Vortex Smoothing And Passive Optical Interface for Fiber-optic End Point Detection System
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
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.