- General Description
- The Plasma Enhanced Chemical Vapor Deposition (PECVD) machine is used to deposit thin dielectric films. It combines up to four gases at pressures between 0.1 and 1 Torr and uses an RF source of up to 200 Watts to ionize the resultant gas mixture, causing film deposition on a heated substrate.
- Films that can be deposited with the system include: SiO2, SiOxNy, and SiN. Currently, PECVD 1 is only used to deposit silicon nitride. Dr. Hawkins must approve any use of PECVD 1.
- PECVD allows us to deposit good-quality films at low temperatures (250-300°C). However, these films are inferior to thermal CVD (ie LPCVD) films in several ways:
- PECVD nitride is amorphous and non-stoichiometric. This means that instead of growing stoichiometric Si3N4, what really is deposited is SiNxHy, with the hydrogen coming from the precursor gas silane. Because of this, the film has lower density than thermally grown Si3N4.
- PECVD nitride is not as good an electrical insulator as LPCVD nitride and often has small pinholes in the film.
- PECVD nitride is physically rougher than some other nitrides.
- PECVD nitride can be deposited with a refractive index from ~1.90-2.30 by varying the ratio of ammonia to silane.
- Operating Instructions
- Turning on the necessary equipment
- The process gases include 5% silane in helium (SiH4/He), ammonia (NH3), and halocarbon cleaning gas (20% O2 in CF4). The tanks are located in the gas cabinet adjacent to the cleanroom. To turn on the 5% silane and ammonia, twist the red shutoff button on the control panel clockwise until it pops up, then press the ‘start’ button. The CF4 is 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. Nitrous oxide (N2O) is connected to the machine, but not used for nitride growth. If it is used, the nitrous oxide does not need to be turned on, just check the gauges above those for the CF4 to make sure there is at least 15-20 psi.
- The vacuum pump for PECVD 1 is located in the back pump room (there is a label indicating the machine - the second machine on the right when you enter the pump room). It can be switched on and off using the switch box mounted on top of the vacuum pump.
- The chiller located on the floor next to the PECVD must be turned on anytime the substrate heater is on. It can be switched on with the on/off button on the front panel. Verify that water is flowing by looking at the flow tube on the front panel. The chiller should not be turned off before the plate has cooled to below 100°C.
- Manual Run
- Push "TAB" to move the cursor, "+" turns an option ON, "-" turns an option OFF. When in a field with numbers, use the arrows to switch positions in the number and the number pad to set the numbers.
- Manual Screens
|Screen 1: ||Oxide 6000ANG ||MANUAL |
| ||Power: OFF ||Watts 100 |
| ||Pressure: ||0.000 Torr |
| ||Vacuum: OFF ||Vent: OFF|
|Screen 2: ||Oxide 6000ANG ||MANUAL |
| ||GAS1: OFF ||MFC1: 16.0% || || (NH3) |
| ||GAS2: OFF ||MFC2: 70.0% || || (SiH4) |
| ||GAS3: OFF ||MFC3: 25% || || (N2O) |
|Screen 3: ||Oxide 6000ANG ||MANUAL |
| ||GAS4: OFF ||MFC4: 10.0% || || (CF4) |
| ||Htr: 250°C ||Temp: 000°C || || Don't worry about these last two lines|
| ||Bias: ||----- Volts|
- How to get back to the Manual Run screen if the machine gets turned off:
- 1. Turn on the power or pull out the emergency kill switch.
- 2. The first screen you see should look like this:
| ||Oxide 6000ANG ||(01) |
| ||Select ||Recipe |
| ||Review ||Recipe |
| || ||Configure ||System |
- 3. Push "ENTER" on the first line, "Oxide 6000ANG (01)".
- 4. Push "TAB" once to "MANUAL RUN", then push "ENTER".
- 5. You should see the familiar Manual Run Screen 1.
- 6. Be sure to reset the correct gas flows for your recipe!
- Starting a process
- 1. Turn on the vacuum and set the pressure to 0.000 Torr.
