| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS+TF-WeA |
| Session: | Plasma Deposition and Plasma Assisted ALD |
| Presenter: | Martijn Vos, Eindhoven University of Technology, Netherlands |
| Authors: | M.F.J. Vos, Eindhoven University of Technology, Netherlands N.F.W. Thissen, Eindhoven University of Technology, Netherlands A.J. Mackus, Eindhoven University of Technology, Netherlands W.M.M. Kessels, Eindhoven University of Technology, Netherlands |
| Correspondent: | Click to Email |
Cobalt is a transition metal which is receiving much interest, among others due to its ferromagnetic properties. One of the promising applications is in multilayers and alloys of Co/Pt, which are used in nonvolatile memory devices such as magnetic random-access memory (MRAM). For many of the applications of Co the key strengths of atomic layer deposition (ALD), i.e. conformality and ultimate thickness control, can be very beneficial. In previous work, the ALD processes using cobaltocene (CoCp2) and NH3 or N2/H2 plasma showed a decent growth-per-cycle (GPC) and good material properties, including a low resistivity.1,2 It was found that the best material properties were obtained for a N2/H2 mixing ratio of ~0.33, corresponding to the highest production of NH3 in the plasma. This result suggests that NH3 is necessary for obtaining high purity Co films.
In this contribution we address ALD of Co films using CoCp2 and subsequent N2 and HH2HHfdfd H2 plasmas. By comparing this ABC process to the AB process with a combined N2/H2 plasma the role of NH3 can be further investigated. Moreover the ABC process offers additional flexibility over the AB process, such as different powers and pressures during the subsequent plasma steps. Films were deposited on different substrates, including Si, SiO2 and Pt, at temperatures from 100 to 300°C yielding a GPC between 0.2 and 0.4 Å. It will be shown that despite the absence of NH3 in the plasma, the ABC process can be used to deposit high-purity films of Co on ALD Pt films, with contamination levels as low as 1 at.%, as measured by X-ray photoelectron spectroscopy (XPS). On the other hand, considerable amounts of C, O and N contamination (2-10 at.%) in Co films deposited on Si and SiO2 suggest that NH3 is a prerequisite for high purity films on these substrates. This difference between deposition on Pt and Si/SiO2 is likely due to the catalytic activity of the Pt, causing the reduction or ‘cleaning’ of the deposited Co. In addition the fabrication of Co/Pt multilayers using ALD will be discussed.
1. Lee, H.-B.-R. et al., Electrochem. Solid-State Lett. 9, G323 (2006).
2. Yoon, J. et al., J. Electrochem. Soc. 158, H1179 (2011).