Oxford PlasmaPro 100 Cobra

Usage rules and instructions

Updated 2024-07-20

Oxford Instruments Plasmapro 100 Cobra 300 dry etching system with loadlock

Process gases: O2, Ar, CF4, CHF3, SF6, C4F8, N2

Configured for 4 inch wafers (capable of up to 8 inch with reconfiguration)

Wide temperature range electrode -150°C up to 400°C with He backside pressure

Plasma power: ICP max 3000 W, table RF max 600 W

Process pressure: ≈3-250 mTorr

Restrictions:

User instructions:

  1. Start software (PTIQ on desktop) and log in as operator if necessary, login information is on the screen.
    Check that there are no red error messages on the tool, if any error is present contact the staff.
    In the "Cobra300" page under the "Manual" tab, check the vacuum (should be in the 10-6 range or lower) in the main chamber, and that the main chamber status is "Ready to Process".

  2. Set the correct temperature by running the ## Set Temperature  — no wafer ## recipe from the "Cobra300" page in the "Manual" tab.

  3. If necessary precondition the chamber, see "Precondition Instructions" below.

  4. Vent the loadlock, either from the "Transport Handler" page in the "Manual" tab, or in the "Automatic" tab. The loadlock can be opened when the vent process reaches "Vent overrun".

  5. Place the 100 mm wafer (carrier or full wafer) in the loadlock with the flat facing away from the main chamber and the edges touching the two metal pins on the arm. Do not exert excessive force on the arm when placing the wafer.

  6. Close the loadlock, and make sure the wafer is detected (wafer icon will appear in the mimic). If the wafer is not detected, make sure it is lying flat on the arm, if it is still not detected contact the staff. Note that fully transparent wafers may not be detectable.

  7. Name the batch in the "Automatic" tab. Recommended name convention is Your name + etch to be run (e.g. "Erik Si-N waveguide etch")

  8. Select the correct recipe from the drop down menu in the "Automatic" tab. Select relevant cleaning procedures (see Cleaning instructions below). Note: Do not use the "Precondition Chamber" option, and do not run recipes meant to run without a wafer (e.g. ##  Cleaning — no wafer ## ) from the "Automatic" tab.

  9. Press ‘Run’ in the “Automatic” tab. This will pump out the loadlock, transfer the wafer into the main chamber, run the chosen recipe, and then transfer the wafer back into the loadlock.

  10. Make sure the loadlock pumps down, if not then gently press the lid.

  11. When the wafer has been loaded, look through the window and make sure the plasma ignites. If the reflected power is low but plasma has not ignited, the process must be interrupted immediately, the power is being dissipated in the AMU which will damage it. The process can be monitored from the ‘Cobra300’ page in the ‘Manual’ tab.

  12. Wait for wafer to unload. IMPORTANT: If there is a red error during unloading call staff, do NOT try to run any further procedures or processes or you risk causing damage to the tool.

  13. After the unload procedure has finished vent the loadlock either from the ‘Transport Handler’ page in the ‘Manual’ tab, or in the ‘Automatic’ tab. Remove the wafer from the loadlock.

  14. If done, make sure the chamber is clean and the loadlock is pumped, and the temperature is set to 20° C.

  15. Log your run in the LOG.txt file on the desktop.

Making recipes:

  1. Recipes saved as #OIPT ...# are Oxford standard recipes, do not change the etching parameters. Only ever change the etching time OR only number of cycles for the Bosch recipes.

  2. All recipes must start with the same three steps: Chamber pump out (down to 5×10-6), setting the correct heating/cooling mode (chiller if in the range -20° to +70° C, heater/LN2 if outside that range), and setting the correct temperature for the process and starting the He backside pressure.

  3. All recipes must end with the same step: Delay before unload (1-5 minutes depending on power levels and etching time)

  4. Be conservative, start with a recipe within the safe limits as described below.

  5. When running a new recipe for the first time, it is VERY IMPORTANT to make sure the plasma starts! If the reflected power is low but there is no plasma the process must be interrupted immediately, the power is being dissipated in the AMU which will quickly cause damage to it.

  6. Do not use ‘Load mode’ power on the ICP or the RF if the power is above 100 W.

  7. Users are not allowed to make recipes that should run without a wafer.

Cleaning instructions:

If a non-polymer building etch is being run (most processes without C4F8, e.g. Si-N etching) the recipe ##  Cleaning no wafer ## should be run from the ‘Chamber view’ page in the ‘Manual’ tab after all samples/wafers have been etched.
If a polymer building etch is being run (all processes with C4F8, e.g. Bosch, Si-O etching), the chamber should be cleaned in between each sample/wafer. This can be done by activating the ‘Clean chamber’ option in the ‘Automatic’ tab, selecting ## Cleaning no wafer ## and setting the interval to 1.
Note: If oxide etch is being run the user MUST make sure the chamber is clean (by monitoring the plasma colour, if it is still white it is still dirty) after finish before leaving the system.

Precondition instructions:

If a non-polymer building etch is being run, precondition with the same recipe for 2-3 minutes on an empty sapphire wafer.
If a polymer building etch is being run, precondition with the ## Cleaning no wafer ## recipe.
Note on cleaning and precondition: Any non-polymer building etch can be run as if it is polymer building, it will be less ideal but still work. The reverse (polymer building as non-polymer building) will not work.

Sample mounting instructions:

All small samples must be secured to the carrier.
Small samples can be mounted to the carrier by: (best to worst thermal contact)
  • photoresist
  • vacuum grease
  • bluetape on the sample, then grease on the bluetape
  • carbon tape
If etching through a sample/wafer one must not stop in the chuck (will damage the tool) or vacuum grease (will contaminate the chamber).

Safe limits:

Do not max out more than 2 at a time
  • table RF 0-100 W
  • ICP RF 250-1500 W
  • Pressure 10-40 mTorr
  • Chiller 5°-40° C
  • Total gas flow 10-100 sccm
  • Total etching time <30 minutes
  • Note on gas flows: MFCs will not work properly below 2% of their maximum range (2 sccm for Ar, N2, CF4, CHF3, O2, 4 sccm for C4F8, 10 sccm for SF6)

End of instructions

Erik Holmgren, Albanova Nanolab, KTH, SU.