Patent Description:
The present disclosure relates to calibrating a resistive heater.

<CIT> (<NUM>-<NUM>-<NUM>) describes methods for measuring temperature and a tool for calibrating temperature control of a substrate support in a processing chamber without contact with a surface of the substrate support.

Pedestal heaters for semiconductor processing typically include a heating plate that has a substrate and one or more resistive heating elements provided at the substrate to define one or more heating zones. In some applications, the resistive heating elements function as heaters and as temperature sensors with only two leads wires operatively connected to the resistive heating element rather than four (e.g., two for the heating element and two for a discrete temperature sensor). In such resistive heating elements, the resistive material defines a temperature coefficient of resistance (TCR), and the temperature of the resistive heating elements can be determined based on the TCR and measured resistance of the heating element.

A pedestal heater, such as a multizone heater, can be controlled by a control system that determines the temperature of the resistive heating elements based on the resistance of the resistive heating element. To control the multizone heater, the control system calculates resistance based on voltage and/or current measurements and determines the temperature of each zone based on the resistance calculated. While predefined resistance-temperature data such as tables that associate resistance values to temperature may be used, heaters may operate differently from each other even if the resistive heating elements are made of the same material. This can be caused by, for example, manufacturing variations, material batch variations, age of the heater, number of cycles, and/or other factors, which causes inaccuracies in the calculated temperatures. These and other issues related to the use of two-wire resistive heaters, for example in multizone applications, are addressed by the present disclosure.

In one form, the present disclosure is directed to a method that includes powering a heater that is in an isothermal environment to a first temperature setpoint, where the heater comprises a resistive heating element having a varying temperature coefficient of resistance. The method further includes concurrently obtaining a plurality of resistance measurements of the resistive heating element and a plurality of reference temperature measurements of a reference member as the heater passively cools from a first temperature setpoint to a second temperature setpoint that is lower than the first temperature setpoint and generating a resistance-temperature calibration table that correlates the plurality of resistance measurements with the plurality of reference temperature measurements.

According to the invention, the method further includes turning-off power to the heater when the heater is at the first temperature setpoint to passively cool the heater.

In yet another form, the reference member is an exterior surface of the heater.

In one form, the plurality of reference temperature measurements of the surface of the heater are obtained with an infrared camera.

In another form, the plurality of reference temperature measurements are obtained with a thermocouple wafer and the reference member is the thermocouple wafer.

In yet another form, to obtain a resistance measurement from among the plurality of resistance measurements, the method further includes measuring at least one of an electric current and a voltage concurrently with the plurality of reference temperatures, and determining the resistance measurement based on the measured at least one electric current and the voltage.

In one form, the present disclosure is directed to a method that includes powering a heater in a designated environment to a first temperature setpoint, where the heater comprises a resistive heating element having a varying temperature coefficient of resistance. The method further includes concurrently obtaining a plurality of resistance measurements of the resistive heating element and a plurality of reference temperature measurements of a reference member as the heater passively cools from a first temperature setpoint to a second temperature setpoint that is lower than the first temperature setpoint and generating a resistance-temperature calibration table that correlates the plurality of resistance measurements with the plurality of reference temperature measurements.

In another form, the designated environment for the heater is an isothermal environment.

In yet another form, the designated environment is a standard operating environment at which the heater is operable to heat a workpiece.

In another form, the reference member is an exterior surface of the heater.

In yet another form, the plurality of reference temperature measurements of the exterior surface of the heater are obtained with an infrared camera.

In one form, the plurality of reference temperature measurements are obtained with a thermocouple wafer and the reference member is the thermocouple wafer.

In another form, to obtain a resistance measurement from among the plurality of resistance measurements, the method further includes measuring at least one of an electric current and a voltage concurrently with the plurality of reference temperatures, and determining the resistance measurement based on the measured at least one electric current and the voltage.

In still another form, the present disclosure is directed to a control system for controlling a heater having a resistive heating element. The control system includes a power converter configured to provide an output voltage that is adjustable to the heater and a controller configured to determine the output voltage to be applied to the heater. The controller includes a memory configured to store a plurality of control programs for controlling the heater, wherein the plurality of control programs includes a calibration process. The controller further includes a processor configured to execute the plurality of control programs, wherein with the heater is in a designated environment. The calibration process includes instructions to turn-on power to the heater to heat the heater to a first temperature setpoint, concurrently obtain a plurality of resistance measurements of the resistive heating element and a plurality of reference temperature measurements of a reference member as the heater passively cools from the first temperature setpoint to a second temperature setpoint, and generate a resistance-temperature calibration table that correlates the plurality of resistance measurements with the plurality of reference temperature measurements.

