Evaluation and Control of Grain Boundaries in Laser-Recrystallized Polysilicon Islands for Device Fabrication

Directions of grain boundaries in laser-recrystallized polycrystalline silicon (polysilicon) islands are found to be arranged along with the laser scan direction, and are connected to the electrical characteristics of MOSFETs fabricated in polysilicon islands. In the case of the laser scan parallel to the channel direction, grain boundaries work as fast-diffusion paths of arsenic from source and drain into the channel, and results in a decrease of effective channel length of MOSFET. But in the case of the laser scan perpendicular to the channel direction, there are few grain boundaries contributing to diffusion paths of arsenic. The maximum electron mobility of 590 cm²/V sec approaching to that on a single crystalline silicon can be obtained in devices with a channel length of 3 µm, though grain boundaries work as an additional potential barriers for carriers. A nine stage ring oscillator is fabricated by applying these results. The minimum propagation delay of 38 nsec is obtained.