Abrading – Precision device or process - or with condition responsive... – By optical sensor
Reexamination Certificate
2000-03-06
2001-08-28
Banks, Derris H. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
By optical sensor
C451S041000, C451S287000, C451S526000
Reexamination Certificate
active
06280290
ABSTRACT:
BACKGROUND
This invention relates generally to semiconductor manufacture, and more particularly to a method for forming a transparent window in a polishing pad for use in chemical mechanical polishing (CMP).
In the process of fabricating modern semiconductor integrated circuits (ICs), it is necessary to form various material layers and structures over previously formed layers and structures. However, the prior formations often leave the top surface topography of an in-process wafer highly irregular, with bumps, areas of unequal elevation, troughs, trenches, and/or other surface irregularities. These irregularities cause problems when forming the next layer. For example, when printing a photolithographic pattern having small geometries over previously formed layers, a very shallow depth of focus is required. Accordingly, it becomes essential to have a flat and planar surface, otherwise, some parts of the pattern will be in focus and other parts will not. In fact, surface variations on the order of less than 1000 Å over a 25×25 mm die would be preferable. In addition, if the irregularities are not leveled at each major processing step, the surface topography of the wafer can become even more irregular, causing further problems as the layers stack up during further processing. Depending on the die type and the size of the geometries involved, the surface irregularities can lead to poor yield and device performance. Consequently, it is desirable to effect some type of planarization, or leveling, of the IC structures. In fact, most high density IC fabrication techniques make use of some method to form a planarized wafer surface at critical points in the manufacturing process.
One method for achieving semiconductor wafer planarization or topography removal is the chemical mechanical polishing (CMP) process. In general, the chemical mechanical polishing (CMP) process involves holding and/or rotating the wafer against a rotating polishing platen under a controlled pressure. As shown in
FIG. 1
, a typical CMP apparatus
10
includes a polishing head
12
for holding the semiconductor wafer
14
against the polishing platen
16
. The polishing platen
16
is covered with a pad
18
. This pad
18
typically has a backing layer
20
which interfaces with the surface of the platen and a covering layer
22
which is used in conjunction with a chemical polishing slurry to polish the wafer
14
. However, some pads have only a covering layer and no backing layer. The covering layer
22
is usually either an open cell foamed polyurethane (e.g. Rodel IC1000) or a sheet of polyurethane with a grooved surface (e.g. Rodel EX2000). The pad material is wetted with the chemical polishing slurry containing both an abrasive and chemicals. One typical chemical slurry includes KOH (Potassium Hydroxide) and fumed-silica particles. The platen is usually rotated about its central axis
24
. In addition, the polishing head is usually rotated about its central axis
26
, and translated across the surface of the platen
16
via a translation arm
28
. Although just one polishing head is shown in
FIG. 1
, CMP devices typically have more than one of these heads spaced circumferentially around the polishing platen.
A particular problem encountered during a CMP process is in the determination that a part has been planarized to a desired flatness or relative thickness. In general, there is a need to detect when the desired surface characteristics or planar condition has been reached. This has been accomplished in a variety of ways. Early on, it was not possible to monitor the characteristics of the wafer during the CMP process. Typically, the wafer was removed from the CMP apparatus and examined elsewhere. If the wafer did not meet the desired specifications, it had to be reloaded into the CMP apparatus and reprocessed. This was a time consuming and labor-intensive procedure. Alternately, the examination might have revealed that an excess amount of material had been removed, rendering the part unusable. There was, therefore, a need in the art for a device which could detect when the desired surface characteristics or thickness had been achieved, in-situ, during the CMP process.
Several devices and methods have been developed for the in-situ detection of endpoints during the CMP process. For instance, devices and methods that are associated with the use of ultrasonic sound waves, and with the detection of changes in mechanical resistance, electrical impedance, or wafer surface temperature, have been employed. These devices and methods rely on determining the thickness of the wafer or a layer thereof, and establishing a process endpoint, by monitoring the change in thickness. In the case where the surface layer of the wafer is being thinned, the change in thickness is used to determine when the surface layer has the desired depth. And, in the case of planarizing a patterned wafer with an irregular surface, the endpoint is determined by monitoring the change in thickness and knowing the approximate depth of the surface irregularities. When the change in thickness equals the depth of the irregularities, the CMP process is terminated. Although these devices and methods work reasonably well for the applications for which they were intended, there is still a need for systems which provide a more accurate determination of the endpoint.
SUMMARY OF THE INVENTION
In general, in one aspect, the invention is directed to a polishing pad for a chemical mechanical polishing apparatus. The polishing pad comprises a polishing surface with an aperture formed therein. The aperture includes a first section with a first dimension and a second section with a second dimension. A substantially transparent plug is positioned in the aperture. The plug has a first portion positioned in the first section of the aperture and a second portion positioned in the second section of the aperture. There is a means for securing the plug in the aperture.
In general, in another aspect, the invention is directed to a method of forming a polishing pad. An aperture is formed in the polishing pad such that the aperture includes a first section with a first dimension and a second section with a second dimension. A substantially transparent plug is placed in the aperture. A first portion of the plug is positioned in the first section of the aperture and a second portion of the plug is positioned in the second section of the aperture. The plug is secured in the aperture.
Implementations include the following. The securing means may include an adhesive material. The first portion of the plug may have substantially the same dimension as the first section of the aperture, and the second section of the plug may have substantially the same dimension as the second section of the aperture. The first dimension may be larger than the second dimension. The plug may be a polyurethane material, and the adhesive may be an elastomeric polyurethane material. The first section of the aperture may be formed in a first layer, and the second section of the aperture may be formed in a second layer. The removing step may include removing the first section from the first layer of the polishing pad and removing the second section from a second layer of the polishing pad. The durometer measurement of the first layer may be greater than the durometer measurement of the second layer. The top surface of the plug may be coplanar with the polishing surface, whereas the thickness of the second portion of the plug may be less than the depth of the second section of the aperture.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized by means of the instrumentalities and combinations particularly pointed out in the claims.
REFERENCES:
patent: 5020283 (1991-06-01), Tuttle
patent: 5081796 (1992-01-01), Schultz
patent: 5177908 (1993-01-01), Tuttle
patent: 5297364 (1994-03-01),
Birang Manoocher
Gleason Allan
Guthrie William L.
Applied Materials Inc.
Banks Derris H.
Fish & Richardson
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