Backside-Illuminated Image Sensor Fabrication Using Reusable Glass Substrates
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Solution Overview
Problem
The existing fabrication processes for backside-illuminated image sensors are costly and time-consuming due to the use of silicon carrier materials and the need for through-silicon vias, which complicate the thinning and packaging of the devices.
Innovation Solution
A method involving the use of glass substrates for bonding and thinning, where a first glass substrate is bonded to the frontside of the device substrate, thinned, and then reused, eliminating the need for silicon carrier materials and through-silicon vias, and allowing for efficient radiation detection from the backside.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon carrier materials and through-silicon vias are used for bonding and thinning, then device warping and breaking are avoided, but fabrication costs and cycle time increase
Solution Approach 1:
The patent changes the material parameter from silicon carrier to glass carrier substrate. This parameter change eliminates the need for through-silicon via formation and reduces fabrication cycle time while maintaining structural support during thinning processes. The glass substrate provides sufficient mechanical strength without requiring complex via structures.
Solution Approach 2:
The patent extracts and eliminates the through-silicon via formation step from the fabrication process. By using glass carrier substrates instead of silicon, the complex TSV formation, filling, and planarization steps are removed, significantly reducing fabrication cycle time and costs while the glass substrate itself provides the necessary mechanical support.
2Strength
If silicon carrier materials are used for bonding, then mechanical support is provided during thinning, but fabrication costs increase
Solution Approach 1:
The patent employs glass carrier substrates that are less expensive than silicon carriers and can be reused after the device is transferred to the final substrate. The glass substrates serve their purpose during thinning and bonding operations, then can be recovered and reused for subsequent devices, reducing per-unit fabrication costs.
Solution Approach 2:
The patent changes the carrier material parameter from expensive silicon to more cost-effective glass. This material substitution maintains adequate mechanical strength during the thinning process while significantly reducing material costs and eliminating the need for expensive TSV formation processes associated with silicon carriers.
3Reliability
If through-silicon vias are formed for interconnect coupling, then electrical connection is achieved, but fabrication complexity increases
Solution Approach 1:
The patent extracts and eliminates the through-silicon via formation process from the fabrication sequence. By using glass carrier substrates, the complex steps of TSV drilling, etching, filling with conductive material, and planarization are completely removed, simplifying the overall fabrication process while electrical connections are achieved through alternative bonding interfaces.
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 reduces fabrication costs and cycle time by eliminating the need for silicon carrier materials and through-silicon vias, simplifying the process and enabling efficient radiation detection while allowing for recyclable glass substrates.
Implementation Method 1
bonding a first glass substrate to the RDL
Implementation Method 2
thinning and processing the device substrate from the backside
Implementation Method 3
bonding a second glass substrate to the backside
Implementation Method 4
removing the first glass substrate
Data Source
AI summary
Provided is a method of fabricating a backside illuminated image sensor that includes providing a device substrate having a frontside and a backside, where pixels are formed at the frontside and an interconnect structure is formed over pixels, forming a re-distribution layer (RDL) over the interconnect structure, bonding a first glass substrate to the RDL, thinning and processing the device substