The gas-phase etching of SiO2 was examined using HF and methanol vapor at low temperature below 0 °C and at low pressure. The etching rate of SiO2 increased with decreasing temperature and showed a maximum around –30 °C. The obtained etching rate was maximum 40 nm/min at plasma-enhansed CVD SiO2. The etching rate of SiN examined for comparison was less than 10 times smaller than that of SiO2 in this condition. As a result, the etching selectivity of SiO2 to SiN was found to be over 20 at –40 °C. Utilizing low temperature less than –30 °C, gas-phase etching of SiO2 which shows high etching rate and selectivity was achieved.

Isotropic atomic layer etching (ALE) has become essential technology for fabrication of logic transistors beyond 2nm-generation and NAND memory with more than 100 layers stacking. There are promising etching technologies for isotropic ALE, like reaction limiting, modification limiting and ligand exchange processes. In this work, isotropic ALEs by using dry chemical removal (DCR) tool are discussed. In DCR, radicals from plasma are delivered to enhance the surface modification. And wafer temperature quickly changed by infrared light and electric static chuck for adsorption and desorption accelerations. Silicon ALE can be realized by the combination of surface oxidation and removal by HF vapor. SiO2 can be etched by the alternate flows of HF and NH3 followed by wafer heating. SiN, TiN and W can be etched in nanometer precision by using the fluorination by hydrofluorocarbon radicals and heating. Co and LaO can be etched by diketon exposure and heating.