1. 1 of 13 Mark Tillack, John Pulsifer, Sam Yuspeh, Matt Aralis HAPL Project Meeting 22-23 October 2008 Madison, WI Progress on GIMM mirror development and damage testing

2. 2 of 13 Our current goal is to test alloy mirrors at very high shot count to complete our proof of principle demonstration of laser damage Fabrication The cause of triangular damage features seen last time was isolated and corrected. 12-µm thick Al-0.5%Cu alloy mirrors were fabricated by thin film deposition at UCSD and then CMP finished at Cabot. Testing 10 7 shots have been achieved now @3 J/cm 2 with no sign of damage. A new homogenizer was designed enable higher fluence (8-9 J/cm 2 ). We remain optimistic that alloy mirrors will exceed damage requirements. Progress since April on fabrication and testing:

3. 3 of 13 homogenized unhomogenized In April we were suffering in the “Tillack zone”: the closer we approach the end, the more difficult the road becomes

4. 4 of 13 The cause of early failure was determined to be delamination resulting from improper fabrication m119, 3 J/cm 2, 5770860 shots Wrinkle New wafers sent for CMP were damaged during polishing (thrown from the wheel): Initially suggested cause was high coating roughness before polishing (P-V of 5 µm). Analysis revealed that the coating had poor adhesion.

5. 5 of 13 Improved cleaning and handling procedures result in good coating adhesion An expert on metallic coatings at UCSD was consulted New wafer cleaning and coating procedures were established SiO 2 growth is now avoided and contamination reduced Poor adhesion vs. Good adhesion A razor can’t peel the coating when adhesion is strong

6. 6 of 13 An additional benefit of the new fabrication procedure is a higher quality surface 12-µm coating of Al-0.5%Cu on each; properly cleaned wafer results in near specular quality prior to polishing. Coating on poorly cleaned wafer P-V: 5 microns RMS: 0.28 microns Coating thickness 12 µm Coating on properly cleaned wafer P-V: 200 nm RMS: 16 nm Coating thickness 12 µm

7. 7 of 13 Grain size remains small in thicker coatings with 0.5% Cu Al-1%Cu SEM image Al-0.5%Cu SEM image (properly-cleaned wafer) Al-0.5%Cu SEM image (poorly cleaned wafer)

8. 8 of 13 The thicker coating (with poor adhesion) already shows signs of improvement (no damage at 10 7 shots)

9. 9 of 13 In fact, the 12-µm poorly-adhered mirror surface improved after exposure to 10 million shots @3 J/cm 2, without failure unexposed area, 3.66 nm RMS laser exposed area, 2.4 nm RMS 500 µm

10. 10 of 13 Our homogenizer is essential to provide quality data, but has limited the achievable fluence to inconveniently low levels Homogenization provides predictable, reproducible results Depth of field limits achievable fluence The current setup is limited to 3-4 J/cm 2

11. 11 of 13 Alternative design options for the optical path have been explored Large standoff desired for reasonable depth of field at the target. Existing 2” optics limit fluence to 4 J/cm 2 since some light is not collected (80% energy recovery) 3-inch optics (fl=2m and 0.72m) with same focal geometry will provide 5 J/cm 2 with 2.78:1 demagnification (0.9 mm image), 95% energy recovery 3-inch optics (fl=2m and 0.6m) with 3.38:1 demagnification will provide 8- 9 J/cm 2 (0.74 mm image) 2.5 x 2.5 mm

12. 12 of 13 Beam path redesign should allow >8 J/cm 2 with a reasonable footprint size and profile With 2.78:1 demagnification, the footprint is ~0.9 mm x 10 mm. Placing the image plane at the center of the footprint, then 5 mm away is the worst case profile at 2.78:1 Imaging results suggest that some amount of out-of-focus is tolerable, such that 8 J/cm 2 (or more) is reasonable at 3.38:1 The footprint will reduce to 0.74 mm x 8 mm At image plane5 mm away10 mm away 10% lower peak fluence 20% lower peak fluence

13. 13 of 13 Summary and Future Plans Data have been obtained up to 10 7 shots with homogenized fluence levels of 3 J/cm 2 over 10 mm 2. Problems with coatings have been resolved and better mirrors are now being fabricated. Testing at 8 J/cm 2 or higher is possible with our improved imaging homogenizer design. Testing beyond 10 7 shots at 8 J/cm 2 is planned after CMP polishing 12-µm thick, well-adhered Al-0.5%Cu mirrors. Further study is needed on chamber contamination and mirror reflectivity issues, reported earlier.