JPH08330260A - Polishing method and its device - Google Patents

Abstract

PURPOSE: To detect the end of polishing easily and with high accuracy, in the case of performing the etch back process to shave, for example, an interlayer insulating film by polishing, in the manufacture process of a semiconductor wafer. CONSTITUTION: Polishing is performed while supplying polishing solution, pressing a wafer 10 and a glass disc 4 against the polishing cloth 23 while rotating them synchronously by means of a motor retaining the wafer 10, where an interlayer insulating film is made all over the surface, with a retainer 10 and the glass disc 4 with a retainer 41. At this time, the light from an optical fiber 5A is applied to the glass disc 4, and the reflected light at the downside is received with an optical fiber 58, and based on the phase difference of this reflected light, the thickness of the glass disk 4, that is, the quantity of polishing is grasped, and based on this quantity of polishing, the quantity of polishing of the wafer 10 is grasped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing method and an apparatus therefor.

[0002]

2. Description of the Related Art Semiconductor wafers (hereinafter referred to as "wafers")
CMP (Chemical m
There is a polishing process referred to as “epitaxial polishing”. This CMP is a method in which a polishing cloth such as polyurethane is attached to a rotary table, and a polishing object of a semiconductor wafer is polished on the surface of the polishing cloth by using a polishing material containing silica (SiO ₂ ) as a main component. Although the mechanism is not clear, it is considered that the combined effect of chemical and mechanical mechanism is greatly related to the polishing mechanism.

CMP is an etch-back process, for example, a process of forming a metal film such as W (tungsten) or Al (aluminum) on an insulating film having a contact hole and then removing unnecessary portions to expose the insulating film. Alternatively, it is used in a step of polishing an interlayer insulating film formed on the entire surface of a wafer to a predetermined thickness.

In the conventional CMP, the rotary table 1 having a polishing cloth 11 formed on the surface thereof as shown in FIG.
2, a wafer holding mechanism 13 called a carrier or the like.
The wafer 10 held on the nozzle 1 is pressed against the nozzle 1 with a predetermined pressure.
While supplying the polishing liquid from 4 to the surface of the polishing cloth 11, the rotary table 12 is rotated and the wafer holding mechanism 13 is rotated by the motor 15, so that the wafer 10 is rotated on the rotary table 12 and relatively revolved. By doing so, the surface of the wafer 10 was polished.

Then, the metal film is scraped off, and a thin T film formed on the insulating film, for example, a silicon oxide film (SiO ₂ ).
In order to detect the time when the surface of the silicon oxide film is exposed (polishing end point) by scraping off the iN (barrier layer), the torque current of the motor 15 rotating the wafer holding mechanism 13 is detected, and the object to be polished is detected. The difference in the frictional force between the polishing cloth and the polishing cloth depends on the material of the object to be polished, that is, there is a difference between the torque during polishing of the metal film and the torque during polishing of silicon oxide. Detect, metal film → barrier layer →
The end point is detected on the basis of the change pattern of the current when the polishing target moves like an insulating film.

Further, when the interlayer insulating film is polished, the method of observing the change in the torque current of the motor cannot be applied. Therefore, for example, the polishing rate is grasped in advance and the polishing time is managed to control the polishing amount. Was doing.

[0007]

However, in the method of detecting the torque current, since the change of the torque current is slight and there is much noise, the end point cannot be detected with high accuracy, and therefore the current changes. While doing
For example, the motor 15 may be slightly ahead of the time when the end point is predicted.
In the case where the wafer holding mechanism 13 is lifted from the rotary table 12 and the operator visually confirms the surface of the wafer W to observe whether the silicon oxide film is completely exposed, and further polishing is required. In practice, the remaining amount of polishing was empirically predicted, and in practice, the change in the torque current was used as a rough guideline for the end point, and the operator's visual observation was the main factor.
As a result, there is a problem in that the end point cannot be detected with high accuracy and the burden on the operator is heavy.

In the method of polishing the interlayer insulating film by time and polishing it to a predetermined thickness, the polishing rate changes depending on the surface condition of the polishing cloth. Therefore, immediately after converting the polishing cloth to a new one and for a long time. The polishing rate after use is subtly different, and therefore the polishing amount of the interlayer insulating film, in other words, the film thickness cannot be controlled with high accuracy, and the polishing amount is planned especially when the polishing cloth deteriorates. The amount of polishing is greatly deviated. Therefore, it is necessary to check the polishing rate at a predetermined frequency.

