WO2004010094A1

WO2004010094A1 - Emissivity corrected radiation pyrometer integral with a reflectometer and roughness sensor for remote measuring of true surface temperatures

Info

Publication number: WO2004010094A1
Application number: PCT/US2003/021835
Authority: WO
Inventors: Robert J. Champetier
Original assignee: Luxtron Corporation
Priority date: 2002-07-19
Filing date: 2003-07-11
Publication date: 2004-01-29

Abstract

An instrument that measures reflectivity, temperature and roughness of a substrate in a processing chamber remotely, without interfering with the process. The roughness of the substrate is estimated on the basis of depolarization measurements. The instrument automatically corrects for emissivity changes.

Description

EMISSIVITY CORRECTED RADIATION PYROMETER INTEGRAL WITH A REFLECTOMETER AND ROUGHNESS SENSOR FOR REMOTE MEASURING OF TRUE SURFACE TEMPERATURES

FIELD OF THE INVENTION

[0001] This invention relates to measurement of the temperature and optical characteristics of a surface.

BACKGROUND OF THE INVENTION

[0002] It is well known that a radiation pyrometer measures the "brightness" or "apparent" temperature of a radiating object, and that to obtain true temperature an emissivity correction needs to be applied. This pertains to pyrometers operating at a single wavelength, or over a broad and extended band of wavelengths. Various methods have been utilized to reduce the uncertainty in the true temperature in cases where the emissivity of the surface is not known. These include

(a) measuring at two different wavelengths at the same time using commonly called "two-color" pyrometers. The measurement in this case assumes that the emissivity has the same value at the two wavelengths. If the surface satisfies that condition, a true measurement is obtained

(b) measuring at three different wavelengths, in which case the assumption becomes that the emissivity is a linear function of wavelength over the range of utilization.

(c) Other schemes using even more wavelengths, which depend on increasingly complex limitations on the wavelength dependence of the spectral emissivity. As the number of wavelengths is increased from 1 to 2 and more, the resulting precision of the measurement suffers, since such measurements are typically limited both in accuracy and also by some level of noise in the signal at each wavelength (d) Selecting a wavelength short enough that the dependence on temperature is very high, so that typical uncertainties in the emissivity value result in small uncertainties in the calculated temperature. In most cases of typical materials the emissivity ranges only from a few percent to a maximum just less than 100%, or a range on the order of 10:1 or 20:1. If the instrument is so configured that the dependence of signal on temperature is to a very high power of the temperature, e.g. the signal varies as the 20th or 30th power of the temperature, then the uncertainty due to unknown emissivity can be bounded. The difficulty with this scheme is that one is forced to utilize wavelengths far short of the blackbody radiation peak. In an example for temperatures of 1000°C, this leads to an ultraviolet wavelength and to extremely small signals. The desired dependence on temperature is obtained, but the measurement is very strongly affected by statistical photon and photoelectron noise in the detector, leading to very poor precision.

(e) A more direct approach is to somehow measure the emissivity while making the radiation temperature measurement. This is logically appealing but not easy to carry out in a real situation, instruments have been devised which make some assumptions as to the roughness or diffuseness of the surface. For instance the Pyrometer Instrument Co. (Northvale, NJ.) markets an instrument which uses a laser probe beam against the target. A portion of the reflected beam is collected by the optics and an emissivity is calculated and applied to the pyrometer readings. The underlying assumption that the target surface is for instance perfectly diffuse, so that a known fraction of the reflected beam can be collected, needs to be confirmed and any deviation taken into account or calibrated separately, for an accurate calculation. Other instruments have been devised to determine the emissivity in real time, but they tend to add devices near the sample, which lead to either an intrusive instrument or one that has very specific and close distance from the sample to the device components.

