Wet electronic chemicals do the cleaning, etching and residue removal that no dry process can fully replace. They are consumed in large volumes, they touch the wafer surface directly at the most defect-sensitive points in the flow, and contamination introduced by a chemical is often not visible until electrical test. This guide covers the grade framework, the process to chemistry mapping and the verification steps that matter when sourcing from China.
The SEMI grade framework
Wet chemicals are graded by the maximum metallic impurity level rather than by assay, because it is trace metal contamination that kills devices, not a one percent assay difference. The industry reference is the SEMI Chemical Grade series, which runs from Grade 1 for general industrial use to Grade 5 for the most advanced nodes. As a rough guide, Grade 1 tolerates metals in the parts per million range, Grade 2 and 3 move into the high parts per billion, and Grade 4 and Grade 5 require low parts per trillion for critical elements such as iron, copper, sodium and potassium. Always specify against the SEMI document for the specific chemical, because the grade names alone do not fix every element.
Process to chemistry mapping
Particle and organic removal
SC-1, also called APM, is a mixture of ammonium hydroxide, hydrogen peroxide and water. It removes particles and organics by slowly etching the surface and lifting contamination away. It is the workhorse clean in front-end wafer processing.
Metal removal
SC-2, or HPM, uses hydrochloric acid, hydrogen peroxide and water to remove metallic contamination, particularly the noble and heavy metals that SC-1 does not fully address.
Photoresist and residue stripping
SPM, the sulfuric acid and hydrogen peroxide mixture often called piranha, strips photoresist and heavy organics. NMP, PGMEA and other solvents handle specific polymer and residue removal, and dedicated strippers are formulated for post-etch and post-implant residues that piranha cannot reach.
Oxide etching
Dilute hydrofluoric acid removes native and chemical oxide. Buffered oxide etchant, BOE, mixes HF with ammonium fluoride to hold a stable etch rate and higher selectivity to photoresist, which matters when the mask must survive the etch.
Photolithography developers and ancillary chemistry
TMAH, tetramethylammonium hydroxide, is the standard metal-ion-free developer for positive photoresist, supplied at a controlled normality. Isopropyl alcohol is used as a drying and surface preparation solvent, and electronic grade sulfuric, nitric, phosphoric and hydrochloric acids are used across cleaning, etching and analytical preparation.
Specification axes
1. Assay and normality
For a developer or an etchant the concentration sets the process result, so specify the assay with a tolerance, for example TMAH at 2.38 percent by weight plus or minus a narrow band, and require the supplier to report the actual measured value per lot rather than a nominal figure.
2. Metallic impurity profile
Require a per element maximum, measured by ICP-MS, for at least iron, copper, sodium, potassium, calcium, aluminium and zinc. A single total metals number hides the elements that matter most for a given step, particularly copper and iron which are strong lifetime killers in silicon.
3. Particle contamination
Particle limits are given as counts above a size threshold, commonly 0.5 micrometre for general grades and 0.2 micrometre or below for advanced grades, per millilitre. Since these chemicals are used to remove particles, adding them is self defeating, so this specification is non-negotiable.
4. Moisture and water content
For organic solvents such as IPA and NMP, water content is a real specification, because absorbed moisture changes drying behaviour and can hydrolyse process residues. Require a maximum water figure measured by Karl Fischer titration.
5. Appearance and colour
Colour and turbidity are quick indicators of organic or particulate contamination and are worth writing into the specification as a receiving check even when the numerical limits pass.
Packaging and storage
- PFA bottles and PFA lined drums for the highest grade chemicals, because glass and untreated plastic leach metals and particles into the product.
- High density polyethylene drums for general grades, in 25 litre, 200 litre and larger formats.
- ISO tanks and bulk road tankers for very high volume acids, specified with the same impurity limits as packaged product.
- Nitrogen blanketing where the chemical is sensitive to air, and opaque or light blocking containers for hydrogen peroxide, which decomposes on exposure to light and heat.
Storage life is a specification too. Hydrogen peroxide and peroxide containing mixtures lose concentration over time and must be rotated on a first in first out basis with a defined maximum storage period. Confirm the shelf life and the storage temperature range for every product, and confirm that the shipping container is compatible with the chemical over that period.
Analysis and documentation
Ask for a certificate of analysis per lot that states the measured value, the unit and the analytical method for each parameter. The relevant methods are ICP-MS for metals, ion chromatography for anions and trace ionic contamination, a liquid particle counter for particles, and Karl Fischer titration for water. A supplier whose certificate lists only assay and colour is not proving an electronic grade claim.
Verification steps before you commit
- Request a sample and analyse it independently against your specification before qualifying a supplier for production volumes.
- Confirm the packaging material and require the supplier to state the container resin and any liner, since packaging can add more contamination than the chemical started with.
- Check lot to lot consistency over several lots, not just the qualification sample.
- Verify the transport and storage chain from fill to your site, including whether the product was temperature controlled or exposed to sunlight.
- Agree a retention sample period so that a contamination event can be traced to a specific lot.
Common sourcing mistakes
- Buying on assay alone and ignoring the metal and particle profile, which is what the grade actually describes.
- Accepting a single total metals figure instead of a per element specification.
- Overlooking packaging. A high grade chemical in the wrong container arrives contaminated.
- Forgetting shelf life, then using off-spec hydrogen peroxide that has been in the warehouse for a year.
- Assuming a developer concentration is correct because it says 2.38 percent, without requiring a per lot measured value.
Sourcing wet electronic chemicals from Hunan and China
China has built substantial domestic capacity across electronic grade acids, solvents and developers, supported by a large base chemistry industry and by the ongoing shift of wafer manufacturing into the region. Hunan hosts electronic chemicals and semiconductor materials suppliers serving both domestic fabs and export customers, backed by the province advanced materials base. LiiFoo maintains verified supplier profiles in the cutting-edge materials cluster with documented grade capability.
For specification matched quotes, qualification samples or a container compatibility review, see the cluster above or contact our sourcing team.
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