Control of head sweep

Abstract

Systems and methods for determining values for a plurality of control parameters to minimize a difference between a target removal profile and an expected removal profile, the plurality of control parameters representing at least a first duration and a second duration and cause the carrier head to, for the first duration, moving the substrate laterally across the polishing pad such that the central region and the edge region of the substrate are positioned over a polishing surface of the polishing pad, and for the second duration, hold the substrate in a substantially laterally fixed position such that the central region of the substrate is positioned over the polishing surface of the polishing pad and the at least a portion of the edge region of the substrate is positioned over a polishing control groove of the polishing pad.

Description

[0001] Attorney Docket No. 44023976W001;05542-1627W01

[0002] CONTROL OF HEAD SWEEP

[0003] TECHNICAL FIELD

[0004] [1] This disclosure relates to chemical mechanical polishing, and in particular to controlling carrier head sweep.

[0005] BACKGROUND

[0006] [2] An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer.

[0007] For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. A conductive filler layer, for example, can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness is left over the non-planar surface. In addition, planarization of the substrate surface is usually required for photolithography.

[0008] [3] Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. An abrasive polishing slurry is typically supplied to the surface of the polishing pad.

[0009] [4] One issue in polishing is non-uniformity in the polishing rate across the substrate. For example, the edge region of a substrate can polish at a higher rate relative to the central region of the substrate.

[0010] SUMMARY

[0011] [5] In general, an aspect disclosed herein is a chemical mechanical polishing apparatus including a platen to support a polishing pad, the polishing pad having an annular polishing control groove at a radial distance from a center of the polishing pad; a carrier head to hold a Attorney Docket No. 44023976W001;05542-1627W01 surface of a substrate against the polishing pad; a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate; and a controller configured to cause the carrier head to determine values for a plurality of control parameters to minimize a difference between a target removal profile and an expected removal profile, the plurality of control parameters representing at least: a first duration such that a central region of the substrate and an edge region of the substrate are positioned over a polishing surface of the polishing pad. and a second duration such that the central region of the substrate is positioned over the polishing surface of the polishing pad and at least a portion of the edge region of the substrate is positioned over the annular polishing control groove, and cause the carrier head to, for the first duration, moving the substrate laterally across the polishing pad such that the central region and the edge region of the substrate are positioned over a polishing surface of the polishing pad, and for the second duration, hold the substrate in a substantially laterally fixed position such that the central region of the substrate is positioned over the polishing surface of the polishing pad and the at least a portion of the edge region of the substrate is positioned over a polishing control groove of the polishing pad..

[0012] [6] Examples may include one or more of the following features. A relationship between the plurality of control parameters and a removal rate may be stored in a data structure representing a first matrix which includes a plurality of columns including a column for a polishing rate of the polishing surface and a row for the edge region on the substrate represented in the expected removal profile, and where the controller may be configured to, as part of selection of the values, calculate the expected removal profile by multiplying the first matrix by a second matrix. The polishing pad further may include slurry supply grooves. The polishing pad can have a single annular polishing control groove. The polishing pad can have exactly two annular polishing control grooves, each of the two annular polishing control grooves being wider than a plurality of slurry supply grooves in the polishing pad. The annular polishing control groove may be near an edge of the polishing pad. The plurality of control parameters may represent a plurality of a projected future pressure changes over time for the edge region, the central region, or both.

[0013] [7] In general, an aspect disclosed herein is a chemical mechanical polishing apparatus including a platen to support a polishing pad, the polishing pad having an annular polishing control groove at a radial distance from a center of the polishing pad; a carrier head to hold a surface of a substrate against the polishing pad; a motor to control a lateral position of the carrier head on the polishing pad; and a controller configured to: cause the motor to sweep Attorney Docket No. 44023976W001;05542-1627W01 the carrier head across the polishing pad in accord with a sweep profile, and select values for a plurality of control parameters to minimize a difference between a target removal profile and an expected removal profile for each of a central region and an edge region of a face of the substrate, the plurality of control parameters including a plurality of dwell time parameters with each respective dwell time parameter of the plurality of dwell time parameters representing an amount of time for each of the central region and a portion of the edge region to spend over a different respective zone on the polishing pad, where at least one zone of the polishing pad may include the annular polishing control groove..

[0014] [8] Examples may include one or more of the following features. A relationship between the plurality of control parameters and a removal rate may be stored in a data structure representing a first matrix which includes a plurality of columns including a column for each dwell time parameter and a row for each position on the substrate represented in the expected removal profile, and where the controller may be configured to, as part of selection of the values, calculate the expected removal profile by multiplying the first matrix by a second matrix representing control parameter values. To select values, the controller may be configured to apply a minimizing algorithm to reduce a difference between an expected thickness profile and a target thickness profile, where applying the minimizing algorithm includes iteratively calculating the expected removal profile using different values for each dwell time parameter. The controller may be configured to calculate a sweep profile from values for the plurality of dwell time parameters. The controller may be configured to set the sweep profile with a respective speed for each respective annular zone of a plurality of annular zones on the platen. The controller may be configured to set the respective speed for each respective annular zone of the plurality of annular zones as a constant value within the respective zone. Values for the plurality of dwell time parameters are in units of a fraction of total time. The controller may be configured to calculate a sweep speed for each respective annular zone of the plurality of annular zones as inversely proportional to the value of the dwell time parameter for the zone.