SUMMARY OF THE INVENTION

[0003] According to one embodiment of the present invention, an instrument measures the temperature, reflectivity and specularity of the surface of a sample. This provides accurate temperature measurement by providing an accurate estimate of the emissivity of the sample surface over a range of temperature. The emissivity may be estimated using both the reflectivity data and the specularity data to compensate for changes in the sample surface that affect emissivity.

[0004] Reflectivity may be calculated by directing light at a sample surface and measuring the amount of light reflected. This may be done at the same wavelength as used for temperature measurement. Temperature and reflectivity may be measured alternately using the same measurement device. To avoid affecting the temperature measurement, the light used for reflectivity measurement may be pulsed. During a light pulse, reflectivity is measured and between light pulses temperature is measured. Emissivity may be calculated from the reflectivity. Thus, the emissivity value is frequently updated based on real-time measurement.

[0005] Emissivity values calculated from reflectivity are based on the reflectivity of a specular surface. Real surfaces may deviate from this model. Measuring the specularity of the surface allows adjustment of the calculated emissivity to take this factor into account. Thus, a more accurate emissivity value may be estimated from specularity and reflectivity than could be estimated from reflectivity alone.

[0006] Specularity may be measured by directing polarized light at a sample surface, then measuring the component of the reflected light that has a polarization perpendicular to that of the incident light. This measurement indicates the degree of depolarization caused by reflection at the sample surface. If the surface is perfectly specular, there will be no depolarization and there will be no light with polarization perpendicular to the incident light. If the surface is at least partially diffuse, a depolarized component will be present in the reflected light.

BRIEF DESCRIPTION OF THE FIGURES

[0007] FIG. 1A is a schematic illustration of optical system 100, a single wavelength temperature and reflectivity measurement system. [0008] FIG. IB is a schematic illustration of optical system 100 with the source off.

[0009] FIG. 1 C is a graph of an optical measurement.

[0010] FIG. 2 is a schematic illustration of optical system 200, a multi wavelength multi measurement system.

DETAILED DESCRIPTION

[0011] There is a type of process metrology which cannot be measured directly by any of the prior methods. There is the need to measure temperature and reflectivity on a surface undergoing a process whereby films are added to (or removed from) a substrate during the measurement period. Most frequently, the substrate wafer is heated from below and the chamber cover is not itself radiating. Good process control requires both substrate temperature measurement as well as a measure of the film growth via changes in reflectivity. The present invention solves this problem and does it with a minimum of intrusion with the process chamber itself. The chamber can then be configured so as to meet other key needs. These needs may include control of process gases, substrate temperature umformity, and film umformity. Process chambers are designed for various applications. Some can accommodate as little as a single stationary small wafer and others have large turntables with numerous substrates being coated and needing continuous in situ monitoring.

[0012] Another need met by the present invention is the measurement of the degree of specularity or roughness of the surface being measured. Although other systems may measure roughness, they have several limitations. In situ reflectometers are either for specular surfaces, in which case the readings are in error if the surface becomes rough, or for diffuse surfaces of various types and are insensitive to roughness level. The latter, however, require part of the reflectometer, usually a diffuse or a specular integrating sphere or collection mirror, to be close to the sample.

This renders the instrument intrusive, and in many cases, the addition of a reflectometer element into the chamber can affect the process performance. This prior type of instrument is also overly cumbersome to add to an existing chamber, requiring that the chamber be taken out of operation thereby incurring substantial costs for the operator. [0013] An instrument based on the present invention has several advantages over prior systems, and can incorporate one or more of the following functions or features. The instrument continuously measures specular reflectivity at one or more selected wavelengths. It also measures brightness temperature at the same wavelength or set of wavelengths. It can detect a loss of specularity, which can be used to either make a correction to the reflectivity reading or warn that the surface is not specular at a particular time. It can further determine the degree of roughness of the surface via an optical depolarization measurement, which is useful over the entire range from specular to diffuse, and can be used directly to compute a correction for the measured reflectivity.

[0014] The optical head is separable from the detector and electronics, in which case the two are linked by multimode optical fibers (this removes the electronics from clean room enclosures and process environment).

