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New diagnostic techniques for plasma-enhanced chemical vapor deposition of amorphous hydrocarbon films

Ira Bradford Graff, University of Massachusetts Amherst


Three novel diagnostic techniques were developed for plasma-enhanced chemical vapor deposition (PECVD), an important step in integrated-circuit manufacture. Results are presented for the deposition of amorphous hydrocarbon films from methane-argon plasmas. The plasma was formed between the powered and grounded electrodes of a 13.56-MHz parallel-plate reactor. A 5-to-1 mixture of methane/argon was fed to the reactor at 15, 30, 60, or 90 sccm. Pressure was held at either 0.1 or 0.5 torr, while rf power was set at 25, 50, 75, or 100 W. The three diagnostic techniques used were molecular-beam mass spectrometry, microprobe mass spectrometry, and Langmuir probing. Molecular-beam mass spectrometry was used to measure stable and radical species concentrations at a fixed point on the grounded electrode. Mole-fraction measurements were made for nine stable (CH$\sb4$, H$\sb2$, $\rm C\sb2H\sb2$, $\rm C\sb2H\sb4$, $\rm C\sb2H\sb6$, $\rm C\sb3H\sb4$, $\rm C\sb3H\sb6$, $\rm C\sb3H\sb8$, and Ar) and three radical species (H, CH$\sb2$, and CH$\sb3$); upper-bound estimates were made for five additional radical species (CH, C$\sb2$H, $\rm C\sb2H\sb3$, $\rm C\sb2H\sb5$, $\rm C\sb3H\sb3$). By applying microprobe mass spectrometry, distinctive in the study of plasma chemistry, detailed one- and two-dimensional spatial profiles of stable species (CH$\sb4$, H$\sb2$, $\rm C\sb2H\sb2$, $\rm C\sb2H\sb4$, $\rm C\sb2H\sb6,$ and Ar) were measured. Particular interest was focused on the entrance region. Langmuir probing was used to determine one-dimensional profiles of electron-energy distribution functions (eedfs). From the measured eedfs, electron densities and average electron energies were determined; furthermore, dissociation rate constants were calculated by integrating the product of the eedf and the dissociation cross section. Rate and rate-constant information were analyzed and correlated. By applying a transport analysis to the axial-centerline microprobe data, spatial rates of convection, diffusion, and reaction were determined. By using electron-density and electron energy profiles along with the reaction-rate profiles, energy-dependent rate constants were determined. A CSTR analysis was applied to bulk-plasma measurements to determine rate coefficients, and the results were compared to the transport-analyzed rate constants. Using a 2$\sp3$ factorially designed experiment, the effect of operating conditions (pressure, rf power, and flowrate) on the plasma chemistry and the deposition rate was explored.

Subject Area

Chemical engineering

Recommended Citation

Graff, Ira Bradford, "New diagnostic techniques for plasma-enhanced chemical vapor deposition of amorphous hydrocarbon films" (1998). Doctoral Dissertations Available from Proquest. AAI9841874.