The JEOL 820 Scanning electron Microscope is a tungsten emitter SEM with a typical resolution <10 nm. The system has a SE and a BSE detector. It is mostly used for electron beam lithography, for which it has been equipped with a motorized stage and a beam blanker. The beam writing is performed by a 300 kHz Elphy Quantum pattern generator with 16 bit resolution in the X and Y direction and electronic beam rotation and scaling via multiplying DAC's. This system routinely writes 70 nm features in 200 nm PMMA. It is pumped by an oil diffusion pump.
In SEM mode, tilt sample holders can be used to look at cross sections of structures. The stage is never tilted because it is accurately calibrated to a 0 deg tilt angle for the writing process.
Mount your sample on the sample holder. The sample holder is kept under a glass cover (where it should be put back) and should be touched only with gloves. The sample holder is not a block of aluminium but a very precisely adjusted micromechanical device. Never push on it (it has been flush-adjusted) and NEVER TOUCH THE CHESSY. The sample holder costs >3000 Euro. That said, you should use the spring to clamp the substrate (at the edge) and tighten the spring carefully with the Allen key. Make a small scratch with the spring to establish good electrical contact if there is resist on the substrate.
If you use a tilt sample holder you can use silverpaint to mount the sample. Use this sample holder only if the use has been demonstrated to you since it is very easy to damage the final lens with it (repair cost: >10000 Euro)!
stage control
window. Never push the init
switch on the console4×4
marker and while doing that, feel good about the fact that now you are doing at least 3 things at the same time!off
(button out)SEM
off
on
, select SEI
detectortv scan
You can navigate with the joystick and set 1 of the 4 moving rates. (Be careful not to push init
!)
Correction of astigmatism is most conveniently done on the chessy. Then you can move to the sample, if it is as thick as the chessy there should hardly be any astigmatism on the sample and you only need to adjust the focus a little bit. Taking a picture can be done in Elphy Quantum by clicking file
→ new image
and setting the slowscan options to the desired value. Then set slow 2
, EBPG
, and blanker External
. Click the scan icon and you take a photo!. To get the micron bars right, see 'write field calibration' in the electron beam lithography manual.
If you decrease the current, the spot gets smaller but the image gets more noisy (large mu poisson distribution=Normal(mu,mu)). This can be overcome by scanning slower, but if you scan too slow you will be bothered by drift.
Increasing the acceleration voltage improves the performance of the electron-optical lens column so the spot gets smaller. High-energy electrons also penetrate deeper into the material (the effect of that depends on what you want to see, your sample and the detector you are using).
Theoretically there is an optimum in the WD because of (among others) competing effects between spherical and chromatic abberations of the lenses. In practice with the 820 to go to really high magnifications you have to be simply at high kV and small WD (minimumL 8 mm!!!)
To correct astigmatism turn the focus knob back and forth, if you see horizontal and vertical (or: these rotated over some angle) lines get out of focus at different points you have to adjust the stigmator. Set focus in the middle between where the horizontal and vertical features are sharp. Optimize X and Y astigmatism. Optimize focus. Repeat until no further improvement is seen.
For currents below 100 pA, use the smallest aperture; between 100 pA and 5 nA use the second smallest and above 5 nA (hardly used) use the third smallest aperture. After changing the aperture, check the alignment by pushing the wobbler button and adjusting the X and Y position of the aperture until the center of the image remains fixed (also at large magnification and max amplitude of the wobbler). Then switch off the wobbler.
Stage control
menu of Elphy Quantum4×4
markerThe manual for electron beam lithography with the JEOL 820 can be found here.