Rapid-thermal annealing of a polysilicon-stacked emitter structure

Second-duration rapid-thermal annealing technique is applied to an As drive-in process from a stacked CVD poly-Si film for shallow emitter formation. Highly effective dopant activation, especially in the stacked film, can be achieved without deep As diffusion into the substrate. Transformation of the poly-Si film into single crystal through a kind of secondary recrystallization, i.e., epitaxial grain alignment is a substantial cause for effective activation in the film. High-frequency bipolar transistors with rapid-annealed emitters are demonstrated in comparison with conventionally processed ones to show technique feasibility.