No assignee for this patent application has been made.
News editors 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. A variety of fabrication processes require planarization of a layer on the substrate. For example, for certain applications, e.g., polishing of a metal layer to form vias, plugs, and lines in the trenches of a patterned layer, an overlying layer is planarized until the top surface of a patterned layer is exposed. In other applications, e.g., planarization of a dielectric layer for photolithography, an overlying layer is polished until a desired thickness remains over the underlying layer.
"Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing 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. Abrasive polishing slurry 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 slurry distribution, 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, as well as variations in the initial thickness of the substrate layer, cause variations in the time needed to reach the polishing endpoint. Therefore, determining the polishing endpoint merely as a function of polishing time can lead to within-wafer non-uniformity (WIWNU) and wafer-to-wafer non-uniformity (WTWNU).
"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."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "A substrate being polished typically includes an overlying layer to be polished and an underlying layer. One approach to optical monitoring is to measure a spectrum of light reflected from the substrate being polished, and find a best matching reference spectrum from a library of reference spectra. A value associated with the reference spectrum can be used for the endpoint control. Although this technique works well where there are small substrate-to-substrate variations in the thickness of the underlying layer, in some manufacturing environments there are large substrate-to-substrate variations in the thickness of the underlying layer. These variations lead to uncertainty or reduced reliability in the predicted endpoint. One approach to optical monitoring that may be able to reliably detect the polishing endpoint is to sum the spectrum-to-spectrum difference in intensity, and determine the endpoint based on the sum reaching a threshold value.
"In one aspect, a method of controlling a polishing operation includes polishing a substrate, during polishing obtaining a sequence over time of measured spectra from the substrate with an in-situ optical monitoring system, for each measured spectrum from the sequence of measured spectra determining a difference between the measured spectrum and an immediate previous spectrum from the sequence, accumulating the difference for each measured spectrum to generate a total difference, comparing the total difference to a threshold, and detecting a polishing endpoint based on the comparison of the total difference to the threshold.
"Implementations can include on or more of the following features. Obtaining the sequence may include scanning a sensor of the optical monitoring system across the substrate. Obtaining the sequence may include generating one measured spectrum per scan of the sensor across the substrate. Polishing the substrate may include rotating a platen that supports the sensor, and one measured spectrum may be generated per rotation of the platen. The in-situ monitoring system may generate a plurality of raw spectra per scan of the sensor across the substrate. Generating the one measured spectrum per scan may include combining at least some of the plurality of raw spectra. Combining at least some of the plurality of raw spectra may include averaging the at least some of the plurality of raw spectra. Generating the one measured spectrum per scan may include selecting a raw spectrum from at least some of the plurality of raw spectra. Determining the difference may include calculating a sum of squared differences between the measured spectrum and the immediate previous spectrum. Determining the difference may include calculating a sum of absolute differences between the measured spectrum and the immediate previous spectrum. Obtaining the sequence of measured spectra may include directing a beam of light onto the substrate and measuring a spectrum of a reflection of the beam. Accumulating the difference may include summing the difference. Detecting the polishing endpoint may include halting polishing if the total difference exceeds the threshold. The total difference may be calculated for each measured spectrum to generate a sequence of total differences, and detecting the polishing endpoint may include fitting a function to the sequence of total differences and determining a time at which the function equals the threshold.
"In another aspect, a method of controlling a polishing operation includes polishing a substrate, for each zone of a plurality of zones on a substrate during polishing obtaining a sequence over time of measured spectra from the substrate with an in-situ optical monitoring system, for each measured spectrum from the sequence of measured spectra for each zone determining a difference between the measured spectrum and an immediate previous spectrum from the sequence, for each measured spectrum from the sequence of measured spectra for each zone accumulating the difference to generate a sequence of total differences, for each zone fitting a function to the sequence of total differences for the zone to generate a plurality of functions, and adjusting a polishing parameter based on the plurality of functions to provide more uniform polishing.
"In another aspect, a computer program product, tangibly embodied in a machine readable non-transitory storage device, includes instructions to carry out the method.
"Implementations may optionally include one or more of the following advantages. The polishing endpoint can be determined more reliably, e.g., in manufacturing environments where there are large substrate-to-substrate variations in the thickness of the underlying layer.
"The details of one or more implementations are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will be apparent from the description and drawings, and from 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 top view of a polishing pad and shows locations where in-situ measurements are taken on a first substrate.
"FIG. 3 illustrates a measured spectrum from the in-situ optical monitoring system.
"FIG. 4 is a flow diagram of an example process for controlling a polishing operation.
"Like reference numbers and designations in the various drawings indicate like elements."
For additional information on this patent application, see: Zhang, Jimin; Lee, Harry Q.; Wang, Zhihong; Tu, Wen-Chiang. Endpoint Detection during Polishing Using Integrated Differential Intensity. Filed
Keywords for this news article include: Patents.
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