Defect detection on SOI wafers using laser scattering tools

Laser scattering tools are used in production monitoring of wafer defectivity. We present SOI wafer specific behavior related to the intrinsic limitations of laser scattering defect detection. An empiric model of accessible thresholds regarding layer thickness is proposed. When removing roughness induced haze on an SOI structure, the haze level of SOI wafers is clearly linked with structure reflectivity. Since the haze varies in the reverse order of the reflectivity, the defect measurement threshold needs to be adapted to avoid reflectivity induced false counts in wafer characterization. Wafer uniformity must also be considered when choosing the measurement threshold, especially in the case of very thin silicon layers, typically targeted for fully depleted applications. For these advanced applications the laser used in detection tools will have to move to UV light in order to reach detection limits under 0.16 /spl mu/m as required by ITRS roadmaps.