EVAPORATION OF A Cr/Cu/Cr MULTILAYER COATING WITH LOW TRANSMISSION IN THE INFRARED REGION Artoni Kevin R. Ang Thesis adviser: Mr. Ivan Culaba

Outline Abstract Introduction Review of Related Literature Design Methodology Results and Discussion Conclusion

Abstract A coating with low infrared transmission and moderate visible transmission has been designed and fabricated… …results of the experiments show samples with minimal transmission in the ,000 nm region. In the visible region, the transmission of the samples peaked in the nm region, with the percent transmissions of samples ranging from 1-60%...

Introduction Design, fabricate and characterize a thin film with low IR transmission The film materials to be used are copper and chromium, and the fabrication method to be used is physical vapor deposition via resistive heating.

Introduction Limitations: –Purity of copper used in evaporation –Thickness monitor controller stopped working –Lack of transmission data in nm

Review of Related Literature To address heat loss in buildings in Germany in the 70’s energy crisis. [3] employ metal thin films, either alone, or in combination with a single or several dielectric layers. [3, 4]. [3] Glaser, H. “History of the development and industrial production of low thermal emissivity coatings for high heat insulating glass units”. Applied Optics 47(13) pp C193-C199, [4]Fan, J. and F. Bachner. “Transparent heat mirrors for solar-energy applications” Applied Optics. 15(4) pp ,

Design employ metal thin films, either alone, or in combination with a single or several dielectric layers. Au and Ag are the most popularly used metals in infrared reflecting coatings [4]. [4]Fan, J. and F. Bachner. “Transparent heat mirrors for solar-energy applications” Applied Optics. 15(4) pp , 1976.

Design Refractive index nk Wavelength (nm)CopperSilverGoldCopperSilverGold Table 4.1. Optical constants of copper, silver and gold in the infrared region [6].

Design For glass substrates, there must be an intermediate adhesion Cr layer [9]. Another Cr layer to help suppress surface oxidation. [11-13]. Oxidation in the Cu layers increase transmission in the visible region by as much as 20% [10]. [9] Graper, E. B. “Thermal Evaporation”. Handbook of Thin Film Process Technology. Ed. Glocker, David and S. Ismat Shak. Institute of Physics Publishing, London [10]Santucci, S., P. Picozzi and L. Paoletti. “Oxidation effect on the optical properties of Copper Discontinuous Films”. Applied Optics. 22(20) pp , [11] Ang, Artoni, Paz. Ramos, Maria Jamero and Ivan Culaba “Evaporation of a multilayer coating with low transmission in the Infrared region”. Proceedings of the 27th SPP Physics Congress. Oct [12] Wetzig, K. and C. Schneider, Metal Based Thin Films for Electronics, Chapter 4, WILEY-VCH, Weinheim, [13]Sirringhaus, H., S. D. Theiss, A. Kahn, and S. Wagner, “Self-passivated copper gates for amorphous silicon thin film transistors,” IEEE Electron Device Letters 18(8), pp , 1997.

Methodology Sample Fabrication Glass slides –Samples mm x 25.5mm x 1.1mm Cleaned with compressed nitrogen gas, soap water solution, and 2-isopropanol. –Samples mm x 25.5mm x 1.1mm.

Blow compressed nitrogen gas to remove dust and grit. Rinse with tap water. Dab with soap water solution using Kimtech Science Kimwipes®. Pat dry with Kimtech Science Kimwipes®. KOH was applied on the surface. Rinse with tap water. Rub CaCO 3 and a few drops of KOH on the surface. Rinse. Repeat thrice. Apply HNO 3 Rinse with distilled water for 5 minutes. Rinse with tap water. Add few drops of 2-isopropanol Perform breath test

Methodology Sample Fabrication Thermal evaporation using the Kinney Vacuum Deposition Set-up Figure 5.1. The Kinney Vacuum Deposition Set-up.

Methodology Sample Fabrication The Cr layers: A of current through the chromium-coated tungsten rod ( nm/s) The Cu layers: A of current through the boat (from nm/s.) Cr coated tungsten rod Molybdenum dimpled boat

Methodology Microscopy Olympus BX60M Optical Metallographic Microscope JEOL JSM-5310 Scanning Electron Microscope Figure 5.6. The JEOL JSM-5310 SEM-EDX unit.

Methodology Optical Properties Ocean-Optics USB Spectrophotometer Shimadzu UV-2401 PC UV-VIS Recording Spectrophotometer Shimadzu IRAffinity 1 FT-IR Spectrophotomer The Shimadzu UV-2401 PC UV-VIS Recording Spectrophotometer. The Shimadzu IRAffinity 1 FT-IR Spectrophotometer.

