Plasma Reactive Ion Etching (RIE)

Purpose: Plasma etching of dielectric films, silicon, metal and III-V layers

Location: Pettit & Marcus Inorganic Cleanrooms

Tools: Plasma Therm RIE, Plasma Therm SLR RIE, Vision RIE 1, Vision RIE 2, Oxford Endpoint RIE, Uniaxis RIE

Supplies Needed: test wafer/wafer pieces, carrier wafer (if necessary), and tweezers

Setup Procedures:

1. Schedule time well in advance.
2. Make sure the back side of the wafer is clean and free of any debris or resist.
   • If etching with a mask, be sure to consider the selectivity of the mask material.
     • Do a test run if no data for selectivity for your mask material and the tool using to etch are available.
3. Make sure that the cleaning recipe has been run on the tool.
4. If the clean recipe was not run, start the clean process.
   • Chamber cleanliness can be determined by monitoring the DC bias. Each machine has a DC bias that is typical of a clean chamber. This should be noted before tool use.
5. After the clean recipe is done, wipe down the o-ring with a dry texwipe.
6. Run an etch test on the tool.
   • Run the tool with an extra patterned wafer or wafer pieces for a fraction of the normal etch time (depends on the thickness of what you are etching).
   • Measure the etch with a profilometer and determine the etch rate.
   • Calculate how long the process step must be run to etch the necessary amount of material.
7. Load the sample and a witness sample (if possible) into the tool and run the process.

Number of substrates: <1 – 4 (4” wafer size)

Process Procedures:

1. Watch the helium leak up rate, if applicable
   • If the helium leak up rate is too high (the tool alarms) clean the back of your sample and try again.
   • A low helium leak up rate means even backside cooling
2. Watch and take notes on the parameters
   • Both set point and actual values
   • If the reflected power is high (5-10% power set point) stop the recipe and run the clean process again
     • If this does not help lower the reflected power, stop the recipe and contact the staff
3. Check and note the color of the plasma
   • Changes in color could be due to contamination
   • If contamination is found, run the clean process
4. Measure the etch to make sure it is the depth that was expected
   • If the etch depth is less than expected:
     • Calculate the etch rate for the full run
     • Place wafer back into the tool
     • Use the new etch rate to determine the time needed for the etch
5. Run the clean recipe on the tool after removing the sample.
   • Stay by the tool until the plasma strikes
   • Run it for the full clean time
6. Log off of the tool and cancel any scheduled time that was not used

Verification:

• Pattern Transfer: can be observed with an optical microscope
• Film Thickness: can be measured accurately with Nanospec Refractometer or the Woollam M2000 Ellipsometer
• Step Height: can be measured with the Dektak 150 Profilometer, Tencor P15 Profilometer, or the Wyko Profilometer NT3300
• Etch Profile: Can be imaged using the Hitachi S-4700 FE-SEM