In-situ ellipsometry study of ion bombardment effects on low temperature Si epitaxy by dc magnetron sputtering

We deposit Si films on Si(100) substrates at temperatures of 300 - 350 °C using dc magnetron sputtering, and characterize the structure by in-situ spectroscopic ellipsometry. Changes in the ion or electron bombardment, produced by biasing the sample with respect to the floating potential, are found to exert a strong effect on the kinetics of the crystalline (epitaxial) to amorphous transition for films deposited just below the apparent minimum temperature (350 °C) for sustained epitaxy. At 320°C, the best results are found at the floating potential, which is 25 V below the plasma potential and produces an ion flux equal to the depositing Si flux on the substrate. At +14 V above the floating potential, the volume fraction of crystalline Si decreases exponentially with thickness, and the characteristic decay length is a function of substrate temperature. At -14 V below the floating potential, the deposited film is amorphous with a large void content. These observations demonstrate the subtle tradeoff between enhanced surface mobility and defect creation by low energy ion bombardment.