Hydrogen‐Related Leakage Currents Induced in Ultrathin SiO2 / Si Structures by Vacuum Ultraviolet Radiation

Abstract

Degradation of thin SiO 2 insulators used in Si-based metal-oxidesemiconductor (MOS) electronic devices in terms of electrical conduction may result in various ways: electrical stress, 1-5 irradiation, 6-8 ion implantation, 9 etc. Particularly vulnerable are ultrathin (oxide thickness, d OX < 10 nm) oxides, which may have a detrimental effect on device performance, e.g., on data retention in electrically erasable memory elements. 6 Development of electrical conduction of initially superb insulating SiO 2 layers points toward the generation of some imperfections (defects) that provide underbarrier pathways for the charge carriers between the electrodes of MOS structures. It is now well established that some kind of electron trap is generated in SiO 2 by injected charge carriers 10-14 and, likely also hydrogen, 5,11 giving rise to leakage current. However, the nature of the traps remains unclear, the main reason being the local nature of the typically studied leakages induced by electrical stress: A small area conductive region may have large impact on the total current across the MOS insulator, but is hardly accessible for physical characterization.In the present work, we compare the electrical conduction of ultrathin SiO 2 layers (d OX ϭ 3-6 nm) induced by conventional electrical stress of the MOS structure and by irradiation with vacuum ultraviolet (VUV) photons. This is successfully studied here because the VUV-induced degradation proceeds in a laterally uniform manner as it is related to the laterally uniform optical absorption. By combining the electrical analysis with photoionization and electron spin resonance (ESR) spectroscopy we will demonstrate two mechanisms involved in the generation of the degradation-induced leakage current. First, there are traps correlated with the presence of atomic hydrogen in the oxide which behave similarly to the donor-like Si/SiO 2 interface states observed in MOS structures with thicker oxides. 15-17 These states are thermally unstable, i.e., they anneal slowly already at room temperature, to disappear completely at 180ЊC after 10 min. They were suggested to be formed by H bonding to the bridging oxygen atoms in SiO 2 resulting in a configuration resembling the hydronium ion (H 3 O) ϩ . 17,18 Second, there are thermally stable oxide traps, related to oxide network damage: the hydrogenated oxygen vacancies and, probably, nonbridging oxygen centers. The current-voltage (I-V) characteristics and the annealing behavior of VUV-irradiated oxides is found to be similar to that observed after electrical stressing suggesting these defects to account largely for the stress-induced leakage currents in ultrathin SiO 2 .Experimental The samples were prepared by oxidation of low-doped p-and ntype Si(100) substrates at 800ЊC in N 2 ϩ 10% O 2 in an industrial cleanroom facility. 19 The oxide thickness was in the range 2.9-5.9 nm as determined ellipsometrically. The thicker oxides (d OX ϭ 36 nm) were grown in dry oxygen at 1000ЊC. MOS capacitors were defined by thermal evaporation of semitr...

Photoinduced Hysteresis of Graphene Field-Effect Transistors Due to Hydrogen-Complexed Defects in Silicon Dioxide

“…However, when the wavelength is 405 or 450 nm, the Δ V CNP is either around 17 V. It suggests that a similar critical wavelength exists between 450 and 532 nm for the recovery process. The critical photon energy is consistent with the energy level of the defects below the conduction band of SiO 2 proposed by Afanas’ev et al. , as well as the energy barrier for the depassivation of [O 3 Si–H] …”

“…In silicon dioxide, hydrogen-related defects are responsible for a bunch of degradation process of SiO 2 -dielectric electronic devices. − For instance, hydrogen-complexed defects are believed to be responsible for the stress-induced leakage current in silica. , The electron spin resonance studies of defects in amorphous SiO 2 have suggested that hydrogen (in forms of H 2 or H 2 O) plays a key role on initializing intrinsic defects during a thermal treatment or irradiation. , The Si–O bond rupture is closely related to the presence of protonic species formed by hole trapping or by hydrogen ionization at the Si/SiO 2 interface. − Hydrogen in different forms (hydroxyl E′ and hydrogen bridge) is well-known as a defect passivator in amorphous SiO 2 . A photon-stimulated tunneling of electrons at the Si/SiO 2 and Si/SiC interfaces has been correlated with defects in SiO 2 with an energy level about 2.8 eV below the conduction band. , Therefore, it is reasonable to believe that a similar process should also happen at graphene/SiO 2 interface.…”

“…32 A photonstimulated tunneling of electrons at the Si/SiO 2 and Si/SiC interfaces has been correlated with defects in SiO 2 with an energy level about 2.8 eV below the conduction band. 33,34 Therefore, it is reasonable to believe that a similar process should also happen at graphene/SiO 2 interface.…”

Charge state of paramagnetic E´ centre in thermal SiO2layers on silicon

“…Also, UV illumination may lead to a photolysis of water adsorbed at the oxide surface resulting in an additional H supply. Finally, E centres were observed even in 5 nm thick oxides [22] in which any presence of trapped holes is excluded because they are neutralized by electron tunnelling from Si and metal [23,24].…”

Defect generation in high κ gate dielectric stacks under electrical stress: the impact of hydrogen

“…As a matter Electron injection from the accuml. layer of fact, it has been suggested that hydrogen-induced overcoordinated oxygen centres in SiO 2 , [Si=O 2 H] + , can be annealed at temperatures higher than 150 • C [27], but cannot be neutralized under electron injection, the energetic level of these defects residing in the SiO 2 conduction band [8,28].…”