Light-Blocking Layer Sequence With Moth-Eye Silicon
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Solution Overview
Problem
Existing light blocking methods in integrated circuits, such as metal layers and black paint, suffer from high reflectance and incomplete light absorption, leading to reduced contrast and efficiency in optical systems, and pose challenges in precision and planarity.
Innovation Solution
A light blocking layer sequence comprising a metal layer and a silicon layer with a moth eye structure, where the silicon layer is at least 2 μm thick and the metal layer has a minimum thickness of 30 nm or more, effectively absorbing and reflecting light across the 180 nm to 1200 nm wavelength range, while allowing for integration into CMOS processes and maintaining a planar surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If metal layers are used for light shielding, then the technological modification is small and integration into CMOS technology is easy, but the reflectance is high causing radiation to scatter back to photosensitive areas
Solution Approach 1:
The patent applies a composite light-blocking structure consisting of a metal layer (aluminum, titanium, or tungsten) combined with a silicon layer having a moth-eye surface structure. This composite approach combines the ease of manufacturing with CMOS technology (from the metal layer) with low reflectance properties (from the silicon moth-eye structure), thereby resolving the contradiction between manufacturability and harmful reflectance.
Solution Approach 2:
The patent changes the surface parameters of the silicon layer by creating a moth-eye structure with specific geometric characteristics (columnar protrusions with 50-500 nm spacing and 100-1000 nm height). This parameter change in surface morphology transforms the optical properties to achieve low reflectance while maintaining compatibility with standard fabrication processes.
2Object-generated harmful factors
If black paint is used for light shielding, then absorption is improved, but the distance to photosensitive areas reduces overlay accuracy and edges cannot be defined precisely
Solution Approach 1:
Instead of using black paint that requires close proximity to photosensitive areas, the patent uses a moth-eye surface structure on silicon that optically mimics the effect of being very close to the photosensitive region. The sub-wavelength structure creates optical effects equivalent to much smaller distances, achieving precise edge definition and high overlay accuracy while maintaining effective light absorption.
3Object-generated harmful factors
If black paint is applied on the surface, then light absorption is achieved, but the surface is not planar and direct application of other layers is not possible
Solution Approach 1:
The patent employs a silicon layer with a moth-eye surface structure that creates a controlled porous or textured morphology. This structure achieves effective light absorption through multiple internal reflections and scattering events within the textured layer, while the overall surface remains planar at the macro scale, allowing subsequent layers to be applied directly without additional planarization steps.
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
The solution achieves nearly zero transmission and minimal reflectance, ensuring effective protection of photosensitive areas with enhanced absorption and compatibility with CMOS technology, allowing for precise integration and efficient light management.
Implementation Method 1
whose surface is provided with a moth eye structure... very efficiently coupling the light into the silicon layer with moth eye structure... no or almost no transmission is given in an interesting wavelength range, for example within the range of 180 nm to 1200 nm, and a much smaller reflectance results
Implementation Method 2
The light, which enters the silicon layer, becomes efficiently absorbed where the absorption can be set by the absorbance characteristics of the silicon layer... By the provided metal layer, a portion of the light which did not become absorbed when crossing the silicon layer once, is reflected
Data Source
AI summary
In an integrated circuit, a light sensitive area is protected against radiation by arranging a light blocking layer sequence (504) on top of the light sensitive area. The light blocking layer sequence comprises one or several metal layers (504a) and a silicon layer (503b, 1) for the purpose of absorption. A moth eye structure is provided on the silicon layer. Thereby, a radiation incident by reflection is minimized in such a way that also stray light can effectively be kept from the light sensitive area below the light blocking layer sequence (504).