Method and system for controlling heating temperature and non-transitory computer readable medium

Abstract

A system and method for heating a workpiece to a desired temperature and a non-transitory computer readable medium are disclosed. The system and method take into account the physical limitations of temperature devices, such as time lag, temperature deviation, and calibration, in creating a hybrid method for more efficiently heating a workpiece. First, the workpiece is heated using open loop control to heat the workpiece to a threshold temperature. After reaching the threshold temperature, a closed loop maintenance mode is utilized. In some embodiments, an open loop maintenance mode is used between the open loop heating mode and the closed loop maintenance mode. In addition, a method for calibrating a pyrometer using a contact thermocouple is disclosed.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to a non-transitory computer-readable medium and a system and method for heating a substrate, and more particularly, for efficiently heating a substrate to a desired temperature. Background Art

[0002] The fabrication of semiconductor devices involves multiple discrete and complex processes. Semiconductor substrates typically undergo many processes during the fabrication process. These processes may be performed in a processing chamber that may be maintained under processing conditions that are different from the environment.

[0003] It is common in many semiconductor manufacturing processes to heat the substrate before and / or after processing. In many cases, the substrate is heated to a high temperature. Such preheating can help prevent substrate warping, cracking, and movement when a cold substrate contacts a hot platen. These phenomena can lead to particle generation and processing errors, and can reduce the overall process yield.

[0004] Additionally, in some embodiments, the substrate may be warmed after being subjected to a cold process to eliminate the possibility of condensation occurring when the substrate leaves the processing chamber.

[0005] The ability to heat a workpiece to a specific temperature is not simple. Generally, there are two techniques for measuring the temperature of a workpiece.

[0006] The first technique is to use a contact thermocouple that is pressed against the workpiece. The thermocouple measures the temperature of the workpiece. However, there are three disadvantages associated with this method. First, the thermocouple may not record the actual temperature of the workpiece. For example, there may not be perfect heat conduction between the workpiece and the thermocouple. Therefore, the temperature measured by the thermocouple may not be accurate. Second, the thermocouple may have a time lag. For example, as the temperature of the workpiece changes, there will be a delay before the thermocouple measures this change in temperature. Third, each new workpiece with a new coating requires a calibration workpiece with a permanently attached thermocouple because the coating changes the emissivity. This is to ensure an accurate temperature reading for a specific workpiece and coating combination. This is a very expensive and time-consuming process.

[0007] The second technique is to use a pyrometer or other infrared sensor to remotely measure the temperature of the workpiece. However, temperature measurements using infrared can be imprecise because the emissivity of silicon changes with temperature. In other words, if the pyrometer is calibrated at a specific temperature, then readings at temperatures that are not close to the calibration temperature will be erroneous.

[0008] Therefore, both of these measurement techniques are problematic when attempting to heat a workpiece from a first temperature (e.g., room temperature) to a second, higher temperature. The temperature deviations and time lags of contact thermocouples can make it difficult to control the heating source to bring the workpiece to the desired temperature. The changing emissivity of silicon makes it difficult, if not impossible, to make temperature measurements over a wide temperature range using a pyrometer.

[0009] Therefore, it would be beneficial if there was a control system to accurately heat a workpiece without utilizing a calibration workpiece with a permanently attached thermocouple. Additionally, it would be advantageous if the control system operated using contact thermocouples and / or pyrometers. Summary of the invention

[0010] A system and method for heating a workpiece to a desired temperature is disclosed. The system and method take into account the physical limitations of temperature devices, such as time lag, temperature deviation, and calibration, in creating a hybrid method for more efficiently heating a workpiece. First, the workpiece is heated using open loop control to heat the workpiece to a threshold temperature. After reaching the threshold temperature, a closed loop maintenance mode is utilized. In some embodiments, an open loop maintenance mode is utilized between the open loop heating mode and the closed loop maintenance mode. Additionally, a method for calibrating a pyrometer using a contact thermocouple is disclosed.

