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The characterization of materials for semiconductor applications has been significantly advanced by the use of photoluminescence and laser-Raman spectroscopy. Photoluminescence is particularly sensitive for identifying impurities and mapping wafers to determine the distribution of dislocation densities over the surface of a wafer. Direct correlation with the threshold voltages of finished devices is one of the practical applications of such data. Laser-Raman spectroscopy can identify surface contaminants and determine lattice disorders, residual strain and free-carrier density. beparate, dedicated systems are normally required for each analytical technique. In this paper, the authors describe a new and totally automated system that incorporates both photoluminescence and Raman capabilities. Wafers up to 4 inches in diameter were characterized at room temperature and while cooled by liquid helium. Sample materials included 8i, GaAs, LiNb0 and InP. Information from spectra, wafer maps and peak shifts is presented and discussed. The efficiency or semiconductor device designs and their mass production depends largely on the quality of information charcterizing the materials from which devices are fabricated. In recent years, spectroscpy has emerged as a primary source of such information for both fundamental research and quality control in manufacturing. There are many reasons for this expanding recognition, not the least of which is the non-contact and non-destructive nature of spectroscopic analysis. Capable of being fully automated through microprocessor control, spectroscopy also generates a range of data unmatched by other methods. And among the spectroscopic techniques currently available, photoluminescence and Raman spectroscopy are especially effective for characterizing semiconductor materials like silicon, gallium arsenide or indium phosphide. basically, photoluminescence (PL) involves exciting a sample with laser light and observing any t'!mission, Besides providing a measure of crystal quality, photoluminescence has been used extensively to study the role of dopants in the production of semi-insulating GaAs and InP. In the evaluation of ion-implanted III-V semiconductors, photoluminescence has been employed to assess distribution of impurities, surface degradation from implantation and annealing, as well as lattice reconstruction during annealing. human spectroscopy complements photoluminescence characterization by providing a more comprehensive structural and molecular picture of semiconductor materials. The important parameters of a Raman semiconductor spectrum are the peak position and line shape of the lattice modes designated longitudinal optic (LO) and transverse optic 0'0). Raman measurement of these parameters can be correlated with factors integral to the successful manufacture of conventional silicon devices or devices made from faster materials like gallium arsenide.
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