Wet Etching Recipes

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Table of Wet Etching Recipes

Use the ↑ ↓ Arrows in the header row to sort the entire table by material, selectivity, etchant etc.

Material	Etchant	Rate (nm/min)	Anisotropy	Selective to	Selectivity	Ref.	Notes	Confirmed By/Date
Photoresist, polymers/organics	H2SO4:H2O2 = 3:1 Piranha Solution	typ. 5-10min etch for polymer residue		Cr, W, Au, Pt, Si, SiO2, SiN			Dangerous boiling hazard - see Piranha Solution section below. Etches Ti	Demis D. John, 2017
InP	H3PO4:HCl = 3:1	~1000	Highly	InGaAsP	High	Lamponi (p.102)
InGaAsP	To Be Added			InP	High
InP	H3PO4:HCl = 3:1	~1000	Highly	InGaAs	High	Lamponi (p.102)
InP	HCl:H2O = 3:1	~5000		InGaAs ~200nm stop-etch	High		Bubbles while etching
InGaAs	H2SO4:H2O2:H2O = 1:1:10	~600		InP	High		Exothermic, may reduce selectivity if hot
GaAs	NH4OH:H2O2 = 1:30		-	AlGaAs, Al > 80% ~200nm stop-etch	High			Garrett Cole
AlGaAs, Al ≥80%	HF:H2O = 1:20		-	GaAs	High			Garrett Cole
Oxide of InP	NH4OH:H2O = 1:10	1min to remove		InP	unknown			Ning Cao
Oxide of GaAs	HCl:H2O = 1:10	1min to remove		GaAs	unknown			Demis D. John
Al2O3 (ALD Plasma 300C)	Developer: 300MIF	~1.6	None	Most non-Al Materials.	High	Measured in-house	Rate slows with time.	JTB
Al2O3 (ALD Plasma 300C)	Developer: 400K	~2.2	None	Most non-Al Materials.	High	Measured in-house	Rate slows with time.	JTB
Al2O3 (ALD Plasma 300C)	Developer: 400K (1:4)	~1.6	None	Most non-Al Materials.	High	Measured in-house	Rate slows with time.	JTB
Al2O3 (ALD Plasma 300C)	NH4OH:H2O2:H2O (1:2:50)	~<0.5				Measured in-house	Rate slows with time	JTB
Al2O3 (IBD)	HF ("Buffered HF Improved", Transene)	~170	None	Photoresist	High	Measured in-house	May need to increase adhesion with thin SiO2 layer, and 100°C baked HMDS.	Biljana Stamenic, 2017-12
Al2O3 (IBD)	Developer: 726 MiF	3.5	None	Most non-Al Materials.	High	Measured in-house		Demis D. John, 2017-11
Al2O3 (AJA#4)	Developer: 300 MiF	4.30	None	Most non-Al Materials.	High	Measured in-house		Demis D. John 2018-02
SiO2 (PECVD #1)	HF ("Buffered HF Improved", Transene)	~550	None	Photoresist	High	Measured in-house	May need to increase adhesion with 100°C baked HMDS.	Biljana Stamenic 2023
SiO2 (PECVD #2)	HF ("Buffered HF Improved", Transene)	~680	None	Photoresist	High	Measured in-house	May need to increase adhesion with 100°C baked HMDS.	Biljana Stamenic 2023
SiO2 (IBD)	HF ("Buffered HF Improved", Transene)	~260	None	Photoresist	High	Measured in-house		Biljana Stamenic 2023
SiO2 LDR (Unaxis VLR)	HF ("Buffered HF Improved", Transene)	~170	None	Photoresist	High	Measured in-house		Biljana Stamenic 2023
SiO2 HDR (Unaxis VLR)	HF ("Buffered HF Improved", Transene)	~230	None	Photoresist	High	Measured in-house		Biljana Stamenic 2023
Si3N4 (PECVD#1)	HF ("Buffered HF Improved", Transene)	~120	None	Photoresist	High	Measured in-house		Biljana Stamenic 2023
Si3N4 (PECVD#2)	HF ("Buffered HF Improved", Transene)	~35	None	Photoresist	High	Measured in-house		Biljana Stamenic 2023
Si3N4 Low-Stress (PECVD#2)	HF ("Buffered HF Improved", Transene)	~30	None	Photoresist	High	Measured in-house		Biljana Stamenic 2023
Si3N4 (IBD)	HF ("Buffered HF Improved", Transene)	~5	None	Photoresist	High	Measured in-house		Biljana Stamenic 2023
SiN (Unaxis VLR)	HF ("Buffered HF Improved", Transene)	~10	None	Photoresist	High	Measured in-house		Biljana Stamenic 2023
SiN Low Stress (Unaxis VLR)	HF ("Buffered HF Improved", Transene)	~135	None	Photoresist	High	Measured in-house		Biljana Stamenic 2023
Ta2O5 (IBD)	HF ("Buffered HF Improved", Transene)	0.07	None	Photoresist	High	Measured in-house		Biljana Stamenic 2023
TiO2 (IBD)	HF ("Buffered HF Improved", Transene)	1.0–2.0	None	Photoresist	High	Measured in-house		Biljana Stamenic 2014-12
Si (<100> crystalline)	KOH (45%) @ 87°C	~730	High, Crystallographic, ~55°	Low-Stress Si3N4 - either PECVD #2 or Commercial LPCVD Si3N4 Other Si3N4 also OK.	LS-SiN: High PR etches quickly, SiO2 etches slowly.	Measured In-House - Search online.	Use the Covered, Heated vertical bath (Dedi cated bath in Bay 4). Slight Bubbler.	Brian Thibeault 2017
Material	Etchant	Rate (nm/min)	Anisotropy	Selective to	Selectivity	Ref.	Notes	Confirmed By/Date

