ARAN - Access to Research at NUI Galway

Numerical Modelling and Measurement of Spatial Coherence in a Lithographic System

ARAN - Access to Research at NUI Galway

Show simple item record

dc.contributor.advisor Dainty, Chris
dc.contributor.author Smith, Arlene
dc.date.accessioned 2011-11-07T16:05:16Z
dc.date.available 2011-11-07T16:05:16Z
dc.date.issued 2011-09-30
dc.identifier.uri http://hdl.handle.net/10379/2284
dc.description.abstract For the last five decades, optical lithography has been used universally for the manufacture of integrated circuits. The drive towards smaller circuit feature size, and the resulting increase in resolution of lithography systems, has been achieved by changing the source type. The original 300 - 400 nm discharge lamps have been replaced with more powerful and monochromatic excimer lasers, operating at user-selectable Ultra-Violet (UV) wavelengths from 157 - 351 nm. The success of UV lithography is due, in part, to the development of industrialized, line narrowed excimer lasers. However, the line narrowing process, along with the intrinsic coherence properties of the laser, results in a source with a considerable amount of spatial coherence. These partially coherent sources are complicated to model. Partially coherent image formation with two-dimensional intensity fields requires evaluating four-dimensional integrals. Thus calculations are complex, slow to process and place demands on system memory. The motivation behind this thesis is an improved understanding of the effects of spatial coherence in optical lithography, including beam homogenization in wafer-stepper systems. In this thesis, we expand the Elementary Function Method, a process similar to coherent mode decomposition, to develop a numerical model of a partially spatially coherent source. We design an experiment to measure the spatial coherence of a partially coherent laser source and present our results. The numerical model is tested on a theoretical Gaussian Schell-model source, and then applied to the excimer source. We examine the traditional method for beam conditioning, the imaging homogenizer, and develop a model of the physical process involved in beam homogenization. Our results show that the imaging homogenizer is designed for use with spatially incoherent sources, where it performs well. However, if the source incident on the homogenizer has any degree of spatial coherence, the intensity output is highly non-uniform. en_US
dc.subject Partial coherence en_US
dc.subject Excimer en_US
dc.subject Modelling en_US
dc.subject Lithography en_US
dc.subject DUV photolithography en_US
dc.subject Applied Optics en_US
dc.title Numerical Modelling and Measurement of Spatial Coherence in a Lithographic System en_US
dc.type Thesis en_US
dc.contributor.funder IRCSET en_US
dc.contributor.funder SFI en_US
dc.local.note The partial spatial coherence of excimer lasers affects image quality in lithography. In this thesis, I develop a new numerical model of the propagation of partially coherent light, measure the partial coherence of two excimer lasers, and apply the results to a standard beam homogenizer employed in lithography. en_US
dc.local.final Yes en_US

Files in this item

This item appears in the following Collection(s)

Show simple item record