CF4 doping effects on SiOF thin films: chemical, structural and dielectric properties in PECVD-deposited films from HMDSO/O2 vapor mixtures

This study investigates the deposition of silicon oxifluoride (SiOF) thin films using a CF4, HMDSO and O2 gas mixture via the microwave electron cyclotron resonance chemical vapor deposition (MW-ECR-PECVD method. Plasma Enhanced Chemical Vapor Deposition (PECVD) is a widely utilized method for depositing these films, offering the ability to finely tune film properties even at relatively low temperatures. Optical Emission Spectroscopy (OES) characterized the plasma environment at varying CF4 flow ratios, identifying key species such as F and C2 using actinometric techniques. Fourier Transform Infrared (FTIR) spectroscopy revealed predominant bonds in the films. The addition of CF4 (carbon tetrafluoride) to the precursor mixture (HMDSO/O2) can influence the chemical composition, structure, and dielectric properties of the deposited films. The OES analysis reveals that as the CF₄ flow ratio increases, the intensity of the C₂ species emission lines decreases, while the intensity of the fluorine species emission lines increases. FTIR analysis demonstrates that lower CF₄ concentrations favor the retention of Si–CH₃ and CH₃ groups, while higher CF₄ concentrations promote competitive bonding and etching effects, reducing carbon-based groups and enhancing fluorine incorporation. The dielectric constant of the films is primarily influenced by their chemical composition (Si–F, Si–OH) and structural properties, which are directly affected by the CF₄ concentration and the equilibrium between deposition and chemical etching processes. The absence of Si-CH₃, CHₓ and CFₓ groups restricts polarization. However, as CF₄ concentration rises, enhanced chemical etching and the introduction of structural defects result in an increase in permittivity. This investigation is crucial for the development of advanced dielectric materials for future generations of electronic devices. Graphical abstract