Advanced temperature control for wafer carriers in plasma processing chambers

Abstract

Advanced temperature control systems and methods for wafer carriers in a plasma processing chamber are described. In one example, a heat exchanger provides temperature controlled thermal fluid to a fluid channel of a workpiece carrier and receives thermal fluid from the fluid channel. A proportional valve is between the heat exchanger and the fluid channel to control a flow rate of the thermal fluid from the heat exchanger to the fluid channel. A pneumatic valve is also between the heat exchanger and the fluid channel to also control the flow rate of the thermal fluid from the heat exchanger to the fluid channel. A temperature controller receives a measured temperature from a thermal sensor of the carrier and controls the proportional valve and the pneumatic valve in response to the measured temperature to adjust the flow rate of the thermal fluid.

Description

[0001] This application is a divisional application of the invention patent application with the application date of March 16, 2017, application number "201780027652.6", and invention name "Apparatus and method for advanced temperature control of wafer carriers in plasma processing chambers".

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Patent Application No. 62 / 332,237, filed May 5, 2016, by Fernando M. Silveira et al., and entitled “Advanced Temperature Control for Wafer Carriers in Plasma Processing Chambers.” Technical Field

[0004] 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 wafers in a processing chamber. Background Art

[0005] Microelectronic and micromechanical devices are typically fabricated in part on silicon or other types of wafers. Once completed, the wafers are diced into many smaller pieces, and each die forms an individual device. The wafers undergo a number of different processes to form all the components of the device. For many processes, the wafer is held on a chuck, susceptor, or some other carrier within a processing chamber. One such chamber is a plasma processing chamber, where the wafer is exposed to a plasma to deposit or remove various materials.

[0006] In plasma processing chambers, such as plasma etch chambers or plasma deposition chambers, the temperature of the wafer and wafer carrier is often an important parameter for controlling the efficiency or speed of the process. For example, during a process recipe, the temperature of the chuck can be controlled to heat or cool the wafer. During a process, the temperature can be varied to a specific set point to influence the process in some way, such as controlling the etch rate. Similarly, during a process recipe, the temperature of the showerhead, top electrode, or other components can also be controlled to influence the process.

[0007] More accurate temperature control provides more precise control over processes such as deposition and etching. As microelectronic features become smaller, allowing for smaller die and resulting products, greater precision is required during fabrication within the process chamber. Furthermore, high-power plasmas generate more heat and require more efficient cooling. Therefore, temperature control systems must be more accurate and operate over a wider range to support many different processes.

[0008] Process chamber components are cooled by circulating a fluid through coolant channels in the components. The amount of cooling is controlled by controlling the temperature of the coolant and the coolant flow rate through the components. In some cases, such as with some wafer chucks, a warm fluid is also used to heat the chuck and, in turn, the wafer. The warm fluid can be driven through the same coolant channels or using a separate system. Resistive heaters can also be used in the wafer chuck in addition to or in place of the coolant. Summary of the Invention

[0009] A thermal control system using a proportional and pneumatic hot fluid delivery control system is described. In one example, the apparatus includes a heat exchanger that provides hot fluid to and receives hot fluid from a fluid channel of a workpiece carrier. The heat exchanger controls the temperature of the hot fluid provided to the hot channel, and the hot fluid in the fluid channel is used to control the temperature of the carrier during workpiece processing. A proportional valve is positioned between the heat exchanger and the fluid channel to control the flow rate of the hot fluid from the heat exchanger to the fluid channel. A pneumatic valve is also positioned between the heat exchanger and the fluid channel to similarly control the flow rate of the hot fluid from the heat exchanger to the fluid channel. A temperature controller receives a measured temperature from a thermal sensor of the carrier and controls the proportional valve and the pneumatic valve in response to the measured temperature to adjust the flow rate of the hot fluid.

[0010] A thermal control system for controlling the temperature of a wafer carrier using closed-loop control and a predictive model is described. Measured temperatures are received from a first thermal sensor at a first thermal zone of the carrier and a second thermal sensor at a second thermal zone. The predictive model is applied to the two 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 the thermal fluid from a heat exchanger to the respective fluid channels. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Embodiments of the invention are illustrated by way of example and not limitation in the accompanying drawings, in which:

[0012] Figure 1 is a diagram of a two-zone temperature control system for an electrostatic chuck according to an embodiment of the present invention;

[0013] Figure 2 is a diagram of coolant flow lines within a water interface tank according to an embodiment of the present invention;

[0014] Figure 3 is a diagram of controlling the temperature of a valve and a heat exchanger of a water interface box according to an embodiment of the present invention;

[0015] Figure 4 is a diagram of a two-zone temperature control system for an electrostatic chuck according to an embodiment of the present invention;

[0016] Figure 5 is a graph of flow rate through a proportional valve of a water interface box at different valve percentages according to an embodiment of the present invention;

[0017] Figure 6 is a process flow diagram of a model-based control loop that may be used to control the temperature of a component using a water interface tank according to an embodiment of the present invention;

[0018] Figure 7 is a schematic diagram of a plasma etching system including a chuck assembly according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The system is described as being applicable to a wFib (water interface box) or any other type of fluid flow control system for electronic wafer handling systems. The wFib, as described herein, is used in conjunction with a digital controller to provide continuous digital control of temperature through a combination of continuous or proportional valves and digital or pneumatic valves. These valves are connected in series between a heat exchanger with a pump and an electrostatic chuck or other wafer support.

