Intelligent process control of indium tin oxide sputter deposition using optical emission spectroscopy

Abstract

The dc sputtering of indium tin oxide (ITO) is a high deposition rate process yielding a low-resistivity, high-transmission thin film that is useful to the display, photovoltaics, and optoelectronics industries. However, a number of deposition variables that are not typically controlled during sputtering, such as target age and history, and water partial pressure, can cause ITO film properties to deviate from their optimum values. Control of such deviations is necessary to maintain high yield and low costs in manufacturing. Optical emission spectroscopy (OES) can be used to monitor the deposition process and maintain optimum film properties. Basic relationships between the OES signals during deposition and the ITO film properties were established. Closed-loop control of the ITO deposition was implemented using OES. Improved yield—specifically, decreased resistivity, decreased variance in resistivity, and decreased variance in thickness—was demonstrated.