An Investigation of the Plasma Chemistry Involved in the Synthesis of ZnO by PECVD

Plasma-enhanced chemical vapor deposition (PECVD) of zinc oxide was accomplished using diethyl zinc, oxygen, and argon in a capacitively coupled reactor. The plasma chemistry was studied by optical emission spectroscopy (OES) with particular focus on the effects of reactant composition and rf power. Process-property relationships were established by comparing plasma behavior with resulting film properties as characterized by the Hall effect, spectroscopic ellipsometry, and X-ray diffraction. In our studies of stoichiometry it was observed that the plasma chemistry was very similar to hydrocarbon combustion, so much so that the results were interpreted by borrowing the concept of the equivalence ratio, ϕ. For fuel-rich conditions deposition was dominated by incorporation of atomic Zn, the films were randomly oriented, and electrically insulating. In contrast fuel-lean conditions produced conducting films with a preferred (0 0 2) orientation. The results indicate that OES may be useful for calibrating oxide PECVD systems that employ bubblers to deliver organometallic precursors. It was also shown that increasing the plasma power had the same effect of decreasing ϕ, which was to drive the chemistry toward complete combustion. Electrical properties improved exponentially with both increased substrate temperature and decreased growth rate, highlighting the importance of surface migration in establishing carriers and controlling mobility.