Etch characteristics of Bi4−xEuxTi3O12 (BET) thin films using inductively coupled plasma

Abstract

Bi 4−x Eu x Ti 3 O 12 (BET) thin films were etched by inductively coupled CF4/Ar plasma. We obtained the maximum etch rate of 78 nm/min at the gas mixing ratio of CF4 (10%)/Ar (90%). This result may suggest that sputtering by Ar ions is more effective than chemical etching by fluorine atoms for Bi4−xEuxTi3O12 (BET) etching. The variation of volume density for F and Ar atoms are measured by optical emission spectroscopy. As CF4 increased in CF4/Ar plasma, the emission intensities of F increase but Ar atoms decrease, which confirms our suggestion that the etch rate of BET thin film and emission intensity of an Ar+ ion is proportional to the volume density of Ar atoms. From x-ray photoelectron spectroscopy, the intensities of the Bi–O, the Eu–O, and the Ti–O peaks are changed with increasing CF4 concentration. By pure Ar plasma, the intensity peak of the oxygen–metal (O–M: TiO2, Bi2O3, Eu2O3) bond seemed to disappear while the intensity of the pure oxygen peak showed an opposite tendency. After the BET thin films were etched by CF4/Ar plasma, the peak intensity of the O–M bond increases slowly, but more quickly than that of peak belonging to pure oxygen atoms due to the decrease of Ar ion bombardment. These results indicate that Bi and Eu have a reaction with little F and those are removed predominantly by argon-ion bombardment. However, Ti reacts with little F radicals and is mainly removed by chemically assisted physical etching. To fabricate high-density ferroelectric random access memory devices, etch processes require stringent critical dimension control to ±0.02 μm and steep etch profiles over 70°. From the scanning electron microscopy, we had an almost perpendicular taper angle of over 85°.