INTRODUCTION:
This procedure describes the wet etch used to remove aluminum. It is called the PAN etch, for its use of phosphoric, acetic, and nitric acids.
SAFETY:
The PAN etch is a very strong acid mixture. Acid protective gear MUST be worn when working at this station. Lab coats, acid-proof gloves (atop the normal clean room gloves), and an acid face mask (with the face shield DOWN) worn over safety glasses, are all required. ALWAYS know the location of the nearest eye wash and safety shower.
I. Solution Preparation
PAN etch solution of H3PO4:DIH2O:HNO3:CH3COOH (16:2:1:1)
*** Always add reactive compounds(acid/base) to water ***a.) 50mL DIH2O
b.) 25mL Acetic Acid (CH3COOH )
c.) 25mL Nitric Acid (HNO3)
d.) 400 ml Phosphoric Acid (H3PO4)
Stir solution with clean teflon rod. Place beaker into the temperature-controlled water bath and adjust the power to maintain the solution at 40 oC.
PROCEDURE:
1. Place wafer(s) on teflon carriers.
2. Submerge the carrier with wafer in the PAN etch solution. Use gentle agitation with Teflon carrier to insure uniform exposure of the wafers to the etchant. The aluminum etching appears as a wave and may take up to 2.5 minutes or more to complete at 40°C. When the etch is complete, make sure to rinse the wafers thoroughly since the etch solution is quite viscous.
3. When the etch is complete, make sure to rinse the wafers thoroughly since the etch solution is quite viscous.
4. Blow dry with nitrogen.
5. Inspect wafers under the microscope to ensure that etching was complete.