How is the semiconductor fab process carried out? How can we ensure success from the very first step of manufacturing?
This article will introduce the basic concepts of semiconductors, manufacturing processes, and future trends, helping the semiconductor industry understand how to make the manufacturing process run more smoothly.
What is a Semiconductor?
Before understanding the semiconductor fab process, it’s helpful to first know the definition, types, and materials of semiconductors to grasp the foundation of modern technology.
Definition of Semiconductor
A semiconductor is a material whose electrical conductivity lies between that of a conductor and an insulator. Under specific conditions, a semiconductor can conduct electricity, while in other situations, it does not.
Its key characteristic is the band gap, usually between 2-3 electron volts (eV), which makes it widely applicable in electronic components like diodes and transistors.
The performance of semiconductors can be adjusted through doping to meet different technological needs.
Types of Semiconductors
Intrinsic Semiconductors
Intrinsic semiconductors are pure materials, such as pure silicon. The flow of current mainly depends on the material’s structure and temperature.
Its electrical conductivity is usually low because the number of free electrons and holes is naturally balanced.
Extrinsic Semiconductors
Extrinsic semiconductors are those that have impurities added through the doping process to significantly change their electrical properties. Doping is divided into two types:
- n-type semiconductors:
Donor impurities with extra free electrons are added, making electrons (negative charge carriers) the majority carriers in the material, thereby increasing electrical conductivity. - p-type semiconductors:
Acceptor impurities lacking electrons are added, producing more holes (positive charge carriers), making it easier for the material to conduct positive charges.
Semiconductor Materials
Silicon is currently the most commonly used semiconductor material, mainly due to its abundant reserves, low cost, and stable performance at high temperatures. Its electrical conductivity is about 1000 S/m, making it an ideal material for mass production.
Although silicon’s electron mobility is relatively low, which may affect certain high-speed applications, mature manufacturing technology still makes it the first choice.
In contrast, gallium arsenide is known for its superior electron mobility and direct energy gap, making it particularly suitable for optoelectronic products like lasers and solar cells. However, gallium arsenide’s higher cost and limited reserves restrict its range of applications.
Additionally, the scientific community is actively researching other potential materials, such as aluminum nitride and carbon nanotubes, which may drive future advancements in semiconductor technology.
These materials could offer more possibilities for higher performance and energy-efficient electronic applications, potentially having a profound impact on the entire industry.
The 12 Semiconductor manufacturing process
The semiconductor fab process is a highly specialized and complex procedure that transforms raw materials into usable electronic components.
This article will introduce each stage of the process, starting from environmental control all the way to the final functional testing.
Environmental Control
The main goal of environmental control is to ensure a dust-free, chemical-free, and stable environment during the manufacturing process to guarantee the quality and performance of semiconductor devices.
Elements like cleanroom management and gas and chemical filtration must be incorporated at the very initial design stage of manufacturing.
Cleanroom
Must undergo high-level filtration to remove tiny particles, aerosols, and contaminants, as these substances can affect precise operations like photolithography and doping on the wafer surface.
The highest cleanliness level is ISO 1, but common processes use ISO 3-5 levels. HEPA and ULPA filters are used to filter the air inside the cleanroom, removing particles as small as 0.3 micrometers or smaller.
Airflow Control
The air inside the cleanroom usually adopts laminar flow, moving vertically or horizontally to maintain stable airflow.
This helps reduce particulate matter in the airflow and prevents dust or other contaminants from passing over wafers or equipment.
Chemical Filtration
In addition to particle control, chemical filters are used to filter volatile organic compounds, acidic or alkaline gases that can contaminate the sensitive surface of wafers, affecting device performance.
👉read more: How to choose the right chemical filter?
Temperature and Humidity Control
Semiconductor processes have very strict requirements for environmental temperature and humidity.
Fluctuating temperatures or excessively high/low humidity can lead to changes in material performance, affecting the precision of manufacturing results.
Static Electricity Control
Electrostatic discharge (ESD) can damage sensitive semiconductor devices. Measures like conductive flooring, anti-static equipment, and workers wearing anti-static clothing must be taken to prevent static electricity accumulation.
Wafer Fabrication
For silicon, the most commonly used growth method is the Czochralski process, which can produce high-quality crystals, laying a solid foundation for subsequent processes.
Other methods include the kyropoulos method , zone melting, and Bridgman–Stockbarger techniques. In this process, single crystals are extracted from the melt and cut into thin wafers.
Subsequently, the wafers undergo fine polishing and cleaning to ensure the surface is suitable for subsequent processing steps.
Oxidation
A thin layer of silicon dioxide (SiO₂) is formed on the wafer surface by exposing it to high-temperature oxygen.
This layer can serve as an insulating or protective layer in circuits and prepares the wafer for the subsequent photolithography process.
Photolithography
A photoresist material is coated on the wafer, and then it is exposed to DUV or EUV light sources through a patterned mask.
