You may be aware of the important role semiconductors play in our everyday lives, but if you’re new to the world of semiconductor manufacturing, you may be wondering what a semiconductor clean room is and what its purpose is. Semiconductor cleanrooms are the factories where all the complicated but important steps of the semiconductor manufacturing process take place. They are essential cogs of the semiconductor industry, and without them, everything from the microchips in your cell phones, video game consoles, or even the latest smart automobiles would not be made.
Let’s find out what role semiconductor cleanrooms play, why they’re so important. and how they are designed with the utmost care.
What Is A Semiconductor Clean Room?
Any modern electronic device that requires a microprocessor or integrated circuits to function requires semiconducting microchips. Everything from the smart refrigerator in your kitchen to the most advanced military equipment needs these microchips to work. A semiconductor cleanroom is a factory where these microchips are manufactured under carefully controlled environmental conditions to ensure they are of the highest quality.
Semiconductor chips are prone to contamination from the tiniest speck of dust, hair, or any airborne particles. Once contaminated, the microchips will no longer function properly, making it a huge waste of resources and money for the manufacturer. Temperature and humidity are similarly important. Therefore one of the primary goals of a semiconductor cleanroom is to completely remove these compromising conditions from the manufacturing environment.
There are many different types of semiconductor cleanrooms depending on the stage of the manufacturing process. Firstly, there are factories where the Silicon required for the microchip is artificially grown. They are called ‘ingots’ and look like cylinders. Later, these ingots are cut into round thin wafers and sent to the cleanroom factory to be processed further.
In the cleanroom, the thin Silicon wafers are exposed to light and then processed with chemicals to build up specific layers into them. This process is called photolithography and the layers form the circuit paths of a microchip. These layers are so tiny that you would need a special semiconductor microscope to look at the patterns in detail. For very complex integrated circuits, there could be multiple cycles of photolithography performed in different semiconductor cleanrooms.
The Importance Of Using A Cleanroom Environment For Semiconductor Manufacturing
There are many reasons for using semiconductor cleanrooms. A cleanroom serves as a quality control system to ensure the semiconductor products are made to the best possible standards. There is constant chemical processing that happens, often with toxic materials. A cleanroom ensures that safe working conditions are maintained for the sake of the cleanroom employees at all times. Finally, the use of a properly designed cleanroom keeps the fabrication efficiency high, and the costs low.
Semiconductor cleanrooms are built with great care to make sure contamination from dust, hair, and particulate matter is reduced as much as possible. Cleanroom employees wear special clothing when they enter the work area to make sure they don’t bring any unwanted particles into the environment. Specially designed air conditioning is used to filter and maintain a suitable airflow.
Apart from keeping the environment clean, the temperature, humidity, electrostatic discharge, and differential pressure of the air can all have an effect on the delicate wafers. These parameters have to be tightly controlled at all times, otherwise, the quality of the final product could be compromised. A single wafer could cost $20,000 or more, taking months to manufacture, making the loss of even one a massive waste of raw materials, money, and time.
The wafers are subject to highly reactive chemical exposures, radiation, the use of lasers, and many other complex processes. While robots take care of some of these steps, human employees are often needed and safety becomes a major concern when hazardous materials are present. A carefully controlled cleanroom environment minimizes the health risks and chance of workplace accidents, ensuring the health and safety of the workers.
The last two points regarding product quality and workplace safety add up in the long run toward cost savings. If there are fewer quality issues and zero accidents, a semiconductor manufacturing company can make significant savings for its business.
The Design Of A Semiconductor Cleanroom
To control the airflow, air purity, temperature, and humidity, semiconductor cleanrooms need to be equipped with the proper facilities. Further, the workbenches, machinery, and other tools used by the cleanroom employees need to be carefully selected as well. These are the common cleanroom considerations.
Air Conditioning For Semiconductor Cleanrooms
The purity of the air is one thing a cleanroom cannot compromise. To ensure that only adequately filtered air is circulating inside the cleanroom, there are special filters called High-Efficiency Particulate Air (HEPA) filters used in cleanrooms. These are capable of removing 99.97% of dust, bacteria, mold, pollen, or any other form of particles that are larger than 0.3 µm.
The HEPA filters are placed at the air inlet or makeup air unit (MAU) which is where fresh air is taken from outside the building. The return air handlers (RAH) where the used air from inside the cleanroom is taken out have their own filters. Finally, there are fan filter units located on the ceiling of the cleanroom as well.
The flow of air inside a cleanroom is done according to vertical laminar flow. Air is blown from the ceiling using the fans towards the floor constantly. This uniform stream of air prevents any particles from building up on top of delicate instruments. In a vertical laminar flow system, the used air is taken out by holes in the floor, purified, and cycled through again.
Finally, the air conditioning system also has the responsibility of keeping the humidity at 18 to 55% which can vary depending on the components and number of workers inside the room as well as controlling temperature at 22 degrees Celsius. The differential air pressure is kept at 15 Pa to 45 Pa.
The furniture, equipment, and instruments used inside a cleanroom are placed along the outer walls of the room as much as possible to keep them away from areas with high airflow. The workstations where employees handle the wafers are called ‘wet benches’ and are also laid out along the outer walls.
There are vapors created from the chemicals used in this environment, and special exhausts are built right into the wet benches to remove these vapors without affecting the airflow of the cleanroom. All equipment and materials used inside a cleanroom are chosen for their durability and resistance to corrosion in an environment of chemicals. They do not degrade easily and are manufactured to minimize the outgassing and shedding of particles.
The wall surfaces of the room often use smooth aluminum to maintain good airflow. Proper grounding and insulative materials are used to control static electricity inside the cleanroom.
Power For Semiconductor Cleanrooms
Finally, backup power is an essential component of cleanroom design to make sure that the air conditioning system keeps functioning to maintain the purity, temperature, and humidity even in the event of a power failure in the main grid.
Classifications For Semiconductor Cleanrooms
The International Organization for Standardization (ISO) has laid down specifications that need to be followed under the ISO 14644 standard. While there are basic requirements included in these guidelines that all semiconductor cleanrooms should follow, the ISO class can vary depending on the wafer size, and process type handled at each cleanroom.
Always Buy From A Manufacturer That Has An ISO 14644 Standard Semiconductor Cleanroom
Now that you understand the importance of proper cleanroom design, remember to only purchase semiconductors from manufacturers that can guarantee their ISO standards for semiconductor cleanroom facilities.
Semiconductor manufacturing is done inside cleanrooms to prevent harmful particles from contaminating the delicate silicon wafers. The temperature and humidity are also controlled to maintain optimum conditions for manufacturing.
Food and beverages are never allowed inside a cleanroom. Wooden products, certain types of plastic, cardboard, powders, oil, and lubricants are some of the materials that cleanroom workers are not allowed to take in.
Personal items including mobile phones are not allowed inside a cleanroom since they can carry bacteria that can contaminate the sterile environment.