Patent Application
20240408650
This disclosure relates to cleaning of substrates after 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.
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.
During polishing, debris and slurry can stick to the surface of the substrate, resulting in defects. Therefore, after polishing the substrate can be transferred to a cleaning system, where the substrate undergoes cleaning, e.g., using one or more of a megasonic cleaner, a rotating brush cleaner, or a buff pad cleaner.
In one aspect, a fluid jet cleaner includes an atomizer nozzle including an input port for a carrier gas, an injection port for a cleaning liquid, and an output port positioned to spray the cleaning liquid entrained in the carrier gas onto a substrate.
In another aspect, a fluid jet cleaner includes a nozzle having a convergent-divergent nozzle to spray a cleaning liquid onto a substrate.
In another aspect, a cleaning module includes a support to hold a substrate and a fluid jet cleaner having plurality of nozzle arranged in a line that extends on a radius of the substrate.
In another aspect, a cleaning fluid is sprayed from a nozzle at a speed of 100-1200 m/s onto a substrate to clean the substrate after polishing.
In another aspect, a chemical mechanical polishing system includes a first polishing station including a first platen to support a first polishing pad, a transfer station to receive a substrate from a robot, a carrier head movable on a predetermined path from the polishing station to the transfer station, a gas flow regulator having an input for a carrier gas, a liquid flow regulator having an input for a cleaning liquid, and a fluid jet cleaner at a position along the predetermined path. The fluid jet cleaner includes an atomizer nozzle including an input port coupled to the gas flow regulator, an injection port coupled to the liquid flow regulator, and an output port positioned to spray the cleaning liquid entrained in the carrier gas onto the substrate held by the carrier head when the carrier head is located above the fluid jet cleaner.
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.
Defects can be reduced without significantly impacting throughput, thereby increasing yield. The cleaning nozzles can be integrated into the polishing system, so that the substrate is pre-cleaned before being transported to a dedicated cleaning system. This can permit a substrate to sit in the polishing system for a longer period of time without increased risk of defects, e.g., due to coagulation of slurry on the substrate, which can increase flexibility in scheduling of delivery of substrates to the cleaning system, which in turn can improve throughput.
The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.
In the figures, like references indicate like elements.
As noted above, after polishing the substrate can be transferred to a cleaning system. However, some time is required to transport the substrate from the last polishing station, through a transfer station, to the cleaner. During this time, any debris or slurry on the substrate can dry and harden, thus becoming more difficult for the cleaner to remove. To combat this effect, the substrate can be sprayed with a mist of deionized (DI) water or water with chemistry, e.g., by nozzles at the transfer station. This can reduce the risk that the substrate dries out. In addition, the spray can rinse loose particles off the substrate. Although such rinsing might be considered a “cleaning” step, a spray at low pressure still leaves some particles on the substrate, which may not be acceptable as customer demand increases for lower defect rates.
A technique that can address this issue is to spray the substrate at relatively high pressure with a cleaning liquid from an atomizer, e.g., a converging diverging (CD) nozzle. This can provide a deeper clean than simply a spray of mist, e.g., from a nebulizer. In addition, one or more atomizers can be provided in the load cup of the transfer station or at an inter-platen cleaning station, so that the substrate can be cleaned while held by the carrier head and while moving along its expected path. Thus, this cleaning technique can be integrated into an existing polishing system without significantly impacting throughput.
Each polishing station 100 of which includes a rotatable disk-shaped platen 120 on which a polishing pad 110 is situated. The polishing pad 110 can be a two-layer polishing pad with an outer polishing layer and a softer backing layer. At each polishing station 100, the platen 120 is operable to rotate about an axis of rotation 122. For example, a motor 124, e.g., a DC induction motor, can turn a drive shaft 126 to rotate the platen 120.