Methodology Adhesion test similar to the pin pull test –3M™ Double sided tape The adhesion is then quantified using the equation F/A, A ~ 1 cm 2. Figure The adhesion testing set-up.

Results Film deposition (air)DepositionWorkingActual LayerRatePressureThickness (glass)(A/sec)(x10^-5 torr)(nm) Cr Sample 1Cu Cr7.228 Cr Sample 2Cu Cr Cr Sample 3Cu Cr Cr Sample 4Cu Cr Table 6.1. Summary of the deposition parameters of the four samples of the first batch.

Results Film deposition Exposure time (sec) CrCuCr Sample Sample 620 Sample Sample Sample Sample At 90 A for Cr layers, 180 A for Cu layers and pressure of 2x10^-5 torr Table 6.2. Deposition time of the six samples of the second batch of coatings.

Results Microscopy pits caused by island growth during thin film deposition [15]. the thin film deposition of pure elements eventually results in the formation of islands and channels [15]. In between these islands are pits where the islands have yet to coalesce. [15] Petrov, I., P. Barna, L. Hultman and J. Greene. “Microstructural evolution during film growth” Journal of Vacuum Science and Technology 21(5) pp S117-S128, μm Figure 6.1. Micrographs of the surfaces of samples 1-4 taken using the optical microscope.

Results Microscopy samples reveal the aggregated structure observed by Santucci, et al, for copper films [10] and by Henderson and Weaver for copper and chromium films [16]. [10] Santucci, S., P. Picozzi and L. Paoletti. “Oxidation effect on the optical properties of Copper Discontinuous Films”. Applied Optics. 22(20) pp , [16] Henderson, G. and C. Weaver. “Optical Properties of Evaporated Films of Chromium and Copper”. Journal of the Optical Society of America. 56(11) pp Figure 6.2. Micrographs of the surfaces of samples 1-4 taken using the electron microscope.

Results Microscopy No sharp boundary between cross section and film surface Figure 6.3. Cross sectional micrographs of the surfaces of samples 1-4 taken using the electron microscope.

Results SamplesMicrograph thickness (nm) Micrograph thickness (nm) Average Micrograph thickness (nm) Total film thickness from Quartz thickness monitor (nm) Table 6.3. Total film thicknesses from the cross sectional micrographs and the quartz thickness monitor.

Results Percent Transmission Actual Thickness (nm) 7.2 Sample Sample Sample Sample

Results Percent Transmission Actual Thickness (nm) 7.2 Sample Sample Sample Sample Taken using the Shimadzu UV-VIS spectrophotometer

Results Recall: –Samples 5-10 were evaporated without the use of the quartz thickness monitor Exposure time (sec) CrCuCr Sample Sample 620 Sample Sample Sample Sample

Results Percent Transmission Sample 5 Sample 7 Sample 6 Sample 8 Sample 9 Sample 10 Taken using the Ocean Optics Spectrophotometer

Results Percent Transmission No data was acquired in the nm region due to the unavailability of equipment. However, in a study conducted by Hass, the percent reflectance of copper films in the nm region is constant at around 90% [17]. [17] Hass, G.”Filmed Surfaces for Reflecting Surfaces” Journal of the Optical Society of America 45(11) pp , 1955.

Results Percent Transmission

Results Adhesion Different cleaning procedures show effect on film adhesion Figure 6.7. Adhesion test results for the ten samples, in force/unit area.

Results Adhesion No significant improvement on film adhesion Figure 6.8. Adhesion test results for the ten samples, and four pure copper thin films on glass substrates, in force/unit area.

Results and Discussions for the adhesion tests performed on the ten samples, no complete delamination occurred. Thus, the force measured by the force sensor is less than the critical force that would be necessary to pull off the film.

Conclusions In the infrared region, the four samples had an average transmission of %, %, % and %, respectively. the transmission of the samples peaked in the nm region, with the percent transmissions of samples ranging from 1- 60%.

Conclusions Adhesion tests show minimal improvement in the adhesion of the film, though different substrate preparations caused improvement in the adhesion of the film.

Recommendations Angular dependence of the visible and infrared transmission The transmission spectra in the nm region Oxidation effects on the optical properties of the film must also be studied. An alternative adhesion test procedure

Acknowledgements Research and Thesis Center of the SOSE School Board Mr. John P. Bermundo Dr. Benjamin Chan Mr. Rey Coria Ms. Carole Loable Mr. Ian Ken Dimzon Dr. Erwin Enriquez Mr. Roel Agas Mr. Numeriano Melaya Ms. Laurice Jamero Ms. Paz Ramos Mr. Myrron Aguila Mr. Ivan Culaba

Thank you for your time and attention!