Advanced temperature control for a wafer carrier in a plasma processing chamber

Abstract

To provide a temperature control system capable of precise temperature control leading to precise temperature control of, for example, deposition and etching.SOLUTION: For a wafer carrier in a plasma processing chamber, heat exchangers supply a thermal fluid under temperature control to a fluid channel of a workpiece carrier 404, and receive the thermal fluid from the fluid channel. In a wFib 440, a proportional valve is provided between the heat exchanger and the fluid channel so as to control a flow rate of the thermal fluid from heat exchangers 450, 460 to the fluid channel, and a gas pressure valve is also provided between the heat exchangers and the fluid channel to further control the flow rate of the thermal fluid from the heat exchangers to the fluid channel. A temperature controller 430 receives a measured temperature value from a thermal sensor of the career, and controls the proportional valve and the gas pressure valve according to the measured temperature value to adjust the flow rate of the thermal fluid.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. Provisional Patent Application No. 62 / 332,237, filed May 5, 2016, by Fernando M. Silveira et al., entitled "ADVANCED TEMPERATURE CONTROL FOR WAFER CARRIER IN PLASMA PROCESSING CHAMBER."

[0002] FIELD OF THE INVENTION

[0002] Embodiments relate to the microelectronics manufacturing industry, and more particularly to thermal control systems that use a thermal fluid circulation system to control the temperature of a wafer carrier or wafer within a processing chamber. [Background technology]

[0003]

[0003] Microelectronic and micromechanical devices are typically fabricated in part on silicon or other types of wafers. Once completed, the wafer is cut into many smaller pieces, with each die forming a separate device. The wafer is subjected to many different processes to form all of the components on the device. In many processes, the wafer is held on a chuck, pedestal, or some other carrier in a processing chamber. One such chamber is a plasma processing chamber, in which the wafer is exposed to a plasma to deposit or remove different materials.

[0004] In plasma processing chambers, such as plasma etch or deposition chambers, the temperature of the wafer and wafer carrier is often a critical parameter controlling the effectiveness or rate of the process. For example, the temperature of the chuck can be controlled to heat or cool the wafer during a process recipe. The temperature may be varied to a particular set point during processing to affect the process in some way (e.g., to control the etch rate). Similarly, the temperature of the showerhead or upper electrode or other components can also be controlled during the process recipe to affect the process.

[0005]

[0005] More precise temperature control results in more precise control of processes such as deposition and etching. As microelectronic features shrink, the die and resulting products can become smaller, requiring greater precision during fabrication within the processing chamber. Additionally, higher power plasmas generate more heat and require more effective cooling. Consequently, temperature control systems must be more precise and operate over a wide range to support many different processes.

[0006]

[0006] Processing chamber components are cooled by circulating a fluid through coolant channels within the components. The amount of cooling is controlled by controlling the temperature of the coolant and the flow rate of the coolant through the components. In some cases, for example, for some wafer chucks, a warm fluid is also used to heat the chuck and then the wafer. The warm fluid can be forced through the same coolant channels or using a separate system. An electrical resistance heater can also be used within the wafer chuck in addition to or instead of the coolant. Summary of the Invention

[0007] A thermal control system using proportional and pneumatic thermal fluid supply control systems is described. In one embodiment, the apparatus includes a heat exchanger for supplying and receiving thermal fluid to and from fluid channels of a workpiece carrier. The heat exchanger controls the temperature of the thermal fluid supplied to the thermal channels, and the thermal fluid in the fluid channels controls the temperature of the carrier during workpiece processing. A proportional valve is present between the heat exchanger and the fluid channels to control the flow rate of the thermal fluid from the heat exchanger to the fluid channels. A pneumatic valve is also present between the heat exchanger and the fluid channels to further control the flow rate of the thermal fluid from the heat exchanger to the fluid channels. A temperature controller receives a measured temperature from a thermal sensor on the carrier and, in response to the measured temperature, controls the proportional valve and the pneumatic valve to adjust the flow rate of the thermal fluid.

[0008] A thermal control system is described that uses closed-loop control and a predictive model to control the temperature of a wafer carrier. Measured temperatures are received from a first thermal sensor in a first thermal zone of the carrier and a second thermal sensor in a second thermal zone of the carrier. A predictive model is applied to both measured temperatures to determine a first flow rate through a first fluid channel of the carrier thermally coupled to the first thermal zone and a second flow rate through a second fluid channel of the carrier thermally coupled to the second thermal zone. A first valve coupled to the first fluid channel and a second valve coupled to the second fluid channel are adjusted to control the flow rate of thermal fluid from a heat exchanger to the respective fluid channels. [Brief explanation of the drawings]

[0009]

[0009] Embodiments of the present invention are illustrated by way of example, and not by way of limitation, in the accompanying drawings in which: [Figure 1] FIG. 1 is a diagram of a two-zone temperature control system for an electrostatic chuck, in accordance with an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram of refrigerant fluid lines within a water interference box according to an embodiment of the present invention. [Figure 3]FIG. 10 is a diagram of the control of the valves and heat exchanger temperature of the water interference box according to an embodiment of the present invention. [Figure 4] 1 is a two-zone temperature control system for an electrostatic chuck according to an embodiment of the present invention. [Figure 5] 10A-10C are diagrams of flow rates through proportional valves of a water interference box at various valve ratios, according to an embodiment of the present invention. [Figure 6] FIG. 1 is a process flow diagram of a model-based control loop that may be used to control component temperature using a water interference box, according to an embodiment of the present invention. [Figure 7] FIG. 1 is a schematic diagram of a plasma etching system including a chuck assembly in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010]

[0017] A system is described that can be used in a wFib (water interface box) or any other type of flow control system for microelectronic wafer processing systems. The wFib described herein, along with a digital controller, provides continuous digital control of temperature through a combination of continuous or proportional valves and digital or gas pressure valves. The valves are connected in series between a heat exchanger with a pump and an electrostatic chuck or other wafer support.

