AFM at NIST investigates nanoscale elastic properties. (News Briefs).

The ever-decreasing length scales in many fields of technology require new non-destructive measurement tools that can cope with submicrometer dimensions. Specifically, the ability to determine mechanical properties on the nanoscale is needed in many applications, particularly in microelectronics. To meet these needs, NIST is developing measurement tools that exploit the spatial resolution of atomic force microscopy ([approximately equal to]10 nm to 100 nm). The NIST approach, called atomic force acoustic microscopy (AFAM), involves vibrating the cantilever at ultrasonic frequencies to excite mechanical resonances. By measuring the resonant frequencies under both free space and surface-coupled conditions, quantitative information about the sample's elastic properties can be extracted.

With AFAM, a value of 67 GPa [+ or -] 7 GPa was obtained for Young's modulus of a 1 mm aluminum film. This compares favorably with literature values of 67 GPa to 71 GPa for bulk aluminum, and a value of 68.6 GPa [+ or -] 0.2 GPa obtained on the same film using surface acoustic wave methods. Furthermore, by holding the excitation frequency constant and measuring the cantilevers vibration amplitude as the tip is scanned across the sample, qualitative images can be created. NIST has obtained preliminary elasticity images of a damascene copper/[SiO.sub.2] dielectric test structure for microelectronics. Such images of relative elasticity may provide valuable information about elastic stiffness variations from one sample region to another.

CONTACT: Donna Hurley, [phone]; [e-mail].