Example of low-k film toughness test using the new NIST technique. The process uses an indentation instrument that punches the triangular hole. Forces and the length of the resulting cracks determines the toughness. (Credit: NIST)

Example of low-k film toughness test using the new NIST technique. The process uses an indentation instrument that punches the triangular hole. The pressure force and the length of the resulting cracks determine the toughness. (Credit: NIST)

NIST has developed a method to measure the toughness (i.e., resistance to fracture) of low-k insulating films found in high-performance ICs. As with other NIST efforts, the technique is aimed at setting standards and testing methodology that will improve reliability and manufacturability. NIST notes, however, that unlike some of new standards that come out of the agency, the toughness test is something microelectronics manufacturers can use with equipment they already own. The low-k films are sandwiched between layers of conductors and components in microprocessor chips and other high-performance semiconductor devices. Resent IC manufacturing efforts have made better – but more brittle – films that can yield defective components NIST researchers are recommending adaptation of a nanoindentation test that presses a diamond tip into the film and then records the amount of pressure it takes to deform the material and the crack lengths. The new test requires only modest modifications to existing nanoindenters. But toughness, the force needed to actually break the material, has been, well, tougher. Thin films were particularly problematic because they necessarily must be layered on top of another stronger material, such as a silicon wafer. The new NIST technique requires a slight modification of the nanoindentation equipment—the probe has to have a sharper, more acute point The measurement technique and model were published in a two-part series in the Journal of Materials Research.

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