Oxford DRIE-ALE

About

Oxford DRIE-ALE system in Etch Bay 1

Films / Materials: This is an Oxford Instruments PlasmaPro dual-mode system combining deep reactive ion etching (DRIE) and atomic layer etching (ALE) on a single platform. It supports high-aspect-ratio Bosch etching of Si as well as precise, atomic-scale (isotropic/anisotropic) removal of materials such as Si, SiO₂, metals, and III-Vs. It is used for both deep-etch and ultra-precise trimming/smoothing processes in micro- and nanofabrication.

Hardware: Inductively coupled plasma (ICP) source with an independently powered RF table for separate control of ion density and ion energy. Temperature-controlled electrode (variable-temperature / cryo capability) and load lock for fast sample exchange. Includes endpoint detection and gas delivery configured for ALE precursors.

Gases:

• Ar (argon -> physical/sputter component; ALE activation step)
• O₂ (oxygen -> ashing, oxidation, surface modification)
• C₄F₈ (octafluorocyclobutane -> sidewall passivation; Bosch passivation step)
• SF₆ (sulfur hexafluoride -> high-rate Si etching; Bosch etch step)
• BCl₃ (boron trichloride -> chlorine-based etching; ALE of metals/III-Vs, native-oxide removal)
• Cl₂ (chlorine -> etching of III-Vs and metals)
• H₂ (hydrogen -> chemistry modification; III-V and carbon processes)
• N₂O (nitrous oxide -> oxidation / oxide-based chemistries)
• CH₄ (methane -> III-V etching; polymer/passivation chemistries)
• CF₄ (tetrafluoromethane -> fluorine-based etching of SiO₂/Si)
• CHF₃ (trifluoromethane -> selective SiO₂ etching, sidewall passivation)

Etch Properties:

• DRIE mode: high-aspect-ratio anisotropic Si etching via the Bosch process (alternating SF₆ etch / C₄F₈ passivation cycles).
• ALE mode: self-limiting, ~1 nm/cycle material removal via sequential plasma/chemical steps for atomic-scale precision.
• Hybrid processes: deep Bosch etch followed by ALE smoothing of scalloped sidewalls or precise dimensional trimming.
• Excellent process control and uniformity across substrates up to 8 (200 mm).

Applications: Deep Si etching for MEMS and through-silicon vias; atomic-scale smoothing of Bosch-scalloped sidewalls; precise feature-size control for advanced MEMS/photonics; controlled etching of 2D materials, III-Vs, and high-k dielectrics. Not for exposed metals (except Cr); polymers may be used as masks only.

Usage: Load sample via the load lock (pieces on carrier wafers up to 200 mm), select DRIE, ALE, or hybrid recipe, and set parameters based on calibrated etch rates. Use endpoint detection for timed or auto-stop processes. Monitor uniformity and particles post-etch.

Detailed Specifications

• Model: Oxford PlasmaPro DRIE-ALE dual-mode system
• Location: Etch Bay 1
• Substrate size: 4 wafer clamp standard; smaller pieces on carrier wafers; 2''–8'' wafers possible
• ICP Power: (max) 3000 W
• Table RF Power: (max) 300 W (13.56 MHz)
• Table temperature: variable-temperature / cryo capable (confirm range with staff)
• Gases: Ar, O₂, C₄F₈, SF₆, BCl₃, Cl₂, H₂, N₂O, CH₄, CF₄, CHF₃ (max flows per SOP)
• Features: ICP source, load lock, temperature-controlled electrode, endpoint detection and ALE precursor gas delivery

Restrictions and Materials Allowed

Restrictions	Materials Allowed
Polymers allowed only as masks Avoid uncalibrated deep or high-aspect-ratio processes Use only qualified recipes; new processes require staff approval No SiNx, SiO2, III-V materials No exposed metals except Cr (unless ALE metal recipe is qualified — confirm with staff) No deep etching polymers (>1 µm), may be used as a mask only	Si only - other materials may be allowed on a case by case basis

Safety & Emergency

Required PPE: Safety glasses, cleanroom gloves, bunny suit.

Toxic / hazardous gases used: C₄F₈, SF₆, CF₄, CHF₃, BCl₃, Cl₂, H₂, N₂O, CH₄ — fluorine byproducts (HF), corrosive chlorine byproducts (BCl₃/Cl₂), and flammable gases (H₂, CH₄) possible. Do not open chamber if a gas alarm is active.