[0015] [9] In general, an aspect disclosed herein is a method for controlling a polishing system. The method includes receiving from an in-situ monitoring system, for each region of a plurality of regions on a substrate being processed, a sequence of characterizing values for the region; for each region, determining a polishing rate for the region; determining that the polishing rate of an edge region is greater than a target polishing rate; and positioning the edge region of the substrate over a polishing control groove such that the polishing rate of the edge region is reduced. Attorney Docket No. 44023976W001;05542-1627W01

[0016]

[0010] Examples may include one or more of the following features. The method may include calculating, before positioning, an adjustment for at least one processing parameter, where calculation of the adjustment includes minimizing, for each region i) a difference between a current characterizing value or an expected characterizing value at an expected endpoint time and a target characterizing value for the region, and ii) a plurality' of proj ected future dwell times for the region and / or a plurality of differences between projected future dwell times and baseline dwell times for the region. Calculation of the adjustment includes minimizing, for each region, a difference between the pressure of the region and an average pressure in the carrier head. The characterizing value is a thickness value of an overlying layer on the substrate. Calculation of the adjustment may include minimizing a cost function. The plurality of regions may include at least a central region and an edge region on the substrate.

[0017]

[0011] In general, an aspect disclosed herein is a computer program product for controlling a semiconductor processing system, the computer program product residing on a non-transitory computer readable medium, the computer program product comprising instructions for causing one or more computers to: receive from an in-situ monitoring system, for each region of a plurality of regions on a substrate being processed, a sequence of characterizing values for the region; for each region, determine a polishing rate for the region; determine that the polishing rate of an edge region may be greater than a target polishing rate; and position the edge region of the substrate over a polishing control groove such that the polishing rate of the edge region may be reduced.

[0018]

[0012] Advantages of implementations can include one or more of the following. Provision of an additional “control knob'’ that affects the polishing rate across the substrate can increase flexibility’ of in selection of other control parameters, e.g., the carrier head chamber pressures. Polishing uniformity can be improved, both within wafer and from wafer-to-wafer.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020]

[0013] FIG. 1 is a schematic cross-sectional view of an example chemical mechanical polishing system with a polishing pad having a groove.

[0021]

[0014] FIG. 2 is a schematic cross-sectional view of an example polishing pad having both slurry’ supply grooves and a polishing control groove.

[0022]

[0015] FIG. 3 is a schematic top view of the polishing pad of FIG. 2.

[0023]

[0016] FIG. 4A illustrates a schematic top-down view of multiple annular zones on an example polishing pad for setting dyvell times. Attorney Docket No. 44023976W001;05542-1627W01

[0024]

[0017] FIG. 4B illustrates a schematic graph of an example carrier head sweep profile.

[0025]

[0018] FIG. 5 is a flow chart diagram showing a method for controlling a polishing system.

[0026]

[0019] To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures.

[0027] DETAILED DESCRIPTION

[0028]

[0020] As noted above, when a substrate is polished by a polishing pad, the edge region of the substrate can polish at a higher rate than a central region of the substrate, resulting in a non-uniformly polished substrate. However, positioning, and holding, the substrate over a polishing control groove can reduce the non-uniformity of the polished substrate. The polishing control groove can be located nearer a perimeter of the polishing pad, nearer a center of the polishing pad, or include multiple grooves such as one nearer the center and another nearer the perimeter.

[0029]

[0021] In many polishing operations, the carrier head can be oscillated laterally, e.g., radially, across the polishing pad in order to sweep back and forth over the polishing pad. This lateral oscillation can be set by a polishing recipe, i.e., a group of instructions set before the polishing operation that set values for various control parameters of the polishing operation over time, e.g.. platen rotation rate, carrier head rotation rate, and, more pertinently, the lateral position of the carrier head. The lateral position of the carrier head can be set in the recipe so as to position a region of the substrate being polished over the polishing control groove to correct the polishing profile for the substrate. The system can hold the region of the substrate over the polishing control groove for a duration sufficient to correct the polishing profile.

[0030]

[0022] One issue with having the lateral position of the earner head set by a polishing recipe is that due to inherent variability in the polishing process, the recipe may not result in the desired polishing uniformity. On the other hand, one issue with the edge correction is that active control of the correction process can be limited by the resolution of control knobs through which users interact with the system to set the dwell durations. A system which utilizes readings from the in-situ monitoring system to calculate and set a dwell time for a carrier head at each of a plurality of radial regions across the polishing pad can provide increased accuracy in correcting the polishing profile.

[0031]

[0023] FIG. 1 illustrates an example of a polishing station of a chemical mechanical polishing system 20. The polishing system 20 includes a rotatable disk-shaped platen 24 on Attorney Docket No. 44023976W001;05542-1627W01 which a polishing pad 30 is situated. The platen 24 is operable to rotate about an axis of rotation 25. For example, a motor 26 can turn a drive shaft 28 to rotate the platen 24. The polishing pad 30 can be a two-layer polishing pad with an outer polishing layer 32 and a softer backing layer 34. The outer polishing layer 32 has a polishing surface 36.

