Yield improvement by localized trimming in semiconductor and MEMS manufacturing

Many applications in semiconductor technology are characterised by extreme requirements in terms of film thickness homogeneity. This often lowers the yield of chips out of a wafer. It is a tremendous challenge in applications where tiny property deviations leads to big changes of device parameters, like the here shown acoustic wave resonators for radio frequency (RF). When manufacturing acoustic wave resonators (SAW, BAW), it is necessary to adjust geometrical dimensions of different materials with accuracies in the sub-nm range. Standard film deposition processes do not fulfil these homogeneity requirements, and thus it is necessary to perform a local correction of dimensions in a follow-up process. The authors here introduce a new method of local device parameter trimming and its technical implementation. During the process, the wafer is moved in front of a focussed broad ion beam. The local milling rate is controlled upon the residence time of the ion beam at certain positions. A modulated velocity pro file is calculated specifically for each wafer in order to mill the material at the associated positions to the tar get geometry. The introduced method helps for yield improvements of several ten percent and hence, makes RF MEMS production cost effective.