KR20050014990A - Chemical mechanical polisher being capable of detecting an end point in the polishing process - Google Patents

Abstract

PURPOSE: A CMP(Chemical Mechanical Polishing) polishing apparatus is provided to improve reliability of a semiconductor device by detecting an abrupt transition of pH of used slurry to determine a polishing end point. CONSTITUTION: A CMP polishing apparatus includes a rotating plate, a polishing head(21), a slurry provider(15), and a pH meter(31). The rotating plate includes a polishing pad provided thereon. The polishing head is provided on the rotating plate and supports a wafer to be polished. The slurry provider provides the slurry to the polishing pad. The pH meter detects pH of the used slurry falling from the polishing pad. During a planarization operation on the wafer, a polishing end point is detected from the pH value detected at the pH meter.

Description

Chemical mechanical polisher being capable of detecting an end point in the polishing process}

The present invention relates to a device capable of detecting an end point of polishing during chemical mechanical polishing (CMP) of a semiconductor device, and more particularly by chemical mechanical polishing to reduce the interlayer step in a semiconductor device having a multilayer structure. The present invention relates to a chemical mechanical polishing apparatus capable of detecting a polishing end point by measuring a time point at which a pH of waste slurry generated when a planarization process is changed.

In general, a semiconductor manufacturing process is a process of forming an electrically driveable driving element on a substrate by a deposition process, a photolithography process and an etching process. Recently, according to the trend of high integration and large capacity of semiconductor devices, a high integration technology for forming a multi-layer structure in a limited area has been developed. In order to cope with this, a leveling process between each layer is increased, and a planarization process is required to reduce it. The CMP apparatus is mainly used in the planarization process.

In general, chemical mechanical polishing (CMP) is applied to the planarization process. Such chemical mechanical polishing flattens a conductive film or an oxide film formed on the wafer surface by mechanical friction and polishing by a chemical abrasive. In the planarization process, mechanical polishing is performed by friction formed between the polishing pad and the wafer surface when the polishing pad is rotated while applying a predetermined load to the wafer while the wafer is mounted on the rotating polishing pad, Polishing is performed by a chemical abrasive called slurry supplied between the polishing pad and the wafer.

At this time, in order to prevent overpolishing of the semiconductor device, it is important to detect the end point (EPD) of the end point of the planarization process, that is, the polishing end point. This is because unwanted membrane quality is removed if the endpoint is not detected correctly.

Conventionally, in order to detect the end point in the planarization process, the torque change or the optical reflectance difference of the polishing head in which the polishing pad is mounted is used. For example, when polishing of the conductive film deposited on the insulating film is finished in the planarization process due to the difference in friction between the conductive film and the insulating pad, the torque is increased as the current value of the motor for rotating the polishing pad is changed. Will change. This change is detected to detect the polishing endpoint.

In addition, after forming a transparent window on the surface of the polishing pad, when the beam is irradiated to the transparent window, the reflectivity of the conductive film and the insulating film has a difference. That is, since the intensity or the wavelength of the beam reflected from the conductive film and the intensity or the wavelength of the beam reflected from the insulating film are different, the polishing endpoint is detected by detecting the difference.

However, since the amount of change in torque is relatively minute, the detection thereof is not easy and the polishing end point cannot be detected accurately. In addition, it is impossible to detect the exact value of the intensity or the wavelength of the beam detected by the foreign matter generated during the planarization process.

On the other hand, in the case of the plug CMP (chemical mechanical polishing on the plug), the density of the metal pattern is small and it is easy to apply the above-described polishing endpoint detection technique. However, the metal pattern of the damascene structure has a very high density, and thus the polishing endpoint detection technique is applied. There is a difficulty. That is, the technique described above in the case of high metal density has a problem that accurate end point measurement is difficult in view of friction and reflectivity.

SUMMARY OF THE INVENTION The present invention has been proposed to solve the conventional problems as described above, and is oxidized to a metal film by a slurry solution when chemically polishing a semiconductor substrate having a multilayer structure in which a metal film and an insulating film are sequentially stacked. The purpose of the present invention is to provide a chemical mechanical polishing apparatus capable of measuring the end point of polishing by measuring the time point at which the pH of the waste slurry used for chemical mechanical polishing is changed by the hydrogen ions generated during the oxidation process. .

In order to achieve the above object, according to the present invention, a chemical mechanical polishing apparatus capable of detecting an end point of polishing is provided with a rotating plate having a polishing pad provided on an upper surface thereof, and a polishing supporting a wafer to be provided and planarized on top of the rotating plate. A head, a supply for supplying slurry to the polishing pad, and a pH meter for measuring the pH of the waste slurry falling from the polishing pad, wherein the planarization of the wafer while the slurry is supplied from the supply to the polishing pad is performed. When performing the process, the polishing endpoint of the wafer is detected from the pH measurement of the waste slurry measured by the pH meter.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention.

As described above, according to the recent trend of high integration and large capacity of semiconductor devices, a high integration technology for forming a multilayer structure is developed, thereby reducing the step difference between layers by chemical mechanical polishing.

As shown in FIGS. 1 and 2, the chemical mechanical polishing apparatus according to the present invention rotates in a predetermined direction about a first rotational axis A1 by driving a motor (not shown) and has a polishing pad on an upper surface thereof. 13) is provided with a rotating plate (11). The upper part of the rotating plate 11 is provided with a pipe 15 for supplying the slurry S. In this case, an inflow groove (not shown) into which the slurry S supplied through the pipe 15 flows is processed on the upper surface of the polishing pad 13. In addition, an upper portion of the rotating plate 11 is provided with a polishing head 21 for sucking and fixing the wafer 22 to be polished. The polishing head 21 rotates in a predetermined direction, for example, in the same direction as the rotating plate 11, around the second rotation shaft A2.

