High quality, stoichiometric thin films of hafnium diboride are deposited by chemical vapor deposition from the precursor Hf͓BH 4 ͔ 4 at deposition temperatures as low as 200°C. An activation energy of 0.43 eV͑41 kJ/ mol͒ is obtained for the overall process as monitored by temperature programmed reaction studies. Films deposited at low temperatures ͑Ͻ500°C͒ are structurally amorphous to x-ray diffraction; a 12 nm thick film is sufficient to prevent copper diffusion into silicon during a 600°C anneal for 30 min. Films deposited above 500°C are crystalline, but have a columnar microstructure with low density. All the films are metallic, but the low temperature amorphous films have the lowest resistivity ϳ440 ⍀ cm. The process is also highly conformal, e.g., a 65 nm wide trench with a 19:1 depth-width aspect ratio was coated uniformly.

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Thermal CVD from the single-source precursor Hf(BH4)4 affords stoichiometric, dense, and hard HfB2 films; this paper reports the growth kinetics in detail. The decomposition reaction starts at 200 °C; mass spectrometry of the material desorbing from the growth surface reveals that, for steady-state deposition at P ≤ 1 × 10-6 Torr, the reaction probability of the precursor is independent of flux and increases with temperature with an apparent activation energy of 0.43 eV. The precursor is less reactive on clean Si and SiO2 substrates than it is on the HfB2 growth surface. By analyzing the thickness profile of films grown on high-aspect-ratio trench structures, we find that the growth rate is proportional to P 0.3 for 1 × 10-4 < P < 1 × 10-2 Torr at a substrate temperature of 250 °C. The reaction probability of the precursor decreases from ∼1 to 1 × 10-4 as the precursor pressure increases from 1 × 10-6 to 1 × 10-1 Torr. This behavior is consistent with a Langmuirian surface-reaction mechanism. The conformality and the surface morphology of the HfB2 film are functions of the reaction probability of the precursor molecule. Extremely conformal and smooth coatings on deep trenches (>20:1 aspect ratio) can be obtained at low growth temperatures (≤300 °C) and high precursor pressures (∼0.1 Torr) with high growth rates (>200 nm/min).

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