Research on Trench Etching and Photolithography Process of SiC Trench MOSFET

In this paper, the development of trench etching process and photolithography process for 6-inch 4H-SiC trench-type power MOSFET devices is mainly studied. Among them, the etching process successfully solved the anisotropy of dry etching of SiC, the different etching rates of different crystal planes, the difficulty of controlling the angle of the trench sidewall, and the easy formation of micro-trenches at the corners, etc. Successfully realized trenches with etch depth greater than 1.2um and sidewall angle greater than 90° in SiC. Subsequently, the trench was filled with SiO2 to achieve no holes in the trench after filling, and then the photolithography process was studied. Photolithography process is resolved at the trench coating, exposing and developing the non-uniformity problem, achieve a full and uniform coating, self-aligned trench overlay and the overlay accuracy of less than 0.1um, and there is no residue of photoresist in the groove after development. This article uses scanning electron microscope (SEM) to measure the morphology of the trench after etching and photolithography to characterize the experimental results, and the results meet the process requirements. The successful development of this process will facilitate the research and development of deeper trench-type power MOSFET devices.

Energy Dissipation and Hydraulics of Flow over Trapezoidal–Triangular Labyrinth Weirs

In this work experimental and numerical investigations were carried out to study the influence of the geometric parameters of trapezoidal–triangular labyrinth weirs (TTLW) on the discharge coefficient, energy dissipation, and downstream flow regime, considering two different orientations in labyrinth weir position respective to the reservoir discharge channel. To simulate the free flow surface, the volume of fluid (VOF) method, and the Renormalization Group (RNG) k-ε model turbulence were adopted in the FLOW-3D software. The flow over the labyrinth weir (in both orientations) is simulated as a steady-state flow, and the discharge coefficient is validated with experimental data. The results highlighted that the numerical model shows proper coordination with experimental results and also the discharge coefficient decreases by decreasing the sidewall angle due to the collision of the falling jets for the high value of H/P (H: the hydraulic head, P: the weir height). Hydraulics of flow over TTLW has free flow conditions in low discharge and submerged flow conditions in high discharge. TTLW approximately dissipates the maximum amount of energy due to the collision of nappes in the upstream apexes and to the circulating flow in the pool generated behind the nappes; moreover, an increase in sidewall angle and weir height leads to reduced energy. The energy dissipation of TTLW is largest compared to vertical drop and has the least possible value of residual energy as flow increases.