Adjusting the Skeleton and Pore Structure of Porous SiCOH Dielectrics

The addition of a carbosilane skeleton precursor to a plasma-enhanced chemical vapor deposition process producing porous SiCOH dielectrics (pSiCOH) is shown to affect the carbon content and the pore structure of pSiCOH. Positron annihilation lifetime spectroscopy (PALS) reveals that added carbosilane reduces pore connectivity. PALS also shows evidence of both smaller ultramicropores and larger supermicropores in these materials. The method of adsorption porosimetry and the alpha-plot analysis provide an understanding of the PALS connectivity results through a correlation of high pore connectivity with a high fraction of porosity as the larger supermicropores. Low pore connectivity correlates with a low fraction of the porosity as supermicropores. A potential figure of merit for pSiCOH is then obtained, which is the amount of the porous volume present as the smallest ultramicropores. This is derived as the difference in porous volumes measured by adsorption vs toluene adsorption. The addition of a carbosilane precursor to pSiCOH deposition results in pSiCOH with a smaller average pore size and reduced pore connectivity.