title: Transport of intensity phase imaging in the presence of curl effects induced by strongly absorbing photomasks.
abstract: We report theoretical and experimental results for imaging of electromagnetic phase edge effects in lithography photomasks. Our method starts from the transport of intensity equation (TIE), which solves for phase from through-focus intensity images. Traditional TIE algorithms make an implicit assumption that the underlying in-plane power flow is curl-free. Motivated by our current study, we describe a practical situation in which this assumption breaks down. Strong absorption gradients in mask features interact with phase edges to contribute a curl to the in-plane Poynting vector, causing severe artifacts in the phase recovered. We derive how curl effects are coupled into intensity measurements and propose an iterative algorithm that not only corrects the artifacts, but also recovers missing curl components.
authors.forename: Aamod
authors.initials: A
authors.lastname: Shanker
authors.forename: Lei
authors.initials: L
authors.lastname: Tian
authors.forename: Martin
authors.initials: M
authors.lastname: Sczyrba
authors.forename: Brid
authors.initials: B
authors.lastname: Connolly
authors.forename: Andrew
authors.initials: A
authors.lastname: Neureuther
authors.forename: Laura
authors.initials: L
authors.lastname: Waller