According to the invention, the calibration process further includes instructions to turn-off power to the heater when the heater is at the first temperature setpoint to passively cool the heater.

In still another form, the second temperature setpoint is lower than the first temperature setpoint.

In yet another form, the designated environment is an isothermal environment.

In another form, to obtain a resistance measurement from among the plurality of resistance measurements, the calibration process further includes instructions to measure at least one of an electric current and a voltage concurrently with the plurality of reference temperature measurements, and determine the resistance measurement based on the at least one electric current and the voltage.

The present disclosure is generally directed toward a resistance-temperature (R-T) calibration process for a heater, which may be a multizone heater, having resistive heating elements that are operable as heaters and sensors. The R-T calibration process described herein generates R-T offset data that correlates a plurality of resistance measurements with a plurality of reference temperature measurements. The R-T offset data is then used during standard operation of the multizone heater to determine a temperature of the resistive heating element(s) based on a measured resistance of the resistive heating element(s).

To demonstrate the R-T calibration process according to the teachings of the present disclosure, an example configuration of a thermal system having a multizone heater and a control system is first provided. Referring to <FIG> and <FIG>, a thermal system <NUM> includes a multizone pedestal heater <NUM> and a control system <NUM> having a heater controller <NUM> and a power converter system <NUM>. In one form, the heater <NUM> includes a heating plate <NUM> and a support shaft <NUM> disposed at a bottom surface of the heating plate <NUM>. The heating plate <NUM> includes a substrate <NUM> and a plurality of resistive heating elements (not shown) embedded in or disposed along a surface of the substrate <NUM>. For example, one such heater is described in co-pending application <CIT> and titled "MULTI-ZONE PEDESTAL HEATER HAVING A ROUTING LAYER", which is commonly owned with the present application and the contents of which are incorporated herein by reference in its entirety.

In one form, the substrate <NUM> may be made of ceramic or aluminum. The resistive heating elements are independently controlled by the heater controller <NUM> and define a plurality of heating zones <NUM> as illustrated by the dashed-dotted lines in <FIG>. It is readily understood that the heating zones could take a different configuration and include two or more heating zones while remaining within the scope of the present disclosure. For example, referring to <FIG>, the heater <NUM> may be a heater <NUM> that includes a dielectric layer <NUM>, a resistive layer <NUM> defining one or more resistive heating traces (i.e., resistive heating elements), and a protective layer <NUM> disposed on a substrate <NUM>.

In one form, the heater <NUM> is a "two-wire" heater in which the resistive heating elements function as heaters and as temperature sensors with only two leads wires operatively connected to the heating element rather than four. Such two-wire capability is disclosed in, for example, <CIT>, which is commonly assigned with the present application and incorporated herein by reference in its entirety. Typically, in a two-wire system, the resistive heating elements are defined by a material that exhibits a varying resistance with varying temperature such that an average temperature of the resistive heating element is determined based on a change in resistance of the resistive heating element. In one form, the resistance of the resistive heating element is calculated by first measuring the voltage across and the current through the heating elements and then, using Ohm's law, the resistance is determined. The resistive heating element may be defined by a relatively high temperature coefficient of resistance (TCR) material, a negative TCR material, or in other words, a material having a non-linear TCR. While the heater <NUM> is provided as a pedestal heater, the present disclosure may be applicable to other types of heaters, such as an electrostatic chuck (ESC) heater, a nozzle heater, or a fluid heater, among others, and should not be limited to pedestal heaters as illustrated and described herein.

The control system <NUM> controls the operation of the heater <NUM>, and more particularly, is configured to independently control power to each of the zones <NUM>. In one form, the control system <NUM> is electrically coupled to the zones <NUM> via terminals <NUM>, such that each zone <NUM> is coupled to two terminals providing power and sensing temperature.

In one form, the control system <NUM> is communicably coupled (e.g., wireless and/or wired communication) to a computing device <NUM> having one or more user interfaces such as a display, a keyboard, a mouse, a speaker, a touch screen, among others. Using the computing device <NUM>, a user may provide inputs or commands such as temperature setpoints, power setpoints, commands to execute a test or a process stored by the control system.

