JP2012508452A - End point control for chemical mechanical polishing of multiple wafers - Google Patents

Abstract

  The computer-implemented method includes a step of simultaneously polishing the polishing substrate group in the polishing apparatus. Each substrate has a polishing rate that can be individually controlled by independently variable polishing parameters. Measurement data that varies with the thickness of each of the substrate groups is acquired from each of the substrate groups during polishing with an in situ monitoring system. The predicted thickness that each substrate will have at the target time is determined based on the measurement data. By adjusting polishing parameters for the at least one substrate to adjust the polishing rate of at least one substrate, the substrate group has a thickness that is closer to the target thickness than without such adjustment. You will have in time.

Description

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

  Integrated circuits are typically formed on a substrate by sequentially depositing a conductive layer, a semiconductor layer, or an insulating layer on a silicon wafer. In one forming step, a filler layer is deposited on a non-flat surface and the filler layer is planarized. In certain applications, the filler layer is planarized until the top surface of the patterned layer is exposed. A conductive filler layer can be deposited, for example, on the patterned insulating layer to fill the trench or hole in the insulating layer. After planarization, portions of the conductive layer remaining between the raised patterns of the insulating layer form via groups, plug groups, and wiring groups that form conductive path groups between the thin film circuit groups on the substrate. In other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness remains over the non-planar surface. Further, photolithography usually requires planarization of the substrate surface.

  Chemical mechanical polishing (CMP) is one accepted planarization method. 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 to press against a rotating abrasive disc pad or belt pad. The polishing pad can be a standard pad or a fixed abrasive polishing pad. Standard pads have a highly durable rough surface, whereas fixed abrasive polishing pads have abrasive grains that are retained in a containment medium. The carrier head applies a controllable load to the substrate and presses the substrate against the polishing pad. A polishing liquid such as a slurry containing abrasive grains is usually supplied to the surface of the polishing pad.

  One solution to CMP is to use a suitable polishing rate to achieve a desired wafer profile, eg, flattened to a desired flatness or thickness, or a desired amount of material is removed. It is to realize a wafer including a substrate layer. Circuit resistance is increased by excessive polishing (too much removal) of the conductive layer or conductive film. On the other hand, an electrical short circuit occurs due to insufficient polishing of the conductive layer (too little removal). When trying to polish multiple wafers, it can be difficult to control the thickness across the entire wafer group. The amount of material removed over the entire substrate group due to variations in the initial thickness of the substrate layer, variations in the slurry composition, variations in the state of the polishing pad, variations in the relative speed between the polishing pad and the substrate, and variations in the load applied to the substrate. Variation may occur.

  In general, in one aspect, a computer-implemented method includes simultaneously polishing a plurality of substrates in a polishing apparatus. Each substrate has a polishing rate that can be individually controlled by independently variable polishing parameters. Measurement data that varies with the thickness of each of the substrate groups is acquired from each of the substrate groups during polishing with an in situ monitoring system. The predicted thickness that each substrate will have at the target time is determined based on the measurement data. By adjusting polishing parameters for the at least one substrate to adjust the polishing rate of at least one substrate, the substrate group has a thickness closer to the same thickness than the case without the adjustment at the target time. To have.

  This and other embodiments can optionally include one or more of the following feature groups. The step of determining the predicted thickness that each substrate will have at the target time may include calculating a current polishing rate. The step of obtaining measurement data can include obtaining a series of thickness measurements. The step of calculating the current polishing rate can include fitting a linear function to the series of thickness measurements, and the step of determining the predicted thickness includes when the linear function is A step of determining whether the target time is reached by extrapolation may be included.

  The step of acquiring measurement data may include the step of acquiring measurement data with an eddy current monitoring system. When using an eddy current monitoring system, polishing can be stopped once the polishing endpoint is detected by the laser monitoring system.

  The step of acquiring measurement data may include the step of acquiring measurement data with an optical monitoring system. A series of current reflected light spectra can be obtained from the substrate. Each current spectrum of the series of current spectra can be compared to a plurality of reference spectra in a reference spectrum library, and a best matching reference spectrum can be selected.

  The polishing parameter may be a carrier head pressure of the polishing apparatus, a rotation speed of the carrier head, or a rotation speed of a polishing surface plate of the polishing apparatus.

