Micropipes in SiC Single Crystal Observed by Molten KOH Etching

Micropipe, a “killer” defect in SiC crystals, severely hampers the outstanding performance of SiC-based devices. In this paper, the etching behavior of micropipes in 4H-SiC and 6H-SiC wafers was studied using the molten KOH etching method. The spectra of 4H-SiC and 6H-SiC crystals containing micropipes were examined using Raman scattering. A new Raman peak accompanying micropipes located near −784 cm−1 was observed, which may have been induced by polymorphic transformation during the etching process in the area of micropipe etch pits. This feature may provide a new way to distinguish micropipes from other defects. In addition, the preferable etching conditions for distinguishing micropipes from threading screw dislocations (TSDs) was determined using laser confocal microscopy, scanning electron microscopy (SEM) and optical microscopy. Meanwhile, the micropipe etching pits were classified into two types based on their morphology and formation mechanism.

Kinetic Study on the Si3N4 Etching in Superheated Water

Wet etching of Si3N4 was conducted in superheated water at 160 °C with different additives type and concentration. In general, etching rate of Si3N4 increased with the pH of solution. However, it is difficult to fully explain the Si3N4 etching behavior just with the pH of solution. The OH- concentration (or pH) in superheated water at 160 °C are different from the pH of solution at room temperature. Therefore, the OH- concentrations in superheated water at 160 °C were calculated using van't Hoff equation, equilibrium constant equations, mass and charge balance equations. The calculated OH- concentration at 160 °C showed better correlation with Si3N4 etching rate than that of initial pH of solution.

Plasma Etching Behavior of YOF Coating Deposited by Suspension Plasma Spraying in Inductively Coupled CHF3/Ar Plasma

Dense yttrium oxyfluoride (YOF) coating was successfully deposited by suspension plasma spraying (SPS) with coaxial feeding. After deposition for 6 min at a plasma power of 105 kW, the thickness of the YOF coating was 55 ± 3.2 µm with a porosity of 0.15% ± 0.01% and the coating rate was ~9.2 µm/min. The crystalline structure of trigonal YOF was confirmed by X-ray diffractometry (XRD). The etching behavior of the YOF coating was studied using inductively coupled CHF3/Ar plasma in comparison with those of the Al2O3 bulk and Y2O3 coating. Crater-like erosion sites and cavities were formed on the whole surface of the Al2O3 bulk and Y2O3 coating. In contrast, the surface of the YOF coating showed no noticeable difference before and after exposure to the CHF3/Ar plasma. Such high resistance of the YOF coating to fluorocarbon plasma comes from the strongly fluorinated layer on the surface. The fluorination on the surface of materials was confirmed by X-ray photoelectron spectrum analysis (XPS). Depth profiles of the compositions of Al2O3, Y2O3, and YOF samples by XPS revealed that the fluorination layer of the YOF coating was much thicker than those of Al2O3 and Y2O3. These results indicate that if the inner wall of the semiconductor process chamber is coated by YOF using SPS, the generation of contamination particles would be minimized during the fluorocarbon plasma etching process.