Control of steam generation for chemical mechanical polishing

Abstract

To provide control of steam generation for a substrate processing tool for chemical mechanical polishing.SOLUTION: A chemical mechanical polishing system includes: a steam generator 410 with a heating element for applying heat to a vessel in order to generate steam; an opening for delivering steam onto a polishing pad; a first valve in a fluid line between the opening and the vessel; a sensor 260 for monitoring a steam parameter; and a control system 200. The control system causes the valve to open and close in accordance with a steam delivery schedule in a recipe, receives a measured value of the steam parameter from the sensor 260, receives a target value of the steam parameter, and performs a proportional integral derivative control algorithm with the target value and measured value as inputs so as to control the first valve and / or a second pressure release valve and / or the heating element so that the measured value reaches the target value substantially just before the valve is opened according to the steam delivery schedule.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to controlling vapor generation for substrate processing tools, for example, for chemical mechanical polishing (CMP). [Background technology]

[0002] Integrated circuits are typically formed on a substrate by successively depositing conductive, semiconductive, or insulating layers on a semiconductor wafer. Various manufacturing processes require planarization of layers on the substrate. For example, one manufacturing step involves depositing a filler layer over a non-planar surface and polishing the filler layer until the top surface of a patterned layer is exposed. As another example, a layer may be deposited over a patterned conductive layer and planarized to allow for subsequent photolithography steps.

[0003] Chemical mechanical polishing (CMP) is one of the accepted methods of planarization. This planarization method typically involves mounting a substrate on a carrier head. The exposed surface of the substrate is typically positioned against a rotating polishing pad. The carrier head applies a controllable load to the substrate, pressing it against the polishing pad. An abrasive slurry, typically containing abrasive particles, is supplied to the surface of the polishing pad.

[0004] The removal rate in a polishing process can be sensitive to temperature, and various techniques have been proposed to control the temperature during polishing. Summary of the Invention

[0005] The chemical mechanical polishing system includes a platen for supporting a polishing pad, a carrier head for holding a substrate in contact with the polishing pad, a motor for generating relative motion between the platen and the carrier head, a steam generator including a container having a water inlet and a steam outlet and a heating element configured to apply heat to a portion of a lower chamber to generate steam, an arm extending across the platen having at least one opening oriented to supply steam from the steam generator onto the polishing pad, a first valve in a fluid line between the opening and the steam outlet for controllably connecting and disconnecting the opening and the steam outlet, a sensor for monitoring a steam parameter, and a control system coupled to the sensor, the valve, and optionally the heating element. The control system is configured to open and close the valve according to a steam supply schedule in a polishing process recipe stored as data in a non-transitory storage device, receive a measured value of the steam parameter from the sensor, receive a target value of the steam parameter, and execute a proportional-integral-derivative control algorithm with the target value and the measured value as inputs to control the first valve and / or the second pressure relief valve and / or the heating element such that the measured value reaches the target value approximately just before the valve opens according to the steam supply schedule.

[0006] Potential advantages may include, but are not limited to, one or more of the following:

[0007] Steam, i.e., gaseous H2O generated by boiling, can be generated in sufficient quantities to allow steam heating of the polishing pad before polishing each substrate, and the steam can be generated at a constant pressure between wafers. The temperature of the polishing pad, and therefore the polishing process temperature, can be controlled and made more uniform between wafers, resulting in less wafer-to-wafer non-uniformity (WIWNU). Excessive steam generation can be minimized to improve energy efficiency. The steam can be a substantially pure gas, e.g., gas with little or no suspended matter in the steam. Such steam, also known as dry steam, can provide gaseous H2O with higher energy transfer and less liquid content than other steam alternatives, such as flash steam.

[0008] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will become apparent from the description and drawings, and from the claims. [Brief description of the drawings]

[0009] [Figure 1A] 1 is a schematic cross-sectional view of an example of a polishing station of a polishing apparatus. [Figure 1B] 1 is a schematic top view of an exemplary polishing station of a chemical mechanical polishing apparatus. [Diagram 2] 1 illustrates a control system including a proportional-integral-derivative control algorithm that may be implemented to control power to a steam generator. [Figure 3A] 1 is a schematic cross-sectional view of an exemplary steam generator. [Figure 3B] 1 is a schematic cross-sectional top view of an exemplary steam generator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Chemical mechanical polishing works by a combination of mechanical polishing and chemical etching at the interface between the substrate, the polishing fluid, and the polishing pad. During the polishing process, friction between the surface of the substrate and the polishing pad generates a significant amount of heat. In addition, some processes include an in-situ pad conditioning step, in which a conditioning disk (e.g., a disk coated with abrasive diamond particles) is pressed against the rotating polishing pad to condition and smooth the polishing pad surface. The polishing of the conditioning process may also generate heat. For example, a typical 1-minute copper CMP process at a nominal downforce pressure of 2 psi and a removal rate of 8000 Å / min may cause the surface temperature of a polyurethane polishing pad to increase by about 30°C.

