The (mainly photographic) adventures of an English physics PhD student living near Paris
Thursday, 3 February 2011
Focused Ion Beam Processing: Thesis Excerpt #1
FIB patterning is like making love to a beautiful woman. You've got to make sure that the sample is lying flat, that it's well bonded and most of all that the upper surface is electrically grounded. Then you start to get things going, you cast around, searching for an edge. Teasing. Playfully skirting around, catching a glimpse of where you want to be, but not lingering. You can't just move in for the kill, you have to put some work in. Get the equipment all set up. So you find an edge, and you trace along it, carefully, not wanting to see more than the faintest sliver, until you get to a corner. At the corner, it's time to really set things in motion. Move a little closer, make sure you've got a nice view and you don't worry too much about flooding the area. The corner isn't your goal.
After a few minutes of playing with the controls, you've got a good grasp of where the corner is, but one is not enough, you need another, you need its opposite. And you have to get there without crossing the body. So you skirt off again, flighty and far away, perhaps touching down once or twice just to make sure you're heading in the right direction. Once at the other corner, it's business as usual. A bit faster this time, you're getting impatient. So's the sample. It wants you. It wants ions all over it. Beating down onto its surface. Milling away material, causing localised regions of negative surface charge accumulation. So you find the height, and get a nice tight focus. Then you rotate the whole stage. Your sample has no idea what's coming next as you aligned you x and y axis to its carefully cleaved edges.
Then it's time to get out your map and find out just how far into the sample you have to move and in which direction. FIB patterning is all about having done your homework. Once you're sure, you check the pattern. Not delivering the goods. Not yet, but just checking. And then, with your eyes closed, you move again into virgin territory and raster out the pattern, the beam of gallium ions drawing out intricate and carefully prepared patterns. After the first one, you let it wait, before moving off and then doing it again. And moving. And patterning. And moving and pattering and again and again until the whole sample surface has been treated.
After that, you just bring her back up to ambient pressure and try not to make eye contact with the technician as you leave the room.