Preparation and properties of fluorinated amorphous carbon thin films by plasma enhanced chemical vapor deposition

Fluorinated amorphous carbon films are proposed as low dielectric constant interlayer dielectrics for ULSI circuits. The films are deposited by plasma enhanced chemical vapor deposition with CH₄, CF₄ and C₂F₆ in a parallel-plate rf (13.56 MHz) reactor and a helicon wave reactor. In a parallel-plate reactor, the dielectric constant of the amorphous carbon films deposited with CH₄ increases with increase in rf power. Addition of CF₄ to CH₄ reduces the dielectric constant to 2.1 and raises the deposition rate. However etching reaction occurs with high CF₄/CH₄ ratios. No film grows with only CF₄ XPS measurement reveals that the F atoms are introduced into the amorphous carbon films. Helicon reactor has higher plasma density and is expected to achieve higher deposition rate for productive use. In this reactor, fluorinated amorphous carbon films without hydrogen content can be obtained with only CF₄ and C₂F₆ gases. The growth rate of the films reaches 0.3 μm/min with C₂F₆ and 0.15 μm/min with CF₄ at a source power of 2 kW and a gas flow rate of 100 scorn. With heating up to 300 °C in a vacuum for 1 hour, the thickness of the films deposited with C₂F₆ does not shrink while that of films with CF₄ shrinks.