New photo-acoustic techniques for improved in-line control of opaque metal film processing

Abstract

In today’s device fabrication the opaque metal film control is generally limited to full-sheet, single layer measurements on monitor wafers since the commonly used techniques require surfaces largely exceeding the typical device dimensions and cannot distinguish multiple layers in a stack. This indirect control method is apart from being expensive and time consuming- not adequate to ensure accurate process control since sampling rates are low and device related process fluctuations remain essentially undetected. Furthermore, for the novel metallization schemes based on damascene structures, the current monitoring is not at all adapted since the final metal thickness obtained after CMP is largely dependent on the device geometry and pattern density. With the introduction of new measurement techniques based on photo-acoustic principles, a new monitoring strategy can be engineered that allows a better and more efficient in-line process control.