table, is pressed against the polishing pad and slightly bent. This prevents the region near the outer edge of the workpiece from becoming excessively thin.

FIG. 1 is a diagram schematically showing an example of a workpiece. FIG. 2 is a cross-sectional view schematically showing an example of a polishing device. FIG. 3 is a diagram schematically showing an example of a holding surface of a chuck table. FIG. 4 is a flowchart schematically showing an example of a polishing method. FIG. 5A is a top view schematically showing a modified example of the chuck table, and FIG. 5B is a cross-sectional view schematically showing a modified example of the chuck table. FIG. 6A is a diagram schematically showing a silicon wafer used in Examples and Comparative Examples, and FIG. 6B is a diagram schematically showing a holding surface of a chuck table used in Examples. be. FIG. 7 is a diagram showing the polishing speed in the vicinity of the outer edge of the silicon wafers of Examples and Comparative Examples.

An embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram schematically showing an example of a work piece to be polished. The workpiece 11 shown in FIG. 1 is a wafer having a disk-shaped shape.

The workpiece 11 is made of, for example, silicon (Si). The surface 11a side of the workpiece 11 is divided into a plurality of regions by a plurality of scheduled division lines 13 intersecting each other, and a device 15 such as an IC is formed in each region. Further, on the outer edge of the workpiece 11, a flat portion indicating the crystal orientation, a so-called orientation flat (orifra) 17, is formed.

There are no restrictions on the material, shape, structure, size, etc. of the workpiece 11. The work piece 11 may be made of, for example, another semiconductor, ceramics, resin, metal, or the like, and the outer edge of the work piece 11 has a V shape indicating a crystal orientation instead of the orifra 17. Notches, so-called notches, may be formed. Similarly, there are no restrictions on the type, quantity, shape, structure, size, arrangement, etc. of the device 15.

A protective member 21 for protecting the device 15 is attached to the surface 11a of the workpiece 11. The protective member 21 has substantially the same shape as the workpiece 11 and is made of, for example, a material such as resin. Further, the protective member 21 may have a laminated structure. For example, the protective member 21 may have a laminated structure including a protective layer made of a material having a low elastic modulus and an adhesive layer attached to the surface 11a of the workpiece 11.

Further, the back surface 11b side of the workpiece 11 may be ground. For example, the protective member 21 may be ground on the surface 11a of the workpiece 11 until the thickness of the workpiece 11 reaches a predetermined thickness t.

FIG. 2 is a cross-sectional view schematically showing an example of a polishing device. The polishing device 2 shown in FIG. 2 polishes, for example, the back surface 11b side of the workpiece 11 shown in FIG. The Z-axis direction shown in FIG. 2 is substantially parallel to the vertical direction.

The polishing device 2 has a disk-shaped chuck table 4. The lower portion of the chuck table 4 is connected to the upper end portion of a columnar rotating shaft (not shown) arranged substantially parallel to the Z-axis direction. The lower end of the rotary shaft is connected to an output shaft of a rotary drive source (not shown) such as a motor. When this rotation drive source is operated, the chuck table 4 rotates in a predetermined direction around a rotation axis parallel to the Z-axis direction.

The chuck table 4 has a disk-shaped frame 6 made of a metal such as stainless steel. A disk-shaped recess is formed in the upper part of the frame body 6, and a disk-shaped porous plate 8 made of porous ceramics or the like is fixed to the recess. The upper surface of the frame body 6 and the upper surface of the porous plate 8 are flush with each other, and form a holding surface 4a of a substantially flat chuck table 4.

On the holding surface 4a, the workpiece 11 is held via the protective member 21. In the chuck table 4, the holding surface 4a is designed to hold a region excluding the outer edge of the workpiece 11. As an example of designing the holding surface 4a in this way, in the present embodiment, the holding surface 4a, that is, the frame body 6 is designed so that the diameter is smaller than that of the workpiece 11.

For example, the holding surface 4a holds a predetermined region including the center of the workpiece 11. In other words, the outer edge of this predetermined region is located between the center and the outer edge of the workpiece 11. The distance between the outer edge of the holding surface 4a and the outer edge of the workpiece 11 is, for example, 5 mm or more and 19 mm or less. Further, this interval is preferably 7 mm or more and 17 mm or less, more preferably 9 mm or more and 15 mm or less, and most preferably 11 mm or more and 13 mm or less.

Further, the shape of the holding surface 4a is preferably similar to that of the front surface 11a and the back surface 11b of the workpiece 11. For example, when a flat portion (orifra) 17 is formed on the outer edge of the workpiece 11 as shown in FIG. 1, the holding surface 4a has a flat portion 6c formed on the outer edge as shown in FIG. It is preferable that the upper surface of the frame body 6 and the upper surface of the porous plate 8 are formed. As a result, in the polishing step described later, it is possible to prevent the region of the workpiece 11 in the vicinity of the orifra 17 from becoming excessively thin.

