JP2001096456A - Polishing head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve uniformity for contacting pressure distribution between a wafer and polishing cloth in a place close to the peripheral part of the wafer in a polishing device. SOLUTION: A wafer 1 is sucked on the lower surface of a top ring 6 by way of a packing pad 8. A pressing ring 23 is disposed to the peripheral part of the top ring 6 along the outer circumference of the wafer 1, and a pressing piston 25 is provided for a place behind the aforesaid place. The control of pressing force by the piston 25 thereby allows the pressing pressure of the pressing ring 23 against pressing cloth 2 to be adjusted. Each groove in the thickness direction is formed in three places at an equal interval in the inner circumferential surface of the pressing ring 23 so as to let each guide pin 21 be housed therein. The wafer 1 is restrained in movement in the horizontal direction by these guide pins 21 so as to be positioned. This constitution thereby allows a distance C between the outer circumference of the wafer 1 and the inner circumference of the pressing ring 23 to be kept constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing head used as a mechanism for holding a workpiece in a polishing apparatus used for polishing the surface of a disk-shaped workpiece such as a semiconductor wafer. Involved
In particular, the present invention relates to improvement of a polishing head structure for improving polishing accuracy.

[0002]

2. Description of the Related Art In recent years, as semiconductor integrated circuits have become finer and multilayered, the beam wavelength of an exposure apparatus used for pattern formation has gradually shifted to a shorter wavelength side, and the margin of depth of focus in photolithography has been reduced. Has become. For this reason, a planarization technique for globally reducing a step on a wafer surface is becoming an indispensable technique for performing multilayer wiring. Among them, the CMP (Chemical M
echanical Polishing) is attracting attention.

FIG. 4 shows a CMP apparatus (Chemical Mechanic).
al Polishing Machine).

[0004] The polishing cloth 2 is mounted on the upper surface of the turntable 3. The top ring 6 is provided at the tip of the polishing head 5 and is arranged at a position facing the polishing pad 2. The wafer 1 to be polished is adsorbed and held on the lower surface of the top ring 6 via a backing pad 8 (described later). A polishing agent (a slurry in which abrasive grains are suspended in pure water or a chemical solution) is supplied from the polishing agent supply nozzle 11 onto the polishing cloth 2, and the rotating polishing cloth is rotated while the wafer 1 is rotated by the polishing head 5. By pressing against the wafer 2, the surface of the wafer 1 is polished.

[0005] A dressing head 30 is arranged adjacent to the polishing head 5. A dresser 31 is attached to a tip of the dressing head 30. Diamond abrasive grains are electrodeposited on the surface of the dresser 31. Dressing is performed by rotating the dressing head 30 above the polishing pad 2 and pressing the rotating dresser 31 onto the rotating polishing pad 2.

FIG. 5 shows a configuration of a main part of a conventional polishing head 5.

[0007] A pressure ring 9 (also called a retainer ring) is attached to the periphery of the lower surface of the top ring 6 along the outer periphery of the wafer 1. Pressure ring 9
Restricts the movement of the wafer 1 in a plane parallel to the surface to prevent the wafer 1 from jumping out during polishing.

A plurality of air supply / exhaust holes 15 are formed inside the top ring 6, and the tips of the air supply / exhaust holes 15 are opened near the center of the lower surface of the top ring 6. These air supply / exhaust holes 15 are connected to an air supply / exhaust passage 13 provided inside the drive shaft 7 via a cavity 14 provided inside the top ring 6. The wafer 1 is attracted to the lower surface of the top ring 6 via the backing pad 8.
The above-mentioned air supply / exhaust hole 15 is used for adsorbing the wafer 1 to the lower surface of the top ring 6 via the backing pad 8 when transferring the wafer 1.

FIG. 6 shows the distribution of the contact pressure in the vicinity of the periphery of the wafer in the polishing head shown in FIG.

In the conventional polishing head 5, the thickness of the pressure ring 9 is usually set to be smaller than the total thickness of the wafer 1 and the backing pad 8.
Therefore, when the wafer 1 is pressed against the polishing cloth 2 during polishing, as shown in FIG.
At the peripheral edge of the wafer 1 sharply increases. As a result, the polishing rate in a region having a width of about 5 mm along the peripheral portion of the wafer 1 becomes non-uniform, and the uniformity of the polishing amount in the plane of the wafer 1 is impaired. As a result, it is difficult to obtain a good chip from the vicinity of the peripheral portion of the wafer 1, which is one of the factors that cause a decrease in yield.

Although the contact pressure distribution shown in FIG. 6 is a result calculated using numerical analysis, the actual measurement data of the wafer polishing result is similar to the shape of this contact pressure distribution, Also, it is considered that such a contact pressure distribution is obtained.

