Inside a fab: the floors that make a cleanroom work.
The tools are the visible part. Above them, below them and beside them sit the systems that keep them running.
- Filtered air flows down through the cleanroom without stopping.
- Wafers travel in sealed pods on overhead rails, between tools.
- Pumps, abatement and gas and chemical supply live in the sub-fab below.
- Ultrapure water, bulk gases, chillers and power come from a utilities building.
A wafer fab is usually drawn as a room full of tools. In cross-section it is a stack of floors, each with its own crews and its own failure modes.
- 1Fan-filter ceiling. Filtered air flows down through the room without stopping.
- 2Overhead transport. Robotic vehicles carry wafer pods (FOUPs) between tools.
- 3Process tools. Deposition, lithography, etch, implant, polish and metrology.
- 4Gowned crews. Operators and technicians on every shift.
- 5Raised floor. Perforated, so air returns and services pass through.
- 6Vacuum pumps. In the sub-fab, below the tools they serve.
- 7Abatement. Treats tool exhaust before it leaves the building.
- 8Gas and chemical distribution. Cabinets and lines that feed every tool.
- 9Utilities. Ultrapure water, bulk gases, chillers and power.
Why the air moves down
Particles are the enemy of yield. Fan-filter units in the ceiling push filtered air straight down through the room and out through a perforated floor, carrying particles away from the wafers. Cleanliness is graded by ISO 14644-1 class, and the most critical areas are the strictest.
Why wafers travel in pods
Wafers rarely meet the room air. They move in sealed carriers, called FOUPs for 300 mm wafers, that dock directly with each tool. Overhead vehicles carry them between tools, which is why a modern fab floor has so few people walking about with wafers.
Why the sub-fab matters as much as the fab
Below each tool sit its vacuum pumps, the abatement that treats its exhaust, and the gas and chemical lines that feed it. When a sub-fab system fails, the tool above it stops, so sub-fab and facilities technicians are part of the production team, not a support function.
The people on each floor
- Cleanroom: operators, process and equipment technicians, process and equipment engineers.
- Sub-fab: facilities, gas, chemical and maintenance technicians.
- Utilities: water, power, gas and HVAC specialists.
A ramp plan that hires only for the top floor will stall on the others. Talent & manpower covers all three.