Front-Side Image Sensor Structure With Carrier-Side Metal Trapping
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Solution Overview
Problem
Existing processes for fabricating front-side image sensors using Silicon-On-Insulator (SOI) substrates are sensitive to metal contamination, which affects the performance of the image sensors, and the formation of trapping layers in these substrates can interfere with photon trajectories and electrical performance.
Innovation Solution
A process involving bonding a donor substrate to a carrier substrate with an electrically insulating layer, implanting gaseous ions into the carrier substrate to form a trapping layer, and epitaxially growing an additional semiconductor layer to create a high-density cavity layer for trapping metal atoms, ensuring good adhesion and minimizing interference with photon and electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trapping layer is formed in the active layer by ion-implanting gaseous species, then metal atoms are trapped, but the trajectory of photons is interfered with and electrical performance is negatively affected
Solution Approach 1:
The substrate is segmented into distinct functional layers: the active layer for photodetection and a separate carrier substrate for metal atom trapping. This spatial segmentation allows the trapping function to be isolated from the active pixel region, preventing photon trajectory interference while maintaining metal atom trapping capability in the carrier substrate.
Solution Approach 2:
The trapping function is extracted from the active layer and relocated to the carrier substrate. By removing the trapping layer formation from the sensitive active region and placing it in the carrier substrate, the harmful effect on photon trajectories is eliminated while the beneficial metal atom trapping function is preserved.
2Ease of operation
If the buried oxide layer is made thin to enable capacitor function, then voltage control is improved, but metal contamination sensitivity increases
Solution Approach 1:
The carrier substrate acts as an intermediary layer between the external environment (source of metal contamination) and the thin buried oxide layer. This intermediary structure provides a trapping function that protects the sensitive thin oxide layer and active region from metal atoms, allowing the oxide layer to remain thin for voltage control while reducing contamination sensitivity.
3Ease of manufacture
If ion implantation is performed before bonding, then trapping layer formation is simplified, but bonding quality deteriorates due to surface damage
Solution Approach 1:
The trapping layer is formed in advance within the bulk of the carrier substrate through ion implantation, before the bonding operation. This preliminary action allows the trapping function to be established without compromising the surface quality needed for bonding, as the ion implantation is performed on the carrier substrate rather than on the bonding surfaces.
Solution Approach 2:
The process is segmented into distinct stages: trapping layer formation in the carrier substrate, followed by bonding of the active layer to the carrier substrate. This temporal and spatial segmentation allows each operation to be optimized independently, maintaining both trapping layer formation capability and bonding quality.
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
The solution effectively traps metal atoms, preventing contamination and ensuring high-quality bonding between the active and carrier substrates, thereby enhancing the performance and reliability of front-side image sensors, especially for near-infrared applications.
Implementation Method 1
implanting gaseous ions into the carrier substrate through the transferred semiconductor layer and the electrically insulating layer
Implementation Method 2
carrying out a heat treatment suitable for forming, from the implanted ions, microbubbles or precipitates
Implementation Method 3
forming, from the implanted ions, microbubbles or precipitates
Implementation Method 4
epitaxially growing an additional semiconductor layer on top of the transferred semiconductor layer
Implementation Method 5
an electrically insulating layer being at the bonding interface
Data Source
AI summary
A structure for a front-side image sensor comprises a semiconductor substrate, an electrically insulating layer overlying the semiconductor substrate, and an active layer overlying the electrically insulating layer. The semiconductor substrate comprises a trapping layer, the trapping layer including cavities therein. The structure further comprises a plurality of electrically isolating trenches extending vertically through the active layer to the electrically insulating layer. The plurality of electrically isolating trenches define a plurality of pixels. Also disclosed is a structure comprises a carrier substrate, an electrically insulating layer overlying the carrier substrate and a trapping layer, and a semiconductive layer overlying the electrically insulating layer. The trapping layer comprises cavities therein. The structure further comprises a plurality of electrically isolating trenches extending vertically through the semiconductive layer to the electrically insulating layer.