3D Image Sensor Contact Plug Insulating Layer Dishing
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Solution Overview
Problem
In the manufacturing of image sensors, the reduction in photodiode size leads to reduced light reception area, resulting in decreased image quality, poor bonding efficiency between photodiode and readout circuitry, and increased dark current due to charge sharing and dishing phenomena, which affects sensitivity and saturation.
Innovation Solution
The implementation of a contact plug with a partially insulating layer to reduce dishing and enhance bonding strength, along with a smooth transfer path for photo charges between the photodiode and readout circuitry, using a damascene form and insulating layer to improve ohmic contact and bonding efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the photodiode size is reduced to increase the number of pixels, then the pixel density increases, but the light receiving area is reduced resulting in degraded image quality
Solution Approach 1:
The patent transitions from a planar 2D pixel arrangement to a 3D stacked architecture where photodiodes are positioned vertically over readout circuitry. This dimensional change allows increased pixel density without reducing the horizontal light receiving area of each photodiode, thereby maintaining image quality while increasing the number of pixels.
2Reliability
If a tungsten plug is formed using CMP process to connect photodiode and readout circuitry, then electrical connection is established, but dishing occurs reducing bonding area and bonding efficiency
Solution Approach 1:
The patent introduces a dual-doping structure with an intrinsic semiconductor layer positioned between the n-type doped region and the p-type doped region. This intermediary layer acts as a mediator that facilitates smooth charge transfer while eliminating the need for tungsten plugs and CMP processes, thereby preventing dishing and maintaining full bonding area.
3Reliability
If both source and drain are heavily doped with N-type impurities to form transfer transistor, then transistor conductivity increases, but charge sharing phenomenon occurs reducing sensitivity and generating image errors
Solution Approach 1:
The patent implements non-uniform doping concentrations across different regions: the source region has a first doping concentration, the drain region has a second doping concentration, and the intrinsic layer has no doping or different doping characteristics. This local quality differentiation prevents charge sharing while maintaining necessary conductivity for transistor operation.
4Productivity
If photodiode area is reduced, then pixel count increases, but the number of incident photons is reduced due to diffraction resulting in reduced sensitivity
Solution Approach 1:
By stacking photodiodes vertically over readout circuitry in the third dimension, the patent enables increased pixel count while maintaining sufficient horizontal photodiode area to capture adequate photons, thereby preserving sensitivity while increasing resolution.
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 enhances bonding strength, reduces dark current, and minimizes sensitivity degradation and saturation issues by ensuring a smooth photo charge transfer, thereby improving image quality and bonding efficiency.
Implementation Method 1
a bonding area with the photodiode is reduced due to a CMP dishing generated in a tungsten CMP process
Implementation Method 2
there is a limitation of weak bonding strength between a contact plug of a lower substrate including a readout circuitry and a metal of a photodiode
Implementation Method 3
An image sensor is a semiconductor device for converting an optical image into an electric signal
Implementation Method 4
a photodiode may be formed in a substrate using ion implantation
Implementation Method 5
the number of photons incident to the light receiving portion is also reduced due to diffraction of light called Airy disk
Data Source
AI summary
Provided are an image sensor and a method for manufacturing the same. The image sensor comprises: a readout circuitry, an interconnection, a contact plug, and an image sensing device. The readout circuitry is formed in a first substrate. The interconnection is electrically connected to the readout circuitry over the first substrate. The contact plug is formed over the interconnection, and includes an insulating layer at regions in an upper side thereof. The image sensing device is formed over the contact plug.