CMOS Image Sensor Photodiode Wells via Cryogenic Ion Channeling
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Solution Overview
Problem
Existing CMOS image sensors face limitations in photodiode well depth due to the maximum energy of existing ion implanters and degradation of ion channeling at high energies and heavy ion masses, which restricts their ability to capture infrared light efficiently.
Innovation Solution
A low-temperature ion implantation process is performed on CMOS image sensors, cooling them to temperatures below −100° C to enhance ion channeling and achieve deeper photodiode wells, allowing for improved sensitivity and uniform doping profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If ion implantation is performed at room temperature with existing ion implanters, then the manufacturing process is simple, but the photodiode well depth is limited due to maximum energy constraints and channeling degradation
Solution Approach 1:
The patent applies parameter changes by cooling the wafer to cryogenic temperatures (below -50°C, preferably below -100°C) during ion implantation. This temperature parameter change enhances ion channeling effects, allowing ultra-high energy ions to penetrate deeper into the semiconductor substrate and form photodiode wells exceeding 20 μm in depth, thereby resolving the depth limitation without requiring more complex high-energy implanters
2Length of moving object
If ion energy is increased to achieve deeper photodiode wells, then the well depth increases, but ion channeling degrades at high energies and heavy ion masses
Solution Approach 1:
The patent changes the temperature parameter to cryogenic levels during ion implantation, which preserves and enhances ion channeling effectiveness even at ultra-high ion energies. The low temperature reduces thermal vibrations in the crystal lattice, maintaining the channeling effect that guides ions along crystal planes to achieve depths exceeding 20 μm without the channeling degradation that occurs at room temperature with high-energy ions
3Length of moving object
If cryogenic cooling is applied to enhance ion channeling, then photodiode well depth increases by approximately 2 μm, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies preliminary action by pre-cooling the wafer to cryogenic temperatures before performing the ion implantation process. This preparatory cooling step ensures optimal conditions for enhanced ion channeling and deeper photodiode well formation, achieving approximately 2 μm additional depth while allowing the subsequent implantation to proceed with standard equipment and processes
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
The low-temperature ion implantation method increases photodiode well depth by approximately 2 μm, enhancing the sensitivity and uniformity of the image sensor's light wavelength response, overcoming the limitations of existing technologies.
Implementation Method 1
cooling the wafer to a temperature less than −50° C.
Implementation Method 2
performing an ion implant to the photoelectric conversion region to form a photodiode well after cooling the wafer
Data Source
AI summary
Provided herein are approaches for forming an image sensor with increased well depth due to cryogenic ion channeling of ultra-high energy (UHE) ions. In some embodiments, a method may include providing a wafer of a semiconductor device, the semiconductor device including a photoelectric conversion region, and cooling the wafer to a temperature less than −50° C. The method may further include performing an ion implant to the photoelectric conversion region to form a photodiode well after cooling the wafer.