Abstract
Sol-gel-derived (Ba0.65,Sr0.35)TiO3 (BST) thin films were etched in CF4∕Ar and CF4∕Ar∕O2 plasmas using magnetically enhanced reactive ion etching technology. Experimental results show that adding appropriate O2 to CF4∕Ar can better the etching effects of BST films for the increase of etching rate and decrease of etched residues. The maximum etching rate is 8.47nm∕min when CF4∕Ar∕O2 gas-mixing ratio is equal to 9∕36∕5. X-ray photoelectron spectroscopy (XPS) data confirm accumulation of reaction products on the etched surface due to low volatility of reaction products such as Ba and Sr fluorides, and these residues could be removed by annealing treatment. The exact peak positions and chemical shifts of the interested elements were deduced by fitting XPS narrow-scan spectra with symmetrical Gaussian-Lorentzian product function for Ba 3d, Sr 3d, and O 1s peaks, meanwhile asymmetrical Gaussian-Lorentzian sum function was used to fit Ti 2p doublet to adjust the multiple splitting and/or shake-up process of transition-metal Ti cations. Compared to the unetched counterparts, the etched Ba 3d5∕2, Ba 3d3∕2, Sr 3d5∕2, Sr 3d3∕2, Ti 2p3∕2, Ti 2p1∕2, and O 1s peaks shift towards higher binding energy regions by amounts of 1.31, 1.30, 0.60, 0.79, 0.09, 0.46, and 0.50eV, respectively. While the etched Ti 2p3∕2 and Ti 2p1∕2 peaks have small chemical shifts for two reasons. One is that Ti fluoride (TiFz) is mostly removed from the etched surface because of its higher volatility in the process of thermal desorption. The other is that there is a shift compensation between TiFz and the etched BST matrix in which Ti4+ cations are partially reduced to form Tix+ (0<x<4) cations in the presence of adequate oxygen vacancies. The simulated formula of each BST surface is obtained to be (Ba0.65,Sr0.35)Ti0.97O2.86, (Ba0.70,Sr0.30)Ti0.24O1.39, and (Ba0.68,Sr0.32)Ti0.95O2.74, and then the average valence of Ti cations is estimated to be +3.84, +3.25, and +3.66 with respect to the electroneutrality principle, respectively. It is inferred that electrical properties of the etched BST film may be partially recovered by postannealed after etched.
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