In-Situ GISAXS Studies on the Evolution of Closed Nanopores in Low-k Organosilicate Dielectric Thin Films

Pohang University of Science & Technology
â—‹Kyeong Sik Jin Jinhwan Yoon Kyuyoung Heo Moonhor Ree

Porous organosilicate materials have recently attracted much interest due to their potential application as low dielectric constant (low-k) interdielectrics. In particular, much effort has been directed towards the development of low-k porous organosilicate dielectric thin films via the templated polycondensation of their soluble precursors in the presence of a thermally-labile, organic polymeric porogen. Pores are subsequently formed in the resulting dielectrics through the sacrificial thermal decomposition of the porogens in the range 350-400C. However, the tendency of porogens to aggregate in organosilicates has limited the ability to reduce the pore size and porosity of the resulting dielectrics, making them unsuitable for use in advanced integrated circuits patterned with small feature sizes. The formation of porous films from an organosilicate precursor polymer/porogen composite is a complex procedure since the matrix precursor readily undergoes crosslinking while the porogen undergoes thermal degradation. In order to understand the structure of pores in the porous film, it is necessary to investigate their generation during the porous dielectric film process. Pore structure evolution during porous film process has rarely been investigated. In this study, we present the in-situ grazing incidence small angle X-ray scattering (GISAXS) study of the evolution of nanopores during porous dielectric film formation in a composite film containing polymethylsilsesquioxane (PMSSQ) precursor and star-shaped four-armed poly(&egr;-caprolactone) porogen in various compositions. Using a synchrotron X-ray source, in-situ GISAXS measurements were carried out during thermal treatment of the PMSSQ/porogen composite films to 400 ?C in vacuum, and continued during the subsequent cooling of the resulting porous films. In addition, thermogravimetric analysis and electron microscopy measurements were performed. Detailed analyses of the measured two-dimensional GISAXS data were accomplished using a recently developed GISAXS formula.