Patent Application
20210402558
The present disclosure relates generally to profile control of a polishing process, and more particularly to a carrier head having a membrane with multiple angularly disposed pressurizable zones.
An integrated circuit is typically formed on a substrate (e.g. a semiconductor wafer) by the sequential deposition of conductive, semiconductive or insulative layers on a silicon wafer, and by the subsequent processing of the layers.
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 or a desired thickness remains over the underlying layer. In addition, planarization may be used to planarize the substrate surface, e.g., of a dielectric layer, for lithography.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier head. The exposed surface of the substrate is placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. In some situations, the carrier head includes a membrane that forms multiple independently pressurizable radially concentric chambers, with the pressure in each chamber controlling the polishing rate in each corresponding region on the substrate. A polishing liquid, such as slurry with abrasive particles, is supplied to the surface of the polishing pad.
In one aspect, a carrier head for holding a substrate in a polishing system includes a housing, a flexible membrane extending below the housing, a first plurality of pressure supply lines, a second plurality of pressure supply lines, and a valve assembly. The flexible membrane divides a volume above the flexible membrane into a multiplicity of independently pressurizable chambers. The valve assembly is coupled to the first pressure supply lines, the second pressure supply lines and the multiplicity of independently pressurizable chambers. The valve assembly has a multiplicity of valves with each respective valve of the multiplicity of valves coupled to a respective pressure chamber from the multiplicity of independently pressurizable chambers. Each respective valve is configured to selectively couple the respective pressure chamber to one pressure supply line from a pair of pressure supply lines that include a pressure supply line from the first plurality of pressure supply lines and a pressure supply line from the second plurality of pressure supply lines.
In another aspect, a carrier head for holding a substrate in a polishing system includes a housing and a flexible membrane extending below the housing, the flexible membrane dividing a volume above the flexible membrane into a multiplicity of independently pressurizable chambers that are arranged in a polar array.
Implementations may include one or more of the following features.
The multiplicity of independently pressurizable chambers may including a first plurality of independently pressurizable chambers, and the multiplicity of valves may include a first plurality of valves. Each different valve of the first plurality of valves may be configured to selectably couple a different pressure chamber of the first plurality of pressure chambers to a different pair of pressure supply lines. The multiplicity of independently pressurizable chambers may include a second plurality of independently pressurizable chambers, and the multiplicity of valves may include a second plurality of valves. Each different valve of the second plurality of valves may be configured to selectably couple a different pressure chamber of the second plurality of pressure chambers to a different pair of pressure supply lines.
At least one valve from the first plurality of valves and at least one valve from the second plurality of valves may couple respective chambers to a same pair of pressure supply lines. For example, for every valve from the first plurality of valves, there may be a corresponding valve from the second plurality of valves that couples respective chambers to a same pair of pressure supply lines.
The multiplicity of independently pressurizable chambers may be arranged in a polar array. The polar array includes a central chamber and a plurality of radial rings. Each radial ring may a plurality of angularly separated chambers. The different pressure supply lines from the first plurality of pressure supply lines may be coupled to chambers of different rings. The different pressure supply lines from the second plurality of pressure supply lines coupled to chambers of different angular segments.
Certain implementations can include, but are not limited to, one or more of the following possible advantages.
Each independent chamber can be pressurized to apply a respective pressure on to a substrate in a manner that the pressure applied varies both radially and angularly about the center of a substrate being polished. This permits profile control in a manner that can compensate for angular variation in thickness of an incoming substrate and/or angular variations in the polishing rate of the polishing process. The pressure applied over a region can be controlled by a valve switching between two magnitudes of pressure to apply to a chamber so that the chamber applies the corresponding pressure onto the region. Thus, polishing process of each region of the layer on the substrate can be controlled independently and with higher definition. Moreover, in comparison to using pressure chambers without valves, this method permits scaling to a larger number of control regions in a more feasible manner. In particular, fewer rotary connections are needed, and the number of rotary connections scales much less than the number of independent pressurizable chambers.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages are apparent from the description and drawings, and from the claims.
