Pre-pumping

• Check crystal life percentage on the CHA display panel.

  • Crystal life must be below 70%. If the crystal life is reaching/has reached 70%, you should change crystals for this run. 

  • A guide on how to change crystals can be found in the folder on the wall behind the CHA bell jar. 
    For purchasing new crystals, see this link: https://utexas.atlassian.net/wiki/x/louuAw

• Push the "Vent/Standby/Start" button switch to Vent.

  • This should start venting the system. Wait until it finishes, the pressure should reach 7.6e+2 torr (sensor readout is on the top right of the panel, and 7.6e+2 is read on the bottom sensor) and the bell jar should lift up.
  • Note: if the bell jar doesn't lift up after the reading has gone to 7.6e+2 for a decent while, it is likely that the process is stuck. A trick to deal with this is to flip the Vent switch to Standby and back to Vent. Most of the time this does the trick. If it doesn't, there are likely some problems and you should contact mertech.
  • Takes about 10 mins. 
  • Can login at this time. 
  • Prepare samples (make sure if your sample preparation takes more time than venting, start preparing it earlier.)

• Chamber preparations

  • If you need to change crystals, change crystals.
  • Use the vacuum cleaner (under the table facing the CHA1) to clean up any visible loose debris in the chamber.
    This step can be more important than you think! Having loose debris around, wherever they came from, not only makes it (even if only slightly) harder to pump down the system, but can sometimes cause shorts and force the electron gun current to shut off. 
  • Check the shutter is working by flipping the Shutter switch (the center one of the three) on the front panel between Open and Closed (don't try Auto, we don't use that here). 
  • (optional) You can also choose to take out the shutter and cleaning it with a clean wipe that's sprayed with DI water. This is more optional than the vacuum cleaning step, and should only be used if you see large metal flakes hanging underneath the shutter. Taking out the shutter always comes with the risk of making it less well seated on the pole when you put it back. A functional shutter may not open or close properly after you take it out and put it back, forcing you to make more adjustments. In short, you don't have to clean the shutter unless it seems really, really bad to you.
  • Bring a second pair of gloves, using the back of your hand, clean the aluminum foil wrapped around the chamber. Also check and look for any major rips, tears or if it is distained (weird colors). If it is really bad, you might consider replacing it, but it is quite the hassle. Usually, just make sure that it is not in the way of the bell jar's path when it comes back down again.  

• Load your samples on the top rotating plate, and load your evaporation targets into their respective crucible pockets

  • Check the front panel to make sure you are putting them correctly! For example, Ti goes into pocket 1, Pt into pocket 3, Au into pocket 4. 
  • For one of our contact recipes, Pd/Ti/Pt/Au, you can put Pd in pocket 2 although it's not listed on the front panel
  • Citing one of the emails Rico sent out:
    
    1. All the pockets are set up for ‘low power’. They are all the same configuration.  (CHA #2 is different)
    2. Use the pockets as designated when available
    3. For multiple materials that have the same crucible pocket assignment use any pocket. (e.g.. If you need to evaporate Cr, Pt and Pd use Cru. 1,2,3 or 1,3,4). 
    4. Do not use any pocket just for the sake of convenience (e.g. Evaporating Cr, Au and using Cru. 1,2, instead of Cru. 1,4)
  • You can load the sample with either magnet or a spring clip (will leave an uncovered spot). 
  • When loading your sample, using the shared sample holder and magnets, it is suggested to move the holder into place and hold it with your hand first, and then slide in the magnet. The magnet is pretty strong, and if magnet goes first, there is a chance that the holder gets sucked to the plate rather hard and your sample undergoes some shock. No need for that to happen.

• Final checks

  • (optional) Switch the shutter to Open position. Look at the rear mirror (a wafer sitting on a metal wire stand) when you are in a sitting position. Make sure you can see your evaporation target clearly. Then, stand up and look at the periscope (another two pieces of wafer configured like a periscope, so that you can see the top of the crucible in the pocket). Close the shutter.
    This step is optional for certification, but Rico will require you to do this after pumping down and starting the recipe, so a good habit to check before pumping down as well.
  • Finally, make sure that no other things are in the way of the bell jar (such as the black filter plate, your pen, your notebook, the LN2 funnel, or your cell phone!)

Pump down the system! 

• Push the button switch from Vent to Start.

  • Now our samples and targets are in the chamber, we are ready to pump down the system. Pushing the switch to Start should start bringing the bell jar down. After the bell jar closes, the pump will kick in and the pressure will start to drop.

• Listen for the crossover.

  • It happens around when the bottom sensor reading approaches 1e-2. It's a loud sound that you shouldn't miss. If you don't hear it, something is wrong, contact mertech about it.
  • After the crossover, the system will enter the HI-VAC state

• After the crossover, wait 5-10 minutes for the pressure to drop. Then, turn on IG2.