[0011] On the other hand, if the polishing pad is heated by a previous polishing operation, when a new substrate is first lowered into contact with the polishing pad, the polishing pad will be at a lower temperature and therefore can act as a heat sink. Similarly, the slurry dispensed onto the polishing pad can also act as a heat sink. Together, these effects result in spatial and temporal variations in the temperature of the polishing pad.

[0012] For example, both chemical reaction-related variables (e.g., variables such as the onset and rate of the reactions involved) and mechanical-related variables (e.g., the surface friction coefficient and viscoelasticity of the polishing pad) in the CMP process are highly temperature-dependent. As a result, the fluctuation of the surface temperature of the polishing pad can cause changes in removal rate, polishing uniformity, erosion, dishing, and residue. By more closely controlling the temperature of the surface of the polishing pad during polishing, the temperature fluctuation can be reduced, and the polishing performance, for example, measured based on the intra-wafer non-uniformity or inter-wafer non-uniformity, can be improved.

[0013] One technique that has been proposed to control the temperature of a chemical mechanical polishing process is to spray steam onto the polishing pad. Steam may be superior to hot water because, for example, less steam may be required to impart the same amount of energy as hot water due to the latent heat of steam.

[0014] In a typical polishing process, steam is applied with a duty cycle (typically measured as a percentage of the total time from the start of polishing one wafer to the start of polishing a subsequent wafer) that can range from 1% to 100%. When the duty cycle is less than 100%, the steam generation cycle can be divided into two sections: a recovery phase and a dispensing phase.

[0015] Typically, during the recovery phase, the steam generation vessel is considered closed, i.e., the valve is closed so that steam cannot escape the vessel. Power is applied to a heater (e.g., a resistive heater) to inject thermal energy into the liquid water in the vessel. Additionally, liquid water may flow into the vessel to replace water lost in the previous dispensing cycle.

[0016] In the dispense phase, a valve is opened to allow steam to be dispensed. During the dispense phase, the steam generator may not be able to keep up with the flow rate of steam. In this case, the dispense phase is accompanied by a pressure drop in the vessel. In some circumstances, when the heated liquid water is exposed to the atmosphere, a rapid phase change of gas, commonly referred to as flash steam, can occur.

[0017] Generally, during the recovery phase, the goal is to add enough heat energy to prepare the steam for the next dispensing phase, as dictated by the parameters (temperature, flow rate, pressure) that may be required for the process. In some cases, for example, if a 20 second dispensing phase is followed by an 80 second recovery phase, the required steam pressure may be achieved with plenty of time before the start of the next dispensing cycle. In this scenario, power to the heater may be turned off to avoid the steam exceeding the required parameters (e.g., pressure). However, since the vessel is not a perfect insulator, some heat loss may occur and the steam may not remain at the desired parameters. Alternatively, power to the heater may be maintained and the excess steam may be released (e.g., vented) to maintain the required parameters (e.g., pressure). However, this consumes too much energy and is not energy efficient.

[0018] To address this issue, during the recovery phase the control system can control the power applied to the heater using, for example, a proportional-integral-derivative control algorithm, so that the required parameters are achieved just before the start of the next dispensing phase.

[0019] 1A and 1B show an example of a polishing station 20 of a chemical mechanical polishing system. The polishing station 20 includes a rotatable, disk-shaped platen 24 on which a polishing pad 30 is placed. The platen 24 is operable to rotate about an axis 25 (see arrow A in FIG. 1B). For example, a motor 22 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 34 and a softer backing layer 32.

[0020] The polishing station 20 may include a supply port, for example, at the end of a slurry supply arm 39, for dispensing a polishing fluid 38, such as a polishing slurry, onto the polishing pad 30. The polishing station 20 may further include a pad conditioner with a conditioning disk to maintain the surface roughness of the polishing pad 30.

