Hydrogenated Amorphous Silicon Layer Formation by Inductively Coupled Plasma Chemical Vapor Deposition and Its Application for Surface Passivation of p-Type Crystalline Silicon

Abstract

The satisfactory surface passivation properties of hydrogenated amorphous silicon (a-Si:H) prepared by inductively coupled plasma chemical vapor deposition (ICP-CVD) at a low temperature (400 °C) on p-type crystalline silicon wafers are reported. Certain parameters, such as SiH4/H2 ratio, annealing temperature, film thickness, and substrate temperature, were varied to determine their optimal levels. Completely amorphous layers with a broad transverse optic (TO) mode peak at approximately 480 cm-1 were identified by Raman spectroscopy, and an optical band gap of approximately 1.6 eV was determined from optical absorption data. A maximum carrier lifetime of 53 µs for an a-Si:H thickness of 15 nm and an annealing temperature of 450 °C was measured for 525-µm-thick p-type crystalline silicon (c-Si) substrates with a resistivity in the range of 1–20 Ω cm by the quasi-steady-state photoconductance (QSSPC) method. The lowest value of interface trapped charge density (Dit) of approximately 3.34 ×1011 cm-2 eV-1 was estimated by capacitance–voltage (C–V) measurement using a metal–insulator–semiconductor (MIS) structure. Furthermore, simple processing with satisfactory results can be achieved with substrate heating at 400 °C during deposition. The optimal conditions of a SiH4/H2 gas ratio of 1/1 and a substrate temperature of 400 °C were implemented for a passivation layer thickness of 5 nm.