Raith Step-by-Step Patterning Guide
Table of Contents
This is a beginning step-by-step guide for writing patterns with the Raith 150TWO e-beam lithography system in the UTD NSERL Cleanroom. Hopefully this will be useful for new users of the tool as an aid to remembering all the steps in basic, single level patterning operations.
STEP 1. Scheduling Calendar (FOM)
Open the Facility Online Manager (FOM) scheduling calendar from the UTD Campus network: http://msefom.utdallas.edu/fom/ .
Log in with your UTD Campus network user ID and password.
Select the Raith EBL Calendar.
Choose a future time to schedule your session by clicking in the desired time box.
A new window will pop up for selecting a task type, beginning and end times and task objective.
When the time comes to use the tool and you arrive at the Raith, open the calendar again and click on your chosen time box.
A new window will open for you to inform the calendar that you are present and ready to use the tool. Click ok. This action will turn on the Raith monitor screens.
STEP 2. Start the Raith Software
Fill out the paper Logbook.
Double Click on the Raith 150 icon on the Right hand monitor desktop.
This will open a “Log-in” box in which you input your Raith user ID and Password.
If the Raith software lands on the left monitor, move it to the right monitor, then click on the “x” to end the program, and then open it again – it should automatically open on the right monitor after that.
If the Electron optics user-interface is not already open, you can open it by clicking on the “Raith EO Interface” eyeball icon in the left side monitor. That will open a log-in box.
Type “training” for the user name and a no-capital “training” for the password. This will open the same SEM user interface as you find on our Zeiss -40 SEM.
Click on the icon at the top of the EO control window to obtain the video image of the stage.
STEP 3. Mount your Sample
Create a light scratch in the lower left corner of the sample as an orientation guide and a focus target for later.
Mount your sample in a sample holder with the scratch at the LL corner. For example for a small square sample, use the 150 mm Universal Sample Holder. Make sure to align the sample chip parallel to the chip clamping rails with a gap you can see (=/<1 mm) from the vertical in order to align on the lower left corner. (see figure below)
STEP 4. Load Sample Holder
Lift the lid of the load lock and insert the sample holder, making sure the closest side to you of the sample holder fits in the “V” fixture on the load arm and the opposite diameter of the holder sits in the two “chair” shaped plastic seats so that the carrier is located in a horizontal plane and centered so that the three ceramic ball-bearings on the stage will seat in the Sapphire sockets on the bottom of the sample holder.
Close the lid and click on the Load/Unload icon near the bottom of the vertical column of icons at the right side of the Raith screen.
Close the lid and click on the Load/Unload icon near the bottom of the vertical column of icons at the right side of the Raith screen. Click on the “Load Sample” button in the upper right corner of the new panel window
When the load operation is complete, about 5 minutes, you can add a sample name in the new window that pops up if you like or not.
The next pop up box window will ask if you want the e-beam column to have the same settings as the last time you used the tool. Choose yes if you want the same beam parameters, no if not. If you choose “no” you will have two choices; 1) you can manually set up the beam parameters and choose the electron detector, just like on the SEM, or 2) you can choose a “canned” column set up from the Column control panel; i.e. 30 um Aperture, 10 KV, 30 um App, 10 mm working distance.
Automatic Beam setup
STEP 5. Finding the Sample
Drive the stage to the clamping clip location by clicking on the “stage” icon in the right side command icons
Highlight the “Positions” Tab and Select “Sample Clip – 1” to drive to the sample location.
STEP 6. Focus at the LL Corner of Chip
Start the electron beam scanning at a low magnification (<100X) by clicking on the resume scan “LCD” icon in the left screen upper command line,, and the “Beam On” icon in the top command line of the right hand screen to un-blank the beam so you can see the SEM image of the edge of the sample and the clamping clip.
- Select a fast e-beam scan (number box icons, top left screen) and move the stage in + y with the joystick until you find the lower left corner of the sample.
- Focus on the chip corner or a particle in the vicinity.
STEP 7. Adjust Global U,V Origin to LL Chip Corner
- Open the” Adjustment UVW” icon and click on the “Origin Correction” tab.
- Click on the “Crosshairs” icon in the upper row of control icons on the left monitor and drive the stage to align the corner edges of the chip to the crosshairs.
- Then click “Adjust” in the upper right window of the Raith screen to accept the origin location.
- Before moving the stage, click on the “Angle Correction” tab and click on the “eye dropper” symbol next to the P1 notation to collect the origin for the chip bottom edge angle measurement.
- Then drive the stage to the left to find the lower right corner of the chip.
- Align the chip to the crosshair at the LR corner and then click on the “eye dropper” symbol next to the P2 notation to collect the second angle measurement.
