Abstract: The present invention is directed to a method and apparatus for simulating digital electronic systems. The signal integrity of a digital electronic system is assessed by analyzing traces (e.g. wires between components) for cross coupling. Problem areas are identified by monitoring storage components or output ports of the electronic system. Wires (traces), which carry signal transitions to the storage component or output ports are analyzed and quantified based on timing windows associated with the wires (traces). The clock transitions into a storage device are analyzed and vulnerability windows are identified for the storage device. The vulnerability windows are time periods when cross coupling may occur on a storage device. If a timing window overlaps a vulnerability window the timing window is considered a critical timing window. Devices driving the transition on wires with critical timing windows are then analyzed.

Abstract: A method of characterizing and simulating electronic systems for signal integrity is presented. Each device in the electronic system is associated with at least one vulnerability table and at least one vulnerability window. The vulnerability table is a three dimensional table that characterizes the operation of the device and includes line length on one axis, coupling efficiency on another axis and drivers size of a gate, on the third axis. In addition a number of vulnerability windows are presented. The vulnerability window is a time period when a storage device may store the wrong data because of signal integrity issues in the electronic system. A vulnerability window is developed for each input to a storage device in the system. In addition a vulnerability window is developed based on a number of failure mechanisms used to characterize the system. Lastly, a mapped vulnerability window is presented for devices such as logical gates, which provide input to the storage device.

Abstract: A pattern is aligned and exposed with a lithography system so that chips larger than the deflection field can be formed by exposing M.times.N fields in a mosaic pattern. The method corrects the deflection field to compensate for the orientation of a previous pattern on a substrate and compensates for errors due to height caused by the beam landing non perpendicular to the target. Two basic procedures disclosed are called "3-mark" which are only applicable to 2.times.2 arrays of fields, and "M.times.N" which covers the general situation, but with slightly less accuracy.

Abstract: A dynamic correction arrangement for an electron beam projection/deflection system provides high order correction values for deflection in accordance with a correction equation. Particularly as applied to high accuracy telecentric deflection, the coefficients of terms of the correction equation may be determined by calibration for a small number of test points. Correction values may be stored in a look-up table or computed in real time by using a math co-processor in a processing pipeline. The correction provided corrects landing angle errors through the third order in telecentric projection/deflection systems such as systems utilizing variable axis immersion lenses.

Abstract: A method of forming inspection patterns for inspecting a workpiece, e.g., for electron beam inspection of optical photomasks. The inspection patterns are formed from the workpiece patterns themselves by applying a first positive windage to the workpiece patterns, inverting the first positive windaged workpiece patterns and applying a second positive windage to the inverted first positive windaged workpiece patterns. The inspection patterns so produced will contain the requisite guard band and the requisite overlap of abutting patterns.

Abstract: An alignment system for registration of a scanning beam in a mask inspection tool. Minimum scan widths (W) in the registration process are attained thereby increasing registration sensitivity. This technique allows initial placement of the E-Beam to be outside the capture range so that the scan on one side is completely off the metal (on glass) and the scan on the other side is completely on the metal. Correction signals are obtained by comparing the backscattered electron signals from the two scans with the magnitude of the signal being indicative of the amount of correction required and the sign being indicative of the direction of correction.

Abstract: This describes an automatic defect inspection system as could be applied to metallized masks or other patterns. The system causes each subfield to be individually aligned for inspection irrespective of the previous alignment of the pattern or any other sub-field. This is accomplished by scanning a preselected portion of each sub-field and adjusting the position of the scan based on the resulting signal while scanning a pre-established portion of the sub-field. In this way a portion of each sub-field is used as an alignment mark and stepping errors avoided.Once alignment is achieved a probe, comparable to the size of the minimum defect to be detected is scanned over the sub-field with an overlapping pattern to find defects such as excessive metal, metal in improper places or points where the metal is missing.

Abstract: In electron beam apparatus having a souce of electrons and a target area toward which the electrons are directed, electron beam forming means are provided along the path from the source to the target. These forming means include a first beam shaping member having a first spot shaping aperture therein, a second beam shaping member having a second spot shaping aperture therein, and means focusing the image of the first aperture in the plane of the second aperture to thereby form a composite spot shape defined by the image of the first aperture and the second aperture. Further means are provided for focusing the image of the composite spot in the target area.Preferably, the apertures are square shaped. Thus, by varying the position of the superimposed image of the first aperture with respect to the second aperture, a wide variety of rectangular shaped composite spots with different dimensions is obtainable. This permits the exposure of rectilinear patterns, e.g.

Abstract: A method and apparatus is described for performing automatic overlay measurements on wafers utilized in semiconductor manufacturing. The overlay measurements are made at selected sites on a given wafer where a single bar pattern has been overlaid over a double bar pattern. The position of the single bar center line with respect to the center line between the double bars is a direct indication of the overlay error of the two patterns. The overlay error is measured in both the X and Y dimensions and is utilized to monitor the overlay error or to produce statistics and correlations to system parameters so that the sources of overlay errors may be identified and the errors eliminated or minimized on subsequent wafers being processed.

Abstract: A beam of charged particles has its alignment and brightness alternately controlled in accordance with the current of the beam. The measurements of the current and any corrections for alignment or brightness are made when the beam is not applied to a target.