| Hafnium diboride (HfB2) and chromium diboride (CrB2) are technologically important materials because of their high melting points, good thermal and electrical conductivity, high bulk hardness and corrosion resistance. This work develops the chemical vapor deposition (CVD) of HfB 2 and CrB2 thin films from Tetrakis(tetrahydroborato)hafnium, Hf[BH4]4, and bis(octahydrotriborato)chromium, Cr[B 3H8]2, respectively. These borohydride precursors are attractive because they are single-source and are free of halogens and organic groups, thus affording high purity films.; CVD from Hf[BH4]4 was investigated in the temperature range 200--900°C. An apparent activation energy of 0.43 eV was obtained for the process, as measured by temperature programmed desorption. Films deposited below 500°C were X-ray amorphous; films deposited above 500°C were crystalline, but had a columnar microstructure with low density. All the films were metallic, but the low temperature amorphous films had the lowest resistivity, ∼ 440 muO-cm. HfB2 films deposited below 300°C were dense and amorphous, and exhibited a respectable hardness of ∼ 20 GPa. Upon annealing to 700°C the films became nanocrystalline and the hardness increased to 40 GPa. Atomic nitrogen was added to the growth flux to obtain Hf-B-N ternary films, composed of HfB2, HfN and BN. The softer BN phase and the lower degree of crystallinity produced a drop in the hardness and elastic modulus. However, a multilayered HfB2/Hf-B-N film exhibited a good combination of high hardness (33 GPa) and low elastic modulus (300 GPa).; Stoichiometric and metallic CrB2 thin films were obtained from Cr[B3H8]2. The films had electrical resistivities of 105--450 muO-cm for growth temperatures spanning a range of 200--400°C. The film microstructure ranged from X-ray amorphous at low growth temperatures to nanocrystalline for substrate temperatures > 500°C.; Both HfB2 and CrB2 depositions were highly conformal. For example, a 65 nm wide trench with a 19:1 depth-width aspect ratio was coated uniformly with HfB2. The coverage improved further when an additional flux of a growth suppressor was added during deposition. Super-conformal CrB2 films were deposited by using atomic hydrogen, produced in a remote plasma source, as the suppressor. Growth suppression by atomic nitrogen enabled bottom-up filling of a 19:1 aspect ratio trench with an Hf-B-N film. |
