Aspects and new developments on edge angle and edge profile metrology at PTB

Abstract

Measurement and control of edge profiles and edge angles is increasingly important in advanced lithography. Especially for critical dimension metrology a sophisticated multi-dimensional shape metrology is highly beneficial. Different types of dimensional metrology instrumentation are in use today for edge profile and edge angle measurement. While destructive cross section SEM measurements often serve as reference, AFM and optical scatterometry systems are commonly used for day-to-day or in-line control. Due to the limitations of these metrology systems (AFM: slow, scatterometry: only integral measurements of periodic structures), the evaluation and modelling of top down SEM images is increasingly considered, too. At the PTB both SEM and AFM as well as optical scatterometry are applied for edge angle and/or edge profile metrology, supported by optical transmission microscopy. At the PTB we have realised a new DUV hybrid scatterometer for measurements over the full range of 6025 format masks which combines essential elements of a reflectometer, an ellipsometer, and a diffractometer. In addition to scatterometric measurements this set-up allows to measure the complete Muller-matrix including transmission, polarisation and depolarisation. This new set-up will be presented in detail. Finally we study the possibilities of evaluating high resolution top down SEM images to determine edge angles. The potential of edge angle evaluation using these new analysis procedures will be discussed. We present an overview of the PTB measurement capabilities with an emphasis on newly developed metrology methods and systems.