Patent Application
20230415295
The disclosure relates to chemical mechanical polishing, and more specifically to controlling platen shape in chemical mechanical polishing.
An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. A conductive filler layer, for example, can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. After planarization, the portions of the metallic 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, e.g., by polishing for a predetermined time period, to leave a portion of the filler layer over the nonplanar surface. In addition, planarization of the substrate surface is usually required for photolithography.
One problem in CMP is variations in the material removal rate, and subsequent thickness profile, of the substrate. Variations in the slurry distribution, polishing pad condition, the relative speed between the polishing pad and the substrate, and the inconsistent load on the substrate from the pressurized chambers of the carrier head can cause variations in the material removal rate. These variations, as well as variations in the initial thickness of the substrate layer, cause variations final substrate layer thickness, particularly in edge regions.
Disclosed herein is a chemical mechanical polishing apparatus including annular flexures in one or more regions of a platen supporting a polishing pad. The annular flexures are controlled to vertically bias the outer edge. The carrier head moves a portion of the substrate over the flexed outer edge to locally increase or decrease the polishing rate, which can reduce the presence of polishing non-uniformities in the polishing substrate. A controller of the apparatus commands the displacement, or position, of the annular flexures through actuators supported by the platen.
The apparatus includes an in-situ monitoring system, such as an optical monitoring system, which receives a signal indicative of a radial thickness profile of an overlying layer of material on the substrate. The controller processes the signal and determines whether additional polishing is needed in an annular region of the substrate, for example an annular region at the edge of the substrate. When additional polishing is needed, the controller causes the actuators to flex the annular flexures upward, whereas when less polishing is needed the controller causes the actuators to flex the annular flexure downward. The carrier head moves a portion of the substrate over the flexed region for additional polishing.
The carrier head moves the substrate off of the flexed annular region and the thickness profile is re-determined. If the thickness profile is within a uniformity threshold, additional polishing (if needed) can be performed without using the annular flexure region. If the thickness profile does not meet the uniformity threshold, the controller determines that additional polishing over the annular flexure is needed.
In one aspect, a chemical mechanical polishing apparatus includes a platen to support a polishing pad, an actuator, 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. The platen has a central section with an upper surface and an annular flexure surrounding or surrounded by the central section and having a top surface with a first edge adjacent to and coplanar with the upper surface and a second edge farther from the central section. The actuator is arranged to bend the annular flexure along an entire circumference of the annular flexure so as to modify a vertical position of the second edge of the annular flexure relative to the central section.
Implementations may include one or more of the following features. The apparatus may include an in-situ monitoring system and a controller configured to receive a signal from the in-situ monitoring system and control the actuator based on the received signal. The in-situ monitoring system may include a sensor head supported by the platen such that the sensor head passes underneath the carrier head and receive optical signals from the substrate held by the carrier head.
In another aspect, a method of polishing a substrate includes supporting a polishing pad with a rotatable platen, the platen comprising at least one annular flexure extending from a central region of the platen and an actuator supported by the platen configured to adjust a vertical height of an edge of the annular flexure relative to the central region along an entire circumference of the annular flexure, positioning the substrate so that a portion of the substrate is over the annular flexure, moving the annular region of the substrate over the annular section, and generating relative motion between a polishing pad and a substrate so as to polish an overlying layer on the substrate.
In another aspect, a chemical mechanical polishing apparatus includes a platen to support a polishing pad, a carrier head to hold a surface of a substrate against the polishing pad, and a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate. The platen has a central section with an upper surface and an annular flexure surrounding or surrounded by the central section and having a top surface with a first edge adjacent to and coplanar with the upper surface and a second edge farther from the central section. The annular flexure is tapered to be thinner toward the second edge. The actuator is arranged to bend the annular flexure so as to modify a vertical position of the second edge of the annular flexure relative to the central section.
In another aspect, a chemical mechanical polishing apparatus includes a platen to support a polishing pad, a carrier head to hold a surface of a substrate against the polishing pad, and a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate. The platen has an upper portion and a lower portion, the upper portion having a central section with an upper surface. An annular flexure surrounds or is surrounded by the central section and has a top surface with a first edge adjacent to and coplanar with the upper surface and a second edge farther from the central section. A pressurizable chamber between the upper platen and lower platen is configured such that modifying pressurization of the chamber bends the annular flexure so as to modify a vertical position of the second edge of then annular flexure.
