Abstract:
Methods and an apparatus for providing a non-contact probe for accurately measuring the temperature of a substrate in a process chamber are disclosed. One exemplary apparatus is a processing chamber, which includes a heating source, where the heating source heats the substrate. Also included is a window maintained at a substantially constant temperature. The window allows only a first wavelength spectrum of energy emitted from the heating source to pass. In addition, the window isolates the heating source from an internal region of the processing chamber. A probe configured to detect a second wavelength spectrum of energy emitted directly from the substrate is included. The energy emitted directly from the substrate corresponds to a temperature of the substrate, and the temperature of the substrate is provided to the controller, which adjusts an intensity of the heating source based on a set point temperature for the substrate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to methods and apparatus for measurement and control of temperature and more particularly for measurement and control of a substrate temperature within a semiconductor process chamber. 
     2. Description of the Related Art 
     Photoresist layers are typically applied and patterned over surfaces of a substrate prior to the formation of features during the manufacture of semiconductor devices. Upon completion of these processes the patterned photoresist must be removed through photoresist stripping or ashing. Quite often a photoresist asher removes a photoresist layer by reacting free radical oxygen atoms with the resist material at an elevated temperature. In addition, the photoresist asher often incorporates a microwave or radio frequency (RF) plasma generator to produce free radical oxygen atoms and oxygen ions, which in turn strip the photoresist through high temperature oxidation. The temperature of the substrate directly impacts the rate of removal of the resist during the process. Photoresist stripping is employed primarily after implant operations where selected areas of a substrate are implanted or “doped” by elements such as boron and phosphorous to define the transistors in an integrated circuit. In another application, patterned photoresist defines regions of dielectric or metal layers that must be removed to form the interconnect wiring that constitute an integrated circuit (IC). 
     The introduction of new materials and the shrinking of feature sizes in integrated circuits are requiring the development of new photoresist formulations and processes. Tight temperature control of the substrate in an ashing chamber is critical as devices on the substrate can become damaged if the temperature overshoots a set point temperature. On the other hand, the process may not run efficiently if the temperature is not high enough. For example, photoresist stripping rate has been measured to increase by approximately 300 Å per minute for each 1° C. change in substrate temperature. One skilled in the art would appreciate that an inaccurate temperature measurement and control can have disastrous consequences for overall device yield. In ashing chambers where the substrate is being heated by lamps, closed loop temperature control is applied to accurately maintain a temperature set point. In a closed loop temperature control system, the temperature of an object, such as the substrate, is measured and the feedback from the temperature measurement is used by a power control system that controls the intensity of a heating source to increase or decrease the temperature. 
     FIG. 1A displays a block diagram  100  representing a prior art closed loop controller for the temperature of a substrate in an ashing chamber. In diagram  100 , a sensor  104  measures the temperature of a substrate  102 . A signal corresponding to the temperature measured by the sensor is sent to the controller, which in turn controls the intensity of heat lamps  108  according to the difference in values of the temperature of the substrate and a set point temperature. 
     The sensor  104  of diagram  100  is a critical component of the control loop since it needs to provide accurate temperature measurement and must be capable of withstanding the harsh environment of the ashing chamber. FIG. 1B illustrates a detailed view of one prior art sensor employed to measure substrate temperature, where lamps are used to heat the substrate. This sensor consists of a thermocouple bead  111  contacting the substrate through an aluminum pad  103  where the aluminum pad  103  and thermocouple is attached to a pin supporting the substrate  102 . FIG. 1B illustrates a diagram of the contact between the substrate  102  and a thermocouple sensor pad  103 . Since the backside surface of the substrate and the aluminum pad surface are not completely smooth, a gas gap  110  exists at the interface of the two surfaces. The gas gap  110  exists even though substrate support extension  101  provides a gimballing effect to support pad  103  against the backside surface of the substrate since the corresponding surfaces are not completely smooth. The gas gap  110  causes inaccuracies in temperature measurement especially under the operating condition for ashing processes as is explained further below. The probe body  105  encases thermocouple wires  109   a  and  109   b , which are routed through a high vacuum seal since the chambers typically operate under low pressures below 2 torr. 
