Neat and Nano – Part 2

by Michael Mullaney on May 4, 2011

Picking up from where we left off yesterday, one of the first stops along the tour of the Rensselaer clean room was a photolithography demonstration from Process Engineer Bryant Colwill. He’s hard at work in the above photo.

There’s a lot going on in photolithography. It’s a key process for the fabrication of microscale and nanoscale devices, including computer chips. The nanoscale transistors deep in the guts of your PC or cell phone – depending on how old they are – likely  measure about 36, 45, or 65 nanometers. And there are billions of these transistors on each and every chip. So rather than build these transistors individually from the ground up, we use photolithography.

Picture it as really small, super-fancy stencils. But reverse stencils. And with light and chemicals instead of crayons.

Photolithography entails using a mix of light and chemicals to generate intricate nanoscale patterns onto a base material. Ultraviolet (UV) light is projected through a mask (kind of like a stencil) and onto a UV-sensitive coating called a photoresist. This photoresist usually coats the surface of a substrate made from silicon, sapphire, diamond, or another crystal. Now, the mask protects the areas that you don’t want to be hit with UV light. The areas that do get hit with UV light undergo a chemical change, which generally allows those areas to be washed away in a solution.

Repeat this process dozens and dozens of times, and pair it with hundreds of other state-of-the-art processes and techniques, and you can make your very own computer chip. During the clean room tour, Bryant helped our friends in the media perform a very basic, barebones photolithography task. Instead of etching nanoscale transistors into what will become a computer chip, Bryant helped them etch a macroscale pattern – visible with the naked eye – into a solar cell wafer:

Tune in again tomorrow for another report from our tour of the Rensselaer clean room.