Jian Liu

Date of Award


Degree Type


Degree Name

Doctor of Philosophy






Hafnium silicate is one of the most promising high dielectric constant (high-ft) candidates being investigated as an alternative to replace Si0 2 as a gate dielec­ tric material in complementary metal-oxide-semiconductor transistors. In this the­ sis, Hf silicate films were grown by atomic layer deposition using the liquid pre­ cursors tetrakis(diethylamido)hafnium (TDEAH) and tris(2-methyl-2-butoxy)silanol (TMBS). The dynamic growth processes were monitored by in situ spectroscopic el- lipsometry. A self-limiting growth with a rate ~1 monolayer per cycle was observed only after several initial cycles —a behaviour that is ascribed to the chemistry of the initial Si substrate surface.

The film composition, as a function of the substrate temperature and TMBS pulse time, was characterized by x-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (MEIS). It was found that the Hf concentration, i.e., the Hf/(Hf+Si) value, can only be adjusted in the range 0.22—0.30; the carbon con­ tamination in the film can be minimized by assuring that the self-limiting condition is achieved for the TMBS precursor. A possible reaction mechanism between the TDEAH and TMBS precursors is proposed.

Hf distributions in the as-grown and annealed Hf silicate films with thicknesses in the range 4—20 nm were investigated by high resolution transmission electron microscopy (HRTEM), angle resolved x-ray photoelectron spectroscopy (ARXPS) and MEIS. HRTEM images showed a layered structure for films thinner than 8 nm. ARXPS data also showed a non-uniform distribution of Hf throughout the film depth. A diffusion of SiC>2 to the film surface after a longer time anneal was observed by MEIS. All these observations provide evidence for surface-directed spinodal decom­ position in the pseudobinary (Hf0 2 )x(Si0 2 )i-x alloy system.



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