- Finally, click on the “Adjust” button at the lower right of the Adjust UVW window to calculate the angle and store it. This has now obtained the orientation and reference origin for the chip. The u,v coordinate system (0,0) location is the lower left corner of the chip.
STEP 8. Focus at LL Corner Scratch
Drive back to the LL corner (origin) by clicking on the “lightning bolt” symbol for the origin (P1).
- When the stage arrives at the Origin, start the beam scanning by clicking on the “Normal scan” icon (monitor icon) at the top row of the left screen.
- Then click on the “Beam on” icon in the top row of the Raith screen to un-blank the beam.
- Drive the stage to find the scratch in the resist you made before mounting the sample and follow it to its end. Focus on a debris particle.
STEP 9. Focus on a Contamination Spot
This contamination spot focus methodology allows establishment of fine focus at the surface of your e-beam resist. This method is better than focusing on a particle because particle focus generally is above the surface of the resist. For patterning tiny line widths particle focus will limit the minimum size achievable, whereas this method does not.
- Move the stage a small distance from the scratch, set the magnification to about 70,000 X, and create a “Burn spot” by right-clicking on the “Spot ” icon, at the top row of the left screen. Wait for about a minute for the spot to form. (This wait time can vary a lot depending on the material, beam voltage, focus status, etc.)
- To end the spot making time, right click again on the “Burn spot” icon. The system will present a reduced field scan of the spot area.
- A spot of contamination should appear as a “bright” dot in the scan field.
- Quickly focus and adjust the astigmatism correction. Note that the spot can degrade rather rapidly with the beam growing an area contamination patch over the spot.
- You may need to move the stage and make a new spot to complete the focus step. Make as many spots as you need to achieve focus.
- Make sure to check the beam alignment as well.
- For a final focus check make a 3 second spot by left clicking on the spot icon. This should make a very small round spot if the focus is correct. If it is not round, re-do the astigmatism correction.
STEP 10. Writefield Alignment
The Writefield alignment aligns the beam scan to the global coordinate system so that printed geometries will align to each other in the global coordinate system. This is achieved by finding a tiny target such as the focus burn spot and moving it a precise distance in the calibrated u,v directions and deflecting a small scan field of the electron beam so it can image the moved spot. Then the operator moves and aligns an alignment cross hair on the SEM image to tell the system where the beam is when it is over the particle. This is repeated over 4 stage movements to set the beam scan angle and its deflection distance scale to match the e-beam deflection coordinates system to the chi (u,v coordinate system) via the precision laser stage movement.
- Locate the stage so that a burn spot is in the center of the scan field.
- Click on the “LCD Screen (with dots in it)” icon, , in the right panel Raith window to open the “Scan Manager ” window (see figure below).
- Click on the expand symbol to the left of “Writefield Alignment Procedures” in the “Scan Manager” window in the right panel of the Raith screen.
- Then click on the expand symbol to the left of “Manual”
- Select the appropriate size Write Field alignment scheme. For example for a 100 um Write Field, click on “100 um WF-Manual ALWF 20 um Marks”
- This will open an alignment Position List and fill it with alignment instructions. It will automatically commence to execute the instructions, resulting in a small window with an image of the burn spot.
- Move the mouse cursor into the image window and hold down the CTRL button on the keyboard and press the left mouse button and then drag the cross hairs center, which is fastened to a stretchable line from the original center of scan, to the burn spot and release the mouse button.
- Then find a small “Macro execution paused” window with the word “Continue” on the screen and click the word. This will capture the alignment position and move the stage to the next one and create a new image. Repeat the alignment for all four locations.
- After the four alignments are made the system will send up another small “Results” window showing the U, V “Zoom” corrections.
- Click “Accept and run the next size smaller alignment process, such as “100 um WF-Manual ALWF 10 um Marks”.
- Repeat the alignment until the U ,V “Z oom ” numbers show 4 zeros or 4 nines for ultimate alignment – 3 zeros if alignment is not critical.
STEP 11. Patterning Setup
- From the “File” menu at the very top left of the Raith user interface, click on “Open New Position List”. This opens the Position List command box at the bottom of the Raith screen. (See Position List header below)
- Click on the “circle, square, triangle” geometry icon at the top of the right hand column of icons on the Raith page and then click on the Yellow Folder icon to load the .gds or .csf pattern file you intend to write.
- Select the file you need and “Open” it. The detailed geometric pattern files will appear in the GDSII Database window in the upper right corner.
- Highlight the pattern file you want to write, and then click on the “Edit” button in the command line above it to open the pattern.
- Click on the “layer” icon in the edit window to view the layers in your pattern. Note which layers you want to print.
- Then click on the pattern name and drag it into the Position list.
