High repetition rate PLD grown titanium oxide thin films

Abstract

In this paper, we present a comprehensive study on the potentials and limitations of high repetition rate pulsed laser deposition (PLD), using a diode-pumped solid state (DPSS) Nd : YAG laser, operated at 532 nm. Titanium oxide thin films were deposited at 5 Pa of oxygen on silicon substrates with a different number of pulses, typically several tens of millions, and at pulse repetition rates (PRR) between 10 and 30 kHz, while keeping the pulse energy at a constant value. The lateral variation of thickness, void content and optical parameters along the radii of the circularly symmetric films were measured by spectroscopic ellipsometry and atomic force microscopy images were taken to reveal the surface topography of the films. In contrast to the conventional, i.e. low repetition rate PLD, the optical and topographical properties of the films were found to be uniform within an area of approximately 50 mm in diameter, while a decrease in the roughness of the films was evidenced towards the edges. The effects of an inherent property of DPSS lasers, namely the interrelated nature of PRR and pulse duration, were investigated. By means of a simple thermal model, it was shown that careful consideration of the characteristics of the laser is required to explain the experimentally revealed trends in the PRR dependence of the film growth rate.