On 300 mm leading-edge logic lines where cobalt is introduced as capping and liner metal to replace TiN in certain damascene levels, wet etch processing between barrier chemical mechanical planarization and dielectric cap deposition comprises at least three steps: copper seed residue micro-etch, TiN barrier trims or post-CMP pull-down, and cobalt capping layer removal from dielectric field areas. The etchants employed are supplied as electronic-grade blends under the same cleanroom metrology rigour as the dielectric etch units, with certificates of analysis referencing SEMI C7 for sulfuric acid, SEMI C8 for hydrogen peroxide, SEMI C9 for nitric acid, and SEMI C14 for ammonium hydroxide, while ultrapure water conforms to ASTM D5127-13(2018) Type E-1 limits and the wet bench operates inside ISO 14644-1:2015 Clause 5 Class 3 laminar flow. A representative copper seed etch formulation is composed of sulfuric acid 5–15 wt%, hydrogen peroxide 1–3 wt%, an azole-based corrosion inhibitor at 0.1–0.5 wt%, and water balance at 28–35°C, yielding etch rates of 0.3–0.8 µm/min on electroplated copper without roughening the underlying dielectric. TiN barrier removal after copper seed etch uses an ammonia-peroxide mixture NH4OH:H2O2:H2O at a volumetric ratio of 1:1:5 at 60–70°C in a recirculated quartz-lined single-wafer spray tool, where the oxy-nitride surface is converted and lifted in 5–20 s, depending on TiN thickness and prior sputter composition. Cobalt capping layer micro-etch is normally performed with hydrogen peroxide and citric acid at a mass ratio of 1:4 in DI water, adjusted to pH 3.5–4.5 with ammonia, at 40–50°C; the etch removes 2–5 nm of Co from field areas while the damascene copper surface remains protected by the azole inhibitor. On production equipment, the principal failure modes are copper pitting when the azole concentration is below 0.1 wt%, TiN particle redeposition when bath life exceeds 8 h or when the peroxide fraction drops below 1 wt%, and galvanic Cu-Co undercut at pH less than 3. End-product types from this etch sequence include high-volume logic SoC wafers, server CPU dies, and advanced-node AI accelerator devices.

What Governs Selective TiN Removal Without Undercutting W in Middle-of-Line Contact Etch?

The selectivity window for TiN removal over tungsten in ammonia-peroxide chemistry is governed by temperature, active peroxide content, and the generated perhydroxyl species concentration at pH 9.0–9.8. A representative production bath blends 29 wt% ammonium hydroxide, 30 wt% hydrogen peroxide, and ultrapure water in a volumetric ratio of 1:1:5 and holds the liquid at 60–70°C in a quartz-lined recirculation tank; under these conditions, TiN etch rate on physical vapour deposited films is 10–30 nm/min, whereas tungsten etch rate remains below 2 nm/min, giving a selectivity ratio of approximately 10:1 to 15:1. The peroxide active fraction is the most unstable process variable because decomposition to oxygen and water shifts the bath pH upward and raises the tungsten undercut rate at the plug-dielectric interface; on static baths without continuous sparging, the TiN-to-W selectivity falls below 5:1 after 6 h, making bath age a specified limit in production recipes. When cobalt liner films are present at the contact bottom, the etch is followed by a dilute hydrogen peroxide/citric acid step at pH 4.0–4.5 to remove 1–3 nm of oxidised cobalt without over-etching the tungsten plug; this two-stage sequence is run sequentially in the same single-wafer spray tool with an intermediate DI water rinse conforming to ASTM D5127-13(2018) Type E-1. Compliance is anchored to SEMI C8 for hydrogen peroxide, SEMI C14 for ammonium hydroxide, SEMI C7 for sulfuric acid used in upstream cleaning, and ISO 14644-1:2015 Clause 5 Class 3 cleanroom conditions; waste collection is segregated for peroxide-bearing ammonia streams because exothermic decomposition in closed piping can exceed 80°C adiabatic limit. The downstream manufacturing process is integrated between contact dielectric etch and tungsten fill, specifically a wet pull-back/clean before PVD Ti/TiN liner deposition or after W CMP to de-passivate the semiconductor surface. Terminal product types are embedded DRAM logic dies, NAND peripheral CMOS wafers, and silicon interposers for advanced packaging where TiN/W contacts are integrated with TSV structures.