  The step of adjusting the polishing parameter may include a step of selecting a reference substrate and a step of adjusting a polishing parameter of a different substrate. The step of adjusting the polishing parameters of the different substrates includes adjusting the polishing rate of the different substrates so that the different substrates have approximately the expected thickness of the reference substrate at the target time. it can. The step of selecting a reference substrate can include a step of selecting a predetermined substrate. The step of selecting a reference substrate can include selecting a substrate having the thinnest predicted thickness or the thickest predicted thickness.

  The step of adjusting the polishing parameters may include calculating an average thickness from an estimated thickness for each substrate. The step of adjusting the polishing parameter may include adjusting a polishing parameter of the substrate group such that the substrate group has a substantially average thickness at the target time. The substrate group can be polished with the same polishing platen.

  In other aspects, a polishing system and a computer program product tangibly embodied in a computer readable medium are provided to perform these methods.

  Certain embodiments may have one or more of the following groups of benefits. When all of the wafer groups on the same polishing surface plate reach the end point almost at the same time, such as scratches caused by the timing of rinsing the substrate with water being too early, or the substrate cannot be properly rinsed. Defects such as corrosion can be prevented. By making the polishing time equal over a large number of substrates, the throughput can also be improved.

  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 invention will be apparent from the detailed description, drawings, and claims.

FIG. 1 shows an example of a polishing apparatus having two polishing heads. FIG. 2A is a flow diagram of an exemplary process for adjusting the polishing rate of one of the plurality of substrates so that the plurality of substrates reach a target thickness substantially simultaneously. FIG. 2B is a flow diagram of an exemplary process for adjusting the polishing rate of one of the plurality of substrates so that the plurality of substrates have substantially the same thickness at a target time. FIG. 3 shows an exemplary graph showing how the polishing progress measured with thickness in the process of adjusting the polishing rate to reach the target time or thickness changes over time. FIG. 4 shows an exemplary graph representing the degree of polishing progress as measured by a spectroscopic index in the process of adjusting the polishing rate to reach a target time or target index. FIG. 5 illustrates two signal variations that result from a process that corresponds to two substrates being polished on the same polishing platen and that adjusts the polishing rate for both substrates.

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

  If multiple substrates are being polished at the same time, for example on the same polishing pad, the polishing rate variation between these substrates can cause these substrates to reach their target thicknesses at different times. is there. On the other hand, if polishing stops at the same time for a group of substrates, some substrates do not have the desired thickness. On the other hand, if polishing on a group of substrates stops at different times, some substrates may have defects and the polishing apparatus operates at a lower throughput.

  By determining the polishing rate for each substrate based on in-situ measurements, an estimated end point time corresponding to the target thickness or an estimated thickness corresponding to the target end point time can be determined for each substrate, and at least one substrate The polishing rate can be adjusted so that these substrates are in a more approximate end point state. “A more approximate end point state” means that the substrate groups reach the target thicknesses of these substrates at a time closer to that at the same time than when such adjustment is not performed, or polishing the substrate groups at the same time. This means that when stopped, these substrates will have a thickness closer to the same thickness than without such adjustment.

  FIG. 1 shows an example of the polishing apparatus 100. The polishing apparatus 100 includes a rotatable disk-shaped polishing surface plate 120, and a polishing pad 110 is installed on the disk-shaped polishing surface plate 120. The polishing platen can be operated to rotate about the axis 125. For example, the motor 121 can rotate the polishing platen 120 by rotating the drive shaft 142.

  The polishing apparatus 100 includes a composite slurry / rinse supply arm 122. During polishing, the arm 122 can operate to supply a polishing liquid 118, such as a slurry, to the polishing pad 10.

  In this embodiment, the polishing apparatus 100 includes two carrier heads 130. Each carrier head 130 is operable to press and hold the substrate 115 against the polishing pad 110. Each carrier head 130 can individually control a set of polishing parameters, such as pressure, associated with each respective substrate.

  Each carrier head 130 is suspended from the support structure 171 and connected to the carrier head rotation motor via the drive shaft, so that the carrier head can rotate about the axis 161. Furthermore, each carrier head 130 can swing laterally. In the operating state, the polishing surface plate rotates about the center axis 125 of the polishing surface plate, and each carrier head rotates about the center axis 161 of the carrier head and crosses across the upper surface of the polishing pad. Translate in the direction.

