JP3573197B2 - Chemical mechanical polishing station with completion point observation device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a chemical mechanical polishing (CMP) station. More particularly, the present invention relates to a chemical mechanical polishing station including a device for monitoring the progress of a wafer polishing operation to facilitate determination of a polishing completion point.
[0002]
[Prior art]
Semiconductor manufacturing has reached the advanced submicron stage. In advanced sub-micron stages, the feature size and depth of focus of photolithographic equipment decrease, and the number of multi-level metal interconnect layers increases. Therefore, how to maintain the flatness of the wafer surface with high precision is a major issue for the investigation.
[0003]
Prior to the submicron stage of semiconductor manufacturing, spin-on-glass was the basic method of planarizing silicon wafers. However, according to this method, an appropriate flatness can be obtained only in a local region of the wafer surface. If the entire surface of the wafer is not flattened, the quality after exposure deteriorates, and it becomes difficult to determine the completion point of the etching, and thus the yield of the wafer deteriorates.
[0004]
Chemical mechanical polishing is now the basic means for globally planarizing silicon wafers. In particular, it is a fundamental measure in the process of forming advanced submicron circuits having feature sizes smaller than 0.18 μm. In addition, copper has been increasingly used instead of aluminum as a material for forming conductive lines in a wafer in a so-called damascene process. Due to the difficulty in removing copper with conventional etchants, a chemical mechanical polishing operation must be used instead.
[0005]
FIG. 1 is a diagram showing a configuration of a conventional chemical mechanical polishing station for polishing a wafer. As shown in FIG. 1, the wafer 18 is firmly held in a holding ring 16a of the polishing head 16. The polishing head 16 provides the necessary rotation for polishing and provides a means for lowering the wafer 18 onto a polishing table having a polishing pad 10. Here, the polishing pad 10 rotates in a direction opposite to the rotation direction of the polishing head 16. Further, a slurry supply device 12 is provided above the polishing pad 10 so as to supply a slurry 14 for providing a polishing action. The slurry 14 contains a certain abrasive. Abrasives include metal oxide particles that provide the necessary polishing action for polishing wafer 18. After a predetermined time, the polishing head 16 is lifted from the polishing pad 10 to prevent the wafer 18 from being excessively polished.
[0006]
[Problems to be solved by the invention]
However, it is difficult to determine appropriate parameter settings in advance because of the rough components of the slurry, the condition of the polishing pad 10, and the unpredictability of the wafer surface. Therefore, in the damascene process, the metal on the dielectric layer is excessively or underremoved. When excessive metal is removed, dents and corrosion of the metal pattern occur, and the electrical characteristics deteriorate. When the undersized metal is removed on the wafer surface, a metal bridging effect occurs and the yield of the wafer is deteriorated.
[0007]
[Means for Solving the Problems]
Accordingly, it is an object of the present invention to provide such a device that allows the progress of a chemical mechanical polishing operation to be monitored and thus the extent of removal of the metal layer on the dielectric layer to be evaluated. Thereby, the completion point for stopping the polishing operation can be determined.
[0008]
To achieve the above and other advantages, and to achieve the objects of the present invention, the present invention provides a chemical mechanical polishing station for polishing a wafer, as described below. The polishing station includes a slurry supply for supplying the slurry, a polishing pad for receiving the slurry, a wafer that can rotate, and a wafer for contacting the wafer with the slurry and the polishing pad during a polishing operation. And a polishing head capable of lowering the pressure. The polishing head further includes a retaining ring for positioning the wafer. The retaining ring also includes a groove for housing a light emitting device for irradiating the light beam onto the slurry and an optical sensor for receiving the light beam reflected back from the slurry. The chemical mechanical polishing station according to the present invention further comprises a monitor and a spectrum analyzer. Both the monitor and the spectrum analyzer are connected to the optical sensor. A spectrum analyzer is used to analyze color changes in the slurry, and a monitor is used to display to the operator data about the color changes in the slurry.
[0009]
It is to be understood that the above general features and the following detailed description are exemplary only, and are intended to describe the invention as defined by the claims.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The accompanying drawings are provided to aid the understanding of the present invention, and are incorporated in and constitute a part of the specification. The accompanying drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
[0011]
FIG. 1 is a diagram showing a configuration of a conventional chemical mechanical polishing station for polishing a wafer.
FIG. 2 is a diagram illustrating a configuration of a chemical mechanical polishing station according to an embodiment of the present invention.
FIG. 3 is a bottom view schematically showing the polishing head in FIG.
