Apparatus and method for in-situ endpoint detection and monitoring for chemical mechanical polishing operations

Claim 2

The apparatus for claim 1, wherein the window comprises: an insert mounted within the platen hole, the insert being transmissive to the laser beam.

Claim 3

The apparatus of claim 2, wherein the window comprises: a portion of the polishing pad, the portion being at least partially transmissive to the laser beam.

Claim 4

The apparatus of claim 1, wherein the window comprises: a plug formed in the pad, the plug being highly transmissive to the laser beam.

Claim 5

The apparatus of claim 1, wherein: the hole through the platen, and the window, are arc-shaped having a radius with an origin coincident with a centre coincident with a centre of rotation of the platen.

Claim 6

The apparatus of claim 1, wherein the endpoint detector further comprises: a position sensor for sensing when the window is adjacent the wafer such that the laser beam generated by the laser interferometer can pass unblocked through the window and impinge on the wafer.

Claim 7

The apparatus of claim 6, wherein: (a) the laser interferometer comprises means for producing a detection signal whenever light reflected from the wafer is detected; (b) the position sensor comprises means for outputting a sensing signal whenever the window is adjacent the wafer such that the laser beam generated by the laser interferometer can pass unblocked through the window and impinge on the wafer; and (c) the endpoint detector further comprises data acquisition means connected to the laser interferometer and position sensor for sampling the detection signal from the laser interferometer for the duration of the sensing signal from the position sensor, the data acquisition means comprising a means for outputting a data signal representing the sampled detection signal.

Claim 8

The apparatus of claim 7, wherein the data acquisition means comprises: (a) means for integrating the sampled detection signal from the laser interferometer over a predetermined period of time; and wherein (b) the outputting means outputs a data signal representing the integrated samples of the detection signal.

Claim 9

The apparatus of claim 7, wherein the data signal output by the outputting means is cyclical, and wherein the endpoint detector further comprises: (a) means for counting a number of cycles exhibited by the data signal; (b) means for computing a thickness of material removed during one cycle of the data signal from the wavelength of the laser beam and the index of refraction of the oxide layer of the wafer; (c) means for comparing a desired thickness of material to be removed from the oxide layer, to a removed thickness comprising a product of the number of cycles exhibited by the data signal from the counting means and the thickness of material removed during one cycle from the computer means; and, (d) means for terminating the CMP whenever the removed thickness equals or exceeds the desired thickness of material to be removed.

Claim 10

The apparatus of claim 7, wherein the data signal output by the outputting means is cyclical, and wherein the endpoint detector further comprises: (a) means for measuring the time required by the data signal to complete one of (i) a prescribed number of cycles, or (ii) a prescribed portion of one cycle, after each occurrence thereof; (b) means for computing a thickness of material removed during the time measured by the measuring means from the wavelength of the laser beam and the index of refraction of the oxide layer of the wafer. (c) means for calculating a rate of removal, said calculating means dividing the thickness of material removed by the time measured obtained from the measuring means; (d) means for ascertaining a remaining removal thickness, said ascertaining means subtracting a cumulative thickness of material removed from a desired thickness of material to be removed from the oxide layer, said cumulative thickness of material removed being provided by a means for summing the thickness of material removed commuted by the computing means after each occurrence of the one of (i) a prescribed number of cycles, or (ii) a prescribed portion of one cycle; (e) means for establishing a remaining CMP time, said establishing means dividing the remaining removal thickness by the rate of removal; and (f) means for terminating the CMP after the expiration of the remaining CMP time.

Claim 11

The apparatus of claim 7, wherein the wafer has an initially irregular surface topography and is planarized during the CMP, and the data signal output by the outputting means is cyclical only after the wafer surface is planarized, and wherein the endpoint detector further comprises: (a) means for detecting cyclic variation in the data signal; and (b) means for terminating the CMP whenever the detecting means detects the cyclic variation in the data signal.

Claim 13

The method of claim 12, wherein the determining step further comprises the step of : sensing when the window is adjacent the wafer such that the laser beam can pass unblocked through the window and impinge on the wafer.