[0032]

[0024] The polishing system 20 can include a supply port or a combined supply-rinse arm 92 to dispense a polishing liquid 94, such as an abrasive slurry, onto the polishing pad 30. The polishing system 20 can include a pad conditioner apparatus 40 with a conditioning disk 42 to maintain the surface roughness of the polishing surface 36 of the polishing pad 30. The conditioning disk 42 can be positioned at the end of an arm 44 that can swing so as to sweep the disk 42 radially across the polishing pad 30.

[0033]

[0025] A carrier head 70 is operable to hold a substrate 10 against the polishing pad 30. The carrier head 70 is suspended from a support structure 50, e.g., a carousel or a track, and is connected by a drive shaft 58 to a carrier head rotation motor 56 so that the carrier head can rotate about an axis 55. Optionally, the carrier head 70 can oscillate laterally, e.g., on sliders on the carousel, by movement along the track, or by rotational oscillation of the carousel itself.

[0034]

[0026] The carrier head 70 includes a housing 72 and a retaining ring 80 to retain the substrate 10 below a flexible membrane 74. The housing 72 can generally be circular in shape and can be connected to the drive shaft 58 to rotate therewith during polishing. There may be passages (not illustrated) extending through the housing 72 for pneumatic control of the carrier head 70.

[0035]

[0027] The carrier head 70 also includes one or more independently controllable pressurizable chambers defined by the membrane 74, e.g., three chambers 76a-76c, which can apply independently controllable pressures to associated zones on the flexible membrane 74 and thus on the substrate 10. Although only three chambers are illustrated in FIG. 1 for ease of illustration, there could be one or two chambers, or four or more chambers, e.g., five chambers.

[0036]

[0028] A controller 190, e.g., a programmed computer including non-transitory storage medium and a microprocessor, is coupled to the motors 26. 56 to control the motors 26, 56 in accord with a processing procedure. The controller 190 can also be coupled to a pressure source to control the pressures in the chambers 76a-c in the carrier head 70.

[0037]

[0029] In some implementations, the polishing apparatus includes an in-situ monitoring system 160, e.g.. an optical monitoring system, such as a spectrographic monitoring system which can be used to measure a spectrum of reflected light from a substrate undergoing Attorney Docket No. 44023976W001;05542-1627W01 polishing. The monitoring system 160 can include a sensor supported on the platen, e.g., an end of an optical fiber that is coupled to a light source 162 and a light detector 164.

[0038]

[0030] Due to the rotation of the platen 24, as the sensor travels below the carrier head 70 and the substrate 10, the monitoring system 160 receives measurements at a sampling frequency causing the measurements to be taken at locations in an arc that traverses the substrate 10. From the measurements, the in-situ monitoring system 160 produces a signal which depends on the thickness of the layer of material being polished, e.g., a thickness profile. Additionally or alternatively, the in-situ monitoring system 160 produces a signal which depends on the polishing rate of the layer of material being polished, e.g., a polishing rate profile.

[0039]

[0031] The controller 190 receives the signal, converts the signal to a process profile, e.g., a thickness profile or polishing rate profile, and compares the process profile to a target profile. For example, the target profile can be a pre-determined target thickness profile for the radially-dependent thickness of the layer at the end of polishing, or a target polishing rate profile storing radially-dependent target polishing rates during polishing. The process profile can be based on measurements over the radial width of the substrate 10, or a region of the radial width of the substrate 10. In some implementations, the controller 190 calculates a process profile for the region of the substrate 10 corresponding to the outermost annular region of the substrate 10, e.g., an edge region, such as the outermost 5%, the outermost 10%, or the outermost 20% of the substrate.

[0040]

[0032] If the controller 190 determines that the profile from the monitoring system 160 needs correction, the controller 190 can control the carrier head 70 such that the edge region of the substrate 10 is over a groove in the polishing pad 30 which can compensate for overpolishing of the edge region of the polishing profile.

[0041]

[0033] Referring to FIG. 2, the polishing pad 30 has at least one polishing control groove 102 formed in the polishing surface 36. Each polishing control groove 102 is a recessed area of the polishing pad 30. Each polishing control groove 102 can be an annular groove, e.g., ring-shaped, e.g., circular, and can be concentric with the axis of rotation 25. Each polishing control groove 102 provides an area of the polishing pad 30 that reduces the rate of polishing, e.g., does not contribute to polishing.

[0042]

[0034] The walls of the polishing control groove 102 are perpendicular to the polishing surface 36. The bottom surface of the polishing control groove 102 is parallel with the polishing surface 36. although in some implementations the bottom surface of the polishing control groove 102 can be angled relative to the polishing surface 36. The bottom of the Attorney Docket No. 44023976W001;05542-1627W01 polishing control groove 102 can have a rectangular or a U-shaped cross-section. In some implementations, the polishing control groove 102 has a depth between 10 and 80 mils. The polishing control groove 102 can have a width between three to fifty millimeters.

