Specific Process Knowledge/Etch/III-V RIE/III V RIE ETCHES

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CHF3/O2 etch

A plasma with a gas mixture of CHF₃ and O₂ is used to etch SiO₂ and Si₃N₄ dielectricas; flour radicals are responsible for etching the dielectrica while oxygen removes the polymer that is formed during the etch. The polymer deposition rate and SiO₂ etch rate are very sensitive to the flow ratio of CHF₃ and O₂ . The current processes have been optimized from this point of view.

There are 3 standard programs:

CHF3/O2 etch rates, nm/min
Process Name	Process parameters	SiO2	Si3N4	AZ5206	ZEP520A	Negative DUV: UVN 2030-0.5	Comments/links
SiO2_602	CHF3-flow: 16 sccm, O2-flow: 2 sccm, Power = 60 W, Vbias = 325 V, Process pressure = 100 mTorr	30{(1)}		29{(2)}	36{(3)}
High selectivity to resist	CHF3-flow: 17 sccm, O2-flow: 0 sccm, Power = 150 W, Vbias = ? V, Process pressure = 150 mTorr	85				10.6	Done dec2019/jan2020 by Qugig@nanolab and bghe@nanolab
Lower etch rate, medium selectivity to resist	CHF3-flow: 17 sccm, O2-flow: 0 sccm, Power = 100 W, Vbias = ? V, Process pressure = 20 mTorr	49-62 (depending on conditioning)			~12		Done dec2019/jan2020 by Qugig@nanolab and bghe@nanolab Images and reproducibility
Si3N4Ti	CHF3-flow: 16 sccm, O2-flow: 2 sccm, Power = 23? W, Vbias = ? V, Process pressure = ? mTorr		38

(1) Measured with laser reflectometry 106 (?) nm on G360 fully etched after 3:30: 05-10-11 (2) From Dektak measurement on G360 2005-10-11 (3) From Dektak measurement on D002 (I & II) 2005-10-12. D002 is a pure InP-wafer. (4) Etch rate measured on 140nm wide holes

CH4/H2 etch

This plasma etch is used for etch of InP and InGaAs(P).

In order to ensure unchanged etching conditions during etch, the chamber needs to be primed before using this etch. There are 2 priming programs, clecond and precond. Clecond also cleans the chamber with Oxygen before priming it.

There are 2 standard etch programs for etching InP, InGaAs and InGaAsP: InPstd is for InP-etch while InGaAs1 is for InGaAs- and InGaAsP-etch.

The etch-rates for the CH₄ / H₂ etch depends highly on the total etching area and on the size of the structrures that are etched, eg ridges or small holes. All rates are given for a total etch area of 2 inches and for etching of ridges, if not otherwise commented. Dektak has been used for the measurement if nothing else is mentioned.

CH4/H2 etch rates, nm/min
Process Name	Process parameters	InP	InGaAs	GaAs	AlAs	SiO2
InPstd	CH4-flow: 8.4 sccm, H2-flow: 42 sccm, Power = 60 W, Vbias = 450 V, Process pressure = 80 mTorr, Base pressure = 0.01 mTorr	29	9			1
InGaAs1	CH4-flow: 8.4 sccm, H2-flow: 42 sccm, Power = 60 W, Vbias = 450 V, Process pressure = 80 mTorr, Base pressure = 0.01 mTorr	29	9

BCB polymer and Resist etch

The BCB-etch is mainly a O₂ etch but a small amount of CHF₃ is added to remove Si. There are 3 standard processes: BCB_LP and BCB30LP are low pressure (anisotropic) medium power etches for planarization of BCB, while BCB100W is a high power etch to totally remove thick layers of BCB.

Other resists (ZEP520A, AZ-resists) can be etched by a O₂ etch. The standard program is called ASH?m, where the process time is optional.

O2/CHF3 etch rates, nm/min
Process Name	Process parameters	BCB	SiO2	AZ5214
BCB_LP	CHF3-flow: 3 sccm, O2-flow: 12 sccm, Power = 30 W, Vbias = 220 V, Process pressure = 10 mTorr	70 +/- ?	6 +/- ?
BCB30LP	CHF3-flow: 6 sccm, O2-flow: 24 sccm, Power = 30 W, Process pressure = 10 mTorr	127
BCB100W	CHF3-flow: 10 sccm, O2-flow: 42 sccm, Power = 100 W, Vbias = ~540 V, Process pressure = 100 mTorr	880		815

O2/ etch rates, nm/min
Process Name	Process parameters	BCB	ZEP520A	AZ5214	SiO2
ASH?m	O2-flow: 50 sccm, Power = 20 W, Vbias = ~170 V, Process pressure = 150 mTorr	?	98	70	6 +/- ?

Chamber Cleaning

Cleaning of the chamber is very important to achieve reproducible etch results. After every etch the chamber should be cleaned. For most CHF₃/O₂ etch programs a simple clean procedure is sufficient. When BCB has been etched one must use cleanbcb, where CHF₃ is added. If CH₄ is used in the process (all programs etching III-V compounds) a vlclean procedure is necessary.

Cleaning programs
Process Name	O2-flow (sccm)	Pressure (mTorr)	Power (W)	Vbias (V)	Time (min)
clean	50				10
Lclean	50				20
vlclean	50				30
cleanbcb	50	100	100		10