KR20160052769A - Endpoint detection in chemical mechanical polishing using multiple spectra - Google Patents

Abstract

A computer implemented method includes obtaining at least one current spectrum with an in-situ optical monitoring system, comparing the current spectrum with a plurality of different reference spectra, And determining whether a polishing endpoint has been achieved for the substrate having the outer layer. The current spectrum is a spectrum of light reflected from a substrate having an outermost layer undergoing polishing and at least one underlayer. The plurality of reference spectra represent spectra of light reflected from substrates having outermost layers having the same thickness and lower layers having different thicknesses.

Description

END POINT DETECTION IN CHEMICAL MECHANICAL POLISHING USING MULTIPLE SPECTRA BACKGROUND OF THE INVENTION [0001]

The present invention generally relates to spectrographic monitoring of substrates during chemical mechanical polishing.

An integrated circuit is typically formed on a substrate by sequential deposition of a conductive layer, a semiconductor layer, or an insulating layer on a silicon wafer. One fabrication step includes depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain application technologies, the filler layer is planarized until the top surface of the patterned layer is exposed. The conductive filler layer may be deposited on the patterned insulating layer to fill, for example, trenches or holes in the insulating layer. After planarization, a portion of the conductive layer that remains between the raised patterns of the insulating layer forms vias, plugs, and lines that provide conductive paths between the thin film circuits on the substrate. For other application techniques such as oxide polishing, the filler layer is planarized until a predetermined thickness remains on the non-planar surface. In addition, planarization of the substrate surface is usually required for photolithography.

Chemical mechanical polishing (CMP) is one method of planarization that is allowed. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is typically positioned against a rotating polishing disc pad or belt pad. The polishing pad may be one of a standard pad or a fixed abrasive pad. The standard pad has a sustainable roughened surface while the fixed-friction pad has friction particles in the containment media. The carrier head provides a controllable rod on the substrate and pushes it against the polishing pad. An abrasive liquid, such as a slurry with friction particles, is typically provided on the surface of the polishing pad.

One problem with CMP is to determine whether the polishing process is complete, i.e. whether the substrate layer has been planarized to the desired flatness or thickness, or when the desired amount of material has been removed. Transient polishing of the conductive layer or film (removing too much) leads to increased circuit resistance. On the other hand, under-polishing (too little removal) of the conductive layer leads to an electrical short circuit. Changes in the initial thickness of the substrate layer, the slurry composition, the state of the polishing pad, the relative speed between the polishing pad and the substrate, and the load on the substrate may cause changes in the material removal rate. These changes cause changes within the time required to reach the polishing endpoint. Thus, the polishing end point can not be determined solely as a function of the polishing time.

In one general aspect, a computer implemented method includes: obtaining at least one current spectrum with an in-situ optical monitoring system; comparing the current spectrum with a plurality of different reference spectra; And determining whether an abrasive endpoint has been achieved for the substrate having the outermost layer undergoing polishing based on the comparison. The current spectrum is the spectrum of light reflected from the substrate having the outermost layer undergoing polishing and the at least one underlying layer. The plurality of reference spectra represent spectra of light reflected from substrates having outermost layers having the same thickness and lower layers having different thicknesses.

Implementations may include one or more of the following: The step of determining whether the polishing endpoint has been achieved may comprise calculating differences between the current spectrum and the reference spectra. Determining whether the polishing endpoint has been achieved may include determining whether at least one of the differences has reached a threshold value. At least one of the cars may be the smallest car. Determining whether the polishing endpoint has been achieved may include activating an endpoint detection algorithm when at least one of the differences has reached a threshold value. The step of determining whether the abrasive end point has been achieved may comprise generating a difference trace comprising a plurality of points, each of the points comprising a plurality of points, each of which is calculated during the rotation of the platen, The smallest of these. The endpoint detection algorithm may include determining whether the difference trace has reached a minimum value. Determining whether the difference trace has reached a minimum value may include calculating a slope of the difference trace or determining whether the difference trace has risen to a threshold value above the minimum value. The reference spectra may be generated a priori or generated from theory.

In another aspect, a computer program product is encoded on a type of program carrier and is operable to cause the data processing apparatus to perform operations comprising steps of the above method.

