Semiconductor Cleanrooms 101

marzo 10, 2023

semiconductor wafer, person in bunny suit

Figure 1. Person in bunny suit holding semiconductor wafer

Semiconductor cleanrooms are the most demanding cleanrooms in the world. As photolithography linewidths go below 0.1 micron these cleanrooms are typically class 10 or class 100 cleanroom classification (ISO-4 or ISO-5). In addition, semiconductor cleanrooms have tight temperature and humidity requirements. These cleanrooms can vary in size from 500 S.F. to 500,000 S.F. In the United States the highest concentration of semiconductor manufacturing cleanrooms can be found in the Bay Area (Silicon Valley CA), Phoenix Arizona and Texas. Other large semiconductor producing countries include Taiwan, Korea, Japan and China.

FED standard cleanroom classification table

Table 1. Cleanroom Classification Table

Semiconductor cleanroom filtration
Semiconductor cleanrooms typically use ULPA filters instead of HEPA filters to stop even the smallest submicron particles from entering the cleanroom. HEPA filters catch 99.97% of particles at 0.3u. ULPA filters catch 99.999% of particles at 0.12u.

Semiconductor cleanroom lighting
Semiconductor cleanrooms are easily recognizable due the amber cleanroom lighting used in photolithography rooms. Normal white light would expose the photoresist that is used to pattern the semiconductor wafers. The photoresist is not sensitive to the wavelengths of the amber colored lights.

interior of white light cleanroom, door to amber lighted class 100 cleanroom, air return walls

Figure 2: Door to amber photolithography room in cleanroom

For class 100 and higher cleanrooms there is often 100% ULPA filter ceiling coverage to avoid having any area of cleanroom without vertical cleanroom air flow. Special teardrop cleanroom lights which mount between the ULPA filters on the t-grid are used to provide lighting in these cleanrooms.

teardrop cleanroom light fixture, amber light

Figure 3. Teardrop cleanroom light fixture in class 100 cleanroom (ISO-5 cleanroom)

Semiconductor cleanroom flooring
The two most common flooring used in semiconductor cleanrooms are static dissipative heat welded vinyl flooring or raised cleanroom flooring. The static dissipative heat welded vinyl flooring helps prevent ESD damage to semiconductor parts during manufacturing. Raised cleanroom flooring allows the ULPA filter air to travel vertically from the ULPA filters in the ceiling in straight path to below the flooring providing the best laminar flow possible. By comparison low wall air returns require the air to move horizontally from the center of the cleanroom to the walls returns.

interior class 100 cleanroom, raised cleanroom flooring, amber cleanroom lighting

Figure 4. Raised cleanroom flooring in class 100 room (ISO-5 cleanroom)

Interior class 1000 cleanroom, heat welded vinyl flooring, cleanroom fume hood, amber cleanroom lighting

Figure 5. Static dissipative heat welded vinyl cleanroom flooring

Semiconductor Cleanroom HVAC
Due to extremely fine linewidths the manufacturing processes in semiconductor cleanrooms are very sensitive to temperature and humidity variations. Typical semiconductor cleanrooms require +1 degree Fahrenheit and +5% or 10% relative humidity. This requires dedicated air handler for each room with hot and cold elements. Most semiconductor cleanrooms have dedicated chiller and boiler to support the HVAC system.

large HVAC cleanroom chiller, outdoor mount

Figure 6. Chiller for class 100 Temperature and humidity controlled cleanroom (ISO-5 cleanroom)

Semiconductor cleanroom garments Personnel working in semiconductor cleanrooms wear bunny suits, booties, hoods, masks, and gloves to prevent personnel from introducing particles into the cleanroom. After garbing up the personnel often pass thru a cleanroom air shower which blows them off with HEPA filtered air to remove any particles which may be on outside of their cleanroom garments.

Figure 7. Class 100 Cleanroom bunny suits and booties (ISO-5 cleanroom)

Figure 8. Interior of cleanroom air shower (class 100 cleanroom / ISO-5 cleanroom)

Summary: Semiconductor cleanrooms are one of the most demanding cleanroom applications. They are typically class 10 or class 100 cleanroom classification with very tight temperature and humidity requirements. Unique features include amber tear drop cleanroom lighting, raised cleanroom flooring, and air showers.

Property American Cleanroom Systems 2023

The author Anthony Chien has worked at American Cleanroom Systems for past 10 years. He has more than 40 years of cleanroom experience. Anthony has a BS and MS in Electrical Engineering specializing in semiconductor manufacturing from the University of Illinois. American Cleanroom Systems is a design build modular cleanroom manufacturer based in Rancho Santa Margarita CA. It is expert in ISO-5 thru ISO-8 (class 100 to class 100k) modular cleanrooms for pharmaceutical cleanrooms, medical device cleanrooms, and industrial cleanrooms.