Results
3.1. Plasma-enhanced and thermal CVD using O2 and CO2
A comparison of the radial thickness profiles of zinc
oxide films grown by four different methods is depicted in
Fig. 2. The process conditions for thermal CVD were
40-mTorr diethylzinc, 0.5 Torr O2, or 1.0 Torr CO2,
800 Torr total pressure, and 181 1C. For PECVD, the same
conditions were used, except with 50W of RF power
applied to the plasma source. It is found that the film
thickness profiles exhibit maxima at a radial position near
the outer edge of the plasma source, suggesting that thediethylzinc is not transported efficiently to the center of the
showerhead prior to exiting the source, i.e., to radii below
1.0 cm. One can see that the amount of material deposited
by PECVD is higher than that observed by CVD. This
difference amounts to the contribution that the plasmainitiated
reaction contributes to the overall deposition
process. The ratio of the area under the profiles for
PECVD versus CVD equals 1.5 when carbon dioxide is the
reactive gas and 1.1 when oxygen is the reactive gas. The
ratio of the maximum film thickness to the average film
thickness is 2.2 for ZnO deposited by PECVD with CO2.
Previous research on the atmospheric pressure plasma
source has shown that the plasma is homogeneous within
the gas volume between the electrodes [12], so it is likely
that the non-uniform mixing of the precursor in the
showerhead is responsible for the wide variation in film
thickness across the wafer.