Film properties of Ti/TiN bilayers deposited sequentially by ionized physical vapor deposition

Abstract

Ionized physical vapor deposition (iPVD) has received much attention as a method for depositing material at the bottom and on the sidewalls of the high aspect ratio features proposed for sub-0.25 micron integrated circuits. In this article, we describe the film properties of Ti/TiN bilayers deposited sequentially using the iPVD technique. The experimental configuration consisted of a planar magnetron sputtering source in combination with an inductively coupled RF plasma. TiN was reactively sputtered from a titanium target which remained non-nitrided throughout the deposition, a process commonly referred to in non-ionized PVD as operating in the non-nitrided mode (NNM). These films were analyzed by cross-sectional scanning electron microscopy and transmission electron microscopy, automated four-point sheet resistance probe, x-ray diffraction, x-ray fluorescence, stress gauge, and Rutherford backscattering. Highly oriented 〈111〉 TiN was observed on 〈002〉 oriented Ti underlayers. At via aspect ratios of 4:1 with vertical sidewalls, bottom coverage approaching 100% was obtained. Varying process parameters did not change the bulk resistivity significantly, and values as low as 23 μΩ cm were measured for the NNM TiN films. Mechanical stress was strongly influenced by substrate temperature, as has been observed for both conventionally sputtered and collimated Ti/TiN. Below 200 °C, the films were highly compressive, but values below 2 GPa were obtained at 400 °C. RF plasma power and pressure were also found to affect stress. Deposition rates of 900 Å/min were measured, corresponding to a specific deposition rate of 1.8 Å/kW s.