[0020] The valves can be controlled using any of a variety of different processes, including open loop, closed loop, predictive, or iterative processes. Although the system is described primarily 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.

[0021] The described embodiment can be operated with a closed-loop temperature control system. A pulse mode can be used on pneumatic valves for low-flow mode control. This overcomes the hysteresis of proportional valves. Proportional valves can be used for general-purpose control to overcome the low reliability of pneumatic valves. The described system has a low serviceability cost.

[0022] Proportional or pulsed fluid delivery systems can be used to control the temperature of a workpiece support, such as an electrostatic chuck (ESC) or vacuum chuck. Proportional valves provide step-by-step analog adjustments to flow rates. Pulsed valves rapidly cycle the fluid valve open and closed to produce an average flow rate that depends on the amount of time the valve is open. The valve determines the amount of fluid flowing to the chuck. The flow rate allowed by the proportional valve meets the cooling requirements of plasma processes with high bias RF power. For cooler processes or when less flow is required, pulsed valves allow precise control of low flow rates.

[0023] Mixing valve configuration

[0024] Figure 1 Figure 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 interface box) 140 is designed with proportional and pneumatic valves. Thermal control can be applied using a thermal controller 130 (such as a MIMO (multiple-input, multiple-output) controller or any other type of controller) to control the valves and regulate the temperature of the chuck or the workpiece held by the chuck. Controller 130 uses temperature readings from multiple probes 112, 114 on the chuck 104 as feedback to control the chuck temperature and its ramp rate.

[0025] The chuck 104 has an upper plate 108 that supports a workpiece 106 (e.g., a silicon wafer or other type of substrate). The upper plate is supported by a cooling plate 110. Below the cooling plate are other supports (not shown) that move and support the workpiece and provide gases, current, and other materials to the upper plate and workpiece. During some manufacturing processes, heat 126 is applied to the workpiece from the plasma 124. The workpiece may also be heated by other components and parts within the processing chamber, including heaters in the chuck. Heat is at least partially conducted through the workpiece to the upper plate and to the cooling plate. The upper plate has thermal probes 112 and 114 to measure the temperature at or near the workpiece.

[0026] The cooling plate 110 has coolant channels 122 that receive coolant from the inlet channel 116 and release it through the outlet channel 118. For simplicity, the arrows indicate a single inlet and outlet; however, there can be multiple independent channels, each with an inlet and outlet. This allows the temperature of different parts of the cooling plate to be independently controlled. As an example, the perimeter of a chuck tends to run hotter than the center of the chuck. Separate peripheral or external fluid channels allow more coolant to be applied to the perimeter of the chuck.

[0027] Although this specification 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 variety of different chambers and for a variety of different processes. Depending on the specific implementation, a different substrate carrier can be used instead of an ESC.

[0028] This diagram shows a two zone or two loop system with two independent coolant flow areas. The wFib 140 has a single fluid input 152 and a single output 154 from the heat exchanger, but produces two separate fluid outputs 142, 146 to the chuck. These can be independently controlled within the wFib and fed to independent coolant channels in the chuck. Fluid returns from each independent channel as two separate and independent return lines 144, 148 from the chuck. The two return lines can be combined at any point after leaving the chuck. In this example, Figure 2 As shown, the return flow rate is monitored within wFib. In order to monitor each circuit independently, the return circuits are kept separate until these lines are measured. Although two circuits are shown, the system described can be expanded to include 3, 4, 6 or more temperature control zones.

[0029] The heat exchanger provides a source 152 and return 154 for cooling fluid to the chuck. A second heat exchanger (not shown) may be used as Figure 4 The heat source is shown. The heat exchanger receives the return fluid and cools it to a predetermined temperature or a regulated amount. The heat exchanger can be thermostatically controlled or can apply a fixed amount of cooling with or without any specific control depending on the design. 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 circuit.

[0030] The temperature controller 130 receives temperature signals from thermal sensors 112, 114 (e.g., optical temperature probes) attached to the workpiece in the processing chamber or to the chuck or carrier 122 to determine the temperature of the substrate directly or indirectly. Based on the received temperature, the controller opens and closes the valve in the wFib 140 and controls the flow rate of the coolant channel 122 through the carrier 104. The temperature controller can generate valve control signals (e.g., analog voltages, digital PWM (pulse width modulation) signals, or pneumatic signals) and provide these signals to a controller including, for example, a CMOS controller. Figure 2 The wFib of the valve shown. The controller also receives pressure, temperature, and other signals from the wFib. The wFib control valve opens or closes the passage from the heat exchanger to the chuck. A higher flow rate allows the fluid to transfer more heat from the carrier.

[0031] Figure 2 yes Figure 1FIG14 is a diagram of the coolant flow lines within the wFib 140 of FIG14. For simplicity, there may be many other components in the wFib that are not shown here. In addition, the controller 130 may be incorporated into the wFib. Although the wFib is referred to as a water interface tank, the coolant is typically not water, but other materials with a higher boiling point, such as, but not limited to, deionized water / ethylene glycol, fluorinated coolants (such as those from 3M), and the like. or from Solvay Solexis, Inc. ) or any other suitable dielectric fluid (such as a dielectric fluid containing a perfluorinated inert polyether).

