SiO2 Wet Etching
- **SAFETY**
- Buffered Oxide Etch (BHF) is extremely hazardous.
Wear face shield, nitrile gloves, vinyl lab apron, and non-woven material shoes.
- Materials and Preparation
- BHF 6:1
- Plastic Beaker for BHF.
Procedure
- Calculate expected etch time for SiO2 thickness. BHF 6:1 etch rate at room temperature is ~1000 Å/min.
- Etch for half the calculated time.
- DI-H2O rinse and N2 dry.
- Calibrate etch rate via profilometry and visual SiO2 characteristics.
- Repeat cycle of etch-inspect until etch depth is attained.
Visual SiO2 Characteristics
- SiO2 is hydrophilic. Si is hydrophobic. If the wafer is silicon and its back side has the same SiO2 film as the front side, neither BHF nor water will sheet across it upon full removal of the SiO2.
- SiO2 film thickness can be roughly estimated by comparison of its color to a SiO2 film thickness color calibration chart.
- With a microscope under white light, dark or light tan color indicates about 700 Å of SiO2 remain.
- The last few hundred Angstroms of oxide do not show color and will appear white, identical to unoxided silicon.