Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1997-11-20
1998-07-14
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
25023118, G01D 534
Patent
active
057808490
ABSTRACT:
An apparatus for detecting objects to be transferred includes a wafer detecting unit having photo-sensors which scan a carrier moved up and down on a lift stage to detect wafers held on respective stages in the carrier, and an indication device provided vertically downward on the lift stage and including light-passing portions and non-light passing portions vertically arranged. The indication device traverses optical axes of a reading unit with, e.g., photo-emitting/detecting device to thereby obtain information of vertical position of a carrier, and, based on combinations of photo-detection signals from the wafer detecting units, absence and presence of wafers on the respective stages are recognized. This arrangement makes it possible that absence and presence of semiconductor wafers on the respective stages in a carrier are quickly and accurately detected, and even when the lift stage is stopped during detection, halting the detection, the detection is resumed at the halted position without returning the carrier to its initial position.
REFERENCES:
patent: 4224603 (1980-09-01), Lallemand
patent: 5148020 (1992-09-01), Machida
patent: 5235181 (1993-08-01), Durana et al.
patent: 5291025 (1994-03-01), Smith
patent: 5423503 (1995-06-01), Tanaka et al.
Pyo Kevin
Tokyo Electron Ltd.
Westin Edward P.
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