The Oxford Plasma Lab inductively-coupled plasma (ICP) reactive ion etching (RIE) system. The system can etch Si, Si3N4, SiO2, and a variety of metals with good selectivity to standard masking materials. This tool is capable of cryogenic silicon etching, and high aspect ratio deep silicon etching (DRIE/Bosch/DSi, ~5:1).
SF6, C4F8, CHF3, CF4, Ar, O2
This instrument was acquired with support from the National Science Foundation under Grant No. 0722583
- Low temperature silicon etch for high aspect ratio features.
*Note that the instructions below may not contain the most recent updates. Please refer to the manuals printed and posted at the equipment.
- Thesystem operates with voltages high enough to cause shock or burn injury. Never open panels or remove covers from the system.
- Thesystem produces electromagnetic radiation from audio to 2.45 GHz frequencies, which can have field strength strong enough to cause death or injury if not properly shielded. Never remove covers or protective shielding.
- The system contains compressed gases including fluorine compoundsthatcan leave toxic residues in the system. Use appropriate caution with gases, never defeat interlocks or try to fixequipment problems, and never open the chamber without appropriate pre-cleaning and without appropriate personal protective equipment and training.
- Etched materials or their byproducts may be toxic. Never open the chamber without proper pre-cleaning and appropriate personal protective equipment and training.
- Thesystem uses liquid nitrogen (LN2) to cool the sample. Direct skincontactwith liquid nitrogen or the plumbing carrying it can cause frostbite.Nevertamper with the tank blow off valves or other LN2 safety features. This can result inover pressurizationand catastrophic/explosivetank failure.Amassive LN2 leak constitutes anasphyxiation hazard,evacuate the lab.
- Thesystem has a substrate heater that can operate at very high temperatures, capable of causing burns on contact. Care must be taken when using the heated stage to avoid contact with any hot areas. The chamber walls are also heated to 60 C.
Allowed Materials and Processes
- SiDRIE (Bosch/DSi,etc.),Si mixed, SiO2, various polymers
Restricted Materials and Processes
- Cryogenic Si etching
- Metal etching (W, Mo, etc.)
- Metal hard masks (Al, Cr, Ni, etc.)
- III-V etching
- LN etching
- Do not ever press theSTOP ALL AUTO PROCESSES button in the upper right side of the screen. If you dopress itby accident, carefully read the message, and then press Noto avoid shutting the system down.
- Do not ever enter service mode. If you doenter service modeby accident, do not press any valves.Press System and then Exit Service. Read the message and click Ok to exit service mode. Do not worry, there is no real DANGER!!! despite the daunting message.
- Be careful not to hit the EMO button accidentally on the front of the tool.
- Do not ever run process steps with IGNORE TOLERANCE selected.
- If you are running long switched processes, for example aDSior DRIE etch, make sure to monitor the process regularly for a change in temperature and to make sure the plasma is still on and the correct color. The switching process is too fast for any tolerance errors to show up.
1. Check reservations and make one.
2. If necessary, login totheequipment. Press System then Password. Then enterOPT and OPTfor the username and password. (Note: you may need to accept a “YELLOW ALERT” that says, “End of process reached”, when you come to thetool.)
3. Equipment checks.
- Press System thenPumping. Ensurethere are no red alerts present, and that all the interlocks on the bottom right of the screen are green except for the Gas-Pod Interlock–itisnormal for this to be redbefore starting a process.
- Check base pressure. Checkthat the penning gauge on the process chamber reads less than 5.0e-6 Torr. If the tool has beenusedrecently, the pressure may be higher. Thisis acceptableifthe pressure is decreasing. If the pressure is above 5.0e-6 Torr and is not decreasing,leave a note that the tool is inoperable and report the issue to staff.
- Check the CM gauge. Press Process, Chamber1. The CM gauge reading, shown in the APC CONTROLLER box (“Chamber Pressure”) on the Chamber1 screen, should be.
- 0.1mTorrwhile the system is at base pressure. If the CM reads 0.0mTorror reads >0.3mTorr,report the issue to staff.If you have extremely critical processes, wait for the tool owner to adjust the CM gauge back to 0.1mTorrbefore continuing.
- Take theEurotherm2404 controller out of manual mode by pressing theleft circular button and verifying that the AUTO LED lights up.The OP2 light will turn on when the actual temperature (top reading) is above the setpoint (lower reading).
- Turn on the liquid nitrogen in the maintenance area.Check the gauge in the center on the topof the tankto ensurethat greater than a quarterof a tank of LN2 remains. These gauges are notoriously inaccurate, so proceed with caution and expect that the level might be lowerthan it appears. If the level is less than one quarter, inform staff and make a conscious decision about whether to proceed with your samples.
- Setthechuck temperature. Press Process and then Recipes and set the operating mode to Manual and No Wafer(i.e. make sure both buttons have yellow dots on them).Press Load,selectthe“System– Set Temp"recipe, and press Ok (Note:do not save previous recipes, butyou may need to acknowledge that you are overwriting a previous recipe).Editthe chuck temperature byleftclicking the only step in the recipe, then selecting EditStep, changing the temperature in the CRYO box to the desired temperature, and pressing Ok. Once back on the Process, Recipes screen, click Run. Read and accept the yellow alert, and then check that the new set point on the Eurotherm2404 iscorrect.
