On-wafer monitoring and control of ion energy distribution for damage minimization in atomic layer etching processes

Abstract

Underlying Si substrate damage during SiN atomic layer etching (ALE) was investigated. We applied a CH3F/Ar plasma in the adsorption step and an Ar plasma in the desorption step. A long Ar desorption process (i.e. for a quasi-self-limited process) causes serious Si damage, owing to the accumulation of incident ions. On-wafer ion energy distribution function (IEDF) monitoring revealed that the damage thickness is defined by the energy at the high energy peak of the IEDF. Adsorbed surface polymer is also a key to reduce the damage thickness, owing to the ion energy loss at the underlying Si surface. By selecting the appropriate ion energy, thickness of adsorbed polymer, and Ar desorption time in the ALE process, Si damage generation is greatly suppressed by sequential deposition of a protective film on the Si substrate.