Alpha-Particle Shielding Effect of Thick Copper Plating Film on Power MOSFETs

We investigated characteristics impact of alpha-particles irradiation to power MOSFETs and demonstrated alpha-particle shielding effect of thick copper plating film on a power MOSFET. We used americium-241 alpha-source for irradiating alpha-particles to the surface of the power MOSFET die. Irradiation under gate-source bias caused threshold voltage (Vth) decrease due to generated trapped holes in gate oxide, however, no Vth shift occurred under drain-source bias. We found that sensitivity to alpha-particles depends on gate structures of trench or planar. Recovery behavior of Vth shift by gate bias or thermal annealing support the hole trapping model in the gate oxide. We evaluated alpha-particle shielding effect of thick copper plating film. We demonstrated more than 15 micrometer thick copper plating on the power MOSFET shielded alpha-particles successfully.

I. Introduction

Continuous cell pitch shrinking of trench power MOSFET has achieved significant chip On-resistance reduction in last three decades [1], [2]. Furthermore, charge coupling technologies such as superjunction [3] and trench Field Plate (FP) MOSFET [4] drastically reduced drift layer resistance and overcame silicon limit. In addition, copper clip source connection technology decreased parasitic package resistance [5], which is especially important for low voltage devices. These technologies enabled us to realize extremely low on-resistance power MOSFET.