[0011] According to one embodiment, a system for controlling the temperature of a workpiece is disclosed. The system includes: a temperature sensor; a heating element; and a controller in communication with the temperature sensor and the heating element, wherein the controller includes a processing unit and a memory device, wherein the memory device contains instructions that, when executed by the processing unit, enable the controller to: operate in an open-loop warming mode, wherein the controller heats the workpiece using open-loop control until a threshold temperature is reached; and operate in a closed-loop maintenance mode, wherein the controller maintains the temperature of the workpiece at a target temperature using closed-loop control. In some embodiments, the temperature sensor has a time lag, and the memory device further contains instructions that, when executed by the processing unit, enable the controller to: operate in an open-loop maintenance mode after reaching the threshold temperature, wherein the controller roughly maintains the temperature of the workpiece using open-loop control; and switch from the open-loop maintenance mode to the closed-loop maintenance mode after a duration. In some embodiments, the duration is at least as long as the time lag. In some embodiments, the threshold temperature is selected so that the temperature of the workpiece does not exceed the target temperature during the open-loop warming mode. In some embodiments, operating in the closed-loop maintenance mode includes: sampling the output of the temperature sensor; correcting for temperature deviation, if any, of the temperature sensor; compensating for time lag, if any, of the temperature sensor; and using the corrected and compensated output of the temperature sensor as an input to a proportional-integral-derivative control loop to determine the output to the heating element. In some embodiments, compensating for the time lag includes utilizing an inverse low-pass filter, wherein the time constant of the inverse low-pass filter is equal to the time lag of the temperature sensor. In some embodiments, the temperature sensor includes a contact thermocouple. In some embodiments, the temperature sensor includes a pyrometer.

[0012] According to another embodiment, a method of heating a workpiece to a target temperature is disclosed. The method includes: operating in an open-loop warming mode, wherein a controller controls a heating element using open-loop control until a threshold temperature is reached; and operating in a closed-loop maintenance mode, wherein the controller maintains the temperature of the workpiece at the target temperature using closed-loop control based on measurements from a temperature sensor. In certain embodiments, the method further includes: operating in an open-loop maintenance mode, wherein the controller uses open-loop control to roughly maintain the temperature of the workpiece for a duration before switching to the closed-loop maintenance mode. In certain embodiments, the temperature sensor has a time lag, and the duration is at least as long as the time lag. In certain embodiments, operating in the closed-loop maintenance mode includes: sampling the output of the temperature sensor; correcting for a temperature deviation of the temperature sensor, if any; compensating for a time lag of the temperature sensor, if any; and using the corrected and compensated output of the temperature sensor as an input to a proportional-integral-derivative control loop to determine an output to the heating element. In some embodiments, compensating for the time lag includes utilizing an inverse low pass filter, wherein the time constant of the inverse low pass filter is equal to the time lag of the temperature sensor. In some embodiments, the temperature sensor includes a pyrometer, and the method further includes: calibrating the pyrometer using a contact thermocouple prior to the open loop warming mode by: heating the workpiece to a known temperature determined by the contact thermocouple; dwelling at the known temperature for a duration greater than the time lag of the contact thermocouple; and correlating the output of the pyrometer to the known temperature determined by the contact thermocouple.

[0013] According to another embodiment, a non-transitory computer-readable medium includes instructions that, when executed by a controller, enable the controller to: operate in an open-loop warming mode, wherein the controller uses an open-loop control to heat a workpiece using a heating element until a threshold temperature is reached, the threshold temperature being measured by a temperature sensor; and operate in a closed-loop maintenance mode, wherein the controller uses closed-loop control to maintain the temperature of the workpiece at a target temperature based on the measurement made by the temperature sensor. In some embodiments, the temperature sensor has a time lag, and the non-transitory computer-readable medium further includes instructions that, when executed by the controller, enable the controller to: operate in an open-loop maintenance mode after reaching the threshold temperature, wherein the controller uses open-loop control to roughly maintain the temperature of the workpiece; and switch from the open-loop maintenance mode to the closed-loop maintenance mode after a duration. In some embodiments, the duration is at least as long as the time lag. In some embodiments, the threshold temperature is selected so that the temperature of the workpiece does not exceed the target temperature during the open-loop warming mode. In some embodiments, operating in the closed-loop maintenance mode includes: sampling the output of the temperature sensor; correcting for temperature deviation, if any, of the temperature sensor; compensating for time lag, if any, of the temperature sensor; and using the corrected and compensated output of the temperature sensor as an input to a proportional-integral-derivative control loop to determine the output to the heating element. In some embodiments, compensating for the time lag includes utilizing an inverse low-pass filter, wherein the time constant of the inverse low-pass filter is equal to the time lag of the temperature sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] For a better understanding of the present disclosure, reference is made to the accompanying drawings, which are incorporated herein by reference, and wherein:

[0015] Figure 1 A processing chamber using a contact thermocouple to measure the temperature of a workpiece according to one embodiment.