- When you release the drag mouse button, a new window will appear above the Position List that shows the various levels in your pattern. Select the layers you want to print and then click OK in the layer box.
- Your pattern will then jump into the position list. You can repeat this with other patterns if necessary.
- You can enter u,v placement coordinates in the Position List in the “u” and “v” column titles to position your patterns in the appropriate places on the sample chip.
- If you click on a Position list pattern line and select “Properties” from the little window menu that pops up, you will get a new window with multiple printing parameters available for change if necessary.
- If you right click on a Position list pattern line and select “Properties” from the little window menu that pops up, you will get a new window with multiple printingparameters availabel for change if necessary
- If you (right click) to “open” the highlighted line in the position list, you will get a new window that shows the line’s pattern.
STEP 11a. Auto Matrix
- There is a handy way to create a matrix of patterns from an original local exposure pattern. If you have a pattern design inside a Writefield area, you can duplicate that pattern in a matrix array by clicking on the Positionlist line containing the pattern you want to duplicate, and then opening the “Filter” menu from the top command line and then clicking on the command “Matrix Copy”. This will bring up a new window (below) that you can use to set the spacing and size of your matrix.
- Once you fill in the required parameters and click “OK”, the software will add the lines to the Positionlist automatically, setting the proper location coordinates.
- For making a dose matrix, there is a “Dose Factor” that multiplies the initial dose by a factor you can set in the “Dose factor” boxes and either add to or multiply the original dose for a dose test.
STEP 12. Measure Faraday Cup Current (Beam Current)
- Click on the Writing icon in the vertical column of icons at the right side of the Raith screen. This will bring up a new right hand side panel with a window titled “Beam Current”.
- Set the SEM magnification to about 2000 X. Then select “Faraday Cup on Holder” and check the “Drive Back” box and then click on “Measure”. (See figure below)
- The stage will move to the Faraday Cup on the sample holder, measure the beam current and then return to the location it just came from (beam will be blanked during travel time). The Beam current will appear in the blue background box in the current units specified in the menu just to the right of the beam current box.
STEP 13. Set up Dose Parameters
- In the “Patterning Parameters” window just above the Beam Current window,(see above figure), check the boxes for the type of geometries you have in your pattern design – like Lines, Dots, Curved Elements, to allow exposure dose settings for each type. Area dose is default.
- Then click on the “Calculator” icon at the top of that window. This will bring up a new window with entry points for dose values for each type of geometry.
- Type in the dose required for each type of geometry required.
- Then click on the “Dwell Time” calculator for each geometry type to calculate the beam “dwell time” for proper exposure.
- Check on the beam speed and try to keep it less than about 20 mm/sec.
- Check Writing time:
- There is a write time calculator in the “Properties” window on each line in the Positionlist. If you right click on a patterning line in the Positionlist and then click on “Properties”, you will see a new window with patterning properties for that line. But in the lower left corner of this window there is a button called “Patterning Parameter”. Clicking on this button will expand the box down, showing lots of parameters. In the lower right corner, there is a button called “Times”. If you click on this, the system will simulate the exposure of the pattern from the line you chose, and will produce an estimate of the time required to expose that pattern. This is a handy value, because it may reveal that you will wait days for the pattern to complete, in which case you might want to trim the pattern for shorter time.
- Click OK to exit.
STEP 14. Patterning Execution
- When all parameters are correct it is time to stop and think “Have I done all the necessary steps and put in all the parameters required for printing, especially the beam current?” This is your last chance to set things right before printing.
- (Optional) Set up “Wafermap” for visual observation of patterning progress. Click on “File” at the Left end of the top command line and click on the ”Open Wafermap” choice and for small samples, select the “150 mm_ush.wlo” file to open. This will show a blue outline of the patterns you have in the Position List and a red square marker will show the location on the stage which is at the electron beam writing field. You may have to use the roller wheel on the mouse to magnify the wafer map to see your pattern locations.
- START PATTERNING by highlighting all the lines in the Position List that you want to print and then clicking on the blue square (“scan” button) in the top row of position list commands.
- You can print individual lines by right-clicking on one and clicking “scan” in the little menu box that pops up.
- When the patterning is complete, the small window that shows print progress will disappear.
STEP 15. Removing the Sample
- When the patterning is complete click on the Load/Unload icon in the right side vertical column of icons and then click on “Unload ” at the top of the right hand panel to unload the sample. (…takes about 5 minutes to unload.)
- When the load-lock is at atmosphere, lift the lid all the way so it will stay up and lift out the sample carrier.
- Remove the sample and return the carrier to the load-lock and close the lid.
STEP 16. Log out of Raith Pgm, Fill in Paper Logbook, Log off FOM Calendar