Methods developed by researchers from NIST, IBM and the University of Texas will help the semiconductor industry move from trial and error to experimentation with materials for next-generation chips.

In the July 19 issue of Science, the researchers describe how they used X-ray and neutron probes to directly measure the spatial location of the chemical processes used to sculpt the components of silicon chips. By getting a nearly molecular view of a model system, researchers could directly link the reaction front along chemically amplified photoresists to the profile and composition of the final developed structure.

Photoresists are light-sensitive polymer films that coat the silicon wafers used to make chips. When exposed to light, parts of the film become soluble and can be washed away. The exposed areas are then used to house the components that make up the chip circuitry.

Chemical amplification is akin to a light-triggered etching process. Light releases acid molecules that, when heated, spread across the exposed areas of the photoresist. As it diffuses, the acid catalyzes a reaction, removing protectant groups from the photoresist in a "deprotection front" that alters the solubility in a developer solution of parts of the photoresist bordering the front.

While complex, these processes have gotten the job of making microchips done. But, according to Eric Lin, who led the research effort, the current understanding of the process is not detailed enough to ensure it can be used to make semiconductors with features smaller than 100 nm.

It is the goal of the semiconductor industry to produce chips with features smaller than 100 nm in 2003. Currently the features are 130 nm.

The researchers examined several possible areas where the existing processes could run into trouble at 100 nm. For example, the acid molecules from chemical amplification could diffuse too far, leading to a blurred pattern. Next-generation semiconductors will also use thinner photoresist films, which could affect their properties.

Measurements of the X-rays and beams of neutrons reflected off model photoresist layers before, during and after the deprotection reaction captured key details on the structure of the interface between the two layers, the profile and advance of the reaction front, local changes in chemical composition and other important aspects of the process.