[0016] Figure 2 is a flow chart showing a sequence for heating a workpiece.

[0017] Figure 3 is a graph showing the temperature of a workpiece and the power applied to a heating element as a function of time.

[0018] Figure 4 A closed control loop is shown which may be used in some embodiments.

[0019] Figure 5A processing chamber using a pyrometer to measure the temperature of a workpiece according to one embodiment.

[0020] Figure 6 A process chamber using a pyrometer and a contact thermocouple for calibrating the pyrometer according to one embodiment.

[0021] Figure 7 is a flow chart showing the sequence for calibrating a pyrometer using a contact thermocouple. DETAILED DESCRIPTION

[0022] As mentioned above, in many applications it is advantageous to preheat a substrate before it is processed. Therefore, a system that can be used to quickly heat a substrate would be beneficial.

[0023] Figure 1 A side view of a substrate heating system 100 according to one embodiment is shown. The substrate heating system 100 includes a process chamber 101, which can be maintained at near vacuum conditions (e.g., less than 100 mTorr). Outside the process chamber 101 is a heating element 110. Light from the heating element 110 can pass through a window, such as a quartz window 102, which serves as a side of the process chamber 101. This heating element 110 can be an array of heating lamps. For example, a tungsten halogen lightbulb can be used to emit energy toward the workpiece.

[0024] The wavelength of the power emitted by the tungsten halogen bulb is in the range from about 400nm to 2600nm, with a peak at approximately 1000nm. Between the wavelength of 600nm and 1800nm, the emitted power is at least half of the maximum emitted power.

[0025] In other embodiments, a light emitting diode (LED) can provide heat energy. In some cases, LEDs are made using gallium and nitrogen (GaN) or indium nitride and gallium nitride (InGaN). The wavelength of light emitted by these LEDs is related to the bandgap energy between the p-type material and the n-type material. Therefore, for LEDs made using GaN and InGaN, the wavelength tends to be around 450nm to 500nm.

[0026] like Figure 1 As shown in FIG. 1 , the heating element 110 may be disposed above the workpiece 10, or may be disposed below the workpiece 10. Therefore, the position of the heating element 110 is not limited by the present disclosure.

[0027] A controller 130 may be provided outside the processing chamber 101. The controller 130 includes a processing unit 131 and a memory device 132. The processing unit 131 may be any suitable component, such as a microprocessor, an embedded processor, an application-specific circuit, a programmable circuit, a microcontroller, or other similar devices. The memory device 132 includes instructions that, when executed by the processing unit 131, enable the controller 130 to perform the functions described herein. The memory device 132 may be a non-volatile memory, such as a Flash Read Only Memory (Flash ROM), an electrically erasable ROM, or other suitable devices. In other embodiments, the memory device 132 may be a volatile memory, such as a random access memory (RAM) or a dynamic random access memory (DRAM).

[0028] The controller 130 is in communication with the heating element 110. The controller may energize the heating element 110 and may also determine the amount of power supplied to the heating element 110. In other words, the controller 130 may determine the appropriate variable amount of power supplied to the heating element 110 to achieve a desired workpiece temperature.

[0029] A workpiece 10 is also disposed in the processing chamber 101 (e.g., on a workpiece support). The contact thermocouple 120 may physically contact the workpiece 10. The controller 130 is in electrical communication with the contact thermocouple 120 via the wire 121. Therefore, the controller 130 can monitor the temperature of the workpiece 10 via the contact thermocouple 120.

[0030] Thus, the contact thermocouple 120 , the controller 130 , and the heating element 110 form a closed-loop control system, wherein the controller 130 monitors the temperature of the workpiece 10 via the contact thermocouple 120 and adjusts the power to the heating element 110 accordingly.