In another aspect, a chemical mechanical polishing apparatus includes a platen that has a lower platen and an upper platen to support a polishing pad, a carrier head to hold a surface of a substrate against the polishing pad, and a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate. The upper platen has a vertically movable central section and an annular outer section surrounding the central section and coupled to the central section by an annular bendable portion. An outer edge of the annular outer section is supported by and vertically fixed relative to the lower platen. An actuator is arranged to adjust a vertical position of the central section and an inner edge of the annular outer section so as to modify a tilt of the annular outer section.
Particular implementations of the subject matter described in this specification can be implemented so as to realize one or more of the following technical advantages.
Radially-specific thickness profile correction can be performed, and within-wafer non-uniformity and wafer-to-wafer non-uniformity can be reduced. Material removal can compensate for thickness profile non-uniformities in edge regions induced following a main polishing step or to correct incoming substrate film thickness profiles before undergoing primary polishing. The amount of flex (e.g., displacement from a planar configuration) by the annular flexures results in a modification of pressure applied to the substrate surface rather than through the substrate backside, increasing the polishing location specificity during location-specific polishing. The dimensions of the region of increased pressure can be small compared to the overall substrate surface area and can be controlled by positioning of the substrate with the carrier head, allowing material removal in highly specific areas.
The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other aspects, features and advantages will be apparent from the description and drawings, and from the claims.
In the figures, like references indicate like elements.
In some chemical mechanical polishing operations, a portion of a substrate can be under-polished or over-polished. In particular, the substrate tends to be over-polished or under-polished at or near the substrate edge. One technique to address such polishing non-uniformity is to have multiple controllable pressurizable chambers in the carrier head. However, pressure applied from the backside of the substrate tends to “spread,” such that compensation for radially localized can be difficult. Another technique is to transfer the substrate to a separate “touch up” tool, e.g., to perform edge-correction. However, the additional tool consumes valuable footprint within the clean room, and can have an adverse effect on throughput.
An alternative approach is to have a platen with independently controllable annular flexures which are deflectable, e.g., upwardly or downwardly. A portion of the substrate is then moved over the deflected flexure, which results in increased or decreased pressure between the polishing pad and the substrate at that portion, and thus enables radially-targeted polishing of an edge portion of the substrate.
Although some approaches for an adjustable platen have been proposed, such systems are not known to be commercialized and can generally be expected to pose other problems. For example, in a system with vertically adjustable concentric platens, the vertical displacement between the platens can create a height discontinuity that poses a danger of damage to the substrate.
The main polishing pad 30 can be secured to the upper surface 28 of the central section 26 of the platen 24, for example, by a layer of adhesive. When worn, the main polishing pad 30 can be detached and replaced. The main polishing pad 30 can be a two-layer polishing pad with an outer polishing layer 32 having a polishing surface, and a softer backing layer 34.
The polishing system 20 can include a polishing liquid delivery arm 39 and/or a pad cleaning system such as a rinse fluid delivery arm. During polishing, the arm 39 is operable to dispense a polishing liquid 38, e.g., slurry with abrasive particles. In some implementations, the polishing system 20 include a combined slurry/rinse arm. Alternatively, the polishing system can include a port in the platen operable to dispense the polishing liquid 38 onto the main polishing pad 30. The polishing system 20 can also include a conditioner system 40 with a rotatable conditioner head 42, which can include an abrasive lower surface, e.g. on a removable conditioning disk, to condition the polishing surface 36 of the main polishing pad 30.
The polishing system 20 includes a carrier head 70 operable to hold the substrate 10 against the main polishing pad 30. The carrier head 70 is suspended from a support structure 72, for example, a carousel or track, and is connected by a carrier drive shaft 74 to a carrier head rotation motor 76 so that the carrier head can rotate about an axis 71. In addition, the carrier head 70 can oscillate laterally across the polishing pad, e.g., by moving in a radial slot in the carousel as driven by an actuator, by rotation of the carousel as driven by a motor, or movement back and forth along the track as driven by an actuator. In operation, the platen 24 is rotated about its central axis of rotation 25, and the carrier head is rotated about its central axis 71 and translated laterally across the top surface of the polishing pad.
