JP2000202761A - Polishing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing device which can realize a high degree of flatness by reducing non-uniformity of a polishing amount in the peripheral edge part of a wafer. SOLUTION: A top ring 6 is fixed to a lower surface of a top block 5, and a guide ring 7 is fixed to a lower surface peripheral edge part of the top block 5 so as to surround the external periphery of the top ring 6. A wafer 1 is sucked to a lower surface of the top ring 6 through a backing pad 8. A thin thickness part 11 is formed in a ring-state along the external periphery in a lower surface side of the top ring 6, and a piston 12 is inserted in a ring-shaped space part surrounded by the thin thickness part 11, lower surface of the top block 5, and an internal peripheral surface of the guide ring 7. A pressure chamber 13 is formed between an upper end surface of the piston 12 and a lower surface of the top block 5. Pressure force by the piston 12 is adjusted by controlling a pressure in the pressure chamber 13, and distribution of contact pressure between a surface of the wafer 1 in the peripheral edge part and a polishing cloth is adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing apparatus used for flatly polishing the surface of a thin disk-shaped workpiece such as a silicon wafer. The present invention relates to a structure of a top ring which is held as a top ring.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have become more highly integrated, wirings have become finer and multilayered, and the wavelength of an exposure beam of an exposure apparatus used for pattern formation has become shorter. For this reason, the depth of focus at which resolution can be ensured in the photolithography process becomes gradually smaller, and it is required to increase the flatness of the wafer surface in order to ensure processing at a shallower depth of focus.

FIG. 2 shows a schematic configuration diagram of a polishing apparatus. In the figure, 1 is a wafer, 2 is a polishing cloth, 3 is a turntable, 4 is a polishing head, 6 is a top ring,
8 denotes a backing pad.

The polishing cloth 2 is attached to the upper surface of the turntable 3 with a double-sided tape. The top ring 6 is attached to the tip of the polishing head 4 and is disposed above the turntable 3 at a position facing the turntable 3. The wafer 1 to be polished is adsorbed and held on the lower surface of the top ring 6 via the backing pad 8.
An abrasive (a slurry in which abrasive grains are suspended) is supplied from the abrasive supply nozzle 9 onto the polishing cloth 2, and the polishing head 4 rotates the wafer 1 in the same direction as the turntable 3 to the polishing cloth 2. The wafer 1 is polished by being pressed against the wafer 1.

FIG. 3 shows an outline of the structure of a conventional polishing head.

[0006] A top block 5 is provided at the lower end of the drive shaft 4a.
Is attached, and a top ring 6 is attached to the lower surface of the top block 5. A guide ring 7 is attached to the lower peripheral edge of the top block 5 so as to surround the outer periphery of the top ring 6. The wafer 1 is sucked and held on the lower surface of the top ring 6 via the backing pad 8. The outer peripheral side of the wafer 1 is guided by a guide ring 7.

[0007] Ventilation holes 25 and 28 are formed in the top block 5 and the top ring 6, respectively, and the pressure in the ventilation holes 25 and 28 is reduced, whereby the wafer 1 is adsorbed. These ventilation holes 25, 2
By pressurizing the inside of the wafer 8, the wafer 1 is released.

(Problems of Conventional Polishing Apparatus) FIG.
FIG. 2 shows an outline of a cross-sectional profile of a wafer when a wafer having a silicon dioxide thin film deposited on a surface of a silicon substrate by CVD is polished using a conventional polishing head (FIG. 3).

Although the surface of the wafer was almost flat before polishing, the central portion and the peripheral portion of the wafer were difficult to be polished, so that the thickness of the silicon dioxide thin film at the central portion and the peripheral portion of the wafer was reduced after the polishing. Is thicker than other parts, and the flatness of the surface is reduced.

