1.0 nm Oxynitride Dielectrics Prepared by RTP in Mixtures of N[sub 2] and O[sub 2] Ambient

Abstract

This work presents a reliable method of growing aggressively scaled, 1.0 nm thick, gate dielectric in mixtures of N 2 and O 2 ambient at 900°C for 15 s by rapid thermal processing ͑RTP͒. These oxynitride films have excellent interface properties, 100 times lower leakage current density, and better charge trapping properties than rapid thermal oxidation SiO 2 of identical thickness prepared in pure O 2 ambient. The effect of interfacial nitrogen concentration on the device characteristics with gate oxynitride films grown in various N 2 /O 2 gas flow ratios was also investigated. The results demonstrate that the uniform nitrogen content increases with the N 2 /O 2 gas flow ratio and that high-quality oxynitride films can be obtained by RTP in an optimum gas flow ratio of N 2 /O 2 ϭ 5/1 (slm).Highly reliable and aggressively scaled gate dielectric films ͓equivalent oxide thickness (EOT р 1 nm͔ are essential for developing complementary metal-oxide semiconductor ͑CMOS͒ technologies beyond the sub-0.1 m regime. However, when the thickness of SiO 2 is reduced below 2 nm, the primary concerns in the use of ultrathin oxides are gate leakage and device reliability. 1 Accordingly, the use of alternative gate dielectrics must be considered. The formation of ultrathin oxynitride gate dielectric using a nitrogencontaining gas ͑such as N 2 O or NO͒ to improve the leakage current, reliability, and superior resistance to boron penetration have been examined extensively. 2,3 However, as the oxynitride thickness continues to be reduced to the 1.0 nm regime, the maximum nitrogen concentration that can be incorporated by the aforementioned processes decreases and the oxynitride film becomes leaky and no longer reliable. 4 Although NH 3 -nitrided SiO 2 films can be used effectively to increase the concentration of incorporated N atoms, increased fixed charge and interface trap densities are unavoidable due to electron trap related N-H bonds introduced from NH 3 . 5,6 An oxynitride growth process that can provide nitrogen-rich oxynitride films, is required to improve electrical characteristics and thus solve these problems and achieve an ultrathin oxynitride film (EOT ϭ 1.0 nm) with more incorporated nitrogen. This paper develops a new technique for fabricating nitrogen-rich ultrathin oxynitride films down to physical thickness 1.0 nm by rapid thermal processing ͑RTP͒ in a high N 2 /O 2 gas flow ratio ambient ͓rapid thermal nitrided oxide ͑RTNO͔͒. The optimum growth conditions and electrical characteristics of oxynitride dielectric by RTNO are also demonstrated. ExperimentalMOS capacitors with high quality 1.0 nm thick oxynitride films were fabricated using a compatible 0.13 m CMOS processing technology. The 3-5 ⍀-cm n-type silicon ͑100͒ wafers were cleaned using piranha (H 2 SO 4 :H 2 O 2 ϭ 5:1) solution for 10 min, and then thoroughly rinsed in deionized ͑DI͒ water. The wafers were then washed in 1% HF acid immediately before the dielectric film was grown. The 1.0 nm thick gate oxynitride films were grown by RTP at various N 2 /O 2 ...