Daniel R. Marshall

A Closed-Loop Optical Scan Correction System for Scanning Probe Microscopes

Piezoelectric actuators are widely used for scanning probe microscopes (SPMs) because they are capable of motions that can be continuously subdivided down to atomic dimensions and smaller. These actuators have three serious drawbacks -- drift, hysteresis, and nonlinearity of displacement versus driving voltage -- that have limited the usefulness of scanning probe microscopes as metrology instruments capable of accurate dimensional measurements down to the nanometer level. This paper describes a novel optical method for measuring and actively controlling multiple translational degrees-offreedom at a single location in a scanning probe microscope using a folded retroreflector. Shot noise-limited resolution is shown to be less than 0.1 nm. This scanner was incorporated in a scanning probe microscope and its performance was characterized. Measured distortion is less than 1% over a 100 p.m x 100 p.m scan range. Lateral thermal drift is less than 0.45 µm per hour.

Focus sensing method with improved pattern noise rejection

Focus error sensing is a subject which has received much effort and ingenuity as the optical data storage industry has matured, yet there is still a need for techniques which provide improved accuracy, responsiveness and noise immunity. This paper discusses a class of techniques which demonstrate common mode rejection of signal corruption, and a particular member of that class which is based on lossless reflection at an interface.