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

Thin films of Cu x S are deposited by both chemical vapor deposition (CVD) and atomic layer deposition (ALD) using copper bis-tetramethylheptanedionate, Cu(thd) 2, and H 2 S as the precursors. Single-phase CuS and Cu 1.8 S 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 Cu 1.8 S 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.