Semiconductor Edge-Mark Alignment for Optical Shielding
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Solution Overview
Problem
The existing methods for manufacturing CMOS image sensors face challenges in improving optical yield and processing accuracy, particularly in aligning photo masks during the formation of color filter arrays and optical shielding layers, which can lead to improper pattern transfer and reduced light sensitivity.
Innovation Solution
A method involving a substrate with edge-marks on both sides, where a first photo mask aligns with the edge-mark to remove a portion of the optical shielding layer corresponding to the alignment mark, allowing the alignment mark to be detected through the substrate, enabling precise patterning of the optical shielding layer without etching the back-side surface, thereby facilitating even formation of the color filter layer and increasing optical yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the back-side surface is etched to expose the alignment mark, then the alignment mark can be detected, but the color filter layer cannot be formed evenly and optical yield is reduced
Solution Approach 1:
The substrate is divided into front-side surface and back-side surface with independent functions. The alignment mark is kept on the front-side surface for detection, while the back-side surface is dedicated to forming the color filter layer and optical shielding pattern, avoiding interference between alignment detection and filter formation processes.
Solution Approach 2:
An optical shielding layer is introduced as an intermediary element on the back-side surface. This layer can be selectively removed to expose the substrate for forming the optical shielding pattern, while the alignment mark remains intact on the front-side surface for continued use in alignment processes.
2Manufacturing precision
If photolithography is used to form the color filter array, then precise patterning is achieved, but alignment errors occur due to improper photo mask alignment
Solution Approach 1:
The alignment process is enhanced by using optical detection of the alignment mark on the front-side surface instead of relying solely on mechanical positioning. The edge-mark and alignment mark provide optical references that enable precise photo mask alignment through optical detection systems.
Solution Approach 2:
The alignment mark is pre-formed on the front-side surface before photolithography processes. This preliminary alignment reference enables accurate photo mask positioning before the actual pattern transfer, ensuring precise alignment without requiring back-side etching.
3Ease of operation
If the alignment mark is formed on the back-side surface, then alignment can be performed, but the color filter layer formation is affected and optical yield decreases
Solution Approach 1:
The alignment function is moved from the back-side surface to the front-side surface of the substrate. By placing the alignment mark on the front-side surface in the active region, the back-side surface is freed for optimal color filter layer formation, resolving the conflict between alignment accessibility and filter quality.
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 method enhances processing accuracy and optical yield by allowing the alignment mark on the front-side surface to be used without etching the back-side surface, ensuring precise patterning and improved light sensitivity in CMOS image sensors.
Implementation Method 1
a first photo mask is aligned to the substrate according to the edge-mark. Next, a portion of the optical shielding layer corresponding with the alignment mark is removed by using the first photo mask
Implementation Method 2
the alignment mark is formed on the substrate for forming scattering site or diffraction edge during the alignment process. Hence, while a light source is provided to illuminate the wafer, the diffraction patterns caused by the light beam passing by the alignment mark are reflectively projected onto the alignment sensor
Data Source
AI summary
A method for fabricating a semiconductor device includes steps as following. First, a substrate with an edge-mark is provided. The substrate has a front-side surface and a back-side surface opposite to each other. The front-side surface has an active region and a peripheral region with an alignment mark formed thereon. Next, an optical shielding layer is formed over the back-side surface of the substrate. Next, a first photo mask is aligned to the substrate by standing on the edge-mark. Next, a portion of the optical shielding layer corresponding with the alignment mark is removed by using the first photo mask. Next, a second photo mask is aligned to the substrate by standing on the alignment mark. Then, a portion of the optical shielding layer corresponding with the active region is removed to expose a portion of the substrate by using the second photo mask for forming an optical shielding pattern.