Failure Mechanism of Aluminum Diffusion in Low-Voltage Trench MOSFET With High Cell Density

Abstract

In this paper, a low-voltage trench metal oxide semiconductor field effect transistor (MOSFET) with high cell density is researched on the process design. The experimental device pitch is reduced to 0.5 ${\mu }\text{m}$ by three-dimensional (3-D) design of P plus region and self-aligned process, while the contact between silicon and metal is convex rather than the concave in conventional trench MOSFET. BV failure was founded because of the particularity of this structure and the failure is caused by the diffusion of aluminum (Al) into the drift region during the final alloy step in the metal forming process. This paper reveals the mechanism of Al / Silicon (Si) double diffusion and presents the refined surface metal film, which can suppress reverse diffusion and forward diffusion simultaneously. The risk of failure is reduced and functional devices are obtained by the application of the proposed surface metal film. Furthermore, it is recommended to use TiN layers in a total 50 nm as the barrier layer in the metallization process to provide a certain diffusion length and the fabricated device achieves a low specific on-resistance of 3.58 $\text{m}\Omega \cdot $ mm ² with a corresponding breakdown voltage of 26.2 V eventually.