Seungjun Lee

The stable Y₅O₄F₇ suspension for dense yttrium oxyfluoride (YOF) coating by suspension plasma spraying (SPS) was developed. Electrostatically and electrosterically stabilized aqueous Y₅O₄F₇ suspensions were prepared and compared with a commercially available Y₅O₄F₇ suspension without dispersant. The wettability and dispersibility of the Y₅O₄F₇ suspensions were evaluated in terms of the zeta potential, average particle size, and size distribution with electrophoretic light scattering (ELS) and dynamic light scattering (DLS). The viscosity was measured and the sedimentation was tested to examine the fluidity and stability of the Y₅O₄F₇ suspensions. When electrostatic (BYK-154) and electrosteric (BYK-199) dispersants were added to the Y₅O₄F₇ suspension, the isoelectric point (IEP) of Y₅O₄F₇ particles in the suspension shifted to lower pH. The zeta potential of both of electrostatically and electrosterically stabilized Y₅O₄F₇ suspensions were higher than ±40 mV at pH of 8.6, respectively, which were much higher than of the Y₅O₄F₇ suspension without dispersant. Meanwhile, the average particle size of the electrosterically stabilized Y₅O₄F₇ suspension was much smaller than that of the electrostatically stabilized one. The electrosteric stabilization had a great effect on improving the wettability and dispersibility of the Y₅O₄F₇ suspension. The coating rate of the electrosterically stabilized Y₅O₄F₇ suspension was the highest among the three tested suspensions. In addition, the YOF coating deposited with the electrosterically stabilized Y₅O₄F₇ suspension had the highest hardness and the lowest porosity.

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.

The recently discovered yttrium oxyfluoride (YOF) coating has been found to be a highly promising plasma-resistant material which can be coated onto the inner wall of the dry etching chambers used in the manufacturing of the three-dimensional stacking circuits of semiconductors, such as vertical NAND flash memory. Here, the coating behavior of the YOF coating which was deposited by suspension plasma spraying was investigated using a high-output coaxial feeding method. Both the deposition rate and density of YOF coatings increased with the plasma power, which was determined by the gas ratio of Ar/H₂/N₂ and the arc current. The coating thicknesses were 58 ± 3.4, 25.8 ± 2.1, 5.6 ± 0.6, and 0.93 ± 0.4 µm at plasma powers of 112, 83, 67, and 59 kW, respectively, for 20 scans with a feeding rate of the suspension at 0.045 standard liters per minute (slm). The porosities were 0.15% ± 0.01%, 0.25% ± 0.01%, and 5.50% ± 0.40% at corresponding plasma powers of 112, 83, and 67 kW. High-resolution X-ray diffraction (HRXRD) shows that the major and minor peaks of the coatings which were deposited at 112 kW stem from trigonal YOF and cubic Y₂O₃, respectively. Increasing the flow rate of the atomizing gas from 15 slm to 30 slm decreased the porosity of the YOF coating from 0.22% ± 0.03% to 0.07% ± 0.03%. The Vickers hardness of the YOF coating containing some Y₂O₃ deposited at 112 kW was 550 ± 70 HV.