What is TTV,Bow,Warp in Semiconductor Wafers

 In wafer manufacturing, TTV, Bow, and Warp are essential parameters that determine wafer flatness and thickness uniformity, significantly impacting critical chip fabrication processes.

 

 

A.Definitions and Measurement Methods of TTV, Bow, and Warp

 

1.TTV (Total Thickness Variation)

 

Definition:
TTV refers to the difference between the maximum and minimum thickness across the diameter of a wafer, assessing thickness uniformity.

 

Measurement:
Measured in a non-clamped state, it calculates the deviation between the minimum and maximum distances from the wafer’s center surface to a reference plane, including both concave and convex variations.

 

Importance:
TTV ensures uniform thickness distribution during processing, preventing adverse effects on subsequent steps and final product performance.

 

2.Bow

Definition:
Bow indicates the curvature of a wafer, representing the vertical distance variation between the center and edges.

 

Measurement:
In a free-standing state, the wafer’s backside serves as a reference plane, and the deviation between the highest and lowest points on the wafer surface relative to this plane is measured.

 

Importance:
Bow is a key parameter for assessing wafer quality and reliability. . Lower Bow values typically indicate cleaner, flatter surfaces with fewer defects during processing.

 

3.Warp

 

Definition:
Warp refers to the overall distortion or irregular deformation of the wafer surface, not limited to localized curvature.

 

Measurement :
Using the surface with the smallest sum of intercepts of all points within the qualified quality area of the wafer surface as the reference plane, measure the deviation between the maximum and minimum distances of the surface from the reference plane.

 

Importance:
WARP is a key metric for measuring the overall flatness of wafers and is crucial for processes such as lithography and etching.

 

B.Differences Between TTV, Bow, and Warp

 

1.TTV: Focuses on thickness variation, independent of curvature or distortion.

 

2.Bow: Focuses on overall curvature, primarily considering the bending between the center and edges.

 

3.Warp: Encompasses both global curvature and distortion across the wafer surface.
While these parameters are related to the wafer’s geometric properties, they measure and describe different aspects, each impacting semiconductor processes and wafer handling uniquely.

 

C.Impact of TTV, Bow, and Warp on Semiconductor Processes

 

Impact on Lithography
Depth of Focus (DOF) Issues: TTV, Bow, and Warp can cause variations in focus depth during lithography, affecting pattern clarity.

 

Alignment issues: These parameters can cause misalignment of wafers, affecting the coverage accuracy between layers.

 

Effect on chemical mechanical polishing
Uneven polishing: During CMP, TTV, bow, and warping can cause
uneven polishing, resulting in surface roughness and residual stress.

 

Impact on Thin Film Deposition
Non-Uniform Deposition: Irregular wafer surfaces may cause uneven thin film deposition.

 

Impact on Wafer Handling
Handling Issues: Warped wafers may suffer damage during automated handling processes.

 

Aluminum Nitride Wafers
AlN wafers are ceramic substrates engineered for cutting-edge electronic and optoelectronic systems, in the semiconductor processes, the aluminum nitride wafers as a bearing substrate for thin film deposition (such as MOCVD), it supports the high-quality epitaxial growth of compound semiconductors such as GaN and AlGaN. Innovacera supplies standard aluminum nitride wafers such as 6” and 8”, if you need it, welcome to contact us at sales@innovacera.com.