NIR CMOS Image Sensor Fabrication via Dual-Surface Dopant Implantation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The increasing depth of vertical photodiodes in CMOS image sensors necessitates higher implant energies for dopant introduction, which is challenging for existing semiconductor processing equipment and may require costly upgrades, especially as photodiodes continue to deepen.
Innovation Solution
Implementing a method where dopants are introduced into the epitaxial layer from both the first and second surfaces, reducing the maximum implant energy required by up to 50% and allowing for deeper photodiodes to be fabricated using current equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If photodiode depth is increased to achieve higher resolution, then more photodiodes can be disposed in the same surface area, but the implant energy required to introduce dopant becomes excessively high (in excess of 10 MeV)
Solution Approach 1:
The dopant implantation process is segmented into two separate implants: a first implant through the front surface and a second implant through the back surface. This segmentation allows each implant to operate at lower energy levels (avoiding the need for excessively high energies above 10 MeV) while collectively achieving the desired dopant distribution in deep photodiodes.
Solution Approach 2:
The approach transitions from a single-direction (one-dimensional) implantation method to a two-directional method by utilizing both the front and back surfaces of the substrate. This dimensional change enables dopant introduction from opposite directions, effectively reducing the required implant energy for each individual implant while achieving the same or better dopant distribution in deeper photodiodes.
2Length of stationary object
If implant energy is increased to introduce dopant into deeper photodiodes, then dopant can reach the required depth, but existing semiconductor processing equipment becomes insufficient and costly upgrades are required
Solution Approach 1:
The implantation process is divided into two separate implantation steps performed with existing equipment. Each step uses moderate energy levels that current semiconductor processing equipment can handle, eliminating the need for costly upgrades to achieve ultra-high energy implants while still achieving the required dopant depth in the photodiode structure.
Solution Approach 2:
By utilizing both front and back surfaces for implantation, the method enables deep photodiode fabrication using conventional equipment. The two-directional approach distributes the implantation task across two moderate-energy steps instead of requiring a single high-energy step, maintaining compatibility with existing manufacturing equipment.
3Device complexity
If single-sided dopant implantation is used in traditional fabrication processes, then the process is simpler, but the maximum implant energy must be extremely high to reach deep photodiodes
Solution Approach 1:
The fabrication process is segmented into two implantation steps from opposite surfaces. While this increases process steps, each step operates at lower energy levels, and the overall process becomes more manageable and compatible with existing equipment. The segmentation trades procedural complexity for reduced energy requirements and equipment compatibility.
Solution Approach 2:
The method introduces a second implantation dimension by utilizing the back surface in addition to the front surface. This two-directional approach distributes the implantation workload, allowing each implant to use lower energy while achieving the cumulative effect of deep dopant penetration required for deep photodiodes.
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 fabrication of deeper photodiodes with reduced implant energy, extending the capabilities of existing semiconductor processing equipment and allowing for next-generation photodiodes that are twice as deep as previously possible without the need for costly upgrades.
Implementation Method 1
performing a first implant by implanting dopant through the first surface and into the epitaxial layer
Implementation Method 2
performing a thermal treatment to anneal the dopant
Data Source
AI summary
A method of fabricating CMOS image sensors is disclosed. In contrast to traditional fabrication processes, the present sequence implants dopants into the epitaxial layer from both the first surface and the second surface. Because dopant is introduced through both sides, the maximum implant energy to perform the implant may be reduced by as much as 50%. In certain embodiments, the second implant is performed prior to the application of the electrical contacts. In another embodiments, the second implant is performed after the application of the electrical contacts. This method may allow deeper photodiodes to be fabricated using currently available semiconductor processing equipment than would otherwise be possible.