[0021] Carrier head 70 is operable to hold substrate 10 against polishing pad 30. Carrier head 70 is suspended from a support structure 72 (e.g., a carousel or track) and connected by a drive shaft 74 to a carrier head rotation motor 76, which enables carrier head 70 to rotate about axis 71. Alternatively, carrier head 70 can be oscillated laterally by movement along a track, or by rotational oscillation of the carousel itself, for example, on a slider on the carousel.

[0022] The carrier head 70 may include a flexible membrane 80 having a substrate mounting surface that contacts the backside of the substrate 10, and a number of pressurizable chambers 82 that apply different pressures to different zones (e.g., different radial zones) of the substrate 10. The carrier head 70 may include a retaining ring 84 that holds the substrate. In some implementations, the retaining ring 84 may include a lower plastic portion 86 that contacts the polishing pad and an upper portion 88 of a harder material (e.g., metal).

[0023] During operation, the platen rotates about its central axis 25 and the carrier head rotates about its central axis 71 (see arrow B in FIG. 1B) and moves laterally across the upper surface of polishing pad 30 (see arrow C in FIG. 1B).

[0024] In some implementations, the polishing station 20 includes a temperature sensor 64 for monitoring the temperature within the polishing station or the temperature of a component of or within the polishing station (e.g., the temperature of the polishing pad 30 and / or the slurry 38 on the polishing pad). For example, the temperature sensor 64 may be an infrared (IR) sensor (e.g., an IR camera) positioned above the polishing pad 30 and configured to measure the temperature of the polishing pad 30 and / or the slurry 38 on the polishing pad. In particular, the temperature sensor 64 may be configured to measure the temperature at multiple points along the radius of the polishing pad 30 to generate a radial temperature profile. For example, the IR camera may have a field of view that spans the radius of the polishing pad 30.

[0025] In some implementations, the temperature sensor is a contact sensor rather than a non-contact sensor. For example, the temperature sensor 64 may be a thermocouple or an IR thermometer positioned on or in the platen 24. Additionally, the temperature sensor 64 may be in direct contact with the polishing pad.

[0026] In some implementations, multiple temperature sensors may be spaced at different radial locations across the polishing pad 30 to provide the temperature at multiple points along the radius of the polishing pad 30. This technique can be used in place of or in addition to an IR camera.

[0027] 1A, the temperature sensor 64 is shown positioned to monitor the temperature of the polishing pad 30 and / or the slurry 38 on the pad 30, but may also be positioned inside the carrier head 70 to measure the temperature of the substrate 10. The temperature sensor 64 may be in direct contact with the semiconductor wafer of the substrate 10 (i.e., may be a contact type sensor). In some implementations, multiple temperature sensors are included within the polishing station 22, for example, to measure the temperatures of various components of or within the polishing station.

[0028] The polishing system 20 further includes a temperature control system 100 for controlling the temperature of the polishing pad 30 and / or the slurry 38 on the polishing pad. The temperature control system 100 includes a heating system 104 that operates by supplying steam, i.e., a temperature-controlled medium, onto the polishing surface 36 of the polishing pad 30 (or onto the polishing liquid already present on the polishing pad). In particular, the medium includes steam, for example, from a steam generator 410 (see FIG. 2A). The steam may be mixed with another gas (e.g., air) or liquid (e.g., heated water), or the medium may be substantially pure steam. In some embodiments, additives or chemicals are added to the steam.

[0029] The medium may be delivered by flowing through apertures, such as holes or slots, provided by one or more nozzles on the heated delivery arm, which may be provided by a manifold connected to a source of heated medium.

[0030] The exemplary heating system 104 includes an arm 140 that extends across the platen 24 and polishing pad 30 from the edge of the polishing pad 30 to or at least near the center of the polishing pad (e.g., within 5% of the total radius of the polishing pad). The arm 140 can be supported by a base 142, which can be supported on the same frame 40 as the platen 24. The base 142 can include one or more actuators, such as a linear actuator for raising or lowering the arm 140 and / or a rotary actuator for swinging the arm 140 laterally over the platen 24. The arm 140 is positioned to avoid collisions with other hardware components, such as the polishing head 70, the pad conditioning disk 92, and the slurry dispensing arm 39.

[0031] A plurality of openings 144 are formed in the bottom surface of the arm 140. Each opening 144 is configured to direct a gas or water vapor, e.g., steam, onto the polishing pad 30. The arm 140 can be supported by a base 142 such that the openings 144 are separated from the polishing pad 30 by a gap 126. The gap 126 can be 0.5 to 5 mm. In particular, the gap 126 can be selected so that heat of the heating fluid is not significantly dissipated before the fluid reaches the polishing pad. For example, the gap can be selected so that steam emitted from the openings does not condense before reaching the polishing pad.