[0015] The instrument can calibrate its temperature channel in situ, thereby correcting for the transmission properties of the windows, window contamination, or any changes made to the optical hardware between the pyrometer and the detectors. A single detector is used for each wavelength, so that analog amplification of reflectivity and temperature signals have the same gains. Additionally, the system does not need to use laser sources, thereby avoiding noise due to speckle

[0016] The above functions are achievable in part because the instrument combines 3 separate measurements: a pyrometer, a reflectometer, and a roughness sensor. The system or instrument comprises optical components and electronic components used for controlling the measurement and signal processing. The optical components include an optical head that can be mounted at a distance from the sample, and can work through an optical window in the process chamber. Thus, it does not intrude on or alter the process in any way.

[0017] FIG. 1A shows a single wavelength measurement system 100, an embodiment of the invention in its simplest form, without the roughness-sensing feature.

[0018] The reflectometer function of system 100 will first be described with regard to FIG. 1 A. The light source 116 is a small source that can be modulated in a square wave fashion, normally it is an LED (light emitting diode) but may be any type of light source that can be modulated on or off by its power source. The term "light" in this context is not limited to the range of light that is visible to the human eye. For example, light may include radiation in the infra-red or ultraviolet range. For example, the light source can also be a laser such as a laser diode or gas laser, an arc lamp such as a high pressure arc lamp. A DC light such as an incandescent filament lamp with an optical chopper or similar light modulator is also feasible. The beam 118 is rendered parallel (collimated) by lens 120. The beam-splitter 124 then transmits about 50% of beam 118 and reflects the rest, along optical axis 150 to lens 112, whose axis is substantially perpendicular to the surface of the sample to be measured. The beam 118 passes through a window 108 in the chamber and is focused on the sample surface 104 to be monitored. Generally the sample is a substrate or wafer that may have various layers on the substrate depending upon what stage of processing it is at. A portion of beam 118 is reflected back up through lens 112 and aperture 114, through the beam-splitter 124, and is then is focussed by lens 128 onto an optical fiber 132. The fiber can be short or can be several meters long if desired. The light exits the fiber 132 and is relayed by the lenses 136 to detector 144. A bandpass filter 140 serves to block radiation outside the desired passband.

[0019] In another embodiment, the detector may be located so that an optical fiber is not necessary. In this embodiment, the light to be analyzed is directly transmitted to the detector. Thus, a single sensing head incorporating sensing detectors and signal amplification electronics maybe placed so that no optical fiber is needed.

[0020] Bandpass filter 140, located, between the fiber and the detector, selectively limits the wavelength range to be measured. The bandpass filter utilized may allow different wavelengths to pass for different applications. The beam 118 from the light source is generally smaller than the limiting aperture 114, which can be placed at lens 112 or lens 128. This affords some tolerance for the sample 104 to have variations in surface flatness or not be in perfect alignment, i.e. it can depart from perfect perpendicularity with optical axis 150 of the optical system 100 shown in FIG 1A.

[0021] Calibration of the reflectometer is effected by placing a reference surface at the sample position and setting the reading of the electronics to match the known reflectivity R of the reference surface. For operation with LED's in the red and near infrared spectrum of less than 1000 nm, an undoped polished silicon wafer is convenient, as it has a very stable and reproducible R in the neighborhood of 0.3.

[0022] The detector signal is processed with signal processing circuitry 148 in synchronism with the source 116 power so as to use the signal difference measured by detector 144 and circuitry 148, when the source 116 is on and when it is off. This difference is proportional to R.

[0023] FIG. IB illustrates the temperature measurement (pyrometer) function of system 100. When the source 116 is off, light 106 radiated by the hot sample 104 (a wafer for instance) passes through limiting aperture 114, and follows the same path as beam 118 would to the detector 144 through the same bandpass filter 140. The signal is processed so as to record temperature when the source 116 is off, and the sum of temperature plus source when the source 116 is on. The difference between the 2 levels of detector signal corresponds to the R of the sample whether or not the sample 104 is emitting light.

