Abstract: A method for detecting the end point of etching wafers and the like by reflective means. Typically, a detected reflectance signal will have a threshold level representing a lack of substantial etching, a dip in the threshold level representing the commencement of etching and an inflection level representing a maximum rate of light amplitude change. The present method involves subtracting the inflection level from the threshold level and taking a predetermined fraction of the resultant level to define a second threshold level further in the etch cycle which anticipates the end of the cycle. By observational experience, the predetermined fraction can be determined. As soon as the second threshold level is reached, brakes are applied to the etching process so that etching will cease shortly after the predetermined level has been identified.

Abstract: An apparatus for in-situ processing of photoplates which minimizes photoplate contamination. Frustro-conical sloping walls are provided in opposed bowl-shaped mating domes containing a centrally disposed photoplate mounted for rotation. Condensing vapor or nozzle drippings are guided by the sloping walls away from the photoplate.