Solid-State Imaging Device Gettering Layer Internal Stress
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Solution Overview
Problem
Existing gettering techniques for solid-state imaging devices using SOI substrates are ineffective in suppressing metal contamination, which leads to noise components and limitations in material selection due to the presence of a silicon oxide film between the active layer and the base substrate.
Innovation Solution
A solid-state imaging device with a gettering layer having internal stress is formed on the front surface of the silicon layer, overlapping the photoelectric conversion portion, to create strained layers that effectively getter metal impurities, thereby reducing noise components and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon oxide layer is provided between the base substrate and the active layer in an SOI substrate, then selectivity is provided when the base substrate is removed, but the layer occupies most areas of the active layer leaving insufficient area for a gettering layer, making it very difficult to suppress noise components due to metal contamination
Solution Approach 1:
The patent introduces a new spatial dimension by forming the gettering layer in the depth direction (thickness direction) of the silicon layer rather than in the planar area. The gettering layer is positioned at a specific depth range (0.5-2.0 μm from the back surface) along the Z-axis, allowing it to coexist with the silicon oxide layer in the XY plane while effectively trapping metal impurities throughout the active layer volume.
Solution Approach 2:
The gettering layer is formed in advance before the metal contamination problem occurs during device operation. By pre-positioning the gettering layer at the appropriate depth in the silicon layer, metal impurities that may be introduced during subsequent processing or operation are immediately trapped, preventing them from reaching and contaminating the photoelectric conversion region.
2Reliability
If gettering sites are formed inside a silicon substrate at a distance of several tens of μm from the back surface, then contaminated seeds are trapped by diffusion phenomenon, but the defect-free zone occupies most areas leaving not enough area for a gettering layer
Solution Approach 1:
The patent transitions from planar gettering (occupying XY plane area) to volumetric gettering by positioning the gettering layer at a specific depth range (0.5-2.0 μm from back surface) in the Z-direction. This allows the gettering function to be distributed throughout the thickness of the silicon layer, providing effective trapping volume without consuming planar area from the photoelectric conversion region.
Solution Approach 2:
The gettering layer is positioned at a specific depth range (0.5-2.0 μm from the back surface) rather than uniformly distributed throughout the silicon layer. This localized positioning optimizes the balance between trapping efficiency and maintaining a defect-free zone at the back surface for light incidence, while ensuring metal impurities diffusing from any region are effectively captured.
3Quantity of substance
If the active layer is formed by a single-crystalline silicon layer with thickness of several μm, then photoelectric conversion area is maximized, but there is not enough area for a gettering layer to suppress noise components
Solution Approach 1:
The patent resolves the area conflict by utilizing the thickness dimension (Z-axis) of the silicon layer for the gettering layer, rather than competing for planar area in the XY plane. The gettering layer is positioned at 0.5-2.0 μm depth from the back surface, creating a three-dimensional gettering structure that preserves the entire top surface area for photoelectric conversion while providing sufficient gettering volume within the layer thickness.
Solution Approach 2:
The gettering layer is pre-formed at the optimal depth position within the silicon layer thickness, ensuring that metal impurities are trapped before they can reach the photoelectric conversion region. This preliminary positioning allows the full thickness of the silicon layer to be utilized for photoelectric conversion while maintaining contamination suppression capability.
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 implementation of a gettering layer with internal stress on the front surface of the silicon layer in the solid-state imaging device effectively gets metal impurities, suppressing noise components and enabling the use of a wider range of materials, thus enhancing image quality and sensitivity.
Implementation Method 1
a gettering layer having internal stress is provided on the front surface side of the silicon layer at a position to overlap the photoelectric conversion portion
Implementation Method 2
a gettering layer having internal stress is formed on the front surface of the silicon layer, overlapping the photoelectric conversion portion, to create strained layers that effectively getter metal impurities
Implementation Method 3
a photoelectric conversion portion that receives an incident light from a back surface side of a silicon layer to perform photoelectric conversion on the incident light
Data Source
AI summary
A solid-state imaging device includes: a photoelectric conversion portion that receives an incident light from a back surface side of a silicon layer to perform photoelectric conversion on the incident light; and a pixel transistor portion that outputs signal charges generated in the photoelectric conversion portion towards a front surface side of the silicon layer, wherein a gettering layer having internal stress is provided on the front surface side of the silicon layer at a position to overlap the photoelectric conversion portion on a plan view layout thereof.