Wafers are the most commonly used semiconductor materials, divided into specifications such as 4 inches, 5 inches, 6 inches, and 8 inches in diameter. Recently, 12 inches or even larger specifications have been developed. The larger the wafer, the more ICs can be produced on the same wafer, which can reduce costs; But the requirements for material technology and production technology are higher. It is generally believed that the larger the diameter of a silicon wafer, the better the technology of the wafer factory. In the process of producing wafers, yield is a very important condition.