[0032] The heating system 104 may include a steam source, such as a steam generator 410. The steam generator 410 is connected to an opening 144 in the arm 140 by a fluid supply line 146. The fluid supply line 146 may be provided by piping, flexible tubing, a passage through a solid material that provides the arm 140, or a combination thereof.

[0033] Steam generator 410 includes a vessel 420 for holding water and a heater 430 for providing heat to the water in vessel 420. Power may be provided to heater 430 from power source 250. A sensor 260 may be disposed within vessel 420 or within fluid delivery line 146 to measure a physical parameter of the steam (e.g., temperature or pressure).

[0034] In some implementations, process parameters (e.g., flow rate, pressure, temperature, and / or liquid to gas mixture ratio) can be controlled independently for each nozzle. For example, the fluid for each opening 144 can flow through an individually controllable heater to individually control the temperature of the heated fluid (e.g., the temperature of the vapor).

[0035] The various openings 144 can direct the vapor 148 onto various radial zones 124 on the polishing pad 30. Adjacent radial zones may overlap. Optionally, some of the openings 144 can be oriented such that the central axis of the spray from that opening is at an oblique angle to the polishing surface 36. The vapor can be directed from one or more of the openings 144 to have a horizontal component in a direction opposite to the direction of motion of the polishing pad 30 at the impact region caused by rotation of the platen 24.

[0036] 1B shows the openings 144 being equally spaced apart, but this is not required. The nozzles 120 may be non-uniformly distributed radially, angularly, or both. For example, the openings 144 may be more tightly clustered toward the center of the polishing pad 30. As another example, the openings 144 may be more tightly clustered at a radius corresponding to the radius at which polishing fluid 39 is delivered to the polishing pad 30 by the slurry delivery arm 39. Additionally, while FIG. 1B shows nine openings, the number of openings may be greater or less.

[0037] When steam is generated (e.g., in steam generator 410 of FIG. 2A), the temperature of the steam 148 may be 90° C. to 200° C. For example, due to heat losses during passage, when the steam is dispensed by nozzle 144, the temperature of the steam may be 90 to 150° C. In some implementations, the steam is supplied by nozzle 144 at 70 to 100° C. (e.g., 80 to 90° C.). In some implementations, the steam supplied by the nozzle is superheated (i.e., at a temperature above its boiling point (for that pressure)).

[0038] When steam is delivered by nozzle 144, the flow rate of the steam can be 1 to 1000 cc / min depending on the power and pressure of the heater. In some implementations, the steam is mixed with other gases, for example, normal atmosphere or N2. Alternatively, the fluid delivered by nozzle 120 is substantially pure water. In some implementations, the steam 148 delivered by nozzle 120 is mixed with liquid water, for example, aerosolized water. For example, the liquid water and steam can be combined in a relative flow ratio (e.g., flow rate in sccm) of 1:1 to 1:10. However, if the amount of liquid water is low (e.g., less than 5 wt%, e.g., less than 3 wt%, e.g., less than 1 wt%), the steam will have excellent heat transfer properties. Thus, in some implementations, the steam is dry steam, i.e., substantially free of water droplets.

[0039] The polishing system 20 may further include a cooling system (e.g., an arm having an aperture for dispensing a cooling fluid onto the polishing pad), a high-pressure rinsing system (e.g., an arm having a nozzle for spraying rinsing fluid onto the polishing pad), and a wiper blade or wiper body for evenly distributing the polishing fluid 38 across the polishing pad 30.

[0040] Referring to FIG. 2, the polishing system 20 includes a control system 200 for controlling the operation of various components (e.g., temperature control system 100), as well as rotation of the carrier head, rotation of the platen, pressure applied by a chamber in the carrier head, etc.

[0041] The control system 200 may be configured to receive pad temperature measurements from the temperature sensor 64. The control system implements a first control loop 202 that may set target parameters for the steam for each cycle (each cycle includes a recovery phase and a dispense phase, as described above). Briefly, the control loop 202 may compare the measured pad temperature to a target pad temperature and generate a feedback signal. The feedback signal is used to calculate revised target parameters for the steam to reach the target pad temperature. For example, if the measured pad temperature did not reach the target pad temperature in a previous dispense phase, the feedback signal causes the temperature control system 200 to supply more heat to the polishing pad in a subsequent dispense phase, but if the measured pad temperature exceeded the target pad temperature in a previous dispense phase, the feedback signal causes the temperature control system 200 to supply less heat to the polishing pad in a subsequent dispense phase.

