In situ plasma diagnostics for 7 nm etching processes
Challenges to process plasmas with regard to reproducibility, chamber conditioning or substrate quality are currently day-to-day business for semiconductor manufacturers. A defined control of plasma parameters seems to be the starting point to be able to also meet the more and more increasing requirements in the future. For this purpose, alternative in situ techniques with a high degree of sensitivity for industry must be tested and established. Motivated by this, process plasmas are analyzed at Fraunhofer ENAS using a spectroscopic method, which is not yet established in plasma analysis. Quantum cascade laser absorption spectroscopy (QCLAS) is used to determine chemical plasma parameters of molecular etching plasmas. The method provides direct access to the concentration and temperature of various process-relevant plasma species. In the project SeNaTe (Seven Nanometer Technology) dry structuring processes of so-called ultra low-k materials (porous materials of very low dielectric constant) are analyzed by QCLAS. The parameters measured during plasma treatment were correlated with the degradation state of etched samples. Thus, it could be shown that by measuring plasma species concentrations the polymerization on surfaces can be observed directly during the process. For the first time, a correlation between the radical temperature in the plasma chamber and the sidewall-degradation of structured substrates was observed. This result also raises a fundamental academic question, which needs to be investigated in further analyses.
Project: SeNaTe funded under H2020-EU.188.8.131.52., Grant agreement ID: 662338