INTRODUCTION:
Aluminum is used to make contacts between your devices and the outside world. Aluminum is deposited by thermal evaporation, a physical vapor deposition technique. Basically, we are creating a huge light bulb, putting Al on the tungsten light bulb filament, and heating it to the point where the Al actually evaporates, and then condenses on our (relatively) cold sample surface (as well as elsewhere in the chamber).
SAFETY:
There are no chemical hazards associated with the vacuum system. The main concerns are maintaining the integrity of the vacuum. Latex gloves should be worn at all times when handling anything on the interior of the vacuum chamber. It is very important to follow the pumpdown sequence below EXACTLY in order not to damage the system (and save you many hours of cleaning up the chamber). In addition, heat and cool the filaments at the rate specified so as not to burn out the heating wire.
ACCESS:
The system is only available to authorized users. To become an authorized user contact the coordinator for MH425 (student taking the processing course are authorized users) to have your name added to the list. Make no changes to the configuration of the system or to which metals it is set to evaporate without obtaining prior permission from the MH425 coordinator. Report any problems with the system immediately to the coordinator.
PROCEDURE:
I. Start the system: (often this will already have been done for you at the time the lab starts)
1.Turn on the water to the diffusion pump.
2.Turn on the pump station main power and the gauge controller power.
3.Make sure all of the vacuum valves are closed (clockwise closes, counterclockwise
opens).
4.Open the mechanical pump vent, turn on the mechanical pump, and then close
the vent.
5.Open the Mechanical Pump to Diffusion Pump valve.
6.When the Foreline TC pressure drops below 30 mtorr, turn on the diffusion
pump and let it warm up for 30 minutes.
7.Carefully add liquid nitrogen to the cold trap until it is fully cooled. (this
step will probably be ignored in the processing course. It will limit our base
pressure).
II. To use the vacuum chamber:
1.Open the chamber vent valve for a couple of minutes; until air no longer
can be heard entering the chamber and the bell jar is free from the baseplate.
Raise the bell jar, and lock it in place.
2.Mount your samples and a glass slide (for thickness monitoring) on the sample
holder. If the Al filament appears to need Al, ask lab coordinator or TA to
help you add some.
3.Carefully, unlock the bell jar and lower it into place.
4.Close the chamber vent valve, close the Mechanical Pump to Diffusion Pump
valve, and open the Mechanical Pump to Bell Jar valve.
5.Rough pump the bell jar with the mechanical pump until the Bell Jar TC pressure
is less than 100 mtorr.
6.Close the Mechanical Pump to Bell Jar valve and then open the Mechanical Pump
to Diffusion Pump valve.
7.Open the Diffusion Pump to Bell Jar valve and turn on the Bell Jar ionization
guage. The system should pump down to approximately 4e-6 torr if the cold trap
is fully cooled with liquid nitrogen. This may take 10-20 minutes.
8. Set the filament selector to your desired filament, make sure the filament
adjust is set to zero, and turn on the filament power.
9. Increase the filament current slowly (~1/2A/sec) by turning up the filament
adjust. Somewhere around 30A the filament should begin to glow. Proceed with
the evaporation.
10. When the evaporation is complete, slowly turn down the filament adjust to
zero, and turn off the filament power.
III. Remove sample and pump down
1. Wait about 5 minutes for the Al filament and chamber region around it to
cool off.
2. Close the Diffusion Pump to Bell Jar valve and turn off the Bell Jar ionization
guage.
3. Open the chamber vent valve for a couple of minutes; until air no longer
can be heard entering the chamber and the bell jar is free from the baseplate.
Raise the bell jar, and lock it in place.
4. Remove your sample and the glass slide.
5. Follow the procedure above beginning at step II-3 and ending at step II-7
to put the chamber under high vacuum. If you are going to leave the system in
this state for a while, turn off the ionization guage.
6. Now you can get a calibration by measuring the thickness of the aluminum
on the glass slide using the profilometer and you can measure the sheet
resistance of the film as well.
IV. To shut down the system
1.Turn off the Bell Jar ionization gauge (and filament power if it is not off).
2.Close the Diffusion Pump to Bell Jar valve.
3.Turn off the diffusion pump power and let it cool for at least 30 minutes.
4.Close the Mechanical Pump to Diffusion Pump valve.
5.Turn off the mechanical pump power and open the mechanical pump vent.
6.Turn off the diffusion pump cooling water.
7.Turn off the gauge controller power and the pump station main power.