Solid-State Image Pickup Device Dark Current Suppression
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Solution Overview
Problem
In solid-state image pickup devices, dark current caused by crystal defects or metal contamination leads to white defects and afterimages in images, as high concentrations of positive holes stored in the light-receiving surface of photodiodes hinder the readout of photoelectrically converted electrons.
Innovation Solution
A manufacturing method for solid-state image pickup devices involves forming a transfer gate electrode and a second conductive charge storage area with a sidewall, where an insulating film extends to partially cover the charge storage area, and P-type impurities are implanted to create layers with varying depths and concentrations, allowing for effective rejoining of electrons with positive holes to suppress dark current and afterimages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high concentration of positive holes is stored in the light receiving surface part of the photodiode to reduce dark current, then white defects are reduced, but photoelectrically converted electrons cannot be read out efficiently, causing afterimages
Solution Approach 1:
The patent applies local quality by creating a spatially varying impurity concentration distribution. The impurity concentration is highest at the light receiving surface to suppress dark current, and gradually decreases toward the interior of the photodiode to maintain electron readout efficiency. This gradient distribution allows different regions to have optimized properties for their specific functions.
Solution Approach 2:
The patent changes the impurity concentration parameter from uniform to gradient distribution. By controlling the implantation conditions (energy, dose, angle) to create a gradient, the patent optimizes both dark current suppression and electron readout efficiency simultaneously, resolving the contradiction between these two requirements.
2Object-affected harmful factors
If ion implantation is used to store positive holes in the light receiving surface, then dark current is reduced, but the potential barrier increases making electron transfer difficult
Solution Approach 1:
The patent changes the impurity concentration parameter from uniform to gradient distribution. By controlling the implantation conditions (energy, dose, angle) to create a gradient, the patent optimizes both dark current suppression and electron readout efficiency simultaneously, resolving the contradiction between these two requirements.
Solution Approach 2:
The patent applies partial action by concentrating impurity implantation primarily in the light receiving surface region rather than uniformly throughout the entire photodiode. This localized approach suppresses dark current where it occurs while minimizing the impact on electron transfer 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 method effectively reduces white defects and afterimages by optimizing the depth and concentration of positive holes in the charge storage layer, enabling efficient transfer of electrons and improving image quality.
Implementation Method 1
a first conductive charge storage layer is formed on the upper surface of the charge storage area, by implanting first conductive impurities from above to the charge storage area which is partially covered with the insulating film
Data Source
AI summary
In a manufacturing method of a solid-state image pickup device according to an embodiment, a transfer gate electrode is formed in a predetermined position on an upper surface of a first conductive semiconductor area, through a gate insulating film. A second conductive charge storage area is formed in an area adjacent to the transfer gate electrode in the first conductive semiconductor area. A sidewall is formed on a side surface of the transfer gate electrode. An insulating film is formed to extend from a circumference surface of the sidewall on a side of the charge storage area to a position partially covering the upper part of the charge storage area. A first conductive charge storage layer is formed in the charge storage area by implanting first conductive impurities from above, into the charge storage area which is partially covered with the insulating film.