Conformal MgO film grown at high rate at low temperature by forward-directed chemical vapor deposition

MgO thin films are deposited by chemical vapor deposition from the precursor magnesium N,N-dimethylaminodiboranate, Mg(H₃BNMe₂BH₃)₂, and water at a substrate temperature of 270-350 °C. Highly conformal coatings with 98% step coverage in trenches of aspect ratio 9 are obtained at a substrate temperature of 270 °C and a growth rate of 7.5 nm/min, most notably through the use of a forward-directed flux, in which some of the precursor molecules travel ballistically down the recessed feature, strike the bottom, and are scattered there to create a virtual source. The deposition conditions can also be adjusted to afford a growth rate up to 200 nm/min with reduced conformality. Most of the films have a dense and column-free microstructure with low surface roughness; the film density, measured by a combination of Rutherford backscattering spectrometry and scanning electron microscopy, is 82%-86% of bulk. Films grown on Si substrates have good adhesion and a low coefficient of friction (∼0.1) in nanoscratch measurements. The refractive index of the films is slightly lower than that of bulk MgO, consistent with the reduced physical densities. Depending on the growth conditions, the C content in the films varies between 0.7 and 6 at. %, and the B content ranges from 1 to 16 at. %. B in the film is present in the B₂O₃ chemical state; after subtracting the O content in B₂O₃, the O/Mg ratio = 1.02 in the MgO matrix. A film grown at a temperature of 270 °C and a growth rate of 6 nm/min has a dielectric constant of 9.5 and a breakdown strength of 6 MV/cm.