[0032] The proportional valve can continuously adjust the flow rate. The pneumatic valve can be used as a shut-off valve and can be used as a pulse valve for flow control in PWM mode. As shown in the figure, the heat exchanger coolant fluid supply line 152 is supplied as an input to the wFib 130. The supply is provided to a T-tube (tee) 176 to divide the supply into two parts. These parts are used to supply coolant to the two outputs 142 and 146 of the wFib to supply coolant to the two coolant channels of the chuck. These two lines have pneumatic valves 166 and 168 and proportional valves 162 and 164 coupled in series, respectively, so that the output of each pneumatic valve is coupled to the input of the corresponding proportional valve. The output of the proportional valve is coupled to the corresponding coolant output line 142 and 146. Alternatively, the order of the valves can be reversed so that the proportional valve is directly coupled to the input and the pneumatic valve is coupled to the output.

[0033] Although two coolant lines are shown coming from the T-piece 176, more coolant lines can be supported by using additional T-pieces or by a fluid distribution manifold having more output lines than the two shown from the T-piece. There can also be pressure compensation, regulation, and distribution components (not shown) within the manifold to individually control the amount of pressure supplied from the heat exchanger input 152 to each pneumatic valve.

[0034] The return lines 144, 148 from the chuck cooling plates are each coupled to a corresponding flow meter 170, 172, which can be used to measure the pressure and flow rate of the return fluid. Temperature can also be measured. The flow meter and, optionally, the temperature value, can be used by the controller 130 to control the heat exchanger and valves. After the flow rates are measured, the return fluids are combined in a return manifold 174, in this case a simple T-piece that returns the fluid to the heat exchanger return line 154.

[0035] In this example, flow control valves 162, 164, 166, 168 are on the supply side between the heat exchanger output and the wafer carrier. The same effect can be achieved by placing the valve on the return side between the wafer carrier and the return input 154 of the fluid returning to the heat exchanger. As another alternative, the valve can be placed in two positions, or one type of pneumatic valve or proportional valve can be placed on one side of the wafer carrier and another type of valve can be placed on the other side of the wafer carrier. Similarly, a flow meter can be placed on either side of the wafer carrier or at another location in the system. In some embodiments, the flow meter is at the heat exchanger. In the example shown, the flow meter measurement can be combined with the flow data from the corresponding heat exchanger.

[0036] The temperature controller 130 controls valves 162, 164, 166, and 168 to achieve the desired flow rate through the chuck. Proportional valves 162 and 164 can be controlled by an electropneumatic regulator. This regulator is supplied with CDA (compressed dry air) at a controlled, typically constant pressure. The regulator modulates the input CDA to produce a precise pneumatic air pressure signal in response to an electrical control signal from the thermal controller. If a stepless analog signal is supplied to the regulator, the regulator can provide a stepless regulator air pressure. This regulated pneumatic control pressure is applied to the pressure-regulated valve to open and close the valve's fluid passageway.

[0037] In some embodiments, CDA is applied to the supply solenoid valve of the regulator 140. As the input control voltage from the controller increases, the solenoid valve opens. The pressure released by the supply valve is measured by a sensor and fed into the control circuit. The supply valve is adjusted until the measured pressure aligns with the pressure indicated by the control signal. An exhaust solenoid valve is provided to release pressure within the regulator back to the CDA supply.

[0038] The pressure-regulated valve provides proportional fluid control in response to the control pressure from the pressure regulator. This allows for stepless control of fluid flow through each coolant flow line 142, 146. Compared to pulse valves, this valve moves less. This provides for a longer hardware life with less maintenance. In addition, the response to temperature changes is smoother. Using variable flow rates with discrete fluid off times during plasma processing smooths the temperature response and reduces temperature oscillations.

[0039] On the other hand, at lower flow rates, the proportional valve does not provide precise flow rate changes.When a lower flow rate is required, the pneumatic valves 166, 168 can be pulsed to increase the accuracy of flow rate control.

[0040] Additional valves (not shown) can 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 can be used to direct the fluid through the heat exchanger without flowing through the carrier. When the pneumatic or proportional valves 162, 164, 166, 168 are closed, the incoming supply fluid is blocked from flowing through the wFib outlets 142, 146. If the bypass valve 178 between the wFib inlet 152 and outlet 154 is opened, the supplied fluid is redirected to bypass the processing chamber and flow directly back to the return line 154. This allows the corresponding heat exchanger to establish a stable temperature and maintain the supply of fluid at the desired temperature. Additional valves can be used to further control the flow direction.

[0041] Figure 3 is a graph of the control valve and heat exchanger temperatures. The control system has multiple inputs 302, which may include recipe conditions (which are based on the process applied to the workpiece and include power, pressure, etc.), the internal and external temperatures of the chuck measured by various temperature sensor probes (SPs), and the temperature ramp rates inside and outside the chuck from the SPs.

[0042] Output 310 may include the expected internal and external channel temperatures (Tesc) of the electrostatic chuck, the internal and external channel flow rates of the chuck, and the internal and external flow temperatures of the chuck.

