An approach to reduce surface charging with cryogenic plasma etching using hydrogen-fluoride contained gases

The surface conductivity influences the etched pattern profiles in the plasma process. In the dielectric film etching, it is vital to reduce the charging build-up, which bends the trajectory of incoming ions for highly anisotropic etching. A significant increase in surface electric conductivity of SiO2 films was observed when exposed to down-flow plasmas containing hydrogen fluoride (HF) at cryogenic temperature (−60 °C). This phenomenon can be attributed to two factors: (i) the absorption of HF and/or its compounds and (ii) the presence of H2O, which is likely originating from the etching by-product of SiO2 and/or within the reactor. Comparing the surface electric resistance of the samples treated with HF plasmas to that of CF4/H2 and C4F8/H2 plasmas, we found that HF plasma treatment enables to be approximately three and six orders of magnitude lower. By using in situ x-ray photoemission spectroscopy, it was revealed that the presence of HF and/or its compounds and H2O were absorbed on the sample surface at −60 °C. These results strongly suggest that the cryogenic plasma etching with HF-contained gases can be used to alleviate the charge build-up issues.