Plasma etching behavior of Y2O3 ceramics: Comparative study with Al2O3

Fluorination of Al2O3 and Y2O3 surfaces was investigated by irradiating high-density, helicon-wave CF4∕O2 and SF6∕O2 plasmas. The Al2O3 surface bombarded by high-flux positive ions of the CF4∕O2 plasma was fluorinated significantly. On contrast, Y2O3 was less fluorinated than Al2O3 when they were irradiated by the same CF4∕O2 plasma. The analysis of the Al2O3 surface irradiated by the CF4∕O2 plasma suggests that the fluorination is triggered by reactions between fluorocarbon deposit and Al–O bonding with the assistance of ion bombardment. On the other hand, irradiation of the SF6∕O2 plasma induced less significant fluorination on the Al2O3 surface. This suggests a lower reaction probability between sulfur fluoride deposit and Al–O bonding. The difference in the fluorination of the Al2O3 and Y2O3 surfaces induced by the irradiations of the CF4∕O2 and SF6∕O2 plasmas is understood by comparing the bonding energies of C–O, S–O, Al–O, and Y–O.

Fluorination mechanisms of Al2O3 and Y2O3 surfaces irradiated by high-density CF4∕O2 and SF6∕O2 plasmas

We have prepared oxides having various yttrium to aluminum ratios and exposed them to fluorine-based plasma. The etch rate of the aluminum oxide decreased abruptly with the addition of yttrium oxide and then slowly with further addition. The yttrium oxide had a more fluorinated surface than the aluminum oxide, indicating that the etch rate was not determined by the surface fluorination, contrary to the etching of Si-based materials. From the X-ray photoelectron spectroscopy (XPS) analysis of a multication YAlO3 single crystal, a similar tendency was observed, showing a higher ratio of Y–F to Y–O bonding than the ratio of Al–F to Al–O. Angle resolved XPS and depth profiling analysis revealed the presence of a fluorinated layer of a few nanometer thick under a roughly 1 nm carboneous top layer. The etching behavior and surface chemical status of these oxides were discussed in terms of thermodynamic aspects of aluminum and yttrium fluoride.

X-Ray Photoelectron Spectroscopy Study on the Interaction of Yttrium–Aluminum Oxide with Fluorine-Based Plasma

Yttrium fluoride (YF3) and yttrium oxide (Y2O3) protective coatings prepared using an atmospheric plasma spraying technique were used to investigate the relationship between surface erosion behaviors and their nanoparticle generation under high-density plasma (1012–1013 cm−3) etching. As examined by transmission electron microscopy, the Y2O3 and YF3 coatings become oxyfluorinated after exposure to the plasma, wherein the yttrium oxyfluoride film formation was observed on the surface with a thickness of 5.2 and 6.8 nm, respectively. The difference in the oxyfluorination of Y2O3 and YF3 coatings could be attributed to Y–F and Y–O bonding energies. X-ray photoelectron spectroscopy analyses revealed that a strongly fluorinated bonding (Y–F bond) was obtained on the etched surface of the YF3 coating. Scanning electron microscopy and energy dispersive X-ray diffraction analysis revealed that the nanoparticles on the 12-inch wafer are composed of etchant gases and Y2O3. These results indicate that the YF3 coating is a more erosion-resistant material, resulting in fewer contamination particles compared with the Y2O3 coating.

Comparison of Erosion Behavior and Particle Contamination in Mass-Production CF₄/O₂ Plasma Chambers Using Y₂O₃ and YF₃ Protective Coatings.

In order to understand the erosion behavior of oxide ceramics during their exposure to fluorocarbon plasma, the thin films of AlF 3 , YF 3 , Al 2 O 3 , Y 2 O 3 and SiO 2 were deposited on silicon and then their surfaces were irradiated with Ar ions of different kinetic energies. When we measured the relative sputtering rates, fluoride was sputtered faster than oxide with strong dependency on its chemistry, while the sputtering rates of oxides were nearly identical. The fact that AlF 3 was sputtered a few times faster than YF 3 is consistent with previously observed faster etch rate in Al 2 O 3 than in Y 2 O 3 under fluorocarbon plasma. These results support that erosion of ceramics under fluorocarbon plasma occurs by a physical removal process of fluorinated surfaces which were simultaneously induced by their interaction with the fluorocarbon plasma. Based on these results, implications for plasma resistance of oxide ceramics and production of contamination particles in the silicon wafer processing chamber under fluorocarbon plasma will be discussed based on their thermal properties and a numerical simulation.

Relative sputtering rates of oxides and fluorides of aluminum and yttrium

The mechanism of particle generation is investigated in order to prevent defects formed on wafers in the plasma etching of multi-layered films composed of tungsten silicide (WSi) and polycrystalline silicon (poly-Si). Particles are measured by an in situ monitoring system using laser light scattering during the etching process. The particles are composed of AlF3, which is presumably generated by reacting the coating material Al2O3 on the etching chamber wall with plasma containing fluorine atoms, F in the presence of H2O absorbed into the chamber parts and materials. We demonstrated successfully that dehydration of the chamber parts and materials by plasma discharge suppresses particle generation.

https://iopscience.iop.org/article/10.1143/JJAP.47.3630/pdf

Masao Matsumoto

Papers

Reduction of Particle Contamination in Plasma-Etching Equipment by Dehydration of Chamber Wall