Browse Prior Art Database

Optical Path Length Compensator

IP.com Disclosure Number: IPCOM000073410D
Original Publication Date: 1970-Dec-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Beaudoin, PL: AUTHOR [+3]

Abstract

Interferometer methods are used for measuring the stress on a unit being investigated such as a silicon substrate. A deference light beam from a coherent light source interferes with a light beam reflected from the unit to form interference patterns. This arrangement automatically compensates for any optical path length differences in the two beams.

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Optical Path Length Compensator

Interferometer methods are used for measuring the stress on a unit being investigated such as a silicon substrate. A deference light beam from a coherent light source interferes with a light beam reflected from the unit to form interference patterns. This arrangement automatically compensates for any optical path length differences in the two beams.

Light source (laser) 1 provides a beam 2 which is partially reflected at beam splitter 3 to provide a reference beam 4 (reflected on mirror 7) for monitoring substrate mount 6. The portion 8 of the light beam transmitted by beam splitter 3 is reflected at substrate 9 and back at beam splitter 3 to interfere with the beam 4 reflected at unit 6 and mirror 7. Interference takes place in a recording medium
10.

During and after the coating on the substrate 9, a stress is developed causing it to flex. This flexing causes a difference in the optical path length between beam 8 reflected from substrate 9 and beam 4 reflected from unit 6. A shift of the interference pattern occurs in medium 10.

The shift in interference pattern is detected by a photodetecting device 11 which provides an output to a differential circuit 12. A reference voltage 13 is also provided to circuit 12. Circuit 12 acts as a switch to activate motor controller 14 through forward and backward controls 15 causing a motor 16 to move in a forward or reverse direction as determined by the differential circuit. Through lead screw...