Inductively Coupled Plasma (ICP) Etch

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

Location: Pettit & Marcus Inorganic Cleanrooms

Tools: Plasma Therm ICP, Plasma Therm ICP (Single Chamber), STS ICP, STS SOE, STS HRM

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

Setup Procedure:

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 being used to etch are available
   • If using an ICP that has a clamp, be sure that there is NO resist around the edges of the wafer. Resist anywhere near the edge will cause the wafer to stick to the clamp and get stuck in the chamber
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, wipe 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 piece 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
   • NOTE: it is better to under etch than over etch. The sample can always be etched again

Number of Substrates: 1

Process Procedures:

1. Load the sample and a witness sample (if possible)into the tool and run the process
2. 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 leak up rate means even backside cooling
3. 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
4. Check and note the color of the plasma
   • Changes in color could be due to contamination
   • If contamination is found, run the clean process
5. 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
6. 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
7. 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