NSF/OUChE Surfactant Adsorption Studies: Pattern Writing is working!!!

A big leap forward was taken yesterday while using the e-beam equipment in Tulsa!! After weeks of not even being able to get an image using the lithographic software I was able to obtain one on my last visit. Then yesterday I was able to etch a pattern, develop it, sputter coat it and view it! I used a few different beam parameters so that I could being optimizing it for the smallest possible lines. I found that high accelerating voltages work the best to get impressions in the PMMA, while low voltages actually give you raised patterns. Not exactly sure why that is at this point but I know it's not what we want. The second parameter that was varied was the dosage (current applied per length/area) used to etch the sample. A pre-designed pattern which has a variety of currents programmed in already was used. Each of 9 wheels is etched with a different dosage and the wheels can then be used as an array to compare the etching quality.

I'm convinced that high voltage is what we want to use because it leaves the best "impressions" in the polymer. However, yesterday the SEM viewing parameters were optimized at a low kV so as not to melt the polymer while viewing it. Therefore, when the beam was switched to 30 kV for the etching, the beam was shifted slightly by changing between the voltages. I don't think that there is a huge difference but when I go back again we may need to choose an area where we can optimize the SEM at a higher voltage, then view at a lower voltage so as not to destroy the areas we are viewing, then for etching increase the voltage again. I believe this will give us accurate results and from there we can determine the correct dosage to use to get the highest resolution lines, which should also mean the thinnest lines.

I brought the sample which was etched yesterday back to OU with me to begin practicing finding such small features using the AFM liquid cell so that once the best sample is produced we can begin using surfactants on it!

I've added some images of some of the etching done as examples. I know they may not look great but considering what it has taken to get to this point I am very proud of them! Figure 1 and 2 shows the capabilities of the e-beam (I thought the map of the USA was pretty cool) and that using low voltages the final product seems to be raised up. Figures 3 and 4 show show that at higher voltages the etch is clean and sunken in, but the lines are about 10 times wider than what we need. Optimizing the microscope at high voltage will hopefully take care of this.

To clarify, the small dots surrounding some of the patterns are the scan lines from the microscope, indicating that shorter exposure times (immediately after etching, not viewing) may be advisable. The patterns that look torn are because the scope shifted the etch onto a line I scraped into the PMMA as a tool to find the patterns post development.