Development review of an angle-resolved light scatter (ARS) sensor LARISSA

Scatterometry is a powerful and fast measurement method to measure surfaces and its properties. The backscattered light from a coherently illuminated surface contains information about integral surface topography constants, material properties, surface defects and contamination. This paper is a continuation a previous paper. In this paper the development of the angle resolved light scatter sensor system LARISSA (Large Dynamic Range Intelligent Scatter Sensor Approach) will be reviewed. In the first part of the paper the system components will be outlined. The system consists of an elliptical mirror optics and a CMOS photodiode detector array. The elliptical mirror optics enables the angle resolved and the integral scatter measurement in a solid angle of Pi sr. The CMOS photodiode detector array consists of 32k single detector elements which are aligned in a circular form. Each single detector element is calibrated in a dynamic range of 7 decades of intensity. The ARS system can be used to realize a scatter measurements without moving parts which is a significant advantage in speed over conventional goniometer setups. In the second part of the paper typical applications will be described which were examined by using the ARS system. Thereby surface roughness measurements in a rms range of 4..32 nm on smooth metallic surfaces will be considered by using BRDF measurements and the Rayleigh-Rice theory. In the third part of the paper the theoretical performance limits of surface roughness measurement will be derived based on measurements and simulation models. Finally the development and measurement results will be summarized and further the system will be outlined.

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