     As mentioned above, the ashing process is performed at a low process pressure, typically below 2 Torr. Therefore, very little gas exists in the gas gap  110  to conduct the heat from the substrate to the contact pad. As a result of the gas being evacuated from the gas gap  110 , the effective thermal conductivity is low, which in turn makes it difficult to accurately measure the temperature of the substrate. This method of temperature measurement requires detailed calibration of each individual sensor. Such calibration is normally performed using instrumented substrates. Consequently, the accuracy of such calibration is dependent on the reproducibility of the quality of the substrate-pad contact. Additionally, the characteristics of thermal interaction between substrate and pad vary with both pressure and substrate temperature. This necessitates detailed calibration over an extensive range of temperatures and operating pressures. Furthermore, the contact between the substrate and the aluminum pad is different for each substrate, thus injecting additional variables into the temperature measurement process, not to mention the poor calibration resulting from the substrate-to-substrate inconsistencies. The aluminum pad also oxidizes over time, thereby changing the characteristics of the pad for each process, which in turn further throws off the calibration. 
     Another type of sensor used in ashing chambers is an optical emissivity sensor. Processing chambers, where the substrate is supported by an RF-excited platen to generate the plasma, cannot use thermocouples since the wires of the thermocouple act as antennas. Because the high voltages induced in the thermocouple lead wires can damage sensitive electronic circuitry to which the thermocouple wires are connected, unshielded thermocouples are typically not used in the presence of RF-excited platens. Therefore, an optical emissivity sensor may be used to measure the temperature of the substrate to avoid this antenna effect. FIG. 1C illustrates block diagram  112  representing a prior art processing chamber employing an optical emissivity probe  124  to measure the temperature of the substrate  102 . The chamber  126  includes a microwave source  114  and a radio frequency (RF) source  118 . When the chamber  126  is operating in the microwave mode, i.e. microwave source activated and RF source deactivated, pins  128  lift the substrate  102  off of the platen  120 . In the RF mode the substrate  102  rests on the platen  120 . Here, the sensor assembly, including the contact pad  122 , is used as one support in conjunction with the pin  128  when the substrate is elevated for microwave processing. Typically, microwave processing is performed at elevated temperatures as high as 300° C. for which lamps  108  are employed. 
     The optical sensor  124  of FIG. 1C measures temperature of the substrate  102  by detecting the emitted infrared radiation from the backside of the pad  122  which is in contact with the substrate  102 . Similar problems as encountered with thermocouples persist with the optical sensor  124 . The pad  122  for the optical sensor also oxidizes over time. Accordingly, the emissivity of the backside of the pad changes with time. In addition, the optical sensor  124  must be contained in a light-proof housing  123 . Since the lamps  108  emit high intensity radiation, any light leak through the housing  123  of the optical sensor  124 , could trigger the optical sensor to measure temperature of the lamps  108 , which is much higher than that of the substrate. Furthermore, the optical sensor  124  must be thermally isolated from the chamber body to prevent inaccurate measurement of substrate temperature due to local cooling of the substrate, since the sensor is being heated at one end and cooled at the other end. 
     For this reason, pyrometers that directly measure substrate temperature are used in most Rapid Thermal Processing (RTP) chambers where substrate temperature is typically above 600° C.. At 600° C. a semiconductor substrate is opaque to the incident radiation from the lamps, and hence blocks incident radiation of the lamps from the pyrometer. However, at temperatures below 600° C., the substrate is not opaque to the incident radiation from the heating lamps. Therefore, radiation from the lamps will be incident on the pyrometer through the substantially transparent substrate. The pyrometer will thus be reading the lamps&#39; filament temperature rather than the substrate temperature. In essence, the transmittance (τ), which is defined as the fraction of radiant energy that is transmitted through the substrate, is approximately 0 at temperatures greater than 600° C. As the temperature of the substrate decreases below 300° C., the transmittance of the substrate substantially increases. Below 300° C., which is a typical temperature range for ashing and photoresist stripping processes, the substrate transmittance increases to 0.8 for the range of wavelengths emitted by a heat source, such as a halogen lamp used in an ashing chamber. Accordingly, pyrometers designed for RTP processes are not useful at the temperatures encountered in an ashing chamber or in photoresist stripping processes. 
