JP2000331971A - Wafer polishing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the end point of the polishing amount of a wafer polishing device accurately detectable by always detecting only the rotational torque of a carrier. SOLUTION: In a wafer polishing device, the main body 21 of a wafer holding head 2 is connected to a carrier 22 and a pair of differential transformers 46 which are torque detecting means is provided on a connecting bar 40 which transmits the rotational force from the main body 21 to the carrier 22 at symmetrical positions with respect to the center axis of the bar 40. The core section 46A of each transformer 46 is fixed to the base section of the bar 40, and the bobbin section 46B of the transformer 46 is fixed to a connecting section 40C of the bar 40. When the signals from the torque-detecting means are added to each other, the rotational torque of the carrier can be detected at all times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer polishing apparatus, and more particularly, to a chemical mechanical polishing method (CMP).
The present invention relates to an apparatus for polishing a semiconductor wafer by ical polishing.

[0002]

2. Description of the Related Art In recent years, microfabrication techniques have been developed for high integration and high performance of LSIs, and IC patterns are formed over multiple layers. It is inevitable that a certain degree of unevenness occurs on the surface of the layer on which the pattern is formed. Conventionally, the pattern of the next layer has been formed as it is. However, when the number of layers increases and the width of a line or hole decreases, it is difficult to form a good pattern, and defects and the like are likely to occur. Therefore, after the surface of a layer on which a pattern is formed is polished to flatten the surface, a pattern of the next layer is formed. In addition, to form a metal layer that connects the layers, it is also necessary to form a metal layer by plating after forming a hole, and to polish and remove the surface metal layer to leave the metal layer in the hole. Have been done. Wafer polishing by a CMP method is used to polish a wafer during the process of forming such an IC pattern.

[0003] However, metal layer is a wiring layer, for example, SiO ₂ is an interlayer insulating film between the Cu layer, a multilayer wiring
Since the polishing characteristics are different between the layer and the layer, which affects the processing state and processing time, it is necessary to change the slurry as the abrasive in each polishing process. Further, in order to prevent excessive cutting of the above layer, delicate control of the polishing amount is required. Therefore, as a device for controlling the polishing amount, that is, as a device for detecting the end point of the polishing amount, a device that detects the rotation torque of the wafer holding head and detects the polishing amount end point based on the rotation torque has been proposed. I have.

In other words, attention is paid to the fact that the frictional force is different between the Cu layer and the SiO ₂ layer, and the rotational resistance is also different. Utilizing the fact that the rotational resistance of the wafer changes as the polishing amount approaches the end point, the change point is determined. The end point was detected by detecting the appearing rotational torque of the wafer holding head. Then, an apparatus for detecting the end detects the rotational torque by detecting a current value that changes due to a torque variation of a motor that rotates the wafer holding head.

However, in the apparatus for detecting the rotation torque of the wafer holding head based on the change in the current value of the motor, the rotation torque including the rotation resistance of the speed reduction mechanism connecting the output shaft of the motor and the wafer holding head is detected. As a result, the rotational torque of only the wafer holding head cannot be detected, so that the polishing amount end point cannot be accurately detected.

Accordingly, the present applicant has proposed an end detecting device as schematically shown in FIG. In this apparatus, a connection bar B, which is a member for suspending and supporting a carrier A on a head body G (not shown), is disposed coaxially with the center axis of the wafer holding head. C and a detector D in its spring are provided. The detector D is a differential transformer, and a parallel spring C
And a coil body F also fixed to the upper surface of the parallel spring C. In this terminal detection device, the rotation torque of the wafer holding head in the output signal is indicated by a sine curve, and the magnitude of the frictional force can be detected by the amplitude of the sine curve, and the output shaft of the motor and the wafer holding shaft are detected. Some improvement was made because the rotational resistance of the coupling mechanism with the head was not lost.

However, the wafer holding head is generally rotating at about 30 to 60 rpm, and the rotation speed is slow, and as described above, one detector can perform only one detection per rotation. The rotational torque can be detected only once per second. On the other hand, in order to know an accurate polishing amount, that is, to prevent excessive shaving, it is necessary to detect the rotation torque in 0.4 to 0.1 seconds and detect the end thereof.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to accurately detect an end point of a polishing amount of a wafer being polished and to constantly detect a lateral force applied to a wafer holding head. An object of the present invention is to provide a wafer polishing apparatus capable of monitoring.