As used herein, the term substrate includes, for example, a substrate (e.g., comprising a plurality of memory or processor dies), a test substrate, a bare substrate, and a gating substrate . The substrate may be in various stages of integrated circuit fabrication, for example, the substrate may be a bare wafer, or it may comprise one or more deposited / deposited or patterned layers. The term substrate may include circular disks and rectangular sheets.

Possible advantages of embodiments of the present invention may include one or more of the following. The endpoint detection system may be less sensitive to changes between substrates in sublayers or patterns and thus the reliability of the endpoint system may be improved. The use of multiple reference spectra (as opposed to a single reference spectrum) improves accuracy in end point determination by providing generally smoother endpoint traces or differences than traces generated using a single reference-spectral technique.

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

Figure 1 shows a substrate.
Figure 2 shows a chemical mechanical polishing apparatus.
Figure 3 shows the overhead view of the polishing pad and the locations where the in-situ measurements are taken.
4 is a flow chart for determining the polishing end point.
Figure 5 shows the car traces from the spectroscopic monitoring system.
Figure 6 is a flow diagram of another embodiment for determining the polishing end point.
In the various drawings, the same reference numerals and symbols refer to similar elements.

Referring to Figure 1, a substrate 10 may include a wafer 12, an outermost layer 14 to be polished, and one or more underlayers 16, some of which are typically the outermost Is patterned between the layer (14) and the wafer (12). One potential problem in spectrophotometric endpoint detection during chemical mechanical polishing is that the thickness (s) of the underlying layer (s) can vary from substrate to substrate. As a result, substrates with the outermost layer having the same thickness can actually exhibit different spectra according to the underlying layer (s). As a result, the target spectrum used to trigger the polishing endpoint for some substrates may not function properly for other substrates, for example, if the underlying layers have different thicknesses. However, it is possible to compensate for this effect by comparing the spectra obtained during polishing for multiple spectra representing variations in the underlying layer (s).

Figure 2 shows a polishing apparatus 20 operable to polish the substrate 10. The polishing apparatus 20 includes a rotatable disk-shaped platen 24 on which the polishing pad 30 is located. The platen is operable to rotate about an axis (25). For example, the motor may rotate the drive shaft 22 to rotate the platen 24.

Optical access 36 through the polishing pad is provided by including an opening (i.e., a hole extending through the pad) or a solid window. Although in some embodiments the solid window can be supported on the platen 24 and projected into the opening in the polishing pad, the solid window can be secured to the polishing pad. A polishing pad 30 is generally placed on the platen 24 such that an opening or window is placed over the optical head 53 located within the recess 26 of the platen 24. The optical head 53 has optical access through the aperture or window to the substrate to be polished as a result. The optical head is further described below.

The polishing apparatus 20 comprises a combined slurry / rinse arm 39. During polishing, the arm 39 is operable to discharge a polishing liquid 38, such as a slurry. Alternatively, the polishing apparatus includes a slurry port operable to drain the slurry onto the polishing pad 30.

The polishing apparatus 20 includes a carrier head 70 that is operable to hold the substrate 10 against the polishing pad 30. The carrier head 70 is suspended from a support structure 72, for example a carousel and is connected to a carrier head rotation motor 76 by a carrier drive shaft 74, It can rotate around. In addition, the carrier head 70 can sidestep sideways within a radial slot formed in the support structure 72. In operation, the platen is rotated about its central axis 25, and the carrier head is rotated about its central axis 71 and moved laterally across the top surface of the polishing pad.

The polishing apparatus also includes an optical monitoring system, which can be used to determine the polishing endpoint as described below. The optical monitoring system includes a light source 51 and a photodetector 52. The light passes from the light source 51 through the optical access 36 in the polishing pad 30 and impinges on the substrate 10 and is reflected back from the substrate 10 through the optical access 36, 52).

A bifurcated optical cable 54 may be used to transmit light from the light source 51 to the optical access 36 and again from the optical access 36 to the optical detector 52. The bifurcated optical cable 54 may include a "trunk" 55 and two "branches" 56 and 58.

