Status of NIST near infrared emittance measurement system

A new capability for the measurement of temperature-dependent emittance of specular samples in the near infrared spectral region has been developed in NIST´s Infrared Spectrophotometry Laboratory. The effort is directed to support needs for emittance data and standards for a broad range of applications including rapid thermal processing (RTP). Our approach employs the indirect method of reflectance and transmittance measurements to obtain emittance and a vacuum goniometer system to control the sample environment and measurement geometry. The system has been developed for the acquisition of emittance data of specular samples and the development of standards. The heart of the system, including the sample, is contained in a vacuum chamber that enables characterization of materials otherwise susceptible to oxidation. Three diode lasers (900 nm, 950 nm, and 1560 nm) and a halogen lamp are used as radiation sources. Internal Si and InGaAs detectors and an external monochromator are used in both reflectance and transmittance modes. The spectral range of the monochromator/detectors is 600 nm to 2300 nm. A cold reference and hot sample are mounted on a horizontal stage, which in turn is mounted on a rotation stage. Reference standard samples (at room temperature) used are un-doped silicon and gold mirrors. The reflectance detector stage is also mounted on a rotation stage to enable measurement of angle dependent emittance. Optical windows and fiber optics are used for light input and output. The sample heater employs a platinum-ceramic element and allows temperatures between 100degC and > 800degC. It is shielded from the black walls of the chamber by a water-cooled shroud. The system has initially been used to characterize the spectral emittance (via reflectance) of a variety of semiconductor wafer samples including bare silicon and silicon substrates coated with SiO₂, Si₃ N₄, and polysilicon films. The spectral range for these measureme- nts is 600 nm to 1100 nm, where Si is opaque; the temperature range is ambient to 800degC. The results are analyzed and compared with those predicted by several models from the literature