[0031] As described above, the contact thermocouple 120 may have two disadvantages; temperature deviation and lag. Therefore, a calibration may be performed to correlate the temperature recorded by the contact thermocouple 120 with the actual temperature of the workpiece 10. For example, a workpiece may be placed in a processing chamber and the workpiece may be heated to a known temperature. This workpiece may be a thermocouple workpiece, which is a workpiece with an embedded thermocouple. The temperature measured by the contact thermocouple is then recorded. This may be performed at multiple temperatures to create a graph or table showing the measured temperature and the actual temperature of the workpiece. As described above, the processing chamber 101 may have a quartz window 102. In this embodiment, the temperature of the quartz window 102 may be a proxy for the temperature within the processing chamber 101. In another embodiment, a device, such as a silicon coupon, may be set within the processing chamber 101. The temperature of the device may be a proxy for the temperature within the processing chamber 101. The calibration process may include the actual workpiece temperature, the temperature within the processing chamber 101, and the temperature measured by the contact thermocouple. Based on this data, a relationship may be determined. Thus, the actual temperature of the workpiece 10 can be determined based on the measurements received from the contact thermocouple 120 and optionally the temperature of the quartz window 102 in the process chamber 101. In certain embodiments, characterization testing to determine temperature deviations can be performed by a system vendor or component supplier. In other words, the calibration techniques described above can be performed separately and at a different time from the rest of the process described below.

[0032] A second problem associated with the contact thermocouple 120 is its time lag. It is estimated that the duration between the time when the workpiece 10 reaches a certain temperature and the time when the contact thermocouple detects this temperature may be several seconds. In certain embodiments, characterization tests for determining the time lag of a particular contact thermocouple 120 may be performed by a system supplier or component supplier. Thus, the actual time lag may be provided to the controller 130 that performs the method described below.

[0033] In other words, a contact thermocouple acts like a low-pass filter, passing the signal with a certain time delay. A low-pass filter can be constructed digitally using the following formula:

[0034] S filtered,i =(1-f)*S filtered,i-1 +f*S raw,i ,

[0035] Among them, S raw,i is the original signal at time i

[0036] S filtered,i is the filtered signal at time i

[0037] S filtered,i-1is the filtered signal at time i-1, and

[0038] f=T sample / (T sample +τ filter ),in

[0039] T sample is the data sampling time interval, and

[0040] τ filter is the time constant of the low-pass filter.

[0041] This equation can be used to approximate the signal delay τ filter .

[0042] The contact thermocouple 120 acts as a low pass filter, causing its measurement to lag behind the actual temperature by a certain time delay. Therefore, in order to reconstruct the original signal, an inverse low pass filter can be created, which recovers the original signal based on the filtered signal. Solving the above equation for S raw,i , and the following results are obtained:

[0043] S raw,i =S filtered,i-1 +(S filtered,i -S filtered,i-1 ) / f

[0044] Therefore, by measuring at regular time intervals (e.g., T sample ) is sampled and the measurements are recorded, and an inverse low-pass filter can be used to reconstruct the actual temperature of the workpiece 10 at the current time.

[0045] This inverse low pass filter may introduce noise and therefore may be more accurate when there are small changes in temperature.

[0046] Having described techniques for eliminating temperature deviations and time lags, a hybrid control system can be created to heat the workpiece 10 .

[0047] Figure 2 Show use Figure 1 The controller 130 may execute Figure 2 This is the process described in Figure 3 First, as shown in process 200, the controller applies a first power level 330 to the heating element 110. This first power level 330 causes the workpiece 10 to heat the workpiece quickly, such as Figure 3300 in FIG. 3. During the first duration 320, the controller 130 operates in an open-loop mode, wherein the controller 130 applies a first power level 330 to the heating element 110 independently of the temperature of the workpiece 10. The mode during the first duration 320 may be referred to as an open-loop warming mode. As is well known, open-loop control means that the temperature of the workpiece 10 does not affect the power supplied to the heating element 110. Therefore, in some embodiments, in the open-loop warming mode, the power applied to the heating element 110 may be kept constant until the threshold temperature 310 is reached.

[0048] Although the first power level 330 applied to the heating element 110 is not dependent on the temperature of the workpiece 10 , the controller 130 still monitors the temperature of the workpiece 10 using the contact thermocouple 120 during the first duration 320 .

[0049] As shown in process 210, the controller 130 remains in the open-loop warming mode as long as the temperature of the workpiece 10 has not reached the threshold temperature 310. Once the temperature of the workpiece 10 reaches the threshold temperature 310, the controller 130 exits the open-loop warming mode.

