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Reference · Revision 3 · Helixon Chemicals, Jurong Island

Wet process chemical qualification checklist

What to establish before a new wet chemistry enters your fab, and what to write into the supply agreement so it stays the same afterwards. Print this page to PDF if you want a copy for the qualification file.

1 SEMI grade comparison

SEMI C1 through C12 define the purity tiers for process chemicals. The grade you need follows from your smallest geometry, not from your budget: a metallic contaminant that is harmless at 1.2 µm becomes a killer defect at 28 nm.

Purity limits by SEMI grade
Grade Single trace metal Total trace metals Particles ≥ 0.2 µm Typical application
C1 / Grade 1≤ 10 ppm≤ 100 ppmNot specifiedReagent grade, non-process use
C2 / Grade 2≤ 1 ppm≤ 10 ppmNot specifiedGeneral process, non-critical steps
C3 / Grade 3≤ 100 ppb≤ 1 ppm≤ 200 / mL≥ 1.2 µm geometry
C4 / Grade 4≤ 10 ppb≤ 100 ppb≤ 50 / mL0.8–1.2 µm geometry
C5 / Grade 5≤ 1 ppb≤ 10 ppb≤ 25 / mL0.2–0.8 µm geometry
C7 / Grade 7≤ 500 ppt≤ 5 ppb≤ 15 / mL0.09–0.2 µm geometry
C8 / Grade 8≤ 100 ppt≤ 1 ppb≤ 10 / mLSub-90 nm, 200 mm and 300 mm
C12 / Grade 12≤ 10 ppt≤ 100 ppt≤ 5 / mLAdvanced node, 300 mm front end

Grade numbering is not continuous across every SEMI document, and some chemistries have chemistry-specific tables that override the general tiers. Always cite the specific SEMI standard for the chemistry, not just the grade number.

2 Trace metal limits by process node

The metals that matter most are the ones that diffuse into silicon and degrade gate oxide integrity or minority carrier lifetime. Sodium, potassium, iron, copper and nickel do the most damage per atom.

Working targets for incoming specification
Node Na, K Fe, Ni, Cr Cu Grade to specify
≥ 0.35 µm≤ 50 ppb≤ 50 ppb≤ 20 ppbGrade 4
0.18–0.35 µm≤ 5 ppb≤ 5 ppb≤ 2 ppbGrade 5
90–180 nm≤ 500 ppt≤ 500 ppt≤ 200 pptGrade 7
45–90 nm≤ 100 ppt≤ 100 ppt≤ 50 pptGrade 8
≤ 45 nm≤ 10 ppt≤ 10 ppt≤ 5 pptGrade 12

Treat these as a starting point for discussion with your own process integration team. Copper limits in particular are tightened well below the general trace metal limit in most front-end specs, because copper plates out of solution onto bare silicon.

3 The 31-point supplier qualification checklist

Work through this before the sample lot arrives, not after. Points marked critical have stopped qualifications outright in our experience.

Specification and analysis

  1. critical The supplier has your incoming spec in writing and has confirmed, item by item, which limits they can hold and which they cannot.
  2. The certificate of analysis reports every metal on your spec, not a subset with the rest marked “conforms”.
  3. Analysis is by ICP-MS, and the method detection limit is at least 10× below your tightest limit.
  4. The COA is lot-specific and carries a batch number traceable to a blend record.
  5. The COA names the releasing chemist and the release date.
  6. Anion content is specified where it matters (chloride and sulphate in peroxide and ammonia especially).
  7. Particle counts are reported per mL at the sizes you care about, from the filled container rather than the bulk tank.
  8. Total organic carbon is specified for cleans and rinse chemistries.
  9. Assay tolerance is stated as a range, not a nominal value.

Manufacture and blending

  1. critical You know whether the supplier blends the chemistry or resells someone else’s drum, and who the upstream producer is.
  2. The blending environment cleanliness class is stated and audited.
  3. Point-of-fill filtration rating is stated, and the filter is downstream of every wetted surface.
  4. Filter change frequency and integrity testing are documented.
  5. Wetted materials in the blend train are compatible with the chemistry (no stainless steel anywhere near HF).
  6. Water used in dilution is stated as 18.2 MΩ·cm at point of use.
  7. The blend recipe is under change control and versioned.
  8. Line clearance between chemistries is documented and evidenced.

Packaging and delivery

  1. critical The qualification lot ships in exactly the container you will use in production, from the same container supplier and lot.
  2. Container material, liner and closure are specified by part number, not by description.
  3. Containers are pre-cleaned to a stated standard and the cleaning is certified.
  4. Headspace gas is specified where it matters (N₂ blanket on solvents and developers).
  5. Light protection is specified for peroxide and photosensitive chemistries.
  6. Shelf life is stated from the fill date, and the fill date is on the label.
  7. Transport temperature limits are stated, and excursions are logged.
  8. Labelling meets GHS and carries the UN number, batch and expiry.
  9. The SDS revision is current, in the destination language, and re-issued on any change.

Continuity and recovery

  1. critical A retained sample of every lot is held, and you know for how long.
  2. Second-source or alternate-site capability exists, and you know what re-qualification it would trigger.
  3. Buffer stock volume and location are agreed in writing.
  4. Excursion response time is contractual, with a named escalation contact.
  5. critical Change notification terms are agreed before first production delivery, not after.

4 Container, liner and filtration decisions

Most incoming specs describe the chemistry in detail and the container in a single word. The container is where a qualified chemistry quietly goes out of spec.

Container guidance by chemistry
Chemistry Container / liner Filtration Watch for
HF, BOE, NH4F PFA-lined or high-purity HDPE. Never glass, never stainless. 0.05–0.1 µm PTFE Fluoride attack on any silica-bearing surface; metal pickup from closures
H2O2 Passivated HDPE, vented closure 0.1 µm Decomposition catalysed by trace metals; pressure build-up; stabiliser residue
NH4OH HDPE with vapour-tight closure 0.1 µm Assay drift from ammonia loss through the closure over shelf life
IPA, NMP, PGMEA HDPE or stainless for bulk, N₂ blanket 0.05 µm Water pickup from atmosphere; extractables from the liner
TMAH developer HDPE, opaque, CO₂-excluded 0.1 µm Carbonate formation shifting normality; surfactant adsorption onto the wall
Bulk mineral acids Lined ISO tank or dedicated road tanker At point of transfer Cross-contamination from previous cargo; receiving tank heel

5 Change control clauses worth writing in

A qualification is only as durable as the change control behind it. These five clauses cost nothing to agree at contract stage and are close to impossible to add later.

  1. Notice period

    Ninety days written notice before any change to blend recipe, raw material source, manufacturing site, filtration rating, container, liner or closure. Notice starts when you acknowledge it, not when it is sent.

  2. Requalification lot

    Any notified change is accompanied by a free qualification lot from the changed process, in production packaging, with a full COA.

  3. Last-time buy

    You may place a final order against the pre-change process, sized to cover your qualification period, at the current price.

  4. Retain access

    Retained samples are held for at least 24 months and released to you on request within one business day during an excursion investigation.

  5. Sub-supplier flow-down

    The same notice terms flow down to the upstream producer and the container supplier. A change you were not told about upstream is still a breach downstream.

Want this reviewed against your incoming spec?

Send us the spec and we will mark up which limits we can hold, which need a grade change, and which are tighter than the chemistry can physically support.

Send us your spec