The carrier head 70 can include a retaining ring 73 to retain the substrate 10 below a flexible membrane 144. The carrier head 70 also includes one or more independently controllable pressurizable chambers defined by the membrane, e.g., three chambers 77a-77c, which can apply independently controllable pressurizes to associated zones on the flexible membrane 144 and thus on the substrate 10. Although only three chambers are illustrated in
A controller 90, such as a programmable computer, is connected to the motors 21, 76 to control the rotation rate of the platen 24 and carrier head 70. For example, each motor can include an encoder that measures the rotation rate of the associated drive shaft. A feedback control circuit, which could be in the motor itself, part of the controller, or a separate circuit, receives the measured rotation rate from the encoder and adjusts the current supplied to the motor to ensure that the rotation rate of the drive shaft matches at a rotation rate received from the controller.
The polishing system 20 also includes at least one annular flexure 50 that is secured to and rotates with the platen 24. A portion of the polishing pad 30 supported on the platen 24 extends above the flexure 50. The flexure 50 is deformable by one or more actuators 52. The polishing system 20 can include an annular flexure 50a that projects outwardly from an outer edge of the platen 24. Or if the platen 24 is itself annular, the polishing system can include an annular flexure 50b that projects inwardly from an inner edge of the annular platen 24. Or there can be two flexures, e.g., flexure 50a and flexure 50b, one for an outer edge and one for an inner edge of the platen 24.
When the annular flexure 50 is flexed upward, a radially-limited outer section of the polishing pad 30 is urged upwardly. If a portion of a substrate 10 is present over the flexure, pressure against that portion will increase. Conversely, when the annular flexure 50 is flexed downward, a radially-limited outer section of the polishing pad 30 is urged downward. If a portion of a substrate 10 is present over the flexure, pressure against that portion will decrease. As used herein, the terms “upward” and “downward” are in reference to the orientation of
The annular flexure 50 extends from the outer edge of the platen 24 by a distance in a range from 5% to 20% of the radius of the polishing pad 30 (e.g., from 5% to 15%, from 5% to 10%, from 10% to 15%, or from 15% to 20%).
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 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. Due to the rotation of the platen, 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.
The controller 90 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 portion of the radial width of the substrate 10. In some implementations, the controller 90 calculates a process profile for the portion of the substrate 10 corresponding to the outermost annular region of the substrate 10, such as the outermost 5%, the outermost 10%, or the outermost 20% of the substrate.
The controller 90 compares the process profile to a target profile. If the process profile differs from the target profile by more than a threshold amount, the controller 90 determines to change a polishing parameter. If the difference occurs in a region of the substrate that is controllable by the flexure, e.g., in an outermost annular region adjacent an edge of the substrate then the flexure can be used to compensate for the departure of the process profile from the target profile.
If the polishing rate of the region of the substrate is above a target polishing rate, the controller 90 can determine to position the region over the flexure and deflect the flexure downward. The downward deflection reduces the polishing rate in that region to achieve the target polishing rate profile. If the polishing rate in that region of the substrate is below the target polishing rate for that region, the controller 90 can determine to position the region over the flexure and deflect the flexure upward to increase the polishing rate of that region.
As shown in the example of
The annular flexure 50 is connected to at least one actuator 52 which is arranged to be supported by the central section 26 of the platen 24. In some implementations, such as the example of
As the actuators 52 provide an inward force, the outer edge of the upper surface of the annular flexure 50 is flexed downward. Conversely, as the actuators 52 provide an outward force, the outer edge of the upper surface of the annular flexure 50 is flexed upward. The controller 90 controls the actuators 52 to adjust the force on the flange 54 to control the outer edge of the upper surface of the annular flexure 50 to flex upward or downward.