[0043]

[0035] In some implementations, the polishing control groove 102 is located near the outer edge of the polishing pad 30, e.g., within 15% or within 10% (by radius) of the outer edge. For example, the polishing control groove 102 can be located at a radial distance of fourteen inches from the center of a platen having a thirty-inch diameter. In some implementations, the polishing control groove 102 is at a radial distance that is located nearer the center of the polishing pad 30, e.g., within 15% or within 10% (by radius) of the center or axis of rotation 25. For example, the groove 102 can be located at a radial distance of one inch from the center of a platen having a thirty -inch diameter.

[0044]

[0036] In some implementations, the polishing pad 30 includes only a single polishing control groove located near the outer edge of the polishing pad 30. In some other implementations, the pad 30 includes a polishing control groove located near the center of the polishing pad 30, such as there can be just a single control polishing groove 102 near the center of the polishing pad 30. In some implementations, the polishing pad 30 includes multiple polishing control groves, for example, a first polishing control groove located near the edge of the polishing pad 30 and second polishing control groove located near the center of the polishing pad 30.

[0045]

[0037] The polishing control groove 102 is sufficiently wide that by positioning a section of the substrate 10 over the groove 102, the polishing rate of that section will be materially reduced. In particular, for edge-correction, the groove 102 is sufficiently wide that an annular band at the edge of the substrate 10, e.g., a band at least 3 mm wide, e.g.. a band 3-15 mm wide, e.g., a band 3-10 mm wide, will have a reduced polishing rate.

[0046]

[0038] When the substrate 10 is positioned over the polishing surface 36 of the polishing pad 30, the polishing surface 36 contacts and polishes the substrate 10, and material removal takes place. On the other hand, when an edge of the substrate 10 is positioned above the polishing control groove 102, there is substantially no contact with the polishing surface 36 to cause material removal or polishing of the edge of substrate 10. The polishing control groove 102 reduces polishing rate due to compression of the regions of the polishing surface along the edge of the polishing control groove 102. or slurry chemistry or dynamics. In some examples for some locations on the surface of the substrate over the control groove 102, the polishing rate is reduced, e.g.. substantially reduced, while in some other locations the polishing rate is substantially zero. Attorney Docket No. 44023976W001;05542-1627W01

[0047] Optionally, the groove 102 can provide a conduit for polishing slurry to pass through without abrading the substrate 10.

[0048]

[0039] The polishing pad 30 can also include one or more slurry supply grooves 112. The slurry supply grooves 112 can be annular grooves, e.g., ring-shaped, or circular grooves, and can be concentric with the polishing control groove 102. Alternatively, the slurry supplygrooves 112 can have another pattern, e.g., rectangular crosshatch, triangular crosshatch, etc. The slurry supply grooves 112 are narrower than the polishing control groove 102. For example, the slurry- supply grooves 112 can be narrower by a factor of at least 3, e.g., 3 to 100. The slurry supply grooves 112 can have a width between about 0.15 and 0.04 inches (between 0.381 and 1.16 mm), such as 0.20 inches, and a pitch between about 0.9 and 0.24 inches, such as 0. 12 inches.

[0049]

[0040] The slurry supply grooves 112 can be uniformly spaced across the polishing pad 30. The polishing control groove 102 can have a smaller, similar, or greater depth than the slurrysupply grooves 112. In some implementations, the polishing control groove 102 is the only- groove on the polishing pad wider than the slurry supply grooves 112. In some implementations, the polishing control grooves 102a and 102b are the only grooves on the polishing pad wider than the slurry- supply- grooves 112. In some implementations, the slurrysupply grooves 112 have a non-uniform pitch, e.g., are not uniformly spaced, across the polishing pad 30. In some implementations, the slurry supply grooves 112 have a non- uniform width, e.g., at least one groove 112 has a width that is different from the rest of the grooves 1 12.

[0050]

[0041] Generally, the substrate 10 is positioned such that the whole of surface of the substrate 10 being polished is contacting the polishing surface 36 of the polishing pad 30, e.g., none of the substrate 10 overlaps the polishing control groove 102. Although portions of the substrate 10 overlap the slurry supply grooves 1 12, the slurry supply grooves 1 12 are relatively closely spaced and relative motion averages out any- effects on the polishing rate.

[0051]

[0042] Referring to both FIG. 1 and FIG. 2, the system 20 is configured to determine the polishing profile at an edge region of the substrate and determine whether to provide compensation to the edge region based on the polishing profile. To provide compensation, the system 20 moves the carrier head 70 such that the edge region of the substrate 10 is over the control groove 102 and thus being minimally- polished, e.g., not being polished. In some examples, the controller 190 is configured to determine a sequence of dwell times in which the edge region of the substrate is over the control groove 102 to provide the compensation. Attorney Docket No. 44023976W001;05542-1627W01

[0052]

[0043] Referring now to FIG. 3, the substrate 10 can be positioned such that the central region 12 of the substrate 10 is polished by the polishing surface 36 and a portion 14a of the edge region 14 of the substrate 10 is above the polishing control groove 102. During the second duration, the substrate 10 can be held laterally fixed in a second position. Thus the central region 12 of the substrate 10 is polished during the second duration, whereas a portion 14a of the edge region 14 of the substrate 10, positioned above the polishing control groove 102, is not polished. The substrate 10 may also rotate. Consequently, the specific portion of the edge region 14 above the polishing control groove 102 varies with the rotation of the substrate. However, since a portion of the edge region 14 (indicated by portion 14b) remains over the polishing surface 36, the edge region 14 will still be polished to some degree.