[0011]

[0018] The valves can be controlled using any of a variety of different processes, including open loop, closed loop, predictive processes, or iterative processes. Although the system is primarily described for use in a plasma chamber with an electrostatic chuck for semiconductor processing, the same techniques can be used to control the temperature of any surface in a semiconductor chamber that uses a fluid to heat or cool the surface.

[0012]

[0019] The described embodiments can operate in a closed-loop temperature control system. For low-flow mode control, a pulsed mode can be used for the gas pressure valve, which overcomes the hysteresis of the proportional valve. To overcome the unreliability of the gas pressure valve, a proportional valve can be used for overall control. The described system has lower service costs.

[0013]

[0020] The temperature of a workpiece support, such as an electrostatic chuck (ESC) or vacuum chuck, can be controlled using a proportional fluid supply system or a pulsed fluid supply system. A proportional valve provides a stepped, analog adjustment to the flow rate. A pulsed valve rapidly cycles the fluid valve between open and closed to achieve an average flow rate that depends on the amount of time the valve is open. The valve determines the amount of fluid that flows to the chuck. The flow rate permitted by the proportional valve meets the cooling requirements of plasma processes involving high bias RF power. For lower temperature processes or when lower flow rates are desired, a pulsed valve allows for precise control of low flow rates.

[0014] Hybrid Valve Configuration

[0021] 1 is a diagram of a two-zone temperature control system 102 for an electrostatic chuck 104 supporting a workpiece 106 in a plasma 124 processing chamber. A hybrid wFib (water interference box) 140 is designed with both proportional and gas pressure valves. A thermal controller 130, such as a MIMO (multiple input multiple output) controller or any other type of controller, is used to apply a thermal control process to control the valves and regulate the temperature of the chuck or a workpiece carried by the chuck. The controller 130 takes temperature readings as feedback from multiple probes 112, 114 on the chuck 104 and controls the chuck temperature and its ramp rate.

[0015]

[0022] The chuck 104 has an upper plate 108 for carrying a workpiece 106, such as a silicon wafer or other type of substrate. The upper plate is supported by a cooling plate 110. Other supports (not shown) exist below the cooling plate for moving and supporting the workpiece and for supplying gases, current, and other materials to the upper plate and workpiece. During some manufacturing processes, heat 126 is applied to the workpiece from a plasma 124. The workpiece may be further heated by other elements and components within the processing chamber, including heaters within the chuck. Heat is transferred, at least in part, through the workpiece to the upper plate and cooling plate. The upper plate has thermal probes 112, 114 that measure the temperature at or near the workpiece.

[0016]

[0023] The cooling plate 110 has coolant channels 122. The coolant channels 122 receive coolant in the inlet channels 116 and discharge the coolant through the outlet channels 118. Although the arrows show a single inlet and outlet for simplicity, there may be multiple independent channels, each with its own inlet and outlet. This allows for independent temperature control of various components of the cooling plate. As an example, the periphery of the chuck tends to get hotter than the center of the chuck. A separate peripheral or external fluid channel allows for more coolant to be applied to the periphery of the chuck.

[0017]

[0024] Although the description herein describes a workpiece carrier in the form of an ESC in the context of a plasma processing chamber, the ESC described herein can be used in a wide variety of chambers and for a wide variety of processes. Depending on the particular implementation, a different substrate carrier may be used in place of the ESC.

[0018]

[0025] The figures herein show a two-zone or two-loop system with two independent coolant flow zones. The wFib 140 has a single fluid input 152 and a single output 154 from the heat exchanger, but provides two separate fluid outputs 142, 146 to the chuck. These can be individually controlled within the wFib and fed to independent coolant channels within the chuck. Fluid returns from each independent channel through two separate and independent return lines 144, 148 from the chuck. The two return lines may be combined at any point after leaving the chuck. In this example, the return flow rate within the wFib is monitored, as shown in FIG. 2. To monitor each loop separately, the return loops remain separate until the lines are measured. While two loops are shown, the described system can be expanded to include three, four, six, or more temperature control zones.

[0019]

[0026] The heat exchanger is provided with a source 152 and return 154 for cooling fluid for the chuck. A second heat exchanger (not shown) can be used as a heat source, as shown in FIG. 4. The heat exchanger receives the returning fluid and cools it to a predetermined temperature or by an adjusted amount. The heat exchanger may be thermostatically controlled or may add a fixed amount of cooling based on the design, with or without any specific control. As described below, the temperature of the coolant circulating through the chuck 104 or any other workpiece carrier is controlled in part by the temperature of the supplied cooling fluid and also by the flow rate of the fluid through the chuck in each coolant loop.

[0020]

[0027] The temperature controller 130 receives temperature signals from thermal sensors 112, 114, such as optical temperature probes. The thermal sensors are attached to the workpiece or chuck or carrier 122 in the processing chamber to directly or indirectly determine the temperature of the substrate. Based on the received temperature, the controller opens or closes valves in the wFib 140 to control the flow rate through the coolant channels 122 of the carrier 104. The temperature controller may generate valve control signals, such as analog voltages, digital PWM (pulse-width modulation) signals, or gas pressure signals, and provide these signals to the wFib. The wFib includes valves as shown in FIG. 2. The controller further receives pressure, temperature, and other signals from the wFib. The wFib controls the valves to open or close the passage from the heat exchanger to the chuck. The higher the flow rate, the more heat the fluid can transfer from the carrier.

