(369d) Predictions of the Etch Behavior of Complex Oxide Films for High-k and Multiferroic Applications

The ongoing quest to improve the performance of integrated circuit devices has led to a burgeoning body of research in synthesizing multifunctional materials. However, these materials are often intrinsically etch resistant and thus ensuring high-fidelity patterning via plasma etching faces significant challenges. This study aims to demonstrate predictive capability for the etch behavior of novel materials, e.g. complex oxides, by combining an established phenomenological model with thermodynamics-based volatility diagram analysis. The material systems studied were the potential high-k dielectric Hf_xLa_yO_z, and the multiferroic candidates Y_xMn_yO_z and Bi_xFe_yO_z.

Experiments to validate the theoretical analysis were conducted an inductively coupled plasma (ICP) reactor equipped with a quadrupole mass spectrometer (QMS) for analyzing etch products and a quartz crystal microbalance (QCM) for measuring the etch rate in situ. The use of the QCM eliminated the need to subject the samples to unwanted reactions in atmosphere prior to etch rate measurement, and also allowed for materials that were unable to be analyzed by other methods such as spectroscopic ellipsometry. The reactor was also connected to a UHV transfer tube which allowed the surface composition to be studied via x-ray photoelectron spectroscopy (XPS) without exposure to ambient conditions.

The calculated etch rates of the Hf_xLa_yO_z films in a 400W, 5 mT, Cl₂ plasma varied from 8.3 to 181.9 Å/min (for -25V to -200V bias voltage, respectively), generally lower than that of pure HfO₂ etched in comparable conditions by ~16 to 31%. The maximum etch rate observed for a 400W, 15mT BCl₃ condition was 61 Å/min (at -175V), with net deposition (1.34 – 4.71 Å/min) observed below -75V bias voltage. QMS was used to characterize the etch products, with LaCl, LaO₃, LaOCl and LaO₂Cl (3.4 : 4.0 : 3.1 : 1.0) and LaB, LaB₂O, LaBOCl and LaO₂Cl (1.2 : 1.1 : 1.3 : 1.0) observed as the dominant La-containing species in Cl₂ and BCl₃ conditions, respectively. The surface compositions of the films post-etching revealed a decrease in the La and Hf fractions after Cl₂ and BCl₃ exposure, with a more significant reduction in La compared Hf (~50% v. ~19%) as determined via XPS. Similar analysis for the multiferroic oxides will be presented and comparative etch behavior analyzed through the aforementioned theoretical framework.