Effects of hydrogen dilution on CNx film properties deposited using rf PECVD from a mixture of ethane, nitrogen and hydrogen

Carbon nitride (CNx) thin films were deposited using radio frequency plasma enhanced chemical vapor deposition (rf PECVD) from a mixture of ethane (C2H6), nitrogen (N2) and hydrogen (H2) gases. The C2H6 and N2 flow rates were kept constant, while the H2 flow rate was varied. The effects of hydrogen dilution on the growth rate and structural properties of the films were studied. It was found that a significant increase in the films growth rate was observed with the introduction of H2 at as low as 25 standard cubic centimeters per minute (sccm). A set of CNx films deposited from C2H6:N2 mixture without any inclusions of H2 were also presented in this work as a reference to compare the differences between those two sets and to understand the roles of H2 to the films properties. At highest H2 flow rate, the structure of the films changed from polymeric to graphitic and the quenching of PL was observed. Furthermore, higher N incorporation with lower Eg was obtained for these films compared to those of C2H6:N2 films. The change in the structure of the films corresponds to changes in their chemical bonding. As N incorporation increased, the porosity of the films increases and thus affects the disorder in the film structures.