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Friday, July 16, 2010

Off to the Clean Room!

This week ended on a definite high note. After lots of not know where to go, and feeling like there was way too much to do, the week ended well. To begin with, our group pulled together some (I hope!) really good materials for NanoCamp. I've posted them over at my Physics 2H page at school, and I plan to use them this year - I think it'll be cool.

Second thing that went right was that we had a good week in the lab. Helen took us back up to the clean room where we got into the extra-clean bunny suits, just like before. She explained that we would be making a negative photoresist on silicon. For those of you who go to concerts and buy t-shirts, it's a lot like screen printing: (That's a link you should follow - it shows you how to screen print.)
Anyway, we did the nasty chemical process last week in making our photomask, and this week got down to business with putting copies of it onto silicon. Helen told us a story along the way that I thought was pretty amazing. Companies like Intel take their people who are the absolute best at spinning silicon disks and trust them with the huge wafers, like that guy is holding up top. She said that if one of those gets dropped, it's thousands of dollars down the drain, and one person banished back to the ordinary clean room. Sad!

We weren't working with any super-expensive units this day, but we did have to be careful. We were spinning 4" silicon disks on the disk spinner (it has a real name but I forgot it.) BTW, you can see how shiny the Silicon discs are - that's John's smiling face reflecting in the wafer that Helen is holding.

Anyway, this part is kind of an art, and it's also a lot different from t-shirt silk screening, too. In putting tiny patterns onto these chips, you can control some of the size of the patterns by controlling the thickness of the photoresist you put on the wafer. And so we have the wafer spinner - works like a carnival spin art machine, except is puts down something like 50-200 micrometers of goo depending on the goo and how you spin it.

After spinning on the photoresist, we baked our wafers in a couple of stages, and then took them to be "screen printed." In reality, we went back to the Suss machine and used our mask to expose our wafers to UV light. Again, wherever we didn't have mask, the photoresisting material gets exposed, cross-links and becomes permanent. Once we wash off the remaining unexposed goo with acetone, we're left with a slick, shiny wafer that has micro-structures cut into it. We looked at our pattern under the microscope, and it looked kind of like this image on the left. This part's beginning to make sense!

Also, what makes me happier is that I can see how what we're doing in the lab fits with what my research group is doing. More on that in the next post, I think!

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