[0053]

[0044] Due to rotation of the substrate 10, the edge region 14 should still be polished in an angularly uniform manner, but at a lower rate than the central region 12 due to reduced polishing in portion 14a. In addition, although portions of the substrate 10 overlap the si urn supply grooves 112, the slurry supply grooves 112 are relatively closely spaced and relative motion averages out any effects on the polishing rate. The controller 190 can cause the support to move the carrier head 70 to oscillate the substrate 10 laterally during the first duration of the dwell times, and to hold the substrate 10 at a fixed position laterally for a time at the second duration of the dw ell times.

[0054]

[0045] To reduce the removal of the edge region 14 of the substrate 10, and to obtain a more uniformly polished substrate 10. a non-polishing area time share can be determined. For example, equation [1] can be used to determine the non-polishing area time share

[0055]

[0046] where a is the angle subtended across the substrate 10 by the polishing control groove 102a relative to the center of the substrate, and can be determined using equations [2]- [3]:

[0056]

[0047] and

[0057]

[0048] and w here £1 is the radius of the inner edge of the groove 102a, r is the radius of the substrate 10, and x is the distance from the center of the polishing pad 30 to the center of the substrate 10. Attorney Docket No. 44023976W001;05542-1627W01

[0058]

[0049] In order to set a sweep profile for the carrier head 70, the polishing control parameters can include multiple parameters representing dwell times. In particular, each respective parameter of the multiple parameters can represent the dwell time of the carrier head 70 at a different respective radial annular zone on the polishing pad 30.

[0059] Dwell Times

[0060]

[0050] For example, referring to FIG. 4A. the polishing pad 30 can be divided up into a plurality of concentric annular zones 200, e.g., zones 200a-200d. Although FIG. 4A illustrates four zones, this is not required; there could be any suitable number of annular zones, e.g., two to twenty zones. For at least one of the zones, e.g., zone 200a, at least a region of the substrate 10 will overlap polishing control groove 102. Each zone can be represented by a radial distance (e.g., the average of the inner and outer radius of the zone), or a range of radial distances (e.g., the inner and outer radius of the zone). For ease of reference, the carrier head 70 is not shown in FIG. 4 A, though it is to be understood that the system 20 moves the carrier head 70 to cause motion of the substrate 10 on the polishing pad 30. In another example, the platen 24 can be divided up into the zones 200.

[0061]

[0051] During operation, the carrier head 70 sw eeps the substrate 10 laterally over the platen 24 and polishing pad 30 (indicated by arrow C), e.g., along a radius of the platen 24. For each zone 200 there can be a corresponding dwell time control parameter representing a dwell time of a region of the substrate 10 within or at that zone 200 for a duration. In some implementations, there can be a dwell time control parameter representing a dwell time of the edge region 14 of the substrate 10 within or at that zone 200. In one example, there is a dw ell time control parameter representing a dw ell time of the edge region 14 within the zone 200a containing the polishing control groove 102.

[0062]

[0052] The substrate 10 may span multiple zones 200, in which case each respective dwell time control parameter can represent a dw ell time of the centerpoint of the substrate 10 (at axis 71) within or at that respective zone. The value for a dwell time parameter value can be in units of the fraction of a total time (i.e., the total of all dwell times would equal 1). although other units, e.g., expected time, e.g., seconds, are possible.

[0063]

[0053] Once the dwell time parameter values are calculated (calculation of the parameter values is discussed below), the dwell time parameter values can be converted into a sweep profile. In general, in the sweep profile the dwell time for each zone will be apportioned according to the dwell time parameter value. Attorney Docket No. 44023976W001;05542-1627W01

[0064]

[0054] In some implementations, the carrier head 70 sweeps the substrate 10 with a speed that is constant within each zone 200, but which can be different for each zone 200 (e.g.. different between zone 200a containing the control groove 102 and zone 200b which does not include the control groove 102).

[0065]

[0055] For example, referring to FIG. 4B, one possible technique is to set the carrier head sweep rate (i.e., the slope of the line 202) for each zone 200a-200d according to the inverse of the fraction indicated by dwell time parameter for that zone. For example, given an oscillation period T, the dwell time for a half sweep (either inward or outward) for a given zone i can be calculated. Then the speed at which the carrier head sweeps across a particular zone can be (determined based on the inner and outer diameters of the zone.

[0066]

[0056] In some implementations, a suitable combination of parameters can be determined by solving for respective parameters that minimize a difference between the expected removal profile and the target removal profile. That is, the value of the difference is minimized by solving for a suitable combination of dwell times, carrier head sweep speed, variations in the oscillation period, or combinations thereof. In many cases, one or more distinct sets of parameters can be determined mathematically that provide an expected removal profile equaling the target removal profile, such that the difference is minimized. In other cases a difference value between the expected removal profile and the target removal profile can be minimized to an acceptable, non-zero value.

