Wednesday, July 13, 2011

What about an ellipsometer? (aka You Should Always Take Notes!)

Making wafers!
Yesterday, we had an interesting and learning experience with an ellipsometer. This experience became even more interesting and learning today! But before I tell you the ellipsometer story, let me introduce you briefly (no more than a couple of thousands words – just kidding!) to what we did on Monday-Tuesday. First of all, I was happy to come on time to our clean room training session at 8:00 am on Monday. Phew! I live in Acton, and morning traffic to Boston is usually unpredictable. So, on Monday morning, we put our fancy “bunny suits” on and entered the fascinating realm of cleanliness. Our training session took place in the “yellow” part of the clean room, where researchers work with photo-sensitive materials and, therefore, plain white light is not allowed. Surrounded by the yellow radiance, we started making our first wafers. No, we did not bake any crispy, delicious, whipped cream-covered things. Though, some sort of baking was involved in the process of making our special wafers. We just took thin glass disks (wafers), about 4-5 inches in a diameter. Then, we poured some amount of photoresist on each disk and put the disks, one by one, on a spinner - to produce a thin uniform film of photoresist on the surface of each disk. Then, we soft-baked them (for 1 min on a hot plate) and imprinted several sets of nanoholes on our disks using a special mask and a light source. We practically made pictures of nanoholes on our wafers with photosensitive films! What fun! Then the exposed wafers were developed in a special developer and rinsed in water. Then we dried them off with nitrogen, hard-baked (for 5 minutes on a hot plate), and inspected using a microscope. Oh no! The microscope inspection showed ugly-looking wavy patterns on some of my pretty nanohole imprints. Well, now I have a valuable experience, and next time my wafer will be better.
Then, David and I made our first set of thiols. A thiol is a mono(molecular) layer of a substance self-attached to a metal-coated glass substrate when it is submerged in a solution of the substance. We prepared the necessary solutions and put our gold-coated chips in the solutions. On the next day, we rinsed the chips, dried them of and went to an ellipsometer to measure the thickness of thiols. And now it happened. When we were first trained on using this ellipsometer, everything appeared to be so easy. There was a detailed manual. Just follow the steps and you will be there. So, I did not take notes on this training, because I was sure that I would be able to handle the thickness measurements easily. So, we came to the clean room. Everything started well. We successfully calibrated the ellipsomer. However, when we had to take actual measurements we realized that we were not quite sure what parameters we should use for a spectroscopic scan. …So, we had to seek help.
Conclusion: take notes! Always! It helps!
….and I will continue my ellipsometer story later…


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