Comparative study of atomic layer deposition and low-pressure MOCVD of copper sulfide thin films

Abstract
Thin films of copper sulfide (Cu_xS) have been prepared on fluor-doped tin dioxide (SnO₂ : F) coated glass and on uncoated glass by atomic layer deposition (ALD) and low-pressure chemical vapor deposition (LPCVD). In both cases, copper(II) bis-tetramethylheptanedionate (Cu(thd)₂) and H₂S are used. Cu_xS films form between 125 and 300 °C with ALD and between 127 and 505 °C with LPCVD. Deposition rates are obtained between 1 and 109 Å/min by LPCVD and between 0.15 and 0.40 Å/cycle by ALD. Self-limited grow by ALD is achieved up to 250 °C at 2 mbar. It is found that in both processes the temperature determines the crystalline phase of the films. CuS is obtained at low deposition temperatures when using either ALD or LPCVD. A phase transition occurs at 175 °C from pure CuS into pure Cu₉S₅ with ALD. In the LPCVD process the phase composition of the films starts to change at 230 °C from pure CuS into a mixture of CuS and Cu₉S₅. Pure Cu₉S₅ is obtained between 285 and 315 °C. The morphology of LPCVD films are fine-structured with an average grain size of ˜100 nm for films of 500 nm, while 40 nm thinn ALD films consist of grains with an average grain size of ˜100 nm grown in columns perpendicular to the surface.