Solid State Imaging Device Dark Current Suppression via Segmented Hole Accumulation
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Solution Overview
Problem
In solid state imaging devices, a desired negative electric potential is not obtained due to the formation of a hole accumulation layer with negative fixed electric charges on the peripheral circuit section, leading to a change in electric potential and increased dark current, affecting pixel characteristics.
Innovation Solution
A solid state imaging device is designed with a layer having negative fixed electric charges formed only on the light receiving surfaces of the sensor sections, and an N-type impurity region is created between the peripheral circuit section and this layer to prevent holes from moving into the peripheral circuit, thereby maintaining the electric potential and reducing dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a hole accumulation layer with negative fixed electric charges is formed on the peripheral circuit section, then the dark current is reduced, but the electric potential changes and pixel characteristics are affected
Solution Approach 1:
The patent divides the semiconductor substrate into distinct regions: sensor sections where the hole accumulation layer is formed, and peripheral circuit sections where it is not formed. This segmentation allows the hole accumulation layer to reduce dark current in sensor areas while preventing electric potential changes in peripheral circuit areas, thus resolving the contradiction between dark current reduction and electric potential stability.
Solution Approach 2:
The hole accumulation layer is selectively formed only in the sensor sections and deliberately excluded from the peripheral circuit sections. This local quality approach ensures that the beneficial dark current reduction effect is applied where needed (sensor sections) while avoiding the harmful electric potential changes in areas where they would affect pixel characteristics (peripheral circuit sections).
2Object-affected harmful factors
If ion implantation and annealing are performed to form the hole accumulation layer, then the dark current is suppressed, but high temperature treatment causes dopant diffusion and increases process complexity
Solution Approach 1:
The patent replaces the traditional ion implantation and high-temperature annealing process with a low-temperature plasma processing method. This substitution eliminates the need for high-temperature treatment, preventing dopant diffusion while still successfully forming the hole accumulation layer, thus reducing manufacturing process complexity while maintaining dark current suppression effectiveness.
Solution Approach 2:
The patent changes the processing temperature parameter from high temperature (700°C or more required for ion implantation activation) to low temperature (plasma processing). This parameter change allows the formation of the hole accumulation layer without high-temperature annealing, avoiding dopant diffusion and simplifying the manufacturing process while achieving the same dark current suppression effect.
3Measurement precision
If the hole accumulation layer is formed to suppress dark current, then sensitivity is improved, but the electric potential change affects pixel characteristics
Solution Approach 1:
The patent segments the device into sensor sections with the hole accumulation layer for improved sensitivity and peripheral circuit sections without it for stable electric potential. This spatial segmentation allows each region to optimize its function: sensor sections benefit from dark current suppression enhancing sensitivity, while peripheral circuit sections maintain consistent electric potential ensuring pixel characteristic uniformity.
Solution Approach 2:
The hole accumulation layer is applied locally only to sensor sections where sensitivity improvement is needed, while being excluded from peripheral circuit sections where electric potential stability is critical for pixel characteristic consistency. This local quality differentiation resolves the contradiction by allowing both sensitivity enhancement and characteristic consistency in their respective regions.
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 configuration effectively suppresses the change in electric potential of the peripheral circuit section, reducing dark current and enhancing image quality by isolating the hole accumulation layer to the sensor sections.
Implementation Method 1
a layer having negative fixed electric charges that is formed on the semiconductor substrate at a light incidence side of the sensor sections in order to form a hole accumulation layer on light receiving surfaces of the sensor sections
Implementation Method 2
An N-type impurity region is formed between the peripheral circuit section and the layer having negative fixed electric charges
Implementation Method 3
a plurality of sensor sections formed in a semiconductor substrate in order to convert incident light into an electric signal
Data Source
AI summary
A solid state imaging device including: a plurality of sensor sections formed in a semiconductor substrate in order to convert incident light into an electric signal; a peripheral circuit section formed in the semiconductor substrate so as to be positioned beside the sensor sections; and a layer having negative fixed electric charges that is formed on a light incidence side of the sensor sections in order to form a hole accumulation layer on light receiving surfaces of the sensor sections.