The control system <NUM> is electrically coupled to a power source <NUM> that supplies an input voltage (e.g., 240V, 208V) to the power converter system <NUM> by way of an optional interlock <NUM>. The interlock <NUM> controls power flowing between the power source <NUM> and the power converter system <NUM> and is operable by the heater controller <NUM> as a safety mechanism to shut-off power from the power source <NUM>. While illustrated in <FIG>, the control system <NUM> may not include the interlock <NUM>.

The power converter system <NUM> is operable to adjust the input voltage and apply an output voltage (VOUT) to the heater <NUM>. In one form, the power converter system <NUM> includes a plurality of power converters <NUM> (<NUM>-<NUM> to <NUM>-N in figures) that are operable to apply an adjustable power to the resistive heating elements of a given zone <NUM> (<NUM>-<NUM> to <NUM>-N in figures). One example of such a power converter system is described in <CIT>, which is commonly assigned with the present application and incorporated herein by reference in its entirety. In this example, each power converter includes a buck converter that is operable by the heater controller to generate a desired output voltage that is less than or equal to the input voltage for one or more heating elements of a given zone <NUM>. Accordingly, the power converter system is operable to provide a customizable amount of power (i.e., a desired power) to each zone of the heater.

With the use of a two-wire heater, the control system <NUM> includes sensor circuits <NUM> (i.e., <NUM>-<NUM> to <NUM>-N in <FIG>) to measure electrical characteristics of the resistive heating elements (i.e., voltage and/or current), which is then used to determine performance characteristics of the zones, such as resistance, temperature, and other suitable information. In one form, a given sensor circuit <NUM> includes an ammeter <NUM> and a voltmeter <NUM> to measure a current flowing through and a voltage applied to the heating element(s) in a given zone <NUM>, respectively. Each ammeter <NUM> includes a shunt <NUM> for measuring the current, and each voltmeter <NUM> includes a voltage divider <NUM>, which is represented by resistors <NUM>-<NUM> and <NUM>-<NUM>. Alternatively, the ammeter <NUM> may measure current using a HAL sensor or a current transformer in lieu of the shunt <NUM>. In one form, the ammeter <NUM> and the voltmeter <NUM> are provided as a power metering chip to simultaneously measure current and voltage regardless of the power being applied to the heating element. In another form, the voltage and/or current measurements may be taken at zero-crossing, as described in <CIT>.

The heater controller <NUM> includes one or more microprocessors and memory for storing computer readable instructions executed by the microprocessors. The heater controller <NUM> is configured to perform one or more control processes in which the heater controller <NUM> determines the desired power to be applied to the zones, such as <NUM>% of input voltage, <NUM>% of input voltage, etc. Example control processes are described <CIT> and also <CIT>, which is commonly assigned with the present application and incorporated herein by reference in its entirety. In one form, a control process adjusts the power applied to the resistive heating elements based on a temperature of the resistive heating elements and/or of the workpiece.

To obtain an accurate temperature measurement, the heater controller <NUM> is operable to perform a R-T calibration process <NUM> of the present disclosure to generate a correlation between the resistance of the resistive heating element with a temperature of a reference area about the heater <NUM> (i.e., a reference temperature). More particularly, during normal operations in which the heater <NUM> is heating a workpiece, the heater controller <NUM> determines the surface temperature of the heater <NUM> upon which the workpiece is positioned based on a current resistance measurement and the R-T offset data. Thus, eliminating the use of a separate discrete sensor.

Referring again to <FIG>, for the R-T calibration process, the thermal system <NUM> is equipped with one or more discrete reference sensors <NUM> to measure a temperature of the reference area. The reference sensor <NUM> may be an infrared camera, a thermocouple (TC) wafer, one or more thermocouples, a resistance temperature detector, and/or other suitable sensor for measuring temperature. For example, in one form, the reference sensor <NUM> is an infrared camera that is arranged above the heater <NUM> to measure the surface temperature of the heater <NUM> with the surface of the heater <NUM> being the reference area and the surface temperature being the reference temperature. In another example, the reference sensor may be a TC wafer having a wafer and a plurality of TCs distributed along the wafer for measuring temperature. During calibration, the TC wafer is positioned on the heater <NUM> and is secured to the surface using various methods including but not limited to pressurizing a chamber having the heater <NUM> and TC wafer, bonding the TC wafer to the heater <NUM>, or by gravity. Each TC of the TC wafer measures a temperature which is provided to the control system <NUM>. With the surface of the TC wafer in contact with the heater <NUM>, the reference area is provided as the surface of the heater <NUM> and the reference temperature is the temperature along the surface of the heater.