     In spite of these properties, previous practitioners of pyrometry for RTP processes have had to implement various sophisticated correction algorithms. Some practitioners have had to implement additional probes in an RTP chamber to compensate for the effect of background radiation on substrate temperature measurement. Others have had to provide a reference source of radiation, separate from that emitted by the heat source, to measure reflective and absorptive response of the substrate to this reference source, and to then infer substrate temperature from such response. In summary, current state-of-the-art does not provide for dynamic substrate temperature measurement with reasonable accuracy at temperatures normally used for photoresist stripping. Moreover, current methods in use for resist stripping chambers employ contact pads that require extensive and frequent calibration to minimize any drift due to pad degradation. Also, pyrometry that is typical in high temperature RTP processes is not feasible in photoresist stripping because of the high transmissivity and low emissivity characteristic of semiconductor substrates at resist stripping temperatures. 
     As a result, there is an urgent need to solve the problems of the prior art to provide a non-contact temperature measuring device capable of accurately operating at low temperatures that are typical in certain semiconductor processes such as photoresist stripping. 
     SUMMARY OF THE INVENTION 
     Broadly speaking, the present invention fills these needs by providing a method and apparatus for measuring the temperature of a body from a remote location. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, or a device. Several inventive embodiments of the present invention are described below. 
     In one embodiment, an apparatus for measuring and maintaining a substantially constant temperature of a substrate in a processing chamber is provided. The processing chamber includes a heating source controlled by a controller, where the heating source emits energy for heating the substrate. Also included is a window maintained at a substantially constant temperature. The window is configured to allow a first wavelength spectrum of energy emitted from the heating source to pass through the window. In addition, the window isolates the heating source from an internal region of the processing chamber. A probe is included. The probe is configured to detect a second wavelength spectrum of energy, distinct from the first wavelength spectrum of energy, emitted directly from the substrate. The energy emitted directly from the substrate in the second wavelength spectrum corresponds to a temperature of the substrate, and the temperature of the substrate is provided to the controller, which adjusts an intensity of the heating source based on a set point temperature for the substrate. 
     In another embodiment, a temperature controlling system for controlling the temperature of a substrate in a chamber is provided. The system includes a heating source and a window. The window is transparent to a first spectrum of wavelengths of energy from the heating source while being opaque to a second spectrum of wavelengths of energy from the heating source. A cooling system is included. The cooling system maintains the window at a substantially constant temperature as the window absorbs the second spectrum of wavelengths of energy from the heating source. A probe is also included. The probe is located remotely from the substrate and configured to detect the second spectrum of wavelengths of energy emitted from the substrate, where the energy emitted from the substrate correlates to a temperature of the substrate. The temperature of the substrate is communicated to a controller of the heating source and the controller of the heating source controls an intensity of the heating source based upon the temperature of the substrate. 
     In still another embodiment, a method for measuring and maintaining a temperature of a substrate in a processing chamber is provided. The method initiates with providing energy from a heating source. Then, a first wavelength spectrum of the energy from the heating source passes through a window entering an internal region of the processing chamber. The substrate is heated by this first wavelength spectrum of the energy from the heating source. Next, a second wavelength spectrum of energy is filtered prior to entering an internal region of the processing chamber. Then, the energy emitted by the substrate is detected by a non-contact probe. The energy emitted by the substrate has a second wavelength spectrum. Then, an intensity of the heating source is adjusted based upon the detected energy emitted by the substrate. 
     In yet another embodiment, a method for measuring a temperature of a body in a chamber is provided. The chamber is configured to introduce heat energy through a window. The window is transparent to a first wavelength spectrum of the heat energy and opaque to a second wavelength spectrum of the heat energy. The method initiates with providing a heat source where the heat source emits the heat energy through the window into the chamber. Then, a cooling system for maintaining the window at a substantially constant temperature is provided. Next, the body is heated with the first wavelength spectrum of the heat energy. Then, the temperature of the body is detected, where the detecting includes providing a probe remotely located from the body and the probe configured to detect an intensity of the body&#39;s emissions of the second wavelength spectrum. Also included in the detecting is translating the detected intensity to the temperature of the body. 
