| AVS 59th Annual International Symposium and Exhibition | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM-TuM |
| Session: | Electrical Testing and Defects in III-V’s |
| Presenter: | H.J. Lim, Seoul National University, Republic of Korea |
| Authors: | H.J. Lim, Seoul National University, Republic of Korea Y.J. Choi, Seoul National University, Republic of Korea S.H. Lee, Seoul National University, Republic of Korea J.H. Ku, Samsung Electronics Co. Ltd., Republic of Korea N.I. Lee, Samsung Electronics Co. Ltd., Republic of Korea H.J. Kim, Seoul National University, Republic of Korea |
| Correspondent: | Click to Email |
GaAs is a promising channel material for sub-20nm logic MOSFET due to high electron mobility. However the instability of its native oxide is considered to generate high density of interface states that can induce Fermi level pinning and frequency dispersion in capacitance-voltage (C-V) curve. Although a variety of dielectric materials have been investigated over the past 4 decades to improve interface properties, a few positive results have been reported: Ga2O3 (Gd2O3) grown by molecular beam epitaxy (MBE) and Al2O3 and HfO2 grown by atomic layer deposition (ALD). In this study, n-type GaAs MOSCAP’s were fabricated with ALD SiO2, Al2O3, La2O3, and HfO2, and measurements of C-V hysteresis, flatband voltage shift (ΔVfb), and frequency dispersion were performed to investigate the dependence of electrical properties on dielectric materials and to find dielectrics suitable for a stable MOSCAP operation.
Only HfO2 revealed good electrical characteristics with a C-V hysteresis of < 80 mV and ΔVfb of 40 mV under constant stress time and voltage, while SiO2, Al2O3, and La2O3 showed significantly degraded characteristics with a C-V hysteresis of > 700mV hysteresis and ΔVfb of 200mV. But even though a single HfO2 dielectric layer had good electrical characteristics, the stacked HfO2/SiO2 dielectric layer on GaAs showed the degraded characteristics like a single SiO2 layer, indicating that the electrical characteristics were mainly dependent not on bulk properties but on the interface properties with GaAs. X-ray photoelectron spectroscopy (XPS) analysis revealed that SiO2, Al2O3, and La2O3 dielectrics produced more elemental As (As0) than HfO2 did at the interface. In addition, for SiO2, Al2O3 and La2O3 dielectrics, As were detected on the top surface of dielectrics by Auger electron spectroscopy (AES) measurement, implicating that the origin of degradation was related with the amount of elemental As, which might diffuse out and induce vacancy defects during subsequent annealing process, at the interface.
Frequency dispersion characteristics in a C-V measurement were also compared. HfO2 showed huge frequency dispersion of about 280 % (ΔC1kHz~1MHz/C1MHz) while SiO2, Al2O3, and La2O3 resulted in the relatively small dispersion of about 50% unlike the C-V hysteresis tendency. However, HfO2 on thin SiO2 led to small dispersion similar to SiO2. Frequency dispersion was strongly correlated with the interface state density (Dit). Therefore, we can conclude that both hysteresis and frequency dispersion in a C-V measurement are dependent on the interface properties of dielectrics, especially the amount of elemental As and Dit level, respectively.