Characterization of Ultra High Purity Silicon Epitaxy Using Photoluminscence Spectroscopy
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CHARACTERIZATION OF ULTRA HIGH PURITY SILICON EPITAXY USING PHOTOLUMINSCENCE SPECTROSCOPY J. E. Huffman*, M. L. W. Thewalt** and A. G. Steele** *Rockwell International Science Center, 3370 Miraloma Avenue, Anaheim, CA 92803 "**Department of Physics, Simon Fraser University, Burnaby, B.C., Canada VSA IS6 ABSTRACT High purity epitaxial silicon samples, grown on indium doped and on ultrahigh resistivity silicon substrates, were analyzed for impurity content using photoluminescence spectroscopy (PL) and spreading resistance analysis SRA indicated typical net carrier concentrations of (SRA). 2 Calibrated < 3xlOl cm- 3 in the epitaxial layers, and about 7xlOll cm- 3 in the substrates. Impurities were identified by collecting highly resolved, very clean no-phonon and TO-phonon replica PL spectra at liquid helium temperatures. Spectra were taken on the substrate material alone and on substrates with epitaxy. Ga, As, Al, B and P contamination was evident in the epitaxy. Correlation of SRA and PL results on samples with various levels of contamination at the epitaxy substrate interface identified Al as the main interfacial impurity. INTRODUCTION Ultrahigh purity (UHP) epitaxial Si is receiving increasing attention for of microwave, CMOS, and electro-optical device applications. While growth 3 layers having less than 1013 electrically active impurities per cm is becoming routine, a technique for identifying the impurity species in these relatively thin layers has not been established. Spreading resistance analysis (SRA) measures only the net carrier concentration as a function of depth into the layer. Secondary ion mass spectrometry (SIMS) is capable of both elemental analysis and depth profiling, but lacks the sensitivity needed for this application. Other techniques (cryogenic Hall effect, capacitancevoltage, etc.) are not capable of elemental analysis when several species are present. Photoluminescence spectroscopy (PL), however, has demonstrated the to identify multiple impurities at required sensitivity and selectivity concentrations well below 1010 cm- 3 in bulk Si.1 While some previous work has dealt with the application 2 of PL to the characterization of epitaxial We report the first application of PL, Si, none has dealt with UHP layers. together with SRA depth profiling, to the study of such layers. As, P and Ga are found to be the main, reproducible contaminants in the epitaxial layer, and a process-related interfacial contaminant layer is shown to be due to Al. EXPERIMENTAL DETAILS UHP silicon epitaxial layers were grown by chemical vapor deposition (CVD) in a horizontal flow RF heated reactor, operating at atmospheric pressure. Using UHP silane (SiH4) in purified hydrogen carrier gas a substrate temperature of 1020%C and silane partial pressure of lO- atm. resulted in a layer growth rate of 0.6 um/min. Measured temperatures were corrected for reflection and absorption of the reactor system and the emissivity of silicon. The substrate material used in several runs was obtained from a 1-in. diameter boule of UHP vac
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