Pulsed DC Sputtered Aluminum Nitride: A Novel Approach To Control Stress And C-axis Orientation

Abstract

ABSTRACTThis paper reports on a novel low temperature sputter deposition of AlN on an Al substrate, yielding films with stresses and crystalline orientation comparable to those of films deposited on Pt. The study focuses on the importance of the initial film growth step on both the stress and crystalline orientation of the film. The AlN layer is deposited using Pulsed DC (250 kHz, 90% duty cycle) magnetron reactive sputtering (93% N2, 7% Ar) using an Al target. The substrates are 150mm Si wafers with an aluminum seed layer (100 nm). The thickness of the AlN films is ≈2.5μm with uniformity across the wafer of 0.4%. The films were deposited in 4 passes of 0.625μm each to avoid overheating of the substrate. The influence of the substrate bias (0 V, 80 V and 120V) and argon pre-sputtering of the aluminum substrate been investigated. The film stress, and to a smaller extent the crystalline orientation, were mainly driven by the properties of the film deposited during the first pass. The bias is useful at the beginning of the film growth for stress control. This study suggests that it is beneficial not to use bias during the entire film deposition. With this approach, it was possible to deposit c-axis oriented AlN layers on Al with a FWHM of the rocking curve of 1.63° and low stress (<300MPa).