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 Al_xGa_{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.