Atmospheric-Pressure Synthesis of Atomically Smooth, Conformal, and Ultrathin Low-k Polymer Insulating Layers by Plasma-Initiated Chemical Vapor Deposition

The straightforward synthesis of ultrathin low dielectric constant insulating polymer layers from four cyclic organosilicon monomers (i.e., two organocyclosiloxanes and two organocyclosilazanes) by atmospheric pressure plasma-initiated chemical vapor deposition (AP-PiCVD) is demonstrated. The combination of ultrashort plasma pulses (ca. 100 ns), as polymerization initiator, with long plasma off-times (10 ms), yields the formation of atomically smooth and conformal polymer layers with excellent insulating properties. Leakage current densities of 10(-9) A cm(-2) are measured for film thicknesses as low as 12 nm. Low dielectric constants are obtained because of the retention of the cyclic structure of the monomers during the deposition. The polymer layers prepared from 1,3,5,7- tetramethyl-1,3,5,7-tetravinylcyclotrisiloxane display the lowest dielectric constant (k = 2.8). The present study demonstrates the ability to vary the dielectric constant of as-deposited polymer layers by varying the monomer bonds, i.e., siloxane and silazane, as well as their ring size.