Investigation of Porogen Behavior during the Curing Process of Ultralow-k Spin-On Materials

Ultralow- integration issues for node and below is a major challenge. Pore creation was studied vs the matrix film cross-linking. After curing at low temperature some bumps were found dispersed at the top of the film surface. The porosity could be changed by varying the porogen loadings and curing program ramp. At higher temperatures ( for ) the porogen degraded, which induces bumps that transition into holes. Faster curing on a hot plate at for was used to more quickly make the matrix rigid, and led to a complete disappearance of bumps in the film surface. It is suggested that the bump formation comes from porogen diffusion taking place in the "soft" matrix. The absence of matrix cross-linking allowed porogen aggregation and bump formation. Porogen diffusion becomes more important as the curing temperature increases and more porogen is mixed into the precursor solution. This means that porogen aggregation is associated with the slow matrix cross-linking kinetics. A strong correlation exists between porogen loading and bump formation which shows that pore interconnection could occur through a preferential channel formation where the porogens diffuse through the channels.