Abstract: An automatic control servo system having a number of cascaded loops equal in number to the number of voltage sources applied to elements of a high-emittance electron source provides accurate and stable electron emission current control independently of beam energy and accommodates large differences in thermal mass between the elements of the electron source, as may be encountered in high-emittance, indirectly heated cathode electron sources. Individual loops of the system may be critically tuned independently of each other.

Abstract: A positioning stage has a base which carries a stage plate slidably on its upper surface. Three rotatable drives engage both the stage plate and the base to move the stage plate on the base to provide motion along the x and y axes plus rotation. The linear drives each include a motor and a capstan driven by the motor and a drivebar frictionally coupled to the capstan. The stage is spring loaded to provide constant down-load force, regardless of the varying extension length of the drivebar. A ball joint permits varying between the cones and the ball of the ball joint dynamically to desired levels. Pitch, roll, and movement in the Z-axis are precisely maintained by the stage plate. X and Y position are determined by an X interferometer and a Y interferometer, respectively. Yaw is measured by a yaw sensor device for determining yaw angle comprising a light emitting source and a position sensing detector, which generates an analog signal that is the input to a yaw servo to correct yaw error.

Abstract: Accuracy of correction of offset drift with temperature and noise are corrected in a high voltage, high current amplifier is improved by thermal isolation and/or temperature regulation of another amplifier having greater gain and connected to a different power supply in a closed loop feedback servo system. A clamping network connected to the higher gain amplifier to avoid hard saturation due to transient feedback signals from a reactive load, especially an inductive load, also prevents hard saturation of the high voltage, high current amplifier. An adjustable feedback circuit connected to the higher gain amplifier allows adjustment to obtain critical damping of a second order system and faster response to achieve proportionality of output current to input voltage with an accuracy of very few parts per million error and with minimum settling time.

Abstract: A system for aligning an electron beam relative to a workpiece employs an alignment fixture immediately above the workpiece fixture through which the electron beam passes. Lateral laser alignment beams in two axes reflect off the alignment fixture to determine alignment fixture position relative to the workpiece fixture by differential interferometry. Energy alignment beams are split off from the electron beam and hit multiple diode detectors mounted on the alignment fixture. The detectors provide an output signal based on the amount of surface area hit by the energy alignment beam to determine the position of the electron beam relative to the alignment fixture. Servo controls use this real time position information to control the precise position of the electron bean relative to the workpiece by making last minute corrections to the electron beam just before it hits the workpiece.

Abstract: A system for aligning an electron beam relative to a workpiece employs an alignment fixture immediately above the workpiece fixture through which the electron beam passes. Lateral laser alignment beams in two axes reflect off the alignment fixture to determine alignment fixture position relative to the workpiece fixture by differential interferometry. Energy alignment beams are split off from the electron beam and hit multiple diode detectors mounted on the alignment fixture. The detectors provide an output signal based on the amount of surface area hit by the energy alignment beam to determine the position of the electron beam relative to the alignment fixture. Servo controls use this real time position information to control the precise position of the electron bean relative to the workpiece by making last minute corrections to the electron beam just before it hits the workpiece.

Abstract: An electron beam nanometer-level metrology tool includes an ambient temperature electron source and a movable stage for mounting a workpiece. The stage is adapted to position the workpiece's surface in a beam interrogation region. Electrostatic focus lenses convert electrons emitted by the electron source into a beam with a focal point that is positioned in the beam interrogation region. The lenses cause the electron beam to traverse a path that is generally orthogonal to the workpiece surface. Along the beam path are positioned upper and lower electrostatic deflection plates which are connected to an adjustable voltage source that applies ganged, opposite-sense d/c potentials thereto. Those potentials enable a scanning of the beam across the beam interrogation region while the beam remains substantially orthogonal to the workpiece surface, thereby enabling more accurate measurements of surface features.

Abstract: A stage positioning apparatus including a stage and a servo control system. The servo control system includes a compensation circuit. The compensation circuit determines the cosine of the angle between the off-axis drive bar and the direction of travel. A voltage, proportional to the cosine, is multiplied by the on-axis drive error signal to develop an off-axis compensation voltage. Each drive's new error signal is compensated by its respective off-axis compensation voltage.

Abstract: A positioning stage has a base which carries a stage plate slidably on its upper surface. Three rotatable drives engage both the stage plate and the base to move the stage plate on the base to provide motion along the x and y axes plus rotation. The linear drives each include a motor and a capstan driven by the motor and a drivebar frictionally coupled to the capstan. The stage is spring loaded to provide constant down-load force, regardless of the varying extension length of the drivebar. A ball joint permits varying between the cones and the ball of the ball joint dynamically to desired levels. Measurement of position is provided by integrated, parallel dual axis plane mirror interferometers.

Abstract: This system employs writing of lithographic patterns with a shaped electron beam exposure system which minimizes the time wasted by workpiece positional requirements. The writing field contains an array of sub-fields written in a raster sequence. The large width of the writing field provided by the VAIL system reduces the number of mechanical scans required to write the pattern on the workpiece which further reduces the time required for workpiece positioning. When patterns are being superimposed over previously written patterns, registration is employed. This system includes a registration field confined to local areas on the workpiece, which is larger than the writing field, without requiring change in focus and without requiring the mechanical system comprising the X-Y work table to change speed during the registration and reregistration of the various fields on a semiconductor wafer or mask.

Abstract: An electron beam is aligned with the center of an aperture in a plate in the path of the beam by cyclically scanning the beam across the aperture through equal distances on opposite sides of an initial beam location, measuring the beam current that flows through the aperture when the beam is on opposite sides of the initial location, which opposite sides correspond to adjacent half cycles of the scan, determining the difference in beam currents flowing in adjacent half cycles, and deflecting the beam in a direction toward the center of the aperture until there is reached a condition wherein the difference in currents is zero, which condition indicates that the beam is aligned with the center of the aperture. The currents may be measured by converting them to signals having a frequency proportional to the current, counting the signal cycles during each half cycle, and then subtracting the count for one half cycle from that of an adjacent half cycle.

Abstract: An automatic focus correction system for E-beam lithography uses optical light from a narrow angle light source to illuminate a horizontal slit, the image of which is projected onto a target surface. Prior to and after reflection of the slit image from the target surface the light beam is projected parallel to the target surface to minimize vertical space requirements in the E-beam column. Variations in height, z-position, cause the slit image to move vertically and the focus of reflection to shift laterally and this image is redeflected in the horizontal plane by a prism to a linear diode array used to produce a video-type output signal. Autofocus electronics are used to convert the video output signal into an analog correction signal to the E-beam fine focus coil. The video-type signal is also converted to a digital height value to be used for corrections in beam magnification and rotation.

Abstract: A method and apparatus for applying focus correction to an E-beam or charged particle system to compensate for wafer warp and mask tilt. In an electron beam system including a registration system which measures the position of four registration marks with the beam and calculates the apparent magnification error of a given chip, means are also provided for using magnification and rotation error information to calculate a height error factor and to apply a compensating current to a dynamic focusing coil of the electron beam to move the effective beam focal plane to a position which matches the wafer or mask plane at each chip site.

Abstract: The location of a beam of charged particles within a deflection field is determined by its orthogonal deflection voltages. With the location of the beam in the field, correction currents are supplied to a focus coil and to each of a pair of stigmator coils to correct for change of focal length and astigmatism due to the beam being deflected away from the center of its deflection field.