     The advantages of the present invention are numerous. Most notably, contact with the backside of the substrate is not required. In addition, the high intensity of broad-band radiation emanating from the lamps does not affect the probe. The probe is protected from the environment of the chamber and can be adjusted on-line for different substrate backside emissivities. Furthermore, by utilizing high wavelength emissions from the substrate, full advantage is taken of the fact that emissions at high wavelengths are comparatively stronger at the operating temperatures typical of photoresist ashing operations. 
     Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, and like reference numerals designate like structural elements. 
     FIG. 1A displays a block diagram representing a prior art closed loop controller for the temperature of a substrate in an ashing chamber. 
     FIG. 1B illustrates a prior art diagram of the contact between the substrate and a thermocouple sensor pad. 
     FIG. 1C illustrates a block diagram representing a prior art processing chamber employing an optical emissivity probe to measure the temperature of the substrate. 
     FIG. 1D illustrates a block diagram representing a more detailed view of a prior art optical sensor contact pad and an optical emissivity probe. 
     FIG. 2A illustrates a graphical representation of the transmittance of quartz over a range of wavelengths in accordance with one embodiment of the invention. 
     FIG. 2B illustrates a graphical representation of the transmittance of sapphire over a range of wavelengths in accordance with one embodiment of the invention. 
     FIG. 3A illustrates a diagram displaying a cross sectional view of a chamber utilizing the non-contact probe for measuring the temperature of a substrate in accordance with one embodiment of the invention. 
     FIG. 3B is an expanded view of the top portion of the probe sight tube in accordance with one embodiment of the invention. 
     FIG. 4 illustrates block diagram displaying an ashing chamber where filtering windows are maintained at a substantially constant temperature in accordance with one embodiment of the invention. 
     FIG. 5A illustrates a diagram displaying a detailed view of the sight tube and probe in accordance with one embodiment of the invention. 
     FIG. 5B is a detailed view of the sight tube end depicting a reflective metal coating on the inner surface of the tube in accordance with one embodiment of the invention. 
     FIG. 6 illustrates a diagram displaying a probe configuration that can be adjusted on-line for different substrate backside emissivities in accordance with one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An invention is described for an apparatus and method for the non-contact measurement of the temperature of a substrate during semiconductor processing and simultaneously eliminating any radiation influence emitted by heating lamps. It will be obvious, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
     The embodiments of the present invention provide an apparatus and method for measuring the temperature of a substrate based upon the substrate&#39;s emissions in the infrared spectrum at wavelengths of greater than approximately 7 microns. The intensity of the radiation in this part of the spectrum is used to accurately calculate the temperature of the substrate without contacting the substrate. Since semiconductor substrates are substantially transparent to infrared radiation at temperatures encountered during photoresist strip processes, traditional pyrometers provide erroneous results because of the interference by direct radiation from an energy source, such as substrate-heating lamps. 
     By concentrating temperature measurement in the spectrum of radiation wavelengths of above 7 microns, the method and apparatus of the present invention take advantage of properties inherent in certain lamp window materials. In one embodiment, the lamp windows isolate the lamps from the internal process chamber where the semiconductor substrate sits. It should be appreciated that the isolation of the lamps eliminates the lamp surface as a potential source of contamination, while also providing a means for sealing the process vacuum inside the chamber against leakage of ambient air. Typically, the lamp windows are either quartz or sapphire. Quartz is opaque to the part of the infrared spectrum that is above about 5.5 microns while sapphire is opaque above about 7 microns. Accordingly, the lamp tray windows eliminate that portion of the lamp&#39;s emissive spectrum in which substrate emissions are being measured. Since the temperature measurement of the substrate is not affected by the radiation from the lamps, the temperature of the substrate surface is measured directly without interference from the lamps or having to compensate for the radiation from the lamps. 
     It should be appreciated that since quartz and sapphire windows absorb radiation above certain wavelengths, 5.5 and 7 microns respectively—these windows undergo heating themselves. As will be discussed below, the windows are cooled so that the windows remain at a substantially constant temperature in order to prevent interference from re-radiation of absorbed energy by the lamp tray windows in one embodiment. Keeping the temperature of the lamp tray windows substantially constant allows for compensation of re-radiation from the windows, while calibrating the substrate temperature measuring instrument itself. Additionally, the present invention measures the temperature of a substrate directly without the use of a prior art contact pad. Inaccuracies due to the non-repeatable nature of the substrate-pad contact and the low thermal conductivity between the substrate and contact pad are eliminated by the various embodiments of the present invention described below. 
