CMOS Image Sensor Slices for Wafer Yield
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Solution Overview
Problem
The inefficiency in manufacturing image sensors due to the mismatch between rectangular-shaped pixel arrays and circularly exposed areas on round wafers leads to wasted space and increased production costs, with non-rectangular shaped image sensors causing technical difficulties and higher mask requirements.
Innovation Solution
The development of CMOS image sensors with semiconductor slices of uniform width but varying lengths, arranged to form semi-rectangular shapes, including pixel arrays with uniform pitch, guard rings, and row-driver circuitry, where the combined width of certain components is less than or equal to one pixel pitch to minimize dead space and production complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If rectangular shaped image sensors are formed over round wafers, then standard photolithography processes can be used, but significant wafer area is wasted and yield potential is decreased
Solution Approach 1:
The patent applies asymmetry by transitioning from traditional rectangular sensor shapes to circular sensor shapes that match the circular wafer geometry. This allows the sensor active area to extend to the wafer edge, maximizing wafer area utilization and yield potential while maintaining compatibility with standard circular wafer processing equipment and photolithography processes.
Solution Approach 2:
The patent utilizes the radial dimension of circular wafers by arranging sensor components in circular patterns rather than rectangular grids. This dimensional change allows components to be positioned optimally across the entire wafer surface, including areas near the wafer edge that would be wasted in rectangular layouts.
2Productivity
If non-rectangular shaped image sensors are formed to match radiation exposure areas, then yield potential increases, but the non-uniform width causes components to contact pixel arrays and become unusable
Solution Approach 1:
The patent employs asymmetric circular geometry where the sensor boundary is defined by a circular seal ring rather than rectangular edges. This circular asymmetry allows uniform positioning of components relative to the pixel array while maximizing the active sensing area within the circular radiation exposure zone, preventing component contact with usable pixels.
Solution Approach 2:
The patent applies local quality by positioning different components (seal ring, guard rings, readout circuitry) at specific locations within the circular sensor structure. The seal ring is placed at the circular periphery, guard rings surround the pixel array at appropriate distances, and readout circuitry is positioned in non-sensitive areas, ensuring each component has optimal local positioning that prevents unwanted contact with pixels.
3Reliability
If non-rectangular image sensors are enclosed with seal-rings, then component contact with pixel arrays is prevented, but additional unit blocks and masks are required significantly increasing production costs
Solution Approach 1:
The patent merges multiple functions into the circular seal ring structure. The seal ring simultaneously serves as the sensor boundary definition, the component isolation barrier, and the structural element that prevents contact between components and pixel arrays. This consolidation eliminates the need for separate isolation structures and reduces the total number of photomasks required for fabrication.
Solution Approach 2:
The circular seal ring structure performs multiple functions: it defines the sensor perimeter, isolates components from the pixel array, provides mechanical support, and serves as a reference for aligning other components. This multi-functionality reduces the overall device complexity and minimizes the number of fabrication steps and masks needed compared to rectangular sensor designs with separate isolation structures.
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
The disclosed embodiments include an image sensor (100) and a method to manufacture thereof. In one embodiment, the method includes forming a plurality of semiconductor slices (104, 106, 108, 110) having a uniform width, at least two of the semiconductor slices having different lengths, and each of the semiconductor slices having a slice edge (152A, 152B, 154A, 154B, 156A, 156B, 158A, 158B) defining a side of the semiconductor slice. The method further includes arranging the semiconductor slices to form a semi-rectangular shape defining boundaries of the image sensor, each of the semiconductor slices being disposed proximate to another semiconductor slice of the plurality of semiconductor slices. Forming each semiconductor slice includes forming a plurality of pixel arrays (112, 114, 116) over the semiconductor slice (104), the pixel arrays having an approximately uniform pixel pitch, and forming a seal ring (160) around the semiconductor slice, the seal ring enclosing the semiconductor slice and the pixel arrays of the semiconductor slice, and each semiconductor slice having a different seal ring.