Atomic layer deposition of lithium containing thin films

Abstract

Five different lithium containing compounds, all representing different chemical systems, were studied in order to deposit lithium containing films by atomic layer deposition ALD. The studied compounds were a lithium β-diketonate Li(thd) (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate), a lithium alkoxide LiO^tBu (O^tBu = tert-butoxide), a lithium cyclopentadienyl LiCp (Cp = cyclopentadienyl), a lithium alkyl n-butyllithium, and a lithium amide lithium dicyclohexylamide. Films containing lithium carbonate (Li₂CO₃) were obtained from alternate pulsing of Li(thd) and ozone in a temperature range of 185–300 °C. The film composition was analyzed by time-of-flight elastic recoil detection analysis (TOF-ERDA). The films grown at 225 °C were polycrystalline lithium carbonate as analyzed by X-ray diffraction (XRD). A 120 nm thick lithium carbonate film grown at 225 °C had a surface roughness of 19 nm as analyzed by AFM. Lithium lanthanate thin films were grown by combining the Li(thd) process with a ALD process for lanthanum oxide from La(thd)₃ and ozone. The film composition was varied by controlling the number of lithium carbonate and lanthanum oxide sub-cycles. Lithium containing films were also obtained from LiCp and water and from LiO^tBu and water.