[0009]

According to the present invention, as a means for solving the above-mentioned problems, there is provided a wafer polishing apparatus described in each of the claims. In the wafer polishing apparatus according to claim 1, the head body and the carrier are connected to each other, and the torque detecting means is provided at a position symmetrical with respect to a center axis of the connecting member that transmits the rotational force from the head body to the carrier. Is provided, the rotational torque of the carrier of the wafer holding head can be constantly monitored, and the end point of the polishing amount can be accurately detected. Also, with respect to the lateral (horizontal) force of the carrier, by monitoring the individual output signals obtained from the respective torque detecting means,
Can be monitored constantly. In the wafer polishing apparatus according to the second aspect, a differential transformer is used as the torque detecting means, and substantially the same effect as that of the apparatus according to the first aspect is achieved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A wafer polishing apparatus according to an embodiment of the present invention will be described below with reference to the drawings. The basic configuration in which the wafer polishing apparatus includes a wafer holding head 2 for holding a wafer 1 and a polishing platen 4 having a polishing cloth 3 relatively moved with respect to the holding head 2 is the same as the conventional one. is there.

FIG. 1 is a longitudinal sectional view showing the structure of a wafer holding head 2 of a wafer polishing apparatus according to the present invention. The wafer holding head 2 includes a head body 21, a carrier 22, a guide ring 23, a retainer ring 24, a rubber sheet 25, and the like. The head main body 21 is formed in a disk shape, and a rotating shaft 26 is fixed on the upper surface thereof coaxially with the center axis of the head main body 21. The rotating shaft 26 is connected to an output shaft of a motor (not shown), and the head body 21 is rotated in the direction of arrow B by the driving force of the motor. Further, air supply paths 27 and 28 are formed in the head main body 21. Each of the air supply paths 27 and 28 extends outside the wafer holding head 2 and is connected to a pump P via a regulator R.

The carrier 22 is formed in a substantially cylindrical shape, and is arranged coaxially with the head main body 21 below the head main body 21. A concave portion 29 is formed on the lower surface of the carrier 22, and a porous plate 30 having air permeability is stored in the concave portion. An air chamber 31 is formed above the porous plate 30, and an air passage 3 formed in the carrier 22 is formed in the air chamber 31.
The air path 32 extends outside the wafer holding head 2 and is connected to a pump P via a regulator R. Therefore, by driving the pump P, the pump P
Is blown into the space between the porous plate 30 and the wafer 1 through the air passage 32, the air chamber 31, and the porous plate 30, and a pressure air layer is formed in this space. The pressing force of the carrier is transmitted to the wafer 1 via the layer. The wafer 1 is pressed against the polishing pad 3 by the pressing force transmitted through the pressure air layer and polished. A suction pump SP is connected to the air path 32 via a switching valve 33. Therefore, by switching the switching valve 33, the suction pump SP
Is driven, the wafer 1 is sucked by the porous plate 30 and held by suction. The porous plate 30 has a large number of air passages inside, and for example, a porous plate made of a sintered body of a ceramic material is used.

The rubber sheet 25 is formed in a single disk shape with a uniform thickness. The rubber sheet 25 is fixed to the lower surface of the head main body 21 by bolts or the like by means of large, medium, and small annular stoppers 34, 35, 36, and the rubber sheet 25 is separated into two parts by an outer part 25A and an inner part 25B.
Has been divided. Inside part 25 of rubber sheet 25 divided into two
B presses the carrier 22, and the outer portion 25 </ b> A presses the retainer ring 24 via the guide ring 23.

When the rubber sheet 25 is divided into two parts as described above, an annular space 37 sealed by the inner part 25B of the rubber sheet 25 and the outer part
An annular space 38 sealed by 5A is formed. The air supply path 27 provided in the head main body 21 communicates with the space 37. Therefore, when the compressed air from the pump P is supplied from the air supply path 27 to the space 37, the inner portion 25B of the rubber sheet 25 expands with the air pressure. As a result, the carrier 22 located below the inner portion 25B is pressed downward by the expansion of the inner portion 25B. Since this pressing force is transmitted to the wafer 1 via the pressure air layer, a pressing force of the wafer 1 against the polishing pad 3 is obtained. Further, if the air pressure is adjusted by the regulator R, the pressing force of the wafer 1 against the polishing pad 3 can be controlled.