[0043] These multiple inputs 302 are applied to a MIMO controller 304, which then operates the valves. These inputs can be used in any of a variety of ways to determine how to operate the valves. The inputs, ESC temperature, various SP values, and recipe conditions are combined with feedback on line 316 from the ESC 308 to control the ESC temperature. In some embodiments, valves can also be used to control the temperature ramp rate or rate of temperature change. In the example shown, the controller generates internal and external channel valve percentages 312, which determine the valve opening percentage for pneumatic and proportional valves. The internal and external valve percentages are applied to wFib 306. The controller also determines internal and external channel flow rates 314, which are compared to the flow rate measured at wFib. The fluid then circulates through the ESC 308. The output 310 from the ESC is returned to the controller in a closed loop to further determine the new valve percentages 312 and flow rates 314.

[0044] In this example, there are two separate fluid channel areas 122 in the ESC. These are designated as inside and outside. The temperature and flow rate of the fluid in each area are independent of the temperature and flow rate in the other areas. For this reason, there are two independent flow supply lines 142, 146, two independent fluid return lines 144, 148, two independent sensor probes 112, 114 and two independent series of valves 162, 166, 164, 168. Each area is monitored and controlled independently, however, the control process can be managed in the MIMO controller 304. Although these areas are referred to as inside and outside, they can be in any desired relative physical location in the ESC. More areas can also be added by providing additional separate coolant channels and related components in the ESC.

[0045] Temperature ramp rates can be used to improve ESC reliability, such as bonding life. Temperature ramp rate control also facilitates process matching between different processing chambers with different thermal characteristics. Controlling the temperature ramp rate also helps improve the process window for HARC (high aspect ratio contact) etching and other processes requiring high precision.

[0046] In the example shown, the valve percentage 312 is applied to the wFib, however, this depends on the configuration of the valve and the control system. The percentage can be in the form of a digital or analog control signal, which is received by a separate valve controller, which then sends a pneumatic or electrical signal to the corresponding valve. The valve controller can be located in the wFib or elsewhere. A PLC (Programmable Logic Controller) within the wFib or in a separate chassis can be used to control proportional valves and pneumatic valves. This operation can be extended to control the resistive heater in the chuck and also control the valves such as Figure 4 Heating fluid supply shown. These additional thermal systems provide the system with more temperature control knobs, which allow for greater control over the chuck and workpiece temperatures and the rates at which they are ramped up and down.

[0047] Figure 4 Figure 4 is a diagram of a two-zone temperature control system 402 for an electrostatic chuck 404 in a plasma 424 processing chamber. This system features dual coolers or heat exchangers 450 and 460 to provide both cooling and heating functions using the chuck's fluid channels. The dual cooler / heat exchanger arrangement provides either hot or cold fluid flow, depending on the requirements of the chamber temperature controller 430.

[0048] Similar to Figure 1In the example of FIG. 4 , a workpiece 406 is attached to a carrier 404 such as an ESC. During certain stages of the manufacturing process, a plasma 424 applies heat to the workpiece. The ESC in this example has a top plate 408 with temperature sensor probes 412, 414 and a lower cooling plate 410 with two zones of coolant channels, although there may be more. The coolant channels have input lines 416 coupled to fluid outputs 442, 446 of a wFib 440. The coolant channels have outputs 418 coupled to return lines 444, 448 that return to the wFib. Although only two coolant channels for two hot zones are shown on the ESC, as in FIG. Figure 1 In the example of , there may be more coolant channels, there may be more coolant channels.

[0049] The temperature regulation system has a hot fluid heat exchanger 450, which has a source output line 452 and a return input line 454 for heat or heating fluid. This return feeds the fluid back to the heat exchanger. The heat exchanger heats the fluid to a predetermined temperature or heats the fluid to a regulated amount and provides the fluid to the supply line 452 under pressure. The fluid temperature can be fixed, or it can be regulated based on a control signal (such as a control signal from a controller 430 or another controller). Similarly, the system has a source or output line 462 and a return line 464 for cooling or cooled fluid for a second heat exchanger 460. The second heat exchanger 460 receives the cooling return fluid and cools it to a predetermined temperature or cooling regulated amount. As shown in the figure, the first and second heat exchangers can be a single unit or two separate devices. Depending on the specific embodiment, the heat exchanger can be thermostatically controlled, or the heat exchanger can apply a fixed amount of heating or cooling with or without specific control. The temperature of the coolant circulating through the substrate carrier 404 is controlled in part by the temperature of the supplied hot 452 and cold 462 fluids, and by the flow rate and mixing of the hot and cold fluids reaching the ESC 404 .

[0050] The hot fluid supply is provided to a 3-way valve 456 which opens or closes the flow of hot fluid from the heat exchanger. Similarly, the cold fluid supply is provided to the same 3-way valve which opens or closes the flow of cold fluid from the second heat exchanger. The fluid allowed to pass through this valve is provided to the wFib 440 in the wafer carrier supply line which is connected to the wafer carrier supply line. Figure 1The wFib uses pneumatic and proportional valves connected in series to regulate flow rates in a similar manner to the wFib. The coolant, at the regulated temperature, then heats or cools the workpiece carrier. An additional, optional three-way valve 466 is coupled to the hot return line 454 and the cold return line 464. Fluid returns from the substrate carrier to this valve in the return line and is allowed to pass through it back to the corresponding heat exchanger from which it came. The three-way valve operates under the control of a temperature controller 430 coupled to both valves. The three-way valve can be included in the wFib, or it can be located in some external rack or fixture.