The present invention has been made under such circumstances, and an object of the present invention is to provide a polishing method and apparatus capable of controlling the polishing amount with high accuracy.

[0010]

According to a first aspect of the present invention, there is provided a method of supplying a polishing liquid to a surface of a polishing body to polish the polishing target, the polishing target being a processing target and a reference polishing target plate. While simultaneously polishing with a common polishing body in conjunction with the above, the polishing amount of the reference polishing plate is monitored, and the polishing amount of the polishing target object is obtained based on the polishing amount. To do.

According to a second aspect of the present invention, in the polishing method according to the first aspect, the surface of the reference polishing plate is irradiated with light and the polishing amount of the reference polishing plate is monitored based on the reflected light. It is characterized by doing.

According to a third aspect of the present invention, in a device for polishing a body to be polished by supplying a polishing liquid to the surface of the body to be polished, a first holding portion for holding the body to be polished to be processed, and a reference workpiece. The polishing plate, the second holding part for holding the reference plate to be polished, and the first holding part and the second holding part are interlocked with each other and relatively rotated while being in contact with the polishing body. Means for, a polishing amount monitoring unit for monitoring the polishing amount of the reference polishing plate, based on the polishing amount monitored by the polishing amount monitoring unit, a polishing end point detection unit for detecting the polishing end point, It is characterized by having.

According to a fourth aspect of the present invention, in the polishing apparatus according to the third aspect, the polishing amount monitoring unit irradiates the surface of the reference polishing plate with light, and based on the reflected light, the reference polishing target. It is characterized in that the polishing amount of the polishing plate is monitored.

[0014]

When the object to be treated and the reference plate to be polished are interlocked and polished by a common polishing body, the object to be polished and the reference plate to be polished are polished. Here, since the reference polishing plate is made of a light-transmissive material, its thickness can be optically detected, so that the polishing amount can be monitored in real time. Therefore, it is possible to monitor the polishing amount of the object to be processed by grasping the relationship between the amounts of the object to be processed and the reference polishing plate in advance. Even if the surface state of the polishing body changes, for example, it deteriorates to some extent, and the polishing rate changes correspondingly, the polishing amount is monitored, so that the polishing amount can be controlled accurately and the end point can be accurately determined. Can be detected.

[0015]

EXAMPLE An example in which the present invention is applied to an apparatus for polishing a surface of a wafer will be described. In the polishing apparatus according to this example, as shown in FIGS. Rotary table 2 that rotates horizontally through
A polishing cloth 23 made of, for example, polyurethane adhered to the surface of the rotary table 2, a wafer holder 3 for holding the wafer 10 as the object to be polished and bringing the wafer 10 into contact with the polishing cloth 23 at a predetermined pressure, A disk holding portion 41 for holding the glass disk 4 as a reference polishing plate and bringing it into contact with the polishing cloth 23 at the same pressure as the contact pressure of the wafer 10, and polishing for supplying a polishing liquid to the surface of the polishing cloth 23. Liquid supply unit, for example, a nozzle 6 and a pair of optical fibers 5A and 5B for irradiating the glass disk 4 with light and detecting the thickness thereof.
And

The wafer holder 3 is equipped with, for example, a vacuum chuck mechanism so that the wafer 10 is sucked and held at a position displaced from the center of the rotary table 2 and brought into contact with the polishing cloth 23. It is designed to rotate horizontally via a vertical rotation shaft 32. The motor 31 is attached to an elevating body 61, and the elevating body 61 is moved up and down via an elevating shaft 64 by an elevating section 63 such as an air cylinder attached to a fixed plate 62.

The disk holding portion 41 is equipped with, for example, a vacuum chuck mechanism, is configured to suck and hold the glass disk 4 at a position displaced from the central portion of the rotary table 2 and bring it into contact with the polishing cloth 23, and a bearing portion. A vertical rotation shaft 43, which is borne by 42, rotates horizontally. The rotary shafts 32 and 43 are, for example, rotary shafts.
It is placed in the target with the center of Bull 2 in between. The bearing portion 42 is fixed to the elevating body 31, and the rotation shaft 43 of the disk holding portion 41 is transferred between the pulleys 33 and 44 provided on the transmission mechanism, for example, the rotation shafts 32 and 43, by the motor 31. It is configured to rotate at a constant speed with the rotation shaft 33 of the wafer holding unit 3 via the belt 34 that is stretched.

