Abstract: A deformable minor system comprising: a deformable mirror surface; a plurality of actuators coupled to the mirror surface to deform the minor surface; and a detector coupled to the actuators to detect, for each actuator, an output signal from a driver of the actuator; and a controller coupled to each of the plurality of actuators, wherein the controller is configured, for each actuator, to: add a test signal to an input signal to form a modified input signal; send the modified input signal to the actuator; receive an indication of the output signal from the driver; determine when a test signal portion of the output signal satisfies a threshold condition; and in response to the test signal portion satisfying the threshold condition, control a subset of adjacent actuators to execute a shutdown sequence.

Abstract: The present invention relates to an apparatus for generating a magnification compensation signal for use in a scanning electron microscope. The apparatus includes an electron beam generator that generates a beam at a predetermined energy level in accordance with a beam energy signal. The apparatus allows for refocussing by varying the beam energy signal about a nominal value corresponding to the predetermined energy level. The apparatus also provides a magnification compensator producing a magnification compensation signal that varies in accordance with the variation of the beam energy signal from the predetermined energy level.

Abstract: The present invention relates to an apparatus for calibrating the magnification of a scanning electron microscope. The microscope includes a generator for generating an electron beam, a scanning signal generator for producing a scanning signal and a unit for scanning the beam. The apparatus is comprised of a calibration object which has a plurality of aligned elements thereon which, when scanned by the electron beam produces a signal having a frequency which has a fundamental periodicity dependent on the spacing of the aligned elements. A detector is provided for detecting the signal and producing an output signal having a data content and the fundamental periodicity. A unit is connected to the detector for determining the fundamental periodicity of the output signal from the entire data content of the output signal. A control unit is provided for producing a desired magnification signal.

Abstract: A differential thermal wattmeter of the type disclosed in U.S. Pat. No. 4,045,734 is modified to remove undesirable in-phase a.c. ripple at the fundamental frequency in the feedback path. This result is achieved by a closed loop system in which the in-phase signal in the feedback path is detected and driven to zero by injecting sufficient signal in opposite polarity into the feedback path to cancel the ripple. The advantages are reduction of error and the ability to use standard, low cost components.