  Although only two carrier heads 130 are shown, more carrier heads can be provided to hold additional substrate groups so that the surface area of the polishing pad 110 can be used efficiently. Accordingly, the number of carrier head assemblies that are adapted to hold the substrates and perform the polishing process simultaneously can be determined based at least in part on the surface area of the polishing pad 110. Although only one slurry / rinse supply arm 122 is shown, additional groups of nozzles such as one or more dedicated slurry arms per carrier head may be used.

  The polishing apparatus further includes an in-situ monitoring system 140 that uses the in-situ monitoring system 140 to determine whether the polishing rate should be adjusted, as will be described below. Alternatively, the adjustment amount of the polishing rate can be determined. In situ monitoring system 140 may include an optical monitoring system, such as a laser monitoring system or a spectroscopy monitoring system, or an eddy current monitoring system.

  In one embodiment, the monitoring system is an optical monitoring system. A light transmissive opening 155 that passes through the polishing pad is provided by incorporating an aperture (ie, a hole through the pad) or a solid window. The optical monitoring system may include one or more components of the following group of components (not shown): a light source, a photodetector, and circuitry for transmitting and receiving signals between the light source and the photodetector. it can.

  The light then strikes the substrate 115 from the light source through the light transmissive aperture 155 of the polishing pad 110, is reflected by the substrate 115, and can travel back through the light transmissive aperture 155 to reach the photodetector. . For example, the detector output can be a digital electronic signal that passes through a rotating coupler, such as a slip ring, in the drive shaft 142 to a controller 145, such as a computer in an optical monitoring system. Reach. Similarly, the power source of the light source can be turned on or off in response to a control command included in a digital electronic signal that reaches the monitoring system from the controller through the rotary coupler.

  The light source can be operated to emit white light. In one implementation, the emitted white light includes light having a wavelength of 200 to 800 nanometers. A suitable light source is a xenon lamp or a xenon mercury lamp.

  The photodetector can be a spectrometer. A spectrometer is an optical measuring instrument that measures the intensity of light in part of the electromagnetic spectrum. A suitable spectrometer is a diffraction grating spectrometer. A typical output of a spectrometer is the intensity of light as a function of wavelength (or frequency).

  The light source and photodetector can be connected to a computing device, eg, a controller, that controls the operation of the light source and photodetector and receives signals from the light source and photodetector. Can be operated to. The computing device can include a microprocessor, such as a programmable computer, located in the vicinity of the polishing apparatus. With respect to control, the computing device can operate the light source in synchronization with the rotation of the polishing platen 120, for example.

  In some embodiments, the sensors of the in situ monitoring system are installed in the polishing platen 120 and rotate with the polishing platen 120. In this case, the movement of the polishing platen causes the sensor to scan across the substrate. In other embodiments, particularly for optical monitoring systems, the sensors of the in situ monitoring system are fixed and positioned below the substrate. In this case, the in-situ monitoring system performs the measurement every time the opening passing through the polishing platen and the sensor are aligned, and light can be transmitted and applied to the substrate.

  In the case of an optical monitoring system, as the polishing platen rotates, the computing device emits a series of flashes that start immediately before the substrate 115 passes over the in situ monitoring module and ends immediately after it passes or polishing. A series of flashes that are started immediately before the opening in the surface plate and the sensor of the in-situ monitoring module are aligned and finished immediately after the alignment can be emitted to the light source. Alternatively, the computing device is started just before the substrate 115 passes over the in situ monitoring module and ends immediately after passing, or the opening in the polishing platen and the sensor of the in situ monitoring module are aligned. The light can be continuously emitted to the light source so as to start immediately before the start and end immediately after the alignment. In either case, spectral measurements can be generated at the sampling frequency by integrating the signal from the detector over the sampling period. When the sensor is installed in the polishing surface plate, each time one of the substrate groups 115 passes over the monitoring module, the alignment position of the substrate with the monitoring module is the alignment position at the previous passage. May be different. When one revolution of the polishing platen is completed, spectra are acquired from different radial positions on the substrate. That is, some spectra are acquired from a plurality of locations closer to the center of the substrate, and other spectra are acquired from a plurality of locations closer to the periphery. Further, when the polishing platen is rotated many times, a series of spectra can be acquired over time.

  In the activated state, the computing device may receive a signal carrying information representing the spectrum of light received by the photodetector, eg, in response to a particular flash of the light source or a detector time frame. Thus, this spectrum is a spectrum measured in situ during polishing.

  Without being bound by any particular theory, the spectrum of light reflected by the substrate 115 changes due to the change in thickness of the outermost layer as polishing proceeds, resulting in a series of time-varying spectra. It becomes. Furthermore, a specific spectrum is represented by a specific thickness of the laminate.

