Reactive magnetron sputtering of tungsten target in krypton/trimethylboron atmosphere

Abstract

W-B-C films were deposited on Si(100) substrates held at elevated temperature by reactive sputtering from a W target in Kr/trimethylboron (TMB) plasmas. Quantitative analysis by Xray photoelectron spectroscopy (XPS) shows that the films are W-rich between ~ 73 and ~ 93 at.% W. The highest metal content is detected in the film deposited with 1 sccm TMB. The C and B concentrations increase with increasing TMB flow to a maximum of ~18 and ~7 at.%, respectively, while the O content remains nearly constant at 2-3 at.%. Chemical bonding structure analysis performed after samples sputter-cleaning reveals C-W and B-W bonding and no detectable W-O bonds. During film growth with 5 sccm TMB and 500 o C or with 10 sccm TMB and 300-600 o C thin film X-ray diffraction shows the formation of cubic 100-oriented WC1-x with a possible solid solution of B. Lower flows and lower growth temperatures favor growth of W and W2C, respectively. Depositions at 700 and 800 o C result in the formation of WSi2 due to a reaction with the substrate. At 900 o C, XPS analysis shows ~96 at.% Si in the film due to Si interdiffusion. Scanning electron microscopy images reveal a fine-grained microstructure for the deposited WC1-x films. Nanoindentation gives hardness values in the range from ~23 to ~31 GPa and reduced elastic moduli between ~220 and 280 GPa in the films deposited at temperatures lower than 600 o C. At higher growth temperatures the hardness decreases by a factor of 3 to 4 following the formation of WSi2 at 700-800 o C and Si-rich surface at 900 o C.

Efficient Synthesis of WB5–x–WB2 Powders with Selectivity for WB5–x Content

“…Figure a,b shows XPS spectra of the W4f region from the samples WB 5– x –WB 2 (50/50%) and WB 5– x –WB 2 (67/33%). Tungsten on the surface of the studied samples is in three states for WB 5– x –WB 2 (50/50%) and four states for WB 5– x –WB 2 (67/33%), namely, WO 2 , WB 2 , and WB 3 or WB 5– x , WO 3 with BE­(W4f 7/2 ) in the intervals 32.15–32.66, 33.57–34.84, and 35.56–36.16 eV, respectively, as well as an additional state with BE­(W4f 7/2 ) in the interval 31.17–31.59 eV allocated only for WB 5– x –WB 2 (67/33%) and related to the W–W bond. − The presence of the latter is confirmed by XRD data for this sample. As it can be seen, the contribution of these states varies depending on the synthesis conditions (current strength, exposure time, etc.…”

“…The B 1s spectra for WB 5– x –WB 2 (50/50%) and WB 5– x –WB 2 (67/33%) were deconvoluted into four and five components, namely, with BE­(B 1s) in the interval 183.92–184.61 eV indicating the presence of a B–B bond of amorphous boron; with BE­(B1s) in the interval 187.08–187.62 indicating the presence of a W–B bond; with BE­(B1s) in the intervals 189.19–189.46 and 190.51–191.11 eV indicating B–O bonds in B x O y (see Figure c,d and Table S5), ,− as well as for the sample of WB 5– x –WB 2 (67/33%), it was additionally identified the B 1s state with BE in the interval 185.01–186.06 eV related to the B–C bond; see Figure d and Table S5 in the Supporting Information. It should be noted that, as in the case of tungsten, the presence of the B–O bond indicates a partial oxidation of the sample surface by atmospheric oxygen.…”