Detection of end point in etching process for superconducting films - by using film deposited on transparent substrate and measuring light absorbed by film remaining

摘要

Thin film, especially of a high temp. superconductor, deposited on a substrate with a transmission which is higher than that of the deposited film, is structured by dry etching. During the process the change in film thickness is measured optically. Pref. the transmission, or esp. the first deriv. of the transmission over time, is measured as a function of time during the etching. Etching is carried on as long as the ratio (T(tn)-T(tn-1))/delta(t) in fixed time intervals delta(t) increases. Especially etching is carried out until the condition: T(tn) is not less than (beta)xT(tn-1) in which beta is not greater than exp(alphaf.x.delta(t)) and tn-tn-1+delta(t). Alphaf= deposited film absorption factor and x = the etch-rate. Also claimed are several arrangements of measurement systems. USE/ADVANTAGE - Gives an accurate determn. of film thickness, avoiding problems of detection that other methods have which detect reaction prods. directly or by or fluorescence and allows the etching to be used on small samples. The end point of the etching process is indicated as a sharp change in the property being measured.