  In some embodiments, the computing device includes a comparison module that generates a series of best match reference spectra by comparing the measured spectrum with a number of reference spectra and determines a goodness of fit of the series of best match reference spectra. . As used herein, a reference spectrum is a predetermined spectrum that is generated before a substrate is polished. The reference spectrum can have a predetermined association with one value of substrate properties, such as the thickness of the outermost layer, i.e. an association defined before the polishing process. Alternatively or additionally, the reference spectrum has a predetermined association with a value representing one time of the polishing process that the spectrum is expected to appear assuming that the actual polishing rate follows the predicted polishing rate. be able to.

  The reference spectrum can be generated experimentally, for example, by measuring the spectrum from a test substrate having a known layer thickness, or can be generated based on theory. For example, to determine the reference spectrum, the spectrum of a “conditioning” substrate having the same pattern as the product substrate can be measured at a measurement station before polishing. Substrate properties, such as the thickness of the outermost layer, can also be measured at the same measurement station or at different measurement stations before polishing. Next, the condition setting substrate is polished while collecting the spectrum. For each spectrum, a value representing the time in the polishing process for which the spectrum was collected is recorded. For example, the value can be the elapsed time or the number of rotations of the polishing surface plate. The substrate is overpolished, i.e., polished beyond the desired thickness, so that the spectrum of light reflected by the substrate when it reaches the target thickness can be obtained. Thus, the spectrum and properties of the outermost layer of the conditioning substrate, such as thickness, can be measured at the measurement station after polishing.

  In addition to being determined experimentally, some or all of these reference spectra can be calculated based on theory, for example using an optical model of the substrate layer. For example, an optical model can be used to calculate a spectrum corresponding to a predetermined outer layer thickness D. A value representing the time in the polishing process for which the spectrum is collected can be calculated, for example, by assuming that the outer layer is removed at a uniform polishing rate. For example, the time Ts corresponding to a specific spectrum can be easily calculated by setting the initial thickness as D0 and the uniform polishing rate as R (Ts = (D0−D) / R). As another example, measurement time T1 and measurement time corresponding to pre-polishing thickness D1 and post-polishing thickness D2 (or other thickness measured at a measurement station) based on thickness D used in the optical model Linear interpolation with T2 can be performed (Ts = T2-T1 * (D1-D) / (D1-D2)).

  As used herein, a reference spectrum library is a set of reference spectra that represents a group of substrates that commonly have one characteristic. However, the properties commonly held in a single library can vary across multiple reference spectral libraries. For example, two different libraries can include reference spectra that represent groups of substrates having two different substrate thicknesses.

  Spectra corresponding to different libraries are generated by polishing a number of “conditioning” substrates with different substrate characteristics (eg, underlayer thickness or layer composition) and collecting the spectra as described above. Spectra obtained from one conditioning substrate can provide a first library, and spectra obtained from another substrate having a different underlayer thickness can provide a second library. . Alternatively, or in addition, reference spectra corresponding to different libraries can be calculated based on theory, for example, the spectrum corresponding to the first library uses an optical model in which the underlying layer has a first thickness. The spectra corresponding to the second library can be calculated using an optical model with a different thickness of the underlayer.

  In some embodiments, one index value is assigned to each reference spectrum. This indicator may be a value representing the time in the polishing process where a reference spectrum is expected to be observed. These spectra can be indexed such that each spectrum in a particular library has a unique index value. The indexing can be performed such that these index values are time-series in the order in which these spectra are measured. One index value can be selected to monotonically change, eg increase or decrease, as polishing proceeds. Specifically, the index values of these reference spectra can be selected such that these index values form a linear function of time or polishing platen speed. For example, these index values can be proportional to the rotational speed of the polishing platen. Thus, each index number can be a total number, and the index number can represent the predicted polishing platen rotation where the associated spectrum will appear.

  These reference spectra and the indices associated with these spectra can be stored in a library. The library can be implemented in the memory of the computing device of the polishing apparatus.

  During polishing, index changes can be displayed corresponding to each library. Each index change includes an index column that forms the change, and each specific index in the column is associated with a specific measured spectrum. For a given library index change, the particular index contained in the column is generated by selecting from the given library the index of the reference spectrum that best matches the particular measured spectrum. In this way, each current spectrum of the series of current spectra is compared with a plurality of reference spectra in the reference spectrum library to produce a series of best matching reference spectra. In more general terms, for each current spectrum, a reference spectrum that best matches the current spectrum is determined.