On the other hand, since the air supply passage 28 similarly provided in the head body 21 is communicated with the space 38, when compressed air from the pump P is supplied from the air supply passage 28 to the space 38, the rubber The outer portion 25A of the sheet 25 can be expanded by air pressure. As a result, the guide ring 23 located below the outer portion 25 </ b> A is pushed down, and the retainer ring 24 arranged below the guide ring 23 is pressed against the polishing pad 3. Further, if the air pressure is adjusted by the regulator R, the pressing force of the retainer ring 24 can be controlled.

The guide ring 23 is formed in a cylindrical shape, and is arranged below the head body 21 coaxially with the center axis of the head body. A flange 23A is formed on the outer periphery of the upper part of the guide ring 23. The flange 23A is formed on a flange 34A formed on the lower inner periphery of the stopper 34 when the wafer holding head 2 is lifted from the polishing pad 3. The guide ring 23 comes into contact with the wafer holding head 2 and is prevented from falling off. In addition, the retainer ring 24
This is a ring for preventing the wafer 1 being polished from jumping out of the wafer holding head 2, and is attached to the lower outer peripheral portion of the carrier 22 via an O-ring 39.

The head body 21 and the carrier 22 are connected by a connecting bar 40 as a connecting member, and the rotation of the head body 21 is transmitted to the carrier 22. The connection bar 40 is arranged coaxially with the central axis of the wafer holding head 2, and includes a base 40 </ b> A and an intermediate shaft 40 </ b> B.
And a connecting portion 40C. Base 40A
Are fixed to the head main body 21 by bolts or the like (not shown), and the connecting portion 40C is inserted into a cylindrical concave portion 41 formed on the upper surface of the carrier 22. Connection part 40C
Has a circular shape, and as shown in FIG. 3, several semicircular notches 42, for example, three semicircular notches 42 are provided around the periphery thereof at equal intervals, and formed on the upper surface of the carrier. Recess 41
By forming a circular space with the three semi-circular grooves 43 formed on the inner surface of the
The connection bar 40 and the carrier 22 are connected. As a result, the carrier 22 is connected to the head main body 21 while being prevented from rotating. The connecting portion 40C is prevented from dropping from the carrier 22 by a retaining ring 45 fixed to the carrier 22 with bolts. Naturally, a ball can be used instead of the pin 44.

Further, the carrier 22 is connected to the connecting bar 40.
A pair of torque detecting means for detecting the rotational torque of the motor is provided. This torque detecting means is a pair of differential transformers 46 provided symmetrically and parallel to the center axis of the connecting bar 40 as shown in FIGS. The differential transformer 46 includes a core 46A and a bobbin 46B.
And a pair of differential transformers 46
A control device 47 for calculating the rotational torque based on the output signal output from the control unit 47 is provided. The core 46A of the differential transformer 46 is fixed to the upper surface of the connecting portion 40C of the connecting bar 40 by a bobbin holder 48, and the bobbin 46B is fixed to the lower surface of the base 40A of the connecting bar 40 by a core holder 49. The two core portions 46A are provided in directions facing each other.

In the thus constructed torque detecting means, as shown in FIG. 4, an output signal A from one differential transformer 46 has a substantially sinusoidal shape deviated from the center as a change in the friction of the wafer 1. The output signal B from the other differential transformer 46 is represented by a curve 18 of the output signal A.
It appears as a similar sine curve with a 0 ° phase shift. Therefore, by adding these two output signals A and B, the rotational torque of the carrier 22 appears almost linearly,
This can be monitored constantly. Polishing surface plate 4
The output due to the force in the rotation direction is canceled, and only the rotation force of the wafer holding head 2 can be detected. The amplitude of each of the output signals A and B depends on the connection bar 4 due to the rotation of the polishing cloth.
This indicates a distortion of 0, that is, a magnitude of friction. By monitoring these, the lateral force applied to the carrier 22 can be monitored. Therefore, according to the torque detecting means of the wafer polishing apparatus of the present invention, the rotational torque of the carrier 22 is smaller than that of the conventional detecting means for detecting the rotational torque of the carrier 22 by the current value of the motor for rotating the wafer holding head 2. Accurate detection and the conventional one per revolution
As compared with the rotation torque detecting means, the rotation torque of the carrier 22 can be constantly monitored, and the end point of the polishing amount of the wafer 1 can be accurately detected.