Polishing rate variations between different regions of a substrate can lead to the different regions of the substrate reaching their target thickness at different times. On the one hand, the different regions of the substrate may not reach the desired thickness if polishing of the regions is halted simultaneously. On the other hand, halting polishing for different zones at different times can result in defects or lower the throughput of the polishing apparatus. Thus, there is a need to be able to independently control the pressure on different regions.
In an idealized process, due to the rotation of the carrier head and the platen, the polishing rate on a substrate would be angularly symmetric about the axis of rotation of the substrate. In practice however, the polishing process can result in angular variation in the polishing rate. In addition, a substrate to be polished can have a top layer with an initial thickness that varies angularly, i.e., that has angular non-uniformity. Finally, in some manufacturing processes it may be desirable to induce angular non-uniformity in the thickness of the layer being polished in order to compensate for non-uniformity in later processing steps, e.g., deposition steps. Eliminating angular non-uniformity induced by the polishing process or when polishing a layer with an angularly non-uniform initial thickness, or purposely providing angular variation in the thickness when polishing a layer, remains a challenge.
However, a carrier head that uses multiple independently pressurizable angularly disposed chambers can address this problem. The pressurizable chambers can be arranged angular and radially around a central axis of the carrier head, and each pressurizable chamber is connected to a respective valve. Each valve can switch between a respective pair of pressure inputs such that pressure within each chamber can be controlled independently, permitting reduction or deliberate introduction of angular non-uniformity.
The polishing apparatus 100 can include a combined slurry/rinse arm 130. During polishing, the arm 130 is operable to dispense a polishing liquid 132, such as an abrasive slurry, onto the polishing pad 110. The polishing apparatus can also include a polishing pad conditioner to abrade the polishing pad 110 to maintain the polishing pad 110 in a consistent abrasive state.
The polishing apparatus 100 includes a carrier head 140 operable to hold a substrate 10 against the polishing pad 110. The carrier head 140 can be configured to independently control a polishing parameter, for example pressure, for each of multiple zones on the substrate 10.
Referring to
The lower surface 200 of the membrane 182 provides a mounting surface for the substrate 10. The membrane 182 can include a horizontally extending main portion 202 which can be circular and can provide the mounting surface, and a plurality of flaps 204 that extend upwardly from the back surface of the main portion 202. The flaps 204 are secured to the support plate 184, e.g., by clamps, such that the flaps 184 divide a volume above the membrane into a plurality of independently controllable pressurizable chambers 185. In particular, as discussed further below, the pressurizable chambers 185 are disposed angularly around the central axis 159 of the carrier head. The membrane 182 can be made of a flexible and somewhat elastic material, e.g., a rubber, such as silicone rubber or neoprene. The membrane can be formed from thermoset materials using a mold such that the molded membrane forms the main portion 202 and flaps 204 as a single body.
In some implementations, the support plate 184 is flexibly connected to the housing 144 such that the support plate is vertically movable relative to the housing. For example, the support plate 184 can be coupled to the housing by a flexure 210, e.g., an annular membrane, formed of a plastic or rubber, e.g., silicon rubber or neoprene. An inner edge of the flexure 210 can clamped between the top of the support plate 184 and a clamp ring 212, and an outer edge of the flexure can be clamped between the retaining ring 142 and the housing 144.
The support plate 184 is more rigid than the membrane 182. For example, the support plate 184 can be a metal, e.g., aluminum or stainless steel, or a hard plastic, e.g., polyether ether ketone (PEEK) or polyphenylene sulfide (PPS). Each independent controllable, pressurizable chamber 185 formed above the membrane 182 is sealed by the support plate 184.
A region between the support plate 184 and the housing 144 can be sealed by an expandable seal 220, e.g., by a flexible membrane or bellows, to form a pressurizable upper chamber 222 between the housing 144 and support plate 184. Alternatively, the flexure 210 could provide the seal. Pressure in the upper chamber 222 can thus control the vertical position of the support plate 184 or downforce of the support plate 184 on the membrane 182. In some implementations, pressure in the upper chamber 222 can control the pressure of the retaining ring 142 on the polishing pad.