  If there are a large number of current spectra, the best match can be determined between each of these current spectra and each of the reference spectral groups of a given library. Each selected current spectrum is compared with each reference spectrum. For example, if the current spectrum is e, f, and g, and the reference spectrum is E, F, and G, then the coincidence coefficient is the next combination of the current spectrum and the reference spectrum: e and E, e and F , E and G, f and E, f and F, f and G, g and E, g and F, and g and G, respectively. The one with the best match coefficient, for example the smallest, determines the reference spectrum and hence the index.

  In another embodiment, the monitoring system is an eddy current monitoring system. The vortex coil monitoring system can include one or more of the following group of components (not shown): a drive coil that generates an oscillating magnetic field, the drive coil of the metal layer on the semiconductor wafer. It can be combined with a conductive region of interest on the substrate 115, such as a portion. The drive coil is wound around a core (not shown), which can be formed of a ferrite material such as MnZn ferrite or NiZn ferrite.

  Due to the oscillating magnetic field, eddy currents are generated locally in the conductive region of the substrate 115. This eddy current causes the conductive region of the substrate to function as an impedance source connected in parallel with a detection coil and a capacitor (not shown). As the thickness of the conductive area of the substrate changes, the impedance changes and the Q value of the system changes. By detecting a change in the Q value, the eddy current detection mechanism can detect a change in the intensity of the eddy current, and thus a change in the thickness of the conductive region. Thus, an eddy current system can be used to determine a group of parameters of the conductive region, such as the thickness of the conductive region, or an eddy current system can be used to determine a group of related parameters, such as the polishing endpoint. it can. Note that while the thickness of a particular conductive region is described above, the relative position of the core and conductive layer may be varied to obtain thickness information for a number of different conductive regions. Similarly, although a specific substrate thickness is disclosed, multiple substrates located on the same polishing platen may be monitored.

  In some implementations, the change in Q value can be determined by measuring the amplitude of the eddy current as a function of time for a constant drive frequency and amplitude. The eddy current signal can be rectified using a rectifier and the amplitude can be monitored via the output. Alternatively, the change in Q value can be determined by measuring the phase of the eddy current as a function of time.

  The monitoring system can include other sensor elements including, for example, lasers, light emitting diodes, and photodetectors.

  In some implementations, measurement data collected by the monitoring system, such as current spectral data or eddy current data, can be collected from multiple substrates. Referring to FIGS. 2A and 2B, as described above, multiple substrates are simultaneously polished with the same polishing pad in a polishing apparatus. During this polishing process, each substrate has a polishing rate for that substrate that can be controlled independently of other substrates by an independently variable polishing parameter, for example, by pressure applied from a carrier head holding a particular substrate (step 201). ). During the polishing process, these substrates are monitored as described above (step 202). In one embodiment, as shown in FIG. 2A, an estimated time that each substrate will reach a target thickness is determined (step 203). The polishing parameters of at least one substrate are adjusted to adjust the polishing rate of the substrate so that the plurality of substrates reach the target thickness substantially simultaneously (step 204). In another embodiment, as shown in FIG. 2B, the predicted thickness that each substrate will have at the target time is determined (step 205). By adjusting the polishing parameters of at least one substrate and adjusting the polishing rate of the substrate, the plurality of substrates have substantially the same thickness at the target time (step 206).

  As shown in FIG. 3, the measured thickness (represented by points 301) collected, for example, in an eddy current monitoring system can be plotted for each substrate against time. For each substrate, a known order polynomial function, eg, a linear function (ie, straight line 302), is fitted to the thickness measurements collected for that substrate, eg, by performing a positive linear fitting.

  To determine the predicted time that one substrate will reach the target thickness, the intersection of the line 301 and the target thickness can be calculated. The end point time depends on the result of fitting the function to the collected thickness measurement value, the polishing rate PR, the initial thickness ST before polishing the substrate, and the target thickness TT (the polishing rate PR and the initial thickness ST). Whereas the target thickness can be calculated by the user based on (set and stored before the polishing process). The end point time can be calculated as a simple linear interpolation value assuming that the polishing rate is constant throughout the polishing process, eg, the end point time Et = (ST−TT) / PR.

