Roberts v. Birang

• Decision Date: 21 December 2002
• Docket Number: Patent Interference 104,424
• Parties: JOHN V. H. ROBERTS, Junior Party, (Patent 5, 605, 760; Reissue Application 09/596, 023), v. MANOOCHER BIRANG and ALLAN GLEASON, Senior Party (Application 09/028, 412).
• Court: Patent Trial and Appeal Board

JOHN V. H. ROBERTS, Junior Party, (Patent 5, 605, 760; Reissue Application 09/596, 023), v. MANOOCHER BIRANG and ALLAN GLEASON, Senior Party (Application 09/028, 412).

Patent Interference No. 104, 424

United States Patent and Trademark Office, Patent Trial and Appeal Board

December 21, 2002

This Opinion is Not binding Precedent of the Board

Attorney for Roberts Raymond W. Green, Esq., BRINKS HOFER GILSON & LIONE.

Attorney for Birang William E. Booth, Esq., FISH AND RICHARDSON, P.C.

Before: SCHAFER, LEE and NAGUMO ^[1] , Administrative Patent Judges.

FINAL JUDGMENT

SCHAFER, Administrative Patent Judge.

This interference is between (1) Roberts' Patent 5, 605, 760 and reissue Application 09/596, 023 (seeking to reissue the Roberts Patent) and (2) Birang Application 09/028, 412. We award judgment against Roberts.

I.

Background - the subject matter of the interference

The common inventive subject matter of the parties relates to polishing pads having a transparent portion used to planarize or polish the surface of silicon wafers in the production of integrated circuits. Polishing is said to be carried out at various points during the integrated circuit production process. The parties state that planarization is an important aspect of the production process. Birang explains:

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 A over a 25 x 25 mm die would be preferable. In addition, if the aforementioned 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.

Birang Specification, p. 1, l. 21 - p. 2, l. 1. The parties say that chemical mechanical polishing (CMP) is often used to polish the wafers. In CMP, the wafer is typically held against a polishing pad affixed to a rotating table or platen. Chemicals and abrasives are applied to the pad during polishing. Roberts tells us:

It is desirable to effect planarization of integrated circuit structures in the form of semiconductor wafers during the manufacture of multilayer integrated circuits. The planarization must be very precise, providing a wafer surface that varies from a given plane by as little as a fraction of a micron. This is usually accomplished by CMP, chemical-mechanical polishing, on an apparatus most often comprised of a rotating table, usually circular, onto which is affixed a polishing pad, a wafer carrier which presses the wafer flatly onto the polishing pad, and a means of supplying chemicals and abrasives to the polishing pad in the form of a slurry. Apparatus for polishing thin, flat semiconductor wafers are well known in the art.

R. Ex.^[2] 2001, col. 1, ll. 13-26. Birang similarly states:

One method for achieving the aforementioned 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.

Birang Specification, p. 2, ll. 10-14. Both parties identify the same existing problem with respect to prior art CMP -determining when the desired degree of flatness (the "end-point") has been obtained. Roberts notes:

A particular problem encountered when planarizing semiconductor wafers on such apparatus is the determination that a wafer has been polished to the desired degree of flatness. Most end-point detection methods shown in the art rely on the change in the surface structure of the wafer as an overlying layer is removed.

R. Ex. 2001, col. 1, ll. 29-34. Birang also speaks to this problem:

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.

Birang Specification, p. 3, ll. 1-5. Both parties describe prior techniques to determine the end-point. Birang says:

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.

Birang Specification, p. 3, ll.6-36. Roberts notes several prior art patents relating to techniques and apparatus for end-point detection by measuring thickness. R. Ex. 2001, col. 1, ll. 36-46 and ll. 54-64. Roberts characterizes these prior art devices as too complicated:

These devices for in-situ measurement of thickness are very complicated and rely on specialized electronic circuitry to accomplish the task. Most often, instead of using a complicated in-situ method, wafers are removed from the polishing apparatus and flatness is measured using a spectroscopic device to measure the oxide film thickness. Usually, the wafer is taken out of the polishing operation before the expected end point is reached so that excess polishing does not occur. Then the wafer is reinserted into the polishing machine for polishing to the desired endpoint.

R. Ex. 2001, col. 1, ll. 43-53. Roberts notes that the prior art also taught the use of laser light interferometry to measure the thickness. R. Ex. 2001, col. 1, ll. 54-64. Both parties note that there is a need for a better end-point detection technique during polishing. Roberts says:

It would be very desirable to have a machine upon which such laser light measurements could be employed while the wafer is continuously under total polishing conditions.

R. Ex. 2001, col. 1, ll. 64-67. Birang similarly notes:

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.

Birang Specification, p. 3, l. 36 - p. 4, l. 2.

The parties both address the problem by utilizing a polishing pad having at least a portion that is transparent. Roberts specification summarizes the invention as follows:

A pad is provided for use on a machine for the polishing of silicon wafers which allows the use of optical detection of the wafer surface condition as it is being polished. This is accomplished by constructing the entire pad or a portion thereof out of a solid uniform polymer sheet with no intrinsic ability to absorb or transport slurry particles and which is transparent to the light beam being used to detect the wafer surface condition by optical methods. Polymers which are transparent to light having a wavelength within the range of 190 to 3500 nanometers are suitable for the construction of these pads.

R. Ex. 2001, col. 2, ll.3-13, emphasis added. Birang also describes a polishing system using optical end-point detection during the polishing process. An essential part of the system is a polishing pad having a window transparent to laser light:

The present invention is directed to a novel apparatus and method for endpoint detection which can provide this improved accuracy. The apparatus and method of the present invention employ interferometric techniques for the in-situ determination of the thickness of material removed or planarity of a wafer surface, during the CMP process.

Specifically, the foregoing objective is attained by an apparatus and method of chemical mechanical polishing (CMP) employing a rotatable polishing platen with an overlying polishing pad, a rotatable polishing head for holding the wafer against the polishing pad, and an endpoint detector. The polishing pad has a backing layer which interfaces with the

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