[0051] In some embodiments, the temperature controller 430 determines the flow rate and heat exchanger to use in the substrate carrier fluid channel to heat or cool the hot fluid. In some embodiments, the coolant fluid provided by the cold heat exchanger is at about 0°C, and the coolant fluid provided by the hot heat exchanger is at about 55°C. Depending on the current temperature of the wafer carrier, one of these fluids or a mixture thereof is delivered to the fluid channel. As an example, if the carrier temperature is above the set point, the fluid from the cold chiller is used. If the temperature is below the set value, the fluid from the hot chiller is used. The fluid delivery system controls the temperature at the workpiece to within an appropriate temperature range. The fluid delivery system also controls temperature ramp-up and overshoot during plasma processing.

[0052] Return paths (not shown) may be provided for both heat exchangers to allow heated fluid to flow from the heat supply 452 to the heat return 454 , bypassing the workpiece 404 and, optionally, the wFib 440 . Figure 2 An example of such a return path is shown with valve 178 open. A similar cooling fluid return valve can be used to allow cooled fluid to flow directly from cooling supply 462 to cooling return 464 without passing through the carrier. When the hot or cold supply is not being supplied to the carrier due to the settings of three-way valves 456 and 466, the hot and cold fluid return valves can be used to allow the fluid to flow through the corresponding heat exchanger without passing through the carrier. This allows the corresponding heat exchanger to establish a stable temperature and maintain the fluid supply at the desired temperature.

[0053] The described temperature regulation system allows the temperature of the fluid flowing through the channels in the substrate carrier to be controlled within a range of, for example, 0° C. to 55° C. The workpiece carrier may have more than one hot fluid channel, in which case the temperature may be replicated. Figure 4Because the mixture entering the wFib and the flow rate through the coolant channels can be independently controlled, a single hot heat exchanger and a single cold heat exchanger can be used to provide fluid to more than one channel.

[0054] Figure 5 Graph 504 shows the flow rate through a proportional valve at different valve percentages. The first upper curve 504 represents different control inputs to the proportional valve over time on the horizontal axis. The vertical axis of the first curve represents the duty cycle of the PWM waveform applied to the valve, as indicated by the scale on the right. Higher duty cycles, shown at the left and right ends of the graph, close the valve. Lower duty cycles, shown near the center of the graph, allow the valve to open more.

[0055] The second curve 502 represents the flow rate through the proportional valve in response to an applied PWM signal 504. The vertical scale of the flow rate on the left scale runs from a lower flow rate at the bottom of the scale to a higher flow rate at the top of the vertical scale. As shown, when the valve is first opened and the flow rate is slowly increased by reducing the PWM duty cycle, there is a region 506 of low flow through the proportional valve. In this region, the valve does not have a consistent linear and repeatable response to the input signal 504. The flow rate in this region 506 is erratic. Similarly, when the valve is closed from a high flow rate in the center of the graph to a low flow rate, the valve has a region 508 when closed, within which the valve response is also not linear or repeatable. In this example, the flow rate suddenly drops to a minimum value and does not recover. Outside of these low flow regions 506 and 508, the proportional valve is regular and has a predictable response to the input signal.

[0056] Figure 5 The figure shows a typical response to a proportional valve. To overcome this nonlinear response, the wFib with two valves in series can be operated in a different manner than a traditional single valve. In an embodiment, the proportional valve is the main valve for higher flow rates and operates in the linear region rather than in the end low flow regions 506, 508. To achieve low flow rates, the proportional valve is closed to a low flow rate region where there is still a predictable response. The flow rate is then further reduced by operating the pneumatic valve. This allows for high accuracy in the low flow rate region. For higher flow rates, a proportional valve is used and no pneumatic valve is used at all. This reduces the wear of the pneumatic valve while still providing precise control of the flow rate.

[0057] Control methods

[0058] The above embodiments include valve controllers 130, 430. Depending on the embodiment, the valve controller can control the valve in different ways. In some embodiments, a MIMO (multiple-input, multiple-output) model-based controller can be used. During wafer processing, the MIMO controller can be used to respond to sensor probe (SP) temperature readings and then control the temperature ramp rate (ramp down and ramp up). The ramp ramp rate is an important parameter for certain processes. As an example, the ramp ramp rate may affect the bonding reliability in certain processes. Although the system is described as being primarily used in a plasma chamber with an electrostatic chuck for semiconductor processing, the same technology can be used to control the temperature of any surface in a semiconductor chamber that uses a fluid to heat or cool the surface.

[0059] The described model-based MIMO system can be used to control temperature ramp rates and manage zone-to-zone crosstalk. Zone-to-zone crosstalk occurs when the temperature of one zone affects the temperature of another, for example due to heat flowing through a plate containing fluid channels in an ESC. The control software can be extended to control wafer temperature by extending the model-based design to include a wafer temperature model in addition to the electrostatic chuck temperature model. In this way, the described embodiments can be used to improve overall temperature matching within the chamber, electrostatic chuck bonding life, and process window.

[0060] Figure 3 The depicted plurality of inputs 302 can be applied to a MIMO controller 304, 130, 430 with model-based design. The input ESC temperature, various SP temperature values, and recipe conditions can be used along with feedback on line 316 from the ESC 308 to control the ESC temperature and its ramp rate. The controller applies the model to generate internal and external channel valve percentages 312 and additional channels for the total number of zones in the system.