As described above, the platen 24 includes a recess 26 in which the optical head 53 is located. The optical head 53 holds one end of the trunk 55 of the bifurcated fiber cable 54 configured to transmit light to and from the substrate surface being polished. The optical head 53 may include one or more lenses or windows that rest on the ends of the bifurcated fiber cable 54. Alternatively, the optical head 53 may only retain the end of the trunk 55 adjacent to the solid window in the polishing pad. The optical head 53 can hold the aforementioned nozzles of the flushing system. The optical head 53 may be removed from the recess 26 as required, for example, to perform preventative or corrective maintenance.

The platen may include a removable in-situ monitoring module 50. The in-situ monitoring module 50 may then include one or more of the following: a light source 51, a photodetector 52, and a circuit for transmitting signals to and receiving signals from the light source 51 and the photodetector 52 . For example, the output of the detector 52 may be a rotary electronic coupler in the drive shaft 22, e.g., a digital electronic signal that passes through the slip ring and passes to the controller for the optical monitoring system. Similarly, the light source may be turned on or off in response to control commands in the digital electronic signals passing from the controller through the rotary combiner to the module 50.

In addition, the in-situ monitoring module can retain the respective ends of the branch portions 56 and 58 of the bifurcated optical fiber 54. The light source is operable to transmit light, which travels through the branch 56 and out of the end of the trunk 55 located in the optical head 53 and impinges on the substrate being polished. The light reflected from the substrate is received at the end of the trunk 55 located in the optical head 53 and passes through the branch 58 to the photodetector 52.

In one embodiment, the bifurcated fiber cable 54 is a bundle of optical fibers. The bundle includes a first group of optical fibers and a second group of optical fibers. The optical fibers in the first group are connected to transmit light from the light source 51 to the substrate surface being polished. The optical fibers in the second group are coupled to receive the light reflected from the substrate surface being polished and to transmit the received light to the photodetector. The optical fibers may be arranged to form a shape such as X that is focused on the longitudinal axis of the bifurcated optical fiber 54 (when viewed in cross section of the bifurcated fiber cable 54) within the second group . Alternatively, other arrangements can be implemented. For example, the optical fibers in the second group may form shapes such as V that mirror the images of each other. A suitable bifurcated fiber is available from Verity Instruments, Inc. of Carrollton, Tex.

The light source 51 is operable to emit white light. In one embodiment, the emitted white light comprises light having wavelengths from 200 to 800 nanometers. A suitable light source is a xenon lamp or a xenon mercury lamp.

The photodetector 52 may be a spectrometer. A spectrometer is basically an optical instrument for measuring the intensity of light through a portion of the electromagnetic spectrum. A suitable spectrometer is a lattice spectrometer. A typical output for a spectrometer is the intensity of light as a function of wavelength.

The light source 51 and the photodetector 52 are coupled to a computing device operable to control their operation and receive their signals. The computing device may include a microprocessor located near the polishing apparatus, for example, a personal computer. With respect to control, the computing device may, for example, synchronize the activation of the light source 51 with the rotation of the platen 24. As shown in FIG. 3, the computer may cause the light source 51 to emit a series of flashes that begin and end immediately after the substrate 10 passes through the in-situ monitoring module. (Each of the illustrated points 301-311 represents the location where light from the in-situ monitoring module is reflected and reflected.) Alternatively, the computer may cause the light source 51 to cause the substrate 10 to be in- It is possible to cause the light to be emitted continuously starting immediately before passing through the module and ending immediately after passing through the module. In either case, the signal from the detector can be integrated over the sampling period to produce spectral measurements at the sampling frequency. Although not shown, each time the substrate 10 passes through the monitoring module, the alignment of the substrate with the monitoring module may differ from the previous pass. Over one revolution of the platen, the spectrum is obtained from different radii on the substrate. That is, some spectra are obtained from positions closer to the center of the substrate and some are closer to the edge. Also, over a number of rotations of the platen, a series of spectra can be obtained over time.

In operation, the computing device may receive a signal that conveys information describing the spectrum of light received by the photodetector 52, for example, during a particular flash of the light source or during a time frame of the detector. Thus, this spectrum is the in-situ measured spectrum during polishing.