For the R-T calibration process, the control system <NUM>, is configured to heat the heater <NUM>, or more particularly, heat the surface of the heater <NUM> to a first temperature setpoint (T_sp1). Once the surface has a uniform temperature profile, the control system <NUM> turns off power to the heater and concurrently measures the reference temperature and the resistance of the resistive heating elements for each zone until the reference temperature is equal to a second temperature setpoint (T_sp2) that is less than the first temperature setpoint. For the resistance measurements, the control system <NUM> acquires the voltage and current measurements from the sensor circuits and determines the resistance of the resistive heating elements. In one form, the reference temperature measurements and the resistance measurements are measured continuously based on a processing rate of the reference sensor and the sensor circuit. In another form, the reference temperature measurements and the resistance measurements are periodically measured (e.g., every 5mins, 10mins, among other time intervals). It should be readily understood that any number of measurements may be taken for determining the temperature offset data and should not be limited to the examples described herein.

The control system <NUM> then correlates the reference temperature measurements with the resistance measurements of the resistive heating elements to obtain R-T offset data. Based on the type and/or number of reference sensors, the control system <NUM> processes the raw measurements from the reference sensor to obtain the reference temperature measurements. For example, for an IR camera, the thermal image provided by the IR camera provides the surface temperature throughout the surface of the heater which is heated by multiple heating zones define by one or more resistive heating elements. Accordingly, for a given heating element, the control system <NUM> associates a resistance of the given resistive heating element with a reference temperature measurement for a respective area heated by the given resistive heating element. A similar correlation may be completed for a TC wafer such that temperatures measurements from TCs provided in a particular area of the wafer are associated with the resistive heating element heating that area.

The control system <NUM> generates and stores the R-T offset data and uses the R-T offset data to determine the reference temperature based on a measured resistance of the resistive heating element. In one form, the R-T offset data may be provided as a table, a chart, and/or an algorithm, among other formats. R-T offset data can be provided as just resistance and temperature measurement or it can be a parameter dependent on resistance and/or temperature, such as TCR vs temperature. For example, <FIG> illustrates a graph that captures R-T offset for a two-zone pedestal heater. Specifically, the graph provides data (TCR vs. temperature) for pedestals A to D, each having a zone <NUM> (Z1) and a zone <NUM> (Z2).

The R-T calibration process of the present disclosure may be performed under different conditions to acquire material properties of the resistive heating elements and correlate the material properties to, for example, the surface temperature of the heater or other reference areas. In particular, the R-T calibration process may be performed as a passive calibration with the heater being thermally isolated, or in an isothermal environment, and/or as an active calibration with the heater provided in its operating environment such as a semiconductor processing chamber.

In lieu of or in addition to a standard R-T curve for a specific material defining the resistive heating elements, the passive calibration generates a custom R-T curve for the resistive heating elements within the heater. To obtain the custom R-T curve, the heater <NUM> is thermally isolated to minimize heat loss from the resistive heating elements such that the surface temperature of the heater is equal to or substantially the same as that of the resistive heating elements.

In an example configuration, <FIG> illustrates a passive calibration setup <NUM> in which a multizone heater is provided in an isothermal environment. Specifically, the passive calibration setup <NUM> includes an isothermal chamber <NUM> that houses a multizone heater <NUM> having a plurality of resistive heating elements. The multizone heater <NUM> is similar to the heater <NUM>. Here, the isothermal chamber <NUM> includes insulating material that encases the heater <NUM> to thermally isolate the heater and thus, reduces heat loss between the resistive heating elements and the surface of the heater <NUM>. It should be understood that the isothermal environment for the multizone heater <NUM> may employ other suitable configurations and should not be limited to the isothermal chamber <NUM>.

The passive calibration setup <NUM> further includes a control system <NUM> that is similar to the control system <NUM> to control power to the heater <NUM>. Here, the reference sensors are provided as multiple TCs <NUM> that are arranged to measure the surface temperature of the heater <NUM> at different locations along the surface such that at least one temperature measurement is acquired for each heating zone.

In this configuration, the control system <NUM> performs the R-T calibration process of the present disclosure to measure the resistance of the resistive heating elements and the surface temperature at each of the zones. An operator may set the frequency of the measurements to, for example, continuously measure resistance and temperature or to periodically obtain the measurements. Based on the data received, the control system <NUM> generates a R-T curve that associates the resistance of resistive heating elements with the surface temperature of the heater <NUM>, which is indicative of the temperature of the resistive heating elements. In one form, the control system <NUM> provides an R-T curve for each heating zone using the resistance measurements for the resistive heating element at a given zone and the temperature measurements taken at the heating zone. For example, <FIG> illustrates R-T curves generated during a passive calibration for various two-zone heaters each having an inner zone and an outer zone.

