Ion Assisted Deposition Processes for Precision and Laser Optics H. Ehlers, T. Groß, M. Lappschies, and D. Ristau Laser Zentrum Hannover e.v. Germany
Introduction Ion assisted deposition (IAD) processes using a Denton CC-105 ion source Main focus on the spectral range between 2 and 4 µm Optical losses and spectral stability In situ broadband optical monitor in combination with ion assisted deposition Vacuum-to-air shift and coating examples Conclusions 2
Experimental Basis Deposition plant: Balzers BAK 760 Ion Source: Denton Discharge Currents of 2.5 to 5 A Tungsten filament Operated with oxygen to assist oxide coating deposition 3
Optical Losses Extinction Coefficient k 0,05 0,04 0,03 0,02 0,01 0,00 Optical Losses SiO 2 Single Layers 2,25 2,50 2,75 3,00 3,25 3,50 3,75 4,00 Substrate: sapphire Wavelength [µm] Comparison of SiO 2 single layers SiO 2 Conventional PVD SiO 2 PRE03013 Data calculated from spectrophotometric transmittance and reflectance data (water absorption band) Conventional PVD: Optical losses in the range between 10 % and 20 % No water could be detected within the IAD coatings 4
Spectral Stability 100 2 µm Mirror, TiO 2 / SiO 2 100 90 Transmittance [%] 100 95 90 85 80 75 70 Conventional PVD (e-beam) 25 C 50 C 75 C 100 C 125 C 1,00 1,05 1,10 1,15 1,20 1,25 1,30 Wavelength [µm] PRE03014 Transmittance [%] 90 80 70 60 50 40 30 20 10 Transmittance [%] 80 70 60 50 1680 1681 1682 1683 1684 1685 Wavelength [nm] 25 C 50 C 75 C 100 C 125 C Thermal stability of TiO 2 / SiO 2 multi layer systems: 0 1,4 1,5 1,6 1,7 1,8 1,9 2,0 2,1 2,2 2,3 2,4 Wavelength [µm] water desorption dominant negative spectral shift water-free layers small positive spectral shift PRE03015 5
Spectral Stability 0,0 TiO 2 /SiO 2 multi layer stacks -5,0x10-3 Relative Spectral Shift -1,0x10-2 -1,5x10-2 Conventional PVD -2,0x10-2 -2,5x10-2 20 30 40 50 60 70 80 90 100 110 120 130 Temperature [ C] PRE03016 Relative Spectral Shift 4,0x10-4 3,0x10-4 2,0x10-4 1,0x10-4 3,3 ppm/ C conventional PVD: -237 ppm/ C 0,0 20 30 40 50 60 70 80 90 100 110 120 130 Temperature [ C] PRE03017 6
In situ monitor and IAD Broadband transmittance measured directly on the moving substrate for each calotte revolution Halogen Lamp IBS monitoring system could be successfully transferred to the IAD process Hot processes are possible Fiber coupled CCD spectrometer Advantages Extended IAD process analysis Ion Source Trigger Process Control Optical Fiber Precise layer termination Enhanced quality management PRE03012 7
In situ monitor and IAD Software realized in LabView target spectrum actual measurement automatic mode to control the BAK 760 deposition plant PRE03018 calculated thickness/ target thickness/ remaining time (optical thicknesses in QWOT) 8
In situ monitor and IAD Performance of the online monitoring system within the IAD process Transmittance [%] 100 90 80 70 60 50 40 30 20 10 0 8 Layers TiO 2 / SiO 2 Thickness ~ 825 nm 600 700 800 900 1000 100 80 60 40 20 Wavelength [nm] 0 in situ, 300 C in situ, cold, vented Commercial Perkin Elmer Spectrophotometer 500 1000 1500 2000 2500 PRE03019 Broadband antireflection coating for 1000 2500 nm, quartz substrate (design optimized for IRG2) Monitored spectral region: 575 to 1060 nm All measurements show a good correspondence 9
Vacuum-to-Air Shift Transmittance [%] 100 90 80 70 60 Conventional PVD Ta 2 O 5 Single Layer 16 QWOT at 532 nm in situ, 300 C in situ, cold, vacuum Commercial Perkin Elmer Spectrophotometer 50 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 Wavelength [nm] PRE03020 Ta 2 O 5 conventional Relative shift λ/λ above 4 % (venting adsorption processes) Vacuum-to-air shift makes test runs and calibration factors for optical in situ monitoring necessary 100 90 Ta 2 O 5 Single Layer 16 QWOT at 532 nm Ta 2 O 5 IAD No significant Vacuum-to-air shift, direct optical in situ monitoring is possible Significant lower absorption (enhanced oxidation by the ions, no annealing necessary) Transmittance [%] 80 70 60 in situ, 300 C in situ, cold, vacuum Commercial Perkin Elmer Spectrophotometer 50 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 Wavelength [nm] PRE03021 10
IAD Process HR System Online monitor in automatic mode 31 layers AOI 45 HR @ 800 nm HR @ 940 nm HR @ 1064 nm Black: target spectrum Red: low (SiO 2 ) Blue: high (Nb 2 O 5 ) One spectra taken each calotte revolution coating movie 11
100 % 90 % Online Monitoring System: Thickness Control Example Automatic Mode Transmittance 80 % 70 % 60 % 50 % 40 % 30 % 20 % 10 % Online Monitoring System: Edge Filter: HR 2100 nm, HT 1840-2016 nm Backside: AR 1800-2100 nm Substrate: Quartz 27 Layers Nb 2 O 5 / SiO 2 (Thickness ~ 8.8 µm) 0 % 1800 1900 2000 2100 2200 2300 2400 2500 2600 Wavelength [nm] PRE03022 Measured Transmittance: below 0.6 % @ 2100 nm above 99.1 % @ 2012 nm above 99.8 % @ 1910 nm 12
Conclusions Ion Assisted Deposition using the CC-105 No water was detectable within the IAD coatings Multi layer systems exhibit a low positive shift In situ monitoring system Broadband transmittance measurements on the moving substrate are possible Combination of IAD and the in situ monitor no significant vacuum-to-air shift appears, direct optical in situ monitoring without test runs and calibration factors is possible 13
ACKNOWLEDGEMENTS The authors thank the German Federal Ministry of Economics and Labour (BMWA) for the financial support of the research project Innovative Ionentechnologien für Beschichtungen in der Präzisionsoptik und Lasertechnik in the framework of an AIF project under contract no. 12695N. 14