论文和技术资料

Efficient, stable, and abrupt doping is challenging in semiconductor fabrication, especially in nano-sheet or nano-ribbon transistors. For example, in epitaxial silicon doped above the solubility of phosphorus, most phosphorus dopants are compensated by vacancies. Some of the phosphorus-vacancy clusters can be mobile around seven-hundred degrees centigrade, further reducing doping efficiency. To overcome the challenge, microwave annealing is a promising alternative to conventional thermal annealing. In microwave annealing, microwave can directly interact with the dopant with minimal lattice heating to prevent broadening of the doping profile and formation of unstable defect clusters.

Currently, most microwave annealers use microwaves to heat a susceptor. In turn, the susceptor heats the sample. Our prototype annealer is unique to allow direct microwave annealing without any susceptor. Our annealer uses a silicon waveguide to guide microwave to the silicon sample efficiently and uniformly without reflection.

We use COMSOL Multiphysics® simulations to optimize the design of our microwave annealer. Simulations show that through the silicon waveguide, a magnetron source can deliver an electric field of one-hundred volts per centimeter with five-percent uniformity, while keeping the sample below three-hundred degrees. Adding another magnetron source can increase the field to four-hundred volts per centimeter while heating the sample to one-thousand degrees. Therefore, we can control the sample temperature by adjusting the microwave duty cycle. With optimized duty cycle, preliminary experiments show fourteen-percent reduction in the sheet resistance of thermally annealed samples, indicating enhanced dopant activation.

In conclusion, our microwave annealer selectively activates metastable phosphorus-vacancy clusters by directly interacting with their dipole moments, while preventing lattice heating above seven-hundred degrees. Our approach allows efficient, stable, and abrupt doping in heavily doped semiconductors. It contributes to the advancement in semiconductor device scaling.