CMOS Image Sensor Microlens Alignment via Dedicated Mark
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Solution Overview
Problem
Existing CMOS image sensors face light loss and image quality deterioration due to misalignment and overlay variations in metal and via formation processes, which affect the alignment of microlenses and lead to light scattering and reflection.
Innovation Solution
The solution involves aligning microlenses directly above the active area of the pixel region, using an alignment key specific to the active area rather than the metal layers, to manage overlay variations and enhance optical efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If microlens alignment uses top metal layer as reference, then metal layer formation is simplified, but overlay variation increases causing light scattering and reflection
Solution Approach 1:
An alignment mark structure is introduced as an intermediary element between the metal layers and microlens formation processes. This alignment mark serves as a dedicated reference feature that mediates the alignment process, allowing microlenses to be precisely positioned relative to the pixel area without being directly dependent on metal layer alignment. The alignment mark structure includes features that can be clearly identified during photolithography alignment, thus improving manufacturing precision while maintaining ease of manufacture.
2Device complexity
If metal and via formation processes are performed without considering light path, then device complexity is reduced, but light loss increases due to misalignment and overlay variation
Solution Approach 1:
The alignment mark structure is formed in advance during the metal layer formation process, specifically as part of the upper metal layer pattern. This preliminary action ensures that the alignment reference is already in place before microlens formation begins. By performing this alignment preparation in advance, the system maintains simple formation processes while enabling precise microlens alignment that prevents light loss from misalignment.
3Ease of manufacture
If alignment key is not provided for active area, then manufacturing process is simplified, but color difference dispersion increases due to misalignment
Solution Approach 1:
The alignment mark structure merges multiple functions into a single integrated feature. It serves both as part of the metal layer structure (specifically the upper metal layer pattern) and as the alignment reference for microlens formation. This merging eliminates the need for separate alignment keys while maintaining precise alignment capability, thus preserving manufacturing simplicity while improving alignment precision and reducing color difference dispersion.
Data Source
AI summary
An image sensor is disclosed that can provide a microlens aligned directly above an active area of a substrate. The image sensor can include a substrate having a pixel area. An active region can be formed on the pixel area and can include photodiodes. Metal lines and an interlayer dielectric can be provided on the pixel area of the substrate. A microlens can be formed above the metal lines and interlayer dielectric to be directly aligned with the active area of the pixel area. To achieve such an alignment, an alignment key of the microlens can be aligned with an alignment key of the active region. In one embodiment, the microlens can avoid being formed right above the metal lines.