Oxidation of Silicon Utilizing a Microwave Plasma System: Electric-Stress Hardening of SiO₂ Films by Controlling the Surface and Interface Roughness

Abstract

Electric-stress hardening of silicon dioxide (SiO 2 ) films under high electric field stresses was studied. SiO 2 films were formed by two-step oxidation utilizing thermal oxidation and plasma oxidation. This process has the advantages of both oxidation processes: the low degradation rate of thermal oxidation and the flat SiO 2 surface and SiO 2 /Si interface obtained by plasma oxidation. Time-dependent dielectric breakdown and stress-induced leakage current were measured to evaluate the degradation rate and the breakdown lifetime of the oxides. Atomic force microscopy was used to evaluate the roughnesses of the SiO 2 surface and interface. The two-dimensional degradation distribution under a current stress was investigated by the stress-induced etched-oxide surface roughness method. Atomically uniform SiO 2 was found to suppress the generation of local weak spots under current stress. We conclude that using an appropriate combination of the oxidation processes can reduce the degradation and enhance the breakdown lifetimes of SiO 2 films. #

Effect of microwave plasma treatment on silicon dioxide films grown by atomic layer deposition at low temperature

“…The lifetime for the as-deposited oxide film is quite short due to the large number of electron traps, and the SPA plasma-grown oxide films have a longer lifetime than the thermal oxide film because the SPA plasma is capable of growing atomically flat surfaces and interfaces. 25 For the plasma-treated films, the dependence of the lifetime on the plasma treatment is stronger than that on the leakage current. Regardless of the inert gas species, the best lifetime improvements are obtained with plasma treatments at a particular P O2 (i.e., the curves show peaks), although this depends on the gas species: 1% for O 2 /Ar plasma and 0.25% for O 2 /He plasma.…”

Cyclic Plasma Treatment during ALD Hf1-xZrxO2Deposition

“…As explained earlier, SPA plasma reduces the number of impurities in the oxide film, which act as trap centers. 18 Also SPA plasma is capable of growing automatically flat surfaces and interfaces, 55 which helps in gate leakage current reduction. Additionally, the conduction process is entirely through the high-κ layer.…”

Oxidation characteristics of silicon exposed to O(1D2) and O(3P2) radicals and stress-relaxation oxidation model for O(1D2) radicals

“…28) Alternatively, since SiO emission from the Si/SiO 2 interface relaxes the stress during oxidation, SiO in the SiO 2 film may be reoxidized. 29,30) HiHOx produces a similar oxygen profile to ThOx, indicating that HiHOx proceeds by permeation, similarly to ThOx. The 18 O ratio in the original Si 18 O 2 film is higher than that for ThOx, implying that little oxygen exchange or little reoxidation of emitted SiO occurs.…”

“…We speculate that the hydrogen is associated with Si-OH and Si-H bonds. 30) All the plasma oxide films contain more hydrogen than the ThOx film, although the HiHOx film contains more hydrogen than the Ox and HOx films. We conjecture that this is due to the lower processing temperature of plasma oxidation (673 K) and active species such as hydrogen radicals (H+) and ions (H + ) generated in the plasma not only from the process gas (H 2 ) but also from water (H 2 O) attached to the cold wall.…”

“…Figure 8 schematically shows our dielectric breakdown model that has two degradation components. 30,53) The vertical and horizontal axes denote the total of the two degradation components and the two-dimensional direction of the degradation in the SiO 2 film, respectively. The dashed line denotes the dielectric breakdown threshold.…”