In some implementations, the support plate 184 is not movable relative to the housing 144. For example, the support plate 184 could be fixed to the housing 144 or be provided by a portion of the housing 144. In this case, there is seal 210 or chamber 222.
Returning to the independently pressurizable chambers 185 formed by the membrane 182, the pressure applied onto a region of the substrate 10 depends on the pressure in the associated chamber 185. Because the chambers are disposed at different angular and radial positions about the center of the carrier head, the pressure on the substrate 10 can be also controlled independently at respective annular and angular positions. Although only ten chambers are illustrated in
A valve assembly 190, e.g., a type of equipment which connects two or more valves in a manner that a variety of isolate valves can be combined in a single body configuration, is secured to the carrier head 140. For example, the valve assembly can be mounted on the top of the housing 144 of the carrier head 140, as shown in
Returning to
The valve assembly 190 can receive a plurality of pressure inputs through a plurality of pressure supply lines 183 from a plurality of pressure sources 181. Again, although only one pressure supply line 183 and one pressure source 181 are shown in
The valve assembly 190 can also receive data through a data line 186 from a controller 190. The voltage supply line 183 and the data line 186 can be routed through the drive shaft 152 and a rotary electrical union 158, e.g., a slip ring, to the stationary components such as the controller 190.
The valve assembly 189 can independently control each valve, based on the data, to switch each corresponding chamber 185 between a pair of corresponding pressure supply lines. That is, each pressure output line 187 can be selectively coupled by an associated valve to one of two pressure supply lines 183.
The data line 186 can transfer a plurality of frames of data, and each frame of a plurality of frames can include data that represents a signal of switching a pressure, or an equivalent pressure signal, for one or more of the independent chamber. In some implementations, a frame of data transmitted by the controller 190 includes a control value and an identification value associated to each valve, or equivalently each chamber, to which the control value applied, and the valve assembly 189 is configured to determine a switch of pressure to a chamber based on the control value and the identification value.
Due to the inclusion of the valve assembly 189, the number of pressure sources and pressure input lines can be reduced at least half as compared to a carrier head having a corresponding number of chambers but without a valve assembly. Thus the number of independently controllable pressurizable chambers can be scaled up with less of an increase in the number of rotary connections, while still maintain adjustability of pressure at each chamber. Given that, the polishing assembly can be simpler in design and more reliable under operation.
Returning to
The pressure source bank 181a and 181b each can include a plurality of pressure sources. As shown in
Each valve inside the valve assembly 189 is connected with two pressure sources, namely a pair of pressure sources, namely a primary pressure and a secondary pressure. The primary pressure can come from a pressure source inside the primary pressure bank 181a and the secondary pressure can come from a pressure source inside the secondary pressure bank 181b. For example, a valve inside the valve assembly is connected to a pair of pressure supplies, e.g., 181a-2 and 181b-1, with a pair of separate pressure supply lines, e.g., 183a-2 and 183b-1. The total number of pressure source banks and pressure sources inside a pressure bank in
The chambers in different rings can be connected to different primary pressure sources, but the chambers in a particular ring can be connected to a common primary pressure source, which will be described further below.
At least two of the rings, e.g., the outer eight rings, are further divided into a plurality of arcuate sections by a plurality of radially-extending membrane walls (provided by the flaps 204 of the membrane 182). For example, a ring can be divided into eight sections by seven radially-extending membrane walls. In some implementations, each section spans the same central angle, e.g., forty-five in degrees or a quarter of 7C in radians. In this case, the arcuate chambers in the rings that are further from the center of the carrier head are longer. In some implementations, the sections are uniformly spaced around the central axis. Alternatively, at least two sections can have a larger central angle, e.g. sixty in degrees, than other sections, e.g., thirty in degrees, according to polishing requirements.
