Decoding the Clean Room; more than meets the eye

In all your time on the internet you must have come across a term called ‘semiconductor manufacturing’ or an Instagram reel telling you about the size of a microprocessor. You might have wondered in what conditions does this manufacturing occur. A nanometer is a billionth of a meter, at that point you are closer to an atom than to a dust particle. Controlling the conditions of your space becomes very crucial when working at such unimaginably small scales. So where does the magic happen?

A clean room is a room that is first and foremost clean. Wow Arjun, thank you for stating the obvious we would never have figured it out. I tell you most of the stuff you see that you might think is complicated has a very obvious name. The thing that actually scares everyone are the scientists’ and physicists’ names attached to the effect/phenomenon. The dirtiest entities inside the room will be us, humans. We carry dust, dirt, grime, even our hair is enough to kill any device we may be trying to fabricate. These culprits are in the range of micrometers which is a thousand times larger than a nanometer. Imagine that you are making something that is only taking up one meter by one meter space and then a one-kilometer huge defect shows up on your hypothetical something. I think you can estimate the severity of this circumstance.

Clean rooms have classes with which they are differentiated based on particulate control. For example: a class ‘X’ cleanroom will mean that this room contains less than ‘X’ number of particles of size 0.5 micrometer in a volume of 1 cubic meter. The classes most seen in semiconductor manufacturing are:

• Class 1: The highest amount of control, humans are not typically allowed entry here. Any process occurring in this room is automated by robots. Used for advanced lithography (EUV patterning), and very critical etching.
• Class 10: Advanced deposition, high resolution lithography
• Class 100: General wafer fabrication
• Class 1000: MEMs fabrication, wet chemical areas
• Class 10000: Gowning rooms, support, sub-fab areas

This level of control is achieved by using a system of air filtration and human decontamination. If you ever get the chance to enter a clean room the first thing you will do is take off your shoes and go to the gowning room. You will be provided with special ‘bunny suits.’ These will cover your whole body and will not allow any contaminants stuck to you to get out. Next you will go through an air shower which will send high velocity nitrogen gas on you to dislodge any particles on you and the suit. Now, you are ready to enter the room. The ceiling and floor are covered with a perforated floor in classes lower than 1000. This allows for air to flow in an a downwards direction which permits laminar flow. The air is filtered through HEPA (high efficiency particulate attenuation) filters and flows from the ceiling to the floor where the air is sent to get filtered again using a series of filters. The air is sent back to the clean room after filtration. There is a small health concern here that if someone is ill inside the room then others might get ill too due to the reused air. Ill people are usually not sent in and the filtration systems may get the contagion out of the air but honestly the risk is the same amount if we were in a traditional office space, if it’s not your day then it just isn’t.

Figure 1: Direction of airflow in a clean room. 

Reference: left: iqsdirectory , right: Cleanroom Industries

This was a rundown of the air filtration systems. This article will not go into much depth on this as it will turn into a full-on textbook otherwise. Please go into detail on these topics if you feel curious as all of this is very interesting. Turning back to the task at hand, this article would not be named the way it is if the only thing we had to think of is particle contamination. A lot of other considerations have to be taken while building a room like this. ‘More than meets the eye’ isn’t there for fun.

Figure 2: Prevention of electrostatic discharge. 

Reference: Desco Europe

In winters you may have experienced tiny shock while wearing woolly clothes. In school they must have told you that these are static shocks. Electric charge buildup at one point and a sudden release of the stored energy. Well, this tiny little phenomenon has the power to seriously damage a device. All rooms where integrated circuits are handled are ESD (electrostatic discharge) safe. This static charge is given a path to flow so that build-up is prevented.

Figure 3: Shock absorbers for vibration damping. 

Reference: STACIS

Imagine that you are drawing and suddenly an earthquake occurs big enough to rock your room. Of course, your first thought will be to run to safety but the first thing to happen would be your drawing being spoilt. Every footstep in the room would be akin to a magnitude 9 earthquake in a clean room. Anti-vibration counter measures would need to be able to dampen the effects of these vibrations by a huge degree, especially in rooms where lithography is taking place. A difference of a micrometer would mean the death of your device.

Figure 4: Sub-fab area of a huge foundry. 

Reference: Construction Physics

The sub-fab area is where the main area is controlled. All the cylinders, pipes, electronic equipment powering the fabrication machines are located there. Since many machines utilize the same gases, it is convenient to store them in one place rather than each machine getting its own cylinder. The place is an absolute nightmare to look at as it is a labyrinth of pipes, valves, and pressure meters. One small leakage of a gas like hydrogen would blow the facility sky high. High voltage machines and dangerous gases in one place is like keeping a habitual smoker in the same room as a petrol tank.

Strict safety mechanisms and very sensitive gas sensors are utilized to keep the safety of the clean room preserved for the devices fabricated and for the well being of the people working there. Protocols have to be followed to the letter and any lapse may result in a fate worse than death, like a drop in shareholder value (amazing world, am I right?).

This article works as an introduction for you and gives a glimpse into the expertise it requires to build and maintain a mammoth operation like this. For further knowledge I highly recommend reading books and other articles covering this because it truly is a marvel in civil engineering.

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