Process monitoring and control of low temperature reactively sputtered AlN

In this article we investigate the potential of controlling the sputtering of AlN using a combination of techniques such as target voltage analysis and ellipsometry. The growth processes for ALN are studied simultaneously at the target, as well as the substrate. Iterative optimization can be replaced almost entirely with in situ, real time process control/monitoring; reducing development time of a new process by more than an order of magnitude. To demonstrate this, AlN was reactively sputtered using an unbalanced magnetron onto 2024-Al, (100)Si, and stainless steel substrates and monitored by an in situ ellipsometer which indicated the index of refraction 'n' values of approximately 2.09-2.16 in the range 1.6-3 eV. Differing ion intensifies were achieved by Varying the bias on the substrate, and the effects were studied by X-ray diffraction, and profilometry. X-ray diffraction confirmed formation of hexagonal aluminum nitride with a preferred orientation of (001) by using a constant bias current substrate instead of a constant bias voltage. The profilometry tests indicated deposition rates of 38 nm/min. A detailed analysis of aluminum nitride formation with varying nitrogen flow was compared with the ellipsometric and target voltage versus nitrogen flow data to determine the optimal N-2 flow rate. The sputtering rate of AlN was minimally 28% of the metal sputtering rate. (C) 1998 Elsevier Science S.A. All rights reserved.