Atomic layer deposition of SnSex thin films using Sn(N(CH3)2)4 and Se(Si(CH3)3)2 with NH3 co-injection

Abstract

This study introduces the atomic layer deposition (ALD) of tin selenide thin films using Sn(N(CH₃)₂)₄ and Se(Si(CH₃)₃)₂ with NH₃ co-injection. The co-injection of NH₃ with Se(Si(CH₃)₃)₂ is essential for film growth to convert the precursor into a more reactive form. The most critical feature of this specific ALD process is that the chemical composition (Sn/Se ratio) could be varied by changing the growth temperature, even for the given precursor injection conditions. The composition and morphology of the deposited films varied depending on the process temperature. Below 150 °C, a uniform SnSe₂ thin film was deposited in an amorphous phase, maintaining the oxidation states of its precursors. Above 170 °C, the composition of the film changed to 1 : 1 stoichiometry due to the crystallization of SnSe and desorption of Se. A two-step growth sequence involving a low-temperature seed layer was devised for the high-temperature ALD of SnSe to improve surface roughness.