Annihilating Nanoscale Defects

Estimated reading time: 4 minutes

Target dates are critical when the semiconductor industry adds small, enhanced features to our favorite devices by integrating advanced materials onto the surfaces of computer chips. Missing a target means postponing a device's release, which could cost a company millions of dollars or, worse, the loss of competitiveness and an entire industry. But meeting target dates can be challenging because the final integrated devices, which include billions of transistors, must be flawless — less than one defect per 100 square centimeters.

Researchers at the University of Chicago and the U.S. Department of Energy's (DOE's) Argonne National Laboratory, led by Juan de Pablo and Paul Nealey, may have found a way for the semiconductor industry to hit miniaturization targets on time and without defects

To make microchips, de Pablo and Nealey's technique includes creating patterns on semiconductor surfaces that allow block copolymer molecules to self-assemble into specific shapes, but thinner and at much higher densities than those of the original pattern. The researchers can then use a lithography technique to create nano-trenches where conducting wire materials can be deposited.

This is a stark contrast to the industry practice of using homo-polymers in complex "photoresist" formulations, where researchers have "hit a wall," unable to make the material smaller.

Before they could develop their new fabrication method, however, de Pablo and Nealey needed to understand exactly how block copolymers self-assemble when coated onto a patterned surface — their  concern being that certain constraints cause copolymer nanostructures to assemble into undesired metastable states. To reach the level of perfection demanded to fabricate high-precision nanocircuitry, the team had to eliminate some of these metastable states.

To imagine how block copolymers assemble, it may be helpful to picture an energy landscape consisting of mountains and valleys where some valleys are deeper than others. The system prefers defect-free stability, which can be characterized by the deepest (low-energy) valleys, if they can be found. However, systems can get trapped inside higher (medium energy) valleys, called metastable states, which have more defects.

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