Effect of different frequency combination on ArF photoresist deformation and silicon dioxide etching in the dual frequency superimposed capacitively coupled plasmas

Abstract

This study investigated the deformation of ArF photoresist (PR) and the etch characteristics of ArF PR and SiO2 layers in a dual frequency superimposed capacitively coupled plasma (DFS-CCP) etcher with multiple frequency sources under different frequency combinations in C4F8∕CH2F2∕O2∕Ar capacitively coupled plasma. In the DFS-CCP etcher, the high-frequency (fHF) power (13.56, 27, and 60MHz) was varied to control the plasma density while a fixed low frequency (fLF) of 2MHz was used to control the ion bombardment energy to the wafer. The morphology of the blanket ArF PR surfaces and line patterns of the ArF PR after etching showed a significant increase in the level of surface roughening and deformation with increasing HF source frequency (fHF) from 13.56to60MHz under the same Vdc and gas flow conditions. This was attributed to the increased F radical flux and possibly ion flux on the surface. The Vdc also played an important role in increasing the surface roughness and ArF PR deformation, which was presumably due to the increased ion flux and ion-bombardment energy, respectively. The etch rates of the ArF PR and silicon oxide layers increased significantly with increasing ∣Vdc∣ and fHF possibly due to the increased ion energy and ion/radical flux density, respectively. The etch selectivity of the SiO2 layer to the ArF PR was enhanced most significantly by the increase in CH2F2 flow rate due to the formation of a thicker and C-rich CFx polymer on the oxide and PR surfaces.