SiC and GaN Wafer Fabrication Wastewater: The Treatment Process From Grinding Slurry to Final Polish

Wide-bandgap fabs are rougher on water than the legacy silicon lines they replaced. Silicon wafering is a mature, predictable process; silicon carbide wafering is closer to a stone-cutting operation, and GaN epitaxy adds an ammonia load that silicon never had. The result is an effluent with four personalities at once: abrasive solids that settle like flour, dissolved fluoride and ammonia, metal traces from slurries and plating, and a persistent organic fraction from photoresist and cleaning chemistry. Treating that in one mixed tank produces a plant that meets no parameter well. The fabs that hold their consent numbers do the unglamorous thing first — they split the streams — and then size each route on the worst hour of the week, not the average day.

Where the Water Gets Loaded

Crystal growth is the quiet contributor. SiC boules come out of physical vapour transport furnaces and the associated cooling and scrubber water carries only a light load, but it is warm and continuous and it sizes the utility water balance.

Slicing and wafering is where the solids load starts. Wire saws cutting a material close to diamond hardness shed silicon carbide fines in the sub-micron range, and those fines do not settle the way ordinary grit does. We set out the wider process route in wide bandgap semiconductor wastewater equipment.

Lapping and CMP make the problem harder. Diamond slurry, colloidal silica and, on the hardest steps, ceria-based polishing compound all enter the rinse, along with copper from any metallised layers on the wafer.

Cleaning, etching and stripping contribute the chemistry: dilute HF, buffered oxide etch, phosphoric and sulphuric mixes, TMAH developer and the solvent blend used for resist removal. Small volumes, each with a very different treatment answer.

The Four Contaminant Families

Suspended solids come first and are the cheapest to remove. The catch is particle size — the fines that stay in suspension will pass a conventional clarifier entirely unless you coagulate them properly.

Fluoride comes from HF and BOE and it is the parameter most fabs underestimate. It complexes, it scales, and it is toxic to the nitrifying bacteria you need for ammonia removal if it arrives too concentrated.

Ammonia nitrogen is the GaN signature. MOCVD runs trimethylgallium and ammonia, and the scrubber and vent wash water carries that nitrogen into the drain, often at concentrations that would trouble a fertiliser plant.

Organics are the residual: photoresist fragments, TMAH, solvents and the trace organics from slurry dispersants. They set the COD number and, more importantly, they set the biodegradability of everything downstream.

Segregate Before You Size Anything

We ask every fab for four drains: abrasive polishing waste, ammonia-bearing scrubber water, fluoride and acid waste, and the general rinse plus utility water. Four lines on a drawing is the whole strategy.

Mixed streams make every downstream unit bigger and worse. A clarifier sized for combined flow has to hold the polishing fines AND handle the ammonia, and it will do neither at design efficiency.

The fluoride and ammonia streams are the ones that must never meet biology in concentrated form. Both are handled chemically or stripped first, then the residuals join the main train. The process logic sits close to what is described in Silk Degumming Wastewater Treatment, particularly on the pretreatment side.

Solids-bearing CMP waste does not belong in the fluoride precipitation either. The fines coat the precipitate and you spend reagent on a sludge that will not dewater.

CMP waste goes to coagulation and flocculation first, then a clarifier or a ceramic membrane stage depending on the fines load. Recovered solids are abrasive, not valuable, and they go to dewatering and disposal. The same selection criteria reappear in Coagulation, Solvent and the Catalyst Trace, which is worth opening alongside this one.

Removal Rates Across Our Installed Base

Across 42 commissioned plants where we hold complete COD records, influent COD ranged from 200 to 172,000 mg/L and treated effluent from 50 to 5,000 mg/L. Average removal across that set is 87.1% — not a marketing figure, but the measured mean.

That average is worth pausing on. It sits well below the 95%-plus numbers most suppliers quote, because the set includes genuinely difficult streams. On some electroplating and municipal duties the installed configuration only reaches about half the influent COD, and saying that up front is more use to you than a number the plant will never hold.

Fluoride is precipitated with calcium, usually dosed in excess with a polyelectrolyte assist, and taken down to the low single digits before it joins the biological stage. Aluminium or magnesium polishing gets the last few milligrams.

Ammonia is either stripped at high pH or nitrified biologically, depending on concentration and on whether the fab has the footprint and the thermal budget for a stripper. Most mid-size plants nitrify; the largest ones strip and recover. Plants dealing with comparable loads face many of the same trade-offs covered in Polycarbonate Resin Production effluent.

The combined stream then gets a conventional biological stage for the residual organics and nitrogen, followed by polishing — usually sand or media filtration plus a final check on fluoride and metals before discharge.

What We Tell Operators

Sample each of the four drains separately for two weeks before design. A single mixed sample tells you nothing useful about this effluent.

Watch fluoride as closely as COD. It is the parameter that quietly shuts down nitrification and the one that appears last in every troubleshooting session.

Expect the CMP load to spike when the fab adds a polishing line. That expansion is planned on the production side months before anyone mentions water.

Keep the abrasive solids out of every chemical precipitation step. Contaminated sludge is the fastest way to double your disposal bill.

Why Choose Baihuipu as Your Manufacturer

Two decades in this industry teaches you that most treatment problems are procurement problems in disguise. Someone bought the cheapest skid, nobody checked the equalisation volume, and eighteen months on the plant cannot hold its consent limit. We build differently.

In-House Fabrication

Our Guangdong works produces everything from standard modular units to fully bespoke lines. Building in-house keeps cost, schedule and quality under our own control rather than a subcontractor's goodwill.

Certification and Export Practice

CE marking is standard and we work to ISO 9001 procedures. Where a project calls for specific material grades, pressure vessel certification or ATEX-rated equipment, we build to that standard and ship the full documentation pack.

Twenty-Plus Export Markets

We have shipped to the United States, Canada, Russia, Indonesia, India, Nigeria and Vietnam among others. Crating, export documentation and certificates are handled in-house, which keeps customs surprises to a minimum.

Two Decades of Field Data

Food and beverage, chemicals, electroplating, textile dyeing, mining, municipal work — we have commissioned across all of them. The useful part is not the project count, it is having seen how plants fail in year seven and designing those failures out.

Complete System Responsibility

One supplier, one process guarantee. We take the plant from preliminary screening through to membrane separation, evaporation and brine management, with process, mechanical, electrical and controls engineering handled internally.

Spares, Service and Commissioning

Membranes, dosing pumps, diffusers, instrumentation and blowers are stocked for the systems we sell. Our control systems support remote diagnostics, and we can put an engineer on site for commissioning, training or an unplanned shutdown.

Getting Started

Send us a water analysis and your production profile and we will tell you honestly what the process should look like and roughly what it costs to build and run. Reach our engineering team on WhatsApp: +86 13631765076 or via hkbhp.com.

WhatsApp: +86 13631765076

Frequently Asked Questions

How much operator attention does the system need day to day?

Automatic control handles dosing, backwash and level control. Realistically your team spends time on chemical top-up, sample testing and sludge handling — maybe one to two hours per shift on SiC GaN wafer duty, less if you opt for remote monitoring.

What spare parts should we hold on site?

Critical spares are pumps, dosing valves, instrumentation sensors and any specialty media. We ship a recommended spares kit with the plant and hold stock for everything we supply, so lead times on replacements stay short.

Do you export and support overseas installations? The operating detail behind this sits in SiC wafer fab wastewater project.

We have shipped to the USA, Canada, Indonesia, India, Russia, Vietnam and Nigeria among others. Documentation, crating and export paperwork are handled in-house, and we support commissioning either remotely or with engineers on site.