     While the invention is described in terms of an ashing chamber for illustrative purposes, it should be appreciated that the invention can be used for any chamber utilizing infrared radiation to heat an object and control the temperature of the object through a closed loop temperature control system. As one skilled in the art would appreciate, under a closed loop temperature control system, the temperature of an object is measured and the feedback from the temperature measurement is fed in to a control system that controls the intensity of a heating source to increase or decrease the temperature of the object. As used herein, substrate can refer to any substrate including a semiconductor substrate also referred to as a wafer. The invention is described in more detail below in reference to the Figures. 
     FIG. 2A illustrates a graphical representation of the transmittance of quartz over a range of wavelengths in accordance with one embodiment of the invention. The transmittance of quartz, represented by line  134 , displays quartz&#39;s ability to absorb infrared radiation at wavelengths greater than about 5.5 microns, while approximately 90% of all incident light is transmitted at wavelengths below about 4 microns with decreasing amounts of incident light being transmitted between wavelengths of about 4 microns and about 5.5 microns. It should be appreciated that any radiation transmitted through the window at a wavelength above about 7 microns will interfere with the temperature measurement of the substrate as the probe will be measuring intensity of the radiation from the heating source. 
     FIG. 2B illustrates a graphical representation of the transmittance of sapphire over a range of wavelengths in accordance with one embodiment of the invention. The transmittance of sapphire, represented by line  132 , displays sapphire&#39;s ability to absorb infrared radiation at wavelengths greater than about 7 microns, while approximately 90% of all incident light is transmitted at wavelengths below 5.5 microns with decreasing amounts of incident light being transmitted between wavelengths of about 5.5 microns and about 7 microns. As mentioned above, since quartz and sapphire both absorb infrared radiation in the spectrum of wavelengths greater than about 5.5 and 7 microns, respectively, the quartz and sapphire undergo heating themselves. 
     FIG. 3A illustrates block diagram  136  displaying a cross sectional view of a chamber utilizing the non-contact probe  152  for measuring the temperature of a substrate  102  in accordance with one embodiment of the invention. Chamber  137  includes heating source  138 . In one embodiment heating source  138  is a lamp. Heating source  138  includes glass bulb  140  covering filament  142 . The use of a single lamp or heating source  138  is shown here for ease of illustration and not meant to be limiting in any way, as multiple lamps or heating sources may be used in another embodiment. Lamp  138  is isolated from the internal processing area of the chamber  137  by the window  144 . Where multiple lamps are used, each lamp is isolated from the internal processing area by a window or one window may isolate multiple lamps. In one embodiment of the invention, the window  144  is constructed from one of quartz and sapphire. In another embodiment, the window is cooled to maintain a substantially constant temperature as will be explained in more detail below. The thickness of the window  144  is sufficient to sustain mechanical loads resulting from the higher external pressures, and to maintain the vacuum of the internal processing area in one embodiment. The substrate  102  is sitting on pins  146 . The substrate  102  rests on pins  146  for high temperature microwave processing and will rest on platen or chuck  148  during low temperature RF processing as the pins are lowered. It should be appreciated that the view of the platen  148  is a cross sectional view and that the platen is a contiguous piece with apertures for the pins  146  and the sight tube  150 . While diagram  136  displays 2 pins  146  to support the substrate  102 , of course more than two pins may be used in another embodiment. 
