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

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.

Damage-free plasma etching of porous organo-silicate low-k using micro-capillary condensation above −50 °C

“… 37 , 38 , VUV emission between 100 nm and 190 nm is the most damaging for Si-CH 3 bonds in the bulk low-k material. As shown in literature 12 , 39 , pure SF 6 does emit in the VUV range.…”

“…Damage evolution by VUV is modeled using the equation 37 : where σ PA is the photo-absorption cross section, ϕ is an adjustment parameter allowing to consider the effective CH 3 out-diffusion, [Si] is the Si concentration into the low-k, and I 0 is the radiation intensity. Typical SF 6 plasma emission spectrum in VUV range is shown in references 12 , 39 . The continuous emission in 100 nm to 150 nm range with local maxima (e.g.…”

“…can cause densification leading to the formation of a top SiO 2 layer, but also sealing against the propagation of radicals 5 . The effect of plasma-emitted UV-VUV light has been recently the subject of intense investigations, showing that photons with wavelength 100 ≤ λ ≤ 200 nm can cause Si-C scissioning deep into the bulk of the materials, but this effect can be significantly reduced by the use of a proper hard-mask system acting against VUV penetration 12 .…”

Vapor-deposited zeolitic imidazolate frameworks as gap-filling ultra-low-k dielectrics

“…This metallization route relies on first patterning the dielectric layer via anisotropic plasma etching before Cu electroplating and planarization. Plasma-induced damage of new potential low-k materials, especially porous ones, during this patterning step is a major roadblock to achieve k -values < 2.4 11,12 . An alternative metallization approach is to first pattern a sacrificial layer that can be removed after the formation of metal interconnect wires, leaving the latter as a patterned top layer 13 .…”

Synergistic effect of VUV photons and F atoms on damage and etching of porous organosilicate films

“…So, strong reduction of plasma damage, especially in the films with high porosity ( P > 30%) was shown, but the remaining damage close to 20 nm is still observed . The detailed study of plasma damage in low‐k films filled by sacrificial polymers was also carried out . It was shown that the low‐k damage by VUV light cannot be completely avoided even when the pores completely filled with the sacrificial polymer.…”