Effect of porosity on etching rate and crater-like microstructure of sintered Al2O3, Y2O3, and YAG ceramics in plasma etching

The changes in the etching rate and surface microstructure of sintered Al2O3, Y2O3, and yttrium aluminum garnet (YAG) ceramics were investigated in high-power plasma. Specimens with four relative densities (75, 95, 99, and 100 %) were plasma-etched under three conditions at CF4/Ar gas ratios of 4, 0.25, and 0. Consequently, when the CF4 concentration was nonzero, the etching rates of Y2O3 and YAG were similar and much lower than that of Al2O3. However, when the CF4 concentration was zero, the etch rate of Al2O3 was the lowest. The etching rates of Y2O3 and YAG were not significantly affected by the absence of CF4; however, the etching rate of Al2O3 decreased sharply in the absence of CF4. For all the materials, an inverse relationship between density and etching rate was observed. Numerous craters were observed in the surface microstructures of all tested specimens, except for sapphire. It was observed that the lower the density (the more pores), the more craters. Moreover, the effects of craters on the etching rate and peculiar etching behavior of Al2O3 were also discussed.