This patent application has not been assigned to a company or institution.
The following quote was obtained by the news editors 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 with a durable roughened surface. 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 using an appropriate polishing rate to achieve a desirable profile, e.g., a substrate layer that has been planarized to a desired flatness or thickness, or a desired amount of material has been removed. Variations in the initial thickness of a substrate layer, the slurry composition, the polishing pad condition, the relative speed between the polishing pad and a substrate, and the load on a substrate can cause variations in the material removal rate across a substrate, and from substrate to substrate. These variations cause variations in the time needed to reach the polishing endpoint and the amount removed. Therefore, determining the polishing endpoint merely as a function of the polishing time may lead to overpolishing or underpolishing, and it may not be possible to achieve a desired profile merely by applying a constant pressure.
"In some systems, a substrate is optically monitored in-situ during polishing, e.g., through a window in the polishing pad. Some optical monitoring systems detect a 'polishing endpoint', after which they continue polishing for a preset overpolishing time. For example, in copper polishing, the optical monitoring system can detect exposure of the underlying layer, and overpolishing can be used to ensure complete removal of any copper residue. However, existing overpolishing and optical monitoring techniques may not satisfy increasing demands of semiconductor device manufacturers."
In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "In one aspect a polishing method includes simultaneously polishing a first substrate and a second substrate on the same polishing pad, storing a default overpolishing time, monitoring the first substrate and the second substrate during polishing with an in-situ monitoring system, determining a first polishing endpoint time of the first substrate with the in-situ monitoring system, determining a second polishing endpoint time of the second substrate with the in-situ monitoring system, determining a difference between the first polishing endpoint time and the second endpoint time, and determining whether the difference exceeds a threshold. If the difference is less than the threshold, then an overpolishing stop time is calculated and polishing of the first substrate and the second substrates is halted simultaneously at the overpolishing stop time. If the difference is greater than the threshold, then a first overpolishing stop time that equals the first endpoint time plus the default overpolishing time is calculated and a second overpolishing stop time that equals the second endpoint time plus the default overpolishing time is calculated, and polishing of the first substrate is halted at the first overpolishing stop time and polishing of the second substrate is halted at the second overpolishing stop time.
"Implementations can include one or more of the following features. Calculating the overpolishing stop time may include calculating an average of the first polishing endpoint time and the second polishing endpoint time. Calculating the overpolishing stop time may include adding the default overpolishing time to the average. The default overpolishing time may be between five and twenty seconds. The default overpolishing time may be between ten and fifteen seconds. The threshold may be between two and six seconds.
"Determining the first polishing endpoint time may include storing a first target value for the first substrate, generating a first sequence of values for the first substrate with the in-situ monitoring system, fitting a first function to the first sequence of values, and determining the first polishing endpoint time by calculating a projected time at which the first substrate will reach the target value based on the first function. Determining the second polishing endpoint time may include storing a second target value for the second substrate, generating a second sequence of values for the second substrate with the in-situ monitoring system, fitting a second function to the second sequence of values, and determining the second polishing endpoint time by calculating a projected time at which the second substrate will reach the target value based on the second function. The first function and the second function may be linear functions.
"The in-situ monitoring system may include a spectrometric optical monitoring system. Generating the first sequence of values may include measuring a first sequence of spectra from the first substrate during polishing with the optical monitoring system, for each measured spectrum in the first sequence of spectra for the first substrate, determining a best matching reference spectrum from one or more libraries of reference spectra, and for each best matching reference spectrum for the first substrate, determining an index value to generate a sequence of first index values. Generating the second sequence of values may include measuring a second sequence of spectra from the second substrate during polishing with the optical monitoring system, for each measured spectrum in the second sequence of spectra for the second substrate, determining a best matching reference spectrum from the one or more libraries of reference spectra, and for each best matching reference spectrum for the second substrate, determining an index value to generate a sequence of second index values.
"The in-situ monitoring system may include an eddy current monitoring system. The first sequence of values and the second sequence of values may be eddy current signal values. Determining the first polishing endpoint time may include detecting clearance of a first overlying layer from a first underlying layer on the first substrate. Detecting clearance of a first overlying layer may include detecting a sudden change in a signal from the in-situ monitoring system. The first substrate and the second substrate may be removed from the polishing pad simultaneously. The polishing pad may be rinsed after removing the first substrate and the second substrate. The default overpolishing time may include a first default overpolishing time for the first substrate and a second default overpolishing time for the second substrate.
"In other aspects, polishing systems and computer-program products tangibly embodied on a computer readable medium are provided to carry out these methods.
"Certain implementations may have one or more of the following advantages. A good balance can be struck between avoiding defects and having the substrates be uniformly polished. By having the substrates on the same platen endpoint at approximately the same time, defects can be avoided, such as scratches caused by rinsing a substrate with water too early or corrosion caused by failing to rinse a substrate in a timely manner. Equalizing polishing times across multiple substrates can also improve throughput. On the other hand, by permitting substrates to be polished for different amounts of time if the potential difference exceeds a threshold, significant variations in polishing can be avoided and wafer-to-wafer polishing uniformity can be increased.
"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 having two polishing heads.
"FIG. 2 illustrates a schematic top view of a substrate having multiple zones.
"FIG. 3A illustrates a top view of a polishing pad and shows locations where in-situ measurements are taken on a first substrate.
"FIG. 3B illustrates a top view of a polishing pad and shows locations where in-situ measurements are taken on a second substrate.
"FIG. 4 illustrates a trace.
"FIG. 5 illustrates a plurality of traces for different substrates.
"FIG. 6 illustrates a calculation of a desired slope for an substrate based on a time that a function fit to a trace reaches a target value.
"FIG. 7 illustrates a calculation of times that a plurality of substrates reach a target value.
"FIG. 8 is a flow diagram of an example process for adjusting the polishing rate of a plurality of substrates such that the plurality of substrates have approximately the same thickness at the target time.
"FIG. 9 is a flow diagram of an example process for calculating overpolishing times.
"FIG. 10 illustrates time vs. endpoint monitor signal curves of two substrates polished simultaneously on a same platen.
"Like reference numbers and designations in the various drawings indicate like elements."
URL and more information on this patent application, see: Zhang, Jimin; Wang, Zhihong; Mai, David H.; Carlsson, Ingemar; Jew, Stephen; Swedek, Boguslaw A. Control of Overpolishing of Multiple Substrates on the Same Platen in Chemical Mechanical Polishing. Filed
Keywords for this news article include: Patents.
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