Frequency
Cleaning Is the Most Repeated Step in the Fab
Cleaning runs before and after nearly every other front-end step, so a leading-edge wafer is cleaned more than 200 times.
A wafer is cleaned before it is oxidized, before every deposition, after every etch, after every resist strip, after every chemical mechanical planarization (CMP) pass and after ion implantation. Each step leaves something behind that would ruin the next: particles, metal ions, polymer, slurry or a few angstroms of unwanted native oxide.
A leading-edge logic flow has more than 200 cleaning steps, and industry reporting puts the range at 200 to 300. The count rises with every node, because each added mask layer brings its own pre-clean and post-clean, and gate-all-around transistors add selective cleans that must remove residue without attacking the nanosheets. Mature nodes at 28nm and coarser run far fewer.
No single cleaning step is hard by the standard of EUV lithography or high-aspect-ratio etch. The difficulty is repetition: a cleaning step that loses a fraction of a percent of die to defects, repeated 200 times, takes a large share of the yield.
What cleaning removes
Each Step Leaves a Different Contaminant
| Contaminant | Where it comes from | Removal chemistry |
|---|---|---|
| Particles | Handling, airborne deposition, residues from the prior step | SC-1 (ammonium hydroxide, hydrogen peroxide, water); megasonic assist for particles below 100 nm |
| Metal ions | Tool parts, implant residue, handling | SC-2 (hydrochloric acid, hydrogen peroxide, water); chelating chemistries |
| Organic residue | Photoresist, lubricants, etch polymer | SPM, also called piranha (sulfuric acid, hydrogen peroxide); oxygen plasma ash; ozonated water |
| Native oxide | Air exposure; silicon dioxide grows on bare silicon within minutes | Dilute hydrofluoric acid (DHF); buffered oxide etch (BOE) |
| Post-CMP residue | Slurry particles and trace metals from polishing | Brush scrub plus acidic or alkaline post-CMP chemistries matched to the slurry |
| Etch polymer | Fluorocarbon byproducts of plasma etch | Amine-based or solvent strippers; wet or plasma post-etch cleans |
RCA sequence
A 1965 Recipe Still Anchors Front-End Cleaning
Werner Kern developed the RCA clean at RCA Laboratories in 1965, and the two-step SC-1 and SC-2 chemistry he published is still the reference front-end clean. Foundries run proprietary variants, but the structure holds: an alkaline peroxide step for particles, an acidic peroxide step for metals and an HF dip for oxide.
| Chemistry | Mix | Typical temperature | Target |
|---|---|---|---|
| SPM (piranha) | Sulfuric acid and hydrogen peroxide, 3 or 4 to 1 | 90 to 130 °C | Bulk organics and resist |
| SC-1 (APM) | Ammonium hydroxide, hydrogen peroxide, water; 1:1:5 originally, 1:4:20 and leaner today | 65 to 80 °C | Particles and light organics |
| SC-2 (HPM) | Hydrochloric acid, hydrogen peroxide, water; 1:1:6 originally, more dilute today | 65 to 85 °C | Metal ions such as iron, copper, nickel and sodium |
| DHF | Hydrofluoric acid in water, 1:50 to 1:100 | Room temperature | Native oxide; leaves hydrogen-terminated silicon |
| BHF (BOE) | Ammonium fluoride and hydrofluoric acid | Room temperature | Controlled oxide etch |
| DIO3 | Ozone dissolved in ultrapure water | Room temperature | Low-damage organic removal; replaces SPM in some steps |
Wet and dry methods
Single-Wafer Tools Took Over at the Leading Edge
| Method | How it works | Where it is used |
|---|---|---|
| Batch wet bench | Racks of 25 to 50 wafers dipped through chemical and rinse tanks | Mature nodes, SPM and HF steps, high-throughput cleans |
| Single-wafer wet | One wafer at a time in a spin chamber with chemistry sprayed on | Leading-edge logic and memory; most defect-sensitive steps |
| Megasonic and spray | Acoustic energy near 1 MHz, or fine droplets, lifts particles | Particles below 100 nm; must be tuned to avoid breaking fine features |
| Plasma ash and dry clean | Oxygen or forming-gas plasma turns organics into gas | Resist strip and descum; post-etch residue |
| Ozone and UV ozone | Ozone gas or ozonated water oxidizes organics | Pre-gate surface prep; reticle cleaning, where RCA chemistry roughens the mask |
| Cryogenic and supercritical CO2 | Carbon dioxide aerosol or supercritical fluid | Specialty; high-aspect-ratio structures that collapse under liquid surface tension |
Single-wafer tools took over at the leading edge because a batch tank lets a contaminant shed by one wafer land on the next, and because each wafer can get a chemistry recipe and dry tuned to its layer. Batch benches survive where throughput matters more than per-wafer control. Pattern collapse is the newer limit: tall fins and memory pillars bend and stick when the rinse water dries, which is why fabs use isopropyl alcohol vapor and supercritical drying on the most fragile layers.
