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, Ni, Hf

Demis D. John, 2017 InP H3PO4:HCl = 3:1 ~1000 Highly InGaAsP High Lamponi (p.102) InP H3PO4:HCl = 3:1 ~1000 Highly InGaAs High Lamponi (p.102) InP HCl:H2O = 3:1 ~5000 InGaAs or InGaAsP

~200nm stop-etch

High Bubbles while etching InGaAs H2SO4:H2O2:H2O = 1:1:10 ~600 InP High Exothermic, may reduce selectivity if hot InGaAsP H2SO4:H2O2:H2O = 1:1:10 ~600 InP High Exothermic, may reduce selectivity if hot

(same as InGaAs stop-etch removal)

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 (ALD -BDEAS 300C) HF ("Buffered")

Diluted with DI BHF:H2O = 1:100

~7.46 Measured in-house Biljana Stamenic

2024

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 (~100nm) Au "seed 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.
  • Leave Open the 4 contact points on the edge of the wafer, or some other contact point, for an electrode to make contact to the Seed layer.
  • Optionally use EBR100 to swab away photoresist from the contact points.
• 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 seed layer all over the wafer (the 100nm removed from the plated regions will be negligible compared to the ~1µm plated).

Chemi-Mechanical Polishing (CMP)

To Be Added

Mechanical Polishing (Allied)

To Be Added