8652
J. Phys. Chem. B 2005, 109, 8652-8658
Pure-Silica-Zeolite MEL Low-k Films from Nanoparticle Suspensions Zijian Li, Christopher M. Lew, Shuang Li, Dora Iliana Medina, and Yushan Yan* Department of Chemical and EnVironmental Engineering, UniVersity of California, RiVerside, California 92521-0403 ReceiVed: December 21, 2004; In Final Form: February 17, 2005
Following our previous works on pure-silica-zeolite (PSZ) MFI, in this study we explore PSZ MEL as a new option for low-k dielectric films. Our motivation has been to increase the microporosity of the spin-on films by moving to structures with a framework density (FD) lower than MFI. Nanoparticle PSZ MEL suspensions were synthesized by a two-stage method that allowed the yield of nanocrystals to be significantly enhanced, while the zeolite nanocrystals remain small. For the first time zeolite nanocrystals of about 50 nm were synthesized with a yield as high as 57%. Nanoparticle suspensions with different particle sizes and crystallinities were spun on silicon wafers to prepare continuous thin films. An ultralow-k value as low as 1.5 was obtained with MEL nanoparticle suspension of high relative crystallinity. The surface roughness of the PSZ MEL film with high relative crystallinity is greatly improved (Rrms ∼ 5.6 nm) compared to MFI films with high relative crystallinity (Rrms ∼ 12 nm).
Introduction Although only a rule of thumb, Moore’s law has been maintained since first proposed by Gordon Moore in 1965,1 and it may still hold true for another 10-20 years. To continue the trend of doubling the number of transistors on a chip in about every 2 years, low-dielectric-constant (low-k) materials are essential for building faster microprocessors by lowering crosstalk noises and power consumption.2 The sub-90-nm technology is expected to be accomplished only with the use of a dielectric material with a k value lower than 2.4, but a manufacturable solution for such a low-k material is still unknown.3 The slower than projected pace of the low-k materials development has made it a hot issue for both industry and academia. Low-k materials are also among the Top Technical Challenges recently released by the International SEMATECH.4 Many polymers have been considered as low-k material candidates, but they suffer from their low thermal stability and poor mechanical strength. Porous inorganic low-k materials, mostly porous silicas, may stand a better chance than their organic rivals. Both sol-gel silica5-7 and surfactant-templated mesoporous silica8-10 take advantage of the robust silica matrix and the low dielectric constant of air. However, there are yet many issues such as low mechanical strength, hydrophilicity, and low thermal conductivity to overcome before these materials can be used commercially. We have been studying a new class of porous silicaspuresilica zeolites (PSZs). They are crystalline microporous silicas whose crystalline nature provides them with uniform micropore sizes (
