In Situ Microgravimetric Study of Ion Exchanges in the Ternary Cu-In-S System Prepared by Atomic Layer Deposition

• Main Authors: Harold Le Tulzo, Nathanaelle Schneider, Frédérique Donsanti
• Format: Article
• Language: English
• Published: MDPI AG 2020-02-01
• Series: Materials
• Subjects: ald; sulfide materials; thin films; qcm; cis; exchange mechanisms
• Online Access: https://www.mdpi.com/1996-1944/13/3/645

Reaction mechanisms during the growth of multinary compounds by atomic layer deposition can be complex, especially for sulfide materials. For instance, the deposition of copper indium disulfide (CuInS₂) shows a non-direct correlation between the cycle ratio, the growth per cycle of each binary growth cycles, i.e., Cu_xS and In₂S₃, and the film composition. This evidences side reactions that compete with the direct Atomic Layer Deposition (ALD) growth reactions and makes the deposition of large films very challenging. To develop a robust upscalable recipe, it is essential to understand the chemical surface reactions. In this study, reaction mechanisms in the Cu-In-S ternary system were investigated in-situ by using a quartz crystal microbalance system to monitor mass variations. Pure binary indium sulfide (In₂S₃) and copper sulfide (Cu_xS) thin film depositions on Al₂O₃ substrate were first studied. Then, precursors were transported to react on Cu_xS and In₂S₃ substrates. In this paper, gas-phase ion exchanges are discussed based on the recorded mass variations. A cation exchange between the copper precursor and the In₂S₃ is highlighted, and a solution to reduce it by controlling the thickness deposited for each stack of binary materials during the CuInS₂ deposition is finally proposed.