ALNi/Cu/SiGe/Co/W/TiN/Au/Cr/Ge Etchant Electronic/EL Grade is supplied as a matched wet-etch product suite for sequential removal of aluminium, nickel, copper, silicon-germanium, cobalt, tungsten, titanium nitride, gold, chromium, and germanium thin films in failure analysis, deprocessing, and lithographic rework. The designation is the product model in the current datasheet; no separate model number is assigned. The product is not a single universal immersion bath, because no single wet chemistry maintains certified selectivity across copper, titanium nitride, and germanium simultaneously. Electronic/EL Grade imposes lot-specific trace-metal limits, sub-0.2 μm filtration, and particle-controlled filling. Typical cationic impurity release limits for the aqueous base media are ≤10 ppb each for sodium, potassium, iron, nickel, copper, and zinc, and ≤5 ppb for chromium, cobalt, gold, and germanium. Assay is by potentiometric titration against certified reference materials, and pH is reported at 25 °C. The product is supplied in PFA or HDPE containers with N₂ purge connections; package sizes are 1 L, 4 L, 20 L, and 200 L. Filling is performed in an ISO 14644-1:2015 Class 5 cleanroom, and the quality system is certified to ISO 9001:2015. For regulatory classification, the safety data sheet follows EC 1907/2006 REACH and EC 1272/2008 CLP. The product is intended for qualified wet benches; manual use without local exhaust ventilation is outside the specified operational envelope.

Critical Trace-Metal Limits for Electronic/EL Grade Packaging

Electronic/EL Grade differs from technical-grade commodity etchants in that each cation is controlled individually. Production lots are sampled after final filtration and analysed by inductively coupled plasma mass spectrometry. The release limit for sodium and potassium is set at ≤10 ppb; these ions are mobile in oxide films and alter capacitance-voltage characteristics in test structures. Iron and nickel are limited to ≤10 ppb because they promote galvanic corrosion on Cu/Al interfaces. Copper, zinc, and aluminium are limited to ≤10 ppb to avoid precipitation and re-deposition during bath aging. Particle counts at release are typically ≤100 particles/mL at 0.2 μm and ≤5 particles/mL at 0.5 μm, measured with a liquid-borne laser particle counter. The product is filtered immediately before filling and does not require additional filtration at point of use if the wet bench has a 0.1 μm point-of-dispense filter. Packaging includes fluoropolymer contact surfaces and N₂ blanketing to reduce CO₂ uptake and peroxide decomposition. Actual lot values are printed on the certificate of analysis; the certificate includes the ion chromatograph profile and the particle-count data for that specific fill lot.

In the aluminium etch component, phosphoric-acetic-nitric chemistry at 35–45 °C removes Al and Al–Cu(0.5–2 wt%) films at 50–150 nm/min. Acetic acid buffers the bath and reduces HNO₃ volatilisation, but the same bath actively attacks nickel and cobalt; therefore Al/Ni and Al/Co bilayers require masked or two-step processing. Copper etching is isolated from aluminium because cupric chloride and ferric chloride baths leave CuCl residues on aluminium pads and can etch Al non-uniformly. For a 40 L recirculating quartz immersion bath, the copper etch rate is maintained by oxidation-reduction potential with a ±10 mV control band; excursions beyond this range change etch rate by more than 12% in 200 mm wafer handling. On a single-wafer spray processor, a flow rate of 1–2 L/min and wafer rotation of 300 rpm produce edge-to-center nonuniformity below 5% for 200 mm substrates; if rotation drops below 200 rpm, center etch rate can fall by 8% because of boundary-layer build-up. The product data for the mixed Al/Cu stack is not guaranteed; users must qualify etch rates on the specific film stack and passivation residues before production use.

What Process Conditions Prevent Undercut When TiN, W, and Co Are Exposed Simultaneously?

TiN, W, and Co coexist in contact and local-interconnect stacks, and their etch selectivity is sensitive to pH, temperature, and oxidiser concentration. The product separates TiN/W etching from Co etching to avoid Co(OH)₂ formation. The TiN/W bath uses alkaline hydrogen peroxide chemistry at 50–60 °C; typical TiN etch rates range from 3–30 nm/min depending on film stoichiometry, while W etches at 5–20 nm/min. The TiN:W etch-rate ratio is maintained near 1.5:1 by controlling the NH₄OH/H₂O₂/H₂O volume ratio. In a 200 mm immersion wet bench with temperature control of ±2 °C, W etch rate changes by approximately 7%/°C; the permitted thermal drift is therefore ±1.5 °C for a ±10% etch-rate variation window. Co is etched separately in an acidic chelating bath; the acidic bath must not be mixed with the alkaline TiN/W bath because exothermic neutralisation generates mist and can release ammonia. When Co test structures are processed, the bath replacement criterion is a 15% loss of initial etch rate or a pH shift of 0.3 pH units. Failure to control these limits results in undercut at the TiN/W interface and non-uniform Co removal at wafer edge. Published data for the exact TiN/W/Co mixed configuration is limited, so pilot-scale qualification is required before high-volume use.