In order to solve the above-mentioned problems, US Pat. No. 5,205,082 discloses the following polishing head structure. That is, a pressure mechanism is provided behind the pressure ring, and the pressure ring can be pressed against the polishing cloth during polishing of the wafer. By using such a polishing head, the position where the contact pressure between the polishing pad and the polishing pad becomes maximum can be moved to the pressure ring side, so that the fluctuation range of the polishing rate in the vicinity of the periphery of the wafer is reduced. It becomes possible to reduce.

However, in this case, the inner diameter of the pressure ring must be made larger by about 1 to 2 mm than the outer diameter of the wafer in order to absorb a positioning error in handling the wafer. As a result, it is not possible to keep the distance between the outer circumference of the wafer and the inner circumference of the pressure ring constant because of the deviation when the wafer is adsorbed or the movement of the wafer in the pressure ring during polishing. Have difficulty. As a result, the amount of polishing in the vicinity of the peripheral portion of the wafer is not uniform along the peripheral portion of the wafer, and the yield of chips obtained from the vicinity of the peripheral portion of the wafer has not been sufficiently improved.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the conventional polishing head, and an object of the present invention is to provide a polishing pad with a wafer near a peripheral edge of the wafer. The object of the present invention is to improve the uniformity of the contact pressure distribution during the process and to improve the yield of chips produced from the wafer.

[0015]

A polishing head according to the present invention is a polishing apparatus for polishing a surface of a work on a disk by pressing the surface of the work against a polishing cloth mounted on a turntable. In a polishing head used as a holding mechanism, a top ring on a disk is provided on a lower surface of the disk via a backing pad 8 to adsorb a work, and a top ring is provided on a lower surface of the top ring along the outer periphery of the work. Grooves in the thickness direction are formed in at least three places of the surface, and a pressure ring pressed against the polishing pad, and each of the pressure rings is disposed in each of the grooves, protrudes from the lower surface of the top ring, and is parallel to the surface. A guide pin for restraining the movement of the work in the plane from the outer periphery of the work.

According to the polishing head of the present invention, a plurality of guide pins are used to perform positioning in a plane parallel to the surface of the work, and a pressure ring is used to position the work in the vicinity of the periphery of the work. The distribution of the contact pressure between the work and the polishing cloth is adjusted. By using a plurality of guide pins, it is possible to precisely position the work, so that the interval between the outer circumference of the work and the inner circumference of the pressure ring can be set to be uniform and narrow in the circumferential direction. it can. As a result, the fluctuation range of the distribution of the contact pressure between the work and the polishing pad in the vicinity of the periphery of the work can be reduced, and the uniformity of the contact pressure distribution in the plane of the work can be increased.

[0017]

FIG. 1 shows the structure of a main part of a CMP apparatus according to the present invention. In the figure, 1 indicates a wafer, 2 indicates a polishing cloth, 3 indicates a turntable, and 5 indicates a polishing head. The polishing head 5 includes a drive shaft 7, a top ring 6, a guide pin 21, a pressure ring 23, a pressure piston 25, and the like.

A plurality of air supply / exhaust holes 15 are formed inside the top ring 6, and the tips of the air supply / exhaust holes 15 are opened near the center of the lower surface of the top ring 6. These air supply / exhaust holes 15 are connected to an air supply / exhaust passage 13 provided inside the drive shaft 7 via a cavity 14 provided inside the top ring 6. The wafer 1 is attracted to the lower surface of the top ring 6 via the backing pad 8.
The above-mentioned air supply / exhaust hole 15 is used for adsorbing the wafer 1 to the lower surface of the top ring 6 via the backing pad 8 when transferring the wafer 1.

Further, the above-mentioned supply / exhaust hole 15 is provided in the wafer 1.
When polishing the wafer 1, it is also used to apply a back pressure to the vicinity of the center of the back surface of the wafer 1 to deform the wafer 1 and adjust the contact pressure distribution in the surface to be polished.

On the periphery of the top ring 6, the wafer 1
A pressure ring 23 is disposed along the outer periphery of the pressure ring. Behind the pressure ring 23, a piston 25 for pressure is provided. A plurality of (preferably about 3 to 12) pistons 25 for pressurization are arranged in the circumferential direction. The pressurizing piston 25 may be a single ring-shaped piston. A working fluid (for example, air) is supplied to each of the pistons 25 via a hose 27. By controlling the pressing force by the piston 25, the pressing pressure of the pressing ring 23 against the polishing pad 2 is adjusted. During polishing of wafer 1, wafer 1
Pressure ring 23 in accordance with the state of
The uniformity of the contact pressure distribution between the wafer 1 and the polishing pad 2 at the peripheral portion of the wafer 1 can be improved by adjusting the pressure applied to the wafer.

Incidentally, at times other than the polishing of the wafer 1,
By applying a negative pressure to each piston 25 via the hose 27, the pressure ring 23 is retracted upward, and the wafer 1
Can be prevented from obstructing the chucking operation or the unchucking operation of the above.

A plurality of guide pins 21 are arranged between the outer periphery of the wafer 1 and the pressure ring 23. In this example, three guide pins 21 are provided at equal intervals along the outer periphery of the wafer 1.

