Stress relief in heavily doped silicon layers

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Abstract
The Raman spectra of epitaxial silicon layers on sapphire substrates, as well as polycrystalline silicon on vitreous quartz, have been measured after various treatments. In silicon on sapphire layers, grown epitaxially near 1000 °C, the Raman peak is broadened and shifted to higher energy compared to that observed in melt-grown single crystals. This is a consequence of the compressive stress exerted on the silicon by the sapphire substrate. Amorphization by dopant ions and rapid thermal regrowth at temperatures near 550 °C results in a Raman band shifted to near the single crystal phonon energy of 521 cm−1. The effect is a consequence of the enhancement of low temperature crystallization by dopant ions and the accompanying stress relief. Polycrystalline silicon on vitreous quartz shows a Raman band shifted to low energy, 515 cm−1, and broadened by a factor of 2 compared to the single crystal half-width of 3.5 cm−1. In this case, the Raman changes are a combination of the effects of tensile stress and polycrystallinity.