Dependenceofporosityinmethyl-silsesquioxanethinfilms onmolecularweightofsacrificialtriblockcopolymer JunXu a, * ,J.Moxom a ,ShuYang b ,R.Suzuki c ,T.Ohdaira c a Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, USA b Bell Laboratories, Lucent Technologies, 600 Mountain Ave. Murray Hill, NJ 07974, USA c National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan Received4June2002;infinalform14August2002 Abstract Positron annihilation spectroscopy is used to characterize pore sizes and their interconnectivity for porous low dielectric constant methyl-silsequioxane thin films, which are templated by triblock copolymers. More than 1 lmof ortho-positronium(o-Ps)diffusionlengthhasbeenobservedforcertainfilms,indicatinghighinterconnectivityofpores. S parametersfromDopplerbroadeningofannihilationphotons(DBAP)showhomogeneousdepthprofilesofthese films. o-Ps3c emissionandlifetimesshowthattheporeinterconnectivitydependsonthecharacteristicsofthetriblock copolymers. Pores generated from polymers with higher molecular mass are smaller and more closed, while pores generatedbypolymerswithlowermolecularmassandsmallerethyleneoxidefractionaremoreinterconnected. Ó 2002PublishedbyElsevierScienceB.V. When feature sizes in integrated circuits (IC) continuetoshrinktoincreasethemicroprocessor speed and the packing density of microelectronic devices, the signal delay from the interconnect becomesthemajorlimitationofchipperformance. Newlowdielectricconstantmaterials(k < 4:0)are neededtoreplacecurrentdielectricmaterial,SiO 2 . Bytakingadvantageofthelowdielectricconstant ofair(1)andintroducingporesintoadielectric material, the dielectric constant can be effectively reducedtolessthan2.0.Thisapproachhasiniti- atedextensiveeffortinsemiconductorinterconnect research and development [1,2]. Porous methyl- silsesquioxane(MSQ)filmsaresomeofthesenew low-k materials that have been actively studied andhasshown k of1.5with50%porosityandhigh breakdownstrength[3,4]. An ideal porous material would consist of a network of closed nanopores with narrow size distribution. However, when the loading of pore generator is high, large and interconnected pores maybeobtained,resultinginhighcurrentleakage andpoormechanicalstrength.Clearly,character- ization and understanding of pore size and inter- connectivity play an important role in optimizing thedesignofporousmaterials.Positronannihila- tion spectroscopy (PAS) has unique advantages forcharacterizingvoidsbecause ortho-positronium 4October2002 ChemicalPhysicsLetters364(2002)309–313 www.elsevier.com/locate/cplett * Correspondingauthor.Fax:1-865-574-8363. E-mail address: xuj2@ornl.gov (J.Xu). 0009-2614/02/$-seefrontmatter Ó 2002PublishedbyElsevierScienceB.V. PII:S0009-2614(02)01369-6