Pulsed plasma polymerization of an aromatic perfluorocarbon monomer: Formation of low dielectric constant, high thermal stability films

The plasma polymerization of the perfluoroallyl benzene monomer [(C6F5)CF2C F=CF2] was carried out under pulsed discharge conditions. Progressive chang es in the composition of the plasma generated polymers were observed with s equential changes in the duty cycle of the pulsed discharge, as other react ion variables remaining constant. In particular, an increased retention of the aromatic ring of the starting monomer in the polymers is obtained with decreasing plasma duty cycles during film formation, as shown by x-ray phot oelectron spectroscopy and Fourier-transform infrared analyses of these fil ms. Dielectric constants of these perfluorinated films are consistently bel ow a value of 2.0, measured over a frequency range of 5x10(2)-1x10(5) Hz. A lthough thermal gravimetric analysis of the plasma films revealed significa nt weight loss beginning at temperature below 300 degrees C, up to 70%, dra matic improvement in the thermal stability of these films was observed foll owing their thermal annealing at temperature of 350-400 degrees C under N-2 . The resultant annealed films exhibit negligible weight loss during subseq uent thermogravimetric analysis at temperature as high as 420 degrees C. Mo st importantly, this gain in thermal stability of the plasma polymers is ac hieved with only minor increases in the dielectric constants, along with re latively minor changes in film compositions, following the thermal annealin g processes. The implications of this study with respect to low dielectric constant requirements for future smaller feature size integrated circuits a re discussed in this work. (C) 2000 American Vacuum Society. [S0734-211X(00 )00402-9].