Thickness measurement of combined a-Si and Ti films on c-Si using a monochromatic ellipsometer

摘要

The authors investigate the possibility of using monochromatic ellipsometry to measure the thickness of amorphous silicon (a-Si), titanium (Ti) and a-Si/Ti overlayers on crystalline silicon (c-Si) substrates. Accurate thickness control of these layer structures are very important in titanium silicide straps formation which are often used as interconnects in integrated circuits. Films with different layer structures, a-Si/c-Si, Ti/c-Si and a-Si/Ti/c-Si are analyzed using a monochromatic ellipsometer operated at 6328 angstroms. The thickness of the desired layer is derived from the theory of ellipsometry implemented on a home-made computer program by knowing the optical constants of the layers from literature. The results illustrate that it is possible to measure the aforementioned layer thicknesses using a commercially available monochromatic ellipsometer. However, the results are sensitive to such factors as native oxide thickness, inaccuracy of the angle of incidence during the experiment, and uncertainty in the layer optical constants. We illustrate the aforementioned sensitivities. Simulation results and a comparison of measurements with theory are discussed.