Reactions for Yttrium Silicate High-k Dielectrics

Abstract

The continued scaling of metal-oxide-semiconductor-field-effect-transistors (MOSFETs) will require replacing the silicon dioxide gate dielectric with an alternate high dielectric constant (high-k) material. We have exploited the high reactivity of yttrium with both silicon and oxygen to form yttrium silicate high-k dielectrics. Yttrium silicate films with composition of (Y)₁₋[subscript x] and x = 0.32 to 0.87 are formed by oxidizing yttrium on silicon where yttrium reacts concurrently with silicon and oxygen. The competition between silicon and oxygen for yttrium is studied using X-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (MEIS). The initial yttrium thickness mediates the silicon consumption, and a critical thickness (~40-80 Å) exists below which silicon is consumed to form yttrium silicate and above which Y forms without silicon incorporation. Engineered interfaces modify the silicon consumption, and a nitrided silicon interface results in film with composition close to Y. The silicon consumption also depends on the oxidation temperature, and oxidation at higher temperature generally results in greater silicon incorporation with an activation energy of 0.3-0.5 eV. Yttrium silicate films (~40 Å) formed by oxidation of yttrium on silicon have an amorphous microstructure and an equivalent silicon dioxide thickness of ~12 Å with leakage current . Yttrium silicate formation on silicon is also demonstrated using plasma oxidation of yttrium on silicon, reactive sputtering of yttrium and annealing/oxidation of yttrium on thermal SiO. The interface reactions described here for yttrium are expected to be active during both physical and chemical vapor deposition of other high-k dielectrics containing Hf, Zr and La.