[0021]

[0028] FIG. 2 is a diagram of the coolant fluid lines within the wFib 140 of FIG. 1. For simplicity, many other components may be present within the wFib, not shown here. Additionally, the controller 130 may be incorporated within the wFib. Although the wFib is referred to as a water interference box, the coolant is typically not water but another material with a higher boiling point. This other material may be, for example, but not limited to, deionized water / ethylene glycol, a fluorinated coolant such as 3M's Fluorinert® or Solvay Solexis's Galden®, or any other suitable dielectric fluid containing, for example, perfluorinated inert polyethers.

[0022]

[0029] The proportional valves can continuously regulate flow. The gas pressure valves can operate as shutoff valves or as pulse valves for flow control in PWM mode. As shown, the heat exchanger coolant fluid supply line 152 is fed to wFib 130 as an input. This feed is fed into a tee 176, which splits the feed into two sections. These sections are used to feed coolant to the two outputs 142, 146 of wFib and to feed coolant to the two coolant channels of the chuck. The two lines each have a gas pressure valve 166, 168 and a proportional valve 162, 164 connected in series, with the output of each gas pressure valve connected to the input of a corresponding proportional valve. The output of the proportional valve is connected to the corresponding coolant output line 142, 146. Alternatively, the valve order can be reversed, with the proportional valves directly connected to the inputs and the gas pressure valves connected to the outputs.

[0023]

[0030] Although only two refrigerant lines are shown from the tee 176, more refrigerant lines can be supported by using additional tees or by using a fluid distribution manifold with more output lines than the two lines shown at the tee. There can also be pressure compensation, regulation, and distribution components (not shown) within the manifold to control the amount of pressure delivered from the heat exchanger input 152 into each gas pressure valve.

[0024]

[0031] Return lines 144, 148 from the chuck cooling plate are connected to corresponding flow meters 170, 172, respectively. The flow meters may be used to measure the pressure and flow rate of the returning fluid. Temperature may also be measured. The flow meter and optional temperature values ​​may be used by the controller 130 to control the heat exchangers and valves. After measuring the flow, the returning fluids are combined in a return manifold 174 (in this case a simple tee), which returns the fluid to the heat exchanger return line 154.

[0025]

[0032] In this example, the flow control valves 162, 164, 166, and 168 are located on the supply side, between the heat exchanger output and the wafer carrier. Alternatively, the same effect can be achieved by placing the valves on the return side, between the wafer carrier and the return input 154 for fluid returning into the heat exchanger. As a further alternative, valves may be located in both locations, or one type of valve, either gas pressure or proportional, may be located on one side of the wafer carrier and the other type of valve on the other side of the wafer carrier. Similarly, flow meters may be located on either side of the wafer carrier or elsewhere in the system. In some embodiments, the flow meters are located in the heat exchangers. In the illustrated example, the flow meter measurements may be combined with flow data from the corresponding heat exchangers.

[0026]

[0033] The temperature controller 130 controls valves 162, 164, 166, and 168 to achieve the desired flow rate through the chuck. The proportional valves 162 and 164 may be controlled through electro-pneumatic regulators. Such regulators are supplied with compressed dry air (CDA) at a controlled, and typically constant, pressure. The regulators adjust the input CDA in response to an electrical control signal from the thermal controller to generate a precise gas pressure signal. If the regulators are supplied with a stepless analog signal, they can provide a similarly stepless regulator gas pressure. This adjusted gas pressure control pressure is applied to a pressure regulating valve to open or close the valve's fluid channel.

[0027]

[0034] In some embodiments, CDA is applied to an inlet solenoid valve of the regulator 140. When the input control voltage from the controller increases, the solenoid valve opens. The pressure released through the inlet valve is measured by a sensor and fed to the control circuit. The inlet valve is adjusted until the measured pressure matches the pressure indicated by the control signal. An exhaust solenoid valve is provided to relieve pressure in the regulator and return it to the CDA supply.

[0028]

[0035] The pressure control valve responds to the control pressure from the pressure regulator to provide proportional fluid control, allowing for stepless control of the flow rate through the coolant flow lines 142, 146. The valve moves much less than a pulse valve, which reduces repairs and extends the life of the hardware. Additionally, it provides a smoother response to temperature changes. Using a variable flow rate with no continuous fluid off-time during plasma processing provides a smoother temperature response and reduces temperature oscillations.

[0029]

[0036] On the other hand, proportional valves do not provide precise flow variation at lower flow rates. If a lower flow rate is desired, the gas pressure valves 166, 168 can be pulsed to add precision to the flow control.

[0030]

[0037] Additional valves (not shown) may be used in the fluid return channels 144, 148 to provide additional control of the flow rate through each channel. An additional bypass valve 178 may be used to allow the fluid to flow through the heat exchanger without flowing through the carrier. When the gas pressure or proportional valves 162, 164, 166, 168 are closed, the incoming feed fluid is blocked from flowing through the wFib outputs 142, 146. When the bypass valve 178 between the wFib inlet 152 and outlet 154 is opened, the feed fluid flow instead returns directly to the return line 154, bypassing the processing chamber. This allows the corresponding heat exchanger to establish a steady state temperature and maintain the fluid supply at the desired temperature. Additional valves may be used to further control the direction of flow.