The pair of optical fibers 5A and 5B are connected to a plate thickness detecting section 71, and the light emitted from the plate thickness detecting section 71 through the optical fiber 5A for emitting light, for example, laser light, is the glass disk 4. It is arranged so that it is reflected by the surface of the polishing cloth 23 through the optical path and is received by the optical fiber 5B for light reception. The optical fibers 5A and 5B and the plate thickness detecting portion 71 constitute a plate thickness detecting device called an ellipsometer, and are fixed to the fixing plate 62 via a mounting member (not shown). There is.

The plate thickness detecting unit 71 is connected to the control unit 7, and the control unit 7 calculates the polishing amount based on the plate thickness detection value from the plate thickness detecting unit 72.
And a polishing end point detection unit 73 that detects the polishing end point based on the polishing amount value from the polishing amount calculation unit 72 and a preset setting value. In this embodiment, the optical fiber 5A, 5B, the plate thickness detecting unit 71, and the polishing amount detecting unit 71 constitute a polishing amount monitoring unit. When the polishing end point detection unit 73 detects the polishing end point, it has a function of controlling the drive of the control unit 71, the motors 21 and 31, and the elevating / lowering unit 63, and controlling the supply and disconnection of the polishing liquid supply unit 25. The motors 21 and 31 are stopped and a signal for raising the wafer holding unit 3 is output to the elevating unit 63. The polishing liquid supply nozzle 24 supplies a polishing liquid from the polishing liquid supply source 25, for example, a colloidal silica or the like, which is a weak alkaline slurry-like polishing liquid containing silica as a main component, for example, near the center of rotation of the polishing cloth 23. Is configured to supply. Next, a method of polishing the surface of the wafer on which the interlayer insulating film made of a silicon oxide film is formed by using the above-mentioned apparatus will be described. As shown in FIG. 3, this wafer has a metal layer 8 forming a wiring portion on a silicon layer 80.
1. For example, an A1 layer is formed, and an insulating film 82 is formed on the entire surface thereof.
Are formed.

First, the wafer holding unit 3 is placed in the raised position by the elevating unit 63, and the surface of the wafer holding unit 3 is faced downward.
The glass plate 4 is vacuum-sucked, and the disk holding part 41 is vacuum-sucked in the vicinity of the center of a circular glass disk 4 having a size of 6 inches, which is a reference polishing plate. Then, the wafer holder 3 and the disk holder 41 are synchronously rotated at a rotation speed of 40 rpm, and the rotation table 2 is rotated at 20 rpm, for example.
While rotating at rpm, both holding parts 3 and 41 are lowered to press the wafer 10 and the glass disk 4 at a predetermined pressure by air pressure of an air cylinder of the elevating part 63 to bring them into surface contact, and a polishing liquid supply nozzle. 4, the polishing liquid is supplied to the surface of the polishing cloth 23. In this way, the wafer 10 and the glass disk 4 rotate and revolve relatively with respect to the rotary table 2, and the silicon oxide film of the wafer 10, the polishing cloth 23 and the polishing liquid are rubbed with each other, and the polishing liquid is generated by the friction heat. The silicon oxide film is polished by the chemical reaction with the component.

The glass disk 4 is also polished in the same manner, but the thickness of the glass disk 4 is detected by the plate thickness detecting section 71 in real time. That is, a part F1 of the light emitted from the optical fiber 5A enters the glass disc 4 as shown in FIG. 4, is refracted at the point A, is reflected at the point B on the lower surface of the glass disk 4, and is reflected at the point C. Then, it exits the glass disk 4 and is received in the optical fiber 5B. On the other hand, a part F2 of the light from the optical fiber 5A is reflected at the point C, so that the glass disk 4 is provided between F1 and F2.
The thickness of the glass disk 4 can be known by detecting this phase difference.
The polishing amount calculation unit 72 takes in the plate thickness detection value from the plate thickness detecting unit 71 and compares the plate thickness at the start of polishing with the polishing amount in real time.

In the method of this embodiment, a wafer similar to the processing wafer is previously polished by the above-mentioned apparatus to detect the polishing amount of the glass disk 4, and at the same time, the insulating film (silicon oxide film) on the wafer surface is detected. ) Is measured, the relationship between the two is grasped and the parameters are stored in memory, and when the processing wafer is actually polished, insulation is performed based on the polishing amount of the glass disk 4 and the parameters. The polishing amount of the film can be detected. That is, the end point detection unit 7
3 stores the parameters and the set value of the polishing amount,
The polishing amount of the insulating film is detected based on the polishing amount of the glass disk 4 and the parameters, and an end point detection signal is output when the polishing amount of the insulating film reaches a set value. When the end point detection signal is output in this way, the wafer holding unit 3 is raised by the control signal from the control unit 7, and the motors 21 and 31 are stopped.

