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====== Description ======
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. 

====== Manual ======
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)!




===== SEM =====
=== Startup ===

{{images:emission.png}}

  * Loading the sample
    - Wear powder free gloves.
    - Mount the sample holder on the transfer stick (Don't use glue or paste).
    - Place the transferstick in front of the loadlock with the excentric hole //down//
    - Push the red button. The loadlock will be evacuated
    - While the loadlock pumps down, start Elphy Quantum and log in
    - Drive the stage to the exchange position with the ''stage control'' window. **Never push the ''init'' switch on the console**
    - While the loadlock pumps down and the stage drives to the exchange position, turn the WD (Working Distance) to the ''4x4'' marker and while doing that, feel good about the fact that now you are doing at least 3 things at the same time!
     - When the red light is off, open the loadlock valve by //carefully// rotating it a quarter turn anti-clockwise, pulling it towards you and rotating it a quarter turn clockwise (so that it is locked and doesn't get sucked in by the vacuum. Get help if this goes even slightly heavy or if the pressure goes up (scale light of current meter goes out)
    - Carefully slide the sampleholder onto the stage. **DO NOT USE FORCE, this is a delicate, micrometer accurate stage!**
    - Unscrew the transferstick //carefully// and pull it back until it clicks
    - //carefully// turn the valve a quarter turn anti-clockwise, let it slide in and turn a quarter turn clockwise.
    - Push the red button to vent the loadlock //while holding the transferstick so that it doesn't fall on the floor// (if you think it is rediculous that I write this you should now admire the cracks in the metal-doped, X-ray blocking glass)
    - If the transfer did not go very smooth or the pressure went up (strangely this is indicated by having no illumination of the current meter and you can't turn on main power), put vacuum grease (next to the transfer stick) onto the transfer stick and slide it back and forth (you are still wearing gloves, so your hands will not get dirty)
    - Put the transfer stick in the holder
  * Activate the System
    - Turn the WD to the desired value (be very careful not too set it too far up, what 'too far' is depends on the sample holder; ask help if unsure
    - Drive the stage to the chessy
    - Turn the monitor contrast and brightness to 2 o' clock
    - PCD ''off'' (button out)
    - Mode ''SEM''
    - Blanker ''off''
    - SEI detector ''on'', select ''SEI'' detector
    - Scan speed ''tv scan''
    - Check that filament heating current setpoint = 0
    - Check that HV setpoint is 20 kV (or lower)
    - Switch on HV (red switch)
    - Switch current meter to 1 nA full scale
    - Slowly turn filament heating current to the indicated value (at the 'shoulder', **see plot**. do not exceed 2.6A. Ask if unsure)
    - You should now measure a current on the sample
    - Adjust contrast and brightness
    - You should now see the chessy


=== SEM operation ===
You can navigate with the joystick and set 1 of the 4 moving rates. (Be careful not to push ''init''!)

== Imaging (astigmatism) ==
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.

== Changing the aperture ==
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.

=== Shutting down ===
  - PCD on (button in)
  - Turn back the filament heating current //slowly// to avoid breaking it
  - Switch off the red main button
  - Drive the stage to the exchange position using the ''Stage control'' menu of Elphy Quantum
  - Turn magnification to max
  - Turn monitor contrast and brightness to zero
  - Turn HV to 20 kV
  - Turn WD to ''4x4'' marker
  - Log out of Elphy Quantum
  - At the end of the day, switch off the LCD monitor
  - Remove the sampleholder from the chamber, unmount the sample and put the sampleholder under the glass cover and the Allen key next to it. (Take into account all warnings under 'Startup')




===== Lithography =====
The manual for [[electron beam lithography]] with the JEOL 820 can be found [[electron beam lithography|here]].