KR20000013554U - Endpoint detection device of chemical mechanical polishing - Google Patents

Abstract

The present invention discloses an end point detection device for chemical mechanical polishing. In the disclosed subject matter, the wafer 1 is fixed to the bottom of the chuck 5, and the polishing pad 3 is disposed below the chuck 5. The slurry 4 is supplied between the polishing pad 3 and the wafer 1, and the chuck 5 and the polishing pad 3 rotate in opposite directions. To the chuck 5 or polishing pad 3, several piezoelectric sensors 10 are attached which sense the vibration generated by the slurry 4 colliding with the pattern 2 of the wafer 1. The electrical signal sensed by the piezoelectric sensor 10 is amplified through an amplifier and filtered by a filter. The filtered electrical signal is input to the controller 12, and the controller 12 recognizes an end point when the frequency is sharply lowered.

Description

Endpoint detection device of chemical mechanical polishing

The present invention relates to an apparatus for detecting an end point at which a polishing stops in a chemical mechanical polishing (CMP) process used to planarize an interlayer insulating film for insulation between films in a semiconductor device. will be.

In a semiconductor device having a multi-layered wiring structure, an interlayer insulating film is deposited on the lower wiring before the wiring is formed for insulation between the respective wirings, and an upper wiring is formed on the interlayer insulating film. At this time, in order to minimize the disconnection problem of the upper wiring caused by the surface irregularities of the lower wiring and the short problem between the wirings, a process of necessarily flattening the interlayer insulating film is performed before the upper wiring is formed on the interlayer insulating film.

A method mainly used in such a planarization process is a chemical mechanical polishing method for achieving planarization by removing a predetermined thickness of an interlayer insulating film by polishing a wafer on a polishing pad using a slurry. In other words, the wafer is fixed to the chuck, the polishing pad and the chuck are rotated at the same time, a slurry is supplied therebetween, and the wafer is rubbed against the polishing pad to polish the insulating film.

In carrying out the planarization process by such a chemical mechanical polishing method, the most important and difficult problem is controlling the polishing thickness. However, until now, since there was no method of measuring the polishing thickness at the same time as polishing, it is inconvenient to measure the thickness after polishing, and if it is polished too much, it must be redeposited and polished again. There was difficulty and difficulty.

In order to solve such inconveniences and difficulties, an optical method such as an ellipsometry method using a laser and a method using a change of a motor current have been proposed in the past.

The ellipsometry method is also classified into two cases where the light source is on the back of the wafer and the back of the polishing pad. In both cases, laser is irradiated to the wafer to show the sinusoidal intensity change according to the thickness of the insulating film, and the intensity of the reflected light and the optical interference are inferred.

The method using the motor current is mainly used to polish metal wires. When the layer with low polishing speed is exposed and the friction between the polishing pad and the wafer increases, the motor current rapidly increases, and this time point is recognized as the polishing end point. .

However, in the conventional ellipsometry method, when the light source is disposed on the back side of the wafer, there is a disadvantage in that each position of the wafer cannot be sensed because the position of the light source is fixed. In the case of the wafer on which the multi-layered wiring is formed, light cannot penetrate the multi-layered wiring, so that end point measurement is completely impossible.

On the other hand, since the light source is disposed behind the polishing pad and the light is irradiated to the front surface of the wafer, the polishing thickness is measured by the intensity of the reflected light by irradiating the laser with the wafer. Since there are not only one layer but several layers and metal wires are formed therebetween, the reflected light causes mutual interference, and due to the noise of the light itself reflected from the metal wires, accurate light intensity cannot be measured. There will be no. For this reason, there was a problem that can not detect the exact end point.

In addition, the method using the motor current is very effective in the case of a wafer having a structure in which a layer having a high polishing rate is polished and a layer having a low polishing rate is revealed, but has a problem in that it is difficult to apply when the polishing rates are the same. .

Therefore, the present invention was devised to solve all the problems of the conventional end point detection method, and detects the end point by using the impact vibration variation between the wafer pattern and the slurry or the polishing pad. It is an object to provide an end point detection device for chemical mechanical polishing that can be stopped.

1 is a view for explaining a detection principle applied to the endpoint detection apparatus according to the present invention

2 and 3 are views showing two modified examples showing the position where the piezoelectric sensor, which is a main part of the present invention, is disposed;

4 is a block diagram showing an endpoint detection apparatus according to the present invention

-Explanation of symbols for the main parts of the drawing-

One ; Wafer 2; pattern

3; Polishing pad 4; Slurry

5; Chuck 10; Piezoelectric sensor

11; Amplifiers and filters 12; controller

In order to achieve the above object, the present invention consists of the following configuration.

