Focused Beam Scatterometry

Focused Beam Scatterometry is used to inspect feature errors that are much finer than the diffraction limit of light. In addition to the critical dimension (feature width) these include (a) sidewall angle (b) feature height (c) oxide thickness and (d) feature pitch.
Focused Beam Scatterometry is used to inspect feature errors that are much finer than the diffraction limit of light. In addition to the critical dimension (feature width) these include (a) sidewall angle (b) feature height (c) oxide thickness and (d) feature pitch.
The instrument used to create an arbitrary, spatially-varying polarization state used in Focused Beam Scatterometry.
The instrument used to create an arbitrary, spatially-varying polarization state used in Focused Beam Scatterometry.

The state of the art in optical lithography continues to push transistor critical dimensions below 18 nm, creating the need for extremely high-resolution metrology techniques as a result. This research aims to develop a novel method of sub-18 nm silicon feature inspection.

Over the past 20 years, optical scatterometry and ellipsometry have evolved as some of the leading low- cost techniques for this application. Our method of scatterometry involves encoding a spatially varying polarization state onto a focused beam. Expanding on polarization improvements, sample scanning methods are being investigated to add more information into the model matching approach. Precision transducers used in sample scanning are a custom displacement measuring interferometer passively measuring piezoelectric-driven flexures closed-loop controlled using capacitance gauges.

Our role in the systems-level instrumentation of this project is a result of collaborations with Professor Thomas G. Brown and Professor Miguel A. Alonso. Dr. Brown’s research involves the creation of unconventional spatially varying polarization states which can be used in conjunction with Dr. Alonso’s weak measurement theory. Weak measurements are being investigated to make our approach as sensitive as possible to the process errors we hope to inspect.