Referring to FIG. 3, the wafer 22 is an insulating film 22b, a barrier film 22c, and a conductive film having a predetermined pattern which are sequentially formed on the silicon substrate 22a by a deposition process, a photolithography process, an etching process, and the like. Has 22d.

Referring back to FIG. 1, in order to perform the planarization process, the wafer 22 is adsorbed and fixed to the polishing head 21 with the upper surface of the conductive film 22d facing the polishing pad 13. Subsequently, the upper surface of the conductive film 22d is polished on the polishing head 21 which is rotating about the second rotating shaft A2 while the rotating plate 11 rotates about the first rotating shaft A1. It descends until it contacts the pad 13. At this time, the slurry S is supplied to the upper surface of the polishing pad 22 through the pipe 15.

Therefore, the conductive film 22d of the wafer 22 is polished and planarized by a mechanical friction action with the polishing pad 13 and a chemical reaction with the slurry S. At this time, the metal M constituting the conductive film 22d is oxidized by the following Reaction Formula 1, and as a result of this oxidation reaction, the metal oxide film and hydrogen ions are generated. The oxide film serves as an antioxidant film of the conductive film 22d.

M + H ₂ O = MO + 2H ⁺ ‥‥‥‥ (1)

Then, the waste slurry S1 used for polishing the conductive film 22d falls from the polishing pad 13.

At this time, according to a preferred embodiment of the present invention, the lower portion of the rotating plate 11 is provided with a pH meter 31 (pH meter) for detecting the pH of the falling slurry (S1). The pH of the waste slurry S1 detected by the pH meter 31 depends on the amount of hydrogen ions generated as a result of the oxidation reaction.

In order to measure the polishing end point according to the present invention, first, the pH reference value of the waste slurry S1 generated by oxidation of the metal constituting the conductive film 22d to be planarized is set. In addition, the pH of the waste slurry S1 falling from the polishing pad 13 during the planarization process by the chemical mechanical polishing apparatus is continuously measured by the pH meter 31.

At this time, the pH measurement of the waste slurry (S1) appears high at the beginning of the planarization process, and then decreases to the pH reference value as the planarization process is performed. After this, the pH measurement will rise again if the planarization process continues. As such, when the pH measurement value is higher than the pH reference value, it means that the amount of hydrogen ions generated as a result of the oxidation reaction of the slurry S to the metal constituting the conductive film 22d is reduced. In particular, after all of the conductive film 22d on the insulating film 22b is polished, the oxidation reaction of the slurry S is drastically reduced, and as a result, the pH of the waste slurry S1 is rapidly increased.

Therefore, since the time point when the pH measurement value measured by the pH meter rises sharply corresponds to the polishing end point of the conductive film 22d, the planarization process for the conductive film 22d of the wafer 22 is terminated.

For example, when the metal constituting the conductive film 22d is tungsten, tungsten oxide (WO ₃ ) and hydrogen ions (6H ⁺ ) are generated during oxidation of the tungsten, as shown in Scheme 2 below.

W + 6Fe (CN) ₆ ^3- + 3H ₂ O → WO ₃ + 6Fe (CN) ₆ ^4- + 6H ⁺ ‥‥‥‥‥ (2)

4, the pH of the tungsten oxide (WO ₃ ) is about 2, indicating strong acidity. Therefore, when the conductive film 22d is made of tungsten, the pH reference value is first set to 2, and then the pH meter 31 continuously measures the pH of the waste slurry generated during the planarization process. When the pH of the waste slurry rises sharply, it recognizes that polishing of the conductive film 22d is completed and stops the operation of the chemical mechanical apparatus.

According to the present invention, unnecessary film quality is removed by the planarization process by measuring the pH of the waste slurry generated when performing the planarization process on the wafer by chemical mechanical polishing, and detecting the time point at which the pH suddenly changes to determine the polishing end point. Can be prevented and the reliability of the semiconductor element can be improved.

The foregoing is merely illustrative of the preferred embodiments of the present invention and those skilled in the art to which the present invention pertains recognize that modifications and variations can be made to the present invention without departing from the spirit and gist of the invention as set forth in the appended claims. shall.

1 is a block diagram of a chemical mechanical device according to the present invention.

2 is a plan view of a chemical mechanical device according to the present invention.

3 is a cross-sectional view of a general semiconductor device.

4 is a graph showing the relationship between tungsten oxide and pH.

<Description of Symbols for Major Parts of Drawings>

11: rotating plate

13: polishing pad

21: polishing head

22: wafer

31: pH meter

Claims (5)

A rotating plate having a polishing pad provided on an upper surface thereof; A polishing head provided on the rotating plate and supporting a wafer to be flattened; A supply unit supplying a slurry to the polishing pad; Including a pH meter for measuring the pH of the waste slurry falling from the polishing pad, A chemistry capable of detecting the polishing endpoint which detects the polishing endpoint of the wafer from the pH measurement of the waste slurry measured by the pH meter when performing the planarization process on the wafer while the slurry is supplied from the supply to the polishing pad. Mechanical polishing equipment. The method of claim 1, The polishing endpoint is a chemical mechanical polishing device capable of detecting the polishing endpoint, characterized in that the pH measurement value of the waste slurry is sharply increased by the pH measuring device. The method of claim 2, The wafer has a conductive film laminated on an insulating film, and in the planarization step, the conductive film is flattened. The method of claim 1, The polishing end point is a chemical mechanical polishing apparatus capable of detecting the polishing end point, characterized in that the pH measurement value of the waste slurry measured by the pH meter is sharply lowered. The method of claim 4, wherein The wafer has an insulating film laminated on a conductive film, and the chemical mechanical polishing apparatus capable of detecting the polishing endpoint, wherein the insulating film is flattened in the planarization step.