The stability of low-pressure chemical vapor-deposited TiB2 films has been investigated for their potenital use as diffusion barriers between A1 or Cu metallurgy and the Si substrate during post-metal annealing at temperatures ranging from 450-640~ for A1, and 500-800~ for Cu. Although no evidence of intermixing was observed via Rutherford backscattering spectroscopy (RBS) for TiB2/Si samples rapid thermal-annealing (RTA) up to 1080~ pyramid-shape pits in the Si, bounded by (111) planes, were observed using transmission electron microscopy for the samples annealed above 950~ Secondary ion mass spectroscopy depth profiles of B in Si originating from the TiB2 solid source suggested enhanced diffusion after RTA. According to RBS spectra coupled with scanning electron microscopy (SEM) examination, A1/TiB2/Si (pre-annealed) stacks appeared to be stable up to 500~ for 30 min in forming gas. For the stacks with as-deposited (amorphous) TiB2 films, plan-view SEM of A1/TiB2/Si showed very limited reaction with A1 up to 600~ in good agreement with sheet resistance measurements. The as-deposited, amorphous TiB2 films were superior diffusion barriers compared to the annealed, polycrystalline TiB2. No interaction took place between sputtered Cu and an underlying, amorphous TiB2 film up to 750~ 30 min in vacuum. Plan-view SEM, RBS, and sheet resistance measurements showed that the structure started to break down at 775~
The correlation between the resistivity of TiB2 and the chemical vapor deposition parameters and subsequent annealing temperature have been studied. The films deposited from TiCl4 and B2H6 above 600 °C are found to be nearly stoichiometric TiB2 with a resistivity of 250 μΩ cm±20%, while those deposited below 600 °C are found to contain excess boron, and exhibit a higher resistivity. The resistivity of the films is observed to be independent of thickness in the thickness range from 15 to 550 nm. After high-temperature rapid thermal annealing (≳1000 °C), the resistivity is reduced to as low as 36 μΩ cm. The grain size in annealed films increases exponentially with temperature. The conductivity and the Hall mobility of the samples increase linearly with the grain size. The activation energy of grain growth, conductivity, and Hall mobility was found to be the same, 1.6–1.7 eV. From these results, it is evident that the carrier mobility of TiB2 is dominated by grain boundary scattering. The lower limit for resistivity of chemical vapor deposited TiB2 films is expected to be attainable only after annealing at temperatures approaching 1300 °C.
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