TTV（Total Thickness Variation）

Definition: TTV is the "total thickness variation" or "total thickness deviation" of a silicon wafer, which refers to the absolute difference between the maximum and minimum thickness of the measured wafer during thickness scanning or a series of point thickness measurements.

Importance: In semiconductor processes, the thickness of silicon wafers must be very uniform across the entire surface to ensure device performance and stability. TTV is an important indicator for measuring the uniformity of silicon wafer thickness.

Typical values: In practical applications, the TTV of a 4-inch silicon wafer is generally less than 2 μ m, and a 6-inch silicon wafer is generally less than 3 μ m.

Bow

Definition: Bow refers to the degree of curvature of a silicon wafer, which is the maximum distance difference between the two ends and the center of the silicon wafer. It reflects the curvature of the silicon wafer on the horizontal plane.

Measurement method: Assuming that the distance difference between the two ends and the center of the silicon wafer is d1 d2， Then Bow=Max (d1, d2).

Importance: The Bow parameter is crucial for evaluating the local bending of silicon wafers, as it directly affects the manufacturing and performance of the device.

Warp

Definition: Warp refers to the maximum deviation of the silicon wafer surface from the plane, that is, the maximum deviation between the height of any point on the silicon wafer and the best fitting plane (usually calculated by the least squares method as the reference plane). It reflects the curvature of the silicon wafer in the vertical plane.

Measurement method: The Warp value is determined by scanning the entire surface of the silicon wafer, measuring the height of all points, and calculating the maximum deviation of these points relative to the best fitting plane.

Importance: The Warp parameter provides information on the overall flatness of silicon wafers and is crucial for evaluating their overall bending and twisting behavior.

Typical value: The SEMI standard for 4-inch silicon wafers is Warp less than 40 μ m.

TIR（Total Indicated Runout）

Definition: TIR refers to the degree of local warping on the surface of a silicon wafer and is a parameter that describes the local warping of the silicon wafer.

Measurement method: Usually, a measuring needle is used to detect the height difference on the surface of the silicon wafer, and then the measurement result is converted into a TIR value.

Importance: The smaller the TIR value, the higher the flatness of the silicon wafer surface, which is crucial for device manufacturing and performance.

In summary, parameters such as TTV, Bow, Warp, and TIR collectively reflect the flatness and thickness uniformity of silicon wafers, and have a direct impact on many key steps in the chip manufacturing process. Therefore, in the process of silicon wafer manufacturing and device production, it is necessary to strictly control these parameters to ensure product quality and performance.