Wet Etching References

1. Etch rates for Micromachining Processing (IEEE Jnl. MEMS, 1996) - includes tables of etch rates of numerous metals vs. various wet and dry etchants.
2. Etch rates for micromachining-Part II (IEEE Jnl. MEMS, 2003) - expanded tables containing resists, dielectrics, metals and semiconductors vs. many wet etch chemicals.
3. Guide to references on III±V semiconductor chemical etching - exhaustive list of wet etchants for etching various semiconductors, including selective etches.
4. Transene's Chemical Compatibility Chart provides a useful quick-reference for which Transene etchants attack which materials.
   1. As a side-note, Transene provides many pre-mixed solutions that you can order, saving you the time and uncertainty of measuring/mixing such chemicals yourself. Make sure you check with us before ordering so we know how to handle the chemical before it arrives.

Compound Semiconductor Etching

Guide to references on III±V semiconductor chemical etching (A.R. Clawson, 2001)

• Impressively vast list of various III-V wet etches, organized by various applications (eg. "selective GaAs against AlGaAs" or "non-selective InP/InGaAsP" etc.)
• Please add any confirmed etches from this reference to the The Master Table of Wet Etching (Include All Materials).

Metal Etching

• Selective Wet Etch of Cr over Ta using Cr Etchant
• Wet Etch of ITO using Heated, Diluted HCl Solution

Silicon etching

Etch rates for micromachining processing

Etch rates for micromachining processing-part II

Please add any confirmed etches from this reference to the The Master Table of Wet Etching (Include All Materials).

Organic removal

Piranha Solution

• Careful! Read about how to prepare and handle this safely:
  • MIT's Piranha Solution safety document
  • Harvard EHS's Handling Document
  • Used for etching away Photoresist residues after dry etching.

PureStrip (Transene)

• Heat to @ 70°C
  • Vertical heated bath on Wafer Toxic-Corrosive bench in Bay 4
  • After a few days heated, it loses potency - must drain + replenish with fresh solution.
  • ~30-90min will remove stubborn, microscopic PR residues from dry etching.

Gold Plating Bench (Technic SEMCON 1000)

Standard plating recipes are described and taught during the equipment training for this tool.

Electroplating first requires a Gold seed layer to be present on all surfaces to be plated. Common ways to produce this are to:

• Sputter-coat a thin (~10nm) Au layer on all surfaces of the wafer, being careful to consider shadowing effects during the dep (eg. in high-aspect ratio trenches).
• Perform photolithography to protect (and prevent plating) in desired areas - areas with no photoresist will be plated.
• Perform the electroplating on the Technic SemCon, contacting the seed layer with electrodes and executing the program for the desired current/time to achieve the plating thickness (typically microns).
• Strip the photoresist using standard solvents.
• Use the Oxford Ion Mill to blanket etch the 10nm seed layer all over the wafer (the 10nm removed from the plated regions will be negligible).

Chemi-Mechanical Polishing (CMP)

To Be Added

Mechanical Polishing (Allied)

To Be Added