If the tool alarms or gas cabinet shows red:

1. Press EMO (Emergency Machine Off) — red button on the front panel.
2. Evacuate Etch Bay 1 and notify staff immediately.
3. Call Nanofab staff: Chandan Ramakrishnaiah, +1 (213) 551-6726.
4. After hours / life-threatening: USC DPS (213) 740-4321, or 911.

Gas leak or chemical exposure: Activate bay alarm, exit cleanroom, call DPS.

Chamber vent failure: Do NOT force open. Leave tool and contact staff.

Dry Etcher Comparison

Use this table to help choose the right etching tool for your process.

Feature	Oxford RIE	Oxford DRIE	Oxford DRIE-ALE	Oxford III-V	XeF2 Etcher
Model	PlasmaPro 80 RIE	Oxford System 100 DRIE	Oxford DRIE + ALE	PlasmaPro 100 Cobra	Custom built (Armani group)
Location	Etch Bay 1	Etch Bay 1	Etch Bay 1	Etch Bay 1	Deposition Bay 1
Substrate Size	Up to 200 mm (8")	Up to 4" clamp; 2", 3", 4", 6", 8" possible	Up to 4" clamp; 2", 3", 4", 6", 8" possible	Up to 4" clamp; 2", 3", 4", 6", 8" possible	Up to 6"
Etch Type	RIE (capacitively coupled)	DRIE / Bosch (ICP)	DRIE + Atomic Layer Etch	ICP-RIE (cryo capable)	Isotropic chemical etch
Table RF Power	300 W max	300 W max	300 W max	1500 W max	N/A
ICP Power	None (RIE only)	3000 W max	3000 W max	1500 W max	N/A
Table Temperature	20°C	20°C	-120°C to 200°C allowed (-150°C to 400°C max)	-120°C to 200°C allowed (-150°C to 400°C max)	20°C
Gases	Ar, O₂, CF₄, CHF₃, SF₆	Ar, O₂, CF₄, CHF₃, SF₆, C₄F₈	Ar, O₂, C₄F₈, SF₆, BCl₃, Cl₂, H₂, N₂O, CH₄, CF₄, CHF₃	Ar, O₂, SF₆, CH₄, H₂, Cl₂, BCl₃, SiCl₄	XeF₂ (crystal source)
Allowed Materials	Si, SiO₂, Si₃N₄, oxide/nitride masks, Cr	Si, SiO₂, SiN, Parylene, Polyimide, LiNbO₃, BCB	InP, InAs, GaN, AlGaAs, GaAs, InGaAsP, ITO, Si, SiC, MoS₂, WSe, Graphene	InP, InAs, GaN, AlGaAs, GaAs, InGaAsP, ITO, Si, SiC, MoS₂, WSe, Graphene	Si only
Disallowed	No metals except Cr; no deep polymer >1 µm	No exposed metals except Cr	No metals except Cr; no deep polymer >1 µm	No metals except Cr; no deep polymer >1 µm	None listed
Endpoint Detection	Optical (LEM G50)	Not Available	TBD	Optical (LEM G50)	Not Available
Best For	Dielectric etching, passivation removal, via openings, resist descum	Deep Si etching, high-aspect-ratio structures, Bosch process	Precise atomic-layer-level etch control	III-V semiconductors, exotic/compound materials, cryo etching	Fast isotropic Si etching, high selectivity
Status	Operational	Operational	Operational	Operational	Operational
SOP	SOP	SOP	TBD	SOP	SOP

Documentation

• SOP – contact lab staff (in preparation)
• Training video – contact lab staff
• Training required – contact lab staff (Donghai Zhu) Request form

Recipes & Data

• See the Dry etching recipes page for DRIE and ALE recipes (Bosch Si etch, ALE cycles for Si, SiO₂, metals, and III-Vs)
• Process control and calibration data – contact lab staff

Troubleshooting

Plasma won't ignite

Check gas flows are stable, pressure is in range, and the ICP/RF matching networks are tuned.

Etch rate or ALE cycle rate drifting

Chamber may need conditioning. Run a clean/season recipe and re-check calibration.

Endpoint detector not triggering

Verify the detector is on, optics are clean, and the correct wavelength is selected.

Chamber pressure won't drop

Possible vacuum leak or pump issue. Stop process, notify staff.

Acknowledgment

If results from this tool appear in a publication, please acknowledge the facility:

"This work was performed in part at the USC Nanofab at the University of Southern California, Michelson Center for Convergent Bioscience."

Please also email the citation to chandanr@usc.edu so we can track facility output.