Real-time spectroellipsometric characterization of nucleation, islanding, and coalescence behavior of boron films grown by soft x-ray excited chemical vapor deposition

Real-time spectroscopic ellipsometry was applied to the in situ monitoring of soft x-ray excited chemical vapor deposition of boron films on a Si(001) substrate. While B(2)H(6) molecules cannot reactively stick to a Si clean surface below 400 degrees C, the decomposition of the precursor molecule through electronic excitation enables boron atoms to secure themselves on the surface. After the incubation period had ended, boron islands began to grow at isolated nucleation centers, exhibiting the Volmer-Weber-type growth. The activation energy for creating the nucleation centers was 2.9 kcal/mol, which presumably corresponded to the clustering of deposited boron atoms. The following growth stage was scaled with an activation energy of 10.3 kcal/mol. The thermally activated process corresponded to the networking of surface-terminating hydrides while releasing H(2). As further growth continued, boron islands coalesced, which eventually became two-dimensional boron film. The amorphous boron films could be transformed into a crystallite phase through postannealing at 1000 degrees C and they were characterized in terms of their optical properties.