Analysis for the Characterization of Oxygen Implanted Silicon (SIMOX) by Spectroscopic Ellipsometry
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Analysis for the Characterization of Oxygen Implanted Silicon (SIMOX) by Spectroscopic Ellipsometryt M.G. Doss, Rudolph Research, Flanders, NJ 07836 D. Chandler-Horowitz and J. F. Marchiando, NIST, Gaithersburg, MD 20899 S. Krause, Arizona State University, Tempe, AZ 85287 S. Seraphin (Visitserngtrakul), University of Arizona, Tucson, AZ 85721 Abstract Samples of SIMOX have been prepared by implantation in a high-current implanter 2 (density es 1 mA/cm ) and by annealing at 1300 *C for 6 hours. Transmission electron microscopy reveals unusual structure in these samples. Spectroscopic ellipsometry has been used to analyze these structures. Ellipsometric measurements were collected at an angle of incidence of 75.5 deg, with photon energies from 1.5 to 5.0 eV, and using a rotating polarizer configuration. The measurements were analyzed with three models: a three-layer model, a four-layer model, and' a five-layer model. The five-layer model provided the best fit of the three. This model identified a layer of crystalline Si inclusions ("islands") within the SiO: layer. A method is presented that provides initial estimates for the thicknesses of the top three layers to help start the regression analysis.
Introduction Devices fabricated on silicon-on-insulator materials, such as SIMOX (Separation by IMplanted OXygen), exhibit a higher packing density, better high-voltage isolation, reduced latch-up, lower parasitic capacitance, improved speed, and enhanced radiation hardness compared to similar devices built with conventional bulk silicon technology. The quality of the device is strongly dependent on the characteristics of the SIMOX wafer. For example, the implant energy and dose of the dopant must be tailored to the thickness of silicon and buried oxide layers; and for fully depleted devices, the threshold voltage scales with the silicon film thickness. To characterize the layered structure of these samples, it is necessary to determine the thicknesses and bulk quality of the layers. This is possible with the sensitive, nondestructive method of spectroscopic ellipsometry (SE) [1-4].
Procedure and Analysis 2
Samples were prepared by implanting a high dose of oxygen ions (1 to 2 xl101 cm- , at 150 to 200 keV) with an Eaton NV200[*] implanter into silicon wafers. The wafer temperature during implantation was between 550 and 700 *C to help maintain the stoichiometry of the buried SiO 2 layer and crystallinity of the top silicon layer. The implanted samples were annealed at 1300 °C in an atmosphere of argon for 6 hours to restore the single-crystal nature of the top silicon layer, making it suitable for device applications. Transmission electron microscopy (TEM) identified precipitate growths, defects, and layered structure in the samples [5-7]. TEM also provided a measure of the thicknesses of these layers. These thickness values provided a comparative check of the values found by modeling the SE measurement data. Ellipsometric measurements on SIMOX samples between 1.5 and 5.0 eV were obtained using a commercial fixed-pol
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