[0050] In some embodiments, the temperature of the workpiece 10 is measured using a contact thermocouple 120. In some embodiments, the threshold temperature 310 is selected based on the rate of temperature increase (i.e., the slope of the line 300). In some embodiments, when determining the threshold temperature 310, the temperature deviation of the contact thermocouple 120 is considered. In some embodiments, when determining the threshold temperature 310, the time lag of the contact thermocouple 120 is considered. In other embodiments, the threshold temperature 310 is determined empirically to achieve a fast warm-up time without causing the temperature of the workpiece 10 to exceed the target temperature 311. Therefore, the threshold temperature 310 is less than the target temperature 311. For example, the threshold temperature 310 may be 20°C to 30°C lower than the target temperature 311.

[0051] When the controller 130 exits the open-loop warming mode, it enters the open-loop maintaining mode, as shown in process 220. In this mode having a second duration 321, the controller 130 adjusts the power applied to the heating element 110 in an attempt to maintain the temperature of the workpiece 10. A second power level 331 may be applied to the heating element 110 during the second duration 321. This second power level 331 is less than the first power level 330. Although the temperature of the workpiece may deviate from this threshold temperature 310, the second power level 331 may keep the temperature of the workpiece 10 roughly at the threshold temperature 310, as shown in FIG. Figure 3. The second power level 331 is selected to roughly maintain the temperature of the workpiece 10 until the second duration 321 expires. The phrase “roughly maintain” means that the temperature of the workpiece may deviate from the threshold temperature 310 by up to 20° C. The second duration 321 may be equal to or greater than the time lag of the contact thermocouple 120. As explained above, the time lag of the contact thermocouple 120 may be a parameter supplied to the controller 130 by the system supplier, for example, or may be input to the controller 130 based on technical data. Therefore, in one embodiment, the controller 130 applies a second power level 331 that is less than the first power level 330 during the entire open-loop maintenance mode, and keeps the second power level 331 constant during the second duration 321.

[0052] In this way, the inverse low pass filter operates using all temperature values ​​that are fairly close to the target temperature 311. This can improve the accuracy of the inverse low pass filter. For example, in some embodiments, the time lag of the contact thermocouple 120 can be about 2.7 seconds. Therefore, in this embodiment, as shown in process 230, the waiting delay can be at least 2.7 seconds.

[0053] After the waiting delay, the controller 130 switches to the closed loop maintenance mode, as shown in process 240. The closed loop maintenance mode has a third duration 322, such as Figure 3 In this mode, the controller 130 uses the measurement from the contact thermocouple 120 to determine the power level 332 applied to the heating element 110. As is well known, closed loop control means that the power supplied to the heating element 110 depends on the temperature of the workpiece 10. A typical closed loop process is as follows Figure 4 as shown in .

[0054] First, the signal from the temperature sensor 400 is sampled. The temperature sensor 400 may be a contact thermocouple 120 as described above, or a pyrometer as described below. Next, as shown in process 410, the temperature deviation inherent in the temperature sensor reading is corrected. This can be achieved by adding a constant to the sampled reading. In another embodiment, this can be achieved by using a lookup table or equation that converts the measured temperature to the actual temperature. Similarly, the algorithm for correcting the temperature deviation can be provided by the system provider or by another method. Once the temperature value has been corrected, the time lag that may be inherent in the temperature sensor 400 is compensated, as shown in process 420. As described above, this can be achieved using an inverse low-pass filter with a time constant equal to the time lag of the temperature sensor 400. The output of the inverse low-pass filter represents the actual temperature of the workpiece 10 at the current time. As shown in process 430, this value is then used as the input of a proportional-integral-derivative (PID) control loop. The output of the PID control loop is used to apply the appropriate amount of power to the heating element 110. In this way, the temperature of the workpiece 10 can be strictly controlled.

[0055] Because the controller 130 uses open-loop control (eg, during the first duration 320 ) and closed-loop control (eg, during the third duration 322 ), this approach may be referred to as a hybrid control system.