[0031]

[0038] 3 is a diagram of the valve and heat exchanger temperature control. The control system has multiple inputs 302. The multiple inputs 302 may include recipe conditions (based on the process being applied to the workpiece and including power, pressure, etc.), internal and external chuck temperatures measured by various temperature sensor probes (SP), and internal and external chuck temperature ramp rates from the SP.

[0032]

[0039] The output 310 may include, as intended, the internal and external channel temperatures of the electrostatic chuck (ie, Tesc), the internal and external channel flow rates of the chuck, and the internal and external flow temperatures of the chuck.

[0033]

[0040] These multiple inputs 302 are applied to a MIMO controller 304, which then operates the valves. The inputs can be used in any of a variety of different ways to determine how to operate the valves. The inputs, ESC temperature, various SP values, and recipe conditions are taken along with feedback on line 316 from the ESC 308 to control the ESC temperature. In some embodiments, the temperature ramp rate or rate of change can also be controlled using the valves. In the illustrated example, the controller generates internal and external channel valve ratios 312, which determine the valve opening rates of the gas pressure valves and proportional valves. The internal and external valve ratios are applied to wFib 306. The controller further determines internal and external channel flow rates 314, which are compared to the flow measured at wFib. The fluid is then circulated through the ESC 308. The output 310 from the ESC is then returned in a closed loop to the controller, where new valve ratios 312 and flow rates 314 are further determined.

[0034]

[0041] In this embodiment, there are two separate fluid channel zones 122 within the ESC. These are designated interior and exterior. The temperature and flow rate of the fluid in each zone is independent of the temperature and flow rate of the other zone. Therefore, there are two independent fluid supply lines 142, 146, two independent fluid return lines 144, 148, two independent sensor probes 112, 114, and two independent sets of valves 162, 166, 164, 168. Each zone is independently monitored and controlled; however, the control process may be managed within the MIMO controller 304. Although the zones are referred to as interior and exterior, they may reside in any desired relative physical location within the ESC. More zones may similarly exist by providing additional separate coolant channels and associated components within the ESC.

[0035]

[0042] The temperature ramp rate may be used to improve the reliability (e.g., bond life) of the ESC. Temperature ramp rate control further facilitates matching processes between various processing chambers with different thermal characteristics. Control over the temperature ramp rate further facilitates improving the process window for HARC (high aspect ratio contact) etching and other processes requiring high precision.

[0036]

[0043] In the illustrated embodiment, a valve rate 312 is applied to wFib, but this depends on the settings and control system for the valve. This rate may be in the form of a digital or analog control signal received by a separate valve controller, which then sends a gas pressure or electrical signal to the respective valve. The valve controller may be in wFib or in another location. A PLC (Programmable Logic Controller) in wFib or in a separate chassis may be used to control both the proportional valve and the gas pressure valve. The process may be extended to control the electrical resistance heater in the chuck and also to control the heated fluid supply shown in FIG. 4. These additional thermal systems provide more temperature control knobs for the system, thereby increasing control over the chuck and workpiece temperature and their ramp rates.

[0037]

[0044] 4 is a diagram of a two-zone temperature control system 402 for an electrostatic chuck 404 in a plasma 424 processing chamber. The system has dual chillers or heat exchangers 450, 460 to provide both cooling and heating functions using the chuck's fluid channels. The dual chiller / heat exchanger arrangement provides hot or cold fluid flow as required by a chamber temperature controller 430.

[0038]

[0045] Similar to the embodiment of FIG. 1 , a workpiece 406 is mounted on a carrier 404, such as an ESC. A plasma 424 applies heat to the workpiece during a particular stage of the manufacturing process. The ESC in this embodiment has an upper plate 408 with temperature sensor probes 412, 414 and a lower cooling plate 410 with two (or more) zones of coolant channels. The coolant channels have input lines 416 connected to fluid outputs 442, 446 of wFib 440. The coolant channels have outputs 418 connected to return lines 444, 446 returning to wFib. While only two coolant channels are shown for the two thermal zones of the ESC, there may be more here, just as there may be more in the embodiment of FIG. 1 .

[0039]

[0046] The temperature conditioning system includes a hot fluid heat exchanger 450 having a source output line 452 and a return input line 454 for hot or heated fluid. The return returns the fluid to the heat exchanger. The heat exchanger heats the fluid to a predetermined temperature or by a regulated amount and supplies the fluid under pressure to a supply line 452. The fluid temperature may be fixed or adjusted based on a control signal (e.g., a control signal from the controller 430 or another controller). Similarly, the system includes a source or output line 462 and a return line 464 for cold or cooled fluid for a second heat exchanger 460. The second heat exchanger 460 receives the returning cold fluid and cools it to a predetermined temperature or by a regulated amount. The first and second heat exchangers may be a single unit, as shown, or may be two separate devices. The heat exchangers may be thermostatically controlled or may add a fixed amount of heating or cooling with or without any specific control, depending on the particular embodiment. The temperature of the coolant circulating through the substrate carrier 404 is controlled in part by the temperature of the supplied hot and cold fluids 452, 462, but also by the flow rate and mixture of the hot and cold fluids reaching the ESC 404.

[0040]

[0047] The hot fluid is fed to a three-way valve 456, which opens and closes the flow of hot fluid from the heat exchanger. Similarly, the cold fluid is fed to the same three-way valve, which opens and closes the flow of cold fluid from the second heat exchanger. Fluid allowed through this valve is fed to wFib 440 in the wafer carrier supply line. wFib 440 regulates the flow rate in the same manner as wFib in FIG. 1, using a series-connected gas pressure valve and a proportional valve. The regulated temperature coolant then heats or cools the workpiece carrier. There is an additional optional three-way valve 466 connected to the hot return line 454 and the cold return line 464. Fluid from the substrate carrier is allowed to return through this valve through the return line to and then through this valve back to its respective heat exchanger. These three-way valves are operated under the control of a temperature controller 430, which is connected to the two valves. The three-way valves may be contained within the wFib or may reside in some external chassis or fixture.

