Michael Rodder's Guide to Raith

M Rodder_Raith Guide 2018_090318 v4.pdf

Very thorough guide! Check this first if new to using Raith.

Sample Loading

• After logging in Raith via the cleanroom computer, bring only the minimum amount of things you need to the SEM room

  • This includes a clean wipe, your samples, any tweezers you need, your notebook and pen and perhaps laptop, and in most cases nothing else.
  • The important thing is, don't bring your entire toolbox! Table room is scarce and Rico will restrict your access if he sees you bringing in the toolbox.

• Gently loosen the load lock doorknob, open the load lock door. Take out the sample holder, put it on a clean wipe

  • Be careful! Don't bump into the transfer rod, especially not from the side.

• Mount your sample on the sample holder, using one of the many clips you can see. 

  • These clips are metallic so there's a path for electrons to escape. This is, essentially, an SEM system and can have charing effects.
  • Do try to put your sample as parallel as possible, but don't worry too much about having it perfectly parallel. This can be corrected later in software.

• Put the sample holder, now holding your sample, back onto the transfer rod. Close the load lock door, and tighten the doorknob

  • A pin stands out at the place where the sample holder sits. The sample holder, correspondingly, has a hole underneath. You won't miss it.
  • Only finger-tight the doorknob! There's no need to over-tighten, load lock pumping will do most of the job. It can actually be hard to reopen later if you over-tighten it.

• Go to the Raith computer, turn on eLINE software, and log in using your account 

  • This is the separate Raith account that Rico will help you create once you finish Raith certification.

• Start the "Load from load lock" process

  • On the toolbar, select the 9th icon from the top (2nd icon from the bottom), which is the Loading tab.

  • At the top "Load from load lock" section, click "load sample", and this will start the loading process

  • Follow the prompt and instructions from the software strictly!
  • To open the load lock valve, when standing at the load lock valve, first pull up the lock pin with one hand.
    Then, with the other hand, rotate the valve rod (counterclockwise, according to the schematic on the panel), and slowly pull out the valve rod until all the way out. Then let go of the lock pin.
  • When inserting/removing the transfer rod, also do it slowly. It should be a gentle and smooth process, to reduce friction and transfer rod wear.

• After loading, initialize the project

  • "Reset coordinate system?" I usually choose Yes.
  • "Use last parameter set xxxxx?" I usually choose No.
  • "Enter sample name" as you wish, and hit enter. This finishes the entire loading process.

E-beam Focusing

• Turn on electron high tension (EHT)

  • In the SmartSEM window (usually on the left monitor), go to the "Gun" tab, double click the first row ("EHT = .... kV"), and enter either 20 or 30 (kV).
  • I like to use 30 kV, resolution is said to improve with higher voltage. Other people in MRC also use 20 kV. Try the difference at your own schedule.
  • In the SmartSEM window, in the bottom right corner, click "EHT", and in the pop-up menu, click "On". This will do the actual turning on of the EHT. Wait for it to run up.

• Find your sample in the SEM 

  • In eLINE window, go to "Files", "Open sample holder map", and choose "100mm_ush".
  • The marker location on the sample holder map indicates the position of the e-beam. Rough navigation can be done by holding down the ctrl key and right-clicking anywhere on the map. 
  • Alternatively, you can use the joystick to the left of the keyboard. Enable the "X" and "Y" axis.
  • Navigate to the edge of the clip holding your sample. You don't want to go to the center of your sample too fast, because any imaging will also involve blasting the surface of your sample with e-beam, and this can cause overexposure of the resist.
  • In eLINE window top toolbar, click the Beam On button (alternatively, ctrl+B keyboard shortcut).
  • In SmartSEM window, "Detectors" tab, switch to SE2 detector. After the Beam is on, there should be an image showing on this window. You can focus on the clip first, and then navigate to the edge of your sample and focus on it. This step is for adjusting the Working Distance, so a good enough focusing will do.

• Adjust the working distance in eLINE, bring your sample to WD = 10mm

  • Once you have a good focus of your sample (indicating an accurate Working Distance in the SEM column focusing), you want to let the eLINE software know what that Working Distance is. This is done by going to the 4th icon from the top of the vertical toolbar (XY→UV) → Adjust W tab → uncheck "read from CCD" box → click the color picker shaped icon → hit Okay when prompted "Adjust column focus" (because we've just done that!) → click "Adjust" on the bottom right corner of this panel. This will make the W coordinate in eLINE accurate with regard to your sample top surface. 
  • Underneath the same panel, you can find the "Stage Control" panel → in the W box, enter 10 (the auto unit is mm) → hit "Start". This will start bringing up the stage until the W coordinate is 10 mm (Raith recommended working distance). Once this is done, clear the textbox.
  • Your sample should now be at the 10 mm working distance from the electron gun! Switch back to SE2 detector, turn On the beam, and adjust the SEM WD to 10 mm (it is still at the value before we rose the stage). This should bring your sample back to focus, and we can enter the next step of alignmnt