  Furthermore, the predicted end point thickness is defined by the location where the straight line intersects the target time at which polishing will stop. Thus, by using the rate of change of thickness of each substrate and extrapolating the thickness, it is possible to determine the thickness that will be achieved at the predicted endpoint time of the associated substrate.

  As shown in FIG. 3, if no adjustment is made for any polishing rate in the group of substrates at the current time, each substrate may have a different end point time (this state depends on this state). Each substrate may have a different thickness if the endpoints are forced simultaneously for all substrates, as defects may occur and throughput may be reduced. Here, for example, the substrate A will reach the end point with a thickness greater than that of the substrate B. Similarly, if both substrates are polished to the same target thickness, substrate A will require an endpoint time that is slower than the endpoint time of substrate B.

  As shown in FIG. 3, if the desired thickness is reached for different substrates at different times, the polishing rate can be adjusted to increase or decrease so that these substrates are adjusted in this way. At the same time, for example, reaching at the same time, or at the same thickness, for example, at a thickness closer to the target thickness, for example, at about the same thickness. You will have in time.

  Therefore, for example, in FIG. 3, starting from time T1, the group of polishing parameters for the substrate A is changed so that the polishing rate for the substrate A is increased and the polishing rate for the substrate B is decreased. The thickness is reached approximately at the same time (or if the polishing of both substrates is stopped simultaneously, the thickness is reached approximately the same). If the predicted endpoint time indicates that these substrates reach the target thickness almost simultaneously, no adjustment is necessary. Substantially simultaneous refers to within 2% of the total polishing time, such as within 1%, such as within 0.5%, or within 5 seconds, such as within 2 seconds, such as within 1.5 seconds. Similarly, if the predicted endpoint thickness indicates that these substrates have approximately the same thickness at the target time, no adjustment is necessary. The substantially same thickness means that the difference in thickness is less than 200 angstroms.

  The polishing rate can be adjusted for different substrates to equalize the polishing time. For example, a reference substrate is selected and processing parameter groups for all other substrate groups are adjusted so that all of these substrates reach the end point in approximately the estimated time of the reference substrate. The reference substrate can be, for example, a predetermined substrate, a substrate having the earliest or latest predicted time of a group of substrates, or a substrate having a desired predicted endpoint. The earliest time is equivalent to the thinnest substrate when polishing is stopped simultaneously. Similarly, the slowest time is equivalent to the thickest substrate when polishing is stopped simultaneously. In another implementation, the polishing parameters can be adjusted so that multiple substrates reach the target thickness at the approximate average predicted time of the substrate group, or reach the target time at the approximate average predicted thickness of the substrate group. . In yet another implementation, the target time is simply a predetermined time, eg, about 40 seconds, or a predetermined thickness, eg, about 1500-2000 angstroms. The user can select a method for selecting the target time or target thickness by using the user interface before polishing, for example, the computer can select one of a plurality of methods for selecting the target time. Receive input from the user to select.

The polishing rate can be adjusted, for example, by increasing or decreasing the pressure of the corresponding carrier head. The change in polishing rate can be assumed to be directly proportional to the change in pressure, for example, it can be assumed to follow a simple Prestonian model. For example, if the substrate A reaches the target thickness at time T _A and the system has set the target time T _T , the carrier head pressure before time T ₁ is multiplied by T _T / T _A and time T carrier head pressure after ₁ can be supplied. In addition, it is possible to develop a substrate polishing control model that takes into account the effects of polishing platen or head rotation speed, secondary effects of different head pressure synthesis, polishing temperature, slurry flow rate, or other parameters that affect polishing rate. it can. At the next time during the polishing process, these rates can again be adjusted as needed.

  As shown in FIG. 4, the index data collected by the optical monitoring system can also be plotted against time, and by making adjustments to one or more substrates, the polishing of all of these substrates can be simplified. It can be finished at the same indicator or time. This system operates similarly to the system of FIG. 3, but the calculation is performed using index values rather than thickness values.

  Referring to FIG. 5, if a particular profile is desired, here a signal level of 62%, the polishing rate as indicated by the signal change can be monitored. If the first substrate change 501 and the second substrate change 502 indicate that these two substrates do not reach the end point at the same expected time, the polishing rate of one or both heads can be adjusted. .

