CMOS Image Sensor Metal Reflective Layer for Dark Current Reduction

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Solution Overview

Problem

Conventional CMOS image sensor manufacturing processes face issues with substrate thinning causing damage and defects, leading to incomplete defect isolation and potential damage to the multilayer interconnect structure due to insufficient or excessive laser annealing.

Innovation Solution

A method involving a metal reflective layer formed on the pixel region, followed by substrate thinning, ion implantation, and annealing, where the metal reflective layer reflects laser light and heat radiation to prevent damage to the interconnect structure while activating dopants effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If laser annealing is performed with high intensity to completely isolate defects, then defect isolation is improved, but the multilayer interconnect structure may be damaged due to excessive thermal radiation

Engineering Contradiction:

Improvedefect isolationVSAvoidthermal radiation damage to interconnect structure

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A reflector layer is introduced as an intermediary component between the laser annealing source and the multilayer interconnect structure. This reflector layer reflects thermal radiation away from the interconnect structure while allowing the laser annealing process to effectively isolate defects in the semiconductor substrate, thus protecting the interconnect structure from damage.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The reflector layer converts the harmful thermal radiation into a beneficial reflected energy pattern that maintains effective defect isolation while preventing damage to sensitive interconnect structures. The reflected thermal radiation is redirected away from the interconnect structure, transforming a potentially harmful effect into a controlled process parameter.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Adaptability or versatility

If substrate thinning is performed to enable backside light reception, then light reception capability is improved, but damage and defects are introduced to the back surface

Engineering Contradiction:

Improvelight reception capabilityVSAvoidsubstrate integrity

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The reflector layer is formed on the front surface of the substrate before the substrate thinning process. This preliminary action ensures that the reflector layer is in place to protect the internal structures and guide light reception before the thinning process introduces potential damage and defects to the back surface.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The reflector layer serves as a protective cushioning layer that mitigates the harmful effects of substrate thinning. By being in place before thinning, it provides a buffer that reduces the introduction of defects and maintains substrate integrity while enabling the necessary thinning for backside light reception.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Reliability

If ion implantation is performed to repair damage and isolate defects, then substrate quality is improved, but additional processing complexity is introduced

Engineering Contradiction:

Improvesubstrate qualityVSAvoidprocessing steps

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The reflector layer acts as an intermediary that enables more effective ion implantation processes. By being in place during ion implantation, it helps concentrate and direct the ion flux, improving substrate quality and defect isolation while potentially reducing the overall processing complexity by making subsequent steps more efficient.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 isolates defects, reduces dark current, and protects the multilayer interconnect structure from thermal radiation, enhancing device performance by ensuring precise dopant activation and minimizing damage.

Implementation Method 1

performing an annealing process on the doped back side of the semiconductor substrate

Methodology Applied

Scientific EffectLaser annealing: Laser

Implementation Method 2

performing an ion implantation process on the thinned back side of the semiconductor substrate to form a doped back side

Methodology Applied

Scientific EffectIon implantation: Ion Implantation

Implementation Method 3

the metal reflective layer reflects laser light and heat radiation to prevent damage to the interconnect structure

Methodology Applied

Scientific EffectThermal radiation reflection: Reflection

Data Source

PatentUS10163958B2CMOS image sensor

Publication Date: 2018.12.25 SEMICON MFG INT (SHANGHAI) CORP

AI summary

A method for manufacturing a semiconductor device includes providing a substrate structure including a substrate having a front side and a back side and a pixel region having a plurality of pixels in the front side, each pixel including a sensor element, forming a metal reflective layer in the front side of the substrate and on the pixel region, thinning the back side of the substrate, doping the thinned back side of the substrate with a dopant, and laser annealing the doped back side of the substrate. The sensor element is configured to receive incident light to the thinned back side of the semiconductor substrate. The metal reflective layer reflects heat generated in the laser annealing process to more fully activate the dopant in the back side of the substrate, thereby effectively reducing dark current and improving the device performance.