X-Ray Porosimetry: A New Method for the Characterizaton of Porous Low-Dielectric-Constant Thin Films Adaptable for the Semiconductor Industry
Christopher L. Soles, Barry J. Bauer, Wen-Li Wu
NIST scientists have developed a new measurementmethod x-ray porosimetry (XRP) for characterizationof porous low-dielectric-constant (low-k) films.The method has application to the semiconductorindustry in their pursuit of new interlayer materialswith low dielectric constants to reduce cross-talk and toincrease processor speed as device features reachnanometer sizes. While candidate materials differ intheir base chemistries, a common theme emerges in thepush to develop low-k dielectric materials nano-scaleporosity must be introduced in a controlled manner tofurther reduce the dielectric constant. Measurementtechniques are needed to accurately and noninvasivelycharacterize the porosity in these films while attachedon a silicon substrate. Over the past several years,NIST scientists in the Polymers Division and at theCenter for Neutron Research have successfullyaddressed these needs through the development of amethodology based upon x-ray reflectivity (XR), smallangle neutron scattering, and ion scattering. However,these measurements require specialized facilities notreadily accessible to industrial laboratories. In contrast,the new method requires x-ray equipment commerciallyavailable to industrial laboratories.In the new method, a controlled solvent environmentis created around the thin film so that an equilibriumamount of adsorption occurs. Under such conditions,XR instrumentation gives accurate values of the totaldensity that is a combination of wall density andsolvent-filled pores. The mass uptake as a function ofpartial pressure is calculated from these results.An additional potential advantage of XRP is theability to quantify not only the average film density, butalso the density profile normal to the film surface.Ongoing work investigates the potential of XRP toextract pore size distributions as a function of depthinto film. To prevent dielectric breakdown, thesemiconductor industry prefers to have low porosity orvery small pores near the surfaces with the majority ofthe porosity in the localized in the center of the thinfilm. XRP has the potential to become a useful methodfor characterizing these types of structures usingcommercially available XR within industriallaboratories.
, Bauer, B.
and Wu, W.
X-Ray Porosimetry: A New Method for the Characterizaton of Porous Low-Dielectric-Constant Thin Films Adaptable for the Semiconductor Industry, Journal of Research (NIST JRES), National Institute of Standards and Technology, Gaithersburg, MD
(Accessed December 11, 2023)