The polishing amount Pr at an arbitrary position on the wafer surface
Is represented by Pr = kpvt by Preston's formula. Here, k is a constant determined by the polishing cloth and the abrasive, p is the pressing pressure at the time of polishing, v is the relative speed between the wafer and the turntable, and t is the polishing time. Among these, the value of v is set by controlling the number of rotations of the polishing head holding the wafer and the number of rotations of the turntable using a servomotor. The value of p is set by controlling the pressing force of the polishing head using an air cylinder or the like.

As shown in FIG. 4, the reason why the polishing amount at the central portion of the wafer is small is that the polishing agent is supplied from the outer peripheral side of the wafer, so that the polishing agent hardly turns to the central portion of the wafer. Can be In addition, the small amount of polishing at the peripheral portion of the wafer is caused by the "effect of load distribution on CMP".
This is probably because the pressing force at the outer peripheral portion of the wafer becomes relatively low as described in (Tripology Conference Osaka 1997/11 Abstracts).

The structure of a polishing head for improving the flatness of a polished wafer is disclosed in Japanese Patent Application Laid-Open No. 9-27467.
And Japanese Patent Application Laid-Open No. 9-225821.

In the polishing head described in Japanese Patent Application Laid-Open No. 9-27467, a piston is provided which comes into contact with the center of the back surface of the top ring, and the pressing force applied from the piston to the center of the back surface of the top ring is adjusted. By doing so, the flatness of the central portion of the wafer after polishing is improved. However, this publication does not specifically describe a method for improving the flatness at the peripheral portion of the wafer.

On the other hand, in the polishing head described in JP-A-9-225821, a plurality of cavities are provided concentrically inside the top ring, and a plurality of cavities extending from each of these cavities to the lower surface of the top ring. A through hole is provided. By independently adjusting the pressure of the pressurized fluid supplied to each cavity, the pressure distribution of the pressurized fluid acting on the back side of the wafer is adjusted, and the flatness of the polished wafer is improved. I have.

However, in this method, since the pressurized fluid is interposed between the lower surface of the top ring and the lower surface of the wafer, the holding of the wafer becomes uncertain.
During polishing, the wafer may move relative to the top ring. For this reason, there is a problem that the relative speed between the wafer and the turntable becomes uneven, and the flatness is reduced.

Further, regarding a plurality of through-holes opened on the lower surface of the top ring, the range affected by each through-hole is considered to be formed in a circular shape centered on each through-hole, so that the flatness is improved. There are limits to the effect.

[0017]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the conventional polishing apparatus, and an object of the present invention is to reduce the nonuniformity of the polishing amount at the peripheral portion of the wafer. An object of the present invention is to provide a polishing apparatus capable of realizing a high flatness by reducing the number of polishing steps.

[0018]

A polishing apparatus according to the present invention comprises a turntable on which an abrasive cloth is mounted on an upper surface, and a disk-shaped polishing device which is disposed above and opposed to the turntable and has a lower surface with a backing pad interposed therebetween. A top ring on which the workpiece is adsorbed, a top block disposed on the upper surface side of the top ring and holding the top ring on the lower surface, and a top block attached to the lower surface peripheral portion of the top block so as to surround the outer periphery of the top ring A guide ring that guides the workpiece from the outer peripheral side, in a polishing apparatus that performs polishing by pressing against the polishing cloth while rotating the workpiece, the top ring is provided along the outer periphery on the lower surface side. The thin part is formed in a ring shape, and this thin part,
A ring-shaped piston is inserted into a ring-shaped space surrounded by the lower surface of the top block and the inner peripheral surface of the guide ring, and between the upper end surface of the ring-shaped piston and the lower surface of the top block. And a pressure chamber to which a pressurized fluid is supplied.

According to the polishing apparatus of the present invention, by controlling the pressure of the pressurized fluid supplied into the pressure chamber, the pressing force of the ring-shaped piston is adjusted, and the elastic deformation of the top ring at the peripheral edge portion is achieved. The condition can be adjusted. Thereby, the in-plane uniformity of the contact pressure between the wafer surface and the polishing cloth can be increased, and the flatness of the polished wafer surface can be improved.

