1. Field of the Invention
The present invention relates generally to charged-particle beam lithography technologies and, more particularly, to a method and apparatus for writing a pattern on a workpiece by use of an electron beam while performing correction of a deflection position of the beam on a real-time basis.
2. Description of Related Art
Lithography techniques indispensable for growing miniaturization of semiconductor devices are to produce patterns unlike other semiconductor fabrication processes and, for this reason, are very important processes. In recent years, as LSI chips further increase in integration density, circuit line widths required for semiconductor devices are becoming smaller year by year. To form a desired circuit pattern on these semiconductor devices, it becomes necessary to use a high-accuracy original image pattern (also called the reticle or photomask). Note here that electron beam (EB) lithography techniques offer inherently excellent image resolutions and are used for production of such high-precision original pattern.
FIG. 13 shows schematically a perspective view of an electron beam optics in prior known variable-shaped electron beam (EB) lithographic apparatus.
As shown herein, the EB lithography tool includes a first aperture 410 having a rectangular opening or hole 411 for shaping an electron beam 330. The EB tool also includes a second aperture 420 having a variable shaping hole 421 for reshaping the electron beam 330 that passed through the hole 411 into a desired rectangular cross-sectional shape. The electron beam 330 that was emitted from a charged particle source 430 and then passed through the hole 411 is deflected by a deflector to penetrate part of the variable shaping hole 421 to thereby fall onto a workpiece 340, which is situated on a stage structure that is continuously movable in a prespecified one direction (e.g., X direction). In brief, only a beam with its rectangular shape capable of penetrating both the hole 411 and the variable shaping hole 421 is permitted to reach a pattern write area of the workpiece as mounted on the stage that continuously moves in the X direction, followed by pattern writing thereon. The scheme for creating any given shape by guiding the beam to pass through the holes 411 and 421 is called the variable-shaped beam (VSB) lithography.
Note here that in the EB lithographic tool, its pattern writing chamber can vary in shape with a change in atmospheric air pressure. This deformation affects a relative distance between an electron lens barrel overlying the writing chamber and the surface of a workpiece such as a photomask disposed within the chamber. If the relative distance is kept out of alignment due to a change in atmospheric pressure, appreciable aberration can occur in position of a pattern to be written and also in focus point of an electron beam, resulting in the lack of an ability to perform highly accurate pattern writing. In particular, while extra-high accuracy is required with growth in miniaturization of on-chip circuit linewidths in recent years, the risk of a decrease in pattern writing accuracy becomes no longer negligible, which is occurrable due to such atmospheric pressure variation-caused relative-distance/focus-point deviations.
A technique adapted for use in ultraviolet (UV) exposure apparatus for exposing a mask image onto wafers is disclosed, for example, in JP-A-7-211612, although it is not specifically directed to EB lithography. This Japanese patent bulletin involves the teaching as to an approach to obtaining the amount of curvature or “warp” of an image plane due to a change in atmospheric air pressure and then driving a stage to move to an optimal position in Z-axis direction.
As previously stated, while higher accuracy is required with further miniaturization of onchip circuit linewidth in recent years, the risk of a decrease in pattern writing accuracy becomes no longer negligible, which is occurrable due to the atmospheric pressure change-caused relative-distance/focus-point deviations. Additionally, a pattern writing position on the workpiece surface is defined two-dimensionally in x- and y-axis directions. Usually the electron beam's deflection position also is corrected two-dimensionally in the x and y directions. However, relative displacements due to atmospheric pressure variation take place three-dimensionally in x, y and z directions, respectively. Thus, it is required to achieve a three-dimensional (3D) correction scheme with handleability of these phenomena. Unfortunately, a technique for correcting deflection position deviations occurring due to atmospheric pressure variations has not yet been established in the prior art.