Electron Beam Field - Page 1
Forum section: electronics / projects

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: July 29, 2019, 07:26:06 pm
content: While reading on Electron Beam Lithography on wiki,https://www.wikipedia.com/en/Electron-beam_lithographyI came accross the following quote:QuoteI find this quote a bit perplexing, especially regarding the writing field limited to between 100um and 1mm , given that Electron beams are used in TV sets, CRO's etc. where they have a large field upto a few feet in some cases, I mean the tip of the beam in a TV set would sweep left and right upto a few feet.Why then is the writing field limited to 1mm in lithography applications?

author: ejeffrey
author_rank: Super Contributor
timestamp: July 29, 2019, 07:35:48 pm
content: Because the electron beam in a TV set isn't trying to make 10 nm steps, nor focus the beam down to a 10 nm spot size. The CRT uses a long lever arm to get that huge beam deflection, but sacrifices resolution and spot size. It basically the same reason a photo enlarger can easily make 8x10" prints but a UV stepper can only expose dies that are 20-30 mm.Also, take a look at your old TV. The glass is curved, either spherically for a conventional CRT or cylindrically for a trinitron. This is because it is hard to keep the image field flat for a large field of view (also it is easier to keep a curved tube strong enough to withstand air pressure).Large field imaging systems, whether optical or e-beam get harder and harder to design as you get further off axis especially if you want good resolution in the peripheral.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: July 29, 2019, 07:54:45 pm
content: Quote from: ejeffrey on July 29, 2019, 07:35:48 pmProfound words indeed!I read that 3 to 4 times over. I sort of understood the curved nature of deflection that you speak of.But I didn't get he resolution part and to some extent the spot size.Resolution of the beam would be dependent on the deflection system correct? I mean how finely do you control the electromagnetic coils. So what kind of problems do you foresee here?Also regarding the spot size once you have focused the beam now to say 10nm if might change to oval shape at the left and right extremes of the scan, is it that what you are referring to?

author: SilverSolder
author_rank: Super Contributor
timestamp: July 29, 2019, 10:20:11 pm
content: The resolution of a TV picture is not super high - e.g. vertically there are only 525/625 lines, depending on what part of the world you are (were) in. Assuming a best case PAL standard TV, the image has a resolution comparable to 704×576 pixels, while NTSC has less resolution (but higher frame rate, in fairness).CRTs did not need to be super high precision with small dot sizes to make a decent representation of the signal. The magnetic deflection in a TV did not need to be high precision engineering either, since the eye is quite tolerant of geometric distortion as long as it is smooth. As you allude to, the focus is not constant across the screen width and is also imperfect on any real TV set with a CRT.The best CRT computer monitors were capable of resolutions up to 2560x1600, far better than any TV tube, requiring high precision manufacturing of the tube as well as extensive amounts of control and correction of the deflection currents (as well as dynamic focus control) - these monitors were probably the peak of the CRT art. If you think in terms of this number of pixels of resolution, on a 20" monitor, you are probably close to what is realistically possible in terms of dot size and placement.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 29, 2019, 10:25:22 pm
content: 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. It's not that good in practice though. If I display a 50% grating pattern, an interference pattern versus the aperture grille / phosphors is visible. This has about 20 fringes across the width of the screen, varying by region. The distortion is imperceptible to the eye (probably, the slight cylindrical face dominates that), but would be measurable with simple tools.I would hope / expect that e-beam litho machines have far greater distortion-free dynamic range; but we're still talking about "pixels" of ~10nm, which would cover a ~20um area for optics and controls comparable to the Trinitron; to get up to ~2mm (equivalent to a 200,000 pixel wide CRT!) is heroic.Corrections could be made -- the repeatable distortion could be mapped and corrected as a preprocess step. What's really important is that tiling can be done correctly, i.e., periodic boundary conditions must be satisfied, to full accuracy. This could be tuned or corrected for, even at the expense of distortion within the field. I'm guessing, what's left is an uncorrectable random error that just can't be nailed down and so, for example, what should be straight lines in your raster end up wobbly and spotty, and some lines overlap and some ends don't match up, and... yeah, a big mess if too much area is done all at once.In short, it's a dynamic range problem, just with signals in different units (distance rather than voltage).Tim

