News Column

Patent Application Titled "Gathering Spectra from Multiple Optical Heads" Published Online

January 30, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventors David, Jeffrey Drue (San Jose, CA); Swedek, Boguslaw A. (Cupertino, CA); Benvegnu, Dominic J. (La Honda, CA); Dhandapani, Sivakumar (San Jose, CA), filed on September 13, 2013, was made available online on January 16, 2014.

The assignee for this patent application is Applied Materials, Inc.

Reporters obtained the following quote from the background information supplied by the inventors: "An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. A conductive filler layer, for example, can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness is left over the non planar surface. In addition, planarization of the substrate surface is usually required for photolithography.

"Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing liquid, such as a slurry with abrasive particles, is typically supplied to the surface of the polishing pad.

"One problem in CMP is determining whether the polishing process is complete, i.e., whether a substrate layer has been planarized to a desired flatness or thickness, or when a desired amount of material has been removed. Variations in the initial thickness of the substrate layer, the slurry composition, the polishing pad condition, the relative speed between the polishing pad and the substrate, and the load on the substrate can cause variations in the material removal rate. These variations cause variations in the time needed to reach the polishing endpoint. Therefore, it may not be possible to determine a desired polishing endpoint merely as a function of polishing time.

"In some systems, a substrate is optically monitored in-situ during polishing, e.g., through a window in the polishing pad. However, existing optical monitoring techniques may not satisfy increasing demands of semiconductor device manufacturers."

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors' summary information for this patent application: "In some optical monitoring processes, a spectrum of a substrate is measured in-situ, e.g., during the polishing processes, by directing light through a window in a polishing pad supported on a platen. If the platen rotates, then the window can pass below the substrate once per rotation. However, for some polishing operations, e.g., where the rotation rate is low or overpolishing needs to be avoided, measuring a spectrum once per rotation of the platen provides insufficient data to halt polishing with a desired precision. By collecting spectra from multiple locations at different angular positions around the platen, the rate of collection of spectra can be increased. In addition, by using a single light source and a single spectrometer, problems of calibrating multiple sensing systems can be avoided.

"In one aspect, a polishing apparatus includes a platen to hold a polishing pad having a plurality of optical apertures, a carrier head to hold a substrate against the polishing pad, a motor to generate relative motion between the carrier head and the platen, and an optical monitoring system. The optical monitoring system includes at least one light source, a common detector, and an optical assembly configured to direct light from the at least one light source to each of a plurality of separated positions in the platen, to direct light from each position of the plurality of separated positions to the substrate as the substrate passes over said each position, to receive reflected light from the substrate as the substrate passes over said each position, and to direct the reflected light from each of the plurality of separated positions to the common detector.

"Implementations can include one or more of the following features. The platen may be rotatable about an axis of rotation. The plurality of separated positions may be spaced equidistant from the axis of rotation. The plurality of separated positions may be spaced at equal angular intervals around the axis of rotation. The optical assembly may be configured such that an angle of incidence of the light from said each position on the substrate is identical. The plurality of separated positions may consist of exactly two positions or three positions.

"The at least one light source may be a common light source. The optical assembly may include a bifurcated optical fiber having a trunk connected to the common light source and a plurality of branches, and each branch of the plurality of branches may be configured to direct light to an associated position of the plurality of positions. The optical assembly may include a first bifurcated optical fiber having a first trunk connected to the common light source and a plurality of first branches and a second bifurcated optical fiber having a second trunk connected to the common detector and a second plurality of branches. Each first branch of the plurality of first branches may configured to direct light to an associated position of the plurality of positions, and each branch of the plurality of second branches may be configured to receive light from an associated position of the plurality of positions. The apparatus may include an optical probe at each position of the plurality of separated positions, and each first branch from the plurality of first branches and each second branch from the plurality of second branches may be optically coupled to an associated optical probe.

"The optical assembly may include a bifurcated optical fiber having a trunk connected to the common detector and a plurality of branches, and each branch of the plurality of branches may be configured to receive light from an associated position of the plurality of positions. The at least one light source may include a plurality of light sources. Each light source of the plurality of light sources may be associated with a different position of the plurality of positions. The optical assembly may include a plurality of optical fibers, each optical fiber of the plurality of optical fibers having a first end connected to a light source of the plurality of light sources and a second end configured to direct light to an associated position of the plurality of positions. The optical assembly may include a bifurcated optical fiber having a trunk connected to the common detector and a plurality of branches, and each branch of the plurality of branches may be configured to receive light from the associated position of the plurality of positions.

"The at least one light source may be a white light source and the detector may be a spectrometer. A plurality of optical shutters may be disposed in light paths from the plurality of positions to the common detector, and a controller may be configured to open one selected optical shutter of the plurality of optical shutters. The controller may be configured to open the one selected optical shutter of the plurality of optical shutters corresponding to a position adjacent the substrate. An optical switch may be configured to pass light from a selected one of the plurality of positions to the detector. The platen may be configured such that relative motion between the carrier head and the platen causes each position of the plurality of separated positions to repeatedly sweep across the substrate. A controller may be configured to receive a group of spectrum measurements from the detector for each sweep of each position across the substrate. The controller may be configured to generate a spectrum in a sequence of spectra from the group of spectrum measurements. The platen may be rotatable, and the controller may be configured to add a number of spectra to the sequence for each rotation of the platen, the number being equal to the number of the plurality of separate positions. The controller may be configured to determine at least one of a polishing endpoint or an adjustment to a polishing parameter based on the sequence of spectra.

"In another aspect, a method of operating an optical monitoring system includes holding a substrate against a polishing pad supported by a platen, generating relative motion between the platen and the substrate, directing light from at least one light source to each of a plurality of separate positions in the platen, the relative motion causing the plurality of separate positions to sweep across the substrate, directing light from each position of the plurality of separated positions to the substrate as the substrate passes over said each position, receiving reflected light from the substrate as the substrate passes over said each position, and directing the reflected light from each of the plurality of separated positions to a common detector.

"In another aspect, a computer program product, tangibly embodied in a machine readable storage device, includes instructions to carry out the method.

"Implementations may optionally include one or more of the following advantages. The rate of collection of spectra may be increased, and polishing may be halted with greater precision. Reliability of the endpoint system to detect a desired polishing endpoint can be improved, and within-wafer and wafer-to-wafer thickness non-uniformity (WIWNU and WTWNU) can be reduced. In addition, by using a single light source and a single spectrometer, problems of calibrating multiple sensing systems can be avoided.

"The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 illustrates a schematic cross-sectional view of an example of a polishing apparatus.

"FIG. 2 illustrates a schematic top view of a substrate having multiple zones.

"FIG. 3 illustrates a top view of a polishing pad having multiple windows.

"FIG. 4 illustrates a top view of a polishing pad and shows locations where in-situ measurements are taken on a substrate.

"FIG. 5 illustrates a measured spectrum from the in-situ optical monitoring system.

"Like reference numbers and designations in the various drawings indicate like elements."

For more information, see this patent application: David, Jeffrey Drue; Swedek, Boguslaw A.; Benvegnu, Dominic J.; Dhandapani, Sivakumar. Gathering Spectra from Multiple Optical Heads. Filed September 13, 2013 and posted January 16, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=2048&p=41&f=G&l=50&d=PG01&S1=20140109.PD.&OS=PD/20140109&RS=PD/20140109

Keywords for this news article include: Applied Materials Inc.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


For more stories covering the world of technology, please see HispanicBusiness' Tech Channel



Source: Politics & Government Week


Story Tools