Specific Process Knowledge/Etch/Wet III-V Etches
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This is a collection of III-V wet-etches; not all etches are currently used at DTU Danchip why the rates should be tested before use. Make sure you have the proper education in mixing of chemicals before use.
It is utterly important that you dispose of chemicals/etches according to the DTU Danchip regulations; more information is found in the III-V cleanroom.
HCl:H3PO4 etch
HCl(37%):H3PO4(85%) is a selective, anisotropic and slow etching of InP. Very slow rate in quarternaries. The etch rates depend on the orientation of the features and have not yet been calibrated at DTU Danchip.
See rates below for InP, PQ(1.n) and InGaAs lattice-matched to InP. The acronym PQ(1.n) denotes a lattice-matched InGaAsP with a band gap corresponding to a wavelength of 1.n mm.
The temperature is 22 degC +/- 1 degC.
| HCl(37%):H3PO4(85%) etch rates, nm/min | |||
|---|---|---|---|
| Etchant | InP | PQ(1.1) | InGaAs |
| 1:4 | 500 +/- 100 | <2 | <1 |
H2SO4:H2O2:H2O etch
H2SO4(10%):H2O2(35%):H2O is a selective etch of InGaAsP with very low etch rate in InP. The acronym PQ(1.n) denotes a lattice-matched InGaAsP with a band gap corresponding to a wavelength of 1.n mm.
The etchrates have not yet been calibrated at DTU Danchip. The temperature is 22 degC +/- 1 degC.
| H2SO4(10%):H2O2(35%):H2O etch rates, nm/min | |||||
|---|---|---|---|---|---|
| Etchant | InP | PQ(1.1) | PQ(1.3) | PQ(1.5) | InGaAs |
| 1:1 | <5 | <50 | |||
Concentrated H2SO4
Concentrated H2SO4(96%) is a selective etch of InP with a very low etch rate in InGaAsP.
| H3PO4(90%) etch rates, nm/min | |||||
|---|---|---|---|---|---|
| Etchant | InP | PQ(1.1) | PQ(1.3) | PQ(1.5) | InGaAs |
| H2SO4(96%) | 13 | ? | <1 | ||
H3PO4:H2O2:H2O etch
H3PO4(85%):H2O2(35%):H2O is a GaAs/AlGaAs-etch which gives a better surface quality than H2SO4-based etches.
| H3PO4(85%):H2O2(35%):H2O etch rates, nm/min | |||
|---|---|---|---|
| Etchant | GaAs | AlGaAs | Comment |
| 1:4:45 | 250 +/- 50 | 250 +/- 50 | 1 |
| 10:2:60 | 200 +/- 100 | 200 +/- 100 | 2 |
| 10:2:30 | ~600 | ~600 | 2,3 |
(1) Temperature of mixture is ~22 C (no heating during etch). data obtained using magnetic stirring with sample on flat basket. (2) Refrigerated H2O used during mixture of etch, and mixture kept at 17 C during etch. (3) 10:2:30 gives smoother etch than 10:2:60.
BHF etch
BHF etches SiO2 and removes native oxide on InGaAs. Do not use BHF unless you know the dangers involved with this chemical and always use 4H gloves!.
| BHF etch rates, nm/min | |||
|---|---|---|---|
| Etchant | SiO2 1 | PECVD2 Si3N4 | E-beam Ti 2 |
| BHF 1:7 | 202 | 52 | 90-120 |
(1) Process SiO2thi1 in PECVD2. (2) Ti from Titest.prg on Physimeca. It seems there is no measurable etchig during first 10 seconds.
Citric Acid etch
C6H8O7:H2O2 is a selective etch of GaAs; does not etch AlxGa{1-x}As if x > 0.45.
Solid C6H8O7 is mixed 1:1 by weight with H2O using magnetic stirring. The solution C6H8O7:H2O is thereafter mixed 4:1 volume ratio with H2O2.
The above C6H8O7:H2O2 solution has an etch-rate of ~360 nm/min in GaAs and < 0.5 nm/min in AlAs @ 25 C.