RTA Processing of W-Polycide Dual-Gate Sub-Micron Structures for Low-Voltage CMOS Technology

Deep submicron CMOS technology for low-power, low-voltage applications requires the use of symmetric n{sup +}/p{sup +} poly gate structures. This requirement introduces a number of processing challenges, involving fundamental issues of atomic diffusion over distances of 1{angstrom} to {approximately} 30 {micro}m. Two of the critical issues are dopant cross-diffusion between P- and NMOS devices with connected gates, resulting in large threshold voltage shifts, and boron penetration through the gate oxide. The authors show that in devices with W-polycide dual-gate structure most of these problems can be alleviated by using rapid thermal annealing, RTA, in combination with a few additional, simple processing steps (e.g., low-temperature recrystallization of a-Si layer and selective nitrogen co-implants). The RTA step, in particular, ensures that the boron activation in the p{sup +} poly-Si remains high and negates any effects of arsenic cross-diffusion. CMOS devices with properly processed gates have low gate stack profiles, small threshold voltage shifts (< 30 mV), and excellent device characteristics.