The chambers in a particular section can be connected to a common secondary pressure source. However, for at some pairs of sections, the chambers in different sections for the pair of sections can be connected to different secondary pressure sources. In some implementations, each section is connected to a different secondary pressure sources. Alternatively, some sections are connected to the same secondary pressure sources, but some sections are connected to different pressure sources. For example, adjacent sections can be connected to different pressure sources.
Optionally, one or more inner ring-shape chambers 185-65 can surrounds the central circular chamber 185-66. For example, there can be a ring-shaped chamber 185-65 positioned between the central circular chamber 185-66 and rings that are divided into sections. Thus, in this implementation, there are sixty-six chambers formed by the membrane. Each chamber of the sixty-four chambers is connected to a respective primary pressure source and a respective secondary source, whereas the inner ring-shape chamber 185-65 and the central circular chamber 185-66 are connected to just a respective primary pressure source. The primary pressure sources for chamber 185-65 and 185-66 can come from a different pressure bank, e.g., 181c.
Referring to
In some implementations, the total number of combinations of primary pressure sources and secondary pressure sources. Given each chamber is connected to a respective valve that can switch a pressure output line between a respective pair of a primary pressure source and a secondary pressure source, among all chambers there are at least two separate chambers where each of the two chambers connects to a separate valve, but each valve couples the associated chamber with the same pair of pressure sources. The two chambers can located in a manner that, for example, they lie on the same ring but a different pair of sections, for another example, they lie on a different pair of rings and a different pair of sections.
In some implementations, each arcuate chamber lying on the same concentric ring share the same primary pressure source. For example, 185-1 and 185-9 are two angular portions of the outmost ring and they share the same primary pressure source 181a-1 through respective pressure output supply lines and respective pressure supply lines, even though they do not belong to the same section. Each arcuate chamber within the same section shares a common secondary pressure source, as explained earlier. For example, the accurate chambers 185-1 to 185-8 lying in the section 185-S8 shares the same secondary pressure source 181b-1. In some implementations, one secondary pressure source is shared by chambers in one or more sections. For example, four independent secondary pressure sources, e.g., 181b-1 to 181b-4, are shared by eight sections, e.g., 185-S1 to 185-S8. Namely, one secondary pressure source is shared by chambers in a pair of sections. For example, chambers in a pair of sections 185-S2 and 185-S6 share the same secondary pressure source 181b-2. For another example, chambers in a pair of sections 185-S8 and 185-S7 share the same secondary pressure source 183b-4. Without losing generality, sections that are most separated apart can share the same secondary pressure source to achieve the best control performance.
In this implementation, there are at least eight primary pressure sources, e.g., 181a-1 to 181a-8, each shared by chambers lying on respective outer concentric rings, two independent primary pressure sources, e.g., 181c-1 and 181c-2, for inner chambers 185-65 and 185-66, and four secondary pressure sources each shared by chambers in a respective pair of four pairs of sections.
Returning to
The polishing apparatus can include an in-situ monitoring system 160, which can be used to determine whether to adjust a polishing rate or an adjustment for the polishing rate as discussed below. In some implementations, the in-situ monitoring system 160 can include an optical monitoring system, e.g., a spectrographic monitoring system. In other implementations, the in-situ monitoring system 160 can include an eddy current monitoring system.
The in-situ monitoring system 160 includes a sensor 164, and circuitry 166 coupled to the sensor for sending and receiving signals between a controller 190, e.g., a computer. The sensor 164 can be, e.g., an end of an optical fiber to collect light for an optical monitoring system, or a core and coil of an eddy current monitoring system. The output of the circuitry 166 can be a digital electronic signal that passes through a rotary coupler 129, e.g., a slip ring, in the drive shaft 124 to the controller 190. Alternatively, the circuitry 166 could communicate with the controller 190 by a wireless signal.
As shown by in
Thus, for any given scan of the in-situ monitoring system across the substrate, based on timing, motor encoder information, rotary position sensor data, e.g., from an optical interrupter sensor positioned to detect a flange attached to an edge of the platen, and optical or eddy current detection of the edge of the substrate and/or retaining ring, the controller 190 can calculate both the radial position (relative to the center of the particular substrate 10 being scanned) and the angular position (relative to the reference angle of the particular substrate 10 being scanned) for each measurement from the scan.
