In situ layer characterization by spectroscopic ellipsometry at high temperatures

The demand for increased cost-effectiveness in semiconductor manufacturing is the driving force for the development of in situ and in-line measurement tools. Some of the most critical manufacturing steps are high-temperature processes such as thermal oxidation and chemical layer deposition. Solutions for accessing batch furnace processes by high-temperature single wavelength and spectroscopic ellipsometry for layer thickness and composition control have been proposed and studied intensively in the past. These techniques require comprehensive knowledge of the optical parameters at high temperatures. Therefore, a systematical study has been started to determine the optical high-temperature data (refractive index, extinction coefficient) of relevant semiconductor materials. Moreover, optical data of amorphous and polycrystalline silicon at high temperature are under investigation. All measurements were performed with a spectroscopic ellipsometer integrated in a vertical LPCVD-batch furnace. Optical access is provided by a special beam-guiding system. The established data are used to develop models for ellipsometric in situ monitoring of layer structure such as thickness, roughness, crystallinity, or density. Accurate and reliable optical models are particularly required for in situ monitoring of polycrystalline silicon because the optical properties vary considerably, depending on the deposition conditions. A Bruggeman-Effective Medium Approximation (B-EMA) is used to calculate the dielectric function of the layer. This method allows to characterize multilayer structures and to obtain all layer thicknesses and optical layer characteristics from one SE measurement. These models are implemented into the measurement programs and they are already used in a commercial spectroscopic ellipsometer for use in industrial applications.