Surface Slope Metrology: High Precision Tilt Stage Achieves 30nrad Absolute Accuracy

A recent paper shows significant advances in the accuracy of long trace profilers, auto-collimator based deflectometers, and other surface metrology instrumentation. Scientists at the ALS X-Ray Optics Laboratory, HZB/BESSY-II and PTB devised a new universal calibration method for deflectometers.  One key component in the system is a high accuracy, piezo-motor-driven flexure tilt stage developed in collaboration with PI (Physik Instrumente). Overall absolute accuracy of better than 30nrad over the entire instrumental dynamic range was achieved.  The flexure stage is made of invar for higher long-term stability and equipped with a pair of 60-picometer resolution SONY LASERSCALE® linear encoders, fed back to a modified E-712 digital piezo controller. The differential evaluation cancels out parasitic linear errors to get the best possible reading of the true angular values.