Monitoring EUV Reticle Molecular Contamination on ASML s Alpha Demo Tool

Transcription

1 Monitoring EUV Reticle Molecular Contamination on ASML s Alpha Demo Tool Uzodinma Okoroanyanwu, 1 Aiqin Jiang, 2 Kornelia Dittmar, 3 Torsten Fahr, 3 Thomas Laursen, 2 Obert Wood, 1 Kevin Cummings, 2 Christian Holfeld, 4 Jan-Hendrik Peters, 4 Bruno La Fontaine, 5 Eric Gullikson. 6 1 GlobalFoundries, 257 Fuller Road, Albany, NY 12203, USA 2 ASML, 25 Corporate Circle, Albany, NY 12203, USA 3 GlobalFoundries, Wilschdorfer Landstrasse 101, D Dresden, Germany 4 AMTC, Rahnitzer Allee 9, D Dresden, Germany 5 GlobalFoundries, 1050 E. Arques Avenue, Sunnyvale, CA 94085, USA 6 LBNL, 1 Cyclotron Road, Berkeley, CA 94720, USA

2 Outline Introduction Experimental techniques & results Auger electron spectroscopic analysis - AES surface analysis results - AES depth profiling results Grazing incidence reflection (GIR) FTIR spectroscopic analysis Scanning electron microscopic analysis - Image quality -CD uniformity At wavelength reflectivity analysis Summary 2

3 Introduction The main aims of the experiments were to assess the molecular contamination risk to the use and lifetime of a given EUV reticle under typical use condition. The reticle was exposed to >1600 J/cm 2 over a period of one year. The reticle comprises areas with gratings and contamination monitoring (CM) open fields. The identity and thickness of the contaminants were determined with Auger electron spectroscopy AES, and verified with Fourier Transform Infrared spectroscopy. The impact of contamination on the quality of image printing and on dose was determined with Scanning electron microscopy of grating features printed on wafer. The impact of contamination on reticle reflectivity was determined with Actinic Inspection Tool at Lawrence Berkeley National Laboratories The results obtained on the exposed gratings, open fields and absorber areas of the reticle are compared to those from the unexposed areas of the same reticle.

4 Reticle architecture Reticle is made of 40 Mo/Si bilayers Silicon capping layer TaN absorber layer TaN Absorber layer SiO 2 buffer layer Si capping layer SiO 2 Buffer layer 40 bilayers of Mo/Si 4

5 Reticle layout Exposed gratings Exposed CM open fields and absorber areas 45-nm grating H-V 4 mm x4 mm openarea arrays Unexposed gratings Unexposed CM open fields & absorber areas used as reference Origin (0,0) MLM reticle substrate with Si cap layer

6 AES spectra obtained on the absorber x Ta, O, C detected, but no Si or N Exposed absorber Ta O Ta Ta c/s Ta C Unexposed absorber Oxidation states/atomic concentration Absorber area of detected elements (%) C(1) N(1) O(1) Ta(2) Exposed absorber 34.4 ± 3 <1.6 ± ± ± 3 Unexposed absorber 47.8 ± 3 <1.8 ± ± ± Kinetic Energy (ev) More C on unexposed absorber 6

7 AES survey spectra of the CM open fields x Si, SiO x, C are detected Exposed open fields Si 12 O c/s Si C Unexposed open field Oxidation states/atomic concentration Open field type of detected elements (%) C(1) O(1) Si(2) Exposed open field ± ± ± 3 Exposed open field ± ± ± 3 Unexposed open field 51.6 ± ± ± Kinetic Energy (ev) More C on unexposed CM open field

8 Overview AES depth profile of an entire exposed CM open field Mo/Si stack Intensity x Si cap layer C1 O1 Si1 Mo1 Carbon & surface oxide contaminants on Si cap detected 4 2 Multilayer structure visible Sputter Depth (nm) Note: The depth scale conversion is based on SiO 2 etch rate

