Integration of chemical vapor deposition Al interconnects in a benzocyclobutene low dielectric constant polymer matrix: A feasibility study

Results are presented from a proof-of-concept study that examined the integration of damascene-processed thermal chemical vapor deposited (TCVD) aluminum (Al) interconnects in a benzocyclobutene (BCB) polymer matrix. In a first phase, the study identified baseline deposition conditions for the formation of structurally and chemically compatible blanket Al/titanium nitride (TiN)/BCB stacks on two types of blanket BCB substrates utilized to simulate the actual surfaces encountered in typical damascene processing: (1) blanket BCB films capped with a silicon dioxide ${\mathrm{SiO}}_{\mathrm{2}}$ layer $({\mathrm{SiO}}_{\mathrm{2}}\mathrm{-BCB}\mathrm{),}$ and (2) plasma reactive ion etched blanket BCB films. The TiN diffusion barrier was grown in two stages. A first (bottom) layer was deposited by physical vapor deposition (PVD), followed by a CVD-grown top layer. The resulting TCVD Al/CVD TiN/PVD TiN/BCB stacks were stable under thermal stressing up to 325 °C for 1 h. In a second phase, an optimized TCVD Al process flow was developed for void-free filling of TiN-coated 320-nm-wide trenches etched in a BCB matrix. The process flow included the demonstration of a chemical mechanical polishing recipe for planarization of the patterned TCVD Al/CVD TiN/PVD TiN/BCB structures. The resulting findings were incorporated in the fabrication of electrically testable TCVD Al/CVD TiN/PVD TiN/BCB interconnect structures on 200 mm wafers. Electrical evaluation for shorting and leakage of the test dice produced an adequate yield for the feasibility study of ∼71% of screened test sites. The electrical tests also generated an upper-bound value of 4.2 μΩ cm for Al line resistivity, a number that did not include corrections for contact resistance and interfacial scattering. These findings demonstrate the feasibility of TCVD Al/BCB based metallization schemes, particularly in terms of chemical, structural, mechanical, and electrical performance.