Effect of surface treatment on dopant diffusion in polycrystalline silicon capped shallow junction bipolar transistors

Abstract

The outdiffusion of boron and arsenic was studied as a function of surface treatment prior to polycrystalline silicon (polysilicon) deposition in the fabrication of bipolar transistors. Secondary ion mass spectrometry and spreading resistance probe analyses were performed to measure boron, arsenic, and concurrent boron-arsenic diffusion after ion implantation and annealing of an undoped (0.25 μm) polysilicon layer. The presence and integrity of an interfacial oxide were examined by Auger electron spectroscopy and transmission electron microscopy. The (20 Å) oxide was found to reduce arsenic diffusion with no effect on boron diffusion. Boron diffusion was reduced in the presence of arsenic and boron was found to reduce arsenic diffusion. The most dramatic reduction in arsenic diffusion occurred when an interfacial oxide and boron were present.