This week included a couple of special visits. First Michelle and I went inside the clean room with four other RET teachers. BU has a Class 100 clean room that is used for photolithography. The Class 100 means that there are no more than 100 particles per cubic foot of air (as compared with 200,000 particles you would normally find). In order to keep the clean room free of any dust particles anyone who enters it has to put on a lot of protective equipment. First we put on white slippers, a jumpsuit, a hairnet, two layers of rubber gloves and safety glasses. That amount of gear let us enter a Class 1000 cleanroom. Once we got in there we put white boots over our white slippers and a white cloth "helmet" over our hairnet. From there we could go into the Class 100 room. Here is a picture of Michelle and me with all of our gear on.
Why are we yellow?
Photolithography is the process of transferring an image onto a silicon wafer. Before coming to the lab we each designed a 3.5 inch diameter mask for our wafers. We just used Word and could put text or pictures on it. Paul Mak, who works in the lab printed our masks onto what looks like an overhead transparency. When we are done we will get to keep our wafer which will have our image etched in gold on it! It will take us two sessions to make it. In our first session we poured a dark purply-red liquid on our wafer called photoresist and put it in a machine that spun it at high speeds so we got a nice thin layer of photoresist on the wafer. We cooked it on a hot plate and then placed our mask on top of it and put it in a machine that shines bright UV light on it. Wherever the mask was clear the photoresist would break down. Wherever it was black it was protected. The yellow light in the room keeps the photoresist from breaking down when we have it out in the open. Then we put it in some developing fluid that washed away the photoresist on the places that were exposed to the UV, and baked it some more. Next week we will return to the lab to do the part of the process that puts gold wherever the photoresist washed away, and then we will wash away the remaining photoresist and have our wafer with our design in gold.
Adaptive Optics in Action
Our second trip of the week was to the Joslin Diabetes Center. They have an adaptive optics system there that they are using to image the retina. They can track the progress of eye disease by counting photoreceptors that have died rather than by waiting for the loss of photoreceptors to affect a person's vision. We met Sonja, a medical student from Vienna who was performing the tests on the patients, and Steve, an engineer from Boston Micro Machines, the company that makes the deformable mirror. He and Dr. Bifano were there to make some adjustments to the system so it would work with a backup laser until the full-function replacement laser comes in. Here we are with Dr. Bifano and the Joslin adaptive optics system.
Lastly, we made a movie about our experience so we can show our students when we get back to school in the fall.