The system can be configured such that the annular flexure 50 flexes along an entire circumference of the flexure 50. In some implementations, there is a single actuator, and the flexure 50 is sufficiently stiff along the angular that pressure from the actuator in a limited area causes the flexure 50 to flex along the entire circumference. In some implementations, there are multiple actuators, and the actuators is electrically ganged to a single control signal such that all actuators are driven in unison. In some implementations, each of the actuators 52 is individually controllable by the controller 90, but the controller 90 controls all of the actuators 52 to flex the annular flexure 50 along the entirety of the circumference.
In many polishing processes, the outer edge of the substrate 10 is under-polished due to reduced pressure control in the outermost radial areas of the three chambers 77a-77c, resulting in increased layer thickness at the edges of the substrate 10. As such, the annular flexure 50 is flexed upward and biased against the bottom surface of the substrate 10 to increase the pressure between the substrate 10 and the polishing pad 30.
The controller 90 operates the actuators 52 to alter a position of an outer edge of the annular flexure 50 upward or downward by a distance. In some implementations, the distance is in a range from 1 micron to 300 microns (e.g., 1 micron to 250 microns, 10 microns to 250 microns, 50 microns to 250 microns, 10 microns to 50 microns, or 1 microns to 50 microns).
Here and throughout the specification, reference to a measurable value such as an amount, a temporal duration, and the like, the recitation of the value should be taken as disclosure of the precise value, of disclosure of approximately the value, and of disclosure of about the value, e.g., within ±10% of the value. For example, here reference to 100 microns can be taken as a reference to any of precisely 100 microns, approximately 100 microns, and within ±10% of 100 microns.
In some implementations, the annular platen 24 includes a recess 27 at the center of the platen 24 which partially extends through the thickness of the platen 24, aligned with the axis of rotation 25. For example, the recess 27 can be circular and the center of the recess 27 can be co-axial with the axis of rotation 25. In some implementations, the recess 27 extends through the entire thickness of the platen 24.
The recess houses a central annular flexure 51 including a flange 54 and one or more actuators 52 to apply a force to the flange 54. The inner edge of the central annular flexure 51 (e.g., nearest the axis of rotation 25) flexes upward or downward based on the force applied to the flange 54 by the actuators 52 while the outer edge of the central annular flexure 51 remains substantially coplanar with the upper surface 28.
The central annular flexure 51 extends from the inner edge of the platen 24 by a distance in a range from 5% to 25% of the innermost radius of the polishing pad 30 (e.g., from 5% to 15%, from 5% to 10%, from 10% to 25%, or from 15% to 25%).
The arrangement of the actuators 52, outer annular flexure 50a, and central annular flexure 50b define regions of the pad 30 in which the pressure between the pad 30 and substrate is controlled at least in part by the amount of flexing provided by the actuators 52. Referring to
Referring to
The substrate 10 is moved by the carrier head 70 such that a portion 12 of the substrate 10 is above the outer region 33. Depending on whether the flexure 50a is biased upwardly or downwardly, the outer region 33 will experience increased or decreased pressure against the portion 12 of the substrate 10. Due to the rotation (shown by arrow A) of the carrier head 70 and substrate 10, an annular section 12a of the substrate 10 experiences an increased or decreased polishing rate (compared to the flexure remaining in a planar state).
Referring to
As the substrate 10 is passed over the inner region 35 by the carrier head 70 (not shown), a portion 13 of the substrate 10 overlaps the inner region 35. As the inner region 35 is flexed upwardly or downwardly by the central annular flexure 51, the portion 13 is subject to increased or decreased pressure. Again, due to the rotation (shown by arrow A) of the carrier head 70 and substrate 10, an annular section 13a of the substrate 10 experiences an increased or decreased polishing rate. In the embodiments of
The carrier head 70 passes the substrate 10 over the central region 31 and the optical monitoring system 160 receives a signal indicative of an updated thickness of the overlying layer of material, e.g., an updated thickness profile, and calculates a new uniformity value for the updated thickness profile.
The controller 90 compares the updated uniformity value to the uniformity threshold. If the uniformity value is below the uniformity threshold, the controller 90 determines to discontinue increased polishing of the region of the substrate 10 corresponding with the region exceeding the uniformity threshold.
