A novel airgap formation scheme by GO nanosheet gap sealing process with extreme low effective dielectric constant

Abstract

In order to reduce the parasitic capacitance between the interconnect metal line, low-k material was developed and integrated into CMOS BEOL process, and airgap is the ultimate low-k material with the lowest dielectric constant close to 1. In this work, a novel airgap formation scheme was proposed to form the airgap by low-cost coating process, in which Graphene Oxide (GO) nanosheet was used as gap-filling suppressor to seal the gap between two adjacent metal line and form the airgap. Traditional non-conformal CVD gap sealing process was firstly developed and compared with the proposed scheme. It was found that the non-conformal CVD sealing process cannot achieve high performance airgap, and there will always be some material deposited into the gap between the metal interconnect line even for very narrow gap. For the proposed scheme, volume ratio of GO sealed airgap to gap region before sealed can reach to about 85% with much wider gap, and calculated effective relative dielectric constant of this region is about 1.57. When increasing the gap CD to value larger than GO nanosheet size, conformal film deposition can be got, which indicate that GO nanosheet with the size larger than gap CD can seal the gap in the very beginning and prevent further material depositing into the gap to make the large ratio airgap formation.