HPM / SC-2 Cleaning Chemistry (Standard Clean 2) Storage & Tank Compatibility

Storing HPM / SC-2 Cleaning Chemistry (Standard Clean 2)? Start Here

HPM / SC-2 ("Standard Clean 2," the hydrochloric/peroxide mixture) is the acidic step of the classic RCA wet-clean used to strip metallic and ionic contamination from silicon wafers after the SC-1 step. It is a formulation, not a single compound: a high-dilution blend of deionized water, hydrochloric acid, and hydrogen peroxide, classically mixed near 6:1:1 or 5:1:1 (H₂O : HCl : H₂O₂) and run at roughly 60-75°C. The acid dissolves residual metal ions while the peroxide keeps them oxidized and in solution. Because it pairs a strong chloride-bearing acid with an oxidizer at elevated temperature, materials of construction matter: storage and bath vessels must resist acid and dilute peroxide without corroding or catalyzing peroxide breakdown. The chemistry is benign toward polyethylene, polypropylene, and fluoropolymers, but aggressive toward steel, copper, and aluminum — and even stainless — so non-metallic vessels are the default. Always work from the blended-bath SDS rather than the concentrate component sheets.

Polyethylene (HDPE / XLPE) Compatibility with HPM / SC-2

Verdict: Suitable (S) for storage and ambient handling of dilute SC-2 components. Published polyethylene resistance data rate hydrochloric acid (including ~35-37% concentrate) as excellent for HDPE and rate 30% hydrogen peroxide as little-to-no attack at 20-50°C, so HDPE and XLPE are chemically appropriate for makeup-water, HCl, and dilute-peroxide storage as well as mixed SC-2 holding at ambient temperature. The real constraint is heat, not chemistry: an active SC-2 bath runs at 60-75°C, at or above polyethylene's recommended continuous-service temperature, so the hot recirculating bath itself is normally polypropylene or fluoropolymer (PVDF/PTFE). For poly tanks, specify heavy-wall / high-density resin, keep stored solutions cool, vent for any oxygen evolved by slow peroxide decomposition, and avoid concentrated (>50%) peroxide, which does degrade PE over time. Do not use carbon steel, copper, brass, aluminum, or even 316 stainless anywhere in the wetted path — chlorides plus the oxidizing acid attack metals.

Material compatibility at a glance

A dilute aqueous bath whose dominant compatibility drivers are a strong mineral acid (hydrochloric acid) plus a dilute oxidizer (hydrogen peroxide), with chloride present, at elevated temperature. HDPE/XLPE, polypropylene, and fluoropolymers handle the chemistry well; the practical limit is heat, not chemical attack. Avoid all common metals — carbon steel, copper, brass, and aluminum corrode and decompose the peroxide, and even 316 stainless suffers chloride-driven pitting in this oxidizing-acid environment.

Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.

The safety that actually matters

• Corrosive / severe burns: the hydrochloric acid makes SC-2 strongly acidic — causes severe skin and eye damage; wear chemical goggles, face shield, and acid-resistant gloves.
• Oxidizer: the hydrogen peroxide component may intensify fire and reacts with reducing agents and many metals; keep away from organics, fuels, and combustibles.
• Gas / pressure generation: peroxide decomposes (faster when hot or metal-contaminated), releasing oxygen — never store in sealed/unvented containers; provide pressure relief and venting.
• Respiratory irritant: acid mist and HCl vapor irritate eyes, nose, and lungs; handle with local exhaust or in a fume hood / ventilated wet bench.
• Heat hazard: working baths run near 60-75°C — burn risk and accelerated off-gassing; do not exceed bath temperature limits.
• Metal corrosion / hydrogen risk: contact with metals generates corrosion and can liberate gas; keep the wetted path non-metallic and segregate from incompatible chemicals.

Common questions

Can I store SC-2 / HPM cleaning chemistry in a polyethylene tank?

Yes for storage and ambient handling of the dilute solution and its components — HDPE/XLPE resist concentrated hydrochloric acid and 30% hydrogen peroxide. Use heavy-wall / high-density poly, keep it cool, and vent it for oxygen off-gassing. The hot active bath (60-75°C) is normally run in polypropylene or fluoropolymer instead, because heat, not chemistry, is the limit.

Why can't I use a metal tank for SC-2?

Carbon steel, copper, brass, and aluminum are attacked by the hydrochloric acid and catalytically decompose the hydrogen peroxide, producing heat and oxygen gas. Even 316 stainless is unsuitable here — chlorides combined with an oxidizing acid drive pitting and stress-corrosion cracking. Non-metallic vessels (poly, polypropylene, fluoropolymer) are the safe default.

Is SC-2 flammable?

No — it is a water-based solution with no flash point. However, the hydrogen peroxide makes it an oxidizer that can intensify a fire involving other materials, so keep it away from fuels, solvents, and other combustibles.

Do I need to vent an SC-2 storage tank?

Yes. Hydrogen peroxide slowly decomposes to water and oxygen — faster when warm or contaminated with metals — so any closed vessel can build pressure. Provide adequate venting or pressure relief and never seal it gas-tight.