False Positives

A few weeks ago I was able to travel to Tulsa to try some new E-beam lithography development procedures and the results were very promising.  The new procedures, both of which used much shorter development times, were different in that one was at room temperature and the other was at -10 degrees Celsius.  The results showed 20 nm trenches and even sub-20 nm trenches in some areas.  At first there was some trouble viewing the samples because when they were sputtered with gold and viewed the PMMA shifted heavily and the movement could be seen to happen in real time under the SEM.  This lead to the theory that if the V shape, which I have discussed in previous posts, was occurring before the sputter coating then perhaps vertical walled trenches were not having the side walls coated effectively.  The samples were brought back to OU and placed in a rotating thermal evaporator and then viewed.  The PMMA was motionless, otherwise moved very slowly, and the trenches were small in width as can be seen in Figures 1, 2 and 3 .  One side of the wheels were larger than the other which lead me to believe that there may have been a stigmation issue.  

However, when trying to replicate the results just recently I saw the larger line widths between 30 and 50 nm that I have gotten in the past, seen in Figure 4.

                          When discussing with Mr. Nabity he thinks that the wedges of the wheels may have shifted causing one side to be smaller in width than the other and not just a stigmation as I originally thought which is supported by the left side of the wheel being wider than the right, shown in Figure 2.  However, because all wheels in the exposure are shifted is seems that it is more than just shifting as I thought if shifting had occurred it would have only been one or two wheels but not all of them.  Attempts will continue to improve the resolution and straight wall profile of the trenches but much more focus will be put on imaging micelles using AFM, which is still moving along slowly.

           I received some free samples from an AFM probe company and have been trying to coax high resolution images out of them but have been having some difficulty.  Part of the problem, I believe, is that all of the literature I have read states that they used cantilevers with very low resonant frequencies and force constants, which makes sense because I am trying to see "soft" things (micelles).  However, some of the probes are so flexible is seems that even after centering the laser off of the cantilever onto the photodetector they are prone to drift heavily.  Also, the autotune function of the AFM has trouble picking up the low resonant frequencies so manual tuning procedures are going to be done in order to work around this.  

           Another issue that I have found is that apparently the gel packs in which the AFM tips are stored and shipped cause contamination.  I am trying to arrange a way of cleaning the tips in an ozone chamber on campus here at OU and depending on scheduling I am hopeful that I can get this done sometime in the next week!

All in all, still working on the trenches but I believe that they are at a good place where I can start using them for initial results once I can image micelles on the silica surface.  

Figure 1.  Trenches developed June 27th using Cold development with shortened time 

Figure 2. Trenches developed June 27th using Cold development with shortened time 

Figure 3. Trenches developed June 27th using Cold development with shortened time

Figure 4. Trenches developed July 18th using Cold development with shortened time