Eiichi Izumi

Active vibration suppression on an image of a scanning electron microscope

This paper proposes a new approach to reducing an effect of floor vibration on an image of a scanning electron microscope. An image-shifting coil is used to move the electron probe in order to cancel undesirable motion of a specimen due to the floor vibration. The floor vibration is structurally transmitted through the microscope and detected by two acceleration sensors at the root of the specimen chamber of the microscope. The outputs of the acceleration sensors are fed forward into a controller to move the electron probe by the image-shifting coil. The feed-forward controllers are designed in two ways. The first one is based on a transfer function from the sensor outputs to the relative displacement of a specimen to the electron probe being at rest. The microscope is put on a table attached to a shaker. Sinusoidal excitation tests are done many times to estimate the transfer functions from vibrating images of a micro scale. Moreover, the second controller is designed by manually amplifying and delaying the sensor outputs so as to minimize amplitude of the vibrating images on a CRT. Those two controllers are implemented as a digital filter running on a digital signal processor.