Abstract: This paper describes studies of heat transfer in a rapid thermal processing-type oven used for several semiconductor wafer processes. These processes include 1) rapid thermal annealing, 2) thermal gradient zone melting, and 3) lateral epitaxial growth over oxide. The heat transfer studies include the measurement of convective heat transfer in a similar apparatus, and the development of a numerical model that incorporates radiative and convective heat transfer. Thermal stresses that are induced in silicon wafers are calculated and compared to the yield stress of silicon at the appropriate temperature and strain rate. Some methods of improving the temperature uniformity and reducing thermal stresses in the wafers are discussed.

Abstract: We report an optical, interferometric technique for measuring the temperature of semiconductor substrates during heating or cooling, which is applicable in vacuum. The technique circumvents many of the problems associated with thermocouple or pyrometer measurements. A low‐power infrared (IR) laser (e.g., λ=1.15‐μm He–Ne laser) having an energy below the band gap is directed at a wafer that is polished on both sides, where either reflected or transmitted laser light is detected by a photodiode. Interference results between reflections off the front and back surfaces of the wafer. As the temperature of the wafer is either increased or decreased, the temperature dependence of the refractive index, along with a smaller contribution from thermal expansion, causes the optical path within the wafer to change by λ/2n (i.e., a full interference cycle) for every ∼3 K for a typical Si, GaAs, or InP wafer thickness of 500 μm. Consequently, temperature changes of ±0.2 K are easily detected. This technique, has been used between room temperature and 600 °C on GaAs substrates in a low‐pressure metal‐organic chemical vapor deposition (MOCVD) system, and in an ultrahigh vacuum thermal desorption experiment. This method can be used well below room temperature, as well as at temperatures above 650 °C with the optimum choice in laser wavelength. Application of this method to other processes such as molecular beam epitaxy (MBE), reactive ion etching, and rapid thermal processing should be straightforward. We also describe a refinement of the method for measuring the sign, as well as magnitude of temperature changes for typical, slightly tapered wafers during heating or cooling cycles. In this case the reflected laser beam contains a series of parallel lines that move toward the thinner end of the region probed by the laser beam as the temperature increases. Sensing the direction that these spatial interference fringes move can be used to determine whether the sample is heating or cooling.

Abstract: A non-contact pyrometric technique is provided for measuring the temperature and/or emissivity of an object that is being heated by electromagnetic radiation within the optical range. The measurement is made at short wavelengths for the best results. The measurement may be made at wavelengths within those of the heating optical radiation, and the resulting potential error from detecting heating radiation reflected from the object is avoided by one of two specific techniques. A first technique utilizes a mirror positioned between the heating lamps and the object, the mirror reflecting a narrow wavelength band of radiation in which the optical pyrometer detector operates. The second technique is to independently measure the a.c. ripple of the heating lamp radiation and subtract the background optical noise from the detected object signal in order to determine temperature and emissivity of the object. Both of these techniques can be combined, if desired.

Abstract: Apparent oscillations in surface temperature occur during the deposition of heteroepitaxial structures when measured using a narrow optical bandpass pyrometer. The oscillation period can be related to the growth rate of the material being deposited, and provides a convenient method for rapid in situ calibration. For Ga1−xAlxAs alloys the oscillation periods can be directly related to the alloy composition. The pyrometer optics can also be used in conjunction with external light sources so that simultaneous pyrometry and reflectrometry can be carried out at multiple wavelengths.

Abstract: Instrumentation for monitoring the thermal history of individual plasma sprayed particles as they impact on a substrate is described. A double-wavelength fibre optic temperature sensor is focused on a small spot on the substrate surface to record the cooling rate of particles impacting on this region. Discrimination against in-flight particles intersecting the pyrometer field of view is obtained by a second fibre optic sensor viewing the same spot at an angle and working in coincidence with the first sensor. Typical recorded thermograms are presented and interpreted with reference to a numerical thermal propagation model.

Abstract: A dual purpose pyrometer is described that allows both accurate radiance temperature measurement and fast temporal response. The system uses two silicon photodiodes with separate optical paths derived from a common spot on the sample. The optical bandwidths and response times of each detection circuit are tailored to the function of each radiometer. The radiance temperature of electromagnetically levitated metallic samples is measured over a narrow optical bandwidth with a high-gain silicon detector. The velocity of solidification of undercooled melts can be deduced from the rise time of the second silicon detector which samples a broad optical bandwidth and has a fast response time. Results from experiments on the undercooling and solidification behavior of electromagnetically levitated pure nickel show that the solidification velocity approaches 17 m/s at high undercooling.