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: July 30, 2019, 09:49:30 am
content: Quote from: SilverSolder on July 29, 2019, 10:20:11 pmNow that you talk about it. I'm just beginning to realise the enormity of the work that the guys at labs like Sony did to get the CRT at the level that it stands today.I wonder how much time did someone like Sony take to perfect the CRT. I mean the Trinitron was a breakthrough technology at its time. How long would have Sony engineers worked on it. 2 years ? probably more?Having said that what kind of resolution would that 2560 x 1600 monitor have for its deflection system.I guess for a TV the information of beam intensity is encoded in the analog signal itself along with the horz and vert sync pulses. So in that way as long as the beam is aligned to the correct spots on screen. the analog signal does its magic. I don't think any digital processing takes place per pixel in a TV. I'm not sure about a PC monitor though.

author: iMo
author_rank: Super Contributor
timestamp: July 30, 2019, 10:49:04 am
content: 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.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).Such a small and precise mechanical step was necessary as you cannot focus the beam well (in order to get a perfect sharp symmetrical stamp) with a larger deflections from vertical.The stamps were variable in their size in order to speed up the writing. The writing is usually into a, say, XXnm thick PMMA layer, you have to adjust for proximity effects, etc. Rocket science, btw.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 30, 2019, 11:04:25 am
content: Ebeam writers are also slow. So as a practical matter I don't think many people write full density structures many mm across. The people I know who have done exposure large enough to have to tile are writing small isolated structures on top of larger designs patterned with lower resolution photolithography. This completely avoids the stitching problem. I'm sure there are people who have calibrated field stitching extremely well and get great results but it's something you avoid if possible, especially in a research environment where you may only run the same process and pattern a handful of times.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: July 30, 2019, 11:25:55 am
content: Quote from: T3sl4co1l on July 29, 2019, 10:25:22 pmThats interesting! I would be further interested to know how the 0.1% error figure was reached.QuoteI'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?QuoteI'm sorry, I ddn't get what this statement meant?

author: iMo
author_rank: Super Contributor
timestamp: July 30, 2019, 11:58:42 am
content: To irradiate the Trinitron RGB pixels with an electron beam is not that difficult as it does not matter on the actual shape of the beam stamp.To paint nice pictures onto a wafer or a mask with say 10nm resolution is a different exercise. Also mind the EBL exposure of the mask pattern must be very "precise" and sharp, not fuzzy.It is not only about the 18bit DAC resolution, that DAC has to feed a big rack full of high current, high voltage, high speed circuitry.Btw, there are some limits with an electron beam when talking the lowest resolution, afaik..

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: July 30, 2019, 12:08:15 pm
content: Quote from: imo on July 30, 2019, 10:49:04 amHow did you get a rectangular shaped stamp? I thought electron beams could only be focused to round spots.QuoteWhat 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?

author: iMo
author_rank: Super Contributor
timestamp: July 30, 2019, 12:33:38 pm
content: 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).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 30, 2019, 08:03:50 pm
content: Quote from: ZeroResistance on July 30, 2019, 11:25:55 amI 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?!)QuoteYes, 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

author: Nominal Animal
author_rank: Super Contributor
timestamp: July 30, 2019, 10:33:52 pm
content: In a way, wider electron beams work more like a jet of water than a ray of light; their control really is an art.

author: coppercone2
author_rank: Super Contributor
timestamp: July 31, 2019, 12:53:37 am
content: try to get a tour of a linear accelerator some time to see how crazy focusing can get

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: July 31, 2019, 06:50:02 am
content: Quote from: Nominal Animal on July 30, 2019, 10:33:52 pmAstounding analogy that one!Quote from: coppercone2Thanks for the tip.

