Grazing incidence interaction of Sn particles with EUV Lithography ruthenium mirrors

TL;DR

This study investigates how tin particles at various energies and angles interact with ruthenium mirrors used in EUV lithography, aiming to understand and mitigate mirror degradation caused by debris from tin plasma sources.

Contribution

It provides a detailed computational analysis of Sn particle interactions with Ru mirrors at grazing incidence, enhancing understanding of surface modifications during EUV lithography.

Findings

Sn particles cause surface modifications on Ru mirrors.

Energy and angle of Sn particles influence sputtering and reflection.

Modeling predicts surface evolution under Sn flux.

Abstract

The new EUV Lithography tools for IC High Volume Manufacture at 22nm make use of EUV radiation at \lambda = 13.5nm. High power Laser (LPP) and Discharge (DPP)EUV light sources are based on Sn plasmas for the optimum conversion of electrical power to in-band radiation. Sn-fueled sources emit debris such as Sn particles in a rather wide energy spectrum: from thermalized Sn to several tens keV fast ions. Tin interaction with the collector mirrors surfaces facing the high power EUV light source leads to the degradation of the optical performance and productivity of the litho tool, therefore debris must be suppressed and the surface modification of the mirror materials during the particle irradiation must be carefully investigated both theoretically and experimentally. For DPP Sn-fueled sources the collector is a grazing incidence mirror that reflects the EUV light in the grazing angle range from about 1\degree to 20\degree. The most used material for these collector mirrors is Ru. The knowledge of the interaction process of Sn particles at different energies and angles with Ru mirrors is crucial to understand mirror degradation and to tune the parameters of the source and of the debris suppression devices to reach optimal mirror lifetime. We carried out a study of the modification of the ruthenium surface exposed to the simultaneous flux of thermalized and energetic Sn at grazing incidence, for energies varying from 300eV to 30keV. The computational study is performed with the Monte Carlo codes TRIDYN and TRIM.SP based on binary collision approximation assumptions. These tools allow to follow dynamically and at steady state the evolution of the surface composition and to model surface binding energy and density for predicting sputtering, reflection, ion-assisted deposition and depth profiles in the nm surface region.