Mechanism of Highly Selective SiO$_{2}$ Etching over Si using New Alternative Gas, C$_{5}$HF$_{7}$

Highly selective etching of oxide for a high aspect ratio contact hole formation is important technologies of IC fabrications. To realize an extreme high etch performances for the future devices, it is important to control the plasma chemistry based on the feedstock gas selection and internal parameters of the plasma. We achieved that highly selective etching of SiO$_{2}$ against Si using a newly-designed gas, C$_{5}$HF$_{7}$, O$_{2}$, and Ar gas mixture employed a dual frequency capacitively coupled plasma (CCP). For the conventional C$_{5}$F$_{8}$/O$_{2}$/Ar plasma, the SiO$_{2}$ etch rate and maximum selectivity were 453 nm/min and 9.4. In contrast, for the newly developed C$_{5}$HF$_{7}$/O$_{2}$/Ar plasma, the maximum selectivity of 57.3 with the etch rate of 445 nm/min was obtained. Gas phase diagnostics were conducted for understanding the plasma chemistries. It was found the density of F radical (Si etchant) in C$_{5}$HF$_{7}$ plasma was lower than that of C$_{5}$F$_{8}$ plasma and appreciable amount of H containing species exist in C$_{5}$HF$_{7}$ plasma. It is considered F content in the CF film on Si was reduced by the H containing species and lower F radical supply, and then the Si etching was prevented. Consequently, C$_{5}$HF$_{7}$/O$_{2}$/Ar chemistry has a great potential for highly selective SiO$_{2}$ etching over Si.