[0056] Figure 5 An embodiment is shown in which a pyrometer 140 is used to measure the temperature of the workpiece 10. In this embodiment, the contact thermocouple 120 is replaced by the pyrometer 140. The pyrometer 140 can be disposed outside the processing chamber 101 and can emit light into the processing chamber 101 through a window. The pyrometer 140 has limitations when used to determine the temperature of a silicon wafer. The optical properties of silicon make it difficult to measure the absolute temperature of a workpiece using infrared techniques. Emissivity is a measure of the ability of a material to emit energy through radiation. At certain temperatures, the emissivity of silicon changes rapidly, and this makes infrared imaging for accurate measurement of absolute temperature an unstable technique. At certain temperatures, the emissivity of silicon is almost zero. As the temperature of silicon increases, the emissivity of silicon also increases. At 800°C, the emissivity of silicon is almost constant at close to 0.7.

[0057] Thus, in order to use the pyrometer 140, the pyrometer 140 is calibrated at a desired temperature. In other words, the workpiece is heated to the desired temperature. For example, the workpiece may be placed in a process chamber and heated to a known temperature. This workpiece may be a thermocouple workpiece, which is a workpiece with an embedded thermocouple. The temperature measured by the pyrometer 140 is then recorded. This may be done at multiple temperatures in order to create a graph or table showing the measured temperature and the actual temperature of the workpiece. Thus, at the desired temperature, the workpiece has a certain emissivity and the pyrometer 140 is calibrated to that emissivity.

[0058] Figure 6 Another embodiment that can be used to calibrate the pyrometer 140 is shown. Unlike the previous embodiment, Figure 6 The embodiment of the present invention does not utilize a thermocouple workpiece. Therefore, this embodiment can be more easily implemented by a customer or user of the system. In this embodiment, only the pyrometer 140 is utilized to control the temperature of the workpiece, and the contact thermocouple 120 is used only to calibrate the pyrometer 140. As described above, in order to use the pyrometer 140, the pyrometer 140 is calibrated at the desired temperature. This calibration process is as follows Figure 7 As shown in . First, as shown in process 700, the workpiece 10 is heated to a known temperature. For example, the workpiece can be placed in a processing chamber and the workpiece is heated to a known temperature defined by a contact thermocouple 120. This known temperature can be a desired temperature to which the workpiece will be heated, or it can be a calibration temperature. Since the contact thermocouple 120 can be used to measure the temperature of the workpiece 10, a thermocouple workpiece is not utilized. As described above, the contact thermocouple 120 can have a temperature deviation. This can be taken into account when determining that the workpiece is at a known temperature. In addition, since the contact thermocouple 120 has an inherent response delay, the workpiece 10 is maintained at a known set point temperature for a sufficient duration, as shown in process 710. This duration is included to ensure that the time delay is zero. For example, this duration is equal to or greater than the time lag of the contact thermocouple 120. The temperature measured by the pyrometer 140 is then recorded, as shown in process 720. This can be implemented at multiple temperatures in order to create a graph or table showing the measured temperature and the actual temperature of the workpiece. The output of the pyrometer 140 is then related to the known temperature determined by the contact thermocouple, as shown in process 730. Thus, at this known temperature, the workpiece has a certain emissivity and the pyrometer 140 is calibrated to that emissivity. Thus, if a different workpiece with a new emissivity is utilized, the pyrometer 140 will be recalibrated.

[0059] Once calibrated, the pyrometer 140 can be used to measure the temperature of the workpiece 10, but only near the calibration temperature. In other words, the pyrometer 140 can be used to detect the threshold temperature 310 during the second duration 321 and the third duration 322, but is ineffective at lower temperatures, such as those found during the first duration 320.

[0060] The pyrometer 140 also differs from the contact thermocouple 120 in other ways. For example, unlike a contact thermocouple, the pyrometer 140 measures the instantaneous temperature of the workpiece 10. In other words, the pyrometer 140 has no time delay.

[0061] These characteristics make Figure 2 The sequence shown in is also applicable to the pyrometer. For example, since the pyrometer 140 cannot measure low temperatures, the open loop warming mode shown in process 200 is used. In this embodiment, the threshold temperature is the temperature at which the pyrometer can accurately measure the temperature of the workpiece 10. Once the threshold temperature is reached, the controller 130 switches to the open loop maintenance mode, as shown in process 220.

[0062] The controller 130 remains in this mode during the waiting delay, as shown in process 230. However, in some embodiments, the waiting delay may be zero or near zero because the pyrometer 140 has no time lag. The controller 130 then switches to the closed-loop maintenance mode, as shown in process 240. Thus, in some embodiments, when the pyrometer 140 is used, the controller 130 moves directly from the open-loop warming mode to the closed-loop maintenance mode when the threshold temperature 310 is reached.

