A sample scanning system with nanometric accuracy for quantitative SPM measurements

A sample scanning device operating in a working volume of 30x30x18 µm with interferometer and capacitance-based controls of displacements, is described. The xy stage uses plane mirror linear interferometers and fast phase-meters for control of displacements of precise ball-bearing stages driven by piezo flexure actuators. The stage operates with a full range bandwidth of 200 Hz, and an estimated accuracy (k=2) of 3 nm + 1­E-3 L, where L/µm is the lateral displacement. A novel z-stage based on a kinematic coupling between two plates, the upper one being moved by three bimorph plates and the distance being measured by three capacitive sensor, is described. The tilt of the z-stage is kept within fractions of a microrad, leading to a full range estimated accuracy of 2 nm + 2E-3 h, where h/µm is the vertical displacement. The control bandwidth is of about 1kHz, thus allowing fast and accurate step-height measurements. In order to test the device used in a scanning probe microscope, micrometric patterned surfaces made using high resolution e-beam lithography and precise metal deposition on silicon have been imaged. Results of pitch measurements are discussed and compared with those obtained using optical diffractometry.