Spectral pyrometry of objects with unknown emissivities in a temperature range of 400–1200 K

A spectrometer with a photodetector array, which consists of 512 InGaAs-based pixels and is sensitive to IR radiation at wavelengths of 0.9–2.5 μm, is described. It allows registering of thermal-radiation spectra of objects with unknown emissivities and calculation of their temperatures near 400 and 500–600 K at storage times of 100–500 and 10 ms, respectively.     

Thermometry of microwave discharge in powder mixtures by the thermal radiation spectrum

The temperature is determined in pulsed microwave discharges in powder mixtures at atmospheric pressure. The effect of microwave radiation of gyrotron (wavelength of 4 mm, power up to 200 kW, pulse duration of 1 to 10 ms) on a finely divided medium causes the emergence of plasma in a gas medium between solid particles; the thresholds (with respect to power) of generation of plasma in powder mixtures are hundreds of times lower than those in gas. The method of determining the discharge temperature consists in recording the radiation in a wide spectral range (200 to 850 nm) and comparing the obtained spectrum with the Planck spectrum in the Wien region. In the case of similarity of two spectra, the discharge temperature is determined as a parameter of the spectrum under observation. In so doing, no data on the emissivity of discharge are required for determining the temperature. It is demonstrated that microwave-discharge plasma in powders is characterized by a temperature of 2000–3000 K.     

An automated laser thermometer for studying plasma processes in the microtechnology

The design and characteristics of an automated temperature sensor of dielectric and semiconductor substrates in apparatuses for film deposition and etching of microstructures are considered. The temperature is measured via the laser interference thermometry technique as wavelengths of 0.633 and 1.15 μm of a He-Ne laser. A signal-to-noise ratio of ～30 dB attained in the system is such that the device is sensitive to a change in the substrate temperature of 0.01 K. The heating and cooling of the wafer are recognized automatically and displayed via a graphic interface in real time. An interferogram recorded during substrate heating or cooling, the time dependence of the temperature after the discharge initiation, and the temperature dependence of the substrate-heating power are displayed on the monitor. For 0.5-mm-thick silicon substrates, the measurement range at a wavelength of 1.15 μm extends from cryogenic temperatures to 650 K.     

Determining the heat of a surface plasmochemical reaction by scanning calorimetry

A method for experimental determination of the heat of an exothermic reaction, which proceeds on a solid surface under the action of a chemically active plasma and is accompanied by the production of volatile compounds, is proposed. Scanning calorimetry in a discharge is used in order to determine the contribution due to the heat release of the chemical reaction to the total heat flux onto the surface. It is shown how necessary it is to consider the contributions of different heat exchange mechanisms when determining the reaction heat in the case of a significant difference between the temperatures of the active and inert calorimeters. The heat of the exothermic chemical reaction of atomic fluorine with a unit mass of single-crystal silicon in a CF₄+O₂ plasma is 31±2 kJ/g or 9 eV per Si atom.     

Thermometry based on the intensity distribution in a thermal-radiation spectrum

A modified method for temperature measurements based on thermal-radiation distribution is considered. A wide portion of the spectrum in the Wien region is recorded, and data are represented in the coordinate plane in which the Planck function is linearized. The temperature is determined from the slope of the straight line without invoking hypotheses about the emissivity. The direct observation of the distribution, of which the desired temperature is one parameter, allows the reliability and accuracy of determining the temperature to be improved. The temperature of reagents during a solid-phase exothermic chemical reaction has been determined using a spectrometer with a silicon CCD array sensitive in the range 200–850 nm.     

Continuous Laser Interference Thermometry of Transparent Plates

A method for quasi-continuous measurements of the nonstationary temperature of plane–parallel plates by using optical Fabry–Perot resonators is discussed. The temperature was earlier determined from interferograms only for time intervals corresponding to the extrema of the reflected or transmitted light intensities, because the deviations of the shapes of plates (polished single crystals and glasses) from the perfect plane-parallel shape distort the geometry of the resonators. It is shown that, for plates with a small surface reflectivity (R< 0.1), when the Fabry–Perot resonances are described by the two-beam interference approximation, thermometry with an arbitrary number of readings n>> 1 within a single interference fringe is implementable. Measurements with 20 temperature readings within each fringe were performed for K-8 glass in a gas-discharge plasma.     

The choice of a spectral interval within which a heated opaque object radiates as a gray body

The temperature of opaque objects with the emissivity ɛ(λ) depending on the wavelength can be rather precisely determined with an error of ≤1–5% from their heat emission spectrum using the model of a gray body ɛ = const(λ). This method is based on the much more strong spectral dependence of the heat emission intensity I(λ) within the short-wavelength region in comparison with that of the emissivity ɛ(λ). At relatively low temperatures T ≤ 3000–4000 K, any opaque object radiates as a gray body in the short-wavelength spectrum region (λ ≤ 350–400 nm), even if it appreciably differs from a gray body in its optical properties. An experimental heat emission spectrum of tungsten (T ≈ 1970 K), for which the influence of the emissivity manifests itself in the long-wavelength region (λ > 580 nm), is given.     

A setup for measuring the temperature dependence of the refractive indices of solids

A setup for measuring the temperature dependences of refractive indices n(T) of semiconductors and dielectrics in the temperature range 300–700 K at the wavelengths of a He—Ne laser λ=0.63, 1.15, and 3.39 μm is described. Samples in the form of plane—parallel plates serve as Fabry—Perot etalons the optical thickness of which depends on the temperature. Upon heating and subsequent cooling of a sample, interference oscillations of the refiected-light intensity are recorded and used to determine the dependence n(T). The values of the refractive index at room temperature and the thermal expansion coefficient used in calculations are taken from the literature. Comparing the interferograms obtained for a heated and cooled sample allows evaluation of the temperature difference between the sample’s probed area and a measuring thermocouple. The relative error in determining thermooptical coefficient dn/dT in the range 300–700 K is within 1%.     

Measuring temperature of silicon monocrystals using spectral pyrometry

Spectrums of the thermal radiation of silicon monocrystals that are heated by a continuous laser beam (wavelength of 1.064 μm) are recorded within the wavelength range λ = 200–2500 nm. Silicon temperatures are determined within the interval T = 900–1700 K using the spectral pyrometry. The processing of a sequence of spectrums recorded with the frequency 100–1000 Hz allows the evolution of the crystal temperature to be restored during laser heating in the case when heating rates are sufficiently small. Peculiarities of different spectral intervals are discussed as applied to the problem of measuring the silicon temperature. During the laser heating of silicon, the temperature of a surface layer is shown to be heterogeneous with respect to depth, which is manifested in differences between average values calculated using thermal radiation spectrums and the surface temperature.     

Measurements of nonstationary temperatures by the spectral pyrometry method

Recording of a sequence of thermal-radiation spectra allows determination of a nonstationary temperature T(t) without using the data on the emissivity of an object. For a КЭФ-4.5 silicon single crystal heated with radiation from a continuous-wave Nd:YAG laser (λ = 1.064 μm), sequences of hundreds of emission spectra in wavelength ranges of λ = 350–760 nm and λ = 650–1000 nm were recorded at a signal storage time of a CCD array of τ = 15–35 ms and a frequency of recording spectra of f ≈ 30–66 Hz. The spectra were automatically processed, and the dependences of the crystal temperature on the time after the irradiation onset were obtained in the range T ≈ 1100–1450 K.