As an example, referring to
For each measurement, the controller 190 can calculate a characterizing value. The characterizing value is typically the thickness of the layer under polishing, but can be a related characteristic such as thickness removed. In addition, the characterizing value can be a physical property other than thickness, e.g., metal line resistance. In addition, the characterizing value can be a more generic representation of the progress of the substrate through the polishing process, e.g., an index value representing the time or number of platen rotations at which the spectrum would be expected to be observed in a polishing process that follows a predetermined progress.
Generally, a desired thickness profile is to be achieved for the substrate at the end of a polishing process (or at the endpoint time when the polishing process stops). The desired thickness profile may include the same predetermined thickness for all zones of the substrate 10, or different, predetermined thicknesses for different zones of the substrate 10. When multiple substrates with non-uniform initial thicknesses are polished simultaneously, the multiple substrates may have the same desired thickness profile or different desired thickness profiles.
In some implementations, to keep the measured thickness relationships between the control zones and the reference zone similar to or the same as the thickness relationships illustrated by the desired thickness profile(s) at the endpoint time throughout the polishing process, the controller and/or computer can schedule to adjust the polishing rates of the control zones at a predetermined rate, e.g., every given number of rotations, e.g., every 5 to 50 rotations, or every given number of seconds, e.g., every 2 to 20 seconds. In some ideal situations, the adjustment may be zero at the prescheduled adjustment time. In other implementations, the adjustments can be made at a rate determined in-situ. For example, if the measured thicknesses of different zones are vastly different from the desired thickness relationships, then the controller and/or the computer may decide to make frequent adjustments for the polishing rates.
During polishing, the pressure applied on each region of the layer on a substrate is equal to the pressure applied in each chamber in the membrane 182, as the pressure is transmitted from a chamber to a corresponding region of the substrate. Thus controlling a pressures applied onto a control region of the substrate includes switching a pressure between a pair of a primary pressure and a secondary pressure associated to the corresponding chamber. In some implementations, a preset of primary and secondary pressure magnitude can be learned from open-loop polishing experiments, where the thickness profile at the end of polishing is measured and analyzed to determine how much difference in magnitude should be between a primary pressure and a secondary pressure.
As used in the instant specification, the term substrate can include, for example, a product substrate (e.g., which includes multiple memory or processor dies), a test substrate, a bare substrate, and a gating substrate. The substrate can be at various stages of integrated circuit fabrication, e.g., the substrate can be a bare wafer, or it can include one or more deposited and/or patterned layers. The term substrate can include circular disks and rectangular sheets.
The above described polishing apparatus and methods can be applied in a variety of polishing systems. Either the polishing pad, or the carrier heads, or both can move to provide relative motion between the polishing surface and the substrate. For example, the platen may orbit rather than rotate. The polishing pad can be a circular (or some other shape) pad secured to the platen. Some aspects of the endpoint detection system may be applicable to linear polishing systems, e.g., where the polishing pad is a continuous or a reel-to-reel belt that moves linearly. The polishing layer can be a standard (for example, polyurethane with or without fillers) polishing material, a soft material, or a fixed-abrasive material. Terms of relative positioning are used; it should be understood that the polishing surface and substrate can be held in a vertical orientation or some other orientation.
Control of the various systems and processes described in this specification, or portions of them, can be implemented in a computer program product that includes instructions that are stored on one or more non-transitory computer-readable storage media, and that are executable on one or more processing devices. The systems described in this specification, or portions of them, can be implemented as an apparatus, method, or electronic system that may include one or more processing devices and memory to store executable instructions to perform the operations described in this specification.
While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system modules and components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.
Particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some cases, multitasking and parallel processing may be advantageous.
Other embodiments are within the scope of the following claims.
This application i claims priority to U.S. Application Ser. No. 63/045,680, filed on Jun. 29, 2020, the disclosure of which is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63045680 | Jun 2020 | US |