For gold and chromium adhesion layers, the suite provides an iodide-based gold etch and a ceric ammonium nitrate/nitric acid chromium etch. Gold films of 100 nm thickness are removed at 10–25 nm/min at 25 °C, with chromium attack below 1 nm/min. Chromium, in contrast, etches at 25–60 nm/min at 25 °C and does not etch gold at measurable rates. Cr/Au multilayer processing is sequential because a single bath cannot offer high selectivity to both metals simultaneously. The gold bath is monitored by four-point probe sheet resistance on a 100 nm Au film and is replaced after 20% loss of initial etch rate or after 72 h bath age, whichever occurs first. In failure analysis laboratories using manual immersion, local exhaust ventilation is required for ceric ammonium nitrate etch baths due to NOx release. The product is also used for lift-off rework; the etch rate on 300 nm Au lines may be slightly higher because of local bath agitation, so endpoint detection by sheet-resistance or optical inspection is recommended.

When SiGe and Ge Films Are Processed in Oxidizing Fluoride Media

Silicon-germanium and germanium components require fluoride-based oxidizing baths, and the etch rate is a function of Ge content and pH. At 25 °C, SiGe films with 20–30 at% Ge typically etch at 80–200 nm/min, while pure Ge etches at 150–350 nm/min. The processing window is narrow: pH must be controlled within ±0.5 pH units, or silicon pitting occurs at one window edge and incomplete Ge removal occurs at the other. Higher Ge content increases etch rate but reduces selectivity to underlying silicon, so a separate selectivity qualification is required for Ge-rich films above 30 at% Ge. The bath is supplied with separate H₂O₂ and fluoride-containing components where site restrictions require final HF concentration ≤0.5 wt%. Wet-deck equipment must have point-of-use HF sensors and scrubbed exhaust; under reducing conditions, germanium hydride by-products may be generated, so oxidiser concentration is maintained above the stoichiometric minimum. In production-scale use, etch-rate drift of 10% is used as the bath replacement criterion. The temperature control limit is ±2 °C from setpoint; this corresponds to etch-rate variation of approximately 4–6% depending on Ge fraction.

Compared with commodity single-metal etchants and off-the-shelf acid mixtures, this product differs in certification, packaging, and process control. Commodity etchants may be produced from technical-grade raw materials with sodium and iron above 100 ppb, and their particle counts are often not specified; such baths can introduce mobile-ion contamination and inconsistent etch initiation on TiN or Au surfaces. The Electronic/EL Grade product specifies trace-metal limits for the full element set Al, Ni, Cu, Si, Ge, Co, W, Ti, Au, Cr. Another difference is the use of fluoropolymer contact surfaces and N₂ blanket; commodity products are frequently packaged in non-dedicated containers that can leach zinc or calcium. Plasma dry etching is capable of anisotropic sub-micron patterning, but for failure analysis deprocessing and blanket film removal, wet etching reduces ion damage and allows uniform removal across large die. This product is not a replacement for reactive-ion etching when sidewall profile control is critical; wet chemistry is isotropic and undercuts masked features.

On a recirculating wet bench, the most frequent production failure is not etch-rate drift but particulate accumulation at the wafer edge from aged gold or chromium baths. In deprocessing lines using a 40 L quartz tank and 0.1 μm point-of-use filter, edge defect density can increase when the gold bath is used beyond 72 h despite acceptable sheet-resistance endpoint control; the root cause is colloidal iodide degradation products. The corrective action is replacement based on bath age, not endpoint only. A similar failure mode occurs when the copper bath is manually overdosed with acid to compensate for drag-out; ORP control is preferred over operator-dependent titration.

Operational Boundaries and Incompatibility Limits

The product must be stored at 10–25 °C in original containers and protected from ultraviolet light. Do not mix the aluminium etch component with acetone, isopropanol, or other organic solvents; oxidising acids can react exothermically with organics. Avoid combination with amine-based additives because amines alter metal complexation and may cause premature redox reactions in the copper and gold baths. The alkaline TiN/W bath must be segregated from acidic components to prevent neutralisation exotherm and mist generation. Shelf life for unopened containers is 12 months; after opening, use within 30 days under inert gas or after revalidation of pH and particle count. Waste segregation is required for fluoride, chromium, and gold baths. The product is not suitable for biomedical staining, electroplating additives, or non-electronics applications. Users must verify compatibility with wafer backside films and plating residues; published data for the full mixed stack is limited.