[0020] Preferably, compressed air is used as the pressurized fluid, and the compressed air is supplied to the pressure chamber via a path formed inside the top block.

Preferably, a ring-shaped protrusion is provided on the lower end surface of the ring-shaped piston along the outer periphery, and a tip end surface of the protrusion is brought into contact with an upper surface of a thin portion of the top plate.

[0022]

FIG. 1 shows the structure of a polishing head constituting a main part of a polishing apparatus according to the present invention. In the figure, 1 is a wafer, 5 is a top block, 6
Denotes a top ring, 7 denotes a guide ring, 8 denotes a backing pad, 11 denotes a thin portion, 12 denotes a piston, and 13 denotes a pressure chamber.

The top block 5 is attached to the lower end of the drive shaft 4a. Flanges 5a and 5b are formed at the upper end and the lower end of the top block 5, respectively. The upper end side flange portion 5a is fixed to the lower end of the drive shaft 4a with bolts. The diameter of the lower flange portion 5b is slightly larger than the wafer 1 to be polished. The top ring 6 is fixed to the lower surface of the lower flange portion 5b with bolts. Further, a guide ring 7 is fixed to the peripheral edge of the lower surface of the lower flange portion 5 b with a bolt so as to surround the outer periphery of the top ring 6.

The top ring 6 has a
A circular recess 27 is formed, and a plurality of through holes 28 are formed between the bottom surface of the recess 27 and the lower surface of the top ring 6. In addition, an O-ring is arranged on the upper surface of the top ring 6 along the outer periphery of the recess 27, and the inside of the recess 27 is sealed.

The top ring 6 has a thin portion 11 formed in a ring shape on the lower surface side along the outer periphery.
, The thickness of the top ring 6 is reduced. A ring-shaped piston 12 is inserted into a ring-shaped space surrounded by the thin portion 11, the lower surface of the top block 5, and the inner peripheral surface of the guide ring 7, and the upper end surface of the piston 12 and the top block 5 A pressure chamber 13 to which a pressurized fluid is supplied is formed between the pressure chamber 13 and the lower surface of the pressure chamber 13. In addition,
An O-ring is arranged on the upper surface of the top ring 6 along the outer periphery of the upper surface, and an O-ring is also arranged on the upper surface of the guide ring 7. By these O-rings, the pressure chamber 13
Is sealed inside.

On the lower end surface of the piston 12, a ring-shaped protrusion 12a is formed along the outer periphery.
Is in contact with the upper surface of the thin portion 11 of the top ring 6 at the peripheral edge thereof.

A backing pad 8 is adhered to the lower surface of the top ring 6 with a double-sided tape. Through holes 29 are formed in the backing pad 8 at positions corresponding to the plurality of through holes 28 formed in the top ring 6. The wafer 1 is attracted to the lower surface of the top ring 6 via the backing pad 8. Wafer 1
Is guided by a guide ring 7 on its outer peripheral side.

A vent hole 23 is formed inside the drive shaft 4a. Flange part 5 on the upper end side of top block 5
A ventilation hole 25a is formed inside a, and a ventilation hole 25b is formed inside the lower flange portion 5b. Vent 23
Is connected to a vacuum source and a high-pressure air source via a rotary joint (not shown). The tip of the ventilation hole 23 is the ventilation hole 25
a, and the tip of the ventilation hole 25a communicates with the ventilation hole 25b via the tube 24. The distal end of the ventilation hole 25 b opens on the lower surface of the top block 5 and communicates with the recess 27.

Vent hole 23, vent hole 25a, tube 2
4. The wafer 1 is sucked by reducing the pressure in the recess 27 through the ventilation hole 25b, while the wafer 1 is released by pressurizing the inside of the recess 27.