[0024] Calibration of the temperature measurement system is normally performed by sighting on a known reference blackbody at selected temperatures. When a real, i.e. non-blackbody wafer 104 is measured, the reflectivity is used to calculate emissivity using the relation valid for opaque surfaces:

R + = l,

where α is the absorptivity, and α in turn is equal to the emissivity ε according to Kirchhoff s law. In this case we have:

ε = l - R,

for routine calculations. The detector 144 reading is then corrected so as to obtain the value detector 144 would read if the target were a blackbody:

blackbody signal for temperature T of the wafer = measured signal x (1/ε).

[0025] The true temperature of the surface can then be obtained from the calibration of the system 100, which can be stored in the form of a lookup table combined with an interpolation function to get to the exact temperature. It can also be stored in the form of a constant or a polynomial with 2 or more constants to adjust radiation levels computed by the system using Planck's equation for black radiation, the adjustment being needed for conversion constants from watts to electrical current, as well as for the finite spectral width of the optical bandpass filters.

[0026] In one embodiment, a change in reflectivity with temperature is used to calibrate the system. The change in reflectivity of a known substrate made of a highly reproducible material may be established by separate experimentation. This gives reflectivity as a function of temperature for this particular reference surface. To calibrate the system, the reflectivity of the reference surface may be measured at two selected temperatures inside the system. A first temperature can be the cold system for instance at 25 degrees C ambient, which is measured with a reliable thermometer. The second temperature can be in the range of 600 to 1000 degrees C or even higher. The change in reflectivity measured between these two temperatures can then be converted to a corresponding difference between the two temperatures to a desired level of accuracy. Thus if the measured change in reflectivity corresponds to a precisely known 1000 degrees C as an example, the second temperature is then determined to be 1025 degrees C in this example. The reflectivity is also used to compute emissivity and the true temperature for the second temperature. This corrected and more accurate value for the second true temperature is used to calibrate the temperature scale of the instrument. This feature is very helpful to achieve "in situ" temperature calibrations of a system and to correct for uncertainties in the transmittance of various optical components in the chamber and in the temperature measuring system, such as vacuum windows, slight misalignment in the positioning of the pyrometer optics, as well as components of the pyrometric system itself such as optical fiber couplers.

[0027] FIG. 1C is a graph illustrating both a reflectivity and radiation measurement. The graph illustrates a first reflectivity measurement portion 180 followed by a combined reflectivity and radiance measurement portion 182 according to one embodiment of the invention. In the reflectivity measurement portion 180, the light source is modulated on and off while the detector or detectors read the intensity of the reflected signal. The modulated signal is directly proportional to the reflectivity of the wafer or substrate being measured. A test wafer or ideally reflective surface with a known reflectivity is used to calibrate the instrument and the reflectivity measurement so that a given detector reading corresponds to a given reflectivity. Two pulses of the source are shown in the reflectivity measurement portion of the graph 180.

[0028] As mentioned previously, the wafer may undergo several different processes where the reflectivity will change depending upon the surface of the substrate or wafer. The difference in the reflected signal corresponds to the reflectivity of the surface of the substrate or whatever material may have been deposited upon the substrate.

[0029] After the wafer has been heated the wafer will radiate energy. When the wafer is hot, the light source will again be modulated on and off, as can be seen in the reflectivity + radiance portion of the graph 182. Although the intensity of the detected signal is much greater when the wafer is hot, the portion of the detected signal due to the radiance is factored out. Thus both the radiance and the reflectivity are measured. The radiance is equal to the emissivity times the radiance of a black body as discussed above. Therefore, the emissivity can also be determined through the signal processing circuit.

