End point detection in ion beam milling of YBa2Cu3O7 thin films

In the processing of high temperature superconductor thin films into devices, the use of calibrated milling rates has proved unreliable as a means of determining the milled depth. This problem has been solved using in situ secondary ion mass spectrometry for identifying interfaces in multilayers based on YBa2Cu3O7. The depth resolution obtained during routine patterning of typical multilayers was ∼4 nm. Accurate termination of milling at an insulator/superconductor interface has been demonstrated. The presence of water vapor during milling has been shown to affect the proportions of the different secondary ion species, but has only a slight affect on the milling rate.