Infrared Filter Integration with Image Sensor Interconnects
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Solution Overview
Problem
Conventional image sensors face challenges in producing infrared filters that can effectively filter both infrared and visible bands due to the absorption of amorphous silicon, resulting in a complex structure with numerous layers and distance issues that affect focus.
Innovation Solution
A method for simultaneously manufacturing infrared bandpass filters and interconnection levels on an image sensor using alternating layers of amorphous silicon and silicon oxide, deposited at controlled temperatures, allowing for a simpler structure and improved focus by optimizing layer thicknesses and positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional infrared filters are produced using numerous alternating layers of amorphous silicon and dielectric materials, then the filter achieves high transmission and narrow bandwidth, but the overall thickness becomes significant and the structure becomes complex
Solution Approach 1:
The patent combines the infrared filter structure with the interconnection levels of the image sensor into a single integrated structure. The alternating layers of amorphous silicon and dielectric materials that form the infrared filter are deposited simultaneously with the interconnection levels, merging two previously separate manufacturing processes into one. This reduces the overall number of layers and simplifies the structure while maintaining the filter's optical performance.
Solution Approach 2:
The alternating layers of amorphous silicon and dielectric materials serve dual functions: they form the infrared bandpass filter structure and simultaneously create the interconnection levels of the image sensor. This multi-functionality eliminates the need for separate filter and interconnection structures, reducing complexity and thickness.
2Ease of manufacture
If a conventional infrared filter is deposited on the surface of interconnection levels, then the filter can be integrated with the sensor, but the distance between microlenses and silicon substrate increases, making effective focusing difficult
Solution Approach 1:
The patent merges the formation of the infrared filter with the formation of the interconnection levels by depositing both structures simultaneously at the same time. This integrated approach ensures that the filter and interconnection levels are created together in a single manufacturing process, preventing any increase in distance between the microlenses and silicon substrate that would occur with sequential deposition.
Solution Approach 2:
The infrared filter structure is formed preliminarily together with the interconnection levels before final assembly with the microlenses. By establishing both structures simultaneously during the deposition process, the patent ensures proper spacing and focusing geometry is maintained from the outset, avoiding subsequent focusing issues.
3Ease of manufacture
If amorphous silicon layers are used in the filter structure, then the filter can be manufactured using standard semiconductor processes, but amorphous silicon absorbs visible light in the 400-600 nm range, preventing visible spectrum filtering
Solution Approach 1:
The patent applies different optical properties to different regions or functions within the filter structure. The amorphous silicon layers provide infrared filtering characteristics while the dielectric materials provide the complementary optical properties needed for visible spectrum filtering. This local differentiation of material properties allows the filter to handle multiple spectral ranges with appropriate materials in their optimal roles.
Solution Approach 2:
The patent uses a composite structure of alternating amorphous silicon and dielectric material layers. Each material contributes its specific optical properties: amorphous silicon for infrared wavelength control and dielectric materials for visible spectrum transmission or filtering. This composite approach combines the advantages of different materials to achieve broad spectral filtering capability while maintaining compatibility with standard semiconductor manufacturing processes.
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 the production of infrared filters with suitable spectral response and electrical performance, maintaining effective focus while reducing the complexity and thickness of the filter structure, enhancing the image sensor's functionality.
Implementation Method 1
interference filters can be obtained by successively depositing alternating dielectric layers with low and high refractive indices
Implementation Method 2
Alternating layers (26-1 to 26-14) of amorphous silicon (high refractive index) and silicon nitride (low refractive index) form the high-pass filter
Implementation Method 3
Another drawback of the filter described in US patent number 5398133 is its numerous layers and significant overall thickness. Furthermore, depositing such a filter on the surface of the interconnect layers of an image sensor increases the distance between the microlenses and the silicon substrate
Data Source
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Figure 3A~3F
Figure 3G~3J
AI summary
The invention relates to an image sensor having a portion comprising interconnection levels formed on a semiconductor substrate (1) covered with a first layer of a dielectric material, comprising conductive tracks (15-1, 15-2, 15-3) separated from each other by insulating layers (6-1, 6-2, 6-3, 6-4), connected to each other by vias (16-1, 16-2, 16-3) passing through the insulating layers, and an infrared bandpass filter comprising filter levels adjacent to the interconnection levels formed by alternating second layers (6-1, 6-2, 6-3) of the dielectric material and silicon layers (5-1, 5-2, 5-3), the refractive index of the dielectric material being less than 2.5 at the maximum transmission wavelength of the filter, one of the second dielectric layers of each filter level being identical to the insulating layer of the adjacent interconnection level.