The electrodeposition of indium on copper substrates is studied in an acid sulfate solution for applications in CuInS 2 (CIS) and Cu(InGa)Se 2 (CIGS) solar cells. The study is focused on the film morphology and thickness uniformity on the nanometer scale. A two-step film growth behavior was observed, a conformal smooth film growth followed by a three-dimensional island growth. A hypothesis involving the Cu-In alloy formation and the Cu-In interdiffusion is proposed. While the room temperature alloy formation promotes the conformal deposition of a few monolayers of alloy, the fast interdiffusion between Cu and In further extends this alloy formation to a thicker layer and delays the typical island formation-growth phenomenon.