[0061] Model-based decisions rely on physical models of the heat absorption and heat transfer characteristics of the system components. These components may include one or more of the following: a chuck, a workpiece, a fluid, a heat exchanger, a tube for carrying the fluid, and cooling channels for different operating conditions through a process recipe. Physical models can be built for two or more regions. For systems with multiple regional cooling channels in a chuck (or any other component), the model can account for crosstalk between two or more regions. Crosstalk accounts for heat transfer between cooling zones affected by different coolant channels. In some embodiments, the model-based controller design uses a linear quadratic controller or similar optimized controller that is designed to handle crosstalk and control the temperature ramp rate.

[0062] Temperature ramp rates can be used to improve ESC reliability, such as bonding lifetime. Ramp rate control also helps match processes between different processing chambers with different thermal characteristics. Control of ramp rates also helps improve the process window for HARC (high aspect ratio contact) etching and other processes requiring high precision.

[0063] Figure 6

[0014] This is a process flow diagram for a model-based control loop that can be used to control the temperature of components within a process chamber using a coolant and at least one control valve. This process can use the hybrid dual-valve system described above, or any other desired flow control system. The model can be established empirically or theoretically before the process begins. The model can be a dynamic linear model that represents the behavior of temperature control components within the plasma chamber under different conditions. Using a predictive model, the future behavior of components (such as the ESC shown above) can be predicted. This allows for control over the rate at which the temperature is ramped. Using the process recipe as input, the controlled temperature can be adjusted before changes in the temperature load or desired temperature set point are made.

[0064] Block 604 represents the application of a linear predictive control system using the model as an ordinary differential equation as described in this example:

[0065]

[0066] Where A and B are matrices derived from the model. For a two-region system, this matrix is ​​a 4×4 matrix. For more regions, the matrix is ​​expanded accordingly. Other models can be used depending on the specific implementation, and nonlinear equations can also be used.

[0067] In this example, is a linear array or a 1x4 matrix, which is defined for a two-region system as This can be extended to accommodate more regions. Two different regions can be treated with the same model to accommodate crosstalk between the regions' temperatures. In the ESC (electrostatic chuck) example, the variables in the array can be assigned the following values:

[0068] x1=ESC inner area temperature

[0069] x2 = ESC outer zone temperature

[0070] x3 = ESC inner area temperature rise and fall rate

[0071] x4 = ESC outer area temperature rise and fall rate

[0072] u = [u1, u2] and represents the control output used to adjust the valve for each zone. In this example, the adjustment is expressed as a percentage of the valve opening or a percentage of the total maximum flow through the valve. The specific value will depend on the values ​​used to determine the model, but is expressed here as:

[0073] u1=Inner zone valve percentage

[0074] u2 = outer area valve percentage

[0075] At block 606, the value of each u may be determined as:

[0076] u=-Kx+K r r

[0077] Where K and K r are constants reflecting controller gains. These can 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 attempts to achieve at the ESC by adjusting the values ​​defined by u above. The setpoints in this example are as follows:

[0078] r1 = ESC internal zone temperature set point

[0079] r2 = ESC outer zone temperature set point

[0080] r3 = ESC internal zone temperature ramp rate set point

[0081] r4=ESC outer zone temperature ramp rate set point

[0082] After the operation of block 606, the desired adjustment of the valves has been determined that will achieve the desired temperature and temperature ramp rate set points. The process can then convert these values ​​of u1, u2 into valve actuations, such as an electrical control signal 612 to open a proportional valve or a pneumatic control signal 614 to open a pneumatic valve. Block 608 represents an example of the operation of a dual valve mixing system as described above. Appropriate

[0083] For each area valve percentage u (ie u1, u2) or for i=1, 2 to implement the operation, check u i -u0. u0 represents the minimum threshold of the proportional valve percentage (such as 10%).

[0084] If the result is positive, ie the proportional valve is set to open more than 10%, then at 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 open less than 10%, then at 614 the proportional valve is set to some low value (e.g. 10%) and the pneumatic pulse is applied to the pneumatic valve. This can be applied to first set the pulse at p i% (usually between 20% and 80%, depending on the characteristics of the valve) and secondly set the proportional valve to (u i / p i )%. This allows the proportional valve to provide the remaining flow control supply above the optimum operating range of the pulse valve.

[0085] The operation of block 608 can alternatively be described as follows. The temperature controller first determines the total flow rate for each thermal zone. The total flow rate is then compared to a threshold value (defined as u0 above). If the total flow rate (as indicated by u1 or u2 above) is above the threshold value, the temperature controller opens the pneumatic valve and adjusts the proportional valve to achieve the desired flow rate. On the other hand, if the total flow rate is below the threshold value, the temperature controller closes the proportional valve to a predetermined flow rate and adjusts the pneumatic valve to achieve the desired total flow rate. In the case of valves connected in series, the restriction of the first valve combines with the restriction of the second valve to achieve an overall restricted flow rate.

[0086] At block 616, the determined valve control values ​​are output to the valves. As mentioned above, in the case of a single valve system from block 606, these can be straightforward flow percentages u (i.e., u1, u2), or for a multiple valve system (as in optional block 608), the control can be more complex. The valve control values ​​can be determined in other ways (not shown in block 608), depending on the specific implementation of the flow control system between the heat exchanger and the process chamber components (e.g., ESC).

