COMPARATIVE-STUDY OF POLYSILICON-ON-OXIDE USING SPECTROSCOPIC ELLIPSOMETRY, ATOMIC-FORCE MICROSCOPY, AND TRANSMISSION ELECTRON-MICROSCOPY

Polysilicon layers prepared by low pressure chemical vapor deposition (LP-CVD) on oxidized silicon were measured by spectroscopic ellipsomet ry (SE), atomic force microscopy (AFM), and transmission electron micr oscopy (TEM). SE was used to determine layer thicknesses and compositi ons using multi-layer optical models. The measured spectra were simula ted and fitted using a linear regression algorithm (LRA). The dielectr ic function of composite materials was calculated by the Bruggeman eff ective medium approximation (B-EMA). The dependence of the surface rou ghness and layer structure on the deposition temperature was studied. The interface layer between the buried oxide and the polysilicon layer , which represents the initial phase of growth, was modeled with a thi n layer having polycrystalline silicon and voids. The precision of the SE layer thickness measurements was determined by a comparison with A FM and TEM results taking into account the 95% confidence limits of th e LRA. The root mean square (RMS) roughness values measured by AFM usi ng different scan sizes were compared to the thicknesses of the top la yer in the SE model simulating the surface roughness. It was shown tha t the correlation between the SE and the AFM surface roughness results are affected by the scan size of AFM and the surface characteristics. (C) 1998 Elsevier Science S.A.