     Continuing with block diagram  136 , sight tube  150  extends through chamber wall  154  into the platen  148 . In one embodiment, the sight tube  150  is a non-conductive ceramic material such as aluminum oxide, other ceramic, quartz, sapphire, etc., so that a conduction path is prevented from forming when operating in a radio frequency (RF) mode. In another embodiment, the inside surface of the sight tube  150  has a reflective coating of one of aluminum and titanium. The sight tube  150  is configured to fit into a threaded connection into the chamber wall  154  in one embodiment. Alternatively, the sight tube  150  can be configured to make a seal through an o-ring or a vacuum seal which are well known in the art. Probe body  152  is contained within the sight tube  150 . It should be appreciated that the probe body  152  contains a probe which detects the emitted radiant energy from the backside of substrate  102 . In one embodiment, the probe body  150  has a sensor window  158  that is transparent to energy emitted in the spectrum between about 8 microns and about 14 microns. A silicon substrate  102  emits energy in this spectrum when it is heated, thus the temperature of the substrate  102  can be measured as a function of the intensity of the energy emitted in this spectrum. In one embodiment, the probe is calibrated to the substrate temperature in the spectrum of about 8 microns to about 14 microns while the temperature of the window  144  remains substantially constant so that the radiant energy emitted by the window is substantially constant and does not interfere with measurement of substrate temperature. 
     The energy emitted by the lamp  138  in the spectrum between about 8 microns and about 14 microns is absorbed by the quartz or sapphire window. By keeping the temperature of the window substantially constant and calibrating the probe under these conditions, the probe substantially responds only to the intensity of the energy emitted by the substrate. It should be appreciated that the temperature of the glass bulb  140  fluctuates as the lamp  138  is cycled to heat the substrate  102 . The glass bulb  140  may contain quartz, thus as the temperature of the bulb  140  fluctuates, the bulb re-emits energy in a broadband spectrum at an intensity dependent on its temperature. However, by maintaining the temperature of the window  144  substantially constant, the window  144  is not affected by the cycling of the glass bulb  140  or the lamp filament  142 . Therefore, the probe  152  can be calibrated for the measurement of the substrate temperature to offset a constant amount of background radiation from the window. In one embodiment, the probe can be calibrated to provide accurate temperature readings over a range of substrate temperatures between about 100° C. and about 400° C. using this non-contact technique, without the use of algorithms for compensation or resorting to provision of a light-proof shroud or probe housing. 
     It should be appreciated that while the temperature of the substrate is approximately 300° C. the environment surrounding the substrate  102  is not at the same temperature as the substrate  102 . The substrate  102  is absorbing the radiant energy emitted from the lamp  138 , but the gases in the chamber such as oxygen, nitrogen and radicals of oxygen and nitrogen, do not absorb in the infra-red spectrum, therefore, the gases in the chamber may not reach the same temperature as the substrate  102 . Additionally, the temperature of the chamber wall is controlled between about 40° C. and about 70° C. in one embodiment. 
     FIG. 3B is an expanded view of the top portion of the sight tube  150  in accordance with one embodiment of the invention. In one embodiment, the distance from the top  161  of the sight tube  150  to the bottom  160  of the substrate  102  is more than twice the diameter of the aperture  162  in the chuck  148 . It should be appreciated that the substrate  102  is resting on the chuck  148  in FIG. 3B which is typical of processing in RF mode. However, the non-contact probe  152  is capable of measuring temperature of the substrate  102  while it is either elevated on pins  146  for high temperature microwave processing or lowered on the platen  148  for RF processing. 
     FIG. 4 illustrates block diagram  164  displaying an ashing chamber where filtering windows  144  are maintained at a substantially constant temperature in accordance with one embodiment of the invention. Windows  144  of block diagram  164  isolate the internal processing chamber  170  from the lamps  138 . In one embodiment, seal  168  surrounds each of the windows  144  in order to maintain a pressure or vacuum in the internal processing chamber  170  and seal the windows  144  to the chamber body. In another embodiment the seal  168  is an o-ring of an elastomeric material. Window cooling system  166  is used to maintain the temperature of the windows  144  at a substantially constant temperature. 
     As mentioned above, the windows  144  are constructed from a material which absorbs energy from the lamps  138  in the spectrum of radiation above a wavelength of about 7 microns and can withstand the conditions of the processing environment. Since the windows  144  absorb the energy, the windows  144  will heat. If the windows are allowed to heat and cool as the filament  142  of the lamp  138  goes on and off or modulates between higher and lower intensities, the window  144  will re-emit varying amounts of energy in the spectrum of radiation above a wavelength of about 7 microns, which will interfere with the temperature measurement. Therefore, the cooling system  166  maintains the window  144  at a substantially constant temperature to eliminate any interference from radiant energy re-emitted by the windows  144 . In one embodiment the temperature of the windows is maintained substantially constant at about 20° C. By maintaining a constant window temperature, one is able to compensate for the background re-emission of energy from the windows while calibrating the probe  152 . 
