Damage by radicals and photons during plasma cleaning of porous low-k SiOCH. I. Ar/O2 and He/H2 plasmas

Abstract

Porous dielectric materials offer lower capacitances that reduce RC time delays in integrated circuits. Typical porous low dielectric (low-k) materials include SiOCH—silicon dioxide with carbon groups, principally –CH3, lining the pores. Fluorocarbon plasmas are often used to etch such low-k materials. These processes leave a fluorocarbon polymer on the SiOCH surface that must be removed, often with oxygen or hydrogen containing plasmas. Pores open to the surface and that are internally connected provide pathways for reactive species to enter into the porous network and produce damage. For example, during cleaning using O2 containing plasmas, reactions of O atoms with –CH3 groups can increase the k-value by removing C atoms. Vacuum ultraviolet (VUV) photons produced by the plasma and that penetrate into the material can scission –Si–CH3bonds and accelerate the removal of –CH3 groups. This paper reports on results from a computational investigation of Ar/O2 and He/H2plasma cleaning of porous SiOCH when including the effects of VUV photons. The authors found that He/H2 plasmas are able to clean CFx polymers deposited during etching while producing milder damage to underlying –CH3 sites compared to O2plasmas due to the lower reactivity of H atoms and the shorter penetration distance of photons produced in He/H2plasmas.