[0087] In addition to controlling the flow through the valve, input parameters are read at 618, namely the current zone temperatures x1, x2. The ramp rates x3, x4 can also be estimated using the derivatives of the temperatures x1, x2 or the time rates of change of the temperatures x1, x2. These values ​​can then be used as inputs to another adjustment loop at block 604. Thus, Figure 6 The control process is as follows Figure 6 The closed loop control system shown in the return loop 622.

[0088] Figure 6 The process can also be described as performing a series of operations on a MIMO controller, a temperature controller, or some other component of the system. Measured temperatures are received from both a first thermal sensor at a first thermal zone of a carrier and a second thermal sensor at a second thermal zone. A predictive model is then applied to the two measured temperatures to determine a first flow rate through a first fluid channel of the carrier and a second flow rate through a second fluid channel of the carrier, wherein the first fluid channel is thermally coupled to the first thermal zone and the second fluid channel is 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.

[0089] This method can also use ramp rates. Using the received measured temperatures, the ramp rates of the temperatures of the first and second thermal zones are estimated. The estimated ramp rates are then used to apply the prediction model.

[0090] Chamber structure

[0091] Figure 7 FIG2 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 can be any type of high-performance etching chamber. Other commercially available etching chambers can similarly utilize the chuck assembly described herein. Although the exemplary embodiment is described in the context of the plasma etching system 700, the chuck assembly and temperature control system described herein are also applicable to other processing systems used to perform any plasma manufacturing process (e.g., plasma deposition systems, etc.).

[0092] refer to Figure 7 , the plasma etching system 700 includes a grounded chamber 705. Process gas is supplied to the interior of the chamber 705 from a gas source 729, which is connected to the chamber through a mass flow controller 749. The chamber 705 is evacuated via an exhaust valve 751, which is connected to a high-capacity vacuum pump stack 755. When plasma power is applied to the chamber 705, a plasma is formed in the processing region above the workpiece 710. A plasma bias power 725 is coupled to the chuck assembly 742 to ignite the plasma. The plasma bias power 725 typically has a low frequency between about 2 MHz and 60 MHz, and can be in the 13.56 MHz band, for example.

[0093] In an exemplary embodiment, the plasma etching system 700 includes a second plasma bias power operating in a frequency band of approximately 2 MHz, which is connected to an RF match. The first plasma bias power 25 is also coupled to the RF match and is also coupled to the lower electrode via a power conduit 728. The plasma source power 730 is coupled to the plasma generating element 735 through another match (not shown) to provide a high-frequency source power to inductively or capacitively excite the plasma. The plasma source power 730 can have a higher frequency than the plasma bias power 725, such as between 100 and 180 MHz, and can be, for example, in the 162 MHz frequency band.

[0094] The workpiece 710 is loaded through the opening 715 and clamped in the chuck assembly 742 within the chamber. The workpiece 710 (e.g., a semiconductor wafer) can be any wafer, substrate, or other material used in the semiconductor processing field, and the present invention is not limited in this respect. The workpiece 710 is disposed on the top surface of a dielectric layer or disk 745 of the chuck assembly, which is disposed on a cooling base assembly 744 of the chuck assembly. A clamping electrode (not shown) is embedded in the dielectric layer. It is coupled to a bias power source 779 to provide an electrostatic force to clamp the workpiece 710. In a specific embodiment, the chuck assembly 742 may include two or more different fluid channel regions, such as an inner channel 741 and an outer channel. Each channel 741 can be independently controlled to the same or different temperature set points.

[0095] The system controller 770 is coupled to various systems to control the manufacturing process in the chamber. The controller 770 may include a temperature controller 775 to execute a temperature control algorithm (e.g., temperature feedback control) and the controller may be software or hardware, or a combination of software and hardware. The system controller 770 also includes a central processing unit 772, a 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 the heat source and / or affect a heat sink outside the plasma chamber 705 for 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, coupled to a fluid supply line, or at any other desired location.

[0096] The thermal fluid zones may include separate, independently controlled thermal fluid heat transfer circuits with separate flow controls based on the zone-specific temperature feedback loops described above. In the exemplary embodiment, a temperature controller 775 is coupled to a first heat exchanger (HTX) / cooler 777 and may be further coupled to a second HTX / heater 778 and further heat exchangers (not shown) as needed, depending on the specific implementation. The flow rate of the heat transfer fluid or coolant through the conduits in the chuck assembly 742 is controlled by the proportional valve system 781, 785 as described above.

[0097] The temperature controller 775 controls the proportional valve systems 781, 785 to independently control the flow rate of the hot fluid or heat transfer fluid to each of the different fluid channels. The temperature controller can also control the temperature set point used by each heat exchanger to cool or heat the hot fluid. Thus, each heat exchanger can bring the hot fluid for its respective coolant channel to a different temperature before providing it back to the fluid channel.

[0098] The heat transfer fluid can be a liquid such as, but not limited to, deionized water / ethylene glycol, a fluorinated coolant (such as from 3M), or from Solvay Solexis, Inc. ) or any other suitable dielectric fluid (e.g., a dielectric fluid containing a perfluorinated inert polyether). Although this specification describes the ESC in the context of a plasma processing chamber, the ESC described herein can be used in a variety of different chambers and for a variety of different processes. Depending on the specific embodiment, a different substrate carrier can be used in place of the ESC.

