Atomic layer deposition of lithium nitride and carbonate using lithium silylamide

Abstract

Lithium silylamide, LiN(SiMe₃)₂, has been explored as precursor for the successful deposition of thin films of lithium nitride, Li₃N, and of lithium carbonate, Li₂CO₃, by atomic layer deposition. Deposition of Li₂CO₃ has been used as a tool in the method development as the compound is stable in air, contrary to Li₃N. Self limiting growth was demonstrated for both Li₃N and Li₂CO₃. The crystalline state of Li₃N depends on the deposition conditions, and varies from amorphous to a phase mixture of α-Li₃N and β-Li₃N. The growth rate of Li₃N is 0.95 Å cycle⁻¹. The Li₂CO₃ is well crystalline and highly oriented with (002) parallel to the substrate as deposited, and has, according to XPS, a low content of silicon at deposition temperatures between 89 and 332 °C. The growth rate of Li₂CO₃ is 0.35 Å cycle⁻¹. A geometrical model has been applied to rationalise the observed growth rates. This is the first example of deposition of nitrides using silylamides, and the first route towards lithium nitride by ALD.