Carbon-Enriched Amorphous Hydrogenated Boron Carbide Films for Very-Low-k Interlayer Dielectrics

A longstanding challenge in ultralarge-scale integration has been the continued improvement in low-dielectric-constant (low-k) interlayer dielectric materials and other specialized layers in back-end-of-the-line interconnect fabrication. Modeled after the success of carbon-containing organosilicate materials, carbon-enriched amorphous hydrogenated boron carbide (a-BxC:H-y) films are grown by plasma-enhanced chemical vapor deposition from ortho-carborane and methane. These films contain more extraicosahedral sp(3) hydrocarbon groups than nonenriched a-BxC:H-y films, as revealed by FTIR and NMR spectroscopy, and also exhibit lower dielectric constants than their nonenriched counterparts, notably due to low densities combined with a low distortion and orientation contribution to the total polarizability. Films with dielectric constant as low as 2.5 are reported with excellent electrical stability (leakage current of 10(-9) A cm(-2) at 2 MV cm(-1) and breakdown voltage of >6 MV cm(-1)), good thermal conductivity of 0.31 +/- 0.03 W m(-1) K-1, and high projected Young's modulus of 12 +/- 3 GPa. These properties rival those of leading SiOC:H materials, and position a-BxC:H-y as an important complement to traditional Si-based materials to meet the complex needs of next-generation interconnect fabrication.