Resolving the contact-channel trade-off in p-type SnO thin-film transistors via self-aligned fluorine plasma treatment

초록

High-performance p-type oxide thin-film transistors (TFTs) are essential for realizing complementary monolithic three-dimensional (M3D) integrated circuits within the back-end-of-line (BEOL) thermal budget. Among p-type oxide semiconductors, SnO has emerged as a promising material because of its relatively high hole mobility. However, the practical implementation of p-type metal oxide TFTs remains limited by an inherent trade-off between contact resistance and gate controllability. Reducing the channel thickness suppresses off-state leakage current but simultaneously increases contact resistance substantially. Here, we report a self-aligned C4F8/He plasma treatment for atomic layer deposition-grown p-type SnO TFTs that overcomes this trade-off in a single fabrication step. The metal source/drain electrodes serve as an intrinsic mask, selectively exposing only the back channel to the plasma while preserving the SnO beneath the contacts in its as-deposited, low-resistance state. The treatment amorphizes the upper region of the back channel and incorporates fluorine via substitution at oxygen sites, thereby reducing the effective conducting thickness and modulating the carrier concentration. This effect is evidenced by an upward shift of the Fermi level relative to the valence band maximum. Crystal orbital Hamilton population analysis further indicates that fluorine substitution strengthens local Sn-O bonding, providing a lattice-level mechanism for suppressing the regeneration of oxygen-related defects during ambient operation. The optimized F-doped SnO TFT with a passivation layer exhibits a width-normalized contact resistance of 0.04 k Omega cm, an on/off current ratio of similar to 106, a field-effect mobility above 2 cm2 V-1 s-1, a substantially reduced subthreshold swing, and negligible degradation after 12 months of ambient storage. These results demonstrate that the proposed self-aligned strategy offers a practical route to high-performance p-type SnO TFTs for BEOL-compatible M3D integration.

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