In-Situ Doped Epitaxial Pinning Layer for Image Sensors
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Solution Overview
Problem
Highly integrated image sensors face difficulties in forming a highly doped and shallow pinning layer using traditional ion implantation and annealing processes, leading to increased depth of the pinning layer and surface defects that generate noise, making it challenging to achieve high light absorption and quantum efficiency.
Innovation Solution
A method involving the formation of a trench in a substrate with a second conductivity type epitaxial layer filling the trench and a first conductivity type epitaxial layer formed over it, using in-situ doping with Si or SiGe to create a shallow and uniform P-type pinning layer, reducing surface defects and improving charge transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If ion implantation and annealing process is used to form pinning layer, then doping concentration can be increased, but depth of pinning layer becomes larger due to dopant diffusion during annealing
Solution Approach 1:
The patent replaces the traditional ion implantation and annealing process with an in-situ doped epitaxial growth process. Instead of mechanically implanting ions and then thermally diffusing them through annealing, the dopants are incorporated directly during the epitaxial growth of the silicon layer, eliminating the diffusion step that causes excessive depth formation.
Solution Approach 2:
The patent changes the fundamental process parameters by transitioning from a two-step process (ion implantation followed by annealing) to a single-step in-situ doped epitaxial growth process. This parameter change allows precise control of both doping concentration and depth simultaneously, resolving the contradiction between achieving high doping concentration and maintaining shallow depth.
2Quantity of substance
If ion implantation process is used to form pinning layer, then doping can be achieved, but surface defects and dangling bonds are generated causing noise
Solution Approach 1:
The patent substitutes the ion implantation process with in-situ doped epitaxial growth. The epitaxial growth process inherently produces high-quality crystalline structures without generating surface defects or dangling bonds, thereby eliminating the noise problem associated with ion implantation while still achieving the required doping concentration.
Solution Approach 2:
The patent converts the potential harm of surface defects generated by ion implantation into a benefit by using epitaxial growth, which naturally produces defect-free surfaces. The in-situ doping during epitaxial growth provides the doping function without the harmful side effects, effectively turning the limitation of ion implantation into an advantage of the new method.
3Quantity of substance
If traditional ion implantation method is used, then pinning layer can be formed, but additional apparatuses and process complexity are required for highly integrated devices
Solution Approach 1:
The patent merges the doping step and the layer formation step into a single in-situ doped epitaxial growth process. This consolidation eliminates the need for separate ion implantation and annealing apparatuses, reducing process complexity and equipment requirements while maintaining the ability to form highly doped pinning layers with precise depth control.
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 creation of a photodiode with enhanced light absorption and quantum efficiency per unit surface area, reducing noise and achieving high sensitivity for short wavelengths without requiring additional apparatuses or altering the device layout, while preventing dangling bonds and surface defects.
Implementation Method 1
forming a first conductivity type second epitaxial layer over the second conductivity type first epitaxial layer
Implementation Method 2
using in-situ doping with Si or SiGe to create a shallow and uniform P-type pinning layer
Implementation Method 3
The second impurity region 111 is formed as the pinning layer of a pinned photodiode, and has been formed by employing an ion implantation and an annealing process
Implementation Method 4
an annealing process for activating dopants implanted into the substrate is performed
Implementation Method 5
An images sensor is a device which converts more than one- or two-dimensional optical information into electrical signals
Data Source
AI summary
An image sensor includes a first conductivity type substrate with a trench formed in a predetermined portion thereof, a second conductivity type impurity region formed in the first conductivity type substrate below the trench and being a part of a photodiode, a second conductivity type first epitaxial layer filling the trench and being a part of the photodiode, and a first conductivity type second epitaxial layer formed over the second conductivity type first epitaxial layer.