Each polishing station 100 can include a port 130 to dispense polishing liquid 132, such as abrasive slurry, onto the polishing pad 110 to the pad (the port is shown at only one station for simplicity). Each polishing station 100 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 50 also includes a carrier head 140 operable to hold a substrate 10. The carrier head 140 is movable between the transfer station 200 and the polishing station(s) 100. In particular, the carrier head 140 is suspended from a support structure 150, e.g., a carousel or track. In the case of a carousel, rotation of the carousel, e.g., by an actuator 152, can orbit the carrier head 140 about a central axis, which can carry the carrier head 140 in a predetermined path 160 from the transfer station 200 to each polishing station 100 in turn, and back to the transfer station 200. In the case of a track, the carrier head 140 can be driven along the track by an actuator 154. The track thus provides a predetermined path 160 for the carrier head to travel from the transfer station 200 to each polishing station 100 in turn, and back to the transfer station 200.
The carrier head 140 can include a retaining ring 142 to retain the substrate 10 below a flexible membrane 144. The carrier head 140 also includes one or more independently controllable pressurizable chambers defined by the membrane, e.g., three chambers 146a-146c, 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
The carrier head 140 is also connected by a drive shaft 156 to a carrier head rotation motor 158, e.g., a DC induction motor, so that the carrier head can rotate about an axis 159. The combination of polishing liquid and the relative motion between the polishing pad 110 and substrate 10, e.g., provided by rotation of the carrier head 140 and platen 120, results in polishing of the exposed surface of the substrate 10.
Optionally each carrier head 140 can oscillate laterally during the polishing operation, e.g., on sliders on the support structure 150, or by rotational oscillation of the carousel itself, or by sliding along the track. In typical operation, the platen is rotated about its central axis of rotation 125, and each carrier head is rotated about its central axis 155 and translated laterally across the top surface of the polishing pad.
Referring to
The transfer station 200 can optionally include one or more nozzles 220, e.g., nebulizers, positioned within the load cup 210 to spray a rinsing fluid 222, e.g., deionized water, on the substrate 10 as the substrate sits on the substrate support 212 and/or is held by the carrier head 140 (see
Returning to
The polishing system 50 can include a controller 90, e.g., a programmed general purpose computer with a processor and non-transitory computer readable media with instructions to cause the computer to control the various components of the polishing system 50, e.g., motors 124, 158, actuators 152, 154, 214, 312, and flow regulators 342, 352.
One or more fluid jet cleaners 300 are located at one or more locations along the predetermined path 160 travelled by the carrier head 140. For example, a fluid jet cleaner 300 can be positioned at the transfer station 200, e.g., within the load cup 210. Alternatively or in addition, a fluid jet cleaner 300 can be positioned at an inter-platen station 240, i.e., at a location along the path 160 between two platens 120 at two different polishing stations 200 that are adjacent along the path 160. Alternatively or in addition, a fluid jet cleaner 300 can be positioned on the path 160 between the last polishing station 200 along the path 160 and the transfer station 200.
As shown in
The cleaning liquid 322 can be water, e.g., deionized (DI) water. In some implementations the carrier fluid is pure water. However, in some implementations other chemistry, such as etchants, surfactants, inhibitors, or pH buffers, can be present in the cleaning liquid 322. For example, the cleaning liquid can include water can be mixed with ammonia.
The carrier gas can be nitrogen, pure air (i.e., air filtered to remove particulates), carbon dioxide, an inert gas such as argon, or a combination thereof.
The nozzle(s) 320 are oriented to spray the cleaning liquid 322 vertically upward, e.g., at an angle of 0° to 60° relative to vertical (gravity). Thus, the cleaning liquid 322 impacts the substrate 10 at angle of 0° to 60° from the normal to the substrate surface. A potential advantage of having the substrate in a face-down position and spraying the cleaning liquid 322 upward is that the cleaning liquid will naturally fall away rather than having to flow across the top surface of the substrate, thus reducing the risk of beading or staining.
In operation, the carrier head 140 holds the substrate in a face-down position. The nozzle(s) 320 spray a cleaning liquid, e.g., DI water, onto the exposed face of the substrate 10. The cleaning liquid is impinges the substrate 10 with a relatively high pressure or energy density (i.e., relative to the nebulizers discussed above). For example, the flow rate of cleaning liquid 322 can be 5 to 500 cc/min, and the atomized fluid can exit the nozzle with a speed of 100-1200 m/s. In some implementations, the atomized fluid exits the nozzle at supersonic speeds, e.g., Mach 1-3.