[0067]

[0057] In some examples, a minimization process (e.g.. minimization of a cost function) may be used to determine an appropriate combination of control parameters to find a minimum difference between the estimated polishing profile and the target polishing profile, e.g., to find a minimum value for A.

[0068]

[0058] Once an appropriate set of control parameter values has been determined, as described above, the controller 190 can be configured to store the parameter values and execute a polishing technique accordingly to provide one or more substrates having the target polishing profile.

[0069]

[0059] In most cases, when all other parameter values are to be held constant, the polishing rate at a particular location in the edge region 14 can vary according to the dwell time of the edge region 14 over the polishing control groove 102. Therefore, adjusting a sweep profile of the carrier head 70 such that the edge region 14 is over the groove 102 for a determined dwell time can correct for over-polishing in the edge region 14.

[0070] Cost Function Attorney Docket No. 44023976W001;05542-1627W01

[0071]

[0060] Based on the measured thicknesses of the substrate and / or the edge region 14 projected thicknesses can be determined for the polishing profile. An example process 500 is shown in FIG. 5, in connection with the example data shown in FIG. 4B. The controller 190 receives information of the substrate 10 (e.g., thicknesses of the central region 12 and / or the edge region 14). The controller 190 can also store the desired polishing profile, as well as a recipe that sets desired polishing parameters, e.g., a sweep profile.

[0072]

[0061] The controller 190 receives, from the in-situ monitoring system 160, a sequence of characterizing values (e g., thicknesses) for each region on the substrate 10, e.g., the edge region 14 and / or the central region 12 (502). An expected endpoint time or an expected thickness at an expected endpoint time can be calculated from the sequence of characterizing values. The expected endpoint time can be a preset time or can be calculated by determining when the linear function fit to the characterizing values is equal to target thickness.

[0073]

[0062] The controller calculates an adjustment of at least one processing parameter (506) in order to achieve closer endpoint conditions. In particular, at least one polishing parameter can be adjusted such that the edge region 14 reaches the target thickness at the same time as the remaining substrate 10, e.g.. the central region 12. Calculating the adjustment of the at least one processing parameter includes minimizing a cost function that incorporates input from each region, e.g., the edge region 14 and / or the central region 12.

[0074]

[0063] In solving for the current adjustment for a polishing parameter, the present technique calculates all of the expected future polishing parameter changes under the cost function.

[0075] This takes into account expected sweep times and future changes to the sweep times. This technique permits the target polishing profile to be achieved more consistently.

[0076]

[0064] The processing parameters that are adjusted are typically the sweep times of the carrier head, although the technique is applicable to other parameters such as one or more chamber pressures, the platen rotation rate, or carrier head rotation rate.

[0077]

[0065] The variables in the cost function can include a difference between the current characterizing value and a target characterizing value for each region (or more generally, a difference between the current polishing profile and the target polishing profile), a difference between an expected characterizing value at the end of polish and the target charactenzing value for each region, the magnitude of the changes in polishing parameters over time (e.g., the magnitude of the plurality of pressure changes over time) for one or more regions, the polishing rate in each zone, and / or a plurality of differences between projected future polishing parameters (e.g.. sweep profiles) over time and a baseline recipe of polishing Attorney Docket No. 44023976W001;05542-1627W01 parameters (e.g., sweep profiles) over time for one or more regions, e.g., the edge region 14 and / or the central region 12.

[0078]

[0066] A '‘Preston matrix”, i.e., a matrix that expresses the relationship between sweep profile and polishing rate, is used to convert a normalized sweep profile to normalized rate change. The units can be modified by multiplying the Preston matrix with a nominal polish rate. An inverted Preston matrix can be used to back-calculate a sweep profile from a rate change.

[0079]

[0067] The controller can further be subject to user specified constraints during the optimization. For example, the user can define a maximum allowed sweep profile dwell durations or minimum and maximum dwell durations.

[0080]

[0068] However, adjusting of the processing parameters is done in order to reach several objectives. Objectives can include reaching the target thickness in the edge region 14 at the expected endpoint.

[0081]

[0069] The objectives can be realized by defining a cost function that includes a term for each objective. The cost function is defined in terms of control inputs (u), e.g.. the polishing parameters to be calculated, and a state (x). Examples of matnces for the control inputs (u) and the state (x) are shown below.

[0082]

[0070] As an example, the cost function includes a term that has, for each region, a difference between a current characterizing value and a target characterizing value for the region. This can represent the objective of reaching the target thickness in each zone at the expected endpoint.

[0083]

[0071] As another example, the cost function includes a term that has, for each region, the plurality of a projected future pressure changes over time for the region. This can represent the objective of applying small pressure changes without deviating far from the baseline pressure.

[0084]

[0072] As another example, the cost function includes a term that has, for each region, the plurality7of differences between projected future dwell times and the dw ell time for the region. This can represent the objective of reducing deviation of the dwell times from a preset dwell times recipe.