Without being limited to any particular theory, the spectrum of light reflected from the substrate 10 evolves as the polishing progresses due to variations in the thickness of the outermost layer, thereby producing a series of time-varying spectra to provide. Also, certain spectra are shown by layer stacks of specific thicknesses.

The computing device may process the signal to determine an end point of the polishing step. In particular, the computing device may execute logic to determine when an endpoint has been reached, based on the measured spectra.

Briefly, a computing device can compare a plurality of reference spectra with measured spectra, and uses the results of the comparison to determine when an endpoint has been reached.

As used herein, the reference spectrum is a predefined spectrum generated prior to polishing of the substrate. The reference spectrum may have a predefined association with a value of substrate properties, such as the thickness of the outermost layer, i.e., an association defined prior to the polishing operation. The reference spectrum can be generated a priori, for example, by measuring the spectrum from a test substrate having known layer thicknesses, or it can be generated from theory.

The reference spectrum may be a target spectrum, which may be an endpoint-process compensated target spectrum or an uncompensated target spectrum. Uncompensated target spectrum refers to the spectrum exhibited by the substrate when the outermost layer has a target thickness. Illustratively, the target thickness may be between 1 and 3 microns. Alternatively, the target thickness may be zero, for example, when the film of interest is removed so that the bottom film is exposed. However, there can be a delay between the time the system receives the spectrum representing the target thickness and the time the polishing stops, which is an endpoint detection algorithm that requires spectra from multiple platen rotations, The time for commands to be transmitted, and the time required to stop the rotation of the platen). Thus, the polishing end point can be set at the time before the target thickness is achieved. The endpoint-process compensated target spectrum is used to trigger a polishing endpoint under a particular endpoint algorithm and a polishing control system when the target thickness is substantially greater than the target thickness, e.g., Lt; RTI ID = 0.0 > substrate. ≪ / RTI >

As described above, there are a number of reference spectra for a particular thickness of interest for the outermost layer. This is because different thicknesses in the lower layer (s) for different substrates can result in different spectra even if the outermost layer has the same thickness. In addition, the substrates for different integrated chip products will have different patterning of layers, which may also result in different spectra, even though the outermost layer has the same thickness. Thus, there may be a plurality of spectra for a particular thickness of the outermost layer, and the plurality of spectra may include different spectra, which may be due to different patterns or lower layers due to the substrate being intended to provide different products Lt; / RTI >

The reference spectra are collected prior to the polishing operation and the association of each reference spectrum with its associated substrate properties is stored. The reference spectra can be determined a priori.

For example, to determine the target spectrum, the characteristics of the "set-up" substrate having the same pattern as the product substrate may be measured pre-polish at the metrology station. The substrate characteristic may be the thickness of the outermost layer. The set-up substrate is then polished and the spectra collected. The set-up substrate can be periodically removed from the polishing system and its properties are measured at the metrology station. The substrate can be over-polished, i. E., Past the desired thickness, so that the spectrum of light that has been reflected from the substrate when the target thickness is achieved can be obtained.

The measured thickness and collected spectra are used to select one or more of the spectra collected, which spectra are determined to be presented by the substrate when the substrate has a thickness of interest. In particular, linear interpolation may be performed using measured pre-polishing film thicknesses and post-polishing substrate thicknesses to determine the time and corresponding spectrum shown when the target thickness is achieved. The spectra or spectra determined to appear when the target thickness is achieved are designated as the target spectra or the target spectra.

These steps can then be repeated for one or more additional set-up substrates having the same pattern as the product substrate but with the lower layer (s) of different thickness to produce additional reference spectra. Thus, the resulting collection of reference spectra includes target spectra for the same target thickness, but they are different from each other due to the different thicknesses in the lower layer (s).

Alternatively or additionally, these steps may be repeated for one or more additional set-up substrates having different patterns from the product substrate to produce additional reference spectra. Thus, the resulting collection of reference spectra includes target spectra for the same target thickness, but they are different from each other due to the different patterns.

Optionally, the collected spectra are processed to improve accuracy and / or accuracy. The spectra may be processed, for example, to normalize them to a common reference, to average them, and / or to filter noise from them.

In addition, some or all of the reference spectra can be calculated from theory, for example, using an optical model of the substrate layers.

