Abstract: A computed axial tomography (CAT) system including a ring assembly surrounding a location at which the object is placed; an X-ray source mounted on the ring assembly; an array of X-ray sensors arranged on the periphery of the ring assembly for measuring X-ray intensity from the object; a drive motor for rotating the ring assembly about the object; measurement control circuitry controlling the drive motor, receiving data from the array of X-ray sensors and generating a plurality of vectors of X-ray data therefrom, said plurality of vectors being represented by a measured column tensor; a memory for storing the measured column tensor; and a computer programmed to left multiply the measured column tensor stored in said memory by a reconstruction tensor T to obtain an estimate of a desired measurement column tensor, wherein said reconstruction tensor T is equal to R.sub.dm R.sub.mm.sup.-1, R.sub.

Abstract: A method and apparatus involving the use of a thickness measurement probe having a predetermined resolution to measure the thickness of a wafer over a two-dimensional area of the wafer, the method including sampling the measured thickness of the wafer with the probe to generate an image of the two-dimensional area of the wafer, the image being a two-dimensional array of measurements, each measurement representing a measurement of the thickness of a different region of the two-dimensional area, the two-dimensional array of measurements being represented by a measured column tensor; and left multiplying the measured column tensor by a reconstruction tensor T to obtain an estimate of a desired measurement column tensor, where the reconstruction tensor T is equal to R.sub.dm R.sub.mm.sup.-1, R.sub.dm being a cross-covariance tensor computed for d, a desired measurement column tensor, and m, the measured column tensor, and R.sub.

Abstract: A lithographic system, having a stepper and exposure station built on a block of granite attached to the ground using isolation legs, includes a servo control system for providing signals a motor associated with the stepper to control the movement of the stepper. The control system includes means to calculate a filter formula used to generate the control signals, which formula is calculated in response to the initial velocity, the movement of the stepper and a certain time between discrete movements, so that a minimum amount of energy is utilized. The filter formula requires that the difference in the velocity of the base and the stepper be zero at the time the stepper reaches the final position. Where time is short, both the base and the stepper initially move with the same velocity and end with the same velocity, and an array processor calculates the time varying filter formula.

Abstract: An automatic wafer flatness station is disclosed for obtaining a flatness profile of a semiconductor wafer or other sample from thickness data. The sample to be flatness profiled is supported so that it maintains its natural shape. A processor coupled to a capacitive thickness sensing head and to the support medium is operative to successively position each of a plurality of preselected points of the sample into proximity with the capacitive thickness sensing head for measuring the thickness of the sample at the corresponding point. An analog-to-digital converter converts the thickness measurement into data that is stored in a data table in system memory, the individual addresses of which correspond to the spacial location on the sample of each such preselected point. The processor is operative after the data table is compiled for each sample to compute the flatness profile of one surface therefrom relative to a selectable plane.

Abstract: The present invention discloses means and method for obtaining an increased spacial resolution from a sensor that includes a probe having a characteristic physical dimension that limits its spacial resolution. Such a probe may include a rectangular sensing surface wherein the probe sensitivity increases with surface area while the spacial resolution decreases with increasing surface area. The probe and an object to be measured are controllably moved relatively to each other in such a way as to define preselected increments of relative movement that are selected to be a fraction of the characteristic physical dimension of the probe.

Abstract: The present invention discloses apparatus and method for electronically determining and compensating mechanical fixture induced errors from desired object related information in a measurement system such that data acquisition is obtained with a precision very much better than the manufacturing tolerances of the mechanical fixture. In the preferred embodiment, bow and warp profiles of a semiconductor wafer are obtained with an X, .theta., and Z moveable wafer-receiving chuck that have an accuracy very much better than the mechanical tolerances of the X, .theta., and Z moveable chuck. The system provides for measurement of objectrelated information in plural orientations. Signal processing is disclosed for separating out of the object related information X and .theta. fixture induced error contributions to the data arising from mechanical tolerance of the fixture. Signal processing is disclosed for compensating bow and warp profiles of semiconductor wafers in accordance with the X and .theta.

Abstract: An automatic wafer alignment station is disclosed for aligning a wafer having flats about its centroid with the flats oriented in a preselected spatial direction. The wafer is held by a vacuum chuck which is operatively connected to a motor driven carriage for controlled movement about an X axis, to a .theta. actuator carried by the carriage for controlled rotation about the axis of the chuck, and to a Z actuator carried by the carriage for controlled motion about a Z axis. An X capacitive sensor and a Z capacitive sensor are positioned near the wafer. An X processing and Z compensating circuit is responsive to the X and the Z capacitive sensor output signals and provides an electrical signal that has values which exclusively represent the position of the edge of the wafer along the X axis only over a predetermined angular range. Circuit means including an A/D converter and a microprocessor respond to the electrical signal and produce a plurality of corrective signals to the X, Y, and .theta.