[0063] Additionally, the closed control loop associated with the closed loop maintenance mode can be Figure 4 Specifically, since the pyrometer 140 is calibrated to the desired temperature, the temperature offset correction shown in process 410 can be omitted. Similarly, since the pyrometer 140 has no time lag, the compensation for time lag shown in process 420 can also be omitted.

[0064] In other words, the output of the pyrometer 140 may be used directly as an input to a PID control loop, as shown in process 430 .

[0065] Although the above disclosure describes a system having a controller having a plurality of functions capable of causing the controller to perform Figure 2, but other embodiments are possible. For example, instructions to perform these functions can be downloaded to an existing system. In other words, these instructions can be downloaded to storage device 132 (such as (for example) through a network connection (not shown), through a compact disc read only memory (CD ROM), or through another mechanism). These instructions can be written in any programming language and are not limited by the present disclosure. Therefore, in some embodiments, there may be multiple computer-readable media containing the instructions set forth herein. The first computer-readable medium can communicate with processing unit 131, such as Figure 1 The second non-transitory computer readable medium may be a CD ROM or a different storage device located remotely from the controller 130. The instructions contained on this second non-transitory computer readable medium may be downloaded onto the storage device 132 to allow the instructions to be executed by the controller 130.

[0066] The above-described embodiments in the present application may have many advantages. First, heating the substrate prior to processing is a common semiconductor manufacturing process. By creating a hybrid control system that uses both open-loop control and closed-loop control, the time to reach the desired temperature can be minimized, thereby improving throughput. In addition, using closed-loop control, compensating for temperature deviations and lags, if any, enables the final temperature of the workpiece to be more tightly controlled. For example, in one test, this hybrid approach was compared with a traditional PID control loop, in which the controller utilized closed-loop control throughout the heating process. In each test, the target temperature was 150°C. The traditional closed-loop control approach allowed the workpiece to reach the target temperature after 22 seconds. In contrast, the hybrid approach of using open-loop control during the warm-up period before utilizing closed-loop control allowed the workpiece to reach the target temperature in about 10 seconds. This dramatic reduction in heating time can significantly improve throughput.

[0067] The present disclosure is not limited in scope by the specific embodiments described herein. In fact, according to the above description and the accompanying drawings, various other embodiments and modifications of the present disclosure other than those described herein will be apparent to those of ordinary skill in the art. Therefore, such other embodiments and modifications are intended to fall within the scope of the present disclosure. In addition, although the present disclosure has been described herein in the context of a specific embodiment in a specific environment for a specific purpose, those of ordinary skill in the art will recognize that its applicability is not limited thereto and that the present disclosure can be beneficially implemented in any number of environments for any number of purposes. Therefore, the above-mentioned claims should be interpreted according to the full breadth and spirit of the present disclosure described herein.

Claims

1. A system for controlling the temperature of a workpiece, comprising: Temperature sensor; Heating elements; as well as a controller in communication with the temperature sensor and the heating element, wherein the controller comprises a processing unit and a memory device, wherein the memory device contains instructions that, when executed by the processing unit, enable the controller to: operating in an open-loop heating mode, wherein the controller heats the workpiece at a first power level using open-loop control until a threshold temperature is reached; operating in an open loop maintenance mode after reaching the threshold temperature, wherein the controller uses open loop control to coarsely maintain the temperature of the workpiece at a second power level different from the first power level, wherein coarsely maintaining means that the temperature of the workpiece may deviate from the threshold temperature by up to 20°C; and operating in a closed-loop maintenance mode, wherein the controller maintains the temperature of the workpiece at a target temperature using closed-loop control, The temperature sensor has a time hysteresis, and the memory device further includes instructions that, when executed by the processing unit, enable the controller to perform the following operations: switching from the open-loop maintenance mode to the closed-loop maintenance mode after a duration at least as long as the time lag, The temperature sensor is used in the open-loop heating mode, the open-loop maintenance mode, and the closed-loop maintenance mode. 2 . The system of claim 1 , wherein the threshold temperature is selected such that a temperature of the workpiece does not exceed the target temperature during the open-loop warming mode.

