Enhancing ON-State Performance of Quasi-Vertical GaN Trench MOSFETs on Sapphire With Nitrogen Plasma Treatment

During the semiconductor processing, dry etching is an important part while it is a source of damage which is produced in the semiconductor through the bombardment of energetic ions. The electrical performances of devices can be adversely impacted by this generated damage, which may take the form of recombination centers, dislocations, and vacancy complexes. In this work, the nitrogen plasma treatment on the gate trench of a quasi vertical GaN trench MOSFET (UMOSFET) grown on sapphire substrate has been ultilized to demonstrate better on-state performance. Before the gate dielectric is deposited, the nitrogen plasma treatment is carried out in an atomic layer deposition (ALD) chamber. Both devices treated with nitrogen plasma and those left untreated demonstrate good performance, according to the testing results. The devices with and without nitrogen plasma treatment exhibit threshold voltages of 1.3 and 1.28 V @1A/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, subthreshold swings of 103 and 114 mV/decade, ON/OFF current ratios (I<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</inf>/I<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</inf>) of ~2.86× 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> and ~2.67 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup>, breakdown voltages of 337 and 358 V, respectively. Notably, the UMOSFETs treated with nitrogen plasma exhibit an increased saturation current density of 2.9 kA/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a higher field-effect mobility (µ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FE</inf>) of 60 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>/V.s, compared to the untreated devices with values of 1.8 kA/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 27 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>/V.s, respectively. This indicates that nitrogen plasma treatment effectively enhances the channel characteristics of the UMOSFETs. This improvement may be attributed to the compensation of nitrogen vacancy defects on the gate trench surface, which are introduced during the inductively coupled plasma etching process that forms the trench structures. The temperature dependence of the maximum µ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FE</inf> in the range of 298 K to 423 K are displayed. According to this, the key influencing elements of the field effect mobility of the UMOSFETs with nitrogen plasma treatment have been explored.