Abstract: The system and method for pyrometrically determining the temperature of a semiconductor wafer within a processing chamber accurately determines the actual emissivity of the semiconductor wafer at a reference temperature using multiple pyrometers operating at different wavelengths. The pyrometers are calibrated for radiation received from the processing chamber and their responses are then corrected to provide the proper temperature indication for a master wafer at a known reference temperature to yield emissivity of the master wafer. Other similar wafers exhibiting extreme values of emissivity are sensed at the reference temperature to provide pyrometer responses that are corrected in accordance with the master emissivity, and such corrected responses are used to establish a correlation between emissivities and the corrected pyrometer responses. The corrected pyrometer responses on other wafers operating near the reference temperature can then be used with the emissivities to determine the true temperature of each such other wafer. The processing temperature of the wafer is then determined and controlled in accordance with the actual emissivity of the wafer for more precise thermal processing.

Abstract: The main problems when measuring surface temperature by means of radiometry (i.e., optical pyrometry) are the unknown emissivity and radiation reflected by the sample. The latter problem becomes critical when the sample is placed in hot surroundings, such as furnaces or combustion chambers; indeed, the reflected flux may then become larger than the emitted flux. In this paper we describe a novel technique, based on the photothermal effect, which allows the surface temperature to be measured without error due to reflected fluxes. The influence of the parameters of the experimental setup are discussed. Experimental data obtained with a sample placed inside a furnace are reported in the (300-1150 K) range. The experimental results show the efficiency of the technique which proves to be a general solution to extend the domain of application of optical pyrometry.

Abstract: The traditional contact methods of temperature measurement for metal processing applications provide accuracies of ±10 K. Noncontact methods based upon emissivity compensation techniques have the potential for improved accuracy with greater ease of use but require prior knowledge of the target emissivity behavior. The features of the basie spectral and ratio methods and five dualwavelength methods are reviewed. Experiments were conducted on a series of aluminum alloys with different surface treatments characterized by x-ray photoelectron spectroscopy in the temperature range 600 to 750 K. Compensation algorithms that account for surface characteristics are required to achieve improved accuracy.

Abstract: The emissivity of silicon wafers in a rapid thermal processing chamber has been measured as a function of the wafer temperature. Wafers with different surface roughness and layers have been studied. For transparent wafers, both sides of the wafer affect the emissivity. This emissivity is not only affected by surface roughness, but also by the layers deposited on the wafer. It has also been observed that while the emissivity increases rapidly as the temperature increases from its room value to 600 °C, the emissivity decreases with a slope of −8.89×10−5 °C−1 for temperatures larger than 600 °C.

Abstract: A method and apparatus for determining the power output of a gas turbine engine utilizes a speed sensor coupled to the engine shaft and a signal developed by a pyrometer coupled to the engine turbine for determining engine temperature. The speed sensor is normally provided in the engine for determining shaft speed and is part of the control system for the engine. The pyrometer is provided also as part of the control system to monitor gas turbine temperatures. A signal from the speed sensor derived from a toothed wheel passing adjacent the sensor is processed to obtain a train of pulse signals representative of angular rotation of the engine shaft. The pyrometer is mounted adjacent at least one of the turbine disks of the engine for detecting instantaneous temperature of each blade of the turbine disk as it passes by the pyrometer. The signal developed by the pyrometer is therefore a signal having peaks corresponding to passage of each blade at the pyrometer. A signal conditioning apparatus processes the signal from the pyrometer to develop a pulse train of shaped signals corresponding to the angular position of each turbine blade as it passes by the pyrometer. The system determines the relative phase difference between the signals developed by the speed sensor and the signals developed on the pyrometer under low load conditions and stores this information as a reference phase difference value. Phase differences under load conditions are thereafter compared to the reference value. The differences in phase are proportional to shaft twist and accordingly to shaft torque.

