Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2001-07-13
2004-11-02
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492230, C700S119000, C716S030000
Reexamination Certificate
active
06812474
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to pattern generation methods and apparatus in which at least one beam (e.g., at least one laser beam or at least one electron beam) is controlled to produce a pattern on a target. In typical embodiments, the invention is a microlithographic method and apparatus in which at least one cell of a set of hierarchical image data is cached and then retrieved during conversion of the image data into beam control data (having pixel or vector format) suitable for causing a beam to produce a patterned mask.
BACKGROUND OF THE INVENTION
Pattern generation equipment is used for microlithographic applications such as the fabrication of masks for use in producing integrated circuits, as well as for other applications.
Some pattern generation systems use a raster writing strategy in which a laser or electron beam is swept over the target along a raster scan path, as the beam intensity is modulated to write pixels which determine a pattern on the target. In some implementations of such systems, the target is mounted on a movable stage and the beam moves back and forth along a first axis (in the plane of the target) while the stage moves the beam along an axis perpendicular to the first axis. In operation of pattern generation systems that use a raster writing strategy, sets of raw image data are received, and a raster engine is employed to rasterize each set of raw image data to generate a set of rasterized data. The rasterized data is in “pixel format” in the sense that it comprises a sequence of pixels to be written (sequentially) during one raster scan. Each pixel in the sequence can be a binary value (0 or 1), or a gray scale value.
U.S. Pat. No. 5,533,170, issued on Jul. 2, 1996, to R. L. Teitzel, et al., describes a raster engine for a pattern generation apparatus, and suggests that the data processed by the raster engine can include data objects that are called like subroutines so that a hierarchical structure can be built by called subroutines.
Other pattern generation systems do not rasterize raw image data into pixel format but instead convert raw image data into “vector format” data. The vector format data comprises a sequence of vectors, each determining a location (at which a scan begins) and a magnitude indicative of the length (or duration) of the scan. Typically, the location is expressed as an offset from a reference point. In response to a set of vector format data, a beam performs a sequence of scans in which it is directed to a first location on the target and executes a scan (e.g., a raster scan over a small area) starting at the first location and having the indicated length or duration, and then jumps to a second location on the target and executes another scan having the length or duration corresponding to the second location, and so on.
In another type of pattern generation system (sometimes referred to as “shaped spot” systems), the target is exposed by a sequence of shots of a variably shaped beam. To perform each shot, the beam is controlled (e.g., by manipulating apertures in the beam path) so that its projection on the target has a selected shape (e.g., a rectangle or triangle), and a selected region of the target is exposed to the shaped beam for a selected duration of time. This type of system converts raw image data into vector format data comprising a sequence of vectors, each vector determining a location (on the target) for one shot (in a sequence of shots) and a magnitude indicative of a configuration of beam control components determining a selected projected beam shape for the shot (and optionally also the shot duration).
Other pattern generation systems used for microlithography are known as “cell projection” systems. A cell projection system is used to expose the target to a sequence of shots. To accomplish each shot, a beam is projected onto the target through a pattern of holes determined by a wafer. The wafer can determine either one pattern or more than one pattern of holes. To accomplish each shot, the beam is controlled so that passes through a selected pattern of holes of the wafer onto a selected region of the target for a selected duration of time. This type of system converts raw image data into vector format data comprising a sequence of vectors, each vector determining a location on the target for one shot (in a sequence of shots) and control bits determining through which pattern of holes (of the wafer) the beam passes for the shot.
U.S. Pat. No. 5,371,373, issued on Dec. 6, 1994, teaches an electron beam lithography apparatus having both a cell projection system (including a selected one of masks 24-28 of FIG. 6, identified as mask 21 in FIG. 3) and a shaped spot system including mask 29 of FIG. 6 (identified as mask 21 in FIG. 3) and mask 19 and mechanism 18 of FIG. 3. The apparatus produces a pattern on object 15 in response to two-level hierarchical image data. Each of masks 24-28 is fabricated in response to a different primary cell of the hierarchical image data. In addition to fabricating masks 24-28, lithographic data (in vector format) is generated by processing the hierarchical image data. Data control system 8 responds to a stream of the lithographic data as follows: in response to each successively received unit of the lithographic data that designates one of the primary cells, a single “cell projection” shot is performed in which the beam passes through the corresponding mask 24, 25, 26, 27, or 28 to project a cell onto object 15; and in response to each successively received unit of the lithographic data that does not designate one of the primary cells, a single “shaped beam” shot is performed in which the beam passes through appropriately controlled pair of masks 19 and 29 to project a selected beam shape onto object 15. However, U.S. Pat. No. 5,371,373 does not teach any method for producing a pattern on object 15 in response to N-level hierarchical image data, where N is greater than two.
SUMMARY OF THE INVENTION
In a class of preferred embodiments of the inventive pattern generation method and system, a graphics engine (“GE”) having a memory receives a set of hierarchical image data (determining a pattern to be imaged on a target), at least one cell (determining a repeated feature set) is stored in the memory, and beam control data is generated in response to the image data. The expression “feature set” is used herein to denote a feature or set of features that occurs in the pattern and the expression “repeated feature set” is denotes a feature or set of features that occurs repeatedly in the pattern. The hierarchical image data includes residual data, the residual data includes at least two subroutine call commands for each cell stored in the memory, and each subroutine call command is indicative of a location on the target and a cell to be retrieved from memory. In response to each subroutine call command, the GE retrieves a cell from the memory, and asserts beam control data that determines a feature set (determined by the cell) to be imaged on the target at (or beginning at) the location identified by the subroutine call command. The subroutine call commands can be distributed throughout the image data transferred to the GE, including in at least one cell to be cached (e.g., in a primary cell, in which case it identifies a secondary cell) as well as in the residual data.
In preferred embodiments, the GE caches each cell of the hierarchical image data in the memory, and generates a set of beam control data in response to each subroutine call command by retrieving a cached cell from the memory and generating the beam control data in response to the retrieved cell. In other embodiments, the GE generates a cell of beam control data in response to each cell of the hierarchical image data, caches each such beam control data cell (rather than the cell of image data corresponding to the beam control data cell) in the memory, and responds to each subroutine call command of the transferred image data by retrieving a cached cell of beam control data from memory and a
Jolley Matthew J.
Klatchko Asher
Sills Robert Marc
Applied Materials Inc.
Church Shirley
Fernandez Kalimah
Lee John R.
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