PROCESS MONITORING AND CONTROL OF LOW-TEMPERATURE REACTIVELY SPUTTERED ALN

In this article we investigate the potential of controlling the sputte ring of AlN using a combination of techniques such as target voltage a nalysis and ellipsometry. The growth processes for ALN are studied sim ultaneously at the target, as well as the substrate. Iterative optimiz ation 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 s puttered using an unbalanced magnetron onto 2024-Al, (100)Si, and stai nless steel substrates and monitored by an in situ ellipsometer which indicated the index of refraction 'n' values of approximately 2.09-2.1 6 in the range 1.6-3 eV. Differing ion intensifies were achieved by Va rying 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 vo ltage. The profilometry tests indicated deposition rates of 38 nm/min. A detailed analysis of aluminum nitride formation with varying nitrog en flow was compared with the ellipsometric and target voltage versus nitrogen flow data to determine the optimal N-2 flow rate. The sputter ing rate of AlN was minimally 28% of the metal sputtering rate. (C) 19 98 Elsevier Science S.A. All rights reserved.