     It should be appreciated that in one embodiment, the quartz bulb  140  covering the radiating filament  142  of the heating lamp  138  substantially filters radiation in the spectrum of wavelengths above 5.5 microns. This causes the quartz bulb temperature to fluctuate as the lamp filaments  142  turn on and off or modulate as per the requirements of a controller in communication with the lamps  138 . Since all direct radiation in the spectrum of wavelengths above 5.5 microns is filtered by the glass bulb  140 , no radiation in this spectrum from the filament  142  is directly incident on the window  144 . All energy in the spectrum of wavelengths above 5.5 microns is absorbed by the quartz bulb  140  which causes the above mentioned temperature fluctuation. The quartz bulb re-emits this absorbed radiation in a broadband of wavelengths. It should be further appreciated, that the fraction of energy in the spectrum above about 7 microns that the quartz bulb  140  now re-emits is absorbed by the window  144 . However, the small magnitude of this energy is more adequately compensated for by provision of a well-designed cooling system  166  for the window  144 . 
     The cooling system  166  of FIG. 4 is any type of cooling system capable of maintaining the window  144  at a substantially constant temperature. For example, the cooling system  166  can be one of a fan-driven forced air type cooling system, a liquid heat exchanging system, or forced nitrogen flow. In addition, the cooling system  166  also provides cooling to the seal  168  in order to maintain integrity of the seal in one embodiment. It should be appreciated that the cooling system  166  will absorb the heat energy which the windows  144  absorbs from the lamps  138 , so that the windows  144  maintain a substantially constant temperature. By maintaining the substantially constant temperature, the probe  152  can be calibrated to offset the effect of any energy emitted by the windows  144 . It should be appreciated that the windows  144  act as a filter by absorbing the light energy in the spectrum above about 7 microns. Furthermore, since the windows  144  filter the radiant heat energy in the spectrum above about 7 microns, it is unnecessary to make the sight tube  150  light proof. That is, the high intensity of broad-band radiation emanating from the lamps  138  does not affect the temperature measuring device because of the filtering performed first by the quartz bulb  140  and then by the windows  144 . Thus the need to protect the probe  152  from light leakage is eliminated. As mentioned previously, any number of windows  144  and lamps  138  may be used and the examples provided herein are not meant to limit the invention to a set number of windows  144  and lamps  138 . 
     FIG. 5A illustrates diagram  168  displaying a detailed view of the sight tube  150  and probe  152  in accordance with one embodiment of the invention. As mentioned above, the body of sight tube  150  is an electrically non-conductive material. In a preferred embodiment the non-conductive material is a ceramic like aluminum oxide, quartz, sapphire, etc. The inner surface  156  of sight tube  150  is coated with a reflective material in order for the radiant energy to reach the sensor window  158  and not be absorbed by the sight tube  150 . One skilled in the art would appreciate that a non-reflective coating would prevent a substantial portion of the energy emitted by the substrate  102  from reaching the sensor window  158 , thereby causing an inaccurate temperature reading. In one embodiment, the reflective coating  157  on the inner surface  156  is one of aluminum, titanium, or stainless steel. 
     FIG. 5B is a detailed view of the sight tube  150  end depicting a reflective metal coating  157  on the inner surface  156  of the tube  150  in accordance with one embodiment of the invention. As illustrated in FIG. 5B, the reflective coating  157  ends at a safe distance from the substrate  102  to prevent arcing between the metal and the substrate  102 . In one embodiment, the reflective coating  157  ends at a distance prior to the top  159  of the sight tube  150  so as to prevent the arcing mentioned above. One skilled in the art of designing such a device would ensure that the reflective lining is electrically uncoupled from the platen electrode  120  and from the grounded chamber wall  126 . Provision of a non-conducting ceramic body to separate the lining from both electrode and chamber wall permits its potential to float thereby preventing current flow and heating of the lining material. It should be appreciated that the lining material must sustain a substantially constant temperature to prevent interference with the measurement. 