The drive shaft 4a further includes a ventilation hole 33 therein.
Are formed. Inside the upper end flange 5a of the top block 5 is a ventilation hole 35a and the lower end flange 5b.
Is formed with a ventilation hole 35b. Vent 33
Is connected to a high-pressure air source via a rotary joint (not shown) and a pressure adjusting device 31. The tip of the ventilation hole 33 communicates with the ventilation hole 35a, and the tip of the ventilation hole 35a communicates with the ventilation hole 35b via the tube 34. Vent 3
The tip of 5 b is opened on the lower surface of the top block 5 and communicates with the pressure chamber 13.

Vent 33, vent 35a, tube 3
4. By controlling the pressure in the pressure chamber 13 through the ventilation hole 35b, the pressure applied to the thin portion 11 by the ring-shaped piston 12 is adjusted. Thereby, the thin portion 11 is elastically deformed to be axially symmetrical, and the contact pressure distribution between the surface of the wafer 1 and the polishing cloth at the peripheral portion of the wafer 1 is adjusted.

Since the appropriate value of the pressure applied by the piston 12 varies depending on the type of the polishing cloth, it is determined in advance by conducting experiments.

[0033]

According to the polishing apparatus of the present invention, by using a ring-shaped piston, the elastic deformation state of the outer periphery of the top ring is appropriately adjusted, so that the surface of the wafer at the periphery of the wafer and the polishing cloth can be adjusted. Can be adjusted, so that the in-plane uniformity of the polishing amount of the wafer can be improved and the flatness after polishing can be improved.

[Brief description of the drawings]

FIG. 1 is an axial sectional view of a polishing head constituting a main part of a polishing apparatus according to the present invention.

FIG. 2 is a diagram showing a schematic configuration of a polishing apparatus.

FIG. 3 is an axial sectional view showing an example of the structure of a conventional polishing head.

FIG. 4 is a schematic diagram showing a cross-sectional shape of a polished wafer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Wafer, 2 ... Polishing cloth, 3 ... Turntable, 4 ... Polishing head, 5 ... Top block, 6 ... Top ring, 7 ... Guide ring, 8 ..Backing pad, 9 ... Abrasive supply nozzle, 11 ... Thin section, 12 ... Piston, 12a ... Ring-shaped projection, 13 ... Pressure chamber, 23 ... Vent hole , 24 ... tube, 25a, 25b ... vent hole, 27 ... recessed portion, 28 ... through hole, 29 ... through hole, 31 ... pressure control device, 33 ... through Pores, 34 ... Tubes, 35a, 35b ... Vents.

Claims (3)

[Claims] 1. A turntable on which an abrasive cloth is mounted on an upper surface, and a top ring which is disposed above and opposed to the turntable, and on which a disk-shaped workpiece is sucked via a backing pad on a lower surface. A top block arranged on the upper surface side of the top ring and holding the top ring on the lower surface; and a guide mounted on the lower peripheral edge of the top block so as to surround the outer periphery of the top ring and guiding the workpiece from the outer peripheral side. A polishing apparatus comprising: a ring; and a polishing device that performs polishing by pressing against a polishing cloth while rotating a workpiece, wherein the top ring has a thin portion formed in a ring shape along an outer circumference on a lower surface side of the top ring. And a ring-shaped space surrounded by the lower surface of the top block and the inner peripheral surface of the guide ring. A polishing chamber, into which a ston is inserted, and a pressure chamber to which a pressurized fluid is supplied is formed between an upper end surface of the ring-shaped piston and a lower surface of the top block. 2. The method according to claim 1, wherein the pressurized fluid is compressed air, and the compressed air is supplied to the pressure chamber via a path formed inside the top block. The polishing apparatus according to claim 1. 3. The ring-shaped piston is provided with a ring-shaped protrusion at the lower end surface thereof along the outer periphery, and a tip end surface of the protrusion contacts an upper surface of a thin portion of the top plate. The polishing apparatus according to claim 1, wherein: