Comparison of Cleaning Methods for Thin Film Surfaces

The Problem Organic contaminants collect on thesurface (Junk).– Interferes with measuring opticalconstants Example with visible light

Question:OutlineHow do we effectively remove contaminants?1. Measurementmethods2. Cleaning methods-Opticlean®-Plasma Etch-UV lamp3. Conclusions

Video Measurement method– Ellipsometry Cleaning methods tested– Opticlean– UV Lamp– Plasma Etch

Short Exposure Contamination Experiment (10 sec)450Additional Thickness (Ǻ)4003503002502001501005045014318 1601Spit onTouched with bare fingers (10s)Dipped in Deionized WaterTouched and rubbed with latex glove (10s)

Opticlean ® Process leaveshydrocarbon residue• Opticlean ® significantlyremoves contaminants,but leaves a residue• Ellipsometric ResultsOpticlean ® residuethickness on two runs:1) 17 Ångstroms2) 22 Ångstromshttp://www.dantronix.com• Opticlean ® made by Dantronix Researchand Technologies, LLC• Ellipsometer Type: J.A. Woollam Co., IncMulti-Wavelength Ellipsometer (EC110)http://www.jawoollam.com/

Scanning ElectronMicroscope showed no thinfilm damage, nor trace ofmaterials used in thin filmson pulled of Opticlean ®films (U, Sc, Va).Does the Opticlean ®process damagethin films?X-Ray PhotoelectronSpectroscopy found notrace of materials used inthin films on pulled ofOpticlean ® .

XPS revealed components of Opticlean ® ,but not heavier metals used in thin films.Prominent thin-film lines: U-380 eV, V-515 eV, Sc-400 eV684 eV (F 1s)527 eV (O 1s)281 eV (C 1s)Photons (Counts)97 eV (Si 2p)148 eV (Si 2s)Photon Energy (eV)

Cleaning residue with “Matrix”Plasma Etch RF Plasma Etching withO 2 Plasma– 0.120 Torr Pressure– 250W RF (max 350)– 0.75 SCCM O 2 flow– No extra heat applied Good for removingpolymers, but not bulkcontaminants (i.e. Dust) Oxygen plasma plusmechanical sputteringremoves surface layersRF

Plasma ResultsMatrix SystemChange in thickness (Å)20-2-4-6-8-10-120 2 4 6 8 10 12 14 16 18Minutes In Plasma

UV Lamp

ConclusionMethodEffectivenessCleaning TimeEase of UseNotesOpticlean®Left residueMust wait forpolymer to cureCan be difficult topeel off.Good for dustetc..Oxygen PlasmaEffective. Cl notcompletely removedSetup takes a fewminutes. Cleanunder a minuteEquipment in cleanroom. Complex tosetup.Builds upsilicondioxideEximer UV LampEffective1 to 5 minutesVery easyLess silicondioxidebuildup thenplasma.Opticlean ® +Oxygen PlasmaEffective Possible 1Å residue or oxideLong, plasmasetup and polymercure time.Complex cleanroom equipmentand skill needed topeel Recommended Procedure:– UV lamp for 5 minutes