For the active calibration process, the R-T calibration process is performed to acquire the R-T offset data with the heater <NUM> provided in the same operating conditions as when the heater <NUM> heats a workpiece. That is, the active calibration process captures the effect the operating conditions has on the heater <NUM> and thus, the resistive heating elements. Specifically, the R-T offset data may be different from the R-T offset data during the passive calibration process due to, for example, heat loss between the resistive heating element and the surface of the heater <NUM>, and between the surface of the heater <NUM> and external environment.

As an example, <FIG> illustrate an active calibration test setup <NUM> in which a heater <NUM> is provided in a semiconductor processing chamber <NUM> that is designed to heat a semiconductor wafer. The heater <NUM> is a multizone heater similar to the heater <NUM>. In this example, the semiconductor processing chamber <NUM> is for testing purposes and mimics actual semiconductor processing chambers. In one variation, the active calibration process may be performed at the actual semiconductor chamber manufacturing facility.

The active calibration test setup <NUM> further includes a control system <NUM> that is similar to the control system <NUM> to control power to the heater <NUM>. Here, the reference sensor is provided as a TC wafer <NUM> that measures a surface temperature of the heater <NUM>, which is the reference area being measured. In lieu of the TC wafer <NUM>, one or more TCs or an IR camera may be used to measure the surface temperature of the heater <NUM>. The control system <NUM> performs the R-T calibration process of the present disclosure to measure the resistance of the resistive heating elements and the surface temperature at each of the zones and generate the R-T offset data as described above.

While not illustrated in the calibration setups of <FIG>, <FIG>, the respective control system is communicably coupled to the other components such as the reference sensors and/or heater.

In one form, a heater (such as, by way of example, the heater <NUM>) may undergo the passive calibration and the active calibration to acquire R-T office data that associates controlled resistance measurements of the resistive heating elements from the passive calibration with the uncontrolled resistive measurements from the active calibration. In another form, the heater may undergo active calibration and not passive calibration.

Referring to <FIG>, a R-T calibration process <NUM> is provided, and may be executed by the control system of the present disclosure. With the reference sensor in place, the control system is configured to apply power to the heating zones to generate heat, at <NUM>, and acquires reference temperature measurements from the reference sensor, at <NUM>. At <NUM>, the control system determines if the acquired reference temperature measurements are equal to a first temperature setpoint (T_sp1). That is, the control system receives temperature measurement for each heating zone of the heater and determines if the surface temperature of the heater is uniform (i.e., is at T_sp1). If so, the control system turns off power to the heater and concurrently measures resistances and reference temperature, at <NUM>. At <NUM>, the control system determines if the reference temperature is equal to a second temperature setpoint (T_sp2). If so, the control system stops measurements and correlates the reference temperatures with the resistance measurements to obtain R-T offset data, at <NUM>.

It should be understood that the R-T calibration process <NUM> is just one example of the R-T calibration process and that other suitable routines may be used.

Unless otherwise expressly indicated herein, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word "about" or "approximately" in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice; material, manufacturing, and assembly tolerances; and testing capability.

As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean "at least one of A, at least one of B, and at least one of C.

In the figures, the direction of an arrow, as indicated by the arrowhead, generally demonstrates the flow of information (such as data or instructions) that is of interest to the illustration. For example, when element A and element B exchange a variety of information, but information transmitted from element A to element B is relevant to the illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is transmitted from element B to element A. Further, for information sent from element A to element B, element B may send requests for, or receipt acknowledgements of, the information to element A.

In this application, the term "controller" may be replaced with the term "circuit". The controller may be part of, or include: an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or group) that executes code; a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip.

Claim 1:
A method of calibrating a heater, the method comprising:
powering the heater in an isothermal environment to a first temperature setpoint, wherein the heater comprises a resistive heating element having a temperature coefficient of resistance;
turning-off power to the heater when the heater is at the first temperature setpoint to passively cool the heater;
concurrently obtaining a plurality of resistance measurements of the resistive heating element and a plurality of reference temperature measurements of a reference member as the heater passively cools from the first temperature setpoint to a second temperature setpoint; and
generating a resistance-temperature calibration table that correlates the plurality of resistance measurements with the plurality of reference temperature measurements.