Vacuum ultra-violet damage and damage mitigation for plasma processing of highly porous organosilicate glass dielectrics

TLDR

VUV damage to low‑k porous organosilicate glass can be partly suppressed by stuffing the matrix with high‑VUV‑absorbing sacrificial polymers and by using a hard mask that also absorbs VUV. The study aims to reduce VUV damage in patterned low‑k structures by combining pore stuffing/material densification with an absorbing hard mask or a low‑VUV‑emitting plasma discharge. The authors exposed 2.0‑k porous organosilicate glass films to 147 nm VUV photons from a Xenon capacitive‑coupled plasma and evaluated processing conditions that reduce photon fluence, pore‑stuffing/material densification, and hard‑mask absorption to minimize VUV damage. Strong methyl‑bond depletion and a corresponding rise in bulk dielectric constant were observed, indicating that VUV photons impair dielectric properties and must be mitigated during patterning and integration.

Abstract

Porous organosilicate glass thin films, with k-value 2.0, were exposed to 147 nm vacuum ultra-violet (VUV) photons emitted in a Xenon capacitive coupled plasma discharge. Strong methyl bond depletion was observed, concomitant with a significant increase of the bulk dielectric constant. This indicates that, besides reactive radical diffusion, photons emitted during plasma processing do impede dielectric properties and therefore need to be tackled appropriately during patterning and integration. The detrimental effect of VUV irradiation can be partly suppressed by stuffing the low-k porous matrix with proper sacrificial polymers showing high VUV absorption together with good thermal and VUV stability. In addition, the choice of an appropriate hard-mask, showing high VUV absorption, can minimize VUV damage. Particular processing conditions allow to minimize the fluence of photons to the substrate and lead to negligible VUV damage. For patterned structures, in order to reduce VUV damage in the bulk and on feature sidewalls, the combination of both pore stuffing/material densification and absorbing hard-mask is recommended, and/or the use of low VUV-emitting plasma discharge.