Solid-State Image Sensor Gettering Layer Noise Suppression
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Solution Overview
Problem
Solid-state image pick-up devices face challenges in suppressing noise generated by gettering layers and preventing metal contamination, especially in semiconductor substrates with SOI structures, where the gettering effect is hindered by insulating films and the removal of gettering layers leads to degradation in element characteristics.
Innovation Solution
A solid-state image pick-up device is designed with a semiconductor substrate that includes an element forming layer and a gettering layer, where a dielectric film is added on top of the gettering layer to induce a second conductive type region, effectively combining electrons and holes at the surface, preventing them from entering photoelectric conversion elements and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a gettering layer is provided to suppress metal contamination, then metal contamination is reduced, but noise is generated due to crystalline defects
Solution Approach 1:
The patent divides the gettering function into two separate layers: a first gettering layer (BSG layer) that suppresses metal contamination, and a second gettering layer (SiO2 layer) that suppresses noise from crystalline defects. This segmentation allows each layer to specialize in one function, preventing the trade-off where a single gettering layer must compromise between contamination suppression and noise generation.
Solution Approach 2:
The patent uses a composite structure combining two different materials (BSG and SiO2) with complementary properties. The BSG layer provides superior metal contamination suppression, while the SiO2 layer provides noise suppression without significant crystalline defect generation. This composite approach achieves both benefits simultaneously.
2Measurement precision
If the element forming layer thickness is decreased to optimize spectral balance, then spectral response is improved, but the layer becomes more susceptible to metal contamination
Solution Approach 1:
The patent applies the gettering layers in advance, before the thin element forming layer is fully processed and before metal contamination can occur during subsequent manufacturing steps. The gettering layers are formed on the element forming layer to create a protective barrier against metal contamination from heavy metals in various processes.
Solution Approach 2:
The gettering layers act as an intermediary protective barrier between the external environment (source of metal contamination) and the thin element forming layer. This intermediary layer prevents metal atoms from reaching and contaminating the sensitive photoelectric conversion elements, allowing the element forming layer to maintain its optimized thin thickness.
3Manufacturing precision
If a silicon oxide film is used in SOI structure to stop etching, then etching control is improved, but the gettering effect is hindered by the insulating film
Solution Approach 1:
The patent moves the gettering function from the substrate dimension (below the element forming layer) to the overlay dimension (on top of the element forming layer). By forming gettering layers on the upper surface of the element forming layer, the patent bypasses the blocking effect of the silicon oxide film in the SOI structure, as the gettering layers are positioned in a different spatial dimension where they can directly intercept metal contaminants.
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 suppresses noise generated by the gettering layer, enhances the signal-to-noise ratio, and improves device characteristics by preventing metal contamination and crystalline defect-induced electron flow into the photoelectric conversion elements.
Implementation Method 1
a dielectric film which is provided on an upper layer of the gettering layer and which induces a second conductive type region in a surface of the gettering layer
Implementation Method 2
a gettering layer provided on an upper layer of an element forming layer to suppress metal contamination
Data Source
AI summary
A solid-state image pick-up device is provided which includes a semiconductor substrate main body which has an element forming layer and a gettering layer provided on an upper layer thereof; photoelectric conversion elements, each of which includes a first conductive type region, provided in the element forming layer; and a dielectric film which is provided on an upper layer of the gettering layer and which induces a second conductive type region in a surface of the gettering layer.