UV-induced porosity using photogenerated acids to catalyze the decomposition of sacrificial polymers templated in dielectric films

Abstract

A UV-initiated process for selective incorporation of porosity and tuning of refractive index in a dielectric film is presented. The formation of porosity via radiation offers the advantages of lower processing temperatures and shorter processing times than most processes that rely on thermallyinduced porosity. The ability to pattern porosity via the use of a photomask allows structures such as porous direct-write waveguides to be made. The direct-write process presented here used UVgenerated acids to catalyze the decomposition of sacrificial polymers templated in a crosslinked matrix, resulting in the formation of porosity and decrease of refractive index and dielectric constant after subsequent removal of the generated acid. In unexposed areas, no acid molecules were generated, thus these areas remained non-porous and their refractive index remained relatively high compared to porous regions. Base-catalyzed gelation was used to crosslink the matrix at temperatures well below the glass transition temperature of the matrix in order to avoid thermal activation of the photoacid generators (PAGs) in the direct-write formulation. After crosslinking the matrix, deep ultraviolet (DUV) radiation was used to initiate the direct-write reactions thus creating a refractive index profile within the film. Neutralization or volatilization of the photogenerated acid was used to deactivate the system. The lowest interline dielectric constant achieved by direct-written films was 2.36 after the volatilization step compared to a value of 2.29 for porous films formed via the traditional template process. At optimum conditions, the average amount of UV-induced porosity was estimated to be as high as 21%. Transmission electron microscopy (TEM) imaging showed that elongated mesopores (10 nm by about 20-30 nm) and elongated macropores (100 nm by about 200 nm in size) were produced within the internal structure of direct-written films. The porous films formed via the traditional template technique had internal structures with large collections of spherical mesopores (5-10 nm) located in close proximity to one another due to phase segregation of the polymer at high temperatures.

Low–Dielectric Constant Insulators for Future Integrated Circuits and Packages

“…A variety of other spin-on dielectrics, including HSQ and MSQ, have been made porous by use of porogens (90)(91)(92)(93)(94)(95). The approach generally involves mixing a thermosetting polymer in a solvent with a second, soluble component, the porogen.…”

Holographic Recording in Cross-Linked Polymeric Matrices through Photoacid Generation

“…Typically, this alteration is a change in the refractive index of the material and refractive index contrast between the bright and the dark regions of the holographic media determines the strength of a volume hologram. It was anticipated that increasing the free volume in the bright regions of the holographic media via the catalytic decomposition of functional groups attached to the backbone of a cross-linked polymer matrix would lead to the evolution of volatile small molecules and a significant change in the refractive index of the material (Figure ). – This release of gaseous products capable of diffusing out of the matrix is anticipated to result in either increased free volume or generation of nanopores filled with air. Incorporation of air (dielectric constant 1.01) in a higher dielectric constant rigid polymeric matrix should result in significant modulation of the refractive index.…”

Incompletely condensed POSS-based spin-on-glass networks for impeccable ultra low-k integration

“…However, the dielectric constant of PMSSQ-based spin-on-glass materials (k B 2.7) is still too high for next generation low-dielectric constant materials, and the search for integration-level feasible ultra low-k materials (k o 2.0) is ongoing today. And while the use of sacrificial porogens has been extensively investigated to utilize the low permittivity of free space (e = 1) formed through pyrolysis, 9 the subsequent degree of depreciation of mechanical properties, as well as the fabrication of smooth interfaces with metal gates, metal leaching, and residual ash have been reported as areas of critical concern. 10 Within the polysilsesquioxane family, polyhedral oligomeric silsesquioxanes, or more commonly known as POSS, have been widely studied due to their 3-dimensional Si-O-Si inorganic polyhedra with organic functional groups radially stemming outwards from the vertices.…”