• Fine align of the sample surface

  • For this step, it is recommended to have some clear shape/pattern already on your sample surface. Usually, there will be very tiny dust particles, but they have unpredictable shapes, sizes, and locations, and can even perish halftway during the alignment. So, you can try having something else. For example,
    • Scratched corners created by scribers. You can wipe one corner of your sample clean of resist and use a scriber to make some scratches on the corner. These primal patterns can be used as shapes in the alignment process. Alternatively,
    • Make some alignment marks first using photolithography. You can do a simple crosshair pattern on one corner of your sample and then etch it down. A nice and well-defined pattern will be very helpful in alignment.
  • Focus, and zoom in on the pattern you choose. Get the best focus you can. We will try to improve it by adjusting stigmation and wobble, just like a regular SEM system.
  • In SmartSEM window, switch to the "Aperture" tab, and adjust the stigmation and wobble, using the knobs on the keyboard and the corresponding panels on this page. Note that for different aperture sizes, the optimal point of stigmation and aperture can be very different. According to our staff, Raith is aligned to the 30 um aperture by default, and the stigmation for this aperture should be very close to the center (X = Y = 0%). For the other apertures, esecially the smaller (10 um) and larger (120 um) ones, it can be quite different.
  • Once you obtain a good enough focus that you like, we can move on to the next step of Coordinate correction

Adjusting the Coordinate System

The goal of this step is to make sure the UV coordinate system is in the direction that you want (angle correction), have the correct unit length that you want (3-point correction or write field alignment?), and are in the position that you want (origin correction).

• Angle correction

  • Go to  the Adjustments (4th icon from the top) tab → Angle Correction tab. This tab uses two points to correct the angle. P1 is always to the left of P2.
  • In the SmartSEM window, turn on the crosshair (10th toolbar icon from the left) → move the spot to a point on the horizontal edge → click the pipette icon of P1 to read in P1 coordinates (XY) → move to another point on the same horizontal edge, which is to the right of P1 → click the pipette icon of P2 → a calculated angle should display → click "Adjust" to apply the changes. You should see the sample holder map rotate a little, according to the Calculated Angle using the two points

• 3-point correction

  • 3-point correction uses three given points to determine the direction and length of UV coordinate base vectors. You can pick three points on the sample, and assign them to be (U1, V1), (U2, V2), and (U3, V3) accordingly, and the software will handle the calculation.
  • The most accurate way to use 3-point correction is probably to put some photolithography pattern on the sample first. For example, three small squares put in an L shape, where the two "arms" of the L have an equal distance of 10 um. Then, the centers of the three squares can be chosen to be (0,0), (10um, 0), and (0, 10um) of the UV coordinate system. Alternatively, (0,0), (10, 0), (0, 5) will also be doable, which should give you a transformed UV coordinate system and make your patterns shrink in the V(Y) direction by half? A fancy trick. The TLDR is that you don't have to define UV base vectors orthogonally. 
    • I never tried using 3-point correction before, because I couldn't (no pre-defined points to do so). Maybe it is a good practice to do so for more accurate writing results – YW).

• Origin correction

  • This correction applies a shift to the UV coordinate system to make the current position the coordinate you tell it to be
  • One simple way to use this is to first move the crosshair to the top left of your sample → record (U1, V1) → move the crosshair to the bottom right of your sample → record (U2, V2) → Use Stage Control, move to ((U1+U2)/2, (V1+V2)/2) (remember to turn off the beam while doing this!) → In Origin Correction, "Set current UV position to": (0, 0) → click "Adjust". This will roughly make the center of your sample the (0, 0) point in UV coordinates. This will be helpful when we think about the positionlist later. 

Pattern & Position List

• Write field alignment

  • Write fields, by default, might not be aligned properly. They can have unexpected rotation angles, distances, and zoom factors. Not doing a write field alignment can cause weirdly rotated and/or weirdly sized patterns, and mostly stitching errors (adjacent write fields don't line up on actual sample).

• Layer 63 alignment

  • I think this is the standard procedure people use to align a to-be-written pattern with existing patterns on the sample (created previously, via photolithography, EBL, or any other patterning techniques).
    This does a similar thing compared to WF alignment (or maybe it should be the other way around)
  • In eLine, Layer 63 is designated to be the alignment layer. 
  • [This section needs update from people that have actually used layer 63 before]

• Measure beam current

• Set up position list

• All set!

Sample Unloading

• Start unloading process

  • At the same "Load from load lock" section as for the loading process, this time click "unload sample"
  • Again, wollow the prompt and instructions from the software strictly!

• Clean up

  • Open load lock door, take out sample holder, take out your sample, put the sample holder back.
  • Close the eLine software. It will likely prompt you to save the positionlist. You can save your positionlist if you will be reusing it.
  • Check if you brought your own flash drive!
  • Write the public logbook, just see how previous users wrote it. Note OK if everything is fine. Note problems otherwise and contact Mertech.
  • Remember to Log Out in the cleanroom system!!