4 illustrates a method 200 for using spectra based on endpoint determination logic to determine an end point of a polishing step. The product substrate is polished using the above-described polishing apparatus (step 402). In each rotation of the platen, the following steps are performed.

At least one spectrum of light reflected from the substrate surface being polished is measured (step 404). Alternatively, a plurality of spectra can be measured, for example, spectra measured at different radii on the substrate can be obtained from a single rotation of the platen, for example, in dots 301-311 (Figure 3) . Once a plurality of spectra are measured, a subset of one or more of the spectra may be selected for use in an endpoint detection algorithm. For example, the measured spectra at sample locations near the center of the substrate (e.g., at points 305, 306, and 307 shown in FIG. 3) may be selected. The spectra measured during the current platen revolution are selectively processed to improve accuracy and / or accuracy.

The difference between each selected measured spectrum and each reference spectrum is calculated (step 406). The reference spectra may be the target spectrum. In one embodiment, the difference is the sum of differences in intensities over a range of wavelengths. In other words,

Where a and b are the lower and upper bounds of the range of wavelengths of the spectrum, respectively, I _current () and I _reference () are the intensity of the current spectra and the intensity of the target spectra, respectively, for a given wavelength. Alternatively, the difference can be calculated as a mean square error, i.e.,

One way to calculate the difference between each of the current spectra and each of the reference spectra is to select each of the current spectra. For each selected current spectrum, the difference is calculated for each of the reference spectra. G and G are given, then the difference is given by the following combinations of current and reference spectra: e and E, e and F, e and e. G, f and E, f and F, f and G, g and E, g and F, g and G, respectively.

The smallest of the calculated cars is added to the car traces (step 408). The car traces are typically updated once per platen revolution. The car traces are generally one plot of the calculated cars (in this case the smallest of the cars computed for the current platen revolution). As an alternative to the smallest car, another one of the cars, for example, the middle or the smallest car, may be added to the trace.

Alternatively, the difference traces may be processed, for example, by smoothing the difference traces by filtering the calculated difference beyond the threshold from the preceding one or more calculated differences.

It is determined whether the second trace is below a threshold (step 410). Once the traces cross below the threshold, the endpoint logic is initiated and may be applied to detect the endpoint condition, e.g., the minimum value of the traces (step 412). For example, the endpoint may be called when the next trace begins to rise past a certain threshold of minimum value, or may be called if the slope of the second trace falls below a threshold near zero, or other window logic may be applied. Once the endpoint logic detects an endpoint condition (step 414), the polishing is stopped (step 416).

In some embodiments, once the difference traces fall below a threshold, certain reference spectra that provided the closest match, e.g., providing the smallest difference from the measured spectrum, are then used for the remainder of the endpoint determination process Lt; / RTI > is used as the only reference spectrum for < RTI ID = This ensures that the termination point is based on target spectra representing the substrate on which the underlying layers are being polished.

By using a plurality of reference spectra representing substrates having lower layers of different thicknesses, the endpoint detection system becomes less sensitive to changes in the lower layers, and thus the reliability of the endpoint system can be improved. Similarly, by using multiple reference spectra representing substrates having different patterns, the endpoint detection system becomes less sensitive to changes in the pattern, and thus the reliability of the endpoint system can be improved.

If it is not determined that the traces have reached the critical range of the minimum value, polishing is allowed to continue and steps 404, 406, 408 are repeated appropriately.

5 is an exemplary graph of a difference trace as a function of time illustrating thresholds. Trace 502 is a car trace, which may be already filtered and smoothed. The endpoint detection 508 is activated when the smoothed difference trace 502 reaches the threshold 504 above the minimum value 506. [

Figure 6 shows a method 600 for determining the end point of a polishing step. Prior to the polishing operation, reference spectra are generated, such as, for example, by polishing the setup substrate and measuring the spectra, or calculated from the theory using, for example, an optical model of the substrate layers. Spectra are stored in the library. However, unlike the process of FIG. 4, where unique target spectra representing the target thickness are used, the reference spectra in the library represent substrates with various different thicknesses in the outer layer. The measured spectra are then compared to the spectra in the library and one of the spectra in the library is selected as a match.

