Electrical characterization of hole transport in heavily-doped shallow implanted emitters

Abstract

Heavily-doped shallow implanted layers are now commonly employed in modern VLSI technology. The knowledge of minority carrier transport in these shallow layers is still sparse, in particular in very heavily doped regions. The purpose of this paper is to present a simple method for the characterization of hole transport in shallow emitters with electrical measurement only. The d.c. transport parameters were estimated based on numerical simulators. The test devices were fabricated in a well-controlled industrial BICMOS processing line. Emitter defects were eliminated by gettering the back-side of the wafers with P. Our measurements for the hole diffusion length as a function of donor density show good agreement with the empirical expression by del Alamo and Swanson (del Alamo and Swanson, IEEE Trans. Electron Devices ED-34, 1580, 1987). While the measured product of equilibrium hole concentration and diffusion coefficient is somewhat lower than that proposed by their empirical expression, which is attributed to the degeneracy effect in the very heavily doped Si. No strong degradation in the hole lifetime was observed. We have extended the donor concentration to 1.75 × 10 20 cm −3, which is very important for modern bipolar transistors.