Electron Beam Lithography

This was done for my BSc thesis. There existed, and fortunately still does :), a Scanning Electron Microscope, SEM, in our thin layer lab. Now we wanted to do Electron Beam Lithography, EBL. The trick is that the SEM scans the surface of a given pattern using a electron beam while we wanted to beam to follow a given pattern instead. This way the parts that where exposed to the beam would be lifted while the rest would stay.

The good news was that the SEM had two analogue inputs that controlled the electron beam. Now all we had to was to turn a bitmap image into a series of analogue control signals and send them to the SEM, simple right.

Now we wanted micro second precision and we just couldn't trust micro-controllers. So we decided to use a FPGA, god bless Xilinx®.

In the end we ended up with a analogue signal generator with 4 MB of memory and a single program controlling the SEM PC over the LAN and the analogue signal generator over UART through USB. Although the program was coded in C++ it was wrapped in a python wrapper which allowed fast scripting of ideas into test runs and patterns.

After 2 years the whole system is still being used, I know this cause I had to do maintenance last month. :)

One of the thinnest crosses that we ever got, we were using photo resists and in theory we should be able to go as down as 10 nm with electron resists.
These people helped me out a lot while making the board.
Me and the SEM operator just before a test run. We would decide on the required features and I would implement them, FPGAs can do wonders!
The board, the big square at the top center is the FPGA which functioned like a sort of a CPU, the two chips at the bottom are the DC to AC converters, the thing on the brown board is the usb module (wrong board design here where I had to patch it up using the brown board), and the four chips beneath it are the memory.
These were used by other lab members to grow nano-tubes or something.


Amir H. Bakhtiary




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