4. Confirmthat thechuck temperature is approachingthesetpoint.
5. Loadadummy waferor monitor wafer.Typically,a dummy wafer is left in the load lock. Check that it isrestingsnugly against the cams with the flat facing away from the process chamber. If there is no wafer present, you will need to load onefollowing the instructions below.
- Loading a wafer. Press System then Pumping. Then, on theleft-handsideloadlockcontrols,(note:never vent the process chamber!) press Stop, read and accept the pop-up message, and press Vent.When the load lock vents, open the lid and loadawafer snugly against the cams with the flat away from the chamber. Close the lid, press Stop and then Evacuate on the load lock controls,provide awafer name, and press Ok. Wait fortheloadlock to report “CyclingLoadlockPumping” and process chamberto report“Base Pressure Reached” before beginning a process.
6. Run "MMF –O2 Clean XXC”. Press Process then Recipesand setthe operating modeto Automatic. Make sure a dummy wafer is in place and that it isintimately seated with the cams. Loadand run the recipe. If you are not running at 20 C, there may be a similar recipe with the appropriate temperature. Otherwise, edit the temperature in each step of the recipe before running it. (Note: do not save the recipe with the edited temperatures.) Verify that the chamber is clean by monitoring the plasma color (generally: dim, slight purple = clean, brightwhitish-blue = dirty). If the plasma is dim, it is ok to stop therecipeand return the wafer to the load lock. When the process is over, read and accept thepop upmessages.
7. Run conditioning recipe(Optional).Press Process, then Recipes. Select Automatic for the operating mode (note: do not save overarecipe unless itisYOUR recipe). Then select and runyourrecipe. Operating in Automatic mode, the tool will load the wafer, run the recipe, and unload the waferautomatically.
8. Run process.Unloadthe dummy wafer, load your wafer, and evacuate theloadlockby pressing Stop and Evacuate on theloadlockcontrols. Enter a wafer ID.The system will report “CyclingLoadlockPumping” and “Base Pressure Reached” when theloadlockand process-chamber are ready to process. Next, edit your etch time and run your recipe. Verify that the wafer loads, the plasma strikes, and the reflected powers for the ICP and RF supplies are less than 10W.Verify that the chuck is at the proper temperature and monitor the temperature during the run.If the temperature increases by more than two degrees, the liquid nitrogen may be out. Monitor and record all parameters to help with troubleshooting and process development.
9. Unload wafer.After the process, acknowledgethe Yellow Alert indicating the process has finished and press OKifthe Process Status widowsays Process Completed OK.The toolwill automatically transfer wafer to load lock after processing. Confirmthat thechamberisat base pressure andloadlockhas reached “CyclingLoadlock Pumping” before proceeding. Press Stop and then Vent on theloadlockcontrols. Wait for theloadlockto vent, remove your wafer, and replace the dummy wafer. Evacuate theloadlockby pressing Stop and Evacuate on theloadlockcontrols.
10. Run clean recipe. A chamber clean is required for etches containing fluorine etch chemistry.Run an automatic recipe with "MMF–O2Clean 20 C."(Note: if your etch contained C4F8 or CHF3, and the total etch time for your conditionandetches was more than 10 minutes, you must edit the cleaning time to be at least 1.25x the total of your condition and etch time.)
11. Close theliquid nitrogenvalve on the tank by turning it clockwise. Use caution; the knob may be very cold. PresstheAUTO/MAN button on theEurotherm controller. Make surethe MAN LED is on, thatthe set point reads 0.0by pressing the up and down arrows,and that OP1andOP2 are not lit.
- A Red Alert is shown on thescreen.
- If you tried to run a clean and it didn’t strike or during your periodic check during aclean, you see a Red Alert window saying, “Forward Power Out ofTolerance,”or,“Auxiliary Reflected Power Our of Tolerance,”accept the message and try restarting the clean a second time. If it fails a second time, shut the tool down in CORAL and note in CORAL how much time is left on your chamberclean.
- Otherwise, shut the tool down.
- Message reads “Do you wish to run a second process on the wafer in theloadlock?"
- If it is a dummy wafer, go ahead! If it is a product wafer, make sure youhaven’t accidentally tried to run a second time.
- Youhad to stop a process in the middle of a run using theSTOP button below Process Control,and apop upreads, “All processes attached to this RecipeTaskhave been stopped manually. Do you wish wafers to be automatically returned toLoadlock?"
- Press Yes to return wafer toloadlock.Read and accept thepop upmessage.
- Temperatureis increasing duringprocess.
- Stop process using the stop square on the upper left side of the screen. A message should pop up saying, “All processes attached to this RecipeTaskhave beenstopped manually. Do you wish wafers to be automatically returned toLoadlock?"Press Yes.Check LN2 level. Ask staff to replace LN2 if you are not qualified to doso.
- You accidentally clicked into service mode.
- Do not press any other buttons. Click “System” and “Exit Service”. Read the DANGER message, and press “Ok” to exit service mode.