An optical profilometer for characterizing complex surfaces under high vacuum conditions

The requirements for high precision metrology devices have increased rapidly in recent years. Furthermore, the applications are spreading to many new branches of science and technology. Hence new demands are appearing which are related not only to classical parameters such as precision and speed but also to other factors including the environment in which the measurements must be performed. In this paper we present a new device for measuring complex surface profiles of samples held under high vacuum conditions. The surface profile is obtained by scanning an optical sensor, held in air, across a standard view-port. The sensor has a lateral resolution of 25 μm and a perpendicular distance resolution of 0.12 μm over a range of 3 mm. The maximum scanning area is a circle, 30 mm in diameter. The device was developed to characterize silicon wafers for use as mirrors for atom optical applications. The mirrors are formed by bending the silicon under an applied electric field, which requires high vacuum conditions to prevent arc discharge. In the last part of the paper we discuss how simulations can be used to determine the required sampling grid spacing for obtaining the surface profile shape with a given accuracy.