Measurement of semi-isolated polysilicon gate structure with the optical critical dimension technique

The semiconductor road map predicts the production of sub-100 nm transistor gates that push further the limits of the size and speed posed by 180 nm gates that are currently in use. With this decrease in gate size, it has become extremely critical to measure these lines accurately using nondestructive techniques. The optical critical dimension (OCD) technique is emerging as one of the most promising CD measurement techniques for sub-0.1 μm device fabrication. Compared to CD scanning electron microscopy and X-SEM, OCD has several distinct advantages. It is nondestructive, has a fast turnaround time, is sensitive to sidewall profiles, and has sensitivity to sub-100 nm linewidths. It has been successfully used in important structures such as photoresist, shallow trench isolation, and polysilicon and tungsten silicide gates. In the OCD technique, a broadband polarized light beam is focused onto a grating at angle normal to the grating surface, and the spectrum of zeroth order reflection is measured. The spect...