Overlay Error Measurement Using Differential Interference Contrast Microscopy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for measuring stacking overlay error in 3D wafer stacking face challenges due to the need for separate focusing on upper and lower layer overlay marks, leading to measurement errors and increased time, especially when multiple wafers are stacked together, affecting wafer yield.
Innovation Solution
A differential interference contrast microscope system is used to measure the stacking overlay mark, focusing on one overlay mark of both the lower and upper layers, with an image analysis scheme to obtain reference positions and compute the overlay error, allowing simultaneous measurement without requiring separate focusing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate focusing on upper and lower layer overlay marks is performed using bright-field optical microscopy, then measurement of stacking overlay error is achieved, but measurement time increases and measurement errors accumulate
Solution Approach 1:
The patent combines the focusing operation for upper and lower layer overlay marks into a single focal plane. By designing the overlay marks with different depths that both lie within the depth of field of a single focal point, the system eliminates the need for separate focusing operations, thereby reducing measurement time while maintaining measurement accuracy through simultaneous capture of both marks in one image.
Solution Approach 2:
The patent transitions from sequential focusing in the depth dimension to simultaneous imaging by utilizing the depth of field dimension. By positioning overlay marks at different depths that both fall within the acceptable depth of field range, the system captures both marks in a single focal plane, effectively converting a time-consuming sequential process into a simultaneous operation.
2Measurement precision
If separate focusing on upper and lower layer overlay marks is performed, then complete measurement data is obtained, but horizontal movement is introduced causing measurement errors
Solution Approach 1:
The patent merges the imaging of upper and lower layer overlay marks into a single captured image by positioning both marks within the depth of field of one focal point. This eliminates horizontal movement between separate focusing operations, ensuring that both marks are measured from the same positional reference, thereby improving measurement consistency and eliminating errors caused by stage movement.
Solution Approach 2:
The patent creates a single comprehensive image copy that contains both upper and lower layer overlay marks simultaneously. This single image copy serves as the complete measurement data source, eliminating the need for multiple sequential images that would require alignment and combination, thereby preventing errors introduced by horizontal movement during sequential imaging.
3Productivity
If bright-field optical microscopy is used to measure both upper and lower layer overlay marks, then measurement capability is provided, but separate focusing is required increasing complexity
Solution Approach 1:
The patent merges the measurement of upper and lower layer overlay marks into a single operational step by utilizing depth of field to include both marks in one focal plane. This eliminates the need for complex sequential focusing operations, reducing operational complexity while maintaining high measurement efficiency through simultaneous capture and analysis of both marks.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate and efficient measurement of stacking overlay error without the need for separate focusing, reducing measurement time and error accumulation, thereby improving wafer yield in 3D wafer stacking processes.
Implementation Method 1
a differential interference contrast microscope system is used to measure the stacking overlay mark
Data Source
AI summary
According to one embodiment of a method for measuring a stacking overlay error, the method may use a differential interference contrast microscope system to measure a stacking overlay mark and focus on one overlay mark of a lower layer overlay mark and an upper layer overlay mark when measuring the stacking overlay mark. Then, the method uses an image analysis scheme to obtain an image of the stacking overlay mark from a photo-detector and obtains a first reference position of the lower layer overlay mark in a direction and a second reference position of the upper layer overlay mark in the direction from the image; and computes the stacking overlay error in the direction according to the first and the second reference positions.