The spectra are indexed so that each spectrum from a collection of spectra representing a substrate with a particular underlayer thickness has a unique index value (spectra representing substrates with different underlayer thicknesses can be associated with the same index value). Indexing is implemented such that the spectra are measured during polishing or the index values are arranged in order in the order in which they are expected to be measured. The index value may be selected to monotonically increase as the polishing progresses, e.g., the index values may be proportional to the number of platen rotations, e.g., linearly proportional. Thus, each index number may be an integer, and the index number may indicate the expected platen rotation in which the associated spectrum is to appear. The library may be implemented in the memory of the computing device of the polishing apparatus.

The substrate from the batch of substrates is polished (step 602) and the following steps are performed during each platen revolution. One or more spectra are measured to obtain current spectra for the current platen rotation (step 604). The spectra stored in the library that best fits the current spectra are determined (step 606). The index of the library spectrum best suited to the current spectrum is determined from the library (step 608) and added to the endpoint index trace (step 610). As discussed previously, the index may be determined prior to the polishing operation and may be stored, for example, as a database associating the spectra with the index for later access. The endpoint is called when the endpoint trace reaches the index of the target spectrum (step 612).

In some embodiments, the indices matching each acquired spectrum are shown in time or platen rotation. The lines are fitted with the index numbers shown using solid line fitting. When a line is encountered, the target index defines the endpoint time or rotation.

As described above, by using a plurality of reference spectra representing substrates having lower layers of different thicknesses, the endpoint detection system becomes less sensitive to variations in the lower layers, and thus the reliability of the endpoint system can be improved.

The method that can be applied during the endpoint process is to limit it to a portion of the library that is searched for matching spectra. The library typically includes a wider range of spectra than would be obtained during polishing of the substrate. The wider range corresponds to the spectra obtained from the thicker starting outermost layer and the spectra obtained after the transient polishing. During substrate polishing, library searching is limited to a predefined range of library spectra. In some embodiments, the current rotating index N of the substrate being polished is determined. N may be determined by searching all of the library spectra. For the spectra obtained during the subsequent rotation, the library is searched within the range of degrees of freedom of N. [ That is, if the index number is found to be N during one revolution, then the range will be retrieved from (N + X) -Y to (N + X) + Y for subsequent rotations after X rotations, . For example, if, in the first polishing revolution of the substrate, the matching index is found to be 8 and the degree of freedom is selected to be 5, only the spectra corresponding to index number 9 +/- 5 It is checked for matches.

Embodiments of the present invention and all of the functional operations described herein may be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including architectural means and structural equivalents thereof, . ≪ / RTI > Embodiments of the present invention may be implemented within one or more computer program products, i. E., A data processing apparatus, e.g., a programmable processor, a computer, or a computer or a plurality of processors or computers, For example, in a machine-readable storage device or in one or more computer programs tangibly embodied in a propagated signal. A computer program (also known as a program, software, software application, or code) may be written in any form of programming language, including compiled or interpreted languages, and may be written as a stand alone program, Routine, or any other form suitable for use in a computing environment. A computer program does not necessarily correspond to a single file. The program may be stored in a file that holds other programs or data, in a single file dedicated to the problematic program, or in a plurality of organized files (e.g., one or more modules, sub-programs, Files that store portions). A computer program can be used to run on a single computer, or on multiple computers that are distributed at one site or across multiple sites and interconnected by a communication network.

The processes and logic flows described herein may be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating an output. Processes and logic flows may also be performed by special purpose logic circuitry, e.g., a field programmable gate array (FPGA) or application-specific integrated circuit (ASIC), and the device may be implemented as the special purpose logic circuit .

The above-described polishing apparatuses and methods can be applied to various polishing systems. The polishing pad, or carrier head, or both, may move to provide relative movement between the polishing surface and the substrate. For example, the platen can orbit rather than rotate. The polishing pad may be a circular (or some other shape) pad fixed to the platen. Some aspects of the endpoint detection system may be applicable to linear polishing systems, for example, a continuous or reel-to-reel belt in which the polishing pad moves linearly. The abrasive layer may be a standard (e.g., polyurethane with or without fillers) abrasive material, a flexible material, or a fixed-friction material. Terms of relative positioning are used; It should be understood that the polishing surface and the substrate may be held in a vertical direction or some other direction.

