Paper TF-ThP2
Pulsed DC Magnetron Sputtered Nickel Thin Films: A Study of Stress, Density and Electronic Properties

Thursday, October 21, 2010, 6:00 pm, Room Southwest Exhibit Hall

With the advent of pulsed magnetron direct current (DC) sputter deposition technology, there have been gains made in the deposition of various inorganic thin films.¹ Most notably used for reactive sputtering of oxides and nitrides, pulsed DC sputtering has led to the deposition of dense coatings with improved properties such as adhesion and wear. The property changes have been attributed to the differences in flux and energy of the species involved with growth.

In this work, we explore the effects of using pulsed DC methods for sputtering monolithic ~ 200 nm-thick nickel films. The power supply used for this study is the Advanced Energy Pinnacle Plus 10kW series, which allows for continuous or pulsed DC sputtering modes. We demonstrate the effects of argon sputter pressure (1-25mT) on residual stress, film density and film resistivity for various pulsed DC processes and contrast these with the properties formed during continuous DC sputtering. For the pulsed DC experiments we show how these three film properties (stress, density and resistivity) depend on argon pressure for each of four different pulse frequencies (50, 150, 250 and 350 kHz - reversal time is held at 1.0 μs). Residual stress is determined through wafer curvature methodologies – working within the assumptions of Stoney’s­ equation². Film density determined using x-ray reflectivity. Room temperature resistivity is determined using four-point probe instruments.

In general, the stress can be tailored during pulsed DC and constant DC sputtering by adjusting argon sputter pressure. For most conditions, the films are in a state of in-plane tensile stress after deposition and cooldown although near-zero stress can be obtained at lower pressures. Pulse frequency is shown to have a minor effect on residual stress for most processes. However, frequency has a greater effect on stress at the lower sputter pressures (1-5mT). We further evaluate the stress of all films in terms of intrinsic and extrinsic contributions to isolate the role of pulsed DC sputtering process parameters on intrinsic stress. Extrinsic stress effects (due to mismatch in thermal expansion coefficients) are factored out from the final, residual stress using known temperatures achieved during deposition and the mechanical properties of the film and substrate.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Co., for the United States Department of Energy’s National Nuclear Security Administration under Contract No. DEAC04-94AL85000.

References:

1) J. Lin, J.J. Moore, W.D. Sproul, B. Mishra and Z. Wu, Thin Solid Films 518 (2009) 1566.

2) G.G Stoney, Proc. Roy. Soc. Ser A, 82 (1909) 172