Study on poly depletion in sub-0.1 μm metal–oxide–semiconductor field effect transistors by scanning capacitance microscopy

We study the relative changes in active concentrations in the n- and p-type poly gates of 90 nm node metal–oxide–semiconductor field effect transistors (MOSFETs) by scanning capacitance microscopy on beveled and backside etched samples. We polished and etched from the backside of MOSFETs to expose the bottom of poly gates. Measurements at different Lg show that the boron and phosphorus concentrations in short-channel devices are lower than in long-channel ones. By using staircase calibration standards and NIST FACTC2D, we estimate that boron concentration is reduced by about 5× while phosphorus concentration is reduced by about 2× when Lg shrinks from 10 μm to 50 nm. The effects of high-frequency voltage on quantitatively determining the dopant concentration are discussed. By beveling the poly, we are able to get the lateral dc/dv profiles in Lg=50 nm MOSFETs. The active boron concentration is lower at the p-poly edge while the phosphorus profile is flatter in n-poly.