OES-based Monitoring Method of Non-maxwellian EEDF and Radical Density for Etch Process Control in Ar/SF6/O2 VHF-CCP

Fine control and monitoring of etch processes are essential due to the increasing difficulty and complexity. To achieve this goal, reliable real-time plasma information (PI) monitoring sensor technology and virtual metrology (VM) for process prediction must be developed. In conventional etch plasma monitoring technique using optical emission spectroscopy (OES) signal, the maxwellian electron energy distribution (EEDF) assumption and simple actinometry is used. However, etch process plasmas, which target sub-nanometer-scale high-aspect-ratio (HAR) processes with very-high frequency (VHF) power, the EEDF shows significant tail deviations due to electron heating mechanisms, such as the bounce resonance heating and plasma series resonance. This becomes a limiting factor in accurately monitoring the electron temperature and radical density of the etch plasma.

This study proposes a method to obtain non-max. EEDF and radical density using OES data in Ar/SF6/O2 VHF-CCP. Non-max. EEDF can be monitored using OES data and 1s state included collisional-radiative model (CRM). The actinometric coefficient, which is proportionality constant between the line intensity ratio and the density ratio, is determined using the obtained EEDF and excitation cross-section data. The proposed PI-OES (Non-max. EEDF and Radical Density) monitoring method can be effectively utilized as a real-time process monitoring technique for mass volume production (MVP) processes, ensuring reliability and accuracy.