Nitrogen profile effects on the growth rate of gate oxides grown on nitrogen-implanted silicon

Abstract

Nitrogen implantation effect on SiO2/Si interface roughness is analyzed and a new method for growing ultrathin gate oxide is proposed. Interface roughness is improved by nitrogen implantation; the root-mean-square values measured by atomic force microscopy are 2.72–2.79 Å, 1.7–2.12 Å, and 2.12–2.33 Å for 0, 1.0×1014/cm2, and 2.0×1014/cm2 nitrogen implantation, respectively. Initial O2 injection method is composed of O2 injection/N2 anneal/main oxidation, and the control process is composed of N2 anneal/main oxidation. The purpose of O2 injection is to form an extremely thin oxide layer that provides a Si/SiO2 interface at which nitrogen is accumulated during N2 annealing process. Time of flight secondary ion mass spectroscopy data show that the initial O2 injection method has a higher peak than that of the control process. The oxidation reduction rates of the control process were: 0.6% (15.4 Å/15.5 Å), 18.2%(26.9 Å/32.9 Å), and 16.4% (34.1 Å/37.4 Å) for the wafers of 1, 10, and 20 min oxidation time, respectively. And the rates of the initial O2 injection method were 7.6% (19.4 Å/21 Å), 25% (23.1 Å/30.8 Å), and 29.5% (28.4 Å/40.3 Å). It is clear evidence that the nitrogen profile can affect oxidation retardation effect as well as the nitrogen dosage. Metal–oxide–semiconductor capacitors with gate oxide thickness of 2 nm have been fabricated. Boron penetration prevention ability is intensified by the initial O2 injection process for the same dose of nitrogen implantation. The oxide reliability was investigated using time-zero dielectric breakdown (TZDB) measurement. The initial O2 injection method shows improved TZDB.