In some implementations, the support 310 is vertically movable, e.g., by actuator 312, so as to adjust the distance between the nozzles 320 and the substrate 10. In some implementations, the support 310 and nozzles 312 are vertically fixed. The outlet port of the nozzle 320 can be located 15 to 100 mm from the surface of the substrate 10.
Where there are multiple nozzles 310, the nozzles can be positioned in a line. For example, as shown in
Referring to
Optionally, as shown in
Referring to
The input port 320 leads to a convergent section 332 where the channel through the nozzle 320 narrows. From the convergent section 332, the gas enters a choke-point, or throat 334, where the cross-sectional area of the nozzle 320 is at its minimum. In some implementations, the throat 334 has a concave curvature relative to the center line of the channel, as opposed to a convex curvature of the convergent section 332. However, other configurations are possible, e.g., the entire CD passage is concave. In addition, as shown in
The diameter of the channel 328 at the narrowest region can be 2 to 10 times less than the diameter of the channel 328 at the inlet port 330. The diameter of the channel 328 at the narrowest region can be 1.5 to 10 times less than the diameter of the channel 328 at the outlet port 338. The velocity of the gas increases as it flows from the convergent section 332, through the throat 33 and to a divergent section 336, and out an output port 338. The throat 204 causes the velocity of the gas flowing through the throat 204 to increase. In some implementations, the velocity of the gas is increased to supersonic speeds.
With the nozzle 320 being an atomizer, the cleaning liquid 322 flows from a cleaning liquid source 350 through an injection passage 360 into the channel 328. A flow rate and/or pressure of the cleaning fluid 348 into an injection port 366 of the injection passage 360 can be controlled by a gas flow regulator 352. The liquid flow regulator 352 can be a pump 352a, one or more valves 352b, or a combination thereof, and optionally can include a pressure and/or mass flow sensor and microcontroller to control the pump 352a and/or valve 352b to achieve a desired cleaning fluid flow rate and/or pressure as set by the controller 90.
The injection passage 360 can simply end in an opening 362 that is flush with the sidewalls of the channel 328. Alternatively, the injection passage 360 can project (shown in phantom) into the channel 328, e.g., into the center of the channel 328. The injection passage 370 can be positioned to inject water droplets into the convergent section 332 (as shown in
In order for the droplets 354 of cleaning liquid in the spray to impinge the substrate at sufficient velocity to performing cleaning (as opposed to simply rinsing), for a nozzle with a channel having a diameter D1 of 1.2 mm at the narrowest section of the throat 334, a diameter D2 of 4 mm at the inlet port, and a diameter D3 of 2.4 mm at the outlet port, the pump 342 (and/or valve 344) can be set by the controller to deliver the carrier gas at a flow rate of 10-150 standard liters per minute (SLPM) per nozzle, and valve 352 can be set by the controller 90 to dispense water into the injection passage 360 at a flow rate of 5-500 cc/min per nozzle. The cleaning liquid flow rate (by volume) can be about 0.001% to 1%, e.g., 0.01 to 0.1% of the carrier gas flow rate.
Returning to
The fluid jet cleaner 300 can be mounted on the load cup 210 or the substrate support 212 so that the support 310 and nozzles 320 move vertically with the load cup 210 or the substrate support 212 under the action of the actuator 214. Alternatively, the fluid jet cleaner 300 is not mounted on the load cup 210 or substrate support 212, but is independently movable by an actuator, e.g., actuator 312.
In operation, the substrate 10 can be sprayed by both the atomizing nozzles 320 of the fluid jet cleaner 300, and by the nebulizer nozzles 220. Thus, the substrate 10 can be impinged by liquids, e.g., the rinsing liquid and the cleaning liquid, at different pressures or energy densities. In particular, the cleaning liquid impinges the substrate 10 with higher pressure or energy density than the rinsing liquid. However, in some implementations just the fluid jet cleaner 300 is used or is present.
Returning to
Although converging-diverging atomizer nozzles have been discussed in the context of a face-down substrate held by a carrier head in a polishing system, the fluid jet cleaner 300 can be used in other situations. For example:
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.
A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other implementations are within the scope of the following claims.
