Specific Process Knowledge/Etch/KOH Etch

KOH etch - Anisotropic silicon etch

KOH belongs to the family of anisotropic Si-etchants based on aqueous alkaline solutions. The anisotropy stems from the different etch rates in different crystal directions. The {111}-planes are almost inert whereas the etch rates of e.g. {100}- and {110}-planes are several orders of magnitude faster.

At Danchip we use as a standard a 28 wt% KOH.

Wet etching of aluminium is done with two different solutions:

H $_{2}$ O:H $_{3}$ PO $_{4}$ 1:2 at 50 ^oC
Pre-mixed etch solution: PES 77-19-04 at 20 ^oC

Both solutions are used in the Aluminium etch bath shown to the right. I must be written on which one is in. Solution no. 1 is the most used solution for etchning oure aluminium. Solution no. 2 is primarily for etching aluminium mixed with a small percentage of silicon.

Comparing the two solutions

	Aluminium Etch 1	Aluminium Etch 2
General description	Etch of pure aluminium	Etch of aluminium + 1.5% Si
Chemical solution	HFailed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle _2} O:H $_{3}$ PO $_{4}$ 1:2	PES 77-19-04
Process temperature	50 ^oC	20 ^oC
Possible masking materials:	Photoresist (1.5 µm AZ5214E)	Photoresist (1.5 µm AZ5214E)
Etch rate	~100 nm/min (Pure Al)	~60(??) nm/min
Batch size	1-25 wafers at a time	1-25 wafer at a time
Size of substrate	4" wafers	4" wafers
Allowed materials	Aluminium Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist	Aluminium Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist