The EUVL Process
Here's how EUVL works:
- A laser is directed at a jet of xenon gas. When the laser hits the xenon gas, it heats the gas up and creates a plasma.
- Once the plasma is created, electrons begin to come off of it and it radiates light at 13 nanometers, which is too short for the human eye to see.
- The light travels into a condenser, which gathers in the light so that it is directed onto the mask.
- A representation of one level of a computer chip is patterned onto a mirror by applying an absorber to some parts of the mirror but not to others. This creates the mask.
- The pattern on the mask is reflected onto a series of four to six curved mirrors, reducing the size of the image and focusing the image onto the silicon wafer. Each mirror bends the light slightly to form the image that will be transferred onto the wafer. This is just like how the lenses in your camera bend light to form an image on film.
According to Sweeney, the entire process relies on wavelength. If you make the wavelength short, you get a better image. He says to think in terms of taking a still photo with a camera.
"When you take a photograph of something, the quality of the image depends on a lot of things," he said. "And the first thing it depends on is the wavelength of the light that you're using to make the photograph. The shorter the wavelength, the better the image can be. That's just a law of nature."
As of 2001, microchips being made with deep-ultraviolet lithography are made with 248-nanometer light. As of May 2001, some manufacturers are transitioning over to 193-nanometer light. With EUVL, chips will be made with 13-nanometer light. Based on the law that smaller wavelengths create a better image, 13-nanometer light will increase the quality of the pattern projected onto a silicon wafer, thus improving microprocessor speeds.
This entire process has to take place in a vacuum because these wavelengths of light are so short that even air would absorb them. Additionally, EUVL uses concave and convex mirrors coated with multiple layers of molybdenum and silicon -- this coating can reflect nearly 70 percent of EUV light at a wavelength of 13.4 nanometers. The other 30 percent is absorbed by the mirror. Without the coating, the light would be almost totally absorbed before reaching the wafer. The mirror surfaces have to be nearly perfect; even small defects in coatings can destroy the shape of the optics and distort the printed circuit pattern, causing problems in chip function.
For more information on EUVL and related topics, check out the links below.