SPAD Image Sensor Contact Structure for Lower Resistance
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Solution Overview
Problem
In solid-state image sensors using Single Photon Avalanche Diode (SPAD) pixels, high contact resistance between the SPAD pixel and the electrode leads to a decrease in Photon Detection Efficiency (PDE) due to voltage drop, and increasing voltage to compensate for this increases power consumption.
Innovation Solution
The solid-state image sensor incorporates a semiconductor substrate with trenches to create a photoelectric conversion element with a specific semiconductor region structure, including a first and second contact, and an inclined contact surface to reduce contact resistance and enhance PDE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the contact is arranged on the outermost periphery of the impurity diffusion region to increase the distance from the PN junction region, then the tunnel effect is avoided, but the contact area between the contact and electrode is reduced, causing high contact resistance and decreased PDE
Solution Approach 1:
The patent transitions from a two-dimensional planar contact arrangement to a three-dimensional structure by forming a contact hole that extends vertically into the semiconductor substrate. This allows the contact to reach the impurity diffusion region at depth while maintaining adequate lateral distance from the PN junction, thus avoiding the tunnel effect while preserving sufficient contact area through the vertical dimension.
Solution Approach 2:
The contact structure is nested within the semiconductor substrate by forming a contact hole that penetrates through insulating films and reaches the impurity diffusion region. This nested configuration allows the contact to be positioned deep within the substrate structure, achieving both electrical connectivity and spatial separation from the PN junction.
2Manufacturing precision
If the voltage is increased to suppress the decrease in PDE caused by high contact resistance, then the PDE is improved, but the power consumption increases
Solution Approach 1:
The patent changes the physical parameters of the contact structure by increasing the contact area through the formation of a contact hole that reaches the impurity diffusion region. This parameter change in contact geometry reduces contact resistance, allowing adequate PDE to be achieved without increasing the operating voltage, thus avoiding increased power consumption.
3Manufacturing precision
If a high-concentration impurity region is formed in the contact portion to achieve low resistance and ohmic contact, then the contact resistance is reduced, but the device complexity increases
Solution Approach 1:
The patent segments the contact formation process into distinct stages: forming the contact hole structure, then selectively forming the high-concentration impurity region only in the contact portion. This segmentation allows the complex impurity doping to be localized to where it is needed, reducing overall device complexity while achieving low contact resistance.
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 high contact resistance, improves PDE, and reduces power consumption by allowing stable avalanche amplification without compromising pixel size or resolution.
Implementation Method 1
a photoelectric conversion region provided in an element region partitioned by the first trench and the second trench in the semiconductor substrate and photoelectrically converting incident light to generate a charge
Implementation Method 2
Single Photon Avalanche Diode (SPAD) has been developed, which amplifies charges generated by photoelectric conversion by means of avalanche multiplication (also referred to as avalanche amplification) and outputs them as an electric signal. The avalanche amplification is a phenomenon in which electrons accelerated by an electric field collide with latticed atoms in an impurity diffusion region of a PN junction to break the bonds
Data Source
AI summary
A solid-state image sensor including a photoelectric conversion region partitioned by trenches, a first semiconductor region surrounding the photoelectric conversion region, a first contact in contact with the first semiconductor region at a bottom portion of the trench, a first electrode in contact with the first contact in the first trench, a second semiconductor region in contact with the first semiconductor region having the same conductive type as the first semiconductor region, a third semiconductor region in contact with the second semiconductor region, between the second semiconductor region and a first surface, and having a second conductive type, a second contact on the first surface in contact with the third semiconductor region, and a second electrode in contact with the second contact, and a second surface at which the first contact and the first electrode are in contact with each other is inclined with respect to the first surface.