[0042] Several techniques can be used, alone or in combination, to control the amount of heat delivered to the polishing pad per dispensing step. First, the period during which steam is delivered, e.g., the duty cycle, may be extended (to deliver more heat) or shortened (to deliver less heat). Second, the temperature at which steam is delivered may be increased (to deliver more heat) or decreased (to deliver less heat). Third, the pressure at which steam is delivered may be increased (to deliver more heat) or decreased (to deliver less heat).

[0043] Thus, if the measured pad temperature does not reach the target pad temperature, the feedback signal can cause the control loop 202 to increase the target vapor temperature, pressure, and / or duty cycle for the subsequent dispensing step. On the other hand, if the measured pad temperature exceeds the target pad temperature in the previous dispensing step, the feedback signal can cause the control loop 202 to decrease the target vapor temperature, pressure, and / or duty cycle. As a result, the parameter target value r(t) of the vapor, e.g., the target value for pressure or temperature, can change from cycle to cycle. In some implementations, the control loop can operate continuously, rather than cycle to cycle, continuously monitoring the temperature of the polishing pad 30 and adjusting the parameter target value r(t) as polishing progresses.

[0044] The parameter target value r(t) is output from the control loop 202 to a proportional-integral-derivative (PID) controller 204. The controller executes a proportional-integral-derivative control algorithm to control the power applied by the power supply 250 to the heater 430. The PID controller 204 may be connected to a sensor 260 to receive a measured value Y(t) of a parameter (e.g., temperature or pressure). The PID controller 204 may be adjusted such that the target parameter value is achieved just before the start of the next dispensing phase. For example, the target parameter may be reached less than 180 seconds (e.g., less than 60 seconds, e.g., less than 30 seconds, e.g., less than 10 seconds, e.g., less than 3 seconds, e.g., less than 1 second) before the valve opens.

[0045] In the PID controller 204, the target parameter value r(t) is compared to the measured parameter value Y(t) from the sensor 260 by a comparator 210. The comparator outputs an error signal e(t) based on the difference.

[0046] The error signal is input to a proportional value calculator 212 which calculates a first proportional output P. The proportional output P is given by: can be calculated based on TIFF2025069155000002.tif11170, where K Pare weights that are set during tuning. The error signal e(t) is also input to an integral calculator 214 that calculates a second integral output I. The integral output I is given by: can be calculated based on TIFF2025069155000003.tif16170, where K I are weights that are set during tuning. The error signal e(t) is also input to a derivative calculator 216 that calculates the third derivative output D. The integral output D is given by can be calculated based on TIFF2025069155000004.tif17170, where K D are the weights that are set during tuning.

[0047] A sum calculator 218 sums the proportional output P, ​​the integral output I, and the derivative output D and outputs a control signal u(t), which sets the power that the power supply 250 outputs to the heater 430.

[0048] Generally, when tuning the PID controller 204, P It is desirable to keep K as low as possible. K is then adjusted as necessary based on the overshoot and set time so that the target parameter value is achieved just before the start of the next dispense step. I and K D can be increased. Various PID tuning methods are available, such as Cohen-Coon, Ziegler-Nichols, Tyreus-Luyben, and Autotune. In some implementations, the amount of heat added is controlled under the assumption that the duty cycle of the valve is constant. In this case, the gain value K I , K P , and K D does not need to change from cycle to cycle. However, in some implementations, if the duty cycle changes from cycle to cycle, K I , K P , and K D can be adjusted for each duty cycle. For example, once the duty cycle is calculated, the gain value K I , K P , and KD The gain value can be selected based on a look-up table relating a gain to a duty cycle percentage.

[0049] In some implementations, rather than controlling the heat applied by the heater 430, the PID controller 204 can control a flow meter or valve 270 that can vent pressure from a vessel in the steam generator 410. In this case, the flow meter or valve is controlled to vent pressure and maintain the steam pressure at a target pressure value. If implemented as a valve, the valve can open and close with a duty cycle that depends on the control signal u(t). If implemented as a flow meter, the control signal u(t) can control the flow rate through the regulator, for example, by adjusting the size of an aperture. In some implementations, the PID controller 204 can control a valve 438, in which case the steam is exhausted through an opening in an arm.

