Electronics > Projects, Designs, and Technical Stuff
Electron Beam Field
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ZeroResistance:

--- Quote from: imo on July 30, 2019, 10:49:04 am ---Many decades back I worked in an EBL lab.. The max "resolution" we had was 100nm, we were able to create a sharp rectangular beam "stamp" of 100nm*100nm size.

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How did you get a rectangular shaped stamp? I thought electron beams could only be focused to round spots.


--- Quote ---The EBL got a mechanical coarse movement of the support (the support holding an Si or GaAs wafer or a glass mask) with say 409.6um step and 100nm positioning precision (we used to use X-Y laser interferometers in the coarse positioning system) and the fine movement of the beam within the coarse step was done by the electromagnetic/electrostatic deflection stuff inside the electron beam optics (similar to the electron beam microscope).

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What is that glass mask you speak about? I thought EBL was maskless...
So your stage would move a max of 409.6um x 409.6um and you could position within 100nm of the target within this stage size? What kind of resolution do the laser interferometers provide can they measure down to 100nm?

iMo:
The ebeam shape: the EBL's electron optics consists of many coils and many electrostatic deflectors, all are driven by dozens of DACs. You may shape the beam as you wish basically, the lowest resolution is given by some quantum properties of the electrons. As I can remember the shape of the pattern was programmable from 100nm*100nm to 10um*10um.

As you go off the vertical you have to adjust the deflectors "on-the-fly" such the required rectangular shape will stay the same (that is the major difficulty).
The SW compiled a picture into the elements of a variable shape, and gave commands to the EBL (several racks full of electronics) like "place a stamp 2um*2um large into the position X=2345 Y=3886 within the current frame". And the electronics had to adjust the electron optics such you get the precise stamp at that position within a frame. The frame resolution was 12bit afaik.

Masks: EBL could be used for so called "direct writing on silicon" where you put a thin layer of PMMA on an SI wafer and do the EBL exposure into it, or, you are producing standard photo-lithographic masks for a mass production.

There were 2 laser interferometers in X and Y direction, so there was a feedback into the mechanical positioning system. As I can remember the resolution was better than the wavelength (red as I can remember).
T3sl4co1l:

--- Quote from: ZeroResistance on July 30, 2019, 11:25:55 am ---
--- Quote from: T3sl4co1l on July 29, 2019, 10:25:22 pm ---Trinitron monitors were probably pushing the limits of e-beam accuracy in a production context.  Consider mine, which does 1600x1200 resolution; for a pixel to be where it ought to be, that's about a 0.1% error, not bad at all. 

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Thats interesting! I would be further interested to know how the 0.1% error figure was reached.

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I was just introducing that as a rough assumption.  One pixel out of 1600 is 0.07%.

I later refine that assumption by noting fringes against the internal structures, probably giving a 0.2 to 1% figure.  (It's noteworthy that the fringes in and of themselves may not be an error -- simply that the intentional screen resolution doesn't match the number of wires in the aperture grille.  Distortion in the fringe pattern would then be the real error, and I think is on the order of several fringes +/- at any given spot.  This would give a figure around 0.1% instead.)

Obviously(?), I haven't measured the geometry with real physical instruments, so I don't know the absolute error independently.  (What if the aperture grille itself is in error and the deflection is actually perfect?!)



--- Quote ---I'm itching to know why would this be considered heroic? A 200,000 step DAC that corresponds to 18bit resolution for the deflection system. I perceive there is more than that what meets the eye, and probably I'm too naive to miss out some important issues. Could you please indicate what kind of complexity is one looking at to get to 10nm steps in a 2mm full field?


--- Quote ---In short, it's a dynamic range problem, just with signals in different units (distance rather than voltage).

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I'm sorry, I ddn't get what this statement meant?

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Yes, precisely -- positioning alone is very high precision.  We can certainly make voltages or currents with 18-bit accuracy and precision, but transducing those signals into other units is another matter.

I don't know if you have an intuitive feel for distances as signals, so I wanted to make that equivalence clear.  It's not like we can simply put down some nanobots with carbon nanoribbon tape measures and have them mark out squares of exact size; even if we did that, the error in each individual measurement would accumulate across a wider area.  We could mark it with an interference pattern, say, which will give reasonable periodicity, but the variance between each fringe will be sloppy, and the pattern may be distorted due to optics (is the fringe pattern actually a projection to a cylindrical or spherical surface, and slightly distorted or defocused when projected onto a flat surface?).

These distortions will dominate the errors in a transducer; we can drive one with a 24-bit DAC as much as we like, but if we're only getting say 14 good bits out of it, it doesn't much matter, right?

It could very well be that unavoidable fluctuations in the electron beam apparatus dominate in this range, so that the spot can't be well enough focused, or that it wobbles in a noisy fashion, or that the projected image is distorted in an inconsistent way.  Needless to say, such apparatus needs to be extremely well shielded from ambient magnetic and electric fields (multiple layers of mu-metal, probably an interior of machined ceramic or aluminum, normalized (annealed, de-stressed)), as well as from fluctuations in temperature (a few mK fluctuation in a local area of the beam tube, and that side tilts up noticeably).  The beam's projection is very sensitive to everything in the beam path, especially the cathode and first grid; up at the top, the electron velocity is low so a huge difference in trajectory can be made from a small influence.

I don't know nearly enough about electron optics to know what magnitude these (and other) effects have on it, or what the ultimate physical limitations are (say due to quantum uncertainty in the position of the cathode, and the fields around it?) and how close to them we can get, but I'm at least going to guess that they're doing a lot of very careful (heroic, you might say) work to tune out probably hundreds of such errors.

Tim
Nominal Animal:
In a way, wider electron beams work more like a jet of water than a ray of light; their control really is an art.
coppercone2:
try to get a tour of a linear accelerator some time to see how crazy focusing can get
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