Comparison of CuxS Films Grown by Atomic Layer Deposition and Chemical Vapor Deposition

Abstract

Thin films of CuxS are deposited by both chemical vapor deposition (CVD) and atomic layer deposition (ALD) using copper bis-tetramethylheptanedionate, Cu(thd)2, and H2S as the precursors. Single-phase CuS and Cu1.8S can be deposited using both techniques, while in CVD also mixed phases can be formed. Comparing the ALD process with the CVD process leads to a better understanding of the reaction chemistry of both processes. The main factor is the decomposition of Cu(thd)2 at 175 °C, which leads to a phase transition from CuS to Cu1.8S in ALD and deposition of mixed phases in CVD. Consequently, the phase transition is sharp in ALD and gradual in CVD. At temperatures higher than 250 °C, decomposition of Cu(thd)2 occurs in the gas phase, leading to a transition from a reaction-limited regime to a thermodynamic regime in CVD and to loss of uniformity and homogeneity in ALD.