Reaction mechanism for HF based cryogenic plasma etching of SiO2

In semiconductor device fabrication, increasing the rate and quality of high aspect ratio (HAR) plasma etching is critical for the continuous scaling of three-dimensional (3D) devices. Cryogenic plasma etching (CPE) of SiO2, in which the substrate is cooled to temperatures between −10 and −100 °C, is emerging as a promising approach for achieving high etch rates in HAR features. CPE of SiO2 is typically performed in capacitively coupled plasmas (CCPs) with HF containing gas mixtures. The reaction between HF and SiO2 generates H2O, and its subsequent adsorption onto SiO2 surfaces is believed to act as a catalyst that enhances the etch rate. The fundamental reaction mechanisms which account for the improved performance of CPE have not yet been clearly defined. In this paper, computational investigations of the surface kinetics in CPE of SiO2 are performed for dual-frequency CCP reactors using CF4/H2/Ar gas mixtures. Temperature-dependent mechanistic differences between cryogenic and room-temperature etching are analyzed through parametric variations of adsorption, condensation, etch yield, redeposition, implantation, specular reflection, and neutral transport. The mechanism is calibrated by comparing to experimental results (performed by others) for etch rates as a function of substrate temperature. The synergistic effects of these mechanisms on the etch rate and profile with respect to temperature are examined, along with the consequences of bias power.