Indium tin oxide, ITO, is a transparent conducting oxide widely known for its low resistivity and high transmission in the visible spectrum. It is most commonly used as a contact in optoelectronic devices, where its transmission is paramount to the function of the device. In this work, a low thermal budget process to sputter ITO films to potentially expand its applications in the RIT cleanroom was developed. The baseline process utilized a dielectric In2O3:SnO2 sputter target and a 2 hour, 400◦C post deposition anneal step to achieve a high quality film. This work achieved films with similar properties, but with anneals of 1-2 hours in the 230-250◦C range. A new processing window using a metal InSn sputter target was derived. By reactively sputtering oxygen deprived ITO films and annealing them at lower temperatures, the overall thermal budget was reduced. DOE techniques were used to define the following optimal parameters: a partial pressure combination of 11.2mT of Ar and 0.8mT of O2, deposition power of 95 or 100W, and a 10 minute presputter at 110W. Using these conditions, anneal DOEs were created and run. It was found that the power was a driving factor in the oxygen content and crystal structure of the film. Films sputtered at 95W were more glass-like and had a strong XRD (622) peak, while 100W films were more metallic and had a preferential (222) peak. It was found that a 95W film annealed for two hours at 230◦C yielded an ITO film with the best combination of low resistivity, 9.55x10−4Ω-cm, and good transmission, 78.54%, over the 380 to 750 nm range. These results are comparable to the baseline process, while reducing the anneal time by 2 hours and temperature by 170◦C. As a proof of concept, an ITO anti reflective coating, ARC, was used on three different silicon solar cells and compared to a SiO2 ARC. The ITO ARC yielded functional cells with an AM1.5 efficiency of 8.8%, a fill factor of 65.37%, and an open circuit voltage of 541.4mV. However, since the ITO is not 100% transparent, it caused a slight decrease in the short circuit current, dropping from 42 to 40mA. The SiO2 ARC cells on the same wafer exhibited lower VOC values, which is indicative of processing issues with the oxide, so we cannot conclude the ITO ARC was better from our limited results. Annealing the ITO at 230◦C for an hour caused a decrease in shunt resistance, from 250 to 15.4Ω, fill factor, from 67.3 to 37.9%, and efficiency, 8.7 to 7.3%. No such degradation occurred with the SiO2 ARC cells on the same wafer, indicating that the 230◦C anneal may have triggered an interaction between the ITO and the Ti/Al films. These results show future work may be needed to further lower the thermal budget for the ITO film process.
Library of Congress Subject Headings
Indium tin oxide--Thermal properties; Microelectromechanical systems--Materials; Thin films
Materials Science and Engineering (MS)
Department, Program, or Center
School of Chemistry and Materials Science (COS)
Flowers, Zachary, "Reduction in the Thermal Budget of Sputtered Indium Tin Oxide (ITO) to Potentially Broaden its use in Microelectronic Devices" (2023). Thesis. Rochester Institute of Technology. Accessed from
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