| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Tuesday Sessions |
| Session TF-TuE |
| Session: | Thin Film Synthesis & Characterization I |
| Presenter: | Gilsang Yoo, Yonsei University, Republic of Korea |
| Authors: | G.S. Yoo, Yonsei University, Republic of Korea I.K. Oh, Yonsei University, Republic of Korea C.W. Lee, Yonsei University, Republic of Korea T.H. Kim, Sungkyunkwan University, Korea, Republic of Korea G.Y. Yeom, Sungkyunkwan University, Korea, Republic of Korea H.B.R. Lee, Incheon National University, Republic of Korea H.J. Kim, Yonsei University, Republic of Korea |
| Correspondent: | Click to Email |
High permittivity (high-k) dielectrics have been explored for an alternative gate insulator to conventional SiO2 in the metal oxide semiconductor field effect transistor (MOSFET) technology. Among various high-k deposition techniques, atomic layer deposition (ALD) appears to be one of the suitable methods due to its excellent process controllability for extremely thin high-k films. Plasma-enhanced atomic layer deposition (PE-ALD) using plasma reactant has been spotlighted because of its several benefits over conventional thermal ALD using gas reactant, such as lower process temperature and improved film properties by the reactive radicals of reactants. However, use of plasma reactants negatively influences electrical properties of high-k films in MOSFET since ion bombardment of energetic radicals generates defects in films. Instead of radio frequency (RF) plasma which is usually used for plasma assisted processes, very high frequency (VHF) plasma for chemical vapor deposition (CVD) process was reported. The negative effects of plasma on film properties were reduced in VHF plasma process due to its lower ion kinetic energy and higher plasma density than RF plasma. Therefore, VHF plasma is expected to be a better plasma reactant for PE-ALD than RF plasma in the context of high growth rate and low ion damage. However, there has been no report on PE-ALD using VHF plasma reactant.
For this study, Al2O3 PE-ALD were developed using Trimethylaluminum (TMA) precursor and O2 plasma reactant on Si substrate. O2 plasma reactant was generated using two different frequencies, 13.56 MHz and 60 MHz for RF and VHF, respectively. The processes exhibited ALD mode with good self-saturation behavior and linear growth as a function of growth cycles. To investigate the characteristics of plasma density and electron temperature, a Langmuir probe was installed in the chamber. The thickness and density of the films was analyzed by spectroscopic ellipsometry and X-ray reflectivity (XRR), respectively. By using VHF plasma, better film properties were observed compared to RF plasma. The growth rate of VHF plasma (2.7 Å/cycle) was higher than that of RF plasma (2.3 Å/cycle). In addition, the VHF PE-ALD film was denser than RF PE-ALD film (3.26 for VHF and 3.11 g/cm3 for RF plasma), since ion and radical density generated by VHF is higher than those by RF. The VHF PE-ALD provides improved film qualities, such as low leakage current and low interface trap density, compared to RF PE-ALD grown film. The VHF plasma reactant for PE-ALD has potentials for various applications which require very thin and dense films in nanoscale regime.