ML3 MicroWriter

The Durham Magneto Optics ML3 MicroWriter direct write machine allows the user to do "mask-less" photolithography. The image is projected onto the substrate. There is no minimum size for the substrate. It uses optical focusing using a yellow filtered white LED light. The actual exposure is done by a 385nm LED UV light source reflecting off of a DLP chip with an array of 1 million moving cantilever reflectors. That image is projected down through microscope optics onto the substrate. The light intensity is controlled by turning each pixel on and off for a certain duty cycle during that particular exposure time. The machine stitches multiple images together to create larger exposure areas. It continually focuses to be able to compensate for bowed or somewhat tilted samples. The machine has four selectable lenses to write in four different pixel sizes: 5-micron, 2-micron, 1-micron, and .6-micron. The most commonly used is 1-micron. The machine uses a ground glass substrate holder. There is no vacuum chuck. It relies on friction, and it is programmed not to make any sudden movements, so there is little risk of the sample moving around during exposure. For larger double-polished wafers that may tend to glide around too easily, a small drop of water placed on the bottom of the wafer works to hold the wafer in place.