Pixel Sensor DTI Metal Insert Layout for Higher Quantum Efficiency
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Solution Overview
Problem
The size and shape of diffusion structures in CMOS image sensors are limited by the metal layer etching process, which restricts their ability to distribute light effectively, leading to low quantum efficiency and limited optical bandwidth, and the use of high-reflectivity metals like copper is impractical due to etching challenges.
Innovation Solution
Forming a metal insert in a deep trench isolation structure by planarization instead of etching, allowing for fully filled recesses with dielectric material, which enables greater flexibility in diffusion structure design and the use of high-reflectivity metals like copper.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If metal layer etching process is used to form diffusion structures, then manufacturing process is simpler, but diffusion structure size and shape are limited and quantum efficiency is low
Solution Approach 1:
Instead of etching the metal layer to form diffusion structures, the patent forms diffusion structures first using dielectric material deposition in recesses, then planarizes the surface to expose the metal insert. This inverted sequence removes the etching constraint on diffusion structure geometry, enabling larger sizes and more flexible shapes while maintaining manufacturing feasibility.
Solution Approach 2:
The patent performs preliminary actions by forming the diffusion structures and planarizing the surface before final metal insert formation. This allows the diffusion structures to be designed with optimal size and shape for light distribution without being constrained by subsequent metal etching capabilities.
2Use of energy by moving object
If high-reflectivity metals like copper are used, then optical reflectivity is improved, but etching challenges make it impractical
Solution Approach 1:
The patent inverts the conventional sequence by forming the metal insert before the diffusion structures. High-reflectivity metals like copper are deposited as the metal insert, then diffusion structures are formed around it through dielectric deposition and planarization. This eliminates the need to etch copper, making high-reflectivity metals practical to use.
Solution Approach 2:
The patent introduces dielectric material as an intermediary that fills the recesses around the metal insert and is subsequently planarized. This intermediary approach allows the metal insert to be formed without etching, while still enabling precise diffusion structure formation around it.
3Productivity
If diffusion structures are limited in size and shape, then manufacturing is easier, but light distribution capability and quantum efficiency are reduced
Solution Approach 1:
By inverting the formation sequence to create diffusion structures before finalizing metal patterns, the patent enables diffusion structures with larger sizes and more complex shapes. These enhanced structures can distribute light more effectively across the photodiode, directly improving quantum efficiency without being constrained by metal etching limitations.
Solution Approach 2:
The patent changes the formation parameters of diffusion structures by using dielectric material deposition and planarization instead of metal etching. This allows diffusion structures to achieve larger dimensions, varied shapes, and optimized positions for light distribution, thereby improving quantum efficiency and optical bandwidth.
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 increases quantum efficiency by enabling diffusion structures to distribute light for specific wavelengths and broader bandwidths, reduces manufacturing complexity and cost, and enhances optical isolation.
Implementation Method 1
Complementary metal oxide semiconductor (CMOS) image sensors utilize light-sensitive CMOS circuitry to convert light energy (e.g., photons) into electrical energy. As the photodiode is exposed to light, an electrical charge is induced in the photodiode (referred to as a photocurrent).
Implementation Method 2
The diffusion structures distribute incident light across the photodiode to reduce the likelihood of optical saturation in an particular area in the photodiode, which may increase the quantum efficiency (QE) of the pixel sensor.
Implementation Method 3
a metal insert is formed in a deep trench isolation (DTI) structure that laterally surrounds the photodiode... the metal insert may be formed in a manner in which a metal layer is formed and planarized to form the metal insert
Data Source
AI summary
A metal insert is formed in a deep trench isolation (DTI) structure that laterally surrounds a photodiode of a pixel sensor, and the metal insert is formed in a manner in which a metal layer is formed and planarized to form the metal insert as opposed to etching the metal layer to form the metal insert. Recesses for diffusion structures are formed and then fully filled with a dielectric material as opposed to partially filling the recesses with a dielectric layer and then forming the metal layer on the dielectric layer. The diffusion structures have a substantially flat top surface on which the metal layer is then formed, which enables the metal layer to be planarized instead of etched to form the metal insert.