Plasma Enhanced Chemical Vapor Deposition (PECVD) 2 Machine PlasmaLab Model DP800 Serial Number - 8B99198 Plasma Technology, Inc., Massachusetts, USA Contact Information:    Faculty Contact:    Aaron Hawkins    Staff Contact:    Don Dawson    Student Contact:   Evan Lunt Maintenance Request for PECVD 2 SCHEDULER IS REQUIRED

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1. General Description
   
   1. The Plasma Enhanced Chemical Vapor Deposition (PECVD) 2 machine is used to deposit thin dielectric films. It combines up to four gases at pressures between 0.1 and 2 Torr and uses an RF source of up to 600 Watts to ionize the resultant gas mixture, causing film deposition on a heated substrate (250-300°C). PECVD2 is only used to deposit SiO₂.
   2. PECVD allows us to deposit fairly high-quality films at a low temperatures (250-300°C). However, these films are inferior to thermal or traditional CVD deposited films in several ways.
   3. 1. PECVD oxide is amorphous and non-stoichiometric. This means that instead of growing stoichiometric SiO₂, what really is deposited is SiO_xH_y, with the hydrogen coming from the precursor gas silane. Because of this, the film is lower density that thermally grown SiO₂.
   4. 2. PECVD oxide is not as good an electrical insulator as thermal oxide.
   5. 3. PECVD oxide is physically rougher than some other oxides.
   6. 4. PECVD oxide can be deposited with refractive index from 1.45-1.47.
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3. Operating Instructions
   
   1. Starting up the necessary equipment
      1. 1. The process gases include 5% silane in helium (SiH₄/He), nitrous oxide (N₂O), and halocarbon cleaning gas (CF₄/O₂ blend). The tanks are located in the gas cabinet adjacent to the cleanroom. To turn on the 5% silane, twist the red shutoff button on the control panel clockwise until it pops up, then press the "START" button. The CF₄ and N₂O are not run through the control panel of the gas cabinet. THe CF₄ must be turned on and off using the valve on top of the cylinder next to the cabinet. The N₂O should always be turned on.
      2. 2. The chiller located on the floor next to the PECVD2 must be turned on anytime the substrate heater is on. The chiller should not be turned off until the plate has cooled to at least 100°C. Flip the chiller switch to "on".
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   2. Depositing Oxide
      1. 1. Set/Verify your parameters
         1. To change or set gas flow rates, heater temperature, pressure, or other settings, turn the key to the "CHANGE STORED PARAMETER" position.
         2. To verify any parameter, hold the "READ" button and select the parameter you want to verify.
         3. To change a parameter, hold the "SET" button and select the parameter you want to set. You will use the numeric keypad to enter the value you want to set, and then press the "STEP/ENTER" button to enter the value.
         4.   GAS 1 - Silane (5% SiH₄, 95% He)   1000 SCCM, calibrated with H₂
         5.   GAS 2 - Nitrous Oxide (N₂0)   200 SCCM, calibrated with N₂O
         6.   GAS 3 - Ammonia (NH₃)   100 SCCM, calibrated with NH₃
         7.   GAS 4 - Halocarbon (CF₄/O₂)   1000 SCCM, calibrated with N₂
         8. When you are finished, turn the key back to "MANUAL OPERATION"
      2. 2. Turn on the hot plate heater by holding "MANUAL" and pressing "HEATER."
      3. 3. With the plate heated up to the process temperature and the gas flow rates, the throttle pressure, and the RF power level set, you are ready to deposit oxide.
      4. 4. Vent the chamber by holding "MANUAL" and pressing "VENT" and wait until the light glows steadily
      5. 5. Turn the heater back on by holding "MANUAL" and pressing "HEATER". (It turns off as part of the venting procedure.)
      6. 6. Open the chamber with the access levers
         1. a. Left Lever - Controls the speed the chamber is raised and lowered. To the left is stop, right is go.
         2. b. Right Lever - Raises and lowers the chamber. To the left is down, right is up.
      7. 7. Place your wafer(s) on the center of the hot plate, surround your wafer with spacer wafers, and then close the chamber with the levers.
      8. 8. Pump down the chamber by holding "MANUAL" and pressing "ROUGH". Wait until the lights for "ROUGH" and "HI-VAC" stop blinking.
      9. 9. Turn on the gases and throttle valve by holding "MANUAL" and pressing "GAS 1", "GAS 2", and "THROTTLE".
      10. 10. Wait for the pressure to stabilize and the throttle valve error to be green. The indicator is about knee level.
      11. 11. Strike a plasma by holding "MANUAL" and pressing "RF". The plasma will take a second or two to strike, so don't start your timer until you see the plasma through the window. If the plasma does not strike, or dies after striking, try increasing the RF level.
      12. 12. When finished, turn off the plasma by holding "MANUAL" and pressing "RF". Turn off the gases and the throttle in a similar manner and vent the chamber (step 3.)
   3. Shutting down the PECVD2
      1. 1. Turn off the heater by holding down the "MANUAL" button and pressing the "HEATER" button.
      2. 2. Pump down the chamber by holding "MANUAL" and pressing "ROUGH."
      3. 3. Close the cutoff valve behind the machine.
      4. 4. Make sure to turn off all gases that were used at the gas cabinet.
      5. 5. Only turn off the chiller if the plate is under 100°C. Turn off the chiller by flipping the power switch to off.
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5. Cleaning Instructions
   
   1. Things to remember:
      1. NO WATER ALLOWED - do not spray water anywhere inside the chamber.
      2. DO NOT TOUCH THE HOT PLATE with your gloves, the vacuum, or anything else (besides clean wafers) when it is hot. In addition to being a safety hazard, you will contaminate the plate with carbon residue that will affect subsequent growth. If this happens, perform a CF₄ clean until the residue is gone.
      3. Clean the outside of the machine. Wipe down the outside of the chamber and the counter behind the lid.
   2. Simple Chamber Clean - use when there is visible powdery residue.
      1. Vacuum the showerhead. This should remove most of the particulate matter. Be careful not to touch the hot plate with the vacuum hose or your gloves.
      2. Use cleanroom wipes moistened with isopropyl alcohol to wipe down the showerhead. Also, wipe out the window on the side of the chamber. Wipe the base plate and the center plate if it is not hot.
      3. Use the nitrogen gun to blow off the hot plate.
      4. Use a cleanroom wipe moistened with isopropyl alcohol to wipe off the O-ring on the base plate.
      5. Close the lid and use cleanroom wipes and the nitrogen gun to clean off the outer surfaces of the PECVD. There should not be any visible dust anywhere on the machine.
   3. CF₄ Clean - must be done every 3 microns of deposited film to clean the hot plate and showerhead.
      1. Perform a simple chamber clean as described above.
      2. Run a CF₄ cleaning process for at least 30 min or until there is no residue on the hot plate or the showerhead.
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7. Process Recipes
   
   1. 250°C Oxide Recipe (3.6-4.2 μm/hour or 60-70 nm/min) - Good Conformality - 1.42 to 1
      1. GAS 1 (silane) - 10%
      2. GAS 2 (nitrous Oxide) - 14.5%
      3. Throttle Pressure - 1040 mTorr
      4. RF Power - 4%
   2. CF₄ Low Pressure Cleaning Recipe (Preferred)
      1. GAS 4 (CF4) - 20%
      2. Throttle Pressure - 400 mTorr
      3. RF Power - 8%
   3. CF₄ High Pressure Cleaning Recipe
      1. GAS 4 (CF4) - 20%
      2. Throttle Pressure - 650 mTorr
      3. RF Power - 10%
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