From the beginning of integrated circuits through the 0.18 mm technology node, silicon dioxide (k = 3.9-4.2) has been the material of choice for inter-layer-dielectric (ILD) applications. As a result, many of the integration procedures that have evolved are based on the deposition, patterning and removal of SiO₂ during processing. This material has remarkable properties for device fabrication including exceptional thermal properties, excellent electrical properties and enviable mechanical properties. In almost every important category (thermal stability, breakdown voltage, leakage current, mechanical properties, etc), except for dielectric constant, the properties of any low-k materials may be expected to be inferior to SiO₂. Historically, transition to lower dielectric materials was necessary to prevent crosstalk between conductor lines and signal delays in the back-end-of-the-line (BEOL) interconnect wiring, as device sizes decrease and device densities increase. When the hunt for new low-k replacements for SiO₂ was heating up, high temperature organic polymers and silicates both received a great deal of attention.^1,2 Interestingly, these two main classes of dielectric materials have very different properties. While both can be thermally stable with good electrical properties, the organics tend to be soft, but tough, with coefficients of thermal expansion (CTE), exceeding 50 ppm. The inorganic materials, on the other hand, have lower CTEs, usually less than 25 ppm, they are hard but brittle and susceptible to stress-corrosion cracking in moist environments. However, the semiconductor manufacturers opted to go with inorganic-like materials with which they were more comfortable through their experiences with oxide insulators. Consequently, Si-Me containing organosilicate materials (k = 2.7-3.0) have been developed and are now manufactured for the current 90 nm technology.^3,4 The presence of methyl groups, while necessary to provide low dielectric constant properties and hydrophobicity, reduces the density, modulus, hardness and fracture energy.^5-7 Moreover, these organosilicates present a power law dependence between their density and their mechanical properties, translating into a rapid decay of the former as soon as porosity is introduced. Unfortunately, it's now well established that device generational extendibility (i.e., similar elemental composition, but progressively decreasing dielectric constant) can only be achieved by embracing the concept of porosity. Escalating integration issues are anticipated with increased porosity because many of the manufacturing processes associated with copper metallurgy require good mechanical properties (e.g chemical mechanical polishing, chip dicing, wire bonding, etc).^8,9 Mechanical instability and the associated reliability issues have been largely responsible for the continuous re-evaluation of the insertion point for porous low-k dielectric materials in the ITRS roadmap.

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