Thermal measuring and testing – Thermal calibration system – By thermal radiation emitting device
Reexamination Certificate
1997-05-22
2001-01-30
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Thermal calibration system
By thermal radiation emitting device
C374S131000, C250S252100
Reexamination Certificate
active
06179465
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to calibrating pyrometers that are used in thermal processing systems.
In rapid thermal processing (RTP), a substrate is heated quickly to a high temperature, such as 1200° C., to perform a fabrication step such as annealing, cleaning, chemical vapor deposition, oxidation, or nitridation. Particularly given the submicron dimensions of current devices, to obtain high yields and process reliability, the temperature of the substrate must be precisely controlled during these thermal processing steps. For example, to fabricate a dielectric layer 60-80 Å thick with a uniformity of ±2 Å, which is typical of requirements in current device structures, the temperature in successive processing runs cannot vary by more than a few ° C. from the target temperature. To achieve this level of temperature control, the temperature of the substrate is measured in real time and in situ.
Optical pyrometry is a technology that is used to measure substrate temperatures in RTP systems. An optical pyrometer using an optical probe samples the emitted radiation intensity from the substrate, and computes the temperature of the substrate based on the spectral emissivity of the substrate and the ideal blackbody radiation-temperature relationship.
When the system is first set up, the optical probe must be calibrated so that it produces a correct temperature reading when exposed to the radiation coming from the heated substrate. In addition, during repeated use, the temperature sensed by the probe might change over time and thus it will be necessary to recalibrate the probe or at least detect the change that has occurred so that corrective action can be taken. For example, the light pipe which is used to sample the radiation being emitted from the substrate as it is being heated, may become dirty or chipped, connections along the optical column transferring the sampled light to the pyrometer may loosen, or the electronic components in the pyrometer may “drift”.
A commonly used method of calibrating the pyrometer is to use a special substrate or wafer in the chamber. The special substrate, which can be purchased from commercial sources, has a previously measured, known emissivity, and it has an “embedded” thermocouple which is attached to the substrate with a ceramic material. When the substrate is heated, its actual temperature is indicated by the thermocouple. Since the substrate's emissivity is known, the radiation that is actually emitted by the substrate can be easily calculated by multiplying the intensity of radiation that would be expected from by an ideal blackbody that is at the predetermined temperature times the emissivity of the substrate. This is the radiation level that will be sampled by the optical probe of the pyrometer. The pyrometer is adjusted so that it produces a temperature reading that corresponds to the actual temperature.
Unfortunately, this method has drawbacks. The actual temperature of the substrate may in fact be different from the temperature measured by the thermocouple. First, the presence of the embedded thermocouple and the ceramic material causes the area with the thermocouple to have a different temperature than other parts of the wafer, i.e., it disturbs the temperature profile on the substrate. Second, at high temperatures (e.g., 1000° C. as is commonly found in RTP processes), the joint between the wafer and thermocouple tends to degrade, so that after four or five uses the thermocouple readings become unreliable. Because of these shortcomings, this calibration technique cannot really guarantee pyrometer accuracy that is better than ten to fifteen ° C.
In addition, there are difficulties associated with placing a thermocoupled substrate inside the chamber and making electrical connection to the thermocouple.
Accordingly, it would be useful if an optical probe could be calibrated accurately without using a wafer with a an embedded thermocouple.
SUMMARY OF THE INVENTION
In one aspect, the invention is directed to an apparatus for calibrating a temperature probe. The apparatus includes a first light source to emit light having a first spectral range and a second light source to emit light having a second spectral range. The second spectral range is different from the first spectral range. A light emitting region is optically coupled to the first and second light sources, and the relative intensities of the first and second light sources are selected such that the total radiation emitted from the light emitting region substantially simulates a blackbody at a predetermined temperature over a predetermined wavelength range.
Implementations of the invention may include the following. The apparatus may include an alignment mechanism, such as an alignment structure to engage a corresponding alignment feature of a thermal processing chamber or to engage the input end of the temperature probe, to align the light emitting region with an input end of the temperature probe. A light combiner may be positioned to receive light from the first and second light sources and direct the combined light to the light emitting region. The first and second light sources may each emit light with an approximately gaussian intensity distribution and have intensity peaks at different wavelengths. The first and second light sources may be LEDs, and the predetermined wavelength range may be in the infrared. The light emitting region may be a surface of an optical fiber or an aperture in a structure enclosing the first and second light sources.
In another aspect, the invention may be directed to a method of calibrating a temperature probe. A first light source generates light having a first spectral range and a second light source generates light having a second spectral range. The second bandwidth is different from the first bandwidth. The light from the first and second light sources is combined and directed to a light emitting region. The relative intensities of the first and second light sources are selected such that a radiation spectrum emitted from the light emitting region substantially simulates a radiation spectrum of a blackbody at a predetermined temperature over a predetermined wavelength range.
In another aspect, the invention may be directed to a method of calibrating a calibration instrument. Light having a first spectral range is generated from a first light source in the calibration instrument, and light having a second spectral range is generated from a second light source in the calibration instrument. The second spectral range is different from the first spectral range. The light from the first and second light sources is combined, and the intensity of the combined light is measured at a first wavelength and at a second wavelength. The relative intensities of the first and second light sources are adjusted such that a ratio of the intensity at the first wavelength to the intensity at the second wavelength is substantially equal to an intensity ratio predicted for a blackbody at a predetermined temperature.
Implementations of the invention include the following. If the first spectral range overlaps a portion of the second spectral range, then the first wavelength may be within the overlapping portion and the second wavelength may be outside the first spectral range. If the first and second spectral range do not overlap, then the first wavelength may be selected such that the first and second light sources have approximately equal normalized intensities at the first wavelength.
Among the advantages of the invention are the following. The spectral output of the calibration instrument closely simulates a blackbody at a specific temperature. Blackbody radiation may be simulated without the use of a calibration filter. The pyrometer may be accurately (e.g., less than 1° C. error) calibrated without using a wafer with an embedded thermocouple. Calibration may be performed more quickly and using less energy. Calibration may be traced to an absolute standard. The pyrometer may be calibrated without removing th
Applied Materials Inc.
Fish & Richardson
Gutierrez Diego
Pruchnic Jr. Stanley J.
LandOfFree
Method and apparatus for infrared pyrometer calibration in a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for infrared pyrometer calibration in a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for infrared pyrometer calibration in a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2445913