Specific Process Knowledge/Etch/Wet III-V Etches

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This is a collection of III-V wet-etches; 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 your dispose of chemicals/etches according to the DTU Danchip regulations; more information is found in the III-V cleanroom.

For dry etching III-V materials see

• III-V ICP
• III-V RIE - Plassys

InP or GaAs substrate etching

When etching InP or GaAs substrates, both 2” wafers and small pieces, you should collect the used chemicals in a waste bottle. This does not apply for etching epilayers.

There should be two bottles in the fumehood one for HCl used to etch InP substrates and one for citric acid: H2O2 or H2SO4 (10%):H2O2 used to etch GaAs substrates. Once the bottles are full, you should bring them in Danchip basement and have a new one in CR. For the GaAs waste you should use empty H2O2 bottles (since they should have a special lid that avoid overpressure), while for InP waste we can use an empty and clean developer bottle.

HCl:H3PO4 etch

HCl(37%):H₃PO₄(85%) is a selective, anisotropic and slow etching of InP. Very slow rate in InGaAsP. 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 on InP with a band gap corresponding to a wavelength of 1.n um.

The temperature is 22 degC +/- 1 degC.

HCl(37%):H3PO4(85%) etch rates, nm/min
Etchant	InP	PQ(1.1)	InGaAs	Contributer
1:4	500 +/- 100	<2	<1	Before 2012 by Tine Greibe
1:0	8700 +/- 500		small	2014-July by Luisa Ottaviano

H2SO4:H2O2:H2O etch

H₂SO₄(10%):H₂O₂(30%):H₂O is a selective etch of InGaAsP with very low etch rate in InP. The acronym PQ(1.n) denotes a lattice-matched InGaAsP on InP with a band gap corresponding to a wavelength of 1.n um.

The etchrates have not yet been calibrated at DTU Danchip. The temperature is 22 degC +/- 1 degC.

H2SO4(10%):H2O2(30%):H2O etch rates, nm/min
Etchant	InP	PQ(1.1)	PQ(1.3)	PQ(1.5)	InGaAs	Contributer
1:1:0 1	<5	<50	230+/-70	1000+/-500	2700+/-1000	Updated 2014-July by Luisa Ottaviano
10:8:71					500	Updated 2014-July by Luisa Ottaviano
10:8:171					180+/-20	Updated 2014-July by Luisa Ottaviano

(1) The etchrates have not yet been calibrated at DTU Danchip.

Concentrated H2SO4

Concentrated H₂SO₄(98%) is used for deoxidation of InP with a very low etch rate in InGaAsP.

H2SO4(98%) etch rates, nm/min
Etchant	InP	PQ(1.1)	PQ(1.3)	PQ(1.5)	InGaAs
H2SO4(98%)	13	?	<1

H3PO4:H2O2:H2O etch

H₃PO₄(85%):H₂O₂(30%):H₂O is a GaAs/AlGaAs-etch which gives a better surface quality than H₂SO₄-based etches.

H3PO4(85%):H2O2(30%):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 degC (no heating during etch). Data is obtained using magnetic stirring with sample on flat basket. (2) Refrigerated H2O used during mixture of etch, and mixture kept at 17 degC during etch. (3) 10:2:30 gives smoother etch than 10:2:60.

BHF, HF etch

BHF etches SiO₂ and partially removes native oxide on InGaAs and InP. Do not use BHF unless you know the dangers involved with this chemical and always use 4H gloves!.

BHF (12.5%), HF etch rates, nm/min
Etchant	SiO2	PECVD2 Si3N4	E-beam Ti 1	Al(x)GaAs, x>0.5, AlAs
BHF (12.5%)	283 2, 175+/-25 3	88 4	90-120
HF:H2O				>10000 5

(1) Ti from Titest.prg on Physimeca. It seems there is no measurable etchig during first 10 seconds.(2) Process SiO2ky2 in PECVD2 (2014-July Luisa Ottaviamo @photonics ). (3) Process STANDARD in PECVD2 (2014-July Luisa Ottaviano @ photonics). (4) Process SINSTD in PECVD2 (2014-July Luisa Ottaviano @ photonics). (5) Appl. Phys. Lett. vol. 51, 2222 (1987).

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 (30%) 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 degC.