Depolarization Measurement

[0030] It is possible to have one, two, three or even more wavelengths in the same optical system and sharing the same "optical head" as shown in FIG. 2. A system for measuring the depolarization of incident light in addition to the temperature and reflectivity may utilize one or more wavelengths or wavelength bands. Depolarization of light occurs when light is reflected by a surface that is not specular (a diffuse, or partially diffuse surface). Depolarization (or scattering) is generally an indication of surface roughness and so the degree of depolarization is sometimes utilized to measure and calibrate the level of the roughness and scattering.

[0031] System 200, of such a system illustrated in FIG. 2, utilizes three different wavelengths, λ_ls λ₂, and λ₃. These are each respectively produced by sources 244, 254, and 246 and pass through lenses 240, 250, and 242. System 200 comprises numerous components: beamsplitters 232, 228, 224, 262, 270, 278, 286, and 294; lenses 240, 250, 242, 212, 260, 276, 282, 290 and 298; mirrors 264 and 272; polarizers PI and P2; and filters 280, 288, and 296. The radiation of wavelength λι may be of any frequency but is preferably 950 nanometers. The number of filters will increase with the number of wavelengths desired. These several wavelengths are combined into one beam 210 incident on the wafer 204, which then is reflected, relayed to the multimode fiber 274 and onto the detector optics. There are as many detectors as there are wavelengths, each wavelength being segregated again by means of dichroic filters. In one embodiment such as system 200, three detectors 284, 292, and 299 together with dichroic filters 280, 288, and 296 are shown. These dichroic filters are used to select the desired wavelengths to be measured by the respective detectors.

[0032] For the roughness channel or measurement, a measure of depolarization is achieved as seen in FIG. 2. In this figure, the measurement of roughness is illustrated for λi (wavelength 1). A polarizer PI renders the beam linearly polarized, e.g. in the vertical plane. The beam is focused (into beam 210) by lens 214 onto the surface of substrate or wafer 204. After reflection off the wafer 204, λi is again separated by another beam splitter 262 and passes through polarizer P2, which is set for polarization perpendicular to that of PI . Mirrors 264 and 272 guide the beam to fiber 274.

[0033] For a well polished substrate or mirror positioned at the sample position, no light passes P2. This is because polarizer P2 is oriented 90° from polarizer PI so that the polarizers PI and P2 polarize the light that passes through them perpendicularly to each other. In other words, if all the light reflected from the surface of wafer 204 is "specular" or specularly reflected, i.e. travels on a path perpendicular to the surface of wafer 204, or parallel to axis 150 it would have a state of polarization SOP1 which cannot pass through P2. On the other hand, as the roughness of the wafer increases, all of the light does not reflect off of the surface of wafer 204 along a trajectory perpendicular to the surface due to inherent features or particular deposits with agglomeration into scattering centers. Therefore, a depolarized portion of the reflected light related to the roughness and diffuse scattering of the surface is passed by P2. A maximum signal is obtained for a perfectly diffuse reflector. Such a diffuse reflector is actually difficult to approximate with common surfaces but results by definition in a total randomization of incident polarization (of light) after reflection. Thus for the diffuse reflector case, equal amounts of light would reach the detector no matter what the orientation of the second polarizer P2. The reflected, depolarized λi signal read by detector 284 is generally proportional to the roughness.

[0034] h another embodiment, the second polarizer might be oriented at less than 90° from the first polarizer to enhance the detection of flaws in devices being manufactured while still providing information about depolarization. In other embodiments, circular or elliptical polarizers could be used and the change in the reflected polarization could be used as described for linearly polarized light.

[0035] In a real or production surface, a reading is obtained that is intermediate between zero and the completely depolarized value. For a perfect diffuser, the fraction of interest here is that portion of the diffusely reflected beam which is collected by the optics and goes to the roughness detector 284. For a perfect diffuser, the fraction is simply the solid angle subtended by the optics divided by π.