  • During this period, you can go and get some liquid nitrogen in the cleanroom passthrough. After you come back and fill the LN2 reservoir, the time should be about okay. Make sure to wear PPE while pouring: pour slowly in the beginning as liquid nitrogen will be splashing due to the difference in temperature. Pour about 2 liters or until the "balance" is reached. Can check the levels with a straw. 
  • IG2 is the sensor for the low-pressure range. The reason to delay turning it on is to protect it. IG2 is also linked to the auxiliary input of the Voltage and Current controls. 
  • Never pour liquid nitrogen when the system is in vented mode.

• Wait for the IG2 reading to reach around 5e-6 before starting the evaporation.

  • This usually takes 30-45 min. May vary depending on pump conditions.

Evaporate metal!

• Turn on the CHA power supply and temperature sensor

• [Turn on source current and voltage

  • Make sure that the crucible selected is the one you meant to deposit

  • Turn on "Current" first by pushing the switch up and listening for one click.

  • Turn on "Voltage" by pushing the switch up, this time hold it a while to listen for two clicks (hold for about one-two seconds).

• Select the correct metal in the CHA display panel

  • Hit "Menu" → go down to "Operating Parameters" → enter the number corresponding to the metal → hit "down" once → hit "menu" gain to go back and apply the change
  • The numbers and corresponding metal can be found on the list attached to the power supply. E.g., some common ones we use: 15 - Ti, 4 - Au
  • After returning to main menu, you can hit "ZERO (numpad 2)" - "STOP" - "RESET" - "STOP" to zero the film thickness reading.
  • If cannot get to "General Parameters" - click "STOP" - "RESET" - set to "process to run" *NEVER click on the "LOCK CODE", mertech will have to reset all the values and you will be banned from the equipment for weeks.

• Check previous logs for reference of the power and deposition rate of the desired metal

  • (Certification check points) There are two major factors that can make these numbers inaccurate: (1) The skill of the users, and (2) the purity of the target

• Hit "Start" on the control panel and let the system run the ramp and soak procedures

  • Every metal has different ramp time and destination power settings, usually let them finish. It can be tricky and slightly different.

• Hit "Manual" to take over power control after the ramps and soaks finish. 

  • Otherwise the system will ramp itself down after the Soak 2 process.
  • Open the shutter and check the status of your target. During the certification, at this point, Rico may ask you to open the shutter and check your target. Remember! There are two positions you can see the target from, as mentioned in the Final Checks of the Pre-pumping section. Usually, the target should be glowing brightly or somewhat brightly, and there might be an initial deposition rate already for some easier to melt metals such as Titanium. You can also sit down to get a better view of the target. Use longitudinal and lateral knobs to adjust the beam position on the target. 
  • You can ramp up power in two ways: keys or wired controller. If using controller, never use your thumb to click, instead hold it perpendicularly or leave it on the holder and use you index finger to ramp up or down. (But keys are safer anyway - so use the wired controller only if really needed.) 
  • Slowly ramp up the power (hitting the "Up" button) to your desired percentage. (Certification check points) There are two reasons you want to do it slowly: (1) This is for protecting the filament, and (2) this can help avoid splattering of the target material. There isn't a clear standard on how slow is slow. 2 clicks every 3 seconds is a pretty safe speed.
  • It is suggested to do the initial 2 nm of deposition at a slower rate, such as 0.2A/s. This is for obtaining a smooth layer. 
  • Remember to let it soak in between a set of clicks to reach smooth deposition. 

• Follow your own recipe to reach the desired power and deposition rates. 

  • Refer to the "recipes" for "cooking" each kind of metal
  • Don't go above 2.5 A/s! Unless you want to get into trouble. 
  • Chamber temperature should be kept under 60 degree C at most circumstances. The chamber reading can be different than your sample temperature, and potential over heating your sample has no real benefits. It may actually harden your photoresist, and cause difficulties when you want to do liftoff

• When the deposition is approaching the desired thickness, ramp down slowly

  • (Certification check points) There are two reasons you want to do it slowly: (1) Same as ramping up, this is for protecting the filament. (2) This is also for protecting the crucible. Crucibles, usually made with graphite, can have significantly different thermal expansion coefficients than the metal it holds. If there is a rapid change of temperature, you are more likely to crack the crucible. For some metals, this will eventually happen over time, but you would want to get the most out of your material (and $$$ you spent to buy them) before that happens.

• Put into Manual (ramps down) and after power reaches 0, turn off source current and voltage]

  • Again, turn off Current first, then Voltage

• Switch to the next metal you want to evaporate, repeat these steps (in [] brackets) until done

Finishing, venting, and cleaning up

• Turn off the CHA power supply, then turn off IG2

• After the chamber temperature reads <40 degrees Celcius, switch to Vent

• After the system vents, take out your samples and your targets

• Switch to start, and wait for the crossover

• After making past crossover, switch to Standby.

• Write down the log information on the public logbook

• Clean up everything you might have brought, such as wipes, vinyl gloves, foils, and so on.

And don't forget to log your deposition in our Wiki logbook as well! CHA1 Logbook