Process-Induced Random Variation: Work-Function Variation in Stacked Nanowire Field Effect Transistor.

Area of Science:

• Semiconductor device physics
• Nanotechnology
• Materials science

Background:

• Work function variation (WFV) is a critical factor affecting the performance of advanced semiconductor devices.
• Stacked nanowire field effect transistors (stacked NWFETs) offer enhanced performance but require careful analysis of WFV effects.
• Understanding WFV impact is crucial for optimizing gate materials in high-k/metal gate stacks.

Purpose of the Study:

• To investigate the impact of work function variation (WFV) on stacked nanowire field effect transistors (stacked NWFETs).
• To quantitatively analyze how the number of stacks and inter-nanowire distance influence WFV-induced threshold voltage (VT) variation.
• To explore mitigation strategies for WFV effects in stacked NWFETs.

Main Methods:

• Utilized technology computer-aided design (TCAD) simulations to model stacked NWFETs.
• Incorporated metal grain granularity with varying work function values and probabilities to represent gate materials.
• Systematically varied the number of nanowire stacks and the distance between nanowires.

Main Results:

• WFV-induced threshold voltage (VT) variation is effectively suppressed in gate-all-around nanowire structures due to smaller effective grain sizes.
• Increasing the number of stacked nanowires in stacked NWFETs significantly suppresses WFV-induced VT variation.
• The distance between nanowires in stacked NWFETs was found to have no discernible impact on WFV-induced VT variation.

Conclusions:

• The number of stacks is a key design parameter for mitigating WFV effects in stacked NWFETs.
• Device scaling and architectural choices in stacked NWFETs can be leveraged to manage performance variations.
• Further research can explore alternative gate materials and fabrication techniques to minimize WFV impact.