Paper PS+2D+SE-WeM11
Pulsed Magnetron Sputtering Plasma Optimization for Large Area Growth of Two-dimensional MoS₂

Wednesday, October 21, 2015, 11:20 am, Room 210B

Pulsed magnetron sputtering process provides and alternative scalable and reduced temperature growth pathway for the direct synthesis of two-dimensional (2D) materials for electronic device applications [1]. To avoid defect generation by excessive ion bombardment, while maintaining sufficient adatom mobility on the condensation surface at low substrate temperatures, the ion flux and kinetic energy must be modulated. In this study a variable intensity magnetic field was used to control chemistry, energy, and spatial density distribution characteristics of plasma produced by pulsed magnetron sputtering of MoS₂ in 15 mTorr argon. An electromagnetic coil positioned above the substrate generated a 5-15 G magnetic field near substrate surface, causing redirection of magnetron particle flux for tuning of electron and ion densities at the substrate surface. Both plasma emission and mass-spectroscopy analysis showed an abundance of excited and ionized Ar as well as Mo and S species with no evidence for MoS radicals. Wavelength specific plasma imaging and mass/energy spectroscopy studies demonstrated that the applied magnetic field mostly affects excited and ionized Ar generated in background gas collisions with electrons trapped by the magnetic field lines, while the trajectories of Mo and S species generated from the target surfaces are influenced to a much lesser degree. The imposed magnetic field intensity was adjusted to selectively filter Ar species from reaching the substrate and to find a balance between reducing unnecessary Ar bombardment and preventing shifting energy distributions of all arriving ions above 8 Ev, where point defect generation is expected for hexagonal MoS₂. Plasma studies were used to select optimum growth conditions for 2D MoS₂ synthesis on SiO₂ surfaces at 700 ⁰C. Film thickness uniformity was verified by producing 2-3 monolayer layer thick hexagonal polycrystalline MoS₂ films over 25-50 mm scale area sizes as confirmed by in-situ Raman spectroscopy and TEM microscopy.

[1]. C. Muratore, J.J. Hu, B. Wang, M.A. Haque, J.E. Bultman, M. L. Jesperson, P.J. Shamberger, M. E. McConney, R.D. Naguy, A.A. Voevodin, “Continuous ultra-thin MoS₂ films grown by low-temperature physical vapor deposition”, Applied Physics Letters 104 (2014) 261604 1-5