Tool vendors
SCREEN Leads Both Single-Wafer and Batch Cleaning
SCREEN is the share leader in both tool types: 34% of single-wafer cleaners and 43% of batch cleaners in 2025, by Gartner data cited by the company. Tokyo Electron, Lam Research and Samsung's captive toolmaker SEMES follow. Cleaning tools are tied into the wet chemistry each fab has qualified, so a toolmaker that wins a layer tends to keep it across generations.
- Made in US
- US planned
- Made abroad
| Vendor | Headquarters | Platforms | Where tools are built | US status |
|---|---|---|---|---|
| SCREEN Semiconductor Solutions | Kyoto, Japan | SU-series single-wafer and FC-series batch cleaners | Japan | Made abroad |
| Tokyo Electron (TEL) | Tokyo, Japan | CELLESTA single-wafer cleaners; batch wet stations | Japan | Made abroad |
| Lam Research | Fremont, CA | EOS and DV-Prime single-wafer wet clean; plasma dry strip | US and Malaysia | Some US volume |
| SEMES | Cheonan, South Korea | Single-wafer and batch cleaners, mainly for Samsung | South Korea | Made abroad |
| ACM Research | Fremont, CA | SAPS and TEBO megasonic single-wafer cleaners; Tahoe hybrid bench | Shanghai; Oregon site from 2H 2026 | US planned |
| Applied Materials | Santa Clara, CA | Post-etch and selective removal, dry strip | US and Singapore | Some US volume |
| NAURA | Beijing, China | Batch and single-wafer cleaners for Chinese fabs | China | Made abroad |
ACM Research is the outlier: a US-listed company whose tools are built by its Shanghai subsidiary and sold mostly to Chinese fabs. Cleaning was $626 million of its $901 million 2025 revenue. TrendForce reports its single-wafer cleaners running on Hua Hong's 28nm lines, and Chinese tools overall reached about 35% of equipment bought by China's fabs in 2025. ACM plans to start operations at a site in Oregon in the second half of 2026, its first US production base. Tool families and specifications are on Cleaning Equipment.
Ultrapure water
Ultrapure Water Is the Largest Input by Volume
Every chemistry in the sequence is mixed into ultrapure water (UPW), and every step ends with a UPW rinse, so cleaning is the largest consumer of water in the fab. UPW is specified at 18.2 megohm-centimeters of resistivity, the theoretical limit for water, with total organic carbon below one part per billion and metals at parts per trillion.
Each fab makes its own UPW on site through reverse osmosis, ion exchange, ultraviolet oxidation, degassing and final polishing loops. The plants come from Kurita Water Industries, Organo, Veolia, Evoqua (now part of Xylem) and Nalco Water. Recycling rates, discharge and the water fights around new US fabs are on Fab Water.
Chemistry supply
Hydrofluoric Acid Has the Fewest Qualified Sources
| Chemistry | Main semiconductor-grade suppliers | Concentration |
|---|---|---|
| Hydrofluoric acid (HF) | Stella Chemifa, Morita Chemical, Solvay, Soulbrain | Japan's 2019 export curbs on HF to South Korea showed how few qualified sources exist |
| Hydrogen peroxide | Evonik, Solvay, Mitsubishi Gas Chemical, Santoku Chemical | Used in SPM, SC-1 and SC-2 |
| Sulfuric acid | Mitsubishi Chemical, Kanto Chemical, BASF, Chemtrade | High volume; recovery and recycling rising |
| Ammonium hydroxide and HCl | BASF, Kanto Chemical, Entegris | Broader supplier base |
| Post-etch and post-CMP chemistries | Entegris, DuPont, Merck (EMD Electronics), Fujifilm | Proprietary formulas qualified per layer |
Every chemistry is qualified per tool and per layer, and metal limits sit at parts per trillion. The full chemical supply picture is on Process Chemicals.
Resist strip
Every Lithography Pass Ends in a Strip and a Clean
Resist strip removes photoresist after it has protected the wafer through an etch or implant. It is harder than general cleaning because etch byproducts and implant damage harden the resist into a carbon-rich crust. Oxygen plasma ashing does the bulk removal and a wet clean follows to take off what remains, so every lithography pass produces a strip and a clean. Strip methods, chemistries and tools are on Photoresist and Development.
Record
Page Record
- Covers
- Wafer cleaning frequency, contaminants, the RCA sequence, wet and dry methods, tool vendors, ultrapure water and chemistry supply
- Sources
- Gartner calendar 2025 share data as cited by SCREEN (via InnovestX, March 2026); ACM Research fiscal 2025 results (February 2026); ACM Research and Mark LaPedus (cleaning step counts, 2024); TrendForce (China equipment localization, January 2026); W. Kern, RCA Review (1970)
- Last verified
- October 2026