[0036] For a surface which is not a perfect diffuser, independent measurements can be made to link the level of depolarization from the roughness sensor and the portion of the reflected beam that reaches the detector. For a given wavelength, the degree of depolarization which occurs for a plane polarized wave incident on a reflective surface is a complex optical problem to analyze theoretically. In general, it is a function of one or more of the following: (a) the optical constants of the base material, (b) the geometrical roughness of the surface itself, that can be described statistically either in terms of its root-mean-square roughness along with the autocorrelation function of the surface height profile, or alternately by its bidirectional scattering distribution function (or BSDF), (c) subsurface defects within the optical depth contributing to the reflection, (d) particulate contamination, which can be extended to include agglomeration and scattering by deposited films that are not homogeneous, and (e) single or multiple thin films stacked on top of the base surface and with different optical properties. While theoretical treatments can be used to describe or understand one or more of the above contributors, a more direct and appropriate approach is to simply measure the depolarization caused by surfaces of interest. Such surfaces could be characterized by measuring their level of depolarization using the present instrument at normal incidence and at one of the operating wavelengths, and relating these values to parameters of direct interest such as separately measured diffuse reflectivity or emissivity at the same or at another wavelength, allowing a true temperature determination. When the surface scattering is a result of process variables and varies with process time, depolarization and emissivity values can be determined by interrupting the process at chosen times, so as to build a calibration curve experimentally. Thus, for surfaces which exhibit an intermediate or high degree of depolarization during phases of the process, the in-situ measurement of depolarization can be used to arrive at the independently measured emissivity value, for instance. Thus the true temperature can still be determined even though the surface is no longer specular. For a process that results in low levels of scattering, the depolarization measurement can be used to warn that the specular reflectivity used to compute emissivity and true temperature is or is not within tolerable errors. If not, the next level of correction to the emissivity based on empirical data or scattering models needs to be employed. Note that for materials at the extreme end of complete depolarization, the theory indicates that such surfaces are optically diffuse, and a Lambertian theoretical scattering model can be used to arrive at an approximate value for the emissivity using the reflectivity value obtained with the present invention.

[0037] The alternate method of temperature calibration will now be described. It requires the use of certain materials in the sample 104 position, that have well known variations in reflectivity as a function of temperature. An example optimum material for this purpose is a silicon wafer with low doping level. This grade of silicon is a high purity single crystal with properties that are quite reproducible in different lots and different laboratories. In addition, this material has been studied extensively, so that its thermal and optical properties are very well known and the object of many publications. The temperature effect on reflectivity at the preferred operating wavelength of 950 nm is very slight, so that the reflectivity increases only by about 0.03 from ambient temperatures to 1025 degrees C. The present instrument, however, can measure this small change with great and reproducible precision. As a result, one can calibrate a temperature scale in situ by knowing the starting temperature of the reference wafer, for instance silicon at 25 degrees C, measuring the reflectivity first, then heating the wafer to a new temperature such as 1025 degrees C, then measuring the reflectivity again. This reflectivity change can be separately calibrated carefully to deteraύne the exact conversion from reflectivity change to temperature, as the existing semi-empirical models are not quite precise enough. This calibration can be carried out using other wavelengths as well, and for each wavelength of interest a conversion table needs to be determined prior to use in the present invention. As indicated, other grades of silicon and materials other than silicon that also have a highly reproducible change of reflectivity with temperature are suitable as well.

[0038] In certain embodiments of the present invention, the temperature of the substrate is not measured but reflectivity and depolarization are measured to gain information about the surface. The surfaces are not limited to silicon but include metals, paints and other coatings.

[0039] In one embodiment, the reflectivity is measured at more than one wavelength while the surface scattering is monitored to give an indication of homogeneity imperfections in the surface. For example, in a coating process, this may give an indication of imperfections in the coating, flaws in the substrate or contamination of the substrate.