[0050] The control system 200 and its functional operations can be implemented in digital electronic circuitry, tangibly embodied computer software or firmware, computer hardware, or a combination of one or more of these. The computer software can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a tangible, non-transitory storage medium for execution by or for controlling the operation of a processor of a data processing device. The electronic circuits and data processing devices can include general-purpose programmable, programmable digital processors, and / or multiple digital processors or computers, and may also be special-purpose logic circuits, for example FPGAs (Field Programmable Gate Arrays) or ASICs (Application Specific Integrated Circuits).

[0051] When a control system is "configured to" perform a particular operation or action, it means that the system has installed thereon software, firmware, hardware, or a combination thereof that, during operation, causes the system to perform that operation or action. When one or more computer programs are configured to perform a particular operation or action, it means that one or more programs contain instructions that, when executed by a data processing device, cause the device to perform the operation or action.

[0052] 3A, steam for the processes described herein or for other uses in a chemical mechanical polishing system can be generated using a steam generator 410. An exemplary steam generator 410 can include a canister 420 that encloses an interior space 425. The walls of the canister 420 can be made of an insulating material (e.g., quartz) that has very low levels of mineral contaminants. Alternatively, the walls of the canister can be formed of another material, for example, the inner surface of the canister can be coated with polytetrafluoroethylene (PTFE) or another plastic. In some implementations, the canister 420 can be 10 to 20 inches long and 1 to 5 inches wide.

[0053] 3A and 3B, in some embodiments, the interior space 425 of the canister 420 is divided into a lower chamber 422 and an upper chamber 424 by a barrier 426. The barrier 426 can be made of the same material as the canister walls, for example, quartz, stainless steel, aluminum, or a ceramic such as alumina. Quartz may be advantageous in that it has a low risk of contamination. The barrier 426 can substantially prevent liquid water 440 from entering the upper chamber 424 by blocking water droplets that are splashed by boiling water. This allows dry steam to accumulate in the upper chamber 424.

[0054] The barrier 426 includes one or more apertures 428. The apertures 428 allow steam to pass from the lower chamber 422 into the upper chamber 424. The apertures 428, and particularly the apertures 428 near the edges of the barrier 426, allow condensation on the walls of the upper chamber 424 to drip into the lower chamber 422, reducing the liquid content in the upper chamber 426 and allowing the liquid to be reheated using water 440.

[0055] The aperture 428 may be located at (e.g., only at) the end of the barrier 426 where the barrier 426 contacts the inner wall of the canister 420. The aperture 428 may also be located near the end of the barrier 426 (e.g., between the end of the barrier 426 and the center of the barrier 426). This configuration may be advantageous in that the barrier 426 does not have an aperture in the center, thus reducing the risk of liquid droplets entering the upper chamber, yet allowing condensation on the sidewalls of the upper chamber 424 to flow out of the upper chamber.

[0056] However, in some implementations, the apertures are positioned further away from the ends, eg, so as to be uniformly spaced across the width of the barrier 426, eg, across the area of ​​the barrier 425.

[0057] 3A, a water inlet 432 can connect a water reservoir 434 to the lower chamber 422 of the canister 420. The water inlet 432 can be located at or near the bottom of the canister 420 to supply water 440 to the lower chamber 422.

[0058] One or more heating elements 430 may surround a portion of the lower chamber 422 of the canister 420. The heating element 430 may be, for example, a heating coil (e.g., a resistive heater) wrapped around the outside of the canister 420. Additionally, the heating element may be provided by a thin film coating on the material of the sidewall of the canister. When an electric current is applied, this thin film coating may function as a heating element.

[0059] The heating element 430 may be disposed in the lower chamber 422 of the canister 420. For example, the heating element may be coated with a material that prevents contaminants (e.g., metal contaminants) from the heating element from migrating into the vapor.

[0060] The heating element 430 can apply heat to the bottom of the canister 420 up to the minimum water level 443a, i.e., the heating element 430 can cover the portion of the canister 420 below the minimum water level 443a, thereby preventing overheating and reducing unnecessary energy consumption.

[0061] A vapor outlet 436 can connect the upper chamber 424 to a vapor supply passage 438. The vapor supply passage 438 can be located at or near the top of the canister 420 (e.g., in the ceiling of the canister 420) to allow vapor to pass from the canister 420 through the vapor delivery passage 438 to reach various components of the CMP apparatus. The vapor supply passage 438 can be used to direct vapor to various areas of the chemical mechanical polishing apparatus, for example, for vapor cleaning and pre-heating of the carrier head 70, the substrate 10, and the pad conditioner disk 92.