FIG. 4 is a cross-sectional view schematically showing a silicon wafer at the start of a metal layer polishing operation in a damascene process.
FIG. 5 is a cross-sectional view schematically showing the silicon wafer just before the end of the metal layer polishing operation in the damascene process.
FIG. 6 is a flowchart showing an operation sequence of the polishing completion point monitor of the present invention.
[0012]
Hereinafter, preferred embodiments of the present invention as illustrated in the accompanying drawings will be described in detail. Wherever possible, the same reference numbers will be used for the same or similar parts throughout the description of the figures.
[0013]
FIG. 2 is a diagram illustrating components used in a chemical mechanical polishing station according to an embodiment of the present invention. FIG. 3 is a bottom view schematically showing the polishing head in FIG.
[0014]
As shown in FIGS. 2 and 3, the wafer 38 is firmly held in a holding ring 39 of the polishing head 36. The retaining ring 39 has a groove 42 at the rim. The polishing head 36 serves as a means for rotating the wafer 38 and a means for lowering the wafer 38 onto the polishing pad 30. The polishing pad 30 rotates in a direction opposite to the rotation direction of the polishing head 36. During the polishing operation, the slurry 34 is supplied to the surface of the polishing pad 30 through a slurry supply device 32 provided above the polishing table. A light emitting device 40 and an optical sensor 41 are provided in a groove 42 of the retaining ring 39.
[0015]
FIG. 4 is a cross-sectional view schematically showing a silicon wafer at the start of a metal layer polishing operation in a damascene process. FIG. 5 is a cross-sectional view schematically showing the silicon wafer just before the end of the metal layer polishing operation in the damascene process. As shown in FIG. 4, a slurry 26 containing an abrasive host polishes the metal that forms metal layer 24, typically copper, at the beginning of a chemical mechanical polishing operation. . Thereby, metal particles are generated. The metal particles are carried away by the slurry 26. These small metal particles also react with the abrasive in the slurry to form by-products 28. The formed by-product changes the color of the slurry 26. This change in color is a definite change and can be observed by the naked eye or by the optical sensor device.
[0016]
When most of the metal in the metal layer 24 has been removed, the material of the dielectric layer 22 located immediately below will be polished. The particles polished from the dielectric layer react with the components of the slurry 26 to form other types of by-products 29. This by-product 29 in the slurry 26 causes yet another color change in the slurry 26. The mixture containing by-product 29 has a different color than the mixture containing by-product 28. Also in this case, the color change can be observed both by the naked eye and by the optical sensor device.
[0017]
FIG. 6 is a flowchart showing an operation sequence of the polishing completion point monitor of the present invention. The light emitting device 40 in the retaining ring 39 can emit a light beam 35 a to the slurry 34. The light beam 35a irradiates the slurry and forms a reflected beam 35b returning to the light sensor 41. Since the light emitting device 40 and the optical sensor 41 are provided in the groove 42 of the holding ring 39, the polishing operation is protected from the polishing operation by the slurry 34 on the polishing pad 30.
[0018]
The optical sensor 41 can be further connected to a spectrum analyzer 43 and a monitor 44. The reflected beam 35b from the slurry 34 can be analyzed by the spectrum analyzer 43. Then, the analysis data can be transmitted to the monitor 44.
[0019]
As the wafer is continuously polished by the polishing station, the ratio of by-product 29 to by-product 28 gradually increases. This is because the metal layer 24 gradually disappears, and the dielectric layer 22 located thereunder is gradually exposed. By-product 29 in the slurry has a different color than the slurry mixture containing by-product 28, so that the color of slurry 34 changes gradually. Therefore, the wavelength of the light reflected from the slurry and returned and analyzed by the spectrum analyzer 43 gradually changes with time.
[0020]
Data resulting from the analysis of the reflected light is transmitted to the monitor 44. By observing the color change on the monitor 44, the operator can know the progress of the polishing operation, and can determine the completion point of the polishing operation to obtain the optimum surface condition.
[0021]
In summary, although factors such as the slurry composition, the rotational speed during polishing, and the initial state of the wafer are different for each polishing operation, there is no need to individually optimize the settings. Since the color change in the slurry is always analyzed by the spectrum analyzer and fed back to the monitor, an accurate polishing completion point can be determined very easily. Therefore, excessive polishing or underpolishing of the wafer can be entirely avoided.
[0022]
It will be apparent to those skilled in the art that various changes and modifications can be made to the structure of the present invention without departing from the scope and spirit of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention that fall within the scope of the appended claims and their equivalents.