[0085]

[0073] As another example, the cost function can include a term that has, for each region, a difference between the pressure of the region and an average pressure in the carrier head. This can represent the obj ective of reducing deviation of the pressures from an average pressure across the carrier head. Attorney Docket No. 44023976W001;05542-1627W01

[0086]

[0074] In some examples, the cost function can include a term that has, for each region, a combination of the above-described parameters. For example, the cost function can include a term that includes the plurality of differences between projected future dwell times and the dwell time for the region, the plurality of a projected future pressure changes over time for the region, difference between the pressure of the region and an average pressure in the carrier head, or a combination thereof.

[0087]

[0075] In some implementations, the control input column vector (u) includes N dwell time changes corresponding to the region Zi, ... , ZN, and the state column vector (x) includes both a difference between the current thickness and the target thickness for each region (e.g., Zi thickness - Zi target thickness), and a difference between the current dwell time and the target dwell time for each region (e.g.. Zi dwell time - Zi baseline dwell time).

[0088]

[0076] In order for each zone to reach its target when the cost function is minimized, one or more of the terms in the state may be defined as offsets. For example, for a region to reach a target thickness the cost function is a function of a square of each difference between the current characterizing value and the target characterizing value for the region. For example, for a region to reach a target dwell time, the cost function is a function of a square of each projected future dwell time, and a square of each difference between the projected future dw ell time and the baseline dw ell time.

[0089]

[0077] Further, the cost function can differently weight the various objectives.

[0090]

[0078] For example, the cost function can include a first constant for each region. The cost function can include a function of the first constant multiplied by the square of the difference between the current characterizing value and the target characterizing value for the region.

[0091]

[0079] In another example, the cost function includes a second constant for each region and the cost function is a function of the second constant multiplied by the square of each projected future pressure change.

[0092]

[0080] In a third example, the cost function includes a quadratic function of the various rates, and the quadratic function is defined in a manner such that deviation of each region’s rate from the average rate of all the regions results in an increase of the cost function.

[0093]

[0081] Matnx Qf below shows the weighing approach of parameters that may be important within the state at the end of polish. The parameters that are excluded are represented by 0 in the matrix. The terms resulting from Qf weighted inner product are presented with an equation for variable Jf that sums the terms and the resulting sum corresponds to the squared deviation from the target thickness for each zone. Attorney Docket No. 44023976W001;05542-1627W01

[0094]

[0082] The evolution of the control inputs in a manner that can avoid underdamped or overdamped behavior is represented by the total cost function as:

[0095]

[0083] Constraints on state evolution are expressed by the same equation that defines the Kalman filter. Therefore, the state X(T) is subject to evolution under the constraints of where A and B are matrices with constant values or pre-defined time-varying values.

[0096]

[0084] The controller computes values for U(T) that minimize the above total cost function. The cost function can be optimized by a linear quadratic regulator (LQR) when combined with a linear equation of state as described above. LQR is a feedback controller that allows operation of a dynamic system at a minimum cost. Attorney Docket No. 44023976W001;05542-1627W01

[0097]

[0085] Q and R can be determined based on the desired aggressiveness of the controller, with larger values of R typically corresponding to less aggressive control and larger values in Q typically corresponding to more aggressive control.

[0098]

[0086] The above cost function also sets the values of Qf based on a fraction of the removal rate amount. For example, the term containing the values of Qf remains relatively large to prevent the stage costs from dominating.

[0099]

[0087] The cost function also may also be subject to inter-zone constraints, or constraints on average pressure by integrating them in the similar manner we followed above for each zone.

[0100]

[0088] A number of embodiments have been described. The invention, however, is not limited to the embodiments depicted and described. Rather, the scope of the invention is defined by the appended claims.

Claims

Attorney Docket No. 44023976W001;05542-1627W01What is claimed is:

1. A chemical mechanical polishing apparatus, comprising: a platen to support a polishing pad, the polishing pad having an annular polishing control groove at a radial distance from a center of the polishing pad;; a carrier head to hold a surface of a substrate against the polishing pad; a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate; and a controller configured to cause the carrier head to determine values for a plurality of control parameters to minimize a difference between a target removal profile and an expected removal profile, the plurality of control parameters representing at least: a first duration such that a central region of the substrate and an edge region of the substrate are positioned over a polishing surface of the polishing pad, and a second duration such that the central region of the substrate is positioned over the polishing surface of the polishing pad and at least a portion of the edge region of the substrate is positioned over the annular polishing control groove, and cause the carrier head to. for the first duration, moving the substrate laterally across the polishing pad such that the central region and the edge region of the substrate are positioned over a polishing surface of the polishing pad, and for the second duration, hold the substrate in a substantially laterally fixed position such that the central region of the substrate is positioned over the polishing surface of the polishing pad and the at least a portion of the edge region of the substrate is positioned over a polishing control groove of the polishing pad.

