Effects of hydrogen transport and reactions on microelectronics radiation response and reliability

The transport and reactions of hydro.-en-related species play critical roles in determining the ionizing radiation response and long-term reliability of Si-based metal-oxide-semiconductor (MOS) and bipolar microelectronics technologies. The role of hydrogen is reviewed in radiation-induced interface-trap formation in metal and polycrystalline-Si-gate devices, with an emphasis on understanding the transport and reaction mechanisms responsible for defect formation. Effects of hydrogen on radiation-induced oxide and border-trap charge densities are discussed. Enhanced low-dose-rate effects in bipolar devices and integrated circuits are sensitive to hydrogen transport and reactions in the oxides that overlie the emitter-base junctions. These enhanced low-dose-rate effects present great challenges for defining practical, cost-effective acceptance tests of bipolar devices for space radiation environments. In addition, a brief discussion is provided of the effects of hydrogen-related species on MOS long-term reliability, including high-field stress, dielectric leakage (e.g., stress-induced leakage current), oxide breakdown, hot-carrier effects, dopant passivation, and low-frequency (I If) noise. The potential impacts on latent interface-trap formation are discussed for retarded hydrogen transport, trapping, and/or dopant passivation. Further, differences in proton transport and reactions are noted for (a) conventional Si/SiO2/Si structures and (b) those with high oxygen vacancy densities that are exposed to high-temperature hydrogen annealing ambients. In the former, hydrogen is consumed irreversibly by processes such as interface-trap formation; in the latter, hydrogen often can be cycled from the gate to the Si interface reversibly without losses for up to 10(6) cycles or more. Moreover, the inferred transport rates are much higher for post-forming-gas anneal transport than for radiation-induced interface-trap buildup. Finally, the motion of hydrogen during post-process, but pre-irradiation, thermal treatments (e.g., burn-in, or temperature cycles during the packaging process) has been associated with significant changes in the radiation response of both MOS and bipolar transistors. Typical mitigation techniques are discussed to reduce the effects of hydrogen on MOS radiation response and long-term reliability. Several unresolved issues and opportunities for future work are identified. The present knowledge of hydrogen effects on the long-term reliability and radiation response of Si based microelectronics will be broadened significantly as alternative dielectrics to SiO2 are increasingly introduced into the manufacturing process. A brief example of the significant effects of hydrogen on dielectric layers other than SiO2 is provided for deposited diamond thin films. (C) 2002 Elsevier Science Ltd. All rights reserved.