When Aluminium Alloy Interconnect Etching Is Run on Legacy 200 mm CMOS Lines

Phosphoric-nitric-acetic etch baths operating at 40–50°C are used for wet patterning of aluminium-copper alloys at 0.35 µm to 0.18 µm trailing nodes, where the Al etch step must produce clean sidewalls with no exposed copper-rich precipitates. The standard formulation contains phosphoric acid at 70–80 wt%, nitric acid at 2–5 wt%, acetic acid at 5–10 wt%, and DI water balance; the nitric acid oxidises aluminium to Al2O3, the phosphoric acid dissolves the oxide, and acetic acid buffers the attack to reduce silicon and aluminium-copper galvanic effects. Etch rate on Al-0.5%Cu films is typically 200–500 nm/min at 42°C, with a ±2°C control band because the apparent activation energy is around 0.5 eV and higher temperatures cause photoresist lifting. Production equipment is a fully automated spray etcher with online refractive index endpoint detection and quick dump rinse, followed by 10 min DI water overflow rinse; an etch uniformity of ±5% across a 200 mm wafer is maintained by nozzle array sweeping at 0.3 m/s surface velocity. Compliance records cite SEMI C11 phosphoric acid, SEMI C9 nitric acid, SEMI C10 acetic acid, REACH (EC) No 1907/2006, and RoHS Directive 2011/65/EU for the Al-bearing integrated circuit scrap stream; the wet bench environment conforms to ISO 14644-1:2015 Clause 5 Class 4. A key operational boundary is that aluminium alloys with copper greater than 2 wt% are not processed in the same bath because Cu2+ accumulation accelerates pitting and reduces selectivity to the TiN underlayer; the bath is replaced when Al3+ concentration exceeds 0.5 mol/L or viscosity increases by more than 10% from baseline. Terminal product types include automotive microcontrollers, analogue power management ICs, and MEMS micro-mirror arrays fabricated on 200 mm aluminium-interconnect flows.

Where SiGe sacrificial layers are released from MEMS inertial sensor structures, the wet chemistry must discriminate against silicon device features, buried oxide, and metallised electrodes, and this requirement pushes the etchant toward ternary mixtures in which the oxidant-to-HF ratio controls the Si/Ge selectivity gate. For germanium substrate thinning or mesa isolation in infrared optics, documented HNO3:HF:H2O volumetric ranges of 3:1:2 to 4:1:5 are circulated in a chilled polypropylene etch bath at 10–20°C, producing germanium removal at 0.5–1.2 µm/min; dilution with acetic acid instead of water shifts the surface from rough pit formation to smooth chemical polishing and lowers the exotherm. SiGe sacrificial etchant blends commonly combine HF, H2O2, and CH3COOH at volumetric ratios between 1:6:3 and 1:10:5, at 25–35°C, with etch rates on Si0.7Ge0.3 of 0.05–0.15 µm/min; selectivity to silicon is controlled by the HF activity, and the bath must be rechilled every 2 h when run in high-throughput cassette-to-cassette tools. Published data for the selectivity of HF-H2O2-CH3COOH blends on strained SiGe at germanium fractions above 25 at% remains sparse; qualified lines use silicon carrier coupons with patterned SiGe test keys to re-validate the etch budget after each bath change. Electronic-grade compliance for these baths requires SEMI C15 hydrofluoric acid, SEMI C9 nitric acid, SEMI C10 acetic acid, and ASTM D5127-13(2018) DI water; the etch tool is installed under ISO 14644-1:2015 Clause 5 Class 4 positive pressure with local exhaust capturing HF vapours at 0.5 m/s face velocity. Downstream production is typically a three-step wet process: solvent pre-clean, controlled immersion etch with ultrasonic agitation at 40 kHz in the SiGe etchant, and a quick dump rinse in a nitrogen-sparged DI water tank to prevent water-mark formation. The terminal products are MEMS inertial measurement units, SiGe-based bolometer arrays, and germanium window blanks for uncooled thermal imaging modules.

