Directed Self-Assembly (DSA)
As anyone who studies computer science knows, the perceived limitations of Moore’s Law, which dictates that the number of transistors on a chip tends to double every 18 months, have caused some consternation with companies like AMD and Intel. It’s getting difficult to increase processing speeds because transistor size is now so small that hundreds of millions of transistors exist on one chip, and it is becoming even harder to include more. Intel has invented new manufacturing methods, and new materials to help decrease the size of transistors, but there is a ceiling, according to IBM, and we are already bumping into it.
“Historically [companies have reduced the size of transistors] by technological advances that allow the process engineers to use smaller and smaller wavelengths in the essential step of photolithography, where a pattern of light is used in a multi-step process to form the circuit patterns,” says Bill Hinsberg, a researcher at IBM Research Almaden. Initially, integrated circuits were patterned using violet light with a wavelength of about 440nm, and today deep-ultraviolet light from a laser source with a wavelength of 193nm is used in the photolithography step. Further reductions in wavelength grow increasingly difficult for technical reasons, so alternate methods for forming circuit patterns are under investigation.”
This is why parallel processing, where multiple cores are used inside a PC, is shaping up to be the future. IBM has also invented a way for nano-particles to “self-assemble” and fit more transistors on a processor core, using a technique where block polymers form a pattern that is not possible for the 193nm photolithography process. With self-assembly, the polymer molecule contains two sections (called blocks) that tend to separate from each other into a pattern, yet do not completely separate.
“Under the right conditions, a thin film of such block copolymers can form regular array patterns of spheres, cylinders, or lines,” says Hinsberg. “The dimensions of these nanostructures depend on the size of the polymer molecules and features smaller than 10nm have been demonstrated. In our work at IBM Almaden, we are designing methods to control this pattern formation in a way useful for semiconductor fabrication by using larger scale templates to orient the patterns. This approach is termed directed self-assembly. Our work has shown that it is possible to do this in a way that produces multiple nanoscale lines from a larger guiding pattern, and that the intrinsic properties of block copolymers allow defects in the guide pattern to heal, improving pattern quality, an important and useful attribute.”
With directed self-assembly, the polymer molecules automatically separate into a pattern, but a chemical bonding agent keeps them from separating completely. The result is a nano-structure that can be used on a transistor that increases processing power beyond the limitations of current photolithography methods.