| AVS 56th International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF2-MoM |
| Session: | Metals and Nitrides (ALD/CVD) |
| Presenter: | D. Seghete, University of Colorado at Boulder |
| Authors: | D. Seghete, University of Colorado at Boulder A.S. Cavanagh, University of Colorado at Boulder S.M. George, University of Colorado at Boulder |
| Correspondent: | Click to Email |
Metal ALD using thermal chemistry is limited and based on combustion reactions (Ru, Pt), organic or H2 reduction (Cu, Pd) or fluorosilane elimination (W). Molybdenum (Mo) is a refractory metal that has applications in alloys, catalysis and electronics. Mo ALD can be achieved with fluorosilane elimination chemistry using MoF6 and Si2H6 as reactants. This process is similar to W ALD using WF6 and Si2H6 as reactants. This study reports Mo ALD using a quartz crystal microbalance (QCM) to monitor the growth of the Mo ALD films and Mo/W alloy films in a hot wall viscous flow reactor.
QCM studies showed that Mo ALD is self-limiting for both MoF6 and Si2H6 reactants. MoF6 produces a large mass gain and Si2H6 produces a small mass loss. A mass gain of 535 ng/cm2 per cycle was observed at 120°C when both reactant exposures were in saturation.
Although long MoF6 residence times were observed on the surface, the Mo ALD growth per cycle was independent of purge time. The Mo film growth reached a linear regime after a short nucleation period of only 3-4 cycles on Al2O3 ALD surfaces. X-ray reflectivity (XRR) experiments confirmed linear Mo ALD growth versus number of cycles. A growth per cycle of 6.4 Å/cycle was measured at 120°C. The average density of the Mo films was 8.7 g/cm3 and there was excellent agreement between the QCM and XRR experiments. The temperature dependence of the Mo ALD growth per cycle was investigated from 90 ºC to 150 ºC.
X-ray photoelectron spectroscopy confirmed negligible F concentrations in the Mo ALD films. However, higher Si concentrations were observed in the Mo ALD films compared with W ALD films. The variation of Si content in the Mo ALD films was examined versus growth temperature and dosing conditions. Various Mo/W alloys can be produced by alternating Mo ALD and W ALD. These alloys can eliminate crystalline grain growth that occurs in the pure metals. This reduction of crystalline grain growth relieves the internal mechanical stress that develops in pure W ALD films.