Below the porous plate 8, as shown in FIG. 2, a flow path 6a extending in the radial direction of the frame body 6 is provided. Although only one flow path 6a is shown in FIG. 2, in the chuck table 4, a plurality of flow paths 6a extending in the radial direction are formed radially.

Further, a flow path 6b extending along the Z-axis direction is formed at the center of the recess of the frame body 6. The upper end portion of the flow path 6b communicates with a plurality of flow paths 6a, and the lower end portion communicates with a suction port of a suction source (not shown) such as an ejector.

Therefore, when the suction source is operated, the gas in the flow path 6a and the flow path 6b is sucked by the suction source, and a negative pressure is generated on the upper surface of the porous plate 8, that is, the holding surface 4a of the chuck table 4. Then, when a negative pressure is generated on the holding surface 4a, the workpiece 11 held on the holding surface 4a via the protective member 21 is attracted to the chuck table 4 via the protective member 21.

Further, a polishing unit 10 is arranged above the chuck table 4. The polishing unit 10 has a cylindrical spindle housing (not shown). The spindle housing accommodates the columnar spindle 12 in a rotatable manner. The longitudinal direction of the spindle 12 is substantially parallel to the Z-axis direction. The upper end of the spindle 12 is connected to a motor (not shown) that rotates the spindle 12.

The lower end of the spindle 12 is connected to the center of the upper surface of the disk-shaped mount 14. The mount 14 is supported by the spindle 12 in a manner rotatable with the spindle 12. Further, the mount 14 has a diameter larger than the diameter of the workpiece 11.

A disk-shaped polishing wheel 16 having substantially the same diameter as the mount 14 is mounted on the lower surface of the mount 14. The polishing wheel 16 is supported by the spindle 12 in such a manner that it can rotate with the spindle 12 via the mount 14.

The polishing wheel 16 has a disk-shaped wheel base 18 connected to the lower surface of the mount 14. The wheel base 18 is made of a metal material such as aluminum or stainless steel or a resin material. A polishing pad 20 having substantially the same diameter as the wheel base 18 is fixed to the lower surface of the wheel base 18. The polishing pad 20 has a diameter larger than the diameter of the workpiece 11.

The polishing pad 20 is, for example, a fixed abrasive grain polishing pad in which abrasive grains are dispersed inside. The polishing pad 20 is manufactured, for example, by impregnating a polyester non-woven fabric with a urethane solution in which abrasive grains having a size on the order of μm are dispersed and then drying the polishing pad 20.

The abrasive grains dispersed inside the polishing pad 20 are made of a material such as silicon carbide, cBN (cubic Boron Nitride), diamond, or metal oxide fine particles. Examples of the metal oxide fine particles include fine particles made of silica (silicon oxide), ceria (cerium oxide), zirconia (zirconium oxide), alumina (aluminum oxide) and the like.

The radial center positions of the polishing pad 20, the wheel base 18, the mount 14, and the spindle 12 are substantially the same, and a columnar through hole 22 is formed so as to penetrate these center positions. The upper end of the through hole 22 communicates with a pipe (not shown) of the polishing liquid supply source (not shown).

The polishing liquid supply source includes a storage tank for the polishing liquid 24, piping, a liquid feeding pump, and the like. The polishing liquid supply source supplies the polishing liquid 24 to the back surface 11b of the workpiece 11 through the through hole 22. The polishing liquid 24 may or may not contain abrasive grains.

The spindle housing accommodating the spindle 12 is connected to a Z-axis direction moving unit (not shown). In this Z-axis direction moving unit, for example, the polishing unit 10 can be positioned so that the workpiece 11 sucked and held by the holding surface 4a of the chuck table 4 and the polishing pad 20 are pressed against each other.

FIG. 4 is a flowchart schematically showing an example of a polishing method for polishing the back surface 11b side of the workpiece 11 by the polishing apparatus 2 shown in FIG. 2. In this method, first, the chuck table 4 holds a region excluding the outer edge of the workpiece 11 (holding step: S1).

Then, the work piece 11 held on the chuck table 4 is polished using the polishing unit 10 (polishing step: S2). Specifically, while the chuck table 4 and / or the spindle 12 is rotating in a predetermined direction, the polishing liquid 24 is supplied from the polishing liquid supply source to the back surface 11b of the work piece 11 while polishing with the work piece 11. The pads 20 and the pads 20 are pressed against each other.

In this method, the workpiece 11 is polished while the region other than the outer edge of the workpiece 11 is held by the chuck table 4 having the holding surface 4a having a diameter smaller than that of the workpiece 11. In this case, the work piece 11 is polished in a state where the region near the outer edge of the work piece 11 that is not held by the chuck table 4 is pressed against the polishing pad 20 and is slightly bent. This prevents the region near the outer edge of the workpiece 11 from becoming excessively thin.

