Electro-optical system for scanning microscopy of extreme ultraviolet masks with a high harmonic generation source.

Patrick P Naulleau,Jongju Park,Weilun Chao,Seno Rekawa,Seong-Sue Kim,Donggun Lee,Kenneth A Goldberg,Erik H Anderson,Changhoon Choi,Christopher N Anderson,Nord Andreson,Eric M Gullikson,Farhad Salmassi,Ryan Miyakawa

doi:10.1364/oe.22.020144

Abstract

A self-contained electro-optical module for scanning extreme ultraviolet (EUV) reflection microscopy at 13.5 nm wavelength has been developed. The system has been designed to work with stand-alone commercially available EUV high harmonic generation (HHG) sources through the implementation of narrowband harmonic selecting multilayers and off-axis elliptical short focal length zoneplates. The module has been successfully integrated into an EUV mask scanning microscope achieving diffraction limited imaging performance (84 nm point spread function).

Highlights

The availability of actinic extreme ultraviolet (EUV) mask metrology tools remains a challenge for the commercialization of EUV lithography
Stand-alone Fresnel zoneplate tools based on plasma sources, EUV lasers [13,14], or high harmonic generation HHG sources [15,16,17,18] are all possible, but each system faces implementation challenges
EUV lasers meet the temporal coherence requirements of zoneplates, but none are currently available at the desired lithography wavelength of 13.5 nm

Summary

Introduction

The availability of actinic extreme ultraviolet (EUV) mask metrology tools remains a challenge for the commercialization of EUV lithography. Stand-alone Fresnel zoneplate tools based on plasma sources, EUV lasers [13,14], or high harmonic generation HHG sources [15,16,17,18] are all possible, but each system faces implementation challenges. EUV lasers meet the temporal coherence requirements of zoneplates, but none are currently available at the desired lithography wavelength of 13.5 nm. The high spatial coherence of EUV lasers is not well suited for a full-field microscope. HHG sources are available at the correct wavelength, and have significantly better temporal coherence than plasma sources, but like EUV lasers, they are spatially coherent. In addition to being well suited for HHG sources, scanning geometries have the added benefit of overcoming field size limitations of zoneplates [21]. In this paper we describe the design, implementation, and testing of such a system, demonstrating diffraction limited performance

System design

Harmonic selecting mirror

Zoneplate lens

Detector

Assembly

Imaging performance