Metal Optical Filter for CMOS Image Sensor Front Face Illumination
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Solution Overview
Problem
Existing integrated imaging devices with front face illumination face challenges due to the limitations of colored filters, which are not robust enough for infrared wavelengths and degrade at high temperatures, and multilayer interference filters are expensive and difficult to integrate, while metal filters formed by metallization levels lack precise dimension control and suffer from optical property degradation due to silicon nitride or carbo-nitride layers.
Innovation Solution
The formation of metal optical filters with customizable dimensions and improved optical properties by placing them within dielectric regions associated with metallization levels, allowing for different metals and heights to be used for each filter, reducing cross-talk and eliminating the need for silicon nitride or carbo-nitride layers, enabling better filtering capabilities for various wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If colored filters with pigments are used, then the device can filter visible light, but the filters are not robust for infrared wavelengths and degrade at high temperatures
Solution Approach 1:
The patent changes the material parameter from organic pigments to inorganic metals (aluminum, copper, silver), which fundamentally alters the thermal stability and wavelength range. Metals do not degrade at high temperatures like organic pigments and can effectively filter infrared wavelengths, thus resolving the reliability issue while maintaining filtering capability.
Solution Approach 2:
The patent creates a composite structure by integrating metal layers with the semiconductor substrate and dielectric layers. This composite approach combines the optical filtering properties of metals with the structural benefits of semiconductor fabrication, achieving both thermal stability and wavelength-selective filtering including infrared range.
2Adaptability or versatility
If multilayer interference filters are used, then the device can filter various wavelengths including UV and infrared, but the fabrication becomes expensive and difficult to integrate
Solution Approach 1:
The patent extracts the filtering function from complex multilayer dielectric stacks and implements it using simple metal layers. By taking out the essential filtering capability and realizing it through metal absorption properties rather than interference effects, the patent dramatically reduces the number of fabrication steps while maintaining wavelength selectivity across UV, visible, and infrared ranges.
Solution Approach 2:
The patent adopts a simpler, more economical approach by using single or few metal layers instead of expensive multilayer dielectric stacks. The metal filters can be fabricated using standard semiconductor metallization processes, making them cheaper and easier to integrate despite potentially shorter operational lifetime in harsh environments.
3Ease of manufacture
If metal filters are formed using metallization level constraints, then the fabrication is simplified, but the pattern dimensions cannot be precisely controlled
Solution Approach 1:
The patent introduces flexibility in the metal filter formation process, allowing the metal layer to be deposited to varying thicknesses and patterns depending on the specific filtering requirements. This dynamic approach enables precise dimension control for different wavelength applications while still using standard metallization processes, resolving the contradiction between fabrication simplicity and precision.
4Ease of manufacture
If silicon nitride or carbo-nitride layers are used in metal filter fabrication, then the metallization process is standardized, but the optical properties of the metal filters are degraded
Solution Approach 1:
The patent extracts the metal filter from the conventional metallization stack by removing the overlying silicon nitride or carbo-nitride layers that would otherwise cover and degrade the metal filter's optical properties. This extraction allows the metal filter to function optimally while the remaining dielectric layers provide sufficient mechanical support and process compatibility.
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 allows for more configurable and optically superior metal filters that can be precisely adapted to specific applications, enhancing imaging device performance by reducing cross-talk and improving color reproduction, particularly for Bayer patterns and other wavelength applications.
Implementation Method 1
Optical filters are known from the prior art comprising one or more metal layers in which patterns (holes or bumps) are formed having dimensions of the order of ten to a hundred nanometers. This type of structure is better known by the term plasmonic filter.
Implementation Method 2
reference may be made to the document 'Light in tiny holes' (C. Genet and T. W. Ebbesen, Nature 445, pages 39-46, 4 Jan. 2007) which describes the transmission of light by nanometer-sized holes.
Data Source
AI summary
An integrated imaging device supports front face illumination with one or more photosensitive regions formed in a substrate. A lower dielectric region is provided over the substrate, the lower dielectric region having an upper face. A metal optical filter having a metal pattern is provided on the upper face (or extending into the lower dielectric region from the upper face). An upper dielectric region is provided on top of the lower dielectric region and metal optical filter. The lower dielectric region is at least part of a pre-metal dielectric layer, and the upper dielectric region is at least part of a metallization layer.