Etec Systems, Inc.

Andrew J Muray

C Neil Berglund

Frank E Abboud

A raster scan lithography system is modified so that the duration of illumination (dose modulation) for particular pixels is varied to lie between the full on and full off normally used. For instance, three levels of pixel intensity are provided, 100%, 70% and 30% (in addition to off which is 0%). The 30% and 70% pixels are used along the edge of a feature so as to locate the edge when written in between the lines of the cartesian raster scan grid. Thus the edges of the feature are moved off the grid, without the need for multiple passes. This pixel dose modulation uses three preset delay lines determining dwell times for each pixel on a pixel-by-pixel basis, as defined by a two (or more) bit deep memory file associated with the pattern to be written. Additionally, the pixel center locations are directly moved off the grid by deflecting the beam as it scans certain pixels located along feature edges. The amount of deflection is controllably variable to achieve various edge locations. This deflection is used by itself or in combination with dose modulation, and is implemented by an electrostatic deflector in the beam lens for an E-beam system.

Dose modulation and pixel deflection for raster scan lithography

A method and apparatus for photolithographically fabricating features on a very large scale integrated circuit wafer by use of a phase shift mask defining discrete regions. This overcomes the problems of intensity nulls at the junction of regions formed by portions of the mask having opposite phase. The mask includes a transition region defining three phases which are assigned to pixels in the transition region, such that the phase assignment of the pixels is synthesized from an algorithm taking into account optical resolution and depth of focus. Each pixel is assigned one of three discrete phases, which thereby creates a transition region simulating a ramp between the two regions of opposite phases, such that intensity variation of the optical image corresponding to the transition region is minimized.

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Fremont, CA, United States of America

Andrew J Muray