Backside Illuminated Image Sensor Contact Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Miniaturization of image sensors increases susceptibility to metal contamination, with copper from electrodes diffusing into semiconductor materials, acting as deep level traps and detrimental to performance.
Innovation Solution
The implementation of a backside illuminated image sensor design with a buffer layer, shallow trench isolation structure, and contact plugs made of different materials to prevent metal contamination during fabrication, including tungsten for contact plugs and copper for metal interconnects, which reduces the risk of contamination and simplifies the fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If image sensors are miniaturized to increase resolution, then higher resolution is achieved, but susceptibility to metal contamination increases
Solution Approach 1:
The contact area is segmented into multiple contact plugs instead of a single large contact. This segmentation reduces the total metal surface area in each contact region, thereby reducing the source of copper atoms that could diffuse into the semiconductor. The multiple smaller contacts achieve the same electrical function while minimizing contamination risk.
Solution Approach 2:
A buffer layer is introduced as an intermediary between the metal contact plugs and the semiconductor material. This buffer layer acts as a diffusion barrier that prevents copper atoms from the contact plugs from diffusing into the semiconductor, while still allowing electrical conduction. The buffer layer mediates the interaction between metal and semiconductor to eliminate harmful contamination.
2Object-affected harmful factors
If different materials are used for contact plugs and metal interconnects, then metal contamination is prevented, but fabrication complexity increases
Solution Approach 1:
The invention changes the material parameter of contact plugs to tungsten while keeping metal interconnects as copper. This parameter change creates a material system where the contact plug material (tungsten) has lower solubility in the buffer layer and semiconductor compared to copper, thereby preventing diffusion contamination. The different materials have complementary properties that solve the contamination problem.
3Object-affected harmful factors
If contact area is reduced to minimize contamination, then metal contamination decreases, but contact reliability may be compromised
Solution Approach 1:
The contact area is divided into multiple contact plugs distributed across the contact region. While each individual contact plug has a smaller area, the collective contact area of all plugs maintains sufficient total contact area for reliable electrical connection. The segmentation approach simultaneously reduces local metal density (lowering contamination risk) and preserves overall contact functionality.
Solution Approach 2:
The contact structure uses a composite material system consisting of tungsten contact plugs embedded in a buffer layer, which itself is part of a larger composite structure including semiconductor material and metal interconnects. This composite structure provides multiple functions: electrical conduction, mechanical support, and diffusion barrier properties, ensuring both low contamination and high reliability.
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 design effectively mitigates metal contamination, enhances image sensor performance, and reduces fabrication costs by minimizing photolithography steps and preventing shorting between contact pads and semiconductor material.
Implementation Method 1
a buffer layer disposed on the semiconductor material between the back side metal and the back side of the semiconductor material
Implementation Method 2
contact plugs made of different materials to prevent metal contamination during fabrication, including tungsten for contact plugs and copper for metal interconnects
Data Source
AI summary
An image sensor includes a semiconductor material having a front side and a back side opposite the front side. The image sensor also includes a shallow trench isolation (STI) structure, an interlayer dielectric, an intermetal dielectric, and a contact area. The STI structure extends from the front side of the semiconductor material into the semiconductor material. The interlayer dielectric is disposed between the front side of the semiconductor material and the intermetal dielectric. The contact area is disposed proximate to a lateral edge of the semiconductor material. The contact area includes a metal interconnect disposed within the intermetal dielectric and a plurality of contact plugs at least partially disposed within the interlayer dielectric. The contact area also includes a contact pad. The plurality of contact plugs is coupled between the contact pad and the metal interconnect.