Method and apparatus for determining line centers in a micromini

Details Method and apparatus for determining line centers in a micromini Method and apparatus for determining line centers in a micromini

1990-06-28

1991-11-05

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

250557, G01N 2186

Patent

active

050633007

ABSTRACT:
Method and an apparatus for determining line centers in a microminiature element such as on a semiconductor wafer or a mask having linewidths and other spacings below the one micron range. The invention uses, two focussed laser beams which are directed across a line on the element, both beams being illuminated successively with a distance therebetween below the classic resolving power. A portion of the incident beam and a portion of the beam reflected from the line is conducted to respective detectors which respectively generate measurement and reference signals. These signals are treated to eliminate high frequency noise components therein. Subsequently, the filtered measurement and reference signals are digitized and synchronously processed to provide two sine shaped curves whose intersection point corresponds to the center of the scanned line.

REFERENCES:
patent: 4373816 (1983-02-01), Laib
patent: 4642468 (1987-02-01), Tabata et al.
patent: 4814624 (1989-03-01), Veltze
patent: 4994990 (1991-02-01), Fujita et al.

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