Investigation of Sidewall High-k Interfacial Layer Effect in Gate-All-Around Structure

In this article, structure optimization of high- {k} interfacial layer (IL), deposited between the gate and the gate sidewall spacer, was performed in a 5-nm node nanosheet field-effect transistor (NSFET). High- {k} IL can be formed during the high- {k} gate dielectric and metal gate (HKMG) with gate-last process. By optimizing the structure of thickness of high- {k} IL ( {T}_{\text {hk}} ) with gate length ( {L}_{\text {G}} ), spacer length ( {L}_{\text {ext}} ), and source/drain (S/D) length ( {L}_{\text {S/D}} ), improved electrical performances were obtained. By optimizing {T}_{\text {hk}} with properly adjusted {L}_{\text {G}} , {L}_{\text {ext}} , and {L}_{\text {S/D}} , highly saturated ON-/OFF-current ratio ( {I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}} ) was obtained with appropriate drain-induced barrier lowering (DIBL). Besides, reduced intrinsic gate delay ( {C}_{\text {gg}} ) properties and OFF-state leakage current were identified. In addition, the reason of increased OFF-state leakage, which can be shown when {L}_{\text {ext}} shrinks with extending {T}_{\text {hk}} , was also investigated. Finally, the optimized electrical characteristics were obtained when {T}_{\text {hk}} is adjusted with {L}_{\text {G}} and {L}_{\text {S/D}}. The power was reduced about 27% with the same performance and 18% enhanced performance was obtained when {T}_{\text {hk}} is optimized through {L}_{\text {G}}. On the contrary, reduced OFF-state leakage current and DIBL were confirmed in the case of optimization point with {L}_{\text {S/D}} , which result in lower static power. Based on this comparison, optimization method and guideline for high- {k} IL was proposed.