[0099] In the following description, many details are set forth; however, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details. In some cases, well-known methods and apparatus are shown in block diagram form rather than in detail to avoid obscuring the present invention. References throughout this specification to "an embodiment" or "one embodiment" mean that the particular features, structures, functions, or characteristics described in conjunction with that embodiment are included in at least one embodiment of the present invention. Therefore, the appearance of the phrase "in an embodiment" or "in one embodiment" in various places throughout this specification does not necessarily represent the same embodiment of the present invention. In addition, the particular features, structures, functions, or characteristics may be combined with one or more embodiments in any suitable manner. For example, the first embodiment may be combined with the second embodiment anywhere that the particular features, structures, functions, or characteristics of the two embodiments are associated but not mutually exclusive.

[0100] Unless the context clearly indicates otherwise, as used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well. It will also be understood that the term "and / or" as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0101] The terms "coupled" and "connected" and their derivatives may be used in this specification to describe functional or structural relationships between components. It should be understood that these terms are not intended to be synonymous with each other. Rather, in certain embodiments, "connected" may be used to indicate that two or more components are in direct physical, optical, or electrical contact with each other. "Coupled" may be used to indicate that two or more components are in direct or indirect (with other intermediate components between them) physical, optical, or electrical contact with each other, and / or to indicate that two or more components cooperate or interact with each other (such as in a cause-and-effect relationship).

[0102] As used herein, the terms "above," "below," "between," and "on..." refer to the relative position of one component or material layer relative to other components or layers, where these physical relationships are significant. For example, in the context of material layers, a layer positioned above or below another layer may be in direct contact with the other layer or may have one or more intervening layers. Additionally, a layer positioned 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 are made in the context of component assemblies.

[0103] It should be understood that the above description is intended to be illustrative rather than restrictive. For example, although the flowchart in the figure shows a specific order of operations performed by certain embodiments of the present invention, it should be understood that such order is not necessary (such as alternative embodiments can perform operations in different orders, combine certain operations, overlap certain operations, etc.). In addition, many other embodiments will be apparent to those skilled in the art after reading and understanding the above description. Although the present invention has been described with reference to specific exemplary embodiments, it will be appreciated that the present invention is not limited to the described embodiments, but can be modified and changed to implement within the spirit and scope of the appended claims. Therefore, the scope of the present invention should be determined with reference to the full scope of the equivalents of the appended claims and the rights claimed in the claims.

Claims

1. A workpiece processing system comprising: plasma chamber; a plasma source for generating a plasma containing gas ions in the plasma chamber; a workpiece holder in the chamber to hold a workpiece and control a temperature of the workpiece during plasma processing, the workpiece holder having a first fluid channel and a second fluid channel; a first flow line coupled to the first fluid passage of the workpiece holder, the first flow line comprising a first supply flow line and a first return flow line, the first return flow line coupled to only a single return manifold; a second flow line coupled to the second fluid passage of the workpiece holder, the second flow line comprising a second supply flow line and a second return flow line, the second return flow line coupled to only the single return manifold, wherein all of the outputs of the first return flow line and the second return flow line are input to the single return manifold, and wherein all of the outputs of the first return flow line and the second return flow line are the same as all of the outputs of the first supply flow line and the second supply flow line; a first proportional valve coupled to the first supply flow line, the first proportional valve being between the single return manifold and the workpiece holder, and the first proportional valve being configured to provide a stepwise adjustment of the flow rate between an open position and a closed position; a second proportional valve coupled to the second supply flow line, the second proportional valve being between the single return manifold and the workpiece holder, and the second proportional valve being configured to provide a stepwise adjustment of the flow rate between an open position and a closed position; a first flow meter, the first flow meter being between the first proportional valve and the single return manifold, the first flow meter being connected in series with the first proportional valve; as well as A second flow meter is provided between the second proportional valve and the single return manifold, the second flow meter being connected in series with the second proportional valve.

2. The workpiece processing system of claim 1, wherein the first flow meter and the second flow meter are between the workpiece holder and the single return manifold.

3. The workpiece processing system of claim 1 , further comprising: A heat exchanger is coupled to the first flow line and the second flow line.

4. The workpiece processing system of claim 1, wherein the first proportional valve comprises a first pressure-regulated valve and the second proportional valve comprises a second pressure-regulated valve.

5. The workpiece processing system of claim 4, further comprising: a first pressure regulator coupled to the first pressure-regulated valve to control the first pressure-regulated valve; as well as A second pressure regulator is coupled to the second pressure-regulated valve to control the second pressure-regulated valve.

6. The workpiece processing system of claim 1 , further comprising: a first pneumatic valve between the single return manifold and the first proportional valve, wherein the first pneumatic valve is a first digital or pulse valve that cycles between an open state and a closed state; A second pneumatic valve is between the single return manifold and the second proportional valve, wherein the second pneumatic valve is a second digital or pulse valve that cycles between an open state and a closed state.

7. The workpiece processing system of claim 1 , further comprising: A temperature controller is configured to receive a measured temperature from a thermal sensor of the workpiece holder and control the first and second proportional valves in response to the measured temperature to adjust the flow rate of the thermal fluid.

8. The workpiece processing system of claim 7, wherein the thermal fluid comprises polyether.

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