Grazing-incidence small-angle X-ray scattering study of porous dielectrics used in advanced microelectronic interconnections

Abstract

The increase of the integration density and of the operation speed in ultra-large-scale integrated microelectronics requires a reduction in the dielectric constant for high-frequency insulation between the copper connections of some tenth-of-micrometre thickness. Recently, the quality of the dielectric has been defined by its dielectric constant k (>1) relative to the unpolarized vacuum (k = 1). Bulk low k will never reach k lower than 3 and the only way to achieve a further decrease in k is to introduce nanoporous dielectric films compatible with the required mechanical behaviour. We compare the merits and the structure determined by grazing-incidence small-angle X-ray scattering (GISAXS) of four different growth processes: plasma-enhanced chemical vapour deposition or spin coating with three variants: dual-phase blend, self-assembled approach, nanoclustering precursor. All of them are baked in order to cure the amorphous SiwOxCyH z 'skeleton' (SiOCH). Depending on the process used, the pore morphologies are very different. They range from well defined pores of 4-5 nm diameter to sub-nanometric ill-defined pores which may be described as density fluctuations. Finally, it appears that the curing process is a key problem, which up to now has been difficult to characterize by GISAXS. © International Union of Crystallography 2007.