Since it's been so long between posts, today I thought I would give a double update! The title of this post was chosen regarding the optimization of the SEM for creating the line widths needed for this project. It is a quote from J.J. Abrams Star Trek, and is an explanation of the difficulty associated with beaming a person onto a ship already travelling at warp speed. While my difficulties are not quite that bad I thought it captured how delicate it sometimes feels to optimize this process.
Since I already did one on the "terrace" portion of the project I will now go onto the "trench" portion. I have uploaded some images below to help with my explanation of how it's going.
First off, my last post in October included the third image of this post, which was a great step forward as before that I hadn't been able to get anything at all, but now that I'm older and wiser I realize how far away I was from getting it right. First off, if my car had a wheel this shape it would shake itself to pieces pretty quickly. By this I mean it is not round it it elliptical. I thought this was just a figment of my imagination or a random mistake but the more samples I ran the more I realized that it was not going away. This is an aspect ratio problem and could only be remedied by re-doing the painful and time consuming calibration I did back in late July. The calibration itself is not hard, but figuring out the set-up can be a little frustrating because it is a DOS based program and therefore not the most user friendly. However, once that was done I saw a marked improvement in the wheel as can be seen in the first and second images below!! The scope was having some beam issues when this were performed which is why things look wavy and one wheel showed up so close to another. This did not affect the calibration and did not appear to affect the etching of individual wheels but the final product was difficult to image because of it and some wheels were moved because their locations relative to each other shifted between wheels. The next thing that should be noted about the third image below is that the line width is up around 200 nm, which is about 10 times what we are shooting for, and the surrounding polymer is dotted where the polymer was exposed surrounding the wheel. That dotting is because I was still naive and did not know that the beam must first be blanked and then the location to be etched is brought to the beam location using the X and Y stage controls. Then the sample is etched and moved back and the beam can be un-blanked. This way the area is not over exposed causing larger lines and the dotting observed in this image. You'll notice that no such dotting is seen in the more recent images, which are the top two. In the second image shown here you can also note that we have reached 50 nm lines!! This is a big achievement because I have been told that improving upon line width, i.e. getting smaller line widths, is a delicate art and we were stuck at 90 nm for so long I was losing hope that we were ever going to get them smaller. The trick, I've learned, is the use of "contamination spots". These are spots made by using the spot mode on the SEM which focuses all of the beams electrons to one spot. If the beam is out of focus this spot will be large, and the more in focus it becomes the smaller the spot. Also, if the stigmators are out, the spot will not be circular but elliptical. Using these it is possible to more accurately determine if the beam is more or less in focus. Before it was more like an eye-test, where you ask yourself "Is 1 or 2 better?", which at some point with the spot mode it is also but it is much easier to tell if a spot is bigger or smaller than it is to tell if an image is more in focus or less in focus to the degree of precision required for obtaining lines bellow 90 nm. Overall, things are steadily moving forward, although the scope issue that was occurring during my last visit to Tulsa got worse and therefore my trips are on hold until this is fixed so I do not know when I will be able to perform more tests but with these steps forward I finally feel as though I am going to be able to start using AFM to look at surfactant in the lines! Woo Hoo!
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