The wafer is fixed to the bottom of the chuck and a polishing pad is disposed below the chuck. The slurry is supplied between the polishing pad and the wafer, and the chuck and the polishing pad are rotated in opposite directions or in the same direction. To the chuck or polishing pad, several piezoelectric sensors are attached that sense the vibration generated by the slurry colliding with the pattern of the wafer. The electrical signal sensed by the piezoelectric sensor is amplified through an amplifier and filtered by a filter. The filtered electrical signal is input to the controller, and the controller recognizes the end point when the frequency is sharply lowered.

According to the above-described configuration of the present invention, as the polishing operation proceeds, the gap between the pattern of the wafer and the polishing pad is reduced, and thus the frequency generated by the collision of the slurry between the patterns is gradually lowered. The piezoelectric sensor detects this and transmits an electric signal to the controller. The controller recognizes the end point of the frequency change.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view for explaining the detection principle applied to the endpoint detection apparatus according to the present invention, Figures 2 and 3 are two modified examples showing the position where the piezoelectric sensor, which is the main part of the present invention is disposed, Figure 4 It is a block diagram showing the end point detection apparatus according to the present invention.

First, as shown in FIG. 1, the wafer 1 is fixed to the bottom of the chuck (not shown), and the polishing pad 3 is disposed below the chuck. The slurry 4 is supplied between the polishing pad 3 and the wafer 1. On the other hand, while the wafer 1 is on the right side, the polishing pad 3 is moved to the left side, and is actually rotated in opposite directions or in the same direction, the wafer 1 is rubbed against the polishing pad 3 and the insulating film is polished.

By the way, the pattern 2 formed in the wafer 1 has a level | step difference of 0.2-2 micrometers depth normally, and the magnitude | size of the slurry 4 is about 0.01-0.5 micrometer. Thus, the slurry 4 also enters between the patterns 2 to cause friction and collision with the patterns 2. As polishing progresses and the thickness of the pattern 2 decreases, that is, when the step is reduced, the space in which the slurry 4 acts also decreases, so that the width of the shock wave caused by the impact of the slurry 4 on the pattern 2 and The cycle will be reduced. That is, the frequency of the shock wave is reduced.

In the present invention, as the polishing proceeds as described above, the principle of detecting the end point is detected by detecting a point in which the step is reduced and the frequency is also reduced.

To this end, as shown in FIG. 2, several piezoelectric sensors 10 for detecting a frequency are disposed on the chuck 5. In this embodiment, the piezoelectric sensors 10 are composed of one in the center and four in total arranged at equal intervals of 90 degrees. However, the number and arrangement of the piezoelectric sensors 10 are not necessarily the same as in the present embodiment, and can be arbitrarily adjusted.

As shown in FIG. 4, the piezoelectric sensor 10 is connected to an amplifier, a filter 11, and a controller 12. This order can be switched as arbitrary, and any circuit having the function of sensing and amplifying the signal and monitoring only the desired frequency is configurable.

That is, the frequency signal sensed by the piezoelectric sensor 10 is amplified by the amplifier and then filtered by the filter 11 and input to the controller 12. The controller 12 may display the change in the frequency signal over time on the monitor 13 so that the operator can visually recognize the change.

In the graph displayed on the monitor 13, the frequency signal decreases sharply at the point of the arrow. Therefore, this point is when the step is mostly called. At this time, if the insulating film thickness is planned in advance, this point becomes the end point where the polishing operation should be stopped. Therefore, the operator should just look at the monitor 13 and stop the grinding operation at that time.

In addition, although the piezoelectric sensor 10 was arrange | positioned at the chuck | zipper 5 in FIG. 2, the same function is exhibited even if it arrange | positions to the polishing pad 3 like FIG.

As described above, according to the present invention, the step of the wafer pattern is reduced by polishing, so that the piezoelectric sensor detects a time point at which the frequency of slurry generated by the slurry colliding with the pattern is rapidly reduced, whereby the polishing endpoint can be accurately detected. Will be.

On the other hand, the present invention is not limited to the above-described specific preferred embodiment, any person having ordinary knowledge in the field to which the present invention belongs without departing from the gist of the present invention claimed in the claims can be variously modified. will be.

Claims (1)

An apparatus for detecting an end point of stopping a polishing operation in chemical mechanical polishing of polishing an insulating film of a wafer while supplying a slurry between a chuck to which a wafer is fixed and a polishing pad, A piezoelectric sensor disposed on the chuck or the polishing pad, the piezoelectric sensor detecting a frequency generated by the slurry colliding with the wafer pattern; And Receives the frequency signal detected by the piezoelectric sensor. And a controller for recognizing and detecting a time point at which the frequency signal rapidly decreases as an end point.