3. The system of claim 1 , wherein operating in the closed-loop maintenance mode comprises: sampling the output of the temperature sensor; If the temperature sensor has a temperature deviation, correct the temperature deviation of the temperature sensor; If the temperature sensor has a time lag, compensating for the time lag of the temperature sensor; as well as The corrected and compensated output of the temperature sensor is used as an input to a proportional-integral-derivative control loop to determine the output to the heating element.

4. The system of claim 3, wherein compensating for the time lag comprises utilizing an inverse low pass filter, wherein a time constant of the inverse low pass filter is equal to the time lag of the temperature sensor.

5. A method for heating a workpiece to a target temperature, comprising: operating in an open-loop warming mode, wherein the controller applies a first power level to the heating element using open-loop control until a threshold temperature is reached; operating in an open loop maintenance mode, wherein the controller coarsely maintains the temperature of the workpiece at a second power level different from the first power level for a duration using open loop control before switching to a closed loop maintenance mode, wherein a temperature sensor has a time lag and the duration is at least as long as the time lag, wherein coarsely maintaining means that the temperature of the workpiece may deviate from the threshold temperature by up to 20°C; and operating in the closed-loop maintenance mode, wherein the controller maintains the temperature of the workpiece at a target temperature using closed-loop control based on measurements from the temperature sensor, The temperature sensor is used in the open-loop heating mode, the open-loop maintenance mode, and the closed-loop maintenance mode.

6. The method of claim 5, wherein operating in the closed loop maintenance mode comprises: sampling the output of the temperature sensor; If the temperature sensor has a temperature deviation, correct the temperature deviation of the temperature sensor; If the temperature sensor has a time lag, compensating for the time lag of the temperature sensor; as well as The corrected and compensated output of the temperature sensor is used as an input to a proportional-integral-derivative control loop to determine the output to the heating element. 7 . The method of claim 6 , wherein compensating for the time lag comprises utilizing an inverse low pass filter, wherein a time constant of the inverse low pass filter is equal to the time lag of the temperature sensor.

8. The method of claim 5, wherein the temperature sensor comprises a pyrometer, the method further comprising: The pyrometer was calibrated using a contact thermocouple prior to the open loop warming mode by: heating the workpiece to a known temperature determined by the contact thermocouple; dwelling at the known temperature for a duration greater than a time lag of the contact thermocouple; and The output of the pyrometer is related to the known temperature determined by the contact thermocouple.

9. A non-transitory computer readable medium comprising instructions which, when executed by a controller, enable the controller to: operating in an open-loop heating mode, wherein the controller heats the workpiece using the heating element at a first power level using open-loop control until a threshold temperature is reached, the threshold temperature being measured by a temperature sensor; operating in an open loop maintenance mode after reaching the threshold temperature, wherein the controller uses open loop control to coarsely maintain the temperature of the workpiece at a second power level different from the first power level, wherein coarsely maintaining means that the temperature of the workpiece may deviate from the threshold temperature by up to 20°C; and operating in a closed-loop maintenance mode, wherein the controller maintains the temperature of the workpiece at a target temperature using closed-loop control based on measurements made by the temperature sensor, The temperature sensor has a time lag, and the non-transitory computer-readable medium further includes instructions that, when executed by the controller, enable the controller to perform the following operations: switching from the open-loop maintenance mode to the closed-loop maintenance mode after a duration at least as long as the time lag, The temperature sensor is used in the open-loop heating mode, the open-loop maintenance mode, and the closed-loop maintenance mode. 10 . The non-transitory computer readable medium of claim 9 , wherein the threshold temperature is selected such that a temperature of the workpiece does not exceed the target temperature during the open-loop warming mode.

11. The non-transitory computer readable medium of claim 9, wherein operating in the closed-loop maintenance mode comprises: sampling the output of the temperature sensor; If the temperature sensor has a temperature deviation, correct the temperature deviation of the temperature sensor; If the temperature sensor has a time lag, compensating for the time lag of the temperature sensor; as well as The corrected and compensated output of the temperature sensor is used as an input to a proportional-integral-derivative control loop to determine the output to the heating element.

12. The non-transitory computer readable medium of claim 11, wherein compensating for the time lag comprises utilizing an inverse low pass filter, wherein a time constant of the inverse low pass filter is equal to the time lag of the temperature sensor.

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