2 D analysis of self aligned LDMOS structures in terms of breakdown voltages

Abstract

This paper deals with breakdown voltage studies on a new Lateral diffusion MOSFFET(LDMOS), structure and dependence of the breakdown voltage, on state resistance etc., on the doping profile such as drift length under field oxide, diffusion time and the Lightly Doped Drain (LDD) dose. In this new structure the channel region (p body) and the LDD structure were formed by a self-aligned process. This approach leads to saving of one mask level during fabrication. On state resistance is also studied in these structures and an optimum drift length has been arrived at. It is shown that the breakdown voltage depends on the drift length only up to a certain value beyond which the breakdown voltage remains nearly constant. Breakdown voltages close to 100 V have been obtained in these structures. On state resistance is also studied in these structures and an optimum drift length has been arrived at. A 2D analysis was carried out on the various parameters such as the horizontal and vertical electric field patterns, the impact generation profiles, generation recombination, impact generation before and after breakdown, the carrier concentration, electron and hole current densities and the conduction current densities of the structure. The results are compared with a similar structure where there is no selfaligned structure.