ATOMIC LAYER DEPOSITION OF HIGH-K DIELECTRICS ON GERMANIUM AND TRANSITION METAL DICHALCOGENIDE
Open Access
- Author:
- Zheng, Yuanxia
- Graduate Program:
- Physics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- November 17, 2017
- Committee Members:
- Roman Engel-Herbert, Dissertation Advisor/Co-Advisor
Nitin Samarth, Committee Chair/Co-Chair
Mauricio Terrones Maldonado, Committee Member
Adri van Duin, Committee Member
Adri van Duin, Outside Member - Keywords:
- Germanium
atomic layer deposition
transition metal dichalcoginide - Abstract:
- Two topics related to atomic layer deposition (ALD) have been studied in this thesis. One is the challenging task of integrating high-k dielectric on germanium (Ge) surface. The other is utilizing an ALD approach to synthesize transition metal dichalcogenide (TMD) of 1T-TaS2. The surface preparation primarily using in-situ H2 plasma to obtain pristine Ge surfaces has been investigated. The reaction mechanism and the resultant material properties have been examined carefully using in-situ and ex-situ metrologies. An optimized process has been proposed and resulted in an oxygen-free and atomically flat Ge surface. The nucleation behavior of Al2O3 ALD was investigated on Ge surfaces with two different chemicals states, hydrogenated and oxidized. The growth mode and the resultant dielectric/Ge interface properties have been clarified using in-situ and ex-situ metrologies. By comparing the experimental results with an atomic scale simulations (from collaborators), the reaction mechanism as well as the thermodynamic properties have been identified. A trilayer dielectric gate stack of HfO2/Al2O3/GeOx has been used to electrically test the aforementioned mechanisms of dielectric ALD on Ge. The optimum process has yielded a highly scaled Ge MOSCap device with superior interface qualities. 1T-TaS2 thin films has been synthesized using TaCl5 and H2S as the precursors in a home-made ALD system. A strong temperature dependence has been identified. A use of ultrathin Ta2O5 seed layer has been found beneficial to facilitate the nucleation of 1T-TaS2. ALD growth at a high temperature of 480 °C has yielded the optimum results. Ferroelectric HfO2 has also been synthesized as the gate insulator for the future transistor fabrication using 1T-TaS2 as the channel material. A process flow for Al-doped HfO2 primarily using ALD approach in conjunction with magnetron sputtering has been developed. The electrical properties for various doping levels have evaluated using electrical polarization measurements.