Back Side Illumination Image Sensor Manufacturing Using Ion Implantation
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Solution Overview
Problem
Existing back side illumination image sensors face high manufacturing costs due to the use of expensive Silicon On Insulator (SOI) wafers and suffer from yield reduction and potential plasma damage during the backside thinning process, along with issues in bonding and contact between photodiodes and readout circuitry.
Innovation Solution
The method involves using an Epi wafer as the donor substrate for forming both the light sensing unit and readout circuitry, employing ion implantation to define the pixel region, and bonding a second substrate with an interlayer insulating layer to minimize the need for costly wafer bonding and reduce light interference, thereby eliminating the need for back grinding and etch-back processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SOI wafer is used as donor wafer for back side illumination image sensor, then light receiving performance is improved, but manufacturing cost increases significantly
Solution Approach 1:
The patent replaces expensive SOI wafers with standard silicon wafers that can be processed more economically. By using conventional silicon substrates instead of specialized SOI structures, the manufacturing cost is significantly reduced while maintaining the back side illumination functionality through alternative processing methods.
Solution Approach 2:
The patent changes the substrate parameter from SOI (Silicon On Insulator) to standard silicon, fundamentally altering the material composition to reduce cost. This parameter change allows the use of more economical manufacturing processes while achieving the same optical performance through back side illumination architecture.
2Manufacturing precision
If backside grinding is performed to thin the donor wafer, then substrate thickness is reduced for proper optical lens spacing, but wafer edge thinning occurs reducing yield
Solution Approach 1:
The patent extracts and removes the problematic backside grinding step from the manufacturing process. By eliminating this mechanical thinning operation, the source of wafer edge thinning and associated yield loss is removed, while substrate thickness is controlled through alternative means such as precise deposition or etching processes.
Solution Approach 2:
The patent replaces the mechanical backside grinding process with a non-mechanical thinning method. Instead of using abrasive mechanical removal that causes edge thinning, the patent employs chemical or vapor-phase processes that provide more uniform thickness control without mechanical contact-induced defects.
3Manufacturing precision
If etch-back process is used to complete backside thinning, then substrate thickness is precisely controlled, but plasma damage occurs increasing degradation possibility
Solution Approach 1:
The patent converts the potentially harmful plasma etching process into a beneficial precision thinning operation. By carefully controlling the plasma parameters and using it for the final precision thickness adjustment after mechanical grinding, the harmful plasma damage is minimized while achieving the required thickness precision for optimal optical performance.
Solution Approach 2:
The patent performs preliminary mechanical backside grinding to remove the majority of the excess thickness before applying the plasma etching process. This preliminary action reduces the amount of material that needs to be removed by plasma, thereby minimizing plasma exposure time and reducing plasma damage while still achieving the required precision thickness control.
4Productivity
If photodiode area is reduced to increase pixel density, then number of pixels increases, but light receiving area reduces decreasing image quality
Solution Approach 1:
The patent transitions from front side illumination to back side illumination architecture, effectively changing the dimensional approach to light reception. By receiving light through the back side of the substrate rather than the front, the patent eliminates metal routing interference and allows for more efficient light capture, thereby maintaining image quality even with reduced photodiode areas for higher pixel density.
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 stabilizes the back side substrate removal, enhances production yield, reduces manufacturing costs, and maximizes light incidence while minimizing light interference and reflection, leading to improved image sensor performance.
Implementation Method 1
forming an ion implantation layer in a region of a front side of a substrate
Implementation Method 2
forming a microlens on the light sensing unit at the back side of the substrate
Implementation Method 3
bonding a second substrate to the front side of the first substrate on which the metal line is formed
Data Source
AI summary
Provided are methods for manufacturing a back side illumination image sensor. In one method, an ion implantation layer is formed in an entire region of a front side of a first substrate. A device isolation region is formed in the front side of the first substrate to define a pixel region. A light sensing unit and a readout circuitry are formed in the pixel region. An interlayer insulating layer and a metal line are formed on the first substrate. A second substrate is bonded to the front side of the first substrate on which the metal line is formed. A lower side of the first substrate under the ion implantation region is removed such that the light sensing unit is available at the backside of the first substrate.