Nanoscale optical critical dimension measurement of a contact hole using deep ultraviolet spectroscopic ellipsometry

Abstract

Highly sensitive optical metrology techniques based on spectroscopic ellipsometry (SE) are required for three dimensional monitoring of line-profiles and critical-dimension (CD) of advanced design-rule devices. In this paper, theoretical and SE-based experimental techniques are used to study elliptical contact holes (CH) in a SiO2 layer. These structures were chosen because measuring their shapes is made difficult by the low optical contrast between air inside the holes and SiO2, as well as the strong coupling between critical shape parameters. Results showed that moving from conventional ultraviolet SE to deep ultraviolet SE (DUVSE) was a key to breaking the correlation between top and bottom CD and obtaining an accurate and physically realistic CH profile. The DUVSE-based CD results were validated using a scanning electron microscope.