[0041]

[0048] In some embodiments, the temperature controller 430 determines the flow rate and the heat exchanger used to heat or cool the thermal fluid in the substrate carrier fluid channels. In some embodiments, the coolant fluid provided by the cold heat exchanger is approximately 0°C, and the coolant fluid provided by the hot heat exchanger is approximately 55°C. Depending on the current temperature of the wafer carrier, one or a mixture of these fluids is supplied to the fluid channels. For example, if the temperature of the carrier is above a set point, fluid from the cold chiller is used. If the temperature is below the set point, fluid from the hot chiller is used. The fluid supply system controls the temperature at the workpiece within an appropriate temperature range. The fluid supply system also controls temperature rise and overshoot during plasma processing.

[0042]

[0049] A return path (not shown) can be provided to the two heat exchangers, allowing heated fluid to flow from the hot supply 452 to the hot return 454, bypassing the workpiece carrier 404 and, optionally, the wFib 440. FIG. 2 shows an example of such a return path, opened using valve 178. A similar cold fluid return valve can also be used, allowing cooling fluid to flow directly from the cold supply 462 to the cold return 464 without passing through the carrier. When either the hot or cold supply is not being supplied to the carrier by the setting of the three-way valves 456, 466, the hot and cold fluid return valves can be used, allowing fluid to flow through the corresponding heat exchanger without flowing through the carrier. This allows the corresponding heat exchanger to establish a steady-state temperature and maintain the fluid supply at the desired temperature.

[0043]

[0050] The described temperature regulation system allows the temperature of the fluid flowing through the channels in the substrate carrier to be controlled, for example, within a range of 0°C to 55°C. A workpiece carrier may have more than one thermal fluid channel. In this case, the system of FIG. 4 may be replicated to support each additional channel. Because the mixture into the wFib and the flow rate through the coolant channels can be controlled independently, a single hot heat exchanger and a single cold heat exchanger may be used to supply fluid to more than one channel.

[0044]

[0051] FIG. 5 shows the flow rate through a proportional valve at various valve ratios. A first upper curve 504 shows various control inputs to the proportional valve, with time on the horizontal axis. The vertical axis for the first curve shows the duty cycle of the PWM waveform applied to the valve, as shown on the scale on the right. Higher duty cycles, shown at the far left and right of the diagram, close the valve. Lower duty cycles, shown near the center of the diagram, allow the valve to open more.

[0045]

[0052] A second curve 502 shows the flow rate through the proportional valve in response to an applied PWM signal 504. The vertical flow rate scale on the left runs from lower flow rates at the bottom of the scale to higher flow rates at the top of the scale. As shown, as the valve is initially opened and the flow rate is slowly increased by lowering the PWM duty cycle, there is a region 506 of low flow rate through the proportional valve. In this region, the valve does not have a steady, linear, and repeatable response to the input signal 504. The flow rate in this region 506 is irregular. Similarly, as the valve is closed from a high flow rate to a low flow rate in the center of the diagram, there is a region 508 where the valve's response becomes less linear or repeatable as it closes. In this example, the flow rate suddenly drops to a minimum and does not recover. At the same time, outside of these low-flow regions 506, 508, the proportional valve is normal and has a predictable response to the input signal.

[0046]

[0053] The diagram in Figure 5 shows a typical response of a proportional valve. To overcome this nonlinear response, wFib, with two valves in series, can operate differently than a conventional single valve. In an embodiment, the proportional valve is the primary valve for higher flow rates, operating in the linear region and not operating in the extreme low-flow regions 506, 508. To achieve low flow rates, the proportional valve is closed to a low-flow region where it still has a predictable response. The flow rate is then further reduced by activating the gas pressure valve. This allows for high accuracy in the low-flow region. At higher flow rates, the proportional valve is used and the gas pressure valve is not used at all. This reduces wear on the gas pressure valve while still accurately controlling the flow.

[0047] Control Methodology

[0054] The above embodiments include a valve controller 130, 430. The valve controller may control the valve in various ways, depending on the embodiment. In some embodiments, a MIMO (multiple-input multiple-output) model-based controller may be used. The MIMO controller can be used to respond to sensor probe (SP) temperature readings during wafer processing and then control the temperature ramp rate (both ramp down and ramp up). The ramp rate is a critical parameter in some processes. For example, in some processes, the ramp rate can affect bond reliability. While the system is primarily described for use in a plasma chamber with an electrostatic chuck for semiconductor processing, the same technique can be used to control the temperature of any surface in a semiconductor chamber that uses a fluid to heat or cool the surface.

[0048]

[0055] A MIMO system based on the described model can be used to control temperature ramp rates as well as manage crosstalk between zones. For example, crosstalk between zones occurs when the temperature of one zone affects the temperature of another zone due to heat flow through the plates of an ESC containing fluid channels. By extending the model-based design to include a wafer temperature model in addition to an electrostatic chuck temperature model, the control software can be extended to control wafer temperature. As a result, the described embodiments can help improve the overall temperature match within the chamber, the electrostatic chuck bond life, and the process window.

[0049]

[0056] 3 may be applied to a MIMO controller 304, 130, 430 with a model-based design. The inputs, ESC temperature, various SP values, and recipe conditions may be taken along with feedback on line 316 from the ESC 308 to control the ESC temperature and its ramp rate. The controller applies a model to produce an inner and outer channel valve ratio 312 and additional channels relative to the total number of zones in the system.

