The Study On The Key Process And Interface Characteristics Of Ga₂O₃-based MIS Structure

Recently,monoclinic gallium oxide??-Ga₂O₃?has attracted widespread interest as a promising wide bandgap?E_g?material which is suitable for the fabrication of high-power transistors and UV detector applications.?-Ga₂O₃ possesses a ultra-wide bandgap?4.8-4.9eV?,a high critical field strength of 8 MV/cm?E_c?and a four-fold and ten-fold higher Baliga figure of merit?BFOM?compared to GaN and 4H-SiC,respectively,which shown tremendous potential in high power application.Ga₂O₃ based MISFET devices have recently achieved a critical breakdown voltage field of 3.8 MV/cm,which exceeds the theoretical limit of conventional GaN and SiC;however,the devices still have many problems including insufficient performance?such as breakdown voltage,operating temperature,and leakage current?,large on-resistance,and the large leakage current under the high electric field.In order to further study the preparation of Ga₂O₃-based MISFET devices and improve device performance,the key processes of Ga₂O₃ MISFET devices are studied in this paper,and the improvement about interface quality of MOS gates is mainly studied.1.In this paper,the process flow of Ga₂O₃-based MISFET device is researched,hence,a reasonable flow and the lithography layout required for the fabrication of the MISFET device is designed.Then,this article investigates the key craft of device fabrication,including Ga₂O₃ pretreatment process,Ga₂O₃ ohmic contact process,atomic layer deposition?ALD?,Ga₂O₃ lithography and stripping process.X-ray diffraction?XRD?,Raman spectroscopy?Raman?,X-ray photoelectron spectroscopy?XPS?and atomic force microscopy?AFM?were used to characterize the?-Ga₂O₃ single crystals and high-k materials.2.In this paper,for the manufacture of gate dielectrics in MISFET devices,hf-based high-k materials?including HfO₂ and HfAlO with different compositional ratios?were used to replace with traditional Al₂O₃,SiO₂ gate dielectrics,and the merit and demerit of Hf-based high-k materials for gallium oxide MISFET devices are explored.Firstly,the energy band structure of Hf-based high-k/Ga₂O₃ was analyzed by XPS.It was found that HfO₂/Ga₂O₃has a smaller conduction band deviation?1.31 eV?and a negative valence band deviation?-0.5 eV?,which may lead to serious leakage current issues,then,HfAlO/Ga₂O₃ improve this to adjust the bandgap of HfAlO film,the HfAlO/Ga₂O₃ band-offset,and achieve larger conduction band-offset?1.42-1.53 eV?and positive valence band band-offset?0.19-0.48eV?with the help of adjusting the Al composition of HfAlO,which makes it more suitable for Ga₂O₃ MISFET devices from the energy band perspective.Secondly,the I-V measurement finds that both HfO₂ and HfAlO could achieve larger equivalent field strengths,HfO₂ has the bigger gate leakage current than that of Al₂O₃,then the HfAlO which owns the smallest leakage current is more suitable for Ga₂O₃ devices.Thirdly,the analysis from C-V measurement found that:?1?the gate oxide film of HfO₂/Ga₂O₃ MOS capacitor owns a larger dielectric constant²2 and comparable Al₂O₃/Ga₂O₃ interface state density 1.51×10¹22 cm^-2eV^-1(Al₂O₃/Ga₂O₃:1.54×10¹² cm^-2eV^-1),which significantly reducing the EOT,and effectively reduce the non-ideal charge of the gate dielectric layer;?2?the gate oxide film of HfAlO/Ga₂O₃ MOS capacitors possess a moderate dielectric constant of 15?between Al₂O₃ and HfO₂?and a small non-ideal charge,but also has a interface state density wich slightly larger than Al₂O₃(2.34×10¹² cm^-2eV^-1),which is attributed to the shortage of the process conditions for ALD deposition of HfAlO thin films;?3?the analysis of leakage current mechanism of Ga₂O₃ MOS capacitors shows that the positive voltage of Ga₂O₃ capacitance is mostly dominated by the Schottky emission mechanism and the F-N tunneling mechanism,and the F-P emission mechanism dominates in most regions under negative pressure.The Hf-based high-k gate dielectric proposed in this paper is suitable for the MOS gate dielectric of Ga₂O₃ devices,which can effectively reduce the EOT,non-ideal defects?such as fixed charge and oxide traps of the gate dielectric?.The interface state density of Hf-based high-k/Ga₂O₃ is found to be comparable to conventional Al₂O₃ and SiO₂,and the concentration of Al components in HfAlO could adjusted to improve the band offset and the gate leakage current.In addition,this paper explores the manufacture process and process flow of Ga₂O₃-based MISFET devices,which has important guiding significance and practical value for the future fabrication and improvement of Ga₂O₃-based MISFET devices.