9 AES depth profiles through CM open field areas Surfaces are oxidized and covered with carbon contamination. SiO 2 thickness ~ 1nm thick on top of both exposed & unexposed areas Carbon contamination on top of the exposed & unexposed areas is completely removed after short sputtering, indicating a thickness < 0.5 nm. 10 x x 10 4 Si1 Si1 Intensity O1 C1 Exposed Mo1 Intensity O1 C1 Unexposed Mo Sputter Depth (nm) Sputter Depth (nm) All profiles were scaled to the same depth, based on the SiO 2 etch rate

10 AES depth profiles through absorber areas Ta x O y is observed on the TaN absorber layer Carbon contamination is observed on both exposed & unexposed areas Carbon contamination is completely removed after short sputtering, indicating a thickness < 0.5 nm x x 105 Exposed Unexposed 1.5 O1 1.5 O1 Intensity 1 Intensity C1 Ta1 0.5 C1 Ta Sputter Depth (nm) Sputter Depth (nm) All profiles were scaled to the same depth, based on the SiO 2 etch rate

11 GIR FTIR spectra of CM open fields of reticle Transmittance [%] Exposed Mo-O Si-O-Mo Si-O Atmospheric moisture Transmittance [%] Unexposed Mo-O Si-O-Mo Si-O Atmospheric moisture Wavenumber cm -1 Wavenumber cm-1 Si-O from oxidized Si capping layer Si-O-Mo and Mo-O from O enrichment in Mo sub layers of Mo/Si stack

12 GIR FTIR spectra of absorber areas of reticle Transmittance [%] Exposed Si-O Atmospheric moisture Transmittance [%] Unexposed Si-O Atmospheric moisture Wavenumber cm Wavenumber cm-1 Si-O observed on the Si-capping layer in both exposed & unexposed areas of the absorber

13 SEM images of gratings in the exposed & unexposed regions of the reticle Exposed Unexposed No discernible difference between gratings in the exposed & unexposed regions of the reticle

14 CD & CD uniformity of patterned gratings in the exposed & unexposed regions of the reticle Wafer layout No discernible CD difference between gratings in the exposed and unexposed regions of the reticle 54 Exposed 52 CD (nm) Unexposed Unexposed die(-2, -1) die(2, -1) die(-2, 1) die(2, 1) Y (mm) 4 fields measured

15 EUV reflectivity of exposed & unexposed CM open fields of reticle Comparable reflectivity between exposed and unexposed areas ~3.4 % reflectivity loss from pristine values relative to values at the end of the experiment could be related to storage effects, mask processing, handling & transportation Location on reticle measured Pristine, before the experiment Mo/Si ML Reflectivity Maximum 64 ± 1%* After 1600 J/cm 2 exposure of CM1 area After 1600 J/cm 2 exposure of CM2 area Unexposed CM6 area Unexposed CM7 area 60.7 ± 0.1%** ± 0.1%** ± 0.1%** ± 0.1%** * Measured by Schott Lithotec at PTB Bessy on 10 August 2006 ** Measured at ALS at LBNL on 9 October 2009

16 Summary Contamination risk to EUV reticle of up to 1600J/cm 2 of exposure dose in ASML s ADT is negligible. Carbon contaminants & oxides are observed on exposed & unexposed Si surfaces of CM open fields and Ta surfaces of absorbers. - Carbon thickness is < 0.5 nm on exposed & unexposed Si surfaces of CM open fields and Ta surfaces of absorbers. - The Si capping layer in the CM open fields is oxidized to a thickness of around ~ 1 nm in both exposed and unexposed areas.

17 Summary, cont d. The slightly lower amount of carbon contaminant in the exposed areas relative to the unexposed areas may be indicative of in-situ cleaning mediated by the interaction of EUV photons & residual oxygen in the reticle space. There is comparable level of reflectivity between exposed & unexposed CM open fields at the end of experiment, corresponding to a reflectivity loss of ~3% relative to pristine values. No discernible CD difference between gratings in the exposed & unexposed regions of the reticle is observed J/cm 2 of EUV exposure dose can support ~620 printed wafers (with 72 exposure a resist sensitivity of 15mJ/cm 2

18 Acknowledgments Sang-In Han & Robert Routh of ASML Part of this work was performed by the Research Alliance Teams at IBM Research and Development Facilities in Albany, NY