ENHANCED STITCHING BY FEATURE REDUCTION AND OVERLAP DOSE
Publication Date: 2014-May-05
The IP.com Prior Art Database
A method for processing exposure data (40) for exposing a pattern on a target (30) using a plurality of charged particle beams (24), the exposure data comprising pattern data (42) representing one or more features (60) to be written on the target (30), the method comprising dividing the pattern data (42) into a plurality of sub-sections (44), each of the sub-sections comprising pattern data describing a part of the pattern to be written in a corresponding subarea (34) of the target (30), wherein the pattern data (42) comprises overlap pattern data (46) describing a part of the pattern to be written in a corresponding overlap area (36) of the target where adjacent sub-areas (34) overlap, and processing the overlap pattern data (46) to reduce a size of one or more features described by the overlap pattern data.
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BACKGROUND OF THE INVENTION
1. Field of the Invention
 The present invention relates to methods and systems for exposing a target using charged particles, and methods and systems for processing exposure data for use in charged particle lithography, and in particular to methods and systems for performing stitching during exposure of a target.
2. Description of the Related Art
 In a multi-beam lithography system, multiple beams are used to expose a target, such as a silicon wafer coated with resist. Charged particle beams, such as electron beams, are usually used. The multiple beams are scanned across the surface of the target, each beam simultaneously writing a portion of the pattern onto a portion of the target. To provide the required precision at a satisfactory throughput, a very large number of beams may be used, e.g. tens or hundreds of thousands, or even millions of beams. An example of such a system is described in M.J. Wieland et al, "Throughput enhancement technique for MAPPER maskless lithography", Proc. of SPIE, Vol. 7637, 76371Z (2010).
 During a single exposure the lithography system usually exposes an area of the target, e.g. a single 26 mm x 33 mm field. Each beam is used to scan a certain allocated sub- area on the target. Where are a very large number of beams are used, these sub-areas are very small.
 As each beam scans across the surface of the target, it is modulated in some way to reproduce the required pattern to be exposed onto the target. In a maskless lithography system, exposure data is used to modulate the beams. The exposure data usually includes pattern data describing the shapes (called features) to be exposed onto the target. As each beam scans over a certain part of the surface of the target, the pattern data may be streamed to the lithography system and used to adjust the intensity of each beam as it scans the target. For example, the pattern data may be used to switch each beam on and off to expose certain parts of the target where a feature is to be formed on the target and not expose other parts along the scan line followed by the beam.
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 The exposure data may also include exposure dose values, providing further modulation of the intensity of the beams as they scan. For example, if the pattern data is used to switch a beam on over a certain portion of its scan path, the exposure dose values may instruct the lithography system to set the intensity of the beam at some value between zero and one hundred percent, e.g. at 70%, during that portion of its scan path. In a raster scan lithography system this exposure dose modulation may be accomplished by dithering the beams, e.g. switching the beams on and off with a certain mark-space ratio to achieve the desired beam intensity. Note that the exposure dose values may also be used to set the intensity of a beam which the pattern data indicates should be switched off. An example of the...