Cross contamination due to dopants in single chamber deposition systems

Abstract

Cross contamination due to dopants in a single chamber deposition system for amorphous silicon is investigated. Deposition of intrinsic a-Si:H, just after the deposition of a doped layer, yields a contaminated material. In order to minimize the effects of the dopants in such a deposition system, an intermediate intrinsic buffer deposition has to be made before obtaining a device quality material. Since, this extra deposition is a time and material consuming step, thickness of this buffer layer must be optimized for various dopants used. In a load-lock single chamber deposition system, a series of intrinsic depositions are made as intermediate buffer layers after N type, and wide bandgap P type depositions. To determine the minimum thicknesses of these layers which are required to eliminate the effects of the dopants, optical and electrical measurements are used for characterization. We have also investigated the compensation caused by different types of dopants used in successive depositions without an intermediate buffer layer. Results indicate that cross contamination produced by P deposition requires at least 1.8 μm of intrinsic buffer layer in order to obtain device quality I layers. Similarly, for N type deposition, buffer layer must be at least 1.2 μm thick. Deposition of P layer just after an N layer did not produce a noticeable change in electrical and optical properties of P layer. On the other hand, activation energy of N layer deposited just after a P layer increased, indicating a compensation effect due to cross contamination.