Specific Process Knowledge/Etch/Etching of Gold

Ething of Gold can be done either wet or dry. For wet etching please see below on this page. Dry etching can be done with IBE by sputtering with Ar ions.

Etching of Gold

Wet Gold Etch: Done in the fumehood positioned in cleanroom 2

Etching of Gold is done wet at Danchip making your own set up in a beaker in the fumehood. We have two different solutions:

1. Iodine etch: KI:I₂:H₂O - 100g:25g:500ml - standard at Danchip. Can be used with AZ resist as mask.
2. Aqua Regia (Kongevand): HNO₃:HCl - 1:3 - A very strong acid witch will etch most metals and are therefore used when you wish to remove all the gold from your wafer. you have to be very carefull when you work with Aqua Regia (Kongevand) It can generate nitrous gases witch are very toxic!!

Comparing the two solutions

	Iodine based gold etch	Aqua Regia (Kongevand)
General description	Etch of pure Gold with or without photoresist mask.	Etch of pure Gold (as stripper).
Chemical solution	KI:I2:H2O (100g:25g:500ml)	HCl:HNO3 (3:1)
Process temperature	20 oC	20 oC
Possible masking materials	Photoresist (1.5 µm AZ5214E)	Unmasked - used as a stripper
Etch rate	~100 nm/min	~(??) nm/min - fast etch
Batch size	1-5 4" wafers at a time	1-5 4" wafer at a time
Size of substrate	2-6" wafers	2-6" wafers

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Etching of Gold

Etching of Gold can be done either by wet etch, dry etch or by sputtering with ions.

• Etching of Gold by wet etch
• Sputtering of Au

Comparison of Gold Etch Methods

	Al wet etch 1	Al wet etch 2	IBE (Ionfab300+)
Generel description	Wet etch of pure Al	Wet etch of Al + 1.5% Si	Sputtering of Al - pure physical etch
Etch rate range	~100nm/min (pure Al)	~60nm/min (Al+1.5% Si)	~30nm/min (not tested yet)
Etch profile	Isotropic	Isotropic	Anisotropic (angles sidewalls, typical around 70 dg)
Substrate size	#1-25 100 mm wafers	#1-25 100 mm wafers	Smaller pieces glued to carrier wafer #1 50mm wafer #1 100mm wafer #1 150mm wafer #1 200mm wafer
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	Silicon Silicon oxides Silicon nitrides Metals from the +list Metals from the -list Alloys from the above list Stainless steel Glass III-V materials Resists Polymers Capton tape