Ceric Ammonium Nitrate Photomask Blank Etching With Sub-50 nm Critical Dimension Uniformity

Chromium films on 6025 quartz photomask blanks are wet-patterned with ceric ammonium nitrate formulations because the resultant etching is isotropic enough for mask CD correction but sufficiently controllable when bath temperature, ceric ammonium nitrate concentration, and acid stabiliser are monitored. A representative bath contains ceric ammonium nitrate at 200–300 g/L, acetic acid at 2–5 vol%, and DI water balance, held at 18–22°C in a chilled quartz vessel with continuous filtration through 0.1 µm PTFE membranes; etch rate on sputtered chromium is 60–100 nm/min, and critical dimension uniformity across a 152 mm square mask is maintained below 3 nm 3σ when the etchant is delivered through a spin-spray nozzle array at 0.2–0.4 MPa. The process sequence is resist develop, descum, chromium wet etch, quick dump rinse, final DI water rinse per ASTM D5127-13(2018), and spin dry under nitrogen; endpoint is detected by reflectivity drop at 550 nm with an abort window of ±0.5 s to prevent chromium line widening. Compliance for the etchant raw materials references SEMI C9 nitric acid where nitric acid-based preclean is used, REACH (EC) No 1907/2006, and RoHS Directive 2011/65/EU for the final photomask article; the production room is ISO 14644-1:2015 Clause 5 Class 5 and the etch tool has local extraction at 0.5 m/s face velocity. A process boundary is that ceric ammonium nitrate baths degrade by autoreduction at temperatures above 30°C, forming cerous precipitates that redeposit as defects on chromium edges; sodium contamination must be controlled below 1 ppb because mobile alkali species compromise mask blank flatband stability. The terminal products are binary chromium-on-quartz photomasks for 248 nm and 193 nm lithography, and chromium hard masks for advanced packaging interposer lithography.

Sequentially after seed sputtering in wafer-level redistribution-layer lines, the wet etch path for Cu, Ni, and Au metallization is split across three dedicated quartz-lined modules to avoid cross-contamination. The copper seed etchant uses sulfuric acid 10–15 wt%, hydrogen peroxide 1–5 wt%, benzotriazole 0.1–0.3 wt%, and water balance at 30–40°C, with an etch rate of 0.4–1.0 µm/min on electroplated copper; the benzotriazole inhibitor suppresses cuprous oxide formation and reduces undercut at the resist edge to less than 0.5 µm per side. For the nickel layer beneath solder bumps, a nitric-phosphoric etchant containing HNO3 10–20 wt%, H3PO4 2–5 wt%, and water balance at 35–45°C removes Ni at 0.2–0.6 µm/min without attacking exposed Cu, provided the phosphoric acid ratio is maintained above 2 wt%. Gold films in the same bump metallization stack are etched with an iodine-potassium iodide solution at pH 7–8, containing I2 2–5 wt% and KI 10–20 wt%, at 45–55°C; the etch rate is typically 0.5–1.5 µm/min on evaporated or sputtered gold, and the neutral pH preserves copper and nickel layers underneath. Electronic-grade material controls align with SEMI C7 sulfuric acid, SEMI C8 hydrogen peroxide, SEMI C11 phosphoric acid, SEMI C9 nitric acid, REACH (EC) No 1907/2006, and RoHS Directive 2011/65/EU; the packaging wet bench operates inside ISO 14644-1:2015 Clause 5 Class 5 cleanroom with DI water per ASTM D5127-13(2018). Production equipment is usually a spin-spray processor with peristaltic dosing, integrated endpoint detection via open-circuit potential shift, and segregated acid/iodine waste manifolds; a key bottleneck on high-volume lines is the gold etch module because KI crystallisation at nozzle tips below 20°C requires heated recirculation lines at 40°C. Terminal product types include wafer-level chip-scale packages, flip-chip redistribution layers, and gold-bumped MEMS capping wafers.