Mario Längle

Pattern placement metrology using PROVE high precision optics combined with advanced correction algorithms

Photolithography is the key technology of the chip production in semiconductor industry. Increasing demands on wafer overlay requirements lead to increasing demands on registration accuracy of photomasks. The PROVETM photomask registration metrology tool has been developed by Carl Zeiss SMS to address the need for high imaging resolution in combination with excellent measurement performance. This paper reports the current status of PROVE™, highlighting its optical performance and correction algorithms. The tool is designed for 193 nm illumination and imaging optics, which enables at-wavelength metrology for current and future photomask manufacturing requirements. Registration and line width metrology is offered by the optical beam path using transmitted or reflected light. The opportunity of selecting optimized illuminations allows a smart adaption of the tool to the measurement task. The short wavelength together with a numerical aperture of 0.6 allows sufficient resolution down to the 32 nm manufacturing technology requirements. The stable hardware platform and the newly developed PROVE™ high precision optics enable a short term repeatability of less than 0.5 nm (3sigma). Distortion can be calibrated by using advanced image analysis and self calibration methods. The optical correction of the entire field of view delivers the requested screen linearity of less than 1 nm. It is shown, that the calculated optics correction is valid for different structure types and all kind of illuminations.