Application of 3D scatterometry to contacts and vias at 90nm and beyond

Abstract

The challenging metrology application for scatterometry and CD-SEM is to accurately measure both CD and profile. To apply this metrology specifically to dual-damascene hole structures is critical for the back-end processing, in order to control both the CD and the process overall. This paper discusses applications of Optical Digital Profilometry-based scatterometry to the advanced 90nm node dual-damascene process. The application includes contact ADI, via AEI, via etch, and via fill. The results show that scatterometry can measure CD, as well as provide sidewall angle and profile information that is unavailable by CD-SEM. Correlations to CD-SEM and cross-sectional SEM are also presented. For future applications, scatterometry is a viable solution for 3D structures, and provides higher precision, and more metrology information than current metrology methods for critical dual-damascene processes. INTRODUCTIONWith the demand for faster devices, the implementation of the damascene process is essential in order to build smaller metal lines, while maintaining acceptably low electrical resistance. The dual-damascene copper process requires the etching of vias and trenches, which are subsequently filled with copper simultaneously. The profile and film thickness determined using ODP gives much more information about the process than previous metrology using CD-SEM 1 , and the objective was to demonstrate ODP capability for damascene. In this process, the via has been etched first, with the trench etch following, and ODP scatterometry has been used to measure the via profile and layer thicknesses, at the following four process steps: (1) Via After-Develop Inspect (ADI); (2) Via After-Etch Inspect (AEI), with resist removed; (3) Via plug, following a resist fill; and (4) following the etch-back of the vias. Figure 1. ODP scatterometry is used to measure damascene via profiles and film thicknesses. From left to right is shown (1) Via ADI; (2) Via AEI; (3) Via fill; and (4) Via etch-back.

Optical dimensional metrology at Physikalisch-Technische Bundesanstalt (PTB) on deep sub-wavelength nanostructured surfaces

“…In the semiconductor industry these methods are well established to monitor structure dimensions, e.g. for wafer or photomask inspections [2][3][4][5][6]. It is based on the analysis of far-field light distribution and properties after interaction (scattering, diffraction, reflection, transmission) with the structured surface.…”