Effects of straggling of incident ions on plasma-induced damage creation in “fin”-type field-effect transistors

We investigated the plasma-induced physical damage (PPD) mechanism in a field-effect transistor (FET) with a fin-type channel, called FinFET. Compared to PPD in planar metal–oxide–semiconductor field-effect transistors (MOSFETs), such as Si loss or Si recess formed by energetic ion bombardment during plasma processing followed by the subsequent wet-etch stripping, it was predicted that PPD in FinFETs are generated primarily by a stochastic process called straggling of incident ions. During the etching of a fin structure in a FinFET, an impinging ion penetrates into the crystalline Si region to be etched, not only in the vertical direction but also in the lateral direction, resulting in lateral damage in the sidewall region, that is, the bulk fin. The damage layer generation mechanism in the fin structure was modeled on the basis of range theory. A molecular dynamics simulation was performed for noble and halogen species impacting on a Si fin structure to verify the proposed mechanism. The calculated results showed that ions with lighter masses and higher incident energies induced a larger amount of damage in the bulk fin owing to the nature of straggling phenomena. It should be noted that the PPD in the bulk fin may lead to latent defect sites in the channel region, and hence to operating speed degradation, which is a problematic concern for high-performance FinFETs.