Have you ever visited Northwest Florida beaches, such as Panama City Beach? If so, you’ve likely felt awed by their beautiful snow-white sand. According to experts, this sand consists of small quartz particles that came ashore about 20,000 years ago.
Interestingly, that type of sand, also called “quartz sand” or “silica sand,” is more than just a beauty to behold. It’s also the primary component of silicon wafers, which power many of today’s electronic devices.
So then, how are silicon wafers made exactly from such sand? What roles do these wafers play in electronic devices in the first place?
This guide breaks down what you need to know, so read on.
The Roles of Silicon Wafers in Technology
Silicon wafers are thin slices of semiconductor materials. This means they have electrical properties that allow them to act as a conductor and an insulator.
A conductor is something that conducts electricity, while an insulator cannot. Silicon wafers, as semiconductors, can do a little bit of both. Thus, they are ideal media to control electrical currents and electronic devices.
Examples of silicon wafers as semiconductors are diodes, integrated circuits (ICs), and transistors.
Where Can You Find Silicon Wafers?
Smartphones, computers, medical equipment, and vehicles are just some of the thousands of products that rely on semiconductors. Many use silicon wafers (although other semiconductors, like germanium and gallium arsenide, exist). Silicon is often the preferred material due to its affordability and conductivity.
How Are Silicon Wafers Made Then?
It all starts with quartz or silica sand, which has a high silicon dioxide (SiO2) content. It also contains oxygen, which, when removed, leaves only pure silicon.
Pure silicon looks like silver rocks. However, they don’t have any practical uses yet at this point. As a result, the semiconductor industry puts them through the following steps to make them useful.
Purification
To manufacture silicon wafers, pure or raw silicon must undergo purification. The required purity level depends on the end product the wafers are for, but for ICs, it must be 99.9999999%. For solar photovoltaic (PV) panels, the purity of the silicon must be 99.9999%.
Silicon purification involves several steps, including refining, zone melting, and solidification. Typical fabrication methods used to purify silicon are the Czochralski (CZ) method and the Floating Zone process.
The solidification process creates a cylindrical silicon rod called an ingot or boule.
The Czochralski Method
The CZ method is a crystal growth process named after its inventor, Polish scientist Jan Czochralski. It starts with a seed crystal (a small piece of single-crystal silicon) dipped into a crucible. A crucible is a container that can withstand extremely high temperatures needed to melt substances.
The crucible used in the CZ method contains molten silicon. The seed, attached to a rod, goes into this and slowly gets pulled upward and rotated.
As the seed gets lifted, molten silicon surrounds it, which cools and solidifies. Wafer manufacturers repeat this step until the tiny seed turns into an ingot or boule.
The Floating Zone Process
Unlike the CZ method, the Floating Zone process doesn’t use a crucible. Instead, it relies on two vertical solid rods, in between of which is a molten zone.
With the Floating Zone method, a single-crystal seed gets grown by dipping it into one end of the molten zone. This zone then moves along the crystal and, in doing so, melts impurities and leaves behind purer material. The impurities move to one side while the other end grows into a more purified ingot.
Slicing
After forming a silicon ingot or boule, the next step is to slice it into thin discs or wafers. Manufacturers use a diamond saw for slicing, as its hardness allows for clean, precise cuts.
Precise cuts are integral to wafer manufacturing because even the tiniest defect can affect the performance and quality of semiconductors. So, a diamond saw helps improve the wafers’ reliability and quality.
As for the semiconductor thickness and size, this depends on the end product or device it will go to. For example, silicon wafers used in PVs are about 100 to 200 mm square in diameter and around 200 to 300 µm (micrometer) thick. On the other hand, wafer sizes used in electronics are often 100 to 300 mm in diameter.
Cleaning and Etching
After slicing, wafers undergo a cleaning process using weak acids. Examples include ammonium hydroxide and acidic hydrogen peroxide solutions. These substances help ensure the wafers’ surfaces have no surface contamination.
Etching methods are also often used, especially for patterned silicon wafers. Etching selectively removes unnecessary parts to achieve the desired circuit patterns on the wafer’s surface.
Polishing
After cleaning and etching, manufacturers polish the wafers to ensure a smooth finish. In patterned wafers, polishing helps remove any residual dust or debris in the etched areas. Both sides of the wafers must undergo this step, which involves using a polishing slurry.
Thin Film Application
Finally, manufacturers deposit a coating or layer, called “thin film,” onto the silicon wafers’ surfaces. The exact material depends on the specific function or property a wafer must have as a semiconductor device.
Some common types of thin films used are dielectric, metal, passivation, and semiconductor. To deposit these thin films, wafer makers use various techniques like the following:
- Atomic layer deposition (ALD)
- Chemical vapor deposition (CVD)
- Physical vapor deposition (PVD)
The type of thin film material and application method depends on the semiconductor device’s specific requirements. For example, silicon wafers for fabricating computer chips often use polymer dielectric films deposited through CVD.
That’s How Silicon Wafers Get Made
And there you have it, the guide answering the question, “How are silicon wafers made?” Now you know it’s a multi-step process that involves purification, slicing, cleaning, etching, polishing, and thin film application. That’s how complex it is to make something so tiny yet so powerful it can run many things, from computers to cars.
So, the next time you step foot on silica sand, remember that it’s the primary component that makes your gadgets run.
