Wafer Pre-alignment Using Circumferential Marks
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Solution Overview
Problem
Existing wafer pre-alignment methods face challenges due to geometric issues like low roundness, inconsistent radii, and edge burrs, which affect the accuracy of substrate positioning in photolithographic equipment, and require high image clarity for notch identification, limiting their universality and robustness.
Innovation Solution
A method involving circumferentially arranged marks on the substrate, using Radon conversion and cluster analysis to identify peak values, and a neighbor coherence principle for reliable mark detection, allowing for accurate orientation without edge notch image binarization and enhancing adaptability to geometric flaws.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If image binarization is used for notch identification, then alignment accuracy can be achieved under ideal conditions, but the method becomes highly sensitive to image clarity and loses universality
Solution Approach 1:
The patent changes the detection parameter from edge/notch identification to circumferential mark identification. By detecting marks at multiple angular positions around the wafer periphery rather than relying on edge notch images, the method transforms the detection approach to one that is less sensitive to image binarization quality and more adaptable to various wafer geometric conditions.
Solution Approach 2:
The patent uses multiple circumferential marks as redundant copies of alignment references. Instead of relying on a single edge notch that requires clear imaging, the method employs several marks distributed circumferentially, allowing the system to select valid marks for alignment even when some are affected by geometric flaws or poor image quality.
2Ease of operation
If edge notch identification is used, then alignment can be performed, but geometric issues like low roundness, inconsistent radius, and edge burrs significantly affect positioning accuracy
Solution Approach 1:
The patent extracts the alignment function from the edge/notch region of the wafer and relocates it to circumferential marks positioned away from the problematic edge zone. By placing marks at a predetermined radius from the wafer center, the method separates the alignment reference from the geometrically flawed edge region, eliminating the impact of low roundness, inconsistent radius, and edge burrs on positioning accuracy.
Solution Approach 2:
The patent performs preliminary action by pre-positioning multiple circumferential marks on the wafer before the alignment process. These marks are placed at known angular positions and a predetermined radius, creating robust reference points that are immune to edge geometric issues. The alignment system then uses these pre-established marks rather than attempting to identify features from the problematic edge region.
3Measurement precision
If high image clarity is required for notch identification, then alignment precision can be maintained, but the method becomes less robust to noise and geometric variations
Solution Approach 1:
The patent introduces dynamics by enabling the system to adaptively select from multiple circumferential marks based on their detection quality. Rather than relying on a single fixed notch identification approach that fails under poor imaging conditions, the method dynamically evaluates multiple mark positions and selects valid ones for alignment, maintaining precision while improving reliability under varying noise and geometric conditions.
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 improves the robustness and universality of wafer pre-alignment by reducing the need for high image clarity, mitigating the influence of geometric issues, and increasing the reliability of mark detection, enabling accurate substrate orientation with enhanced noise immunity and adaptability.
Implementation Method 1
obtaining an image of the selected mark by illuminating a selected mark from the plurality of marks on the surface of the substrate with light
Data Source
Figure 1
Figure 2a
Figure 2b~3a
AI summary
A method for pre-aligning a substrate includes the steps of: 1) providing a substrate having a plurality of marks are arranged circumferentially on a surface thereof, wherein each of the plurality of marks consists of at least one first stripe extending in a first direction and at least one second stripe extending in a first direction; 2) aligning a center of the substrate with a given point on a substrate carrier stage; 3) illuminating a mark selected from the plurality of marks on the surface of the substrate with light and obtaining an image of the selected mark; 4) processing the image to obtain first projection data corresponding to the first direction and second projection data corresponding to the second direction; 5) identifying a set of first peak values corresponding to the at least one first stripe of the selected mark from the first projection data and a set of second peak values corresponding to the at least one second stripe of the selected mark from the second projection data; 6) selecting first peak values and second peak values that a) correspond to numbers of the at least one first stripe and the at least one second stripe and b) are deemed authentic, from the set of first peak values and the set of second peak values identified in step 5) and proceeding to step 7); otherwise selecting a next mark as the selected mark and returning to step 4); 7) calculating a current position of the selected mark relative to the substrate carrier stage based on the first and second peak values selected in step 6); and 8) rotating the substrate, according to the current position of the selected mark relative to the substrate carrier stage calculated in step 7), a relative position of the selected mark on the substrate and a desired rotation angle of the substrate relative to the substrate carrier stage, until the substrate is oriented at the desired rotation angle.