A Spectroscopic Investigation of the Amorphous to Microcrystalline Transition in Silicon Prepared by Reactive Magnetron Sputtering

Abstract

Reactive magnetron sputtering of a c-Si target in an atmosphere containing argon and a varying partial pressure of hydrogen has been used to prepared a series of samples which span the transition from amorphous to microcrystalline silicon. Samples prepared at a substrate temperature of 200 °C, power of 100 W, and Ar partial pressure of 2.10 mtorr can be divided according to the partial pressure of H2, PH2, used in the deposition. Samples deposited using PH2 ≤ 1.00 mtorr are amorphous, those deposited using P H2≥ 1.25 mtorr are microcrystalline. Raman scattering is used to confirm amorphousity/microcrystallinity. Two types of changes are observed using infrared, IR, spectroscopy. First, the IR absorption spectrum changes at the onset of microcrystallinity. The absorption centered at 630 cm-1 changes shape while the feature at 2000 cm-1 appears to shift upward to 2090 cm-1. Second, microcrystalline samples deposited using PH2 ≥ 1.50 mtorr show significant post-deposition contamination upon atmospheric exposure. This is most clearly noted by the strengthening, over time, of Si02 related absorption features which appear at 1050 and 1150 cm-1, and a weakening of a narrow component of the 630 cm-1 absorption. This narrow component is not observed in amorphous material. The strength of the O-related absorption suggests that the oxide is a bulk property. The porous, low density network which is necessary for this contamination to occur is confirmed using HRTEM.