[0050]

[0057] Model-based determination relies on physical models of the heat absorption and heat transfer characteristics of the system's components. These components may include one or more of the chuck, workpiece, fluid, heat exchanger, fluid delivery pipes, and cooling channels through various operating conditions of the process recipe. Physical models may be established for two or more zones. For systems with multiple zones of cooling channels in the chuck (or any other component), the model may account for crosstalk between two or more zones. Crosstalk accounts for heat transfer between cooling zones affected by various coolant channels. In some embodiments, the model-based controller design uses a linear-quadratic controller or similar optimization controller designed to handle crosstalk and control the temperature ramp rate.

[0051]

[0058] The temperature ramp rate may be used to improve the reliability (e.g., bond life) of the ESC. Temperature ramp rate control further facilitates matching processes between various processing chambers with different thermal characteristics. Control over the temperature ramp rate further facilitates improving the process window for HARC (high aspect ratio contact) etching and other processes requiring high precision.

[0052]

[0059] FIG. 6 is a process flow diagram of a model-based control loop that can be used to control the temperature of components within a processing chamber using a coolant and at least one control valve. This process can use the hybrid two-valve system described above, or any other desired flow control system. The model can be established empirically or theoretically before processing begins. The model can be a dynamic linear model that describes the behavior of temperature-controlled components within a plasma chamber under various conditions. A predictive model can be used to predict the future behavior of a component, such as the ESC shown above. This can further control the temperature ramp rate. Using a process recipe as input, the controlled temperature can be adjusted in advance of a temperature load or change in the desired temperature setpoint.

[0053]

[0060] Box 604 represents the application of a linear predictive control system using the model as an ordinary differential equation. In this example, the ordinary differential equation is: TIFF0007762237000001.tif6170, where A and B are matrices derived from this model. For a two-zone system, the matrix is ​​a 4x4 matrix. For more zones, the matrix scales accordingly. Depending on the particular implementation, other models may be used, and non-linear models may also be used.

[0054]

[0061] In this example, TIFF0007762237000002.tif5170 is a linear array or 1x4 matrix, TIFF0007762237000003.tif6170 is specified for a two-zone system. This may be expanded to accommodate more zones. To accommodate crosstalk between zone temperatures, two different zones are treated within the same model. In the ESC (electrostatic chuck) example, the variables in the array may be assigned the following values: x1=ESC internal zone temperature x2=ESC external area temperature x3=ESC internal zone temperature ramp rate x4=ESC external area temperature ramp rate Let u = [u1, u2] represent the control output used to adjust the valve for each zone. In this example, adjustment is expressed as the rate at which the valve opens or as a percentage of the maximum total flow through the valve. The specific values ​​will depend on the values ​​used to determine the model, but here: u1=inner area rate u2=external area ratio It is expressed as: In box 606, the value for each u is u=-Kx+K r r where K and K rare constants reflecting the controller gains. These may vary over time based on learning and are initially determined by the model for each u (i.e., u1, u2). r is the temperature setpoint (i.e., the temperature the system is trying to achieve with the ESC by adjusting the valve as defined by u above). The setpoints in this example are as follows: r1=ESC internal zone temperature set point r2=ESC external area temperature set point r3=ESC internal zone temperature ramp rate set point r4=ESC external zone temperature ramp rate set point

[0055]

[0062] After the operations of box 606, the planned valve adjustments are determined to achieve the desired temperature and ramp rate set points. The process can then convert these values ​​for u1, u2 into valve acts (such as an electrical control signal that actuates a proportional valve 612 or a gas pressure control signal 614 that actuates a gas pressure valve). Box 608 shows an example of the operations of the two-valve hybrid system described above.

[0056]

[0063] The calculation is performed for each valve rate u (i.e., u1, u2) or, i=1, 2, check u i -u0, where u0 represents the minimum threshold for the proportional valve ratio (e.g., 10%).

[0057]

[0064] If the result is positive, i.e., the proportional valve is set more than 10% open, then in 612 the corresponding proportional valve is set to the calculated value u i %. On the other hand, if the result is negative, i.e., the proportional valve is set to less than 10% open, then in 614 the proportional valve is set to some low value (such as 10%) and gas pressure pulsing is applied at the gas pressure valve. This is done by first setting the pulsing to p i % (typically between 20% and 80%, depending on the valve characteristics), and secondly, the proportional valve (u i / p i) %, this allows the proportional valve to provide residual flow control beyond the optimum operating range of the pulse valve.

[0058]

[0065] The operations of box 608 can alternatively be described as follows: The temperature controller first determines the total flow rate for each thermal zone. This total flow rate is then compared to a threshold value, defined as greater than u0. If the total flow rate, denoted above as u1 or u2, exceeds the threshold value, the temperature controller opens the gas pressure valve and adjusts the proportional valve to achieve the desired flow rate. On the other hand, if the total flow rate is less than the threshold value, the temperature controller closes the proportional valve to a predetermined flow rate and adjusts the gas pressure valve to achieve the desired total flow rate. With valves in series, the restriction of the first valve combines with the restriction of the second valve to achieve the limited total flow rate.

[0059]

[0066] In box 616, the determined valve control values ​​are output to the valves. As noted above, these values ​​may be direct flow rates u (i.e., u1, u2) in the case of a single valve system in box 606, or the control may be more complex in a multiple valve system, as in optional box 608. Depending on the particular implementation of the flow control system between the heat exchanger and the processing chamber components (such as the ESC), the valve control values ​​may be determined in other ways not shown in box 608.