[0040] In another embodiment, the reflectivity and depolarization measurements may be made on substrates that have distinctive reflectivity and depolarization characteristics. For example, particular semiconductor integrated circuits, radio frequency devices and optical devices may each have a distinctive optical "signature" that can be recognized. If the apparatus detects any deviation from this signature it signifies some defect. Thus, the system could be used for process control or quality control purposes.

[0041] In another embodiment, the optical characteristics of a particular coating may be important for aesthetic reasons. For example, certain painting applications require the paint to have a specific appearance. Using reflectivity and depolarization measurements may allow the appearance to be monitored in-situ and in real time. The measurement may be used for quality control purposes.

[0042] In another embodiment, the surface finish of manufactured materials such as rolled or stamped metals may be monitored using reflectivity and depolarization. Surface roughness and microscopic features such as striations could be measured in this way. [0043] In another embodiment, an apparatus according to the invention may be used to monitor diffuseness of surfaces that are intentionally diffuse. For example, certain grades of quartz are required to be "milky." The milkiness is achieved by having a certain density of bubbles in the quartz. The diffuseness may be used to indicate the correct level of milkiness and thus the quality of the product.

[0044] In another embodiment, an apparatus according to the invention may directly measure the optical properties of paper or paint. Hiding power and other important characteristics are related to the level of scattering and may be inferred from the measured level of scattering.

[0045] In another embodiment, an apparatus according to the invention may measure the optical qualities of densely scattering media such as optical pigments used in paint manufacture. The measurement of reflectivity and depolarization may give information on the size distribution and agglomeration level of the scattering materials.

[0046] While embodiments of the present invention have been shown and described, changes and modifications to these illustrative embodiments can be made without departing from the present invention in its broader aspects. Thus, it should be evident that there are other embodiments of this invention which, while not expressly described above, are within the scope of the present invention and therefore that the scope of the invention is not limited merely to the illustrative embodiments presented. Therefore, it will be understood that the appended claims set out the metes and bounds of the invention. However, as words are an imperfect way of describing the scope of the invention, it should also be understood that equivalent structures and methods while not within the express words of the claims are also within the true scope of the invention.

Claims

1. An instrument for measuring properties of a substrate comprising: a reflectometer that measures the reflectivity of the substrate; a pyrometer that measures the temperature of the substrate; and a depolarization measurement system.

2. The instrument of claim 1 wherein the depolarization measurement system comprises two or more optical polarizers.

3. The instrument of claim 2 wherein the optical polarizers are configured such that for a perfectly specular reflecting surface no light incident on the surface of the wafer will pass the polarizers.

4. The instrument of claim 1 wherein the depolarization measurement system measures the entire depolarization range from specular to diffuse and wherein the depolarization measurement is used to compute a correction for the reflectivity measurement.

5. The instrument of claim 1 wherein the temperature measurement and reflectivity measurement are conducted at a first wavelength.

6. The instrument of claim 5 wherein the depolarization measurement is conducted at a second wavelength.

7. The instrument of claim 1 wherein the temperature measurement and reflectivity measurement are conducted at different wavelengths.

8. The instrument of claim 7 wherein the depolarization measurement is conducted at a different wavelength than the temperature and reflectivity measurements.

9. The instrument of claim 1 wherein the substrate is within a chamber and the instrument is without the chamber, and wherein the instrument measures the in-situ properties of the substrate through a window in the chamber.

10. The instrument of claim 9 wherein the instrument calibrates the temperature measurement in-situ, correcting for windows, window contamination, and the optical hardware between the pyrometer and a detector.

11. The instrument of claim 1 wherein the instrument calculates in real time the emissivity of the substrate.

12. The instrument of claim 11 wherein the instrument calculates the temperature in real time based upon the calculated emissivity.

13. The instrument of claim 1 wherein the instrument warns a user that the substrate surface is not specular, and that the temperature readings may be in error.

14. The instrument of claim 1 wherein the instrument utilizes a beam, and wherein for a randomly diffuse surface a portion of the beam reflected from the substrate may be altered in optical polarization, and wherein the instrument estimates a depolarized portion of the reflectivity measurement.