Certain embodiments of the invention have been described. Other embodiments are within the scope of the following claims. For example, the acts described in the claims may be performed in a different order and still achieve the desired results.

Claims (15)

A method for detecting an end point in a chemical mechanical polishing,
Acquiring at least one current spectrum with an in-situ optical monitoring system, the current spectrum being a spectrum of light reflected from a substrate having an outermost layer undergoing polishing and at least one underlying layer;
Comparing the current spectrum with a plurality of different reference spectra, the plurality of reference spectra representing spectra of light reflected from a reference substrate having outermost layers and lower layers, wherein the outermost layers of the reference substrates are identical The lower layers of the reference substrates having different thicknesses from one another; And
Determining whether an abrasive end point has been achieved for the substrate having the outermost layer undergoing polishing based on the comparing step
Containing
A method for detecting an end point in a chemical mechanical polishing. The method according to claim 1,
Wherein determining whether the polishing endpoint has been achieved comprises calculating differences between the current spectrum and the reference spectra.
A method for detecting an end point in a chemical mechanical polishing. 3. The method of claim 2,
Wherein determining whether the polishing endpoint has been accomplished comprises determining whether at least one of the differences has reached a threshold value.
A method for detecting an end point in a chemical mechanical polishing. The method of claim 3,
Wherein at least one of the cars is a smallest one among the cars or a median difference among the cars,
A method for detecting an end point in a chemical mechanical polishing. 3. The method of claim 2,
Wherein determining whether the polishing endpoint has been accomplished comprises activating an endpoint detection algorithm when at least one of the differences has reached a threshold value.
A method for detecting an end point in a chemical mechanical polishing. 6. The method of claim 5,
The step of determining whether the polishing endpoint has been achieved comprises generating a difference trace comprising a plurality of points, each point representing the smallest of the differences calculated during the rotation of the platen ,
A method for detecting an end point in a chemical mechanical polishing. The method according to claim 6,
Wherein the endpoint detection algorithm comprises determining whether the difference trace has reached a minimum value.
A method for detecting an end point in a chemical mechanical polishing. 8. The method of claim 7,
Wherein determining whether the difference traces has reached a minimum value comprises calculating a slope of the difference traces.
A method for detecting an end point in a chemical mechanical polishing. The method according to claim 6,
Wherein the endpoint detection algorithm comprises determining whether the difference trace has risen to a threshold above a minimum value.
A method for detecting an end point in a chemical mechanical polishing. The method according to claim 1,
≪ / RTI > further comprising obtaining a plurality of current spectra at different times,
A method for detecting an end point in a chemical mechanical polishing. 11. The method of claim 10,
Wherein the plurality of current spectra comprise a series of current spectra from a plurality of sweeps of the in-situ optical monitoring system across the substrate,
A method for detecting an end point in a chemical mechanical polishing. 11. The method of claim 10,
Wherein the plurality of current spectra comprises a plurality of current spectra from the same sweep of the in-situ optical monitoring system across the substrate,
A method for detecting an end point in a chemical mechanical polishing. 13. The method of claim 12,
Further comprising comparing the plurality of current spectra from the same sweep with the plurality of reference spectra to produce a plurality of differences between the current spectra and the reference spectra.
A method for detecting an end point in a chemical mechanical polishing. 14. The method of claim 13,
Further comprising determining the smallest of the plurality of differences and using the smallest of the plurality of differences to determine whether an abrasive end point has been achieved,
A method for detecting an end point in a chemical mechanical polishing. A computer-readable medium comprising instructions that cause a data processing device to perform operations,
The operations include,
Acquiring at least one current spectrum with an in-situ optical monitoring system, the current spectrum being a spectrum of light reflected from a substrate having an outermost layer undergoing polishing and at least one underlying layer;
Comparing the current spectrum with a plurality of different reference spectra, the plurality of reference spectra representing spectra of light reflected from a reference substrate having outermost layers and lower layers, wherein the outermost layers of the reference substrates are identical The lower layers of the reference substrates having different thicknesses from one another; And
Determining whether an abrasive end point has been achieved for the substrate having the outermost layer undergoing polishing based on the comparing operation
/ RTI >
Computer-readable storage medium.

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