AVS 61st International Symposium & Exhibition
    Selective Deposition as an Enabler of Self-Alignment Focus Topic Wednesday Sessions
       Session SD-WeM

Paper SD-WeM6
Surface Chemistry during ALD of SiNx from BTBAS and N2 Plasma

Wednesday, November 12, 2014, 9:40 am, Room 318

Session: Fundamentals of Selective Deposition
Presenter: Erwin Kessels, Eindhoven University of Technology, Netherlands
Authors: C.K. Ande, Eindhoven University of Technology, Netherlands
K. de Peuter, Eindhoven University of Technology, Netherlands
H.C.M. Knoops, Eindhoven University of Technology
S.D. Elliott, Tyndall National Institute, Ireland
W.M.M. Kessels, Eindhoven University of Technology, Netherlands
Correspondent: Click to Email
There is an urgent need for a scalable, low-temperature ALD process for the deposition of high-quality silicon nitride (SiNx). However the development of such process by thermal ALD has been challenging, particularly when the use of halide-free precursors is required. Plasma-enhanced ALD processes can provide a solution as we have recently demonstrated by the development of an ALD process based on SiH2(NHtBu)2 (BTBAS) precursor and N2 plasma. This process yields high-quality SiNx with a low wet etch rate and a good conformality on surface features with an aspect ratio of <5. In this contribution the surface chemistry during the SiNx ALD process will be addressed. On the basis of mass spectrometry and optical emission spectroscopy, the surface reactions during precursor adsorption will be discussed as well as the interaction of the N2 plasma species with the growth surface. In particular, the question will be addressed why the ALD process is feasible when using a pure N2 plasma but not when using a H2-N2 plasma or a NH3 plasma. On the basis of carefully-designed experiments involving multiple plasma and gas exposures of the surface during an ALD cycle, it will be shown that the presence of under-coordinated N atoms at the surface is key for precursor adsorption. This will be supported by first-principles simulations in which the interaction of a Si3N4(0001) surface with precursor molecules and various co-reactants (atomic H, atomic N and NH3) was probed. These atomic scale simulations reveal that atomic H and NH3 passivate the under-coordinated N and Si atoms on the surface rendering it unreactive towards the BTBAS precursor. N atoms on the other hand bind to under-coordinated surface N and Si atoms, but still leave behind under-coordinated N atoms on the surface. This understanding is vital to advance the precursor design for SiNx ALD as well as for further development and improvement of the SiNx ALD processes and material properties.