[0060]

[0067] In addition to controlling the flow through the valves, input parameters, i.e., the current zone temperature values ​​x1, x2, are read at 618. Ramp rates x3, x4 may also be estimated at 620 using the derivative or time rate of change of the temperature values ​​x1, x2. These values ​​may then be used as input values ​​for another cycle of adjustment at box 604. The control process of Figure 6 is therefore a closed-loop control system, as indicated by return loop 622 in Figure 6.

[0061]

[0068] The process of FIG. 6 may further be described as performing a series of operations in a MIMO controller, a temperature controller, or some other component of the system. Measured temperatures are received from both a first thermal sensor in a first thermal zone of the carrier and a second thermal sensor in a second thermal zone of the carrier. A predictive model is then applied to both measured temperatures to determine a first flow rate through a first fluid channel of the carrier thermally coupled to the first thermal zone and a second flow rate through a second fluid channel of the carrier thermally coupled to the second thermal zone. Using these determined flow rates, the controller adjusts a first valve coupled to the first fluid channel and a second valve coupled to the second fluid channel to control the flow rate of the thermal fluid from the heat exchanger to the respective fluid channels.

[0062]

[0069] The method may also use a ramp rate, where the temperature ramp rates of the first and second thermal zones are estimated using the received measured temperatures, and a predictive model is then applied by applying the estimated temperature ramp rates.

[0063] Chamber Structure

[0070] 7 is a schematic diagram of a plasma etching system 700 including a chuck assembly 742 according to an embodiment of the present invention. The plasma etching system 700 may be any type of high performance etching chamber. Other commercially available etching chambers may similarly utilize the chuck assemblies described herein. While the exemplary embodiment is described in connection with the plasma etching system 700, the chuck assemblies and temperature control systems described herein are also adaptable to other processing systems (e.g., plasma deposition systems, etc.) used to perform any plasma manufacturing process.

[0064]

[0071] Referring to FIG. 7, a plasma etching system 700 includes a grounded chamber 705. Process gases are supplied to the chamber 705 from one or more gas sources 729 connected to the chamber through mass flow controllers 749. The chamber 705 is evacuated via an exhaust valve 751 connected to a high-volume vacuum pump stack 755. When plasma power is applied to the chamber 705, a plasma is formed in a processing region above a workpiece 710. A plasma bias power 725 is coupled to the chuck assembly 742 to excite the plasma. The plasma bias power 725 typically has a low frequency between about 2 MHz and 60 MHz, and may be in the 13.56 MHz range, for example.

[0065]

[0072] In the illustrated embodiment, the plasma etching system 700 includes a second plasma bias output 725 connected to an RF matcher and operating in approximately the 2 MHz band. The first plasma bias output 725 is also coupled to the RF matcher and to the lower electrode via an output conduit 728. The plasma source output 730 is coupled to a plasma generating element 735 through another matcher (not shown) to provide a high frequency source power for inductively or capacitively exciting the plasma. The plasma source output 730 may have a higher frequency than the plasma bias output 725 (e.g., between 100 MHz and 180 MHz), and may be in the 162 MHz band, for example.

[0066]

[0073] The workpiece 710 is loaded through the opening 715 and clamped to the chuck assembly 742 within the chamber. The workpiece 710, such as a semiconductor wafer, may be any wafer, substrate, or other material used in semiconductor processing technology; the invention is not limited in this respect. The workpiece 710 is disposed on the upper surface of a dielectric layer or puck 745 of the chuck assembly, which is disposed above a cooled base assembly 744 of the chuck assembly. A clamping electrode (not shown) is embedded within the dielectric layer. The clamping electrode is coupled to a source of bias output 779 and provides an electrostatic force to clamp the workpiece 710. In particular embodiments, the chuck assembly 742 may include two or more distinct fluid channel sections, such as an inner channel 741 and an outer channel. Each channel 741 may be individually controllable to the same or different temperature setpoints.

[0067]

[0074] The system controller 770 is coupled to a variety of systems that control the fabrication process within the chamber. The controller 770 may include a temperature controller 775 to execute temperature control algorithms (e.g., temperature feedback control), which may be either software or hardware, or a combination of both. The system controller 770 further includes a central processing unit 772, memory 773, and an input / output interface 774. The temperature controller 775 outputs control signals that affect the rate of heat transfer between the chuck assembly 742 and heat sources and / or heat sinks external to the plasma chamber 705 for the various fluid channels. The temperature controller may be coupled to one or more temperature probes 743, which may be in or on the substrate carrier, connected to fluid supply lines, or in any other desired location.

[0068]

[0075] The thermal fluid zones may include separate, independently controlled thermal fluid heat transfer loops with separate fluid controls controlled based on zone-specific temperature feedback loops as described above. In the exemplary embodiment, a temperature controller 775 is coupled to a first heat exchanger (HTX) / cooler 777 and may also be coupled to a second HTX / heater 778 and more heat exchangers (not shown) as desired, depending on the particular implementation. The flow rate of the heat transfer fluid or coolant through conduits within the chuck assembly 742 is controlled by proportional valve systems 781, 785, as described above.

[0069]

[0076] The proportional valve systems 781, 785 are controlled by a temperature controller 775, which independently controls the flow rate of thermal or heat transfer fluid to each different fluid channel. The temperature controller can also control the temperature setpoint used by each heat exchanger to cool or heat the thermal fluid. Thus, each heat exchanger can bring the thermal fluid for the corresponding refrigerant channel to a different temperature before returning it to the fluid channel.