author: dzseki
author_rank: Frequent Contributor
timestamp: July 31, 2019, 09:53:20 am
content: Quote from: ZeroResistance on July 30, 2019, 09:49:30 amAnother art were the professional CRT projectors, these could fit 2000 pixels on a ~13cm wide picture tube, while the beam current was approaching 1mA (!) (@ 34kV), without cooling the tube the beam could melt the glass of the tubeface in normal operation!

author: SilverSolder
author_rank: Super Contributor
timestamp: July 31, 2019, 11:01:49 am
content: Yes, one of the pleasures of looking under the hood of old equipment is admiring the extreme skill that was used to get the absolute best out of whatever technology was available at the time! At some point, art and science begin to overlap. Of course this principle still applies today...

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: July 31, 2019, 11:58:56 am
content: Quote from: dzseki on July 31, 2019, 09:53:20 amWhat is the significance of the ! sign after the 1mA.1mA * 34000 = 34WWhat caused the glass to melt at these power levels. I would understand that the heat capacity of glass would be very low.Wouldn't the beam current in a color TV be of similar levels, around 1mA.

author: dzseki
author_rank: Frequent Contributor
timestamp: July 31, 2019, 01:52:51 pm
content: Quote from: ZeroResistance on July 31, 2019, 11:58:56 amThe significance is two fold:a.) as the beam current gets higher it is more difficult to keep it in a tight spot. 2000 pixels on 13cm wide tube would suggest 65um "big" beam spot, whereas the typical pixel pitch on a conventional CRT monitor was 0.24mm and the beam current was 100uA at best.b.) 34W only, yes, concentrated to a 65um spot, that translates to an insane power density...

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: July 31, 2019, 04:07:52 pm
content: Quote from: dzseki on July 31, 2019, 01:52:51 pmIf we supply 34W of electric power, what kind of beam power are we looking at. Is an electron gun in a CRT 80 to 90% efficient?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 31, 2019, 06:40:36 pm
content: Referring to 2nd anode current and voltage only, the efficiency is 100%. The beam may not be perfectly collimated (there may be some leakage to the sides of the drift area, or the 2nd anode inside the electron gun); although in this case with focus being especially prioritized, we can probably assume they did very well at keeping the electron current towards just the phosphor screen.30W in such a small area, is comparable to the power density of a soldering iron. Maybe not glass-meltingly hot (as long as the raster keeps going), but that kind of heat could easily crack open the tube, even made with hard (borosilicate) glass. These tubes are water cooled, with a clear jacket over the face.The phosphor efficiency is probably in the 30% range, so not all of that is deposited as heat. I don't know if they were able to push efficiency crazily high, but figures like that were typical of fluorescent lamps at least (given that fluorescents go plasma --> UV --> phosphor, more like 20% overall).Tim

author: Ultron81
author_rank: Contributor
timestamp: August 01, 2019, 03:44:06 am
content: When it comes to an electron optics, the biggest limitation on what you can do has to do with the aberrations in the lens system. The objective lens is in charge of focusing the beam to a spot. The scan coils are in charge of deflecting the beam (scanning in an SEM or positioning in the case of an e-beam). The field created by the Objective Lens is only so uniform, and if the beam travels outside of that uniform field, the beam will become defocused and you will see distortions in your image on an SEM, or your writing pattern on an e-beam system.So beam deflection can only get you so far. The next solution is to move the stage under a stationary beam. In this case, the accuracy, step size, and reproducibility of the stage come into play. As was said above, e-beams use laser interferometers to keep track of stage positioning. This is only so accurate, and has a limit to step size. Also, it is important that the stage position can be reproducible - if you move to a different position and need to move back to a previous position, willful be in the exact same spot as before?Also, as far as deflection is concerned, an e-beam’s electron beam is energized to 50kV or 100kV. An electron beam in a CRT, for examples, is usually less than 20kV. The deflection system in an e-beam needs to be strong enough to deflect a beam with such high energy. Also, the distance between the CRT grid and screen is larger than the distance from the objective lens to the sample in an e-beam. Therefore, the beam in a CRT can have a larger sweep area.I repair/install SEMs and TEMs for work. Occasionally I work on an E-beam.

