Nitrogen-added Al rare-earth alloys for thin film transistors

The effects of nitrogen addition to aluminum-rare-earth alloys were investigated. Yttrium and gadolinium were employed as respective alloy components. The electrical properties and hillock densities of alloy films were investigated, and their nanostructures were studied by cross-sectional transmission electron microscopy. Nitrogen effectively decreases the grain size, and causes the columnar structure, that is generally present in aluminum-based alloys, to disappear. Nitric aluminum-rare-earth alloys have a strong resistance to hillock formation, and formed no micro-voids even after annealing at 450°C. An N2 flow rate of 1.3-10% in the sputtering gas gives a low hillock density of 2.0E + 1-7.7E - 1 pcs/mm2 after annealing at 350°C in both nitric Al-rare-earth alloys. In the case of patterned nitric aluminum-yttrium alloys, an N2 flow rate of less than 1.3% causes large side-hillocks after annealing at over 350°C. As an optimum value, an N2 flow rate of 2.5% results in a low hillock density of 1.9E + 1 pcs/mm2 and a low resistivity of 8.6 μΩ cm after annealing at 350°C. © 1999 Published by Elsevier Science S.A. All rights reserved.