Avalanche Capability Improvement by Optimizing p+ Contact Resistance for N-Channel Trench Power MOSFETs

In the process of Nch silicon MOSFET, BPSG is generally used as an interlayer film. BPSG has the purpose of gettering mobile ions and reflowing the BPSG film by annealing to reduce the steps on the wafer surface. This annealing process also activates the p+ diffusion layer. However, because the annealing temperature at which BPSG is reflowed is high, phosphorus oxide diffuses outward from the BPSG film and penetrates into the contact part. If the contact resistance increases, a serious problem occurs in which the avalanche capability decreases. We have devised two countermeasures to this problem and verified them through experiments. By changing the annealing conditions and increasing the titanium thickness, we were able to reduce the p+ contact resistance by 3 to 4 orders of magnitude and confirmed an improvement in avalanche capability. These countermeasures can be used universally by adjusting them even if the annealing condition changes.