[0070]

[0077] The heat transfer fluid may be a liquid, such as, but not limited to, deionized water / ethylene glycol, a fluorinated refrigerant such as Fluorinert® from 3M or Galden® from Solvay Solexis, or any other suitable dielectric fluid, for example, containing a perfluorinated inert polyether. While this specification describes an ESC in the context of a plasma processing chamber, the ESC described herein may be used in a wide variety of chambers and for a wide variety of processes. Depending on the particular implementation, a different substrate carrier may be used in place of the ESC.

[0071]

[0078] Although numerous details are set forth in the following description, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details. In order to avoid obscuring the present invention, well-known methods and devices are sometimes shown in block diagram form, rather than in detail. Throughout this specification, references to "an embodiment" or "one embodiment" mean that a particular feature, structure, function, or characteristic described in connection with that embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in an embodiment" or "in one embodiment" in various places throughout this specification do not necessarily refer to the same embodiment of the present invention. Furthermore, particular features, structures, functions, or characteristics may be combined in any suitable manner in one or more embodiments. For example, a first embodiment and a second embodiment may be combined if the particular features, structures, functions, or characteristics associated with the two embodiments are not mutually exclusive.

[0072]

[0079] As used in describing this invention and in the appended claims, the singular indefinite and definite articles "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It will be further understood that the expression "and / or," as used herein, denotes and includes any and all possible combinations of one or more of the associated listed items.

[0073]

[0080] The terms "coupled" and "connected," as well as their derivatives, may be used herein to describe a functional or structural relationship between elements. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, "connected" may be used to indicate that two or more elements are in direct physical, optical, or electrical contact with each other. "Coupled" may be used to indicate that two or more elements are in direct or indirect physical, optical, or electrical contact with each other (through other intervening elements) and / or that two or more elements cooperate or interact with each other (e.g., are causally related, etc.).

[0074]

[0081] As used herein, the expressions "over," "under," "between," and "on" refer to the relative location of one component or layer of material with respect to another, where such physical relationship is noteworthy. For example, in the context of layers of material, a layer disposed above or below another layer may be in direct contact with the other layer or may have one or more intervening layers. Furthermore, a layer disposed between two layers may be in direct contact with the two layers or may have one or more intervening layers. In contrast, a first layer "on" a second layer is in direct contact with the second layer. Similar distinctions should be made in the context of assembly of components.

[0075]

[0082] It should be understood that the above description is intended to be illustrative, and not limiting. For example, while the flow diagrams in the drawings indicate a particular order of steps performed by certain embodiments of the present invention, it should be understood that such order is not required (e.g., alternative embodiments may perform steps in a different order, combine certain steps, overlap certain steps, etc.). Moreover, many other embodiments will become apparent to those skilled in the art upon reading and understanding the above description. While the present invention has been described with reference to certain exemplary embodiments, it will be recognized that the invention is not limited to the described embodiments, but can be practiced in modification and alternative forms within the spirit and scope of the appended claims. The scope of the present invention should, therefore, be determined with reference to the appended claims, along with the full range of equivalents to which such claims are entitled.

Claims

1. 1. A workpiece processing system comprising: plasma chamber, a plasma source for generating plasma containing gas ions within said plasma chamber; a workpiece holder in the plasma chamber for holding a workpiece during plasma processing and controlling a temperature of the workpiece, the workpiece holder having a first fluid channel and a second fluid channel; first flow lines coupled to the first fluid channels of the workpiece holder, the first flow lines including a first supply flow line and a first return flow line, the first return flow line being coupled to only a single return manifold; second flow lines coupled to the second fluid channels of the workpiece holder, the second flow lines including a second supply flow line and a second return flow line, the second return flow line coupled to only the single return manifold, the single return manifold coupled to a corresponding single heat exchanger, the single heat exchanger coupled to the first supply flow line and the second supply flow line, all outputs of the first return flow line and the second return flow line input to the single return manifold, and all outputs of the first return flow line and the second return flow line being the same as all outputs of the first supply flow line and the second supply flow line; a first proportional valve and a first gas pressure valve coupled to the first return flow line, the first proportional valve and the first gas pressure valve being between the single return manifold and the workpiece holder; a second proportional valve and a second gas pressure valve coupled to the second return flow line, the second proportional valve and the second gas pressure valve being between the single return manifold and the workpiece holder; a first flow meter between the workpiece holder and the single return manifold, the first flow meter in series with the first proportional valve and the first gas pressure valve; a second flow meter between the workpiece holder and the single return manifold, the second flow meter in series with the second proportional valve and the second gas pressure valve; and a temperature controller that receives a measured temperature from a temperature sensor in the workpiece holder and controls the first and second proportional valves and the first and second gas pressure valves in response to the measured temperature to adjust a flow rate of thermal fluid, the temperature controller determining a total flow rate, and if the total flow rate exceeds a threshold, the temperature controller opens the first and second gas pressure valves and adjusts the first and second proportional valves to obtain a desired flow rate, and if the total flow rate is below the threshold, the temperature controller closes the first and second proportional valves to a predetermined flow rate and adjusts the first and second gas pressure valves to obtain a desired flow rate; A workpiece handling system comprising:

2. 10. The workpiece processing system of claim 1, wherein the first proportional valve comprises a first pressure regulator valve and the second proportional valve comprises a second pressure regulator valve.

3. a first pressure regulator coupled to the first pressure regulating valve for controlling the first pressure regulating valve; a second pressure regulator coupled to the second pressure regulating valve for controlling the second pressure regulating valve; The workpiece handling system of claim 2 further comprising:

4. The workpiece handling system of claim 1 , wherein the thermal fluid comprises a polyether.

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