(530b) Hot Wire Assisted Chemical Vapor Deposition (HWCVD) of Niobium Nitride Thin Films

Niobium nitride films are very interesting materials due to their extraordinary properties and their potential applications in corrosion inhibition, wear prevention, superconduction and catalysis, among others.While there have been several efforts in the past to obtain thin films of this material by different techniques (e.g. PVD, thermal atmospheric CVD, PECVD, and ALD methods), yet the prior art clearly fails to disclose a method to deposit niobium nitrides via hot-wire assisted chemical vapor deposition. Furthermore, the mechanisms associated with HWCVD are, to certain extent, still not very well understood. 

This study evaluates two HWCVD experimental approaches differing mainly in the method of supplying niobium species in the reaction zone. The first of which comprises feeding NbCl₅ precursor (99%) along with different N₂/H₂ ratios into a hot-filament assisted reactor operating under mid-vacuum.  Alternatively, the reaction vessel is fed with N₂/H₂ atmospheres and a pure niobium filament (99.99%) is used as metal source. 

Specifically, the effect of substrate temperature is evaluated in the range 700-1100ºC at total pressures between 10 and 100 mbar, for deposition on Si [100] treated with ethanol/acetone solutions. Deposit samples have been characterized in their composition and morphology by SEM-EDS, XRD and AFM finding that niobium compounds grow both on filaments and on silicon substrates. 

It is apparent from our preliminary results, however, that homogeneous, well-adhered films are obtained at low growth rates. Scanning electron micrographs reveal the formation of nano-structured intergrown multifaceted rodlike crystal arrays. The inhibition of nitride formation induced by oxide growth is a problem that remains to be overcome.

In view of the foregoing, it is the objective of the work at hand to gain insight into the mechanisms of film growth and elaborating on the phenomena governing heterogeneous nucleation by comparing different chemical routes and process conditions, to obtain conformal niobium nitride thin films.