Solid-State Imaging Device Impurity Concentration Control
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Solution Overview
Problem
The challenge in solid-state imaging devices is the high impurity concentration in source and drain diffusion regions causing defects on the semiconductor substrate, leading to leak current sources and deteriorating pixel characteristics, especially when high-temperature sintering is used to prevent ion implantation damage, which degrades photoelectric conversion characteristics.
Innovation Solution
A solid-state imaging device configuration with a pixel unit having a photoelectric conversion film and a floating diffusion, and a peripheral circuit unit with transistors having source and drain diffusion regions with higher impurity concentrations than the floating diffusion, along with a manufacturing method that includes specific heat treatments to minimize thermal diffusion and repair defects, allowing for miniaturization and reduced leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-temperature sintering is used to prevent ion implantation damage, then source and drain diffusion regions can be formed with high impurity concentration, but photoelectric conversion film characteristics are degraded
Solution Approach 1:
The patent divides the heating process into two distinct stages: a first heating process performed before ion implantation to form the photoelectric conversion film, and a second heating process performed after ion implantation to activate impurities in source and drain diffusion regions. This segmentation allows each heating process to be optimized independently, preventing the photoelectric conversion film from being exposed to high-temperature sintering that would degrade its characteristics, while still achieving the necessary impurity activation in the peripheral circuit transistors.
Solution Approach 2:
The first heating process is performed preliminarily before ion implantation to form the photoelectric conversion film at controlled temperatures that preserve its characteristics. By establishing the photoelectric conversion structure before the damaging high-temperature sintering step, the patent ensures that the film is not exposed to conditions that would cause crystal grain growth or characteristic degradation.
2Speed
If transistor size is miniaturized to increase peripheral circuit speed, then driving capability is improved, but leakage current increases due to defects from high impurity concentration
Solution Approach 1:
The patent segments the impurity concentration control by device type: peripheral circuit transistors receive high impurity concentration doping to ensure low resistance and high-speed operation, while pixel region diffusion structures receive controlled impurity concentrations to minimize leakage. This is achieved through separate ion implantation steps with different doping conditions, allowing each region to be optimized independently without compromise.
Solution Approach 2:
Different impurity concentration levels are applied to different regions of the semiconductor substrate according to their specific functional requirements. Peripheral circuit transistors are doped with high impurity concentrations to reduce resistance and improve switching speed, while pixel region diffusion structures are doped with lower impurity concentrations to minimize leakage current. This local differentiation of doping quality allows simultaneous optimization of both speed and leakage performance.
3Power
If high impurity concentration is used in source and drain diffusion regions, then transistor driving capability is improved, but defects are generated on semiconductor substrate
Solution Approach 1:
A preliminary heating process is performed before ion implantation to prepare the semiconductor substrate and form the photoelectric conversion film. This preliminary action creates a controlled thermal environment that reduces substrate defects before the high-impurity-concentration doping step, ensuring that subsequent high-power transistor regions can be formed with minimal defect generation.
Solution Approach 2:
The patent employs rapid thermal processing during the second heating process to quickly activate impurities in source and drain diffusion regions. By rushing through the high-temperature exposure period, the process achieves necessary impurity activation while minimizing the time that defects can form or propagate in the semiconductor substrate, thereby maintaining high driving capability with reduced defect density.
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 achieves both transistor miniaturization and reduced defects, improving pixel sensitivity and driving capability while preventing photoelectric conversion film degradation.
Implementation Method 1
a photoelectric conversion film which converts incident light into charges
Implementation Method 2
performing a first heat treatment after step (b)
Data Source
AI summary
A solid-state imaging device includes: a semiconductor substrate; a pixel unit formed on the semiconductor substrate; and a peripheral circuit unit formed on the semiconductor substrate, at a periphery of the pixel unit, in which the pixel unit includes: a photoelectric conversion film which converts incident light into charges; and a floating diffusion which holds the charges, the peripheral circuit unit includes a transistor including a gate electrode and two source and drain diffusion regions, and the two source and drain diffusion regions have a higher impurity concentration than an impurity concentration of the floating diffusion.