  The process of obtaining the predicted time at which the substrate group will reach the target thickness and adjusting the polishing rate group can be repeated many times during the polishing process, for example, every 30-60 seconds. For example, in FIG. 5, the end point group is predicted at four points during polishing, and the polishing pressure of the head having a low rotation speed is increased to increase the polishing speed. Here, the pressure on the first substrate indicated by change 501 is multiplied by a magnification of 1.25 at the time of 31 seconds (510), and multiplied by a magnification of 1.02 at the time of 51 seconds (511). Next, the pressure on the second substrate indicated by change 502 was multiplied by a magnification of 1.20 at the time of 70 seconds (512) and multiplied by a magnification of 1.27 at the time of 91 seconds (513). In FIG. 5, the final endpoints of the two substrates were separated by 0.4 seconds.

  During the polishing process, the polishing rate can be changed only a few times, for example, four times, three times, twice or once. Adjustments can be made at a point near the beginning of the polishing process, at an intermediate point, or at a point toward the end point.

  The method used to adjust the end point can vary based on the type of polishing applied. When polishing copper bulk, a single eddy current monitoring system can be used. When copper removal CMP is performed on a single polishing platen for a large number of wafers, a single eddy current monitoring system is first used to ensure that all of the substrates reach the first breakthrough simultaneously. be able to. The eddy current monitoring system can then be switched to a laser monitoring system to remove these wafers and provide overpolishing. An optical monitoring system can be used when performing barrier and dielectric CMP on a single polishing platen for multiple wafers.

  Embodiments of the invention and all of the functional operations described herein are implemented in digital electronic circuitry, or in computer software, firmware, or disclosed in the present specification. It can be implemented in hardware that includes a physical equivalent, or a combination of these elements. Embodiments of the present invention can be implemented as one or more computer program products, ie, one or more computer programs, which are tangibly embodied in a machine-readable storage medium for data processing. It is executed or controlled by an apparatus, such as a programmable processor, computer, or multiprocessor or multicomputer. As an alternative or in addition, the computer program may be encoded on an information carrier, for example a transmission signal. A computer program (also referred to as a program, software, software application, or code) can be written in any form of programming language, including a compiled language or an interpreted language, and the computer program is a stand-alone program Or any form including module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file. A program is a file that stores other programs or data, a single file dedicated to the program, or multiple adjustment files (eg, one or more modules, subprograms, or files that store portions of code) ) Can be stored in the portion stored. A computer program is implemented to run on one computer or on multiple computers at one site, or distributed on multiple sites and run on multiple computers interconnected in a communications network Can do.

  The processes and logic flows described herein may be performed by one or more programmable processors, which execute one or more computer programs to perform multiple functions and input data. Perform by manipulating and generating output. The process and logic flow can also be performed by an application specific logic circuit, such as an FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit), and the device can also be an application specific logic circuit, such as an FPGA (Field Programmable). It can be implemented as a gate array) or an ASIC (application specific integrated circuit).

  The polishing apparatus and method described above can be applied in various polishing systems. Either the polishing pad or the carrier head, or both, can move to achieve relative movement between the polishing cloth surface and the substrate. For example, the polishing surface plate may be moved around instead of rotating. The polishing pad can be a circular (or some other shape) pad that is rigidly secured to the polishing platen. Some forms of endpoint detection system can be applied to a linear polishing system, in which case, for example, the polishing pad is a linear belt or a continuous reel-to-reel belt. The abrasive layer can be a standard (eg, polyurethane with or without filler) abrasive material, a soft material, or an abrasive fixed abrasive material. It should be understood that the condition of “relative positioning” is used; the polishing cloth surface and the substrate can be held in a vertical position or in some other position.

  A particular embodiment of the present invention has been described. Other embodiments are within the scope of the following claims.

Claims (15)

