Low-k Materials: Recent Advances

From a historical point of view, the search for new low-k and ultra-low-k materials has always been dictated by industrial needs, resulting in a strong connection between fundamental research and technology. Although a variety of potential candidates has been reported in the literature during the past decade, integration is the deciding factor driving the selection of the most promising materials for a given technology node [1]. For instance, the industry flirted briefly with organic polymers [2–7]. Besides the anticipated thermal stability challenges, this class of materials, known to be tough and crack-resistant, had other issues, such as softness, large coefficient of thermal expansions (CTE) and delamination. While most of these problems were mitigated by material reengineering and chip redesign, solutions occurred too late, relegating the organic polymers to possible hybrid build applications [8]. For the new low-k materials, it was expected that their electrical and mechanical properties would be comparable to those of silicon dioxide [9, 10], the insulating material of reference for the quite conservative semiconductor industry. Chemical modification of the silicon network, first by introduction of fluorine and eventually by the addition of carbon, was then adopted as the lower risk path to introducing low-k materials in the back-end-of-the-line (BEOL) [1]. At that time, silicates and