After exposure, the photoresist undergoes chemical changes, allowing selective removal of certain materials, thereby forming complex circuit patterns on the wafer surface.
Etching
Materials on the wafer surface not protected by the photoresist are removed to form the required circuit patterns.
This can be achieved through two main methods: dry etching uses plasma and other chemical gases for etching, while wet etching uses liquid chemical reagents to corrode and remove materials.
Ion Implantation
By introducing impurities (such as trivalent or pentavalent elements) into the semiconductor material, its electrical properties are significantly altered.
An ion beam is used to bombard the wafer, embedding ions into the material to form the required n-type or p-type regions, ensuring the normal operation of semiconductor devices.
Thin Film Deposition
Various techniques are used to deposit a thin film on the wafer surface, which can be a conductive layer, insulating layer, or protective layer:
- Physical Vapor Deposition (PVD):
Deposits materials through evaporation orsputtering. - Chemical Vapor Deposition (CVD):
Uses chemical reactions to deposit gaseousmaterials into solid thin films.
Annealing
The wafer is heated to restore the material’s crystal structure and reduce defects, activating the implanted ions while repairing damage caused by the implantation process.
Metallization
A metal layer is deposited on the wafer surface to form conductive connections within the chip. Common metal materials include aluminum and copper, with copper gradually replacing aluminum due to its excellent electrical conductivity and thermal properties.
Chemical Mechanical Planarization (CMP)
The wafer surface undergoes planarization to ensure flatness, allowing subsequent processes to proceed smoothly.
Packaging
After the chip is manufactured, it needs to be packaged to protect it from physical damage. This can involve traditional single-chip packaging, advanced multi-chip packaging, or 3D packaging technologies. Wire bonding is then used to connect the chip electrically to external circuits.
Testing
The chip must undergo functional testing to check whether its electrical performance meets design requirements, known as yield inspection. Tests include voltage tests, functional tests, and reliability tests.
👉read more: What is Filtration in Separating Mixtures?
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👉read more: What is Filter Media?
Future Trends in Semiconductor Fab Process in 2024
Environmental control is the first step to ensure the success of semiconductor manufacturing. However, as industry demand continues to grow.
The semiconductor fab process must continuously seek more efficient and energy-saving methods and explore more potential development areas.
This article summarizes five directions in which the semiconductor industry can improve
3D Integration
By vertically stacking multiple layers of chips, higher functional density and performance optimization are achieved, improving efficiency in a smaller space.
It relies on Through-Silicon Vias (TSVs) and advanced integrated circuits to ensure that vertically stacked chips can transmit signals quickly and effectively.
Compared to traditional planar architectures, 3D integration significantly increases storage density and interconnection performance.
It also supports heterogeneous integration in a single package, allowing different functional components to work together.
Specialized Applications
With rapid technological development, market demand for specialized semiconductor devices designed for specific applications is increasing, such as AI chips, Internet of Things (IoT) devices, autonomous vehicles, and advanced sensors.
Semiconductor manufacturers are increasingly focusing on developing these specialized chips to meet the unique needs of different applications, usually featuring low-power designs, excellent computing performance, strong connectivity, and high integration.
The rise of specialized application chips not only enhances the performance of electronic products but also promotes the diversification and specialization of semiconductor technology, further consolidating its core position in various industries
Emerging Materials
Gallium nitride (GaN) and silicon carbide (SiC) perform excellently in high-power, high-frequency applications, particularly suitable for electric vehicles, communications, and power conversion fields.
Their high thermal conductivity and superior electrical properties help reduce energy loss and improve efficiency.
Graphene, as a two-dimensional material with excellent electrical conductivity and flexibility, offers great potential for the development of flexible electronic products and higher-speed transistors
Advanced Process Nodes
Moore’s Law predicts that the number of transistors on a chip will approximately double every two years, driving the continuous miniaturization of semiconductor technology.
The 5-nanometer and smaller process nodes have entered mass production and represent the forefront of modern semiconductor technology.
These advanced nodes can place more transistors in limited space, significantly enhancing the chip’s computing power and performance while reducing power consumption.
Higher transistor density not only makes devices more powerful but also more energy-efficient, which is especially critical for high-performance computing, AI, and 5G communications.
Advanced Packaging Technologies
As device performance demands increase and sizes shrink, traditional packaging methods can no longer meet the needs of new-generation technologies.
Innovative packaging methods such as Fan-Out Wafer-Level Packaging (FOWLP), System inPackage (SiP), and chiplet technologies are gradually becoming focal points.
- FOWLP:
Provides high-density interconnections while reducing manufacturing costs and package size, beneficial for modern mobile devices, IoT, and wearable devices with limited space. - SiP:
Integrates different components (such as processors, memory, and wireless modules) into one package, offering flexible and efficient solutions for IoT, communication devices, and consumer electronics. - Chiplet Technology:
Allows manufacturers to produce different functional modules separately and ultimately integrate them into one package, making design more flexible and adaptable to changing technological needs.
What Is the Importance of the Semiconductor fab process? | FAQ
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