[Brief description of the drawings]
FIG. 1 is a view showing a configuration of a conventional chemical mechanical polishing station for polishing a wafer.
FIG. 2 is a diagram illustrating a configuration of a chemical mechanical polishing station according to an embodiment of the present invention.
FIG. 3 is a bottom view schematically showing the polishing head in FIG. 2;
FIG. 4 is a cross-sectional view schematically illustrating a silicon wafer at the start of a metal layer polishing operation in a damascene process.
FIG. 5 is a cross-sectional view schematically showing a silicon wafer immediately before the end of a metal layer polishing operation in a damascene process.
FIG. 6 is a flowchart showing an operation sequence of the polishing completion point monitor of the present invention.
[Explanation of symbols]
26 Slurry 30 Polishing Pad 32 Slurry Feeder 34 Slurry 35a Light Beam 35b Reflected Beam 36 Polishing Head 38 Wafer 39 Retaining Ring 40 Light Emitting Device 41 Optical Sensor 42 Groove 43 Spectrum Analyzer 44 Monitor

Claims (10)

A chemical mechanical polishing station for polishing a wafer in a damascene process,
A slurry supply for supplying the slurry;
A polishing pad for receiving the slurry;
A polishing head for holding and rotating the wafer, and for lowering the wafer so that the wafer comes into contact with the slurry and the polishing pad during a polishing operation, and a holding ring for positioning the wafer. A polishing head;
A light emitting device mounted within the retaining ring such that a light beam can be directed onto the slurry;
An optical sensor mounted within the retaining ring to receive the light beam reflected back from the slurry;
A spectrum analyzer for analyzing a color change in the slurry, the spectrum analyzer being connected to the optical sensor;
A chemical mechanical polishing station comprising: The chemical mechanical polishing station according to claim 1,
A chemical mechanical polishing station for polishing a buried copper line in a wafer in a damascene process. The chemical mechanical polishing station according to claim 1,
The chemical mechanical polishing station according to claim 1, wherein the retaining ring has a groove on a rim for receiving the light emitting device and the optical sensor. The chemical mechanical polishing station according to claim 1,
A chemical mechanical polishing station for monitoring a color change in the slurry, the monitor including a monitor connected to the optical sensor. In a damascene process, a chemical mechanical polishing station for planarizing a wafer having an embedded copper line,
A slurry supply for supplying the slurry;
A polishing pad for receiving the slurry;
A polishing head for holding and rotating the wafer, and for lowering the wafer during the polishing operation to bring the wafer into contact with the slurry and the polishing pad, and a holding ring for positioning the wafer; and A polishing head with a retaining ring having a groove;
A light emitting device for irradiating a light beam onto the slurry and mounted in the groove;
An optical sensor for receiving a light beam reflected back from the slurry and mounted in the groove;
A spectrum analyzer for analyzing a color change in the slurry, the spectrum analyzer being connected to the optical sensor;
A monitor for observing a color change in the slurry, the monitor being connected to the spectrum analyzer;
A chemical mechanical polishing station comprising: A chemical mechanical polishing station for polishing a wafer in a damascene process,
A slurry supply for supplying the slurry;
A retaining ring for positioning the wafer;
A light emitting device for irradiating a light beam onto the slurry and mounted in the retaining ring;
An optical sensor for receiving the light beam reflected back from the slurry and mounted in the retaining ring;
A spectrum analyzer for analyzing a color change in the slurry, the spectrum analyzer being connected to the optical sensor;
A chemical mechanical polishing station comprising: The chemical mechanical polishing station according to claim 6,
A chemical mechanical polishing station for polishing a buried copper line in a wafer in a damascene process. The chemical mechanical polishing station according to claim 6,
The chemical mechanical polishing station according to claim 1, wherein the retaining ring has a groove on a rim for receiving the light emitting device and the optical sensor. The chemical mechanical polishing station according to claim 6,
A chemical mechanical polishing station for monitoring a color change in the slurry, the monitor including a monitor connected to the optical sensor. In a damascene process, a chemical mechanical polishing station for planarizing a wafer having an embedded copper line,
A slurry supply for supplying the slurry;
A retaining ring for positioning the wafer, the groove having a groove on a portion of the rim;
A light emitting device for irradiating a light beam onto the slurry and mounted in the groove;
An optical sensor for receiving a light beam reflected back from the slurry and mounted in the groove;
A spectrum analyzer for analyzing a color change in the slurry, the spectrum analyzer being connected to the optical sensor;
A monitor for observing a color change in the slurry, the monitor being connected to the spectrum analyzer;
A chemical mechanical polishing station comprising:

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