Claim 14

The method of claim 13, wherein: (a) a detecting step comprises the step of producing a detection signal whenever light reflected from the wafer is detected; (b) the sensing step comprises the step of outputting a sensing signal whenever the window is adjacent the wafer such that the laser beam generated by the laser interferometer can pass unblocked through the window and impinge on the wafer; and, (c) the determining step further comprises the step of data acquisition, the data acquisition step comprising, (c1) sampling the detection signal from the laser interferometer for the duration of the sensing signal, and, (c2) outputting a data signal representing the sampled detection signal.

Claim 15

The method of claim 14, wherein the data acquisition step further comprises: (a) integrating the sampled detection signal over a predetermined period of time; and wherein, (b) the outputting step comprises outputting a data signal representing the integrated samples of the detection signal.

Claim 16

The method of claim 14, wherein the data signal is cyclical, and wherein the determining step further comprises the steps of; (a) counting a number of cycles exhibited by the data signal; (b) computing a thickness of material removed during one cycle of the data signal from the wavelength of the laser beam and the index of refraction of the oxide layer of the wafer; (c) comparing a desired thickness of materials to be removed from the oxide layer, to a removed thickness comprising a product of the number of cycles exhibited by the data signal and the thickness of material removed during one cycle; and, (d) terminating the CMP whenever the removed thickness equals or exceeds the desired thickness of material to be removed.

Claim 17

The method of claim 14, wherein the data signal is cyclical, and wherein the determining step further comprises the steps of: (a) measuring the time required for the data signal to complete one of (i) a prescribed number of cycles, or (ii) a prescribed portio of one cycle; (b) computing a thickness of material removed during the time measured from the wavelengths of the laser beam and the index of refraction of the oxide layer of the wafer; (c) calculating a rate of removal by dividing the thickness of material removed by the time measured; (d) ascertaining a remaining removal thickness by subtracting the thickness of material removed from the desired thickness of material to be removed from the oxide layer; (e) establishing a remaining CMP time by dividing the remaining removal thickness by the rate of removal; and (f) terminating the CMP after the expiration of the remaining CMP time.

Claim 18

The method of claim 14, wherein the wafer has an initially irregular surface topography and is planarized during the CMP, and the data signal is cyclical only after the wafer surface is planarized, and wherein the determining step further comprises the steps of: (a) searching for a cyclic variation in the data signal; and (b) terminating the CMP whenever the cyclic variation in the data signal is discovered.

Claim 19

The method of claim 14, wherein the wafer has an initially irregular surface topography, and the data signal is cyclical only after the wafer surface is planarized, and wherein the determining step further comprises the steps of: (a) filtering the data signal to pass only a component of the data signal having the predetermined frequency; (b) counting a number of cycles exhibited by the filtered data signal; (c) computing a thickness of material removed during one cycle of the filtered data signal from the wavelength of the laser beam and the index of refraction of the oxide layer of the wafer; (d) comparing a desired thickness of material to be removed from the oxide layer, to a removed thickness comprising a product of the number of cycles exhibited by the filtered data signal and the thickness of material removed during one cycle; and, (e) terminating the CMP whenever the removed thickness equals or exceeds the desired thickness of material to be removed.

Claim 20

The method of claim 14, wherein the wafer has an initially irregular surface topography, and the data signal is cyclical only after the wafer surface is planarized, and wherein the determining step further comprises the steps of: (a) filtering the data signal to pass only a component of the data signal having the predetermined frequency; (b) counting a number of occurrences of a portion of a cycle exhibited by the filtered data signal; (c) computing a thickness of material removed during the portion of the cycle of the filtered data signal from the wavelength of the laser beam and the index of refraction of the oxide layer of the wafer; (d) comparing a desired thickness of material to be removed from the oxide layer, to a removed thickness comprising a product of the number of occurrences of the portion of the cycle exhibited by the filtered data signal and the thickness of material removed during the portion of the cycle; and (e) terminating the CMP whenever the removed thickness equals or exceeds the desired thickness of material to be removed.

Claim 21

An in-situ method of measuring uniformity of a layer on a substrate during polishing of said layer, said method comprising: (a) directing a light beam toward said layer during polishing; (b) monitoring an interference signal produced by said light beam reflecting off said substrate; and (c) computing a measure of uniformity from said interference signal.

