Solid-State Imager Dark Current Suppression via Reverse Polarity
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Solution Overview
Problem
Existing solid-state imager devices face challenges in minimizing dark current generation from the substrate rear surface boundary, particularly due to the limitations of ion injection methods and heat treatment processes, which affect blue sensitivity and spectral balance.
Innovation Solution
A solid-state imager device with a reverse-polarity voltage applied to the insulation film on the rear surface, creating a positive hole accumulation layer or electron accumulation layer on the substrate boundary surface, reducing dark current generation without ion injection or heat treatment, and incorporating a leakage current inhibiting region under the pad portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ion injection is performed from the substrate rear surface to prevent negative current generation, then dark current suppression is improved, but blue sensitivity deteriorates due to the injection process affecting the shallow region
Solution Approach 1:
Instead of injecting ions from the rear surface (conventional approach), the patent applies reverse polarity voltage to the insulation film on the rear surface, creating an accumulation layer that suppresses dark current without ion injection from the affected side. This inverted approach avoids damaging the blue-sensitive shallow region while achieving dark current suppression.
Solution Approach 2:
The patent introduces an insulation film as an intermediary layer on the rear surface, to which reverse polarity voltage is applied. This intermediary structure enables dark current suppression through electric field effect without requiring direct ion injection into the silicon substrate, thereby protecting the blue sensitivity.
2Reliability
If heat treatment is applied to activate the ion injected p+ layer, then negative current prevention is improved, but the wiring layer is melted causing manufacturing defects
Solution Approach 1:
The patent replaces the thermal activation process (heat treatment) with an electrical field effect approach. By applying reverse polarity voltage to the insulation film, the accumulation layer is formed electrically rather than thermally, avoiding the risk of melting the wiring layer while achieving the same negative current prevention effect.
3Reliability
If high energy ion injection is performed from the substrate front surface to form p+ layer in deep region, then negative current suppression is improved, but blue sensitivity is reduced due to photoelectron capture in shallow region
Solution Approach 1:
The patent extracts the ion injection process entirely from the fabrication sequence and replaces it with an electrical field effect applied to the insulation film. This eliminates the need to form a p+ layer through high energy ion injection, thereby preventing the capture of photoelectrons in the shallow blue-sensitive region while still suppressing negative current through the accumulation layer effect.
4Area of stationary object
If polishing is applied to the substrate rear surface to form light receiving surface, then high aperture ratio is achieved, but the p+ layer distribution spreads reducing blue sensitivity
Solution Approach 1:
The patent performs polishing to form the light receiving surface on the rear surface before applying the insulation film and subsequent reverse polarity voltage treatment. This preliminary action enables high aperture ratio while the subsequent electrical field approach (rather than deep ion injection) prevents blue sensitivity degradation.
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 approach effectively decreases dark current and leakage current, enhances blue sensitivity, and simplifies the production process by eliminating the need for ion injection and heat treatment, while maintaining high aperture ratio and spectral balance.
Implementation Method 1
voltage applying means for applying a voltage of reverse-polarity with respect to the potential of the semiconductor substrate to the insulation film
Implementation Method 2
creating a positive hole accumulation layer or electron accumulation layer on the substrate boundary surface
Data Source
AI summary
In a case when a structure of forming a p+ layer on a substrate rear surface side is employed in order to prevent dark current generation from the silicon boundary surface, various problems occur. According to this invention, an insulation film 39 is provided on a rear surface on a silicon substrate 31 and a transparent electrode 40 is further provided thereon, and by applying a negative voltage with respect to the potential of the silicon substrate 31 from a voltage supply source 41 to the insulation film 39 through the transparent electrode 40, positive holes are accumulated on a silicon boundary surface of the substrate rear surface side and a structure equivalent to a state in which a positive hole accumulation layer exists on aforesaid silicon boundary surface is to be created. Thus, various problems in the related art can be avoided.