Summer Research Collaboration Project Final Update

1. Summer Research Collaboration Project Final Update Presbyterian College, Form Factor, Auburn Universtiy, and Air Force Institute of Technology

2. Progress at Auburn University • Samples were manufactured using a cylindrical magnetron sputtering system • 22 total samples were sputtered with varying background argon pressure to investigate any correlation to stress and IMC growth and whisker growth.

3. Progress at Presbyterian College • Visited all collaborators • SEM was struck by lightning • The planned daily local whisker observations was modified to weekly observations at the University of South Carolina • Observations are summarized

4. Summary of observations from Presbyterian College • June 26 • No whiskers found • Samples 2 and 4 mTorr were scanned • Total area scanned: 0.175 mm2 • July 10 • 2 whiskers found on the 2 mTorr sample • Samples 2,4,6,10,16, and 20 were scanned • Total area scanned: 5.95 mm2 • July 16 • 2 whiskers found 1 on each of the 16 and 18 mTorr Samples • Samples 10, 12, 14, 16, 18, and 20 were scanned • Total area scanned: 5.25 mm2

5. Summary of observations from Presbyterian College • July 23 • 4 whiskers were found 2 on each of the 16 and 18 mTorr samples • All samples were scanned • Total area scanned: 9.11 mm2 • July 29 • 7 total whiskers were found on the 4, 12, 14, and 16 mTorr samples • All samples were scanned • Total area scanned: 8.93 mm2 • August 27 • 0 whiskers were found. • Samples 2, 6, 10, 14, 18, and 20 mTorr were scanned • Total area scanned: 5.78 mm2

6. Selected Whisker Micrographs 4 mTorr 6/26 16 mTorr 7/16 4 mTorr 7/23 16 mTorr 7/23 18 mTorr 7/29

7. Summary of conclusions from PC’s data • Initially, whiskers were found at low and high pressures, not at middle pressures. May support Thornton's theory • Approximate incubation time of 31 days for 2 mTorr, 37 days for 16 and 18 mTorr. Longer incubation for other pressures • Whisker density is not uniform through out the sample. • Whisker density is fluctuates with each observation • Average whisker length at this point is <3 μm • At this point whisker population density seems to increases faster than length

8. Formfactor’s Final Results

9. Abstract • FIB performed on Sn sputtered brass substrate at two different vacuums • 2 mT • 20 mT • Samples were cut in both June and July which are separated by 20 days • Findings: • No clear IMC layer is identified • No Sn whisker is identified

10. Example: FIB Cross-Section (2 mT in June) Pt layer Sputtered Sn layer

11. Example: FIB Cross-Section (2 mT in June) Pt layer Sputtered Sn layer

12. Example: FIB Cross-Section (2 mT in June) Cu L Sn L Pt M There is no IMC layer from chemical composition mapping Pt layer Sputtered Sn layer

13. Sample Sputtered in 2 mT July 30 June August 18 July 15 Possible IMC growth

14. Sample Sputtered in 20 mT July 30 June No Possible IMC growth July 15 August 18

15. Summary of intermediate conclusions from Formfactor’s data • Deposited Sn layer is uneven • No IMC formation at sputter deposition time • No IMC formation on 20 mTorr as of July 15 • Possible IMC formation on 2 mTorr as of July 15 • IMC growth is not necessary for whisker growth • Whiskers were found on samples 16 and 18 on July 16

16. Air Force Institute of Technology’s Final Results

17. Progress at AFIT • Initial data was collected using a Zygo interferometer to measure the curvature of the samples • Results are summarized on the following slide • Raman Spectroscopy and x-ray diffraction techniques to measure stress were explored and rejected • Steps are being taken to devise a new set of samples and new measurement techniques to obtain better data

18. Progress at AFIT • New samples were cut into perfect circles using laser cutting samples • The samples were shipped to Auburn University where they were sputtered at varying background Argon pressures • The samples were shipped back to AFIT, and our Major Starman was deployed to Afgahnastan. • Godspeed to Major Starman and his men

19. Summary of initial Observations from AFIT • Initial curvature was measured using an IFM. • A sample screen capture is shown • Subtracting out the estimated pre-sputter curvature, and using Stoney’s equation, the film stress was back calculated at PC. • The resulting graph is shown

20. Plot of Argon Background Pressure vs. Film stress Stress (Mpa) Background Argon Pressure during deposition (mTorr)

21. Intermediate Conclusions from AFIT’s Data • Initial data shows Thornton's theory false • Pre-sputter curvature is estimated and are microscopic in nature, therefore results are subject to speculation • Raman Spectroscopy and XRD are not suitable for this study • A Macroscopic data collection method is needed for this study • pre-sputter data is also necessary for comparison purposes • Curvature of a given sample varies widely within a given sample