Interfacial reactions and surface analysis of W thin film on 6H-SiC

Abstract

Tungsten (W) thin film was deposited on bulk single crystalline 6H-SiC substrate and annealed in vacuum at temperatures ranging from 700 to 1000 ºC for 1 hour. The resulting solid-state reactions, phase composition and surface morphology were investigated by Rutherford backscattering spectroscopy (RBS), grazing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM). XRD was used to identify the phases present and to confirm the RBS results. The RBS spectra were simulated using the RUMP software in order to obtain the deposited layer thickness, composition of reaction zone and detect phase formation at the interface. RBS results showed that interaction between W and SiC started at 850 °C. The XRD analysis showed that WC and CW 3 were the initial phases formed at 700 ºC and 800 °C. The concentration of the phases was however, too low to be detected by RBS analysis. At temperatures of 900 °C and 1000 °C, W reacted with the SiC substrate and formed a mixed layer containing a silicide phase (WSi 2 ) and a carbide phase (W 2 C). The SEM images of the as-deposited samples showed that the W thin film had a uniform surface with small grains. The W layer became heterogeneous during annealing at higher temperatures as the W granules agglomerated into island clusters at temperatures of 800 °C and higher.

Surface and interface structural analysis of W deposited on 6H–SiC substrates annealed in argon

“…Based on this model, one can expect the hydrogen annealed samples to have smaller crystallites than the vacuum annealed samples -as was observed. 24,26 Because Ar is a noble gas with no chemi-sorption and little physio-sorption expected on the surfaces, the Ar annealed samples should have the largest crystallites -also observed in this study. This model of impurities sticking on the crystallites surface might also be the reason for the different phases being formed in the different annealing environments.…”

“…3. The average crystal sizes of the Ar annealed (from 700 C to 1000 C) W-SiC samples are larger and more randomly orientated when compared to vacuum annealed 26 and hydrogen annealed W-SiC samples. 24 A slow crystal growth in the form of grains was observed during annealing in hydrogen.…”

“…The formation of large crystals and spaces between crystals on the W-SiC surfaces was also observed on W-SiC samples annealed in vacuum. 26 These cavities are formed during the parasitic growth of crystallites and crystal surfaces at elevated temperatures. Parasitic growth follows Wulf's law 31 and is due to the feeding from crystal surfaces with lower surface energies to surfaces with higher surface energies, resulting in the former growing faster than the latter thereby exposing larger areas of crystal surfaces with lower surface energies.…”

“…In fact, WO 3 was detected in those samples aer annealing. 26 Hydrogen is a reacting gas which is commonly physio-sorbed or chemi-sorb on surfaces. According to the step-ow mechanism 32 of crystal growth, impurity atoms on the growth surfaces of crystallites inhibit the growth process of the crystallites.…”

The effect of thermal annealing in a hydrogen atmosphere on tungsten deposited on 6HSiC

“…Recently, we reported on the vacuum annealing of a thin tungsten layer deposited on 6H-SiC [14]. In this study, we report on the effect of thermal annealing of the same system in hydrogen and the reactions which occur due to annealing.…”