Machine Design

Film Test for Better ICs

As IC electronics have become more densely packed, cross-talk among them has become a problem. One means of preventing cross-talk among chip components has used electrically insulating dielectric films (also called low-k films) inserted between the layers of conductors and components on the IC. Engineers have been making these films porous with nanoscale voids to let them more effectively stop cross-talk. But these voids make films brittle, which complicates IC reliability and manufacturing. Until now, there has been no way designers could measure the fracture resistance of these films.

NIST researchers have refined a test called nanoindentation to gauge these extremely thin (2.3 microns), low-k films. The upgraded test uses a sharp diamond probe which is punched through a film of interest deposited on a piece of silicon. An electron microscope measures the resulting cracks, some as small as 300 nm. Crack formation depends on indentation force, film thickness and stress, and elastic properties of the film and silicon substrate. Plugging these variables into a mechanical model developed by NIST predicts fracture toughness and the critical film thickness for spontaneous fracture. One advantage of the test is that it uses equipment state-of-the-art microelectronics companies already own. It will also eliminate some candidate films without further testing or prototyping.

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