September 1, 2011

2 Min Read
Controlled Collapse of Nanopillars Builds Chips for Nanoscale Devices

Device components like microfluidic chips, biosensor mechanical systems, or computer chip transistors have required the photolithography process to manufacture, and as they shrink in size, the limitations of light wavelengths used in photolithography will make other fabrication methods necessary. When a team of researchers were working on ways to prevent the collapse of nanopillars, they discovered that they could control the way they collapse, resulting in intricate patterns. Massachusetts Institute of Technology's (Cambridge, MA) Research Laboratory of Electronics, along with Singapore's Engineering Agency for Science, Technology and Research (A*STAR), developed a way to create chip patterns with a width of just 10 nanometers, or approximately 30 atoms, using existing methods to deposit narrow pillars of plastic on a chip's surface, and causing them to collapse in predetermined directions.

In the photolithography process, a layer at a time of the structure is deposited, and then coated with a light-sensitive resist material. A stencil, or mask, exposes the resist on the parts of the chip intended to remain to light, hardening them, and the rest of the resist is washed away. The chip is then exposed to an acid or plasma and the areas unprotected by the resist are etched away, and the process repeats to build the next layer.

The wavelength of light used constrains the size of features that can be etched in the chip, and the alternative method of using beams of electrons is a slower process since they have to scan across the chip a row at a time. But to etch a nanopillar into the resist, the electron beam needs to only focus on that particular spot. The water used to wash away the resist is enough to submerge the pillars, and as it evaporates, the surface tension is enough to cause the pillars to collapse.

The researchers have found that placing pillars close to each other cause them to collapse towards one another, and by modifying the shape of the pillar to have one flattened side, it will collapse in the direction opposite the flat side. But there are limitations--the range of patterns can't be too closely packed together as they would need to be on computer chips, since regardless of shape, pillars too near each other will collapse together.

By combining this discovery with research that has been conducted at Harvard University on the collapse of structures on the micrometer scale, creating materials with novel optical qualities, the researchers predict that some very interesting applications will be discovered. By opening the way to create structures that has not been possible before, the ideal use for this technology may not have been imagined yet.

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