Phase shift mask etch process development utilizing a scatterometry-based metrology tool

Abstract

Phase, along with defect levels and CD, must be closely monitored on 45nm technology node masks. The final phase shift of a mask is highly dependent on the ability of the etch tool to stop at precisely the correct depth. Developing etch processes and endpoint recipes for successful phase shift processing depends on rapid and accurate measurement of etch depth. In many mask shops, these measurements are made by either direct phase measurement tools or atomic force microscopes (AFM). These tools have relatively low throughput. In the case of the direct phase measurement tool, the large measurement spot size precludes the measurement of the small features most interesting to mask makers. A need exists for a relatively fast measurement tool that can be applied to features <1µm in size.As part of Oerlikon USA's continuous etch process improvement efforts, the etch depth measurement capabilities of a scatterometry based metrology tool were explored. Phase shift masks (one EAPSM, one AAPSM) were created to act as standards for our experiments. Regions of each mask were etched to various depths using an Oerlikon Mask Etcher system, and then measured with both a commercial AFM and an n&k Technology 1700-RT scatterometry tool. Using this data, recipes capable of measuring quartz trench features, partially-etched MoSi trench features, and bulk MoSi films were developed on the n&k 1700-RT. Phase uniformity data taken from actual etch experiments will be provided, as well as data showing the repeatability of each system, and a comparison of the relative measurement times.