Claim 22

The method of claim 21 wherein said computing step comprises: extracting feature information from said interference signal; and computing said measure of uniformity from said extracted feature information.

Claim 23

The method of claim 22, further comprising comparing said measure of uniformity to a reference and generating an alert when said measure of uniformity diverges from the reference by more than a predetermined amount.

Claim 24

The method of claim 22, wherein said interference signal includes a low frequency component and wherein said extracting step comprises: measuring a first characteristic of said low frequency component; and deriving said extracted information from said first characteristic.

Claim 25

The method of claim 24, wherein said interferometer signal includes a high frequency component and wherein said extracting step further comprises: measuring a second characteristic of said high frequency signal; and deriving said extracted information from said first and second characteristics.

Claim 26

The method of claim 25, wherein said first characteristic is an amplitude of said high frequency signal and said second characteristic is an amplitude of said low frequency signal, and wherein said deriving step comprises computing a ratio of the amplitudes of said high and low frequency signals.

Claim 27

An in-situ method of characterising a process for polishing a substrate having a layer formed thereon, said method comprising: (a) directing a light beam toward said layer during polishing; (b) monitoring an interference signal produced by said light beam reflecting off of said substrate; (c) extracting a signature from said interference signal; (d) comparing said extracted signature with stored information, wherein said stored information represents a desired operating point for the polishing process; and (e) when said extracted signature diverges from said stored information by more than a predetermined amount, generating an alert signal.

Claim 28

The method of claim 27, further comprising displacing the interference signal on a visual display device for an operator to view.

Claim 29

The method of claim 27, wherein said step of extracting comprises: determining a polishing rate from said interference signal; and determining a measure of uniformity from said interference signal, and wherein said comparing step comprises comparing said polishing rate and said measure of uniformity to said stored information.

Claim 30

A substrata polishing system comprising: (a) a platen which during processing holds a polishing pad; (b) a polishing head which during processing holds the substrate against the polishing pad on the platen; (c) an interferometer capable of generating a collimated light beam which during processing is directed at and impinges on a side of said substrate that is being polished, said interferometer generating an interferometer signal; and (d) a data processing programmed to compute a measure of uniformity from said interference signal.

Claim 31

The polishing system of claim 30, wherein said polishing head is rotatable so that it rotates during processing.

Claim 32

The polishing system of claim 31, wherein said platen is rotatable so that it rotates during processing.

Claim 33

The polishing system of claim 32, wherein said interferometer is a laser interferometer.

Claim 34

The polishing system of claim 32, wherein said data processor is further programmed to: extract feature information from said interference signal; and compute said measure of uniformity from said extracted feature information.

Claim 35

The polishing system of claim 34, wherein said data processing is further programmed to: compare said measure of uniformity to a reference; and generate an alert when said measure of uniformity diverges from the reference by more than a predetermined amount.

Claim 36

The polishing system of claim 35, wherein said interference signal includes a low frequency component and wherein said data processor is programmed to extract feature information by: measuring a first characteristic of said low frequency component, and deriving said extracted information from said first characteristic.

Claim 37

The polishing system of claim 36, wherein said interferometer signal includes a high frequency component and wherein said data processor is programmed to extract feature information by: measuring a second characteristic of said high frequency signal; and deriving said extracted information from said first and second characteristics.

Claim 38

The polishing system of claim 37, wherein said first characteristic is an amplitude of said high frequency signal and said second characteristic is an amplitude of said low frequency signal, and wherein said data processor is programmed to derive said extracted information by computing a ratio of the amplitudes of said high and low frequency signals.

Claim 40

The apparatus of claim 39, further comprising the polishing pad mounted on said platen and wherein said window is formed in said polishing pad and is aligned with said passage.

Claim 41

A polishing pad for use in a chemical mechanical polishing system, said polishing pad comprising: (a) polishing surface; and (b) a bottom surface, wherein said bottom surface and said polishing surface of said polishing pad includes a window formed therein, said window being transmissive to light from an interferometer and having a diffuse bottom surface.