Evaluation of CF2 Radical as a Precursor for Fluorocarbon Film Formation in Highly Selective SiO2 Etching Process Using Radical Injection Technique

A radical injection technique (RIT) was developed to evaluate CF2 radical as a precursor for fluorocarbon film formation in a highly selective SiO2 etching process. Using RIT, the CF2 radical was successfully injected into electron cyclotron resonance (ECR) downstream plasmas employing Ar and H2/Ar mixtures. The fluorocarbon films formed on the Si surfaces exposed to ECR downstream plasmas were investigated using X-ray photoelectron spectroscopy. The deposition rate of fluorocarbon films was measured by varying microwave power in the Ar and H2/Ar ECR plasmas while keeping CF2 radical density constant using RIT. From the experimental results, it was found that the CF2 radical was the important precursor for fluorocarbon film formation only with the assistance of the surface activation due to the plasma exposure and that H atoms and CF2 radicals in the plasma played an important role in the formation of carbon-rich fluorocarbon film resulting in highly selective SiO2 etching. Furthermore, the highly selective SiO2 etching was demonstrated using the H2/Ar ECR downstream plasma with CF2 radical injection.