author: David Hess
author_rank: Super Contributor
timestamp: August 01, 2019, 09:03:39 pm
content: Quote from: dzseki on July 31, 2019, 09:53:20 amThat points to what limited oscilloscope CRT performance. Optimizing for vertical bandwidth meant using scan expansion after deflection but this also expanded the dot size. The last generation of oscilloscope CRTs without scan expansion were about 50 MHz and easily exceeded the resolution of NTSC video on a relatively tiny screen area. Later oscilloscopes were faster but had poorer resolution and image quality yet eventually still produced outstanding resolution although not as good as a CRT projector. If those early CRTs had been scaled up, they would have handily outperformed color CRTs but there was no need for such a thing in monochrome.This is why Tektronix developed their color LCD shutter technology. It allowed using a monochrome high resolution CRT in basic color applications where shadow mask technology had insufficient resolution. HP did something similar in their early DSOs with monochrome raster CRTs that had doubled horizontal resolution. LCDs in test instruments have barely caught up.

author: coppercone2
author_rank: Super Contributor
timestamp: August 01, 2019, 09:52:45 pm
content: Quote from: Nominal Animal on July 30, 2019, 10:33:52 pmnot sure if it qualifies but I think the distinction between heavy particle stream collider and ultra fast collider sees this distinction (the heavy collider is underappreciated engineering wise because its not as fast)

author: Nominal Animal
author_rank: Super Contributor
timestamp: August 02, 2019, 12:34:09 am
content: Note: I'm trying to provoke a correct intuitive picture here, and not be technically accurate.When we think of a light ray, we think of something like a laser beam. Such a beam can be collimated (so its cross section stays the same in perfect vacuum), or focused to a point. We can generate beams with relatively large cross sections, with a desirable (usually Gaussian) distribution wrt. distance from the beam axis. Larger cross section laser beams are used in holography, for example.In many ways, electron beams behave in an analogous manner; and both exhibit particle-wave duality. However, electrons are fermions and not bosons like photons are. When the beam is very thin, or focused to a point, the electrons are easiest to control.It is when you have a wider diameter (larger cross section) high-intensity beam (relatively high density of electrons in the beam) that the differences start to really appear. Unlike photons, electrons cannot occupy the same place and state at the same time, and trying to do so generates "pressure" that opposes that, diverging your beam. If you have a thin electron beam, that "pressure" is aligned on the axis of the beam, and can basically be ignored. If you have the spatial/deflection control, you can use such a sharp beam to scan the target surface, with pretty good evenness. If you want a wide electron beam, you essentially have an internal pressure you need to counter, while simultaneously controlling the collimation/focus of the beam, and the axial intensity distribution of the beam.When doing lithography, you want the rays that passed through the mask to either be collimated (all have the same direction), or focused (so that the direction of each ray is a function of its location with respect to the target), so that the image created by the mask has sharp edges. (Perfectly collimated rays generate sharp edges from a flat mask to a flat surface, focused rays are sharpest from spherically curved masks to a spherically curved surface, at constant distances from the focal point.) Any variance in the ray directions is analogous to defocusing, and causes all edges to become "blurry".(You can see this if you do shadow puppets. Try using a 30cm × 30cm panel light, and all you see is fuzzy shadows. Use a small pinpoint light, and you can get pretty sharp shadows. You'd need a laser light panel -- collimated light from the entire panel surface -- to get a panel light to yield sharp shadows; but then, the shadow would be exactly the same size as the object, regardless of the distance.)It reminds me of controlling high-pressure water jets. With the correct nozzles, the jet looks more like a beam than anything else, until it hits something. The hardware looks simple, but it really is more of an art. Not because we cannot describe it mathematically, because we can; but because saying that you want something to behavethusand actually making it so, are two completely different things. Proper engineering needed!