The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the workpiece 11 is held by the chuck table 4 having the frame body 6 designed to have a diameter smaller than that of the workpiece 11, but the workpiece 11 is placed on the upper portion. It may be held on a chuck table having a frame provided with an annular groove.

FIG. 5A is a top view schematically showing such a chuck table, and FIG. 5B is a cross-sectional view schematically showing such a chuck table. The chuck table 4'shown in FIGS. 5 (A) and 5 (B) has a disk-shaped frame 6'made of a metal such as stainless steel.

The upper surface of the frame body 6'has an inner region 6d that is flush with the upper surface of the porous plate 8. In the chuck table 4', the holding surface 4a'of the chuck table is formed by the inner region 6d of the upper surface of the frame body 6'and the upper surface of the porous plate 8.

A groove 6e is provided on the upper portion of the frame body 6'so as to surround the inner region 6d. In the chuck table 4', the groove 6e is designed so that the outer edge of the workpiece 11 is located in the groove 6e when the workpiece 11 is held by the holding surface 4a'. Further, the upper surface of the frame body 6'has an outer region 6f provided so as to surround the groove 6e.

When the workpiece 11 is polished while holding the region excluding the outer edge of the workpiece 11 on the chuck table 4', the region near the outer edge of the workpiece 11 becomes excessively thin as in the above-described embodiment. Is prevented.

In addition, the structures and methods according to the above-described embodiments and modifications can be appropriately modified and carried out as long as they do not deviate from the scope of the object of the present invention.

Hereinafter, examples of the present invention will be described. In this embodiment, a silicon wafer having an orifra formed on the outer edge is prepared as a workpiece (see FIG. 6A). The silicon wafer had a diameter of 6 inches (150 mm) and a thickness of 650 μm.

Further, as a chuck table for sucking and holding the silicon wafer, a chuck table having a holding surface having a shape similar to the front surface and the back surface of the silicon wafer was prepared. Specifically, this chuck table has the same shape as the chuck table 4 shown in FIG. 2, and the holding surface thereof is the same as the holding surface 4a shown in FIG. 3 with the upper surface of the frame body. , It was composed of the upper surface of a circular porous plate (see FIG. 6B).

A flat portion was formed on the outer edge of the frame so as to correspond to the orifra formed on the workpiece. Further, the inner diameter of the upper surface of the frame and the diameter of the upper surface of the porous plate were both 116 mm. Further, the length of the straight line passing through the center of the upper surface of the porous plate was 126 mm, with the starting point and the ending point being two points of the outer edge other than the flat portion formed on the outer edge of the frame.

The silicon wafer was polished while holding the region excluding the outer edge of the silicon wafer prepared on this chuck table. Specifically, silicon is held in a state where the centers of the silicon wafer and the chuck table are overlapped in the vertical direction and the silicon wafer is held by the chuck table so that the directions from the centers of the two toward the flat portion (orifra) coincide with each other. The wafer was polished.

Then, the polishing speed of the region near the outer edge in the direction from the center of the silicon wafer toward the outer edge other than the orifra (edge direction) was measured. Further, as a comparative example, the polishing speed when the silicon wafer was polished while the entire surface of the silicon wafer was held by the chuck table was measured.

FIG. 7 is a diagram showing polishing speeds of Examples and Comparative Examples in a region near the outer edge of a silicon wafer. As shown in FIG. 7, the polishing rate of the silicon wafer of the comparative example increased significantly from the center toward the outer edge.

On the other hand, the polishing rate of the silicon wafer of the example did not increase significantly from the center toward the outer edge. That is, it was found that in the polishing method of the example, the region near the outer edge of the silicon wafer was prevented from becoming excessively thin.

11: Work piece 13: Scheduled division line 15: Device 17: Orientation flat (orifra)
21: Protective member 2: Polishing device 4: Chuck table (4a: Holding surface)
4': Chuck table (4a': Holding surface)
6: Frame body 6a, 6b: Flow path 6c: Flat part 6': Frame body 6d: Inner area 6e: Groove 6f: Outer area 8: Porous plate 10: Polishing unit 12: Spindle 14: Mount 16: Polishing wheel 18: Wheel base 20: Polishing pad 22: Through hole 24: Polishing liquid

Claims (1)

It is a polishing method that polishes the work piece.
A holding step of holding a region excluding the outer edge of the work piece with a chuck table having a holding surface having a diameter smaller than that of the work piece.
A polishing step of pressing the polishing pad against the workpiece held on the chuck table to polish the workpiece while rotating a polishing pad having a diameter larger than that of the workpiece.
A polishing method.

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