Effect of substrate temperature on the plasma polymerization of poly(methyl methacrylate)

Low-power, plasma-enhanced (PE)CVD together with polymerization of methyl methacrylate (MMA) can be used to deposit thin films of poly(methyl methacrylate) (PMMA) with minimal loss of functional groups, as shown by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Raman spectrometry (RS). Retention of functional groups decreases with increased substrate temperature, corresponding to decreased deposition rates. From XPS data, the calculated percentage loss of functional groups ranges from 0.9 % to 43.4 %, changing as a function of deposition conditions. RS confirms the presence of C=C bonds in the polymer backbone as a result of scission of the ester group from MMA. The thermal properties of PECVD-produced films from MMA can be tailored by varying the substrate temperature. Onset of thermal decomposition increases with increased substrate temperature by eliminating thermally labile peroxide linkages in the polymer backbone, and by crosslinking that occurs at radical sites generated via scission of functional group bonds. The post-anneal thicknesses of the remaining polymer is of the order of 4 nm or less, indicating that low-power PECVD of PMMA is a viable candidate to act as a sacrificial material for air-gap fabrication.