[0062] In some implementations, a filter 470 is coupled to the vapor outlet 438 configured to reduce contaminants in the vapor 446. The filter 470 may be an ion exchange filter.

[0063] Water 440 can flow from a water reservoir 434 through the water inlet 432 and into the lower chamber 422. The water 440 can fill the canister 420 at least to a water level 442 that is above the heating element 430 and below the barrier 426. Upon heating the water 440, a gaseous medium 446 is generated that rises through an aperture 428 in the barrier 426. The aperture 428 allows the vapor to rise and simultaneously dissipate condensate, resulting in a gaseous medium 446 in which the water is a substantially liquid-free vapor (e.g., there are no liquid water droplets suspended in the vapor).

[0064] In some implementations, the water level is determined using a water level sensor 460 that measures the water level 442 in a bypass tube 444. The bypass tube connects the water reservoir 434 to the steam supply passage 438 in parallel with the canister 420. The water level sensor 460 can indicate where the water level 442 is in the bypass tube 444, and therefore in the canister 420. For example, the water level sensor 444 and the canister 420 are equally pressurized (e.g., both receive water from the same water reservoir 434, both have the same pressure above, e.g., both are connected to the steam supply passage 438), so the water level 442 is the same between the water level sensor and the canister 420. In some embodiments, the water level 442 of the water level sensor 444 can indicate the water level 442 of the canister 420 in other situations, e.g., the water level 442 of the water level sensor 444 is scaled to indicate the water level 442 of the canister 420.

[0065] During operation, the water level 442 in the canister is above a minimum water level 443a and below a maximum water level 443b, where the minimum water level 443a is at least above the heating element 430 and the maximum water level 443b is well below the steam outlet 436 and the barrier 426, providing enough space for the gaseous medium 446 (e.g., steam) to pool near the top of the canister 420 while still being substantially free of liquid water.

[0066] In some implementations, the controller 200 is coupled to a valve 480 that controls the flow of fluid through the water inlet 432, a valve 482 that controls the flow of fluid through the steam outlet 436, and / or a water level sensor 460. Using the water level sensor 460, the controller 200 is configured to control the flow of water 440 into the canister 420 and control the flow of gas 446 out of the canister 420 to maintain a water level 442 above a minimum water level 443a (and above the heating element 430) and below a maximum water level 443b (and below the barrier 426, if present). The controller 200 may further be coupled to a power source 250 for the heating element 430 to control the amount of heat provided to the water 440 in the canister 420.

[0067] While measurements of pad temperature and supplying steam to the pad have been described, this should be understood to include measurements of the slurry on the pad or supplying steam to the slurry on the pad.

[0068] Although several embodiments of the present invention have been described, it should be understood that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. 1. A chemical mechanical polishing system comprising: a platen for supporting the polishing pad; a carrier head for holding a substrate in contact with the polishing pad; a motor for generating relative motion between the platen and the carrier head; a steam generator including a vessel having a water inlet and a steam outlet, and a heating element configured to apply heat to a portion of the lower chamber to generate steam; an arm extending across the platen having at least one opening oriented to deliver steam from the steam generator onto the polishing pad; a first valve in a fluid line between the opening and the vapor outlet for controllably connecting and disconnecting the opening and the vapor outlet; A sensor for monitoring a steam parameter, a control system coupled to the sensor, the valve, and optionally the heating element, opening and closing the valve according to a vapor supply schedule in a polishing process recipe stored as data in a non-transitory storage device; receiving a measurement of the steam parameter from the sensor; receiving a target value for the steam parameter; executing a proportional-integral-derivative control algorithm with the target value and the measured value as inputs to control the first valve and / or the second pressure relief valve and / or the heating element such that the measured value reaches the target value approximately immediately prior to the valve opening in accordance with the steam delivery schedule. The control system is configured as follows: A chemical mechanical polishing system comprising:

2. The system of claim 1 , wherein the steam parameter is steam temperature, the measured value is a measured steam temperature value, and the target value is a target steam temperature value.

3. The system of claim 1 , wherein the steam parameter is steam pressure, the measured value is a measured steam pressure value, and the target value is a target steam pressure value.

4. The system of claim 1 , wherein a controller is configured to execute the proportional-integral-derivative control algorithm to control the valve at times other than delivery periods in the steam delivery schedule.

