Development of a new type of optical microscope

Along with the development and application of nanometer technology, a machine that allows deterministic position and manufacturing at the atomic level is required. An optical microscope of the machine was designed particularly to locate line features on a grid plate. It was designed to achieve nanometer level repeatability. The microscope uses a modulated light-emitting diode as its light source. It has two channels for optical imaging: one consists of two slits for precision measurement of line positions and the other of a camera for direct visual observation. A lock-in amplifier is used for demodulating the electrical signal from the photodiodes behind the slits. Initial experiments locating crosses on a grid plate indicate a repeatability of approximately 1 nm, one standard deviation. It was found that the measured line position is related not only to the focus but also to the illumination. There exists a particular orientation of the illumination where the measured line position is relatively insensitive to the focus, because of which the microscope is able to achieve nanometer level repeatability. Repeated measurements were performed on both an uncalibrated and a calibrated plate. Repeatabilities of better than 1 nm were obtained over time periods of several days; however, the ultimate accuracy of the machine still has to be demonstrated.