- 2. Wait for the chamber to pump down to at least 30 mTorr and the temperature to come up to the set temperature.
- 3. Turn on the process gases.
- 4. Wait 5 seconds, then set the process pressure.
- 5. Wait for pressure to stabilize, then turn on the RF power and start a timer.
- Stopping a process
- 1. Turn off the RF power.
- 2. Turn off the process gases.
- 3. Set the pressure to 0.000 Torr, wait until the chamber pressure is at least 40 mTorr.
- 4. Briefly purge the chamber by turning on the vent for 1-2 seconds.
- 5. Wait until the chamber pressure is at least 40 mTorr, then turn on the vent and turn off the vacuum.
- 6. Open chamber and remove samples.
- Shutting off the PECVD
- After cleaning out the chamber, set the pressure to 0.000 Torr and turn on the vacuum for about 3 minutes.
- Turn off the vacuum on the control panel.
- Make sure the gases are turned off in the back.
- Turn off the vacuum pump in the back room.
- The chiller next to the PECVD can be switched off when the PECVD has cooled down to at least 100°C.
- Don't forget to sign the log book!
- Cleaning Instructions
- Things to remember:
- NO WATER ALLOWED - do not spray water anywhere inside the chamber. The only approved use of DI water is using moistened cleanroom wipes to wipe down the inside of the chamber to loosen the film residue.
- Do not touch the hot plate with your gloves, the vacuum, or anything else 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.
- No hard scrubbing of the hot plate. Applying pressure to the hot plate will push the thermocouple out of contact with the hot plate, causing erroneous temperature readings.
- Clean the outside of the machine. Wipe and blow down the outside of the chamber.
- Simple Chamber Clean - use at least after every 60 minutes of nitride growth.
- Vacuum the chamber lid including the showerhead. Pay special attention to the screws in the showerhead as well as the groove around the showerhead. This should remove most of the particulate matter. Vacuum around the bottom plate (but NOT the heated center plate if it is hot). Be careful not to touch the hot plate with the vacuum hose or your gloves.
- Use cleanroom wipes moistened with isopropyl alcohol to wipe down the chamber lid and walls. Again, pay special attention to the showerhead and the groove at the base of the showerhead. Also, wipe out the window at the top of the chamber. Wipe the base plate and the center plate if it is not hot.
- Use the nitrogen gun to blow out any remaining particles from the showerhead groove and the hot plate. If you did the previous steps properly, you shouldn't see any particles flying around. If you do, stop and go back to step 2.
- Use a cleanroom wipe moistened with isopropyl alcohol to wipe off the O-ring on the chamber lid.
- 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. Pay attention to the controller.
- Full Chamber Clean - perform when necessary.
- Run cleaning recipe for 60 min
- Open and wipe out
- You can use wipes wet with DI water on side walls to help films peel up
- wipe out thoroughly with IPA after using water-before pumping down!
- Repeat steps 1 and 2 until chamber is mostly clean
- You can use scotchbrite pads wetted with DI water to scrub walls and showerhead to cleanness
- Remove showerhead before scrubbing
- Do not scrub hotplate
- If you have to scrub base plate-only scrub parallel to o-ring sealing surface
- Wipe down chamber with IPA when done
- Season chamber for 1 hr and then perform simple chamber clean
- Process Recipes
- MFC flow rates
- To determine the flow for each gas, multiply the percentage by the full flow in sccm.
- Gas 1 (NH3) : 35 sccm
- Gas 2 (SiH4) : 200 sccm
- Gas 3 (N2O) : 71 sccm
- Gas 4 (CF4/20% O2) : 651 sccm
- Silicon Nitride
- 70 W
- 1000 mTorr
- 26% NH3 (gas 1) - adjust for index
- ~96% SiH4 (gas 2) - adjust for index
- ~11.5nm/min 6 min test
- CF4 Clean
- 800 mTorr
- 20% CF4 (gas 4)
- 120 W RF - watch reflected power and lower power so it stays about 7-8 W
- Old Process Recipes