Method and apparatus for endpoint detection in a semiconductor w

Details Method and apparatus for endpoint detection in a semiconductor w Method and apparatus for endpoint detection in a semiconductor w

1991-02-05

1991-12-31

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

G01J 120

Patent

active

050774646

ABSTRACT:
A method for focussing a radiant energy beam characterized by the steps of scanning a beam of radiant energy across a test pattern including areas of differing reflectivity, detecting the variance in a reflected portion of the scanned beam and adjusting the beam to minimize the variance. Preferably, the test pattern includes areas of varying widths, e.g. relatively non-reflective areas of varying widths separated by reflective areas of uniform widths. As the beam is scanned perpendicularly across the test pattern it will be highly reflected by the reflective areas and will be partially absorbed by the non-reflective areas. If the beam is wider than a non-reflective area a portion of the beam will be absorbed and a portion of the beam will be reflected, resulting in a greater total reflection than if the beam is narrower than the non-reflective region. In consequence, the intensity of the reflected beam will vary as the energy beam is scanned across the test pattern as it encounters non-reflective areas of varying widths. The amount of variance in the reflected beam is related to the width of the beam and, therefore, the beam can be focussed by adjusting the beam to minimize this variance.

REFERENCES:
patent: 4569717 (1986-02-01), Ohgami et al.
patent: 4618262 (1986-10-01), Maydan et al.
patent: 4818886 (1989-04-01), Drucker
IBM Tech. Disclosure Bulletin, Oct. 85, vol. 28, No. 5 pp. 2147-2148.

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