Wafer: Groundwork for the Modern Semiconductor Industry

Semiconductor wafers are the most common semiconductor base material, and their diameters range from 4 to 8 inches.

FREMONT, CA: The term wafer often appears in articles or discussions about the semiconductor industry. How does a wafer work? An "8" or "12" wafer refers to what? Can large-size wafers be produced quickly? This article provides a step-by-step explanation of the wafer, one of the semiconductors' most crucial components.

A wafer is a silicon wafer used to manufacture silicon semiconductor integrated circuits. Due to its round shape, it is referred to as a wafer. A wafer is a substrate used to manufacture integrated circuits. A wafer is typically a single-crystal silicon wafer. Wafers are the most common semiconductor base material, and their diameters are classified into 4 inches, 5 inches, 6 inches, and 8 inches. The larger the wafer, the greater the number of ICs manufactured on a single wafer, which helps reduce production costs. However, larger wafers have higher needs for material technology and production technology. It is commonly assumed that the greater the diameter of the silicon wafer, the more advanced the fab's technology. In fabricating wafers, the yield rate is a crucial factor.

Wafers serve as the foundation for the production of computer chips. Chip production can be compared to building a house with Lego blocks; by stacking layer by layer, we can achieve the desired shape (the selected chip). However, if the structure lacks a solid basis, it will be distorted and unsatisfactory. A stable base plate is essential to building a perfect house. This substrate for wafer manufacture is the wafer mentioned next.

In solid substances, a particular crystal structure exists: monocrystalline. It possesses the property of atoms stacked tightly one after another, forming a flat atomic surface. Therefore, employing a single crystal to create a wafer can satisfy the criteria above. To manufacture such a substance, however, there are two essential steps: purification and crystal pulling.

How to Create a Crystal Wafer

The purification process consists of two steps. The initial step is metal purification. This technique includes primarily adding carbon to silicon oxide to transform it via redox into silicon with a purity greater than 98 percent. Most metals, such as iron and copper, are refined in this manner to achieve acceptable purity. However, 98 percent still needs to be increased for wafer fabrication and further enhanced. Therefore, the Siemens method will be employed for additional purification to get the high-purity polysilicon required for the semiconductor process.

Next is the crystal extraction procedure. Liquid silicon is created by melting high-purity polysilicon already acquired. Then, a single-crystal silicon seed is brought into contact with the liquid's surface and slowly withdrawn while rotating. Silicon single-crystal seeds are required to commence the arrangement of silicon atoms on the crystal as it grows. The neatly placed monocrystalline silicon pillars are completed once the silicon atoms exiting the liquid solidify on the surface of the crystal.

However, what do 8 and 12 inches represent? This pertains to the diameter of the completed crystal column. How challenging is it to produce huge wafers? As previously stated, the buildup of the crystal is analogous to the process of making cotton candy. As the center is rotated, successive layers are added until the desired diameter is reached. If you have ever manufactured cotton candy, you understand that it becomes more challenging to create a homogeneous product as the center grows larger. The same holds for the tugging of crystals. The rotational speed and temperature regulation will impact the quality of the crystal column. Therefore, the larger the size, the higher the speed and temperature requirements for crystal pulling, making it more challenging to produce 12-inch wafers of superior quality than 8-inch wafers.

Thin slices must be sliced off this silicon pillar to obtain the wafer. The silicon pillars are sliced laterally into wafers using a diamond knife, and the wafers' surfaces are then polished to make the final, completed wafers. Once the wafer substrate is complete, chip production is concluded by stacking the circuits onto the wafer.