Effects of O2 and He on the properties of the trimethyl silane based low-k films

Abstract

In this work, chemical vapor deposited carbon doped oxide films using trimethyl silane precursors with dielectric constant in the range of 2.75 to 3.62 were studied. Process parameters studied included low frequency RF (LFRF) and high frequency RF (HFRF) power, pressure, and helium flow rates as the oxidation influencing agents. Reliability and thermal stability of the films were studied and the dielectric constant (k), breakdown voltage, and leakage current were measured at 1 MHz. Numerous film properties (film stresses, hardness, modulus, refractive indices, and chemical bonding) were characterized. Results indicate that reduction of LFRF or HFRF power and the increase in pressure reduces the dielectric constant. Helium gases dissociate the Si–CH3 and C–H bond in the structure causing the dielectric constant to increase linearly as the helium flow rate increased while keeping the oxygen flow rate constant (O2+He process). It was observed that the O2 process window lowers the k value range and imparts slightly higher hardness and modulus compared with a O2+He process. In both processes, it was found that the dielectric constant was inversely proportional to the Si–CH3/Si–O ratio. Furthermore, the dielectric constant was found to have a linear relationship with hardness and modulus. It is believed that introduction of a methyl group in the film has reduced the covalency of the Si–O bond thus reducing its dielectric constant in comparison with silica. In terms of films electrical properties and stability, all films show Ebd and Jleak values comparable to silica, stress value ranged −10–70 MPa, and good thermal stability.