The upper platen 312 includes a tapered region 350, which can provide the flexure 50. For the outer annular flexure 50a the tapered region can be an annular outer region 316 of the upper platen 312; for the inner annular flexure 50b the tapered region can be an annular inner region of the upper platen 312. The tapered region 350 can have a reduced thickness compared to the inner central region 314. In addition, the tapered region 350 tapers to a minimum edge thickness at the outer edge of the outer region 316 (or at the inner edge of the inner region). The example of
The example of
In some implementations, the upper platen 312 includes rotary actuators 364 that are connected to the adjustment screws 362. The controller 90 controls the rotary actuators 364 to translate the adjustment screws 362 inward, e.g., toward the central axis 125, or outward, e.g., away from the central axis 125. The force applied in the plane of the upper platen 312 flexes the tapered region 350 downward or upward based on the translation of the adjustment screws 362 inward or outward, respectively. Screws can provide a mechanical advantage in that rotation of the screw can generate significant force in the linear direction.
Alternatively, the upper platen 312 includes static threaded recesses aligned with the aperture 329 such that adjustment screws 362 extending through the flange 354 are manually driven or withdrawn into the upper platen 312 to adjust the degree of flex of the tapered region 350.
The example of
The gas pressure applies force uniformly to the inner surfaces of the void 372. In some examples, the annular seal 374 connecting the outer edge of the upper platen 312 to the outer edge of the platen 310 maintains the position of the upper platen 312 edge when the gas pressure in the void 372 increases above the threshold. This achieves a curved upper surface of the outer region 316 of the upper platen 312 with a point between the edge of the central region 314 and the outer edge of the outer region 316 being the most displaced.
In some implementations, the upper platen 312 is constructed from multiple sections which are independently actuated to achieve the desired configuration of the polishing pad 30.
The lower platen 410 includes a recess 428 in which an actuator, or actuators, is arranged. The actuator provide a vertical force to the inner section 418. In such implementations, the vertical position of the inner section 418 is controlled to adjust the polishing rate in the outer region 416. In the example of
In some implementations, the upper platen 412 is divided into more than two regions having differential polishing rates. In the example implementation of
The processor 510 is capable of processing instructions for execution within the system 500. The term “execution” as used here refers to a technique in which program code causes a processor to carry out one or more processor instructions. In some implementations, the processor 510 is a single-threaded processor. In some implementations, the processor 510 is a multi-threaded processor. The processor 510 is capable of processing instructions stored in the memory 520 or on the storage device 530. The processor 510 may execute operations such as controlling a polishing operation as described herein.
The memory 520 stores information within the system 500. In some implementations, the memory 520 is a computer-readable medium. In some implementations, the memory 520 is a volatile memory unit. In some implementations, the memory 520 is a non-volatile memory unit.
The storage device 530 is capable of providing mass storage for the system 500. In some implementations, the storage device 530 is a non-transitory computer-readable medium. In various different implementations, the storage device 530 can include, for example, a hard disk device, an optical disk device, a solid-state drive, or a flash drive. In some implementations, the storage device 530 may be a cloud storage device, e.g., a logical storage device including one or more physical storage devices distributed on a network and accessed using a network.
The input/output interface devices 540 provide input/output operations for the system 500. In some implementations, the input/output interface devices 540 can include one or more of a network interface device, e.g., an Ethernet interface, and/or a wireless interface device. A network interface device allows the system 500 to communicate, for example, transmit and receive data by way of a network. In some implementations, mobile computing devices, mobile communication devices, and other devices can be used.
Software can be realized by instructions that upon execution cause one or more processing devices to carry out the processes and functions described above. Such instructions can include, for example, interpreted instructions such as script instructions, or executable code, or other instructions stored in a computer readable medium.
Although an example processing system has been described in
A computer program (also known as a program, software, software application, script, executable logic, or code) can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile or volatile memory, media and memory devices.
While this specification contains many details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular examples. Certain features that are described in this specification in the context of separate implementations can also be combined. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple embodiments separately or in any suitable subcombination.
This application claims the benefit of priority to U.S. Application No. 63/355,996, filed on Jun. 27, 2022, the contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63355996 | Jun 2022 | US |
