Polymerization of Organosilicones in Microwave Discharges. II. Heated Substrates

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Abstract
Organosilicone vapors [hexamethyldisiloxane (HMDSO), hexa-methyldisilazane (HMDSN), and hexamethylcyclotrisilazane (HMCTSN)] have been polymerized in a microwave plasma. The reaction kinetics, structure, and density of the plasma polymer films were studied as a function of substrate temperature (Ts) to 800°C, using metal or glass as the substrate. Deposition rates for both HMDSO and HMDSN decrease with substrate temperature from near 80 Å sec−1 on an unheated substrate to about 30 Å sec−l above 400°C. The densities of plasma polymers, already high (∼1.7 g/cm3) compared with conventional organosilicone polymers (∼1.0 g/cm3) when Ts = 25°C, increase further with increasing substrate temperature. These high densities (near 1.9 g/cm3) indicate that for T above ∼500°C, little “organic” content remains in the plasma polymers. Infrared spectra of plasma polymerized HMDSO, HMDSN, and HMCTSN show that these materials differ structurally from their more familiar counterparts, confirm the increasing importance of inorganic linkages at rising Ts, and support the concept that the plasma polymers are intensely cross-linked. The great complexity of plasma polymerization reactions is further documented by the reported results.