Why Do 4-inch And 6-inch Silicon Wafers Need To Have Flat Edges?

What is the flat edge of a silicon wafer?

Flat can also be called a positioning edge.

2, 4, and 6-inch silicon wafers are not completely round, but have a missing corner cut off. After the silicon ingot is pulled out by the CZ method, before it is cut into silicon wafers, once the crystal orientation is determined, one or more flat edges will be cut on the ingot with a diamond saw. Therefore, the silicon wafer has 1-2 positioning edges, the long positioning edge is at the bottom of the wafer, and the short positioning edge is not fixed in position, changing with the crystal orientation and doping type.

What is the relationship between the positioning edge position and the crystal orientation?

There are generally three types of crystal orientations for silicon wafers: <111> <110> <100>.

When the angle between the main positioning edge and the secondary positioning edge is 45°, the silicon wafer type is n-type <111>; when the angle between the main positioning edge and the secondary positioning edge is 90°, the silicon wafer type is p-type <100>; when the angle between the main positioning edge and the secondary positioning edge is 180°, the silicon wafer type is n-type <100>. Since the <110> crystal orientation is not a mainstream silicon wafer crystal orientation, there is no standard to represent it. The <110> crystal orientation can be represented according to the silicon wafer supplier's own standards.

Are the lengths of the primary and secondary positioning edges fixed?

Yes, because they need to match semiconductor manufacturing equipment, the lengths and positions of the primary, primary and secondary positioning edges are fixed.

Generally, the length of the primary positioning edge of a 2-inch silicon wafer is 15.8 mm, the length of the primary positioning edge of a 4-inch silicon wafer is 32.5 mm, and the length of the primary positioning edge of a 6-inch silicon wafer is 57.5 mm. The length of the secondary positioning flat edge of a 4-inch silicon wafer is about 18 mm, and the length of the secondary positioning flat edge of a 6-inch silicon wafer is about 22 mm.