Laser Annealing Boundary Control for BSI Sensor Stripe Reduction
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Solution Overview
Problem
Backside illuminated (BSI) CMOS image sensors experience dark mode image stripe patterns due to laser scanning boundary effects during the laser annealing process, which affects the quantum efficiency and image quality.
Innovation Solution
A method to detect and adjust the location relation between the laser beam boundary and the image sensor array boundary using a light source and optical detector, ensuring the laser beam boundary is outside the sensor array boundaries, thereby preventing stripe patterns by fine-tuning the laser annealing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the substrate is thinned and ion implantation is performed to improve quantum efficiency, then quantum efficiency is improved, but crystal defects are caused requiring laser annealing which in turn causes stripe patterns
Solution Approach 1:
The patent applies preliminary action by performing the laser annealing process with carefully controlled parameters before the stripe patterns can form. By optimizing the laser scanning speed, power, and substrate temperature in advance, the process activates the implanted ions and repairs crystal defects without causing the harmful stripe patterns that would otherwise appear in the final image sensor product.
2Reliability
If laser annealing is performed to activate implanted ions and repair crystal defects, then quantum efficiency is improved, but dark mode image stripe patterns are caused due to laser scanning boundary effects
Solution Approach 1:
The patent applies parameter changes by systematically optimizing the laser annealing parameters including reducing laser power, adjusting scanning speed, and controlling substrate temperature. These parameter modifications change the thermal distribution during laser scanning to eliminate the boundary effects that cause stripe patterns, while still achieving the desired ion activation and crystal defect repair for high quantum efficiency.
3Productivity
If the laser beam boundary falls within the sensor array boundary, then the annealing process is complete, but stripe patterns are generated at the boundaries
Solution Approach 1:
The patent applies local quality by creating a controlled temperature gradient during laser annealing where the substrate temperature is maintained below a threshold value in the regions where the laser beam boundary passes through the sensor array. This localized temperature control ensures that the laser beam boundary does not cause stripe patterns at critical locations, while still allowing complete annealing treatment throughout the entire sensor array area.
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 reduces image stripe patterns and maintains high quantum efficiency by ensuring uniform energy distribution during the laser annealing process, improving the overall image quality of BSI image sensors.
Implementation Method 1
a laser annealing process may be performed to activate the implanted P+ ions as well as repair crystal defects caused by the ion implantation process
Implementation Method 2
a laser annealing process may be performed to activate the implanted P+ ions as well as repair crystal defects
Implementation Method 3
A CMOS image sensor utilizes light-sensitive CMOS circuitry to convert photons into electrons. The light-sensitive CMOS circuitry typically comprises a photo-diode formed in a silicon substrate. As the photo-diode is exposed to light, an electrical charge is induced in the photo-diode.
Data Source
AI summary
An apparatus comprises an optical detector configured to receive scattered light signals from a surface of a wafer including a plurality of sensor arrays, each of which has a boundary smaller than a boundary of a laser beam, a light source optically coupled to the surface of the wafer, wherein light from the light source hits the surface with a small incident angle and a processor configured to measure a distance between a sensor array boundary and a laser beam boundary, wherein a laser annealing process is recalibrated if the distance is less than a predetermined value.