Home / Semiconductor
What a cleanroom is
A cleanroom is a tightly controlled space where the air is filtered to remove almost all dust particles, and where temperature, humidity and vibration are held steady, so that delicate manufacturing can happen without contamination. In chip making it is essential, because the features on a chip are far smaller than a speck of dust and a single stray particle can ruin the chips beneath it. The Dholera fab's cleanroom fit-out is reported to be underway in 2026 as part of the plant's construction.
Last checked 2026-08-11 · every figure below carries its source
What a cleanroom is
A cleanroom is a sealed, controlled environment built to keep contamination to an absolute minimum. The most important thing it controls is airborne particles, tiny bits of dust, skin, fibre and other matter that float in ordinary air in enormous numbers. A cleanroom filters the air continuously so that very few particles remain, and it also holds temperature, humidity, air pressure and vibration within narrow limits. Cleanrooms are classified by how many particles of a given size are allowed in a volume of air, with the strictest classes permitting only a handful of the smallest particles. They are used wherever tiny contamination causes big problems, including pharmaceuticals, precision optics, aerospace and, most demandingly, semiconductor manufacturing. A chip fab contains some of the cleanest indoor spaces humans have ever built, far cleaner than a hospital operating theatre, because the tolerances involved leave no room for even microscopic dirt.
Why chips need such clean air
The reason a fab needs an extreme cleanroom comes down to scale. The features etched onto a modern chip are measured in nanometres, far smaller than a particle of household dust, which can be tens of thousands of nanometres across. If such a particle lands on a wafer while circuits are being built, it can block a lithography step, cause a short circuit or leave a defect that kills every chip beneath it. Because a fab processes a wafer through hundreds of steps over weeks, there are hundreds of opportunities for a stray particle to do damage, and a single lost wafer represents a large amount of value. Keeping the air almost perfectly clean is therefore not a nicety but a core requirement for the fab to achieve acceptable yield, the share of good chips per wafer. This is why cleanroom performance is watched as closely as any process tool, and why the cleanroom fit-out is one of the most demanding stages of building a fab.
How a cleanroom stays clean
A cleanroom keeps particles out and sweeps them away through a combination of filtration and airflow. Air is drawn through high-efficiency filters, often mounted across the entire ceiling, that trap the vast majority of particles. The clean air then flows downward in a smooth, even stream and exits through vents in or near the floor, so any particle that does appear is carried away from the wafers rather than allowed to settle. This top-to-bottom pattern is called laminar flow. The room is also kept at higher pressure than the spaces around it, so that when a door opens, air pushes outward and dirty air cannot rush in. People enter through airlocks and gowning rooms, and the whole structure uses smooth, non-shedding materials that do not generate particles themselves. Temperature and humidity are held steady because even small changes can affect sensitive chemical steps and cause materials to expand or contract at the wrong moment.
The people and the bunny suits
People are the largest source of contamination in a cleanroom, because a human body constantly sheds skin flakes, hair, fibres and moisture. To contain all of this, staff wear full coverall garments, commonly called bunny suits, along with hoods, masks, gloves and special boots, so that almost none of their body is exposed to the room's air. The suits are worn not to protect the person but to protect the wafers from the person. Getting dressed happens in a dedicated gowning area, following a strict order so that the outer garments never touch a dirty surface. Even movement is disciplined, because sudden gestures stir up particles. Increasingly, though, the most sensitive handling is done by machines rather than people. Wafers travel between tools inside sealed carriers, often on automated overhead tracks, so that they are exposed to open air as little as possible. This automation both improves cleanliness and reduces the risk of human error in a very expensive environment.
Building a cleanroom is a project in itself
A fab cleanroom is far more than a well-sealed room. It is an intricate building system with enormous air-handling capacity, banks of filters, raised floors, vibration-isolated foundations and a web of utilities delivering ultrapure water, specialty gases, chemicals and clean power to each tool. The structure often spans multiple levels, with the cleanroom floor above and support systems, sometimes called the subfab, below and around it. Building and certifying a cleanroom is one of the last and most demanding phases of constructing a fab, and it must be completed before the process tools can be installed, connected and qualified. At Dholera, major structural and civil work is reported complete as of mid-2026, with cleanroom fit-out and equipment move-in underway, a status best described as reported rather than certified. This sequence, sealing and certifying the cleanroom before running wafers, is part of why first trial silicon at Dholera is targeted only around December 2026.
The cleanroom in the Dholera timeline
Because the cleanroom is a gating step, its progress is a good marker of how close a fab is to making chips. Once the cleanroom shell is complete and certified to the required particle class, the process tools are moved in, connected to their utilities and calibrated, then qualified by running test wafers to confirm each step performs correctly. Only after that can full wafer lots run through the complete process to yield first silicon. At Dholera, the reported status of structural work complete with cleanroom install started fits a plant working toward its first trial silicon target of around December 2026, with commercial-scale production reported for about mid-2028. No source confirms a chip has been produced yet, so these remain targets. The cleanroom is also one reason a fab demands such reliable power and ultrapure water, since the environment and the tools within it cannot tolerate interruptions, which ties the fab tightly to Dholera's utility and infrastructure backbone.