Abstract: Measurements of the radiance temperature of graphite at 655 nm have been performed in the vicinity of its triple point by means of a rapid pulse-heating technique. The method is based on resistively heating the specimen in a pressurized gas environment from room temperature to its melting point in less than 20 ms by passing an electrical current pulse through it and simultaneously measuring the radiance temperature of the specimen surface every 120 μs by means of a high-speed pyrometer. Results of experiments performed on two different grades of POCO graphite (AXM-5Q1 and DFP-1) at gas pressures of 14 and 20 MPa are in good agreement and yield a value of 4330±50 K for the radiance (or brightness) temperature (at 655 nm) of melting graphite near its triple point (triple-point pressure, ∼ 10 MPa). An estimate of the true (blackbody) temperature at the triple point is made on the basis of this result and literature data on the normal spectral emittance of graphite.

Abstract: Apparatus and process for determining the emissivity of a test specimen including an integrated sphere having two concentric walls with a coolant circulating therebetween, and disposed within a chamber which may be under ambient, vacuum or inert gas conditions A reference sample is disposed within the sphere with a monochromatic light source in optical alignment therewith A pyrometer is in optical alignment with the test sample for obtaining continuous test sample temperature measurements during a test An arcuate slit port is provided through the spaced concentric walls of the integrating sphere with a movable monochromatic light source extending through and movable along the arcuate slit port A detector system extends through the integrating sphere for continuously detecting an integrated signal indicative of all radiation within its field of view, as a function of the emissivity of the test specimen at various temperatures and various angle position of the monochromatic light source A furnace for heating the test sample to approximately 3000 K and control mechanism for transferring the heated sample from the furnace to the test sample port in the integrating sphere is also contained within the chamber

Abstract: A new dynamic technique for the measurement of thermal conductivity at high temperatures has been developed at the IMGC. The specimen is brought to high temperatures with a current pulse; during cooling the heat content is dissipated by radiation and by conduction. The differential equation describing this process contains terms related to the heat capacity, the hemispherical total emittance, and the thermal conductivity of the material. If the first two properties are determined using the same specimen during subsecond pulse heating experiments, thermal conductivity may be evaluated by accurate measurements of the round-shaped temperature profiles established on the specimen during cooling. High-speed scanning pyrometry makes possible accurate measurements of temperatures and of temperature derivatives (with respect to space and time), which enables the differential equation describing the power balance at each point of the specimen to be transformed into a linear equation of the unknown thermal conductivity. A large overdetermined system of linear equations is solved by least-squares techniques to obtain thermal conductivity as a function of temperature. The theory underlying the technique is outlined, the experimental apparatus is described, and details of the measurement technique are given.

Abstract: A simple model for the components that make up a rapid thermal processing system is given. These components are the furnace, the pyrometer used to measure temperature, and the control system that utilizes the pyrometer measurement to control the power to the lamps. The models for each of the components are integrated in a numerical code to give a computer simulation of the complete furnace operation. The simulation can be used to investigate the interaction of the furnace, temperature-sensing technique, and the control system. Therefore, the interplay of heat transfer (furnace) properties, optical (pyrometer) parameters, and control gains can be studied. The objective is to define variability in wafer temperature as process parameters change. The following three applications of the model are included: (1) a simulation of open-loop operation; (2) a simulation of the ramp up and subsequent operation with a step change in wafer optical properties; and (3) a simulation of the rapid thermal chemical vapor deposition of polysilicon on silicon oxide which demonstrates the applicability model for actual processes. A technique for correction of pyrometer output to improve temperature control is also presented. >

Abstract: An apparatus and process for a temperature measuring pyrometer probe that measures gas temperatures above the melting point of conventional thermocouple material. The apparatus is used to calculate radiation heat losses and compensate for pneumatic cooling from the thermocouple junction of the pyrometer probe. The pyrometer probe has an inner hollow body which defines an inner chamber. The inner hollow body has an open end and the inner chamber is in communication with ambient gas surrounding the pyrometer probe. The inner hollow body is mounted within an outer hollow body and such mounting defines cooling channels. The cooling channels accommodate fluid flow which cools the inner hollow body. The ambient gas is directed into a converging-diverging nozzle, mounted within the inner hollow body, toward a thermocouple junction. The converging-diverging nozzle has a wall suction channel through which a boundary layer of the ambient gas is drawn away from the thermocouple junction. The thermocouple junction is mounted within a throat section of the converging-diverging nozzle. The pyrometer probe is intermittently cooled with gas by pulsing reverse cooling gas flow through the pyrometer probe. A computing system is used to continuously acquire temperature signals from the thermocouple and alternate the cooling gas flow and the ambient gas flow through the inner chamber of the pyrometer probe based on the temperature response. The computing system calculates radiation heat transfer losses, pneumatic cooling of the pyrometer probe, and instantaneous gas temperatures.

