Capacitance-voltage characteristics of gamma irradiated Al2O3, HfO2, and SiO2 thin films grown by plasma-enhanced atomic layer deposition

Abstract

Radiation-hardened electronics used in space, nuclear energy and radiation medicine applications require robust dielectric materials to be used as passivation layers and gate insulators. Thus, there is a need to understand the response of these materials under radiation exposure (e.g., gamma, neutron and proton) to develop radiation-tolerant and reliable electronic systems. In addition, as the size of transistors continues to scale down there is a need to have physically thicker dielectric layers with similar capacitance values to ultra-thin SiO2. High permittivity (high-k) dielectrics lend themselves well to this task as they have capacitance values similar to ultra-thin SiO2 while not facing issues of high leakage current and power dissipation as ultra-thin SiO2. Atomic layer deposition (ALD) of thin films has gained interest in the development of radiation-hardened electronics as this process results in high quality (continuous and pinhole-free) and conformal gate dielectric thin films with precise thickness control to the angstrom level. Here, we examine the impact of gamma-irradiation on plasma-enhanced ALD dielectric layers using metal-oxide semiconductor (MOS) capacitors. In this work, three ALD gate dielectric films: Al2O3, HfO2 and SiO2 (between 22 and 24 nm thick) are utilized. The capacitance-voltage (C-V) response of plasma-enhanced ALD-based MOS capacitors upon gamma irradiation (Co-60) up to 533 krad without any shielding is observed. It is shown that ALD grown HfO2 films are resistant to gamma irradiation based on the negligible shift in flat band voltage and hysteresis characteristics. Additionally, ALD grown Al2O3 films exhibited minimal generation of mobile traps but generation of trapped charges was observed. Furthermore, the flat band and hysteresis of ALD grown SiO2 films showed development of both trapped and mobile charges which may suggest that this material lends itself to radiation dosimetry applications. These initial findings support the use of plasma-enhanced ALD grown films in the development of radiation-hardened electronics and sensors.