According to the above-described embodiment, the glass disk 4 is used as a reference plate to be polished, the plate thickness of the glass disk 4 is optically detected, the polishing amount is obtained, and the wafer 10 is polished based on this. Because I try to grasp the amount,
The amount of polishing can be monitored in real time and on the order of a few angstroms. Therefore, if the end point is determined based on this polishing amount, the polishing amount can be controlled with high accuracy and accurate polishing can be performed even if the surface condition of the polishing pad 23 changes and, for example, the polishing rate changes and the polishing rate changes. it can.

If the polishing amount within a predetermined time is less than the predetermined amount (when the time required for a certain polishing amount is a predetermined time or more), it is judged that the polishing cloth 23 is deteriorated. It can also be used as a life monitor. Furthermore, the surface roughness and scratches of the polishing cloth can be detected by observing the scattering of the reflected light.

In the above, the present invention can be applied to the case of polishing a silicon nitride film other than the silicon oxide film, and also to the case of polishing a wafer having a surface structure as shown in FIG. Applicable. Here, in the wafer of FIG. 5, a metal film 94, for example, an aluminum film is formed on the entire surface of the insulating film 92, for example, a silicon oxide film on which the contact holes 91 are formed, with a thin barrier layer 93 made of, for example, a titanium nitride film interposed. The metal film 94 is formed until the insulating film 92 is exposed by the above-described polishing apparatus.
And the barrier layer 93 is polished. In this case, the polishing amount of the metal film 94 is monitored, and after reaching the polishing amount corresponding to the film thickness of the metal film 94, the polishing is delayed by, for example, the time required for polishing the barrier layer 93 (which is an extremely short time). It suffices to finish the polishing.

As described above, the present invention can be applied to the case where a homogeneous film is polished by a predetermined amount, or the case where one film of a laminated structure of heterogeneous films is polished and removed.

[0027]

As described above, according to the present invention, when polishing the surface of, for example, a wafer, the amount of polishing can be accurately controlled, and accurate polishing can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a polishing apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a main part of a polishing apparatus according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a laminated structure on the surface of a wafer used in an example of the present invention.

FIG. 4 is an explanatory diagram showing how a polishing amount of a glass disk, which is a reference object to be polished, is detected.

FIG. 5 is an explanatory view showing another example of the laminated structure on the surface of the wafer to which the present invention is applied.

FIG. 6 is a schematic side view showing a conventional polishing apparatus.

[Explanation of symbols]

 10 semiconductor wafer 2 rotary table 23 polishing cloth 3 wafer holding part 31 motor 34 belt 4 glass disk 42 bearing part 5 disk holding part 5A, 5B optical fiber 63 lifting part 71 polishing amount detection part 72 control part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuaki Iwashita, Yamanashi Plant, Tokyo Electron Kyushu Co., Ltd., 1238-2, Kitashitajo, Fujii-cho, Nirasaki City, Yamanashi Prefecture

Claims (4)

[Claims] 1. A method for polishing an object to be polished by supplying a polishing liquid to the surface of the object to be polished, wherein the object to be treated and the reference object plate are interlocked and simultaneously polished by a common object. However, the polishing amount of the reference plate to be polished is monitored, and the polishing amount of the object to be polished is determined based on the polishing amount. 2. The polishing method according to claim 1, wherein the surface of the reference polishing plate is irradiated with light, and the polishing amount of the reference polishing plate is monitored based on the reflected light. Polishing method. 3. An apparatus for supplying a polishing liquid to the surface of a polishing object to polish an object to be polished, a first holding portion for holding an object to be polished, a reference polishing plate, and A second holding part for holding the reference plate to be polished; a means for interlocking the first holding part and the second holding part to relatively rotate them while contacting with the polishing body. A polishing amount monitoring unit for monitoring the polishing amount of the reference polishing plate; and a polishing end point detecting unit for detecting the polishing end point based on the polishing amount monitored by the polishing amount monitoring unit. Polishing device characterized by. 4. The polishing apparatus according to claim 3, wherein the polishing amount monitoring unit irradiates the surface of the reference polishing plate with light and polishes the reference polishing plate based on the reflected light. A polishing device characterized by monitoring the.