The biggest threats to semiconductor manufacturing are often particles too small to be seen by the human eye. In advanced fabs, Particle Counters serve as a critical line of defense for cleanroom control and yield protection.

Walk into a semiconductor fab and you will see cleanliness controls everywhere: personnel fully covered in cleanroom garments, highly filtered air, and dedicated piping systems supplying ultrapure water and high-purity chemicals.

There is a reason for this extreme level of control. Particles at the nanoscale can be enough to cause defects on a semiconductor wafer.

A tiny contaminant landing on a critical area of a wafer can interfere with lithography, disrupt thin-film deposition, or cause abnormalities during etching. As semiconductor processes continue to shrink, particles that were once considered negligible can become significant contributors to yield loss.

Many people think of a Particle Counter as a single piece of equipment. In reality, particle monitoring can be part of a broader contamination monitoring system, covering airborne particles, gases, ultrapure water, process chemicals, process chambers, and component surfaces.

01

How Can Tiny Particles Damage a Chip?

Chip manufacturing involves hundreds or even thousands of process steps, including deposition, lithography, etching, cleaning, CMP, and more.

Particle contamination can come from almost anywhere: personnel movement, mechanical friction, equipment wear, filters, piping, chemicals, ultrapure water, and even the process itself.

Inorganic debris, metal particles, and polymer residues ranging from tens to hundreds of nanometers can all become potential sources of defects:

✅ Lithography: Particles can interfere with the photoresist and cause pattern defects.

✅ Deposition & Etching: Particles can block critical areas, resulting in abnormal lines, features, or holes.

✅ Cleaning: Particles carried by water or chemicals can introduce contamination instead of removing it.

A cleanroom cannot be judged by what the eye can see. It has to be measured with data.

Under standards such as ISO 14644-1, particle counters are used to measure particle concentrations and particle-size distributions as part of cleanroom classification and monitoring.

02

What Does a Particle Counter Actually Monitor?

Think of a semiconductor fab as a city. A Particle Counter is part of the contamination warning network distributed throughout that city.

• Airborne particles: Air Particle Counters (APCs)

• Particles in ultrapure water and process chemicals: Liquid Particle Counters (LPCs)

• Process chambers: In-situ and exhaust-side particle monitoring

• Equipment contamination: Pre- and post-process wafer scans to identify newly added particles, or particle adders

At its core, particle monitoring helps answer four questions:

① Are particles present in the environment?

② When did an abnormal particle event occur?

③ Is the contamination coming from the facility system, raw materials, or equipment?

④ Could the particle event affect wafers currently in production?

⚠️ An important distinction: Particle monitoring is different from AMC (Airborne Molecular Contamination) monitoring. AMC monitoring focuses on molecular contaminants such as acids, bases, and organic compounds, while Particle Counters are designed to detect particulate contamination.

Traditional approaches often rely on monitoring wafers to assess equipment cleanliness. However, the results may only become available after a process has been completed—making it essentially a post-event detection approach.

The value of real-time particle monitoring is that abnormal particle events can be detected as they occur, enabling earlier investigation and response.

03

How Can an Instrument Detect Particles We Cannot See?

Airborne Particles | Light Scattering + CPC Technology

A widely used approach for airborne particle measurement is single-particle light scattering. As a particle passes through a laser beam, it scatters light. A photodetector converts the scattered light into an electrical signal, allowing the instrument to count particles and estimate their optical-equivalent size.

Particle counters are calibrated according to standards such as ISO 21501-4, depending on the applicable instrument and measurement requirements.

⚠️ A useful point to remember: The particle size reported by an optical particle counter is an optical-equivalent particle size, not necessarily the particle's actual physical diameter. The result can be affected by factors such as particle material, shape, and refractive index.

When particles become extremely small, conventional optical detection becomes increasingly challenging. This is where CPCs (Condensation Particle Counters) can be useful.

A CPC uses a working fluid to grow very small particles into larger droplets that can be detected and counted, enabling measurement of particles in the nanometer range for applications where such detection is required.

04

It's Not Just About Counting: Turning Particle Data into Process Insight

If particle monitoring only produces a number, it is using only part of its potential.

The real value comes from correlating particle data with process and equipment information.

For example, if a monitoring trend suddenly shows a sharp spike, engineers can investigate whether it coincided with a chamber opening, robot movement, recent preventive maintenance, or a specific step in the process recipe.

If particle levels gradually increase over several days, this may indicate equipment wear, accumulation of deposits inside a chamber, or declining filter performance.

This is why particle monitoring systems increasingly need to connect with FMS (Facility Monitoring Systems), equipment logs, and SPC (Statistical Process Control).

By correlating particle trends with process steps and wafer defect data, particle monitoring can evolve from a simple measurement tool into a tool for equipment health monitoring and contamination source investigation.

Industry standards are also continuing to evolve. For example, standards such as SEMI E194 address particle contamination evaluation methods for semiconductor manufacturing equipment and components.

The broader direction is clear: moving from investigating defects after they occur toward detecting and responding to particle events as they happen.

Advanced semiconductor manufacturing cleanliness is not simply about keeping a facility clean.

It is a continuous effort to detect and control particles at scales far beyond what the human eye can see—before they have a chance to affect wafer quality and yield.

The future of Particle Counters will not simply be about detecting smaller particles. Airborne nanoparticles, particles in ultrapure water and process chemicals, transient particle events in process chambers, and contamination on equipment components can all become part of a broader monitoring and analysis framework.

For advanced semiconductor manufacturing, particle monitoring is becoming an increasingly important part of the infrastructure supporting process control and yield management.

Partially reproduced from the WeChat account “芯域前沿”.