Ion Assisted Deposition Processes for Precision and Laser Optics

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1 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

2 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

3 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

4 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

5 Spectral Stability µm Mirror, TiO 2 / SiO Transmittance [%] 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 [%] Transmittance [%] 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 PRE

6 Spectral Stability 0,0 TiO 2 /SiO 2 multi layer stacks -5,0x10-3 Relative Spectral Shift -1,0x ,5x10-2 Conventional PVD -2,0x ,5x 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, Temperature [ C] PRE

7 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 PRE

8 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

9 In situ monitor and IAD Performance of the online monitoring system within the IAD process Transmittance [%] Layers TiO 2 / SiO 2 Thickness ~ 825 nm Wavelength [nm] 0 in situ, 300 C in situ, cold, vented Commercial Perkin Elmer Spectrophotometer PRE03019 Broadband antireflection coating for nm, quartz substrate (design optimized for IRG2) Monitored spectral region: 575 to 1060 nm All measurements show a good correspondence 9

10 Vacuum-to-Air Shift Transmittance [%] 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 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 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 [%] in situ, 300 C in situ, cold, vacuum Commercial Perkin Elmer Spectrophotometer Wavelength [nm] PRE

IAD Process HR System Online monitor in automatic mode 31 layers AOI 45 HR @ 800 nm HR @ 940 nm HR @ 1064 nm Black:

11 IAD Process HR System Online monitor in automatic mode 31 layers AOI nm 940 nm 1064 nm Black: target spectrum Red: low (SiO 2 ) Blue: high (Nb 2 O 5 ) One spectra taken each calotte revolution coating movie 11

12 100 % 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 nm Backside: AR nm Substrate: Quartz 27 Layers Nb 2 O 5 / SiO 2 (Thickness ~ 8.8 µm) 0 % Wavelength [nm] PRE03022 Measured Transmittance: below nm above nm above 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

13 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

14 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 N. 14

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