     Returning to FIG. 5A, the sensor window  158  is constructed from a material transparent to the light energy in the wavelength range between about 8 microns and about 14 microns in one embodiment. It should be appreciated that energy emitted by the substrate  102  at wavelengths between about 8 and about 14 microns is used to infer substrate temperature. Therefore, the sensor window  158  must be transparent at these wavelengths of emitted energy from the substrate  102 . In a preferred embodiment, the sensor window is made from one of calcium fluoride (CaF 2 ) and Germanium. In order to protect the sensor window  158  from being etched by the stripping chemicals, such as fluorine and oxygen, a bleed gas port  170  is included. The bleed gas port  170  allows an inert gas to continuously flow over the sensor window  158  and through the sight tube  150  in order to provide a shield against the stripping chemicals. Bleed gas port  170  is located outside the chamber wall  154 . In one embodiment the inert gas is one of helium, nitrogen, argon, etc. In another embodiment, the flow rate of the inert gas is up to 10 standard cubic centimeters per minute (sccm) in order to maintain a positive pressure compared to outside the sight tube  150 . The positive pressure prevents the process chemicals from entering the sight tube  150 . The path of the inert gas is depicted by arrows  172 . In one embodiment, the inert gas is used only when the substrate is on the pins  146 , i.e., for microwave processing. 
     Continuing with FIG. 5A, sensor window  158  is attached to probe body  152 . Probe body  152  is inserted into sight tube  150 . In one embodiment, probe body  152  is inserted through threaded connections  174 . In another embodiment the probe body  152  can be installed in the sight tube  150  through an o-ring seal or a compression fitting. As demonstrated by FIG. 5A, the sensor window  158  and probe body  152  are located outside of the chamber wall  154 , thus allowing for easy access to the sensor window  158  and the probe body  152 . Additionally, there is no contact between the sensor window  158  or the probe and the substrate  102 , thereby eliminating all of the disadvantages of having the sensor contact the substrate  102 . As mentioned above the need to light-proof the sight tube  150  is eliminated due to the filtering capability of the windows  144 . 
     FIG. 6 illustrates diagram  176  displaying a probe configuration that can be adjusted on-line for different substrate backside emissivities in accordance with one embodiment of the invention. The probe body  152  includes a signal conditioner  178 . The signal conditioner  178  is configured to amplify the raw electrical signal from the probe  152  through a signal amplification factor. In one embodiment the signal conditioner includes the application electronics for the probe. The signal amplification factor is internally used to amplify or attenuate the signal that the probe detects, which is dependent on the emissivity of the surface that the probe is monitoring i.e., the backside of the substrate. For example, if the probe is monitoring a black body, which is a perfect absorber and efficiently re-emits radiant energy, the probe signal will have to be attenuated through the signal amplification factor. On the other hand, if the probe is monitoring a reflective and transmissive surface, that is one with a low emissivity, the probe signal must then be amplified. 
     The capability to adjust the signal from the probe is a useful tool since substrates can have different backsides. For example, substrates can include backsides of silicon nitride, silicon dioxide, silicon carbide, etc. It should be appreciated that the different materials of construction of the backside layers on the substrate have different optical characteristics. With the capability to calibrate the probe for an optical characteristic of a particular type of material, the probe of probe body  152  can be e compensated in situ for the type of substrate being used in accordance with one embodiment. As substrates typically come in lots, the probe can be calibrated for a certain lot of substrates. Thus, the probe contained in probe body  152  can be fine-tuned to the characteristics of the substrate, which is difficult for temperature measurements using a contact pad. 
     Controller  180  of FIG. 6 is in communication with signal conditioner  178 . In one embodiment, the controller  180  sends a signal to adjust the signal conditioner  178  depending on the type of substrate being looked at by the probe. For example, if the backside of the substrate is silicon nitride, then the controller  180  sends a signal to the signal conditioner to adjust the amplification suitable for the optical characteristics of silicon nitride. It should be appreciated that since the probe is actually looking at the backside of the substrate where the characteristics are well defined, a much more accurate reading is obtained than when looking at an aluminum pad where the characteristics are not well defined. 
     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.