porous material may be reduced by increasing the porosity of the film. Relative dielectric constants lower than 2.0 have been reported. Integration difficulties related to porous silicon dioxide implementation include low mechanical strength and difficult integration with etch and polish processes. Porous organosilicate glass (carbon-doped oxide) Porous organosilicate materials are usually obtained by a two-step procedure where the first step consists of the co-deposition of a labile organic phase (known as porogen) together with an organosilicate phase resulting in an organic-inorganic hybrid material. In the second step, the organic phase is decomposed by UV curing or annealing at a temperature of up to 400°C, leaving behind pores in the organosilicate low-κ materials. Porous organosilicate glasses have been employed since the 45 nm technology node. Spin-on organic polymeric dielectrics Polymeric dielectrics are generally deposited by a spin-on approach, which is traditionally used for the deposition of photoresist materials, rather than chemical vapor deposition. Integration difficulties include low mechanical strength, coefficient of thermal expansion (CTE) mismatch and thermal stability. Some examples of spin-on organic low-κ polymers are polyimide, polynorbornenes, benzocyclobutene, and PTFE. Spin-on silicon based polymeric dielectric There are two kinds of silicon based polymeric dielectric materials, hydrogen silsesquioxane and methylsilsesquioxane. Air gaps The ultimate low-κ material is air with a relative permittivity value of ~1.0. However, the placement of air gaps between the conducting wires compromises the mechanical stability of the integrated circuit making it impractical to build an IC consisting entirely of air as the insulating material. Nevertheless, the strategic placement of air gaps can improve the chip's electrical performance without compromising critically its durability. For example, Intel uses air gaps for two interconnect levels in its 14 nm FinFET technology. See also Dielectric High-κ dielectric Relative static permittivity References External links Nasa on Low-k The evolution of interconnect technology for silicon integrated circuitry Semiconductor fabrication materials Materials science