ArF photoresist deformation in dual frequency superimposed capacitively coupled plasma (DFS-CCP) with different frequency combinations

In this study, we investigated deformation and etching characteristics of the ArF photoresists in a dual frequency superimposed capacitively coupled plasma (DFS-CCP) etcher by varying the process parameters such as low-frequency (LF)/high-frequency (HF) power ratio (P_LF/P_HF). CF ₄/CHF₃ flow ratio, and O₂ flow rate in the CF₄/CHF₃/O₂/Ar capacitively coupled plasmas. In the DFS-CCP etcher, HF power (13.56, 27.12 and 60 MHz here) is used to enhance plasma density and LF power (2MHz here) is used to control ion bombardment energy to the wafer. Morphological investigation of blanket ArF resist surfaces and patterned line and space patterns of the resists after etching by field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) generally shows an increased surface roughness and deformation with increasing the P_LF/P_HF, the HF source frequency (f _HF), CF₄/CHF₃ flow ratio, and O₂ flow rate. The increased surface roughening and deformation with the increasing the CF₄/CHF₃ flow ratio and O₂ flow rate is presumably attributed to an increase in the density of reactive O and F radicals in the plasma. The etch rates of the ArF resists were also increased significantly with the P_LF/P_HF, f_HF, CHF ₃ flow rate increased due to the increased ion energy and increased ion/radical flux density, respectively. The etching of the ArF PR was found to proceed by an ion-assisted sputtering mechanism under the experimental conditions investigated.