Next, the operation of the wafer polishing apparatus of the present invention configured as described above will be described. First, the wafer 1 to be polished is sucked and held by the porous plate 30, and in this state, the wafer holding head 2 is positioned at a predetermined position on the polishing cloth 3,
The suction holding of the wafer 1 is released, and the wafer 1 is placed on the polishing pad 3. Next, the switching valve 33 is switched, the pump P is driven, and the compressed air is supplied from the air passage 32 to the air chamber 31.
Is injected from the porous plate 30 between the carrier 22 and the wafer 1 to form a pressure air layer therebetween. at the same time,
The compressed air from the pump P is supplied to the space 37 via the air supply path 27, and the inner part 25B of the rubber sheet 25 is expanded by the internal air pressure to press the carrier 22. Thus, the wafer 1 is pressed against the polishing pad 3 by the pressing force of the carrier 22 transmitted through the pressure air layer. Then, the air pressure is adjusted by the regulator R to control the internal air pressure to a desired pressure, and the pressing force of the wafer 1 against the polishing pad 3 is made constant.

Similarly, the compressed air from the pump P is supplied to the space 38 through the air supply passage 28, and the outer portion 25A of the rubber sheet 25 is expanded by the internal air pressure, and the retainer ring 24 is expanded through the guide ring 23. Then, the retainer ring 24 is pressed against the polishing pad 3. Then, the regulator R adjusts the air pressure to control the internal air pressure to a desired pressure, and keeps the pressing force of the retainer ring 24 against the polishing pad 3 constant.

In this state, the polishing of the wafer 1 is started by rotating the wafer holding head 2 and the polishing platen 4. During this polishing, the wafer 1 is polished in a state in which the wafer 1 is prevented from jumping out of the wafer holding head 2 by the outer peripheral portion being in contact with the inner peripheral portion of the retainer ring 24.

On the other hand, during wafer polishing, the wafer 1
The polishing amount is monitored by constantly detecting the rotational torque of the carrier 22 by the torque detecting means and the control device 47. When the detected rotational torque changes abruptly, it is assumed that the polishing amount has reached the end point. The polishing of the wafer 1 ends.
Thereafter, the polished wafer 1 is sucked and held by the porous plate 30, and is conveyed to the next step by the unloading operation of the wafer holding head 2.

[0024]

As described above, according to the wafer polishing apparatus of the present invention, the head body constituting the holding head and the carrier are connected by the connecting member, and a set of torques is symmetrically provided on the connecting bar with respect to its axis. Since the detecting means is provided so that only the rotation of the carrier can be always detected by the torque detecting means, the end point of the polishing amount can be quickly and accurately detected.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a wafer holding head of a wafer polishing apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged longitudinal sectional view showing a state where the torque detecting means of the present invention is attached to the wafer holding head.

FIG. 3 is a cross-sectional view of a state where the torque detecting means shown in FIG. 2 is mounted.

FIG. 4 is a graph showing the relationship between time and torque detected by the torque detecting means of the present invention.

FIG. 5 is a partially enlarged longitudinal sectional view showing a conventional torque detecting means.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Wafer 2 ... Holding head 3 ... Polishing cloth 4 ... Polishing surface plate 21 ... Head main body 22 ... Carrier 40 ... Connection bar 44 ... Pin 46 ... Differential transformer 48 ... Bobbin holder 49 ... Core holder

Claims (2)

[Claims] 1. A polishing apparatus for holding a wafer on a holding head and pressing the wafer against a polishing cloth on a rotating polishing table to polish the wafer, wherein the holding head is rotated and arranged to face the polishing table. A head body, a carrier disposed below the head body and holding the wafer, and a connecting member for connecting the head body and the carrier and transmitting a rotational force from the head body to the carrier. Along with the configuration, the coupling member is provided with torque detecting means at positions symmetrical with respect to the center axis thereof, and detects the rotational torque of the carrier applied to the coupling member from the carrier,
A wafer polishing apparatus for detecting an end point of a polishing amount of a wafer based on the detected rotation torque. 2. The wafer polishing apparatus according to claim 1, wherein said torque detecting means is a differential transformer.