5. The system of claim 1 , wherein a controller is configured to execute the proportional-integral-derivative control algorithm to control the heating element.

6. The system of claim 1 , wherein the controller is configured to execute the proportional-integral-derivative control algorithm such that the measured value reaches the target value less than 10 seconds before the valve is opened.

7. 7. The system of claim 6, wherein the controller is configured to execute the proportional-integral-derivative control algorithm such that the measured value reaches the target value less than 3 seconds before the valve is opened.

8. 8. The system of claim 7, wherein the controller is configured to execute the proportional-integral-derivative control algorithm such that the measured value reaches the target value less than one second before the valve is opened.

9. 2. The system of claim 1, further comprising a water level sensor for monitoring a water level in the vessel, the controller being configured to receive a signal from the water level sensor and modify a flow rate of water through the water inlet based on the signal from the water level sensor to maintain a water level in the vessel above the heating element and below the steam outlet.

10. The system of claim 1 , wherein the controller is configured to open the valve during a dispense phase of a cycle and to close the valve during a recovery phase of the cycle.

11. The system of claim 10 , wherein each cycle corresponds to polishing a single substrate.

12. 11. The system of claim 10, wherein each cycle consists of a single dispense phase and a single restore phase.

13. The system of claim 10 further comprising a temperature sensor location for measuring a temperature of the polishing pad.

14. 14. The system of claim 13, wherein the controller is configured to receive a signal from the sensor representative of the temperature of the polishing pad and set the target value of the vapor parameter based on the signal.

15. The system of claim 14 , wherein the controller is configured to set the target value on a cycle-by-cycle basis.

16. The system of claim 14 , wherein the controller is configured to set the target value continuously throughout a cycle.

17. 1. A chemical mechanical polishing system comprising: a platen for supporting the polishing pad; a carrier head for holding a substrate in contact with the polishing pad; a motor for generating relative motion between the platen and the carrier head; a steam generator including a vessel having a water inlet and a steam outlet, and a heating element configured to apply heat to a portion of the lower chamber to generate steam; an arm extending across the platen having at least one opening oriented to deliver steam from the steam generator onto the polishing pad; a first valve in a fluid line between the opening and the vapor outlet for controllably connecting and disconnecting the opening and the vapor outlet; a second valve or flow regulator in the fluid line between the first valve and the vapor outlet, the second valve configured to controllably vent pressure from the vessel; A sensor for monitoring a steam parameter, a control system coupled to the sensor, the valve, and optionally the heating element, opening and closing the first valve according to a vapor supply schedule in a polishing process recipe stored as data in a non-transitory storage device; receiving a measurement of the steam parameter from the sensor; receiving a target value for the steam parameter; executing a proportional-integral-derivative control algorithm with the target value and the measured value as inputs to control the second valve such that the measured value reaches the target value approximately immediately prior to the valve opening in accordance with the steam delivery schedule; The control system is configured as follows: A chemical mechanical polishing system comprising:

18. 1. A steam generating assembly comprising: a steam generator including a vessel having a water inlet and a steam outlet, and a heating element configured to apply heat to a portion of the lower chamber to generate steam; a first valve in a fluid line from the vapor outlet for controllably connecting and disconnecting the vapor outlet to and from the opening; A sensor for monitoring a steam parameter, a control system coupled to the sensor, the valve, and optionally the heating element, opening and closing the valve according to a vapor supply schedule in a polishing process recipe stored as data in a non-transitory storage device; receiving a measurement of the steam parameter from the sensor; receiving a target value for the steam parameter; executing a proportional-integral-derivative control algorithm with the target value and the measured value as inputs to control the first valve and / or the second pressure relief valve and / or the heating element such that the measured value reaches the target value approximately immediately prior to the valve opening in accordance with the steam delivery schedule. The control system is configured as follows: A steam generating assembly comprising:

19. 1. A computer program product comprising a non-transitory computer-readable medium having instructions for causing one or more processors to: accessing a polishing process recipe stored as data in a non-transitory storage device; opening and closing a first valve between the outlet of the steam generating device and the opening according to a steam supply schedule; receiving a measurement of a vapor parameter of vapor within the vapor generating device from a sensor; receiving a target value for the steam parameter; executing a proportional-integral-derivative control algorithm with the target value and the measured value as inputs to control the first valve and / or the second pressure relief valve and / or the heating element such that the measured value reaches the target value approximately just before the valve opens in accordance with the steam delivery schedule; Computer program products.

Images