Specific Process Knowledge/Etch/Wet Silicon Nitride Etch

Wet Silicon Nitride Etch

Wet Etching of silicon nitride is done in a dedicated laminar flow bench with an integrated quartz tank (Tiger Tank - TT-4). The quartz tank can take up to one 6" wafer carrier. The flow bench is placed in cleanroom 4.

The etch solution is initially 85 wt% H $3$ PO $4$ which is heated up to the boiling temperature - ca. 157 ^oC. Water is allowed to boil off thus raising the concentration and the boiling temperature of the solution until a boiling temperature of 180 ^oC is reached. Thereafter, the wafers are submerged into the bath and the water-cooled lid is closed to maintain the concentration and the boiling temperature. In some cases a lower boiling temperature is chosen - typically 160 ^oC - which lowers the etch rate and improves the selectivity R_Si₃N₄ / R_SiO₂

Comparing the two solutions

	Iodine based gold etch	Aqua Regia (Kongevand)
General description	Etch of pure Gold	Etch of pure Gold
Chemical solution	KJ:J $_{2}$ :H $_{2}$ O (100g:25g:500ml)	HCl:HNO $_{3}$ (3:1)
Process temperature	20 ^oC	20 ^oC
Possible masking materials:	Photoresist (1.5 µm AZ5214E)	Photoresist (1.5 µm AZ5214E)
Etch rate	~100 nm/min (Pure Al)	~(??) nm/min
Batch size	1-25 wafers at a time	1-25 wafer at a time
Size of substrate	2-6" wafers	2-6" wafers