What is Notch on Wafers?

Silicon wafers are the foundation of integrated circuits and semiconductor devices. They have an interesting feature - flat edges or tiny grooves on the sides .It is not a defect, but a deliberately designed functional marker.In fact, this notch serves as a directional reference and identity marker throughout the entire manufacturing process.

In the early days, wafers mostly used a “flat” as the marker, meaning a short straight segment ground on the circular edge. The position and number of these flats were used to distinguish crystal orientations and doping types. As wafer size increased and process precision improved, mainstream 200 mm and 300 mm wafers have largely standardized on a small arc-shaped notch design. The position of this notch is defined by standards and is located at a fixed orientation, used to indicate the wafer’s crystal orientation (for example <100> or <111>) and to provide a common reference point for subsequent equipment.

What is the function of the wafer notch? 

• First, it provides a reference for wafer alignment. Key steps such as lithography, etching and ion implantation require multiple pattern layers to be stacked. If the coordinate system of each layer is not consistent, the final devices will be misaligned and scrapped. By detecting the notch position, equipment can quickly establish a unified coordinate system and then use alignment marks to achieve precise overlay.
• Second, it encodes wafer information. Different crystal orientations and different doping types (such as P-type and N-type) have distinct material properties and design considerations. The notch orientation, combined with back-side markings and other means, allows the production line to quickly identify wafers during automated handling and sorting, avoiding mix-ups between different product types.
• Third, it ensures safety in automated handling. Modern fabs make extensive use of robot arms and Automated Material Handling Systems (AMHS). These systems rely on the notch to determine the front/back side and orientation of the wafer, preventing misloading or flipping that would otherwise lead to yield loss.

For device and process engineers, the notch on a wafer may look insignificant, but it runs through the entire process chain from crystal pulling, epitaxy and wafer fabrication all the way to pre-packaging test. Whenever “direction” is involved—crystal orientation, layout alignment, stress orientation, or even the structure design of certain power devices—this small geometric marker is almost always in the background. Once you understand the role of the notch, it becomes much easier to follow how a wafer “moves” through the production line and how each process step builds its coordinate system around this piece of silicon.