The effect of deterministic spatial variations in retrograde well implants on shallow trench isolation and latchup immunity

The retrograde well implants for sub-0.18 μm CMOS are done at a normal or near-normal incidence to minimize shadowing due to the thick photoresist edges. The endstation geometry in the high energy implanter results in an incident angle variation across the wafer, which causes strong spatial variations in the well profile and can negatively affect device performance. We show that the spatial variations can have significant impact on shallow trench isolation (STI), latchup immunity, well resistance and capacitance. The spatial variations can cause in a deterministic way the failure of a large number of isolation structures on a single wafer