As shown in the bottom view of FIG.
On the inner peripheral surface of the device, grooves in the plate thickness direction are formed at three places at equal intervals, and the guide pins 21 are accommodated in these grooves. The movement of the wafer 1 in the horizontal direction (the direction parallel to the surface of the wafer 1) is restricted from the outer periphery by the guide pins 21 and is positioned. As a result, the distance C between the outer circumference of the wafer 1 and the inner circumference of the pressure ring 23 is kept constant. In addition, as the value of the interval C increases, the adjustment effect of the pressure ring 23 on the contact surface pressure between the wafer 1 and the polishing pad 2 decreases, so that the value of the interval C hinders the handling of the wafer 1. It is desirable to be as small as possible within the range not present.

A tapered taper is formed at the tip of the guide pin 21 (see the partial sectional view of FIG. 3), so that the wafer 1 is smoothly guided by the guide pin 21 and positioned. Note that the guide pin 21 is attached to the wafer 1
In the horizontal direction, but in the vertical direction (thickness direction)
The arrangement is set such that a slight gap is secured between the guide pin 21 and the outer periphery of the wafer 1 so as not to hinder the movement of the wafer 1.

The guide pin 21 can be opened and closed in the radial direction of the wafer 1.

In the case of this polishing head, during operations such as wafer transfer, chucking and unchucking,
Even if the pressure ring 23 is retracted above the wafer 1, the wafer 1 can be handled stably because the horizontal position of the wafer 1 is determined by the guide pins 21.

FIG. 3 shows the distribution of the contact pressure between the polishing pad 2 and the wafer 1 and the pressure ring 23 in the vicinity of the periphery of the wafer 1. The contact pressure increases rapidly at the peripheral edge of the pressure ring 23 and becomes constant and stable near the inner peripheral portion of the pressure ring 23. Thereby, the wafer 1
In the plane, the distribution of the contact pressure becomes uniform, the polishing rate becomes constant, and the polishing accuracy is improved. As a result, good chips can be obtained from the vicinity of the periphery of the wafer 1,
The yield of products produced from the wafer 1 is improved.

[0028]

According to the polishing head of the present invention,
Using a guide pin, restrict the movement in a plane parallel to the surface of the work, position the work in the above-mentioned plane, and use a pressure ring to make contact with the work near the periphery of the work. The distribution of the contact pressure with the polishing cloth is adjusted. The use of guide pins allows precise positioning of the work, so the distance between the outer circumference of the work and the inner circumference of the pressure ring can be directly adjusted using the pressure ring without using the guide pins. As compared with the case where the work is positioned (conventional case), it can be set uniformly and narrowly in the circumferential direction.

As a result, the fluctuation range of the distribution of the contact pressure between the work and the polishing pad in the vicinity of the peripheral edge of the work can be reduced, and the uniformity of the distribution of the contact pressure in the plane of the work can be improved. As a result, the uniformity of the polishing rate in the plane of the work can be improved, and the polishing accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is an axial sectional view showing the structure of a polishing head according to the present invention.

FIG. 2 is a bottom view of the polishing head according to the present invention.

FIG. 3 is a diagram showing a contact pressure distribution in the vicinity of a peripheral portion of a wafer in a polishing head according to the present invention.

FIG. 4 is a diagram showing a schematic configuration of a CMP apparatus.

FIG. 5 is an axial sectional view showing a structure of a polishing head of a conventional CMP apparatus.

FIG. 6 is a view showing a contact pressure distribution in the vicinity of a peripheral portion of a wafer in a conventional polishing head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Wafer (work), 2 ... Polishing cloth, 3 ... Turntable, 4 ... Drive shaft, 5 ... Polishing head, 6 ... Top ring, 7 ... Drive shaft 8 backing pad 9 pressure ring 13 supply / exhaust passage 14 cavity / cavity 15 supply / exhaust hole 17 O-ring 11 Abrasive supply nozzle, 21: guide pin, 23: pressure ring, 25: piston, 27: hose, 28: O-ring, 30: dressing head, 31 ...・ Dresser, 32 ... Drive shaft.

Continuing from the front page (72) Inventor Akihiro Kasahara 1 Toshiba R & D Center, Komukai Toshiba-cho, Saitama-ku, Kawasaki-shi, Kanagawa F term (reference) 3C058 AA07 AA09 AA12 AB04 CB03 DA17

Claims (1)

[Claims] 1. A polishing head used as a mechanism for holding a workpiece by a polishing apparatus for polishing the surface by pressing the surface of the workpiece on a disc against a polishing cloth mounted on a turntable. A top ring on a disk which adsorbs the work on the lower surface thereof via a backing pad 8; and a bottom surface of the top ring provided on the lower surface of the top ring along the outer periphery of the work. Is formed and pressed against the polishing cloth; and a pressure ring disposed in each of the grooves, protrudes from the lower surface of the top ring, and moves the work in a plane parallel to the surface to the outer periphery of the work. And a guide pin for restraining the polishing head.