Abstract: An optical pyrometer has been developed which resolves 20 μm at a working distance of 24 in. and measures relative temperature differences of ±2 °C over the range 1000–2000 °C. The instrument is particularly suitable for measuring temperature or emissivity distributions in very small heated objects.

Abstract: The emissivity of silicon wafers determine the temperature control in closed loop rapid thermal processing (RTP) systems. Silicon surface roughness, doping, and layers affect the intrinsic wafer emissivity, while RTP chamber walls reflectance reduces the amplitude of these effects. For temperatures below 600V, device side topography and layers also affect the emissivity of the wafer. Narrow band and wide band pyrometers show similar behavior with respect to layers on the wafer, as indicated by experimental and modeling techniques.

Abstract: A fibre-optic bundle (6) with a plane face (8) towards the interior (1) of the reactor (2) is split into branches (9.1 etc.) coupled by cpd. lens systems (10) and optical filters (13) to optoelectronic converters (11). Two are connected to flame-monitoring processors (20) and a safety circuit (21) operating a rapid-closure valve (22) in the O2 supply line (23). Two other converters (11.3, 11.4) supply different wavelength signals to a ratio pyrometer (24) and controller (25) of fuel supply (28). USE/ADVANTAGE - In plants performing partial oxidn. of pulverised fuels or hydrocarbons. High availability and unrestricted technical security are guaranteed by appts. insensitive to contamination.

Abstract: Quartz glass or material (2) contg. the OH band is used to absorb optical radiation components esp. from halogen or arc lamps or resistance heaters (1) between 2.6 and 2.8 microns wavelength. The quartz material is partially or completely placed between the radiation source and the object to be measured esp. when the object is a semiconductor wafer (3). The temp. radiation (5) emitted by the wafer is coupled out by a lens melted in a quartz reactor. The focal point of the quartz lens, of glass not covering the OH band lies precisely between two halogen lamps. The partial beam (5) coupled out is guided to a pyrometer (7) via a narrow band optical notch filter (6). Interference radiation deriving from the lower quartz lamps is kept from the pyrometer by a shutter (8). USE/ADVANTAGE - Differentiating between halogen lamp interference radiation and wafer in gastight, enclosed quartz reactor. Excludes interference from prim. radiation esp. during double sided irradiation.

Abstract: It is a problem of pyrometric temperature measuring of melts in a vacuum that the material of the melt will be deposited on mirrors, windows and other optical devices so that the radiation will be screened more and more effectively, the closer it comes to the pyrometer. In order to avoid vapor desposition in the path of radiation, a grating arrangement is provided between the melt and the pyrometer, which focusses the incoming radiation and concentrates it onto the pyrometer. The grating arrangement is partly permeable to the molecules of the melt material. The direct path between the melt and the pyrometer is blocked by a screen. In this way, vapor deposition on the window prefixed to the pyrometer are avoided, while the radiation can reach the pyrometer.

Abstract: The effective emissivity of silicon varies with both temperature and the backside roughness of a wafer. Both of these variations need to be accounted for in the calibration of infrared optical pyrometers used in rapid thermal processing. A fully integrated hardware and software approach is described which calibrates the optical pyrometer over a temperature range of 350°C to 1275°C and provides for recalibration due to wafer to wafer variations in effective emissivity based on room temperature optical characterization of wafer backsides.

Abstract: A high‐power proportional temperature controller, using a fast infrared pyrometer, has been developed to change and control the temperature of metallic ribbon samples with microsecond response. The apparatus provides uniform and controlled heating for time‐resolved x‐ray scattering studies of structural phase transitions. When high‐power pulse heating is used, the system is capable of increasing the sample temperature at rates in excess of 106 K/s, without overshoot and with subsequent control to ±1 K at temperatures as low as 650 K.