15. The instrument of claim 14 wherein for a randomly diffuse surface, the instrument utilizes the estimate of the depolarized portion to calculate the emissivity and true temperature of the substrate.

16. The instrument of claim 1 wherein the instrument utilizes a beam, and wherein for a randomly diffuse substrate a portion of the beam reflected from the substrate is depolarized, and wherein the instrument estimates the specular and diffuse portions of the reflectivity measurement through an independent measurement of depolarization.

17. The instrument of claim 1 wherein the reflectivity of the substrate changes with temperature, and wherein the instrument calibrates the temperature scale of the instrument in situ taking into account the temperature based reflectivity change of the substrate.

18. The instrument of claim 17 wherein the calibration utilizes emissivity correction and the reflectivity of the substrate at a known hot temperature.

19. An in-situ wafer process monitoring system having an optical head, the system comprising: signal processing and control circuitry; temperature sensing optics; reflectivity sensing optics; and roughness sensing optics, individual temperature, reflectivity and roughness sensing optical beams being collected in the optical head, the optical head coupled to an optical fiber, the system remotely monitoring in real time wafer processing in a process chamber via the optical fiber.

20. The system of claim 19 wherein the system calculates in real time the emissivity of the wafer.

21. The system of claim 20 wherein the system calculates the temperature in real time based upon the calculated emissivity.

22. The system of claim 19 wherein the system warns a user when the wafer surface is not specularly reflecting that the temperature readings may be in error.

23. The system of claim 19 wherein the instrument utilizes a beam, and wherein for a randomly diffuse surface a portion of the beam reflected from the substrate may be depolarized, and wherein the instrument estimates the depolarized portion of the reflectivity measurement.

24. The system of claim 23 wherein for a randomly diffuse surface, the instrument utilizes the estimate of the depolarized portion to calculate the emissivity and true temperature of the substrate.

25. The system of claim 19 wherein the system utilizes a beam, and wherein for randomly diffuse substrate a portion of the beam reflected from the wafer may be depolarized, and wherein the system estimates a scattered portion of the reflectivity measurement through an independent measurement of scattering.

26. The system of claim 19 wherein the reflectivity of the wafer changes with temperature, and wherein the instrument calibrates the temperature scale of the instrument in situ taking into account the temperature based reflectivity change of the wafer.

27. The instrument of claim 26 wherein the calibration utilizes emissivity correction and the reflectivity of the wafer at a known hot temperature.

28. A device for monitoring the condition of a substrate comprising: means for measuring the reflectivity of the substrate; means for measuring and calculating the temperature of the substrate; and means for measuring the roughness of the substrate, the device monitoring the in-situ condition of the substrate in a processing chamber while the substrate is being processed, the device located entirely outside of the processing chamber therefore not interfering with any processing within the chamber.

29. An apparatus for determining a roughness of a surface, comprising: a source of light, the light being polarized in a first plane and being directed at the surface; a polarizer that allows light that is reflected from the surface and that is polarized in a second plane to pass through; a light sensitive device that receives light that has passed through the polarizer; and a processing unit that receives a signal from the light sensitive device and calculates the roughness.

30. The apparatus of claim 29 wherein the second plane is perpendicular to the first plane.

31. The apparatus of claim 29 wherein the source of light comprises a light emitting diode and a polarizer.

32. The apparatus of claim 29 wherein, if the surface is a specular surface no light passes through the polarizer.

33. An apparatus for measuring the temperature of a surface, comprising: a light measurement device that measures the light received from the surface; a light generating device that intermittently generates a light beam that is directed towards the surface, the light generating device being a solid state device that contains no moving parts; and a processing device that calculates an emissivity value from the measured light that is reflected from the surface when the light beam is on and that calculates the temperature from the emissivity and the measured light from the surface when the light beam is not on.

34. The apparatus of claim 33 wherein the light generating device is a light emitting diode.