Journal of Electronic Materials

, Volume 37, Issue 10, pp 1534–1546 | Cite as

Air-Gaps for High-Performance On-Chip Interconnect Part II: Modeling, Fabrication, and Characterization

  • Seongho Park
  • Sue Ann Bidstrup Allen
  • Paul A. Kohl
Open Access


Air-gaps are the ultimate low-k material in microelectronics due to air having a low dielectric constant close to 1.0. The interconnect capacitance can further be reduced by extending the air-gaps into the interlayer dielectric region to reduce the fringing electric field. An electrostatic model (200 nm half-pitch interconnect with an aspect ratio of 2.0), was used to evaluate the dielectric properties of the air-gap structures. The incorporation of air-gaps into the intrametal dielectric region reduced the capacitance by 39% compared with SiO2. Extending the air-gap 100 nm into the top and bottom interlayer SiO2 region lowered the capacitance by 49%. The ability to fabricate air-gaps and ‹extended air-gaps’ was demonstrated, and the capacitance decrease was experimentally verified. Cu/air-gap and extended Cu/air-gap interconnect structures were fabricated using high-modulus tetracyclododecene (TD)-based sacrificial polymer. The aspect ratio of the air-gap was 1.8 and the air-gap was extended 80 nm and 100 nm into the top and bottom interlevel SiO2 region, respectively. The measured effective dielectric constant (k eff) of the Cu/air-gap and the extended Cu/air-gap structures with SiO2 interlevel dielectric was 2.42 and 2.17, respectively. The effect of moisture uptake within the extended Cu/air-gap structure was investigated. As the relative humidity increased from 4% to 92%, the k eff increased by 7%. Hexamethyldisilazane was used to remove adsorbed moisture and create a hydrophobic termination within the air-cavities, which lowered the effect of humidity on the k eff. A dual Damascene air-gap and extended air-gap fabrication processes were proposed and the challenges of using a sacrificial polymer placeholder approach to form air-cavities are compared to other integration approaches of dual Damascene air-gap.


Air-gap low-k Damascene 



The authors gratefully acknowledge the support of Promerus LLC.


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Copyright information

© TMS 2008

Authors and Affiliations

  • Seongho Park
    • 1
  • Sue Ann Bidstrup Allen
    • 1
  • Paul A. Kohl
    • 1
  1. 1.School of Chemical and Biomolecular EngineeringGeorgia Institute of TechnologyAtlantaUSA

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