LOCOS vs. shallow trench isolation latch-up using MeV implantation for well formation down to 0.18 μm design rules

We report on a detailed comparative study of various MeV twin and triple well structures with either LOCOS or STI (shallow trench isolation) isolation structures for latch-up resistance for 0.35 μm, 0.25 μm and 0.18 μm design rules. Diffused twin well, retrograde twin well, BL/CL (buried layer with connecting layer) twin well, BILLI (buried implant layer for lateral isolation) twin well and modified BILLI (BILLI+BL) twin well structures were all compared at various energies and doses. For LOCOS isolation structures the modified BILLI structure gave the best latch-up performance, delaying the need for STI until 0.18 μm design rules. With STI, the modified BILLI structure also gave excellent latch-up isolation characteristics with the additional benefit of process simplification. Good defect control with excellent gate oxide integrity was achieved. The BILLI triple well structure was also found to be most desirable for triple well technology, since blanket buried layer designs cannot be used