Chemical and structural characterization of Hf-based high-k dielectrics by X-ray spectroscopy

Full text: For years, silicon oxide (SiO₂) had been used as gate dielectric for field effect transistors; however, in sub-100nm devices, this material presents high leakage currents, due to loss of their dielectric properties. For this reason, different high k materials have been suggested as candidates to substitute the SiO₂ and SiO_xN_y as gate dielectric. The most promising candidate to substitute the conventional gate dielectrics is the HfO₂, although its low crystallization temperature (≈ 500°C) is an important restriction so that to improve its thermal stability, the incorporation of Al or Si in the phase of the HfO₂ has been proposed. Usually, when these ones are thermally treated, the nanoparticles formation takes place. In order to investigate the conditions that allow the formation of nanoparticles, 50 − mol%Hf mixed with Al and O were deposited on silicon substrate by atomic layer deposition and annealed at 1000°C in two different environments (N₂ and N₂ + 5%O₂) during 60 s by two methods: rapid thermal processing (RTP) and laser annealing. Following, the films were chemical and structurally characterized by X-ray reflectance (XRR, λ = 1.749), grazing incidence small angle scattering (GISAXS, λ = 1.749), and X-ray diffraction (XRD, λ = 1.542). The results show that the thickness of the deposited layers was about 28.8 nm and the surface roughness varied as function of the annealing environment. The roughness of the film annealed in N₂ + 5%O₂ was larger (1.3 nm) than that for the films annealed in N₂ (≈ 0.9nm). For the case of the critical angle (θc), it is larger for the film annealed by laser (θ_c = 0.430°) compared to those annealed by RTP (0.413 and 0.414 ). On the other hand, the GISAXS analysis shows the formation of spheroidal nanoparticles with different radius (R) and height (H) depending on both thermal method and environment. The largest nanoparticles are formed when the films are annealed by laser (R=2.0 nm; H=4.4 nm) while the smallest ones are obtained when the film is treated by RTP in N2 (R=1.41 nm; H=2.94 nm). The addition of 5% of O into the annealing environment yields slight variation of the size (R=1.45 nm; H=2.85 nm). XRD reveals larger formation of HfO₂ phases for films annealed by RTP, whereas after annealing by laser the films remain predominantly amorphous with the lowest nanoparticles of Al_2.4O_3.6. In summary, the most adequate thermal treatment to avoid the nanoparticle formation was shown to be the annealing by laser. (author)