Polishing a plurality of substrates simultaneously in a polishing apparatus, wherein each substrate has a polishing rate that is individually controllable by independently variable polishing parameters;
Acquiring measurement data from each of the plurality of substrates during polishing with an in-situ monitoring system, wherein the measurement data varies with the thickness of each of the plurality of substrates;
Based on the measurement data, the predicted thickness that each substrate of the plurality of substrates has at the target time, or the predicted time for each substrate of the plurality of substrates, the substrate reaching the target thickness Obtaining a predicted time to become;
Adjusting polishing parameters for the at least one substrate to adjust the polishing rate of at least one substrate, whereby the plurality of substrates have the same thickness than without such adjustment. Adjusting to have a near thickness at the target time, or to allow the plurality of substrates to reach the target thickness at a time that is closer together than if no such adjustment is made; ,
A computer-implemented method comprising:   Obtaining a predicted thickness that each of the plurality of substrates will have at a target time based on the measurement data; and polishing parameters for the at least one substrate to adjust the polishing rate of at least one substrate. 2. The method of claim 1, further comprising adjusting the plurality of substrates to have a thickness at the target time that is closer to the same thickness than without such adjustment. Computer execution method.   Based on the measurement data, determining a predicted time for each of the plurality of substrates, the predicted time at which the substrate reaches a target thickness, and adjusting the polishing rate of at least one substrate Adjusting the polishing parameters for the at least one substrate so that the plurality of substrates reach the target thickness at a timing that is closer at the same time than without such adjustment. The computer-implemented method according to claim 1.   The step of determining the predicted thickness that each substrate will have at a target time or the predicted time that each substrate will reach the target thickness comprises calculating a current polishing rate. 2. The computer execution method according to 1.   The computer-implemented method of claim 4, wherein obtaining the measurement data includes obtaining a series of thickness measurements.   The computer-implemented method of claim 5, wherein the step of calculating a current polishing rate includes fitting a linear function to the series of thickness measurements.   The computer-implemented method of claim 1, wherein obtaining the measurement data comprises obtaining a series of current reflected light spectra from the substrate with an optical monitoring system.   The step of obtaining measurement data further includes comparing each current spectrum of the series of current spectra to a plurality of reference spectra in a reference spectrum library and selecting a best matching reference spectrum. The computer-implemented method according to claim 7.   The computer-implemented method according to claim 1, wherein the polishing parameter is a pressure of a carrier head of the polishing apparatus.   2. The step of adjusting the polishing parameter includes: selecting a reference substrate from the plurality of substrates; and adjusting the polishing parameter for a different substrate of the plurality of substrates. Computer execution method.   The step of adjusting the polishing parameters of the different substrates causes the different substrates to have approximately the expected thickness of the reference substrate at the target time by adjusting the polishing rate of the different substrates. The computer-implemented method of claim 10, wherein the different substrate reaches the target thickness at approximately the expected time of the reference substrate.   The method of claim 11, wherein the step of selecting a reference substrate includes the step of selecting a substrate having a thinnest thickness or a thickest predicted thickness of the plurality of substrates from the plurality of substrates. The computer execution method as described.   The step of adjusting the polishing parameter includes calculating an average thickness from the predicted thickness for each substrate of the plurality of substrates, or calculating an average time from an estimated time for each substrate of the plurality of substrates. The computer-implemented method of claim 1, comprising: A computer program product that is tangibly embodied in a computer-readable storage medium, said computer program product comprising a set of instructions by which a processor:
Causing the polishing apparatus to polish a plurality of substrates simultaneously with each substrate having a polishing rate that can be individually controlled by independently variable polishing parameters;
Measurement data is received from an in situ monitoring system during polishing from each of the plurality of substrates, the measurement data changing with the thickness of each of the plurality of substrates;
Based on the measurement data, the predicted thickness that each substrate of the plurality of substrates has at the target time, or the predicted time for each substrate of the plurality of substrates, the substrate reaching the target thickness Find the expected time to become; and
By adjusting polishing parameters for the at least one substrate to adjust the polishing rate of at least one substrate, the plurality of substrates have a thickness that is closer to the same thickness than without such adjustment. Having at a target time, or allowing the plurality of substrates to reach the target thickness at a time that is closer together than if no such adjustment is made,
Computer program product. Polishing device:
A plurality of carrier heads that press and hold a plurality of substrates against the polishing surface, each carrier head having individually controllable pressures acting on the substrates held by the carrier heads;
An in situ monitoring system for generating measurement data from each of the plurality of substrates during polishing, wherein the measurement data varies with the thickness of the substrate to be measured;
A controller, the controller comprising:
Causing the polishing apparatus to polish the plurality of substrates simultaneously;
Receiving the measurement data;
Based on the measurement data, the predicted thickness that each substrate of the plurality of substrates has at the target time, or the predicted time for each substrate of the plurality of substrates, the substrate reaching the target thickness Find the estimated time to become
By adjusting polishing parameters for the at least one substrate to adjust the polishing rate of at least one substrate, the plurality of substrates have a thickness that is closer to the same thickness than without such adjustment. Configured to have a target time, or to allow the plurality of substrates to reach the target thickness at a timing that is closer at the same time than without such adjustment.
Polishing equipment.

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