2. The polishing apparatus of claim 1, wherein a relationship between the plurality of control parameters and a removal rate is stored in a data structure representing a first matrix which includes a plurality of columns including a column for a polishing rate of the polishing surface and a row for the edge region on the substrate represented in the expected removal profile, and wherein the controller is configured to. as part of selection of the values, calculate the expected removal profile by multiplying the first matrix by a second matrix.Attorney Docket No. 44023976W001;05542-1627W013. The polishing apparatus of claim 1, wherein the polishing pad further comprises slurry supply grooves.

4. The polishing apparatus of claim 1, wherein the polishing pad has a single annular polishing control groove.

5. The polishing apparatus of claim 1, wherein the polishing pad has exactly two annular polishing control grooves, each of the two annular polishing control grooves being wider than a plurality of slurry supply grooves in the polishing pad.

6. The polishing apparatus of claim 1, wherein the annular polishing control groove is near an edge of the polishing pad.

7. The polishing apparatus of claim 1, wherein the plurality of control parameters representing a plurality of a projected future pressure changes over time for the edge region, the central region, or both.

8. A chemical mechanical polishing apparatus, comprising: a platen to support a polishing pad, the polishing pad having an annular polishing control groove at a radial distance from a center of the polishing pad; a carrier head to hold a surface of a substrate against the polishing pad; a motor to control a lateral position of the carrier head on the polishing pad; and a controller configured to: cause the motor to sweep the carrier head across the polishing pad in accord with a sweep profile, and select values for a plurality of control parameters to minimize a difference between a target removal profile and an expected removal profile for each of a central region and an edge region of a face of the substrate, the plurality of control parameters including a plurality of dwell time parameters with each respective dwell time parameter of the plurality of dwell time parameters representing an amount of time for each of the central region and a portion of the edge region to spend over a differentAttorney Docket No. 44023976W001;05542-1627W01 respective zone on the polishing pad, wherein at least one zone of the polishing pad comprises the annular polishing control groove.

9. The polishing apparatus of claim 8, wherein a relationship between the plurality7of control parameters and a removal rate is stored in a data structure representing a first matrix which includes a plurality of columns including a column for each dwell time parameter and a row for each position on the substrate represented in the expected removal profile, and wherein the controller is configured to, as part of selection of the values, calculate the expected removal profile by multiplying the first matrix by a second matrix representing control parameter values.

10. The polishing apparatus of claim 8, wherein, to select values, the controller is configured to apply a minimizing algorithm to reduce a difference between an expected thickness profile and a target thickness profile, wherein applying the minimizing algorithm includes iteratively calculating the expected removal profile using different values for each dwell time parameter.

11. The polishing apparatus of claim 8, wherein the controller is configured to calculate a sweep profile from values for the plurality of dwell time parameters.

12. The polishing apparatus of claim 1 1, wherein the controller is configured to set the sweep profile with a respective speed for each respective annular zone of a plurality of annular zones on the platen.

13. The polishing apparatus of claim 12, wherein the controller is configured to set the respective speed for each respective annular zone of the plurality of annular zones as a constant value within the respective zone.

14. The polishing apparatus of claim 13. wherein values for the plurality of dwell time parameters are in units of a fraction of total time.

15. The polishing apparatus of claim 13, wherein the controller is configured to calculate a sweep speed for each respective annular zone of the plurality of annular zones as inversely proportional to the value of the dwell time parameter for the zone.Attorney Docket No. 44023976W001;05542-1627W0116. A method for controlling a polishing system, the method comprising: receiving from an in-situ monitoring system, for each region of a plurality of regions on a substrate being processed, a sequence of characterizing values for the region; for each region, determining a polishing rate for the region; determining that the polishing rate of an edge region is greater than a target polishing rate; and positioning the edge region of the substrate over a polishing control groove such that the polishing rate of the edge region is reduced.

17. The method of claim 16, comprising calculating, before positioning, an adjustment for at least one processing parameter, wherein calculation of the adjustment includes minimizing, for each region: i) a difference between a current characterizing value or an expected characterizing value at an expected endpoint time and a target characterizing value for the region, and ii) a plurality of projected future dwell times for the region and / or a plurality of differences between projected future dwell times and baseline dwell times for the region.

18. The method of claim 17, wherein calculation of the adjustment includes minimizing, for each region, a difference between a pressure of the region and an average pressure in a carrier head.

19. The method of claim 17, wherein the positioning of the edge region over the polishing control groove is based on the one of the plurality of projected future dwell times for the edge region.

20. The method of claim 16, wherein the plurality of regions includes at least a central region and an edge region on the substrate.

21. The method of claim 17, wherein the characterizing value is a thickness value of an overlying layer on the substrate.Attorney Docket No. 44023976W001;05542-1627W0122. The method of claim 17, wherein calculation of the adjustment includes minimizing a cost function.

23. A computer program product for controlling a semiconductor processing system, the computer program product residing on a non-transitory computer readable medium, the computer program product comprising instructions for causing one or more computers to: receive from an in-situ monitoring system, for each region of a plurality of regions on a substrate being processed, a sequence of characterizing values for the region; for each region, determine a polishing rate for the region; determine that the polishing rate of an edge region is greater than a target polishing rate; and position the edge region of the substrate over a polishing control groove such that the polishing rate of the edge region is reduced.

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