Development of self-aligned polysilicon-gate MOSFETs in 6H silicon carbide

Nan-Hsi Pan, Purdue University

Abstract

Silicon carbide is a wide bandgap semiconductor with remarkable thermal and electronic properties. Unlike other wide bandgap semiconductors, silicon carbide can be thermally oxidized with dry and wet oxidation techniques. MOS transistors have been fabricated with a non-self-aligned process in 6H-SiC by several research groups. The many advantages with the self-aligned process, including reduction of the MOSFET channel length and the dimensions of SiC integrated circuits, become the motivation of this research. The difficulty in fabricating self-aligned MOSFETs in 6H-SiC arises because a high temperature implant activation anneal (typically 1200-1500$\sp\circ$C) must be performed after the gate oxide and polysilicon gate electrode are formed. We are thus faced with conflicting requirements for adequate activation of the implant while maintaining the integrity of the polysilicon gate and underlying oxide. We have measured capacitance-time (C-t) transients on n-type 6H-SiC MOS capacitors to obtain information on the generation lifetime near the SiO$\sb2$/SiC interface. Surface-channel n-MOSFETs in 6H-SiC are fabricated with n$\sp{+}$ polysilicon gates on thermally grown gate oxide (80 and 25 nm) using a self-aligned process. Thermal activation of nitrogen-implanted 6H-SiC is studied, which is important for fabrication of self-aligned MOSFETs and other devices in silicon carbide.

Degree

Ph.D.

Advisors

Cooper, Purdue University.

Subject Area

Electrical engineering|Condensation|Materials science

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