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Vortex Smoothing And Passive Optical Interface for Fiber-optic End Point Detection System

IP.com Disclosure Number: IPCOM000062739D
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Dewitt, JR: AUTHOR [+3]

Abstract

The monitoring of photoresist development using interferometry typically requires the placement of a plastic cap near the surface of a lead wafer in a boat. A fiber-optic cable is then attached to the plastic cap. A problem with this approach is that the presence of the plastic cap near the surface of the lead wafer causes swirl patterns around and in front of the cap, inducing faster removal of exposed photoresist on the lead wafer. All other wafers in the batch are in a "protected" fluid flow, due to the presence of wafers on each side, and photoresist develops at a slower rate. This discrepancy in development rates leads to poor correlation between the leading wafer end point and the rest of the wafers.

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Vortex Smoothing And Passive Optical Interface for Fiber-optic End Point Detection System

The monitoring of photoresist development using interferometry typically requires the placement of a plastic cap near the surface of a lead wafer in a boat. A fiber-optic cable is then attached to the plastic cap. A problem with this approach is that the presence of the plastic cap near the surface of the lead wafer causes swirl patterns around and in front of the cap, inducing faster removal of exposed photoresist on the lead wafer. All other wafers in the batch are in a "protected" fluid flow, due to the presence of wafers on each side, and photoresist develops at a slower rate. This discrepancy in development rates leads to poor correlation between the leading wafer end point and the rest of the wafers.

This problem can be solved by the use of a dummy wafer having a field lens in the center and a mechanical termination for the fiber-optic cable. The use of the dummy wafer allows for a "protected" fluid flow between the dummy wafer and the lead wafer in the boat so that the swirl patterns are avoided and the interferometric measurement on the lead wafer is more representative of the remaining wafers in the boat. The dummy wafer ca fabricated from any material which can withstand the chemical developer.

Disclosed anonymously.

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