【International Papers】Impact of process anneals on high-k/β-Ga₂O₃ interfaces and capacitance

      Researchers from the Department of Materials Science and Engineering at the University of Texas at Dallas have published a dissertation titled "Impact of process anneals on high-k/β-Ga₂O₃ interfaces and capacitance in the scientific journal "Journal of Vacuum Science & Technology A. This dissertation mainly explores the thin films between the wide bandgap semiconductor material β-Ga₂O₃ widely used in high-power electronic devices and the high dielectric constant material HfO₂, and studies the effect of interface annealing on device performance.

      Gallium oxide (β-Ga₂O₃) is becoming a popular material for high power electronic devices due to its wide bandgap and ease of processing. In this work, β-Ga₂O₃ substrates received various annealing treatments before atomic layer deposition of HfO₂ and subsequent fabrication of metal–oxide–semiconductor (MOS) capacitors. Annealing of β-Ga₂O₃ with forming gas or nitrogen produced degraded capacitance–voltage (C–V) behavior compared to a β-Ga₂O₃ control sample with no annealing. A sample annealed with pure oxygen had improved C–V characteristics relative to the control sample, with a higher maximum capacitance and smaller flat-band voltage shift, indicating that oxygen annealing improved the C–V behavior. X-ray photoelectron spectroscopy also suggested a reduction in the oxygen vacancy concentration after O₂ annealing at 450 °C, which supports the improved C–V characteristics and indicates that O₂ annealing of β-Ga₂O₃ may lead to better MOS device performance.

      When using thin film deposition techniques to grow HfO₂ high dielectric constant films on a β-Ga₂O₃ substrate, in order to fabricate metal-oxide-semiconductor (MOS) devices, electrodes need to be prepared on the HfO₂ film. Figure 1 shows a typical shadow mask MOS capacitor structure, in which metal (Cr/Au) top electrodes and Ti/Au bottom electrodes are prepared using a shadow mask method, and these electrodes are separated from the β-Ga₂O₃ substrate by the HfO₂ film.

FIG.1. Schematic of shadow-mask MOS capacitor structure on β-Ga₂O₃

FIG.2. Characteristics of the stabilized capacitance–voltage measurement showing different C_ox/A results for each process condition. The control sample showed C_ox/A of approximately 1.22 μF/cm². The samples annealed in either nitrogen or forming gas showed much lower C_ox/A and were shifted to the right. The oxygen-annealed sample showed the best results, with C_ox/A of approximately 1.3 μF/cm² and was shifted slightly to the left of the control, indicating less interface charging.