Stereoscopic and electron tomographic observation methods using TransmissionElectron Microscope (TEM) were examined to characterize three-dimensionallya shape and size of pores and spatial distribution in porous low dielectricconstant (low-k) films. In a case of TEM observation, nm size pores in anamorphous film are difficult to be imaged since contrast from the amorphouslayer affect the pore imaging. An optimum image capture method at a modifiedelectron beam condition was studied in which the amorphous contrast from theporous low-k film is weakened to enhance scattering contrast from the poresand a matrix. As a result, a stereoscopic observation and 3-D reconstructionimages clarified that the shape of pores was not spherical but distorted andalmost pores were partially connected. For measuring pore size and spatialdistribution, connected pores were segmented into smaller pores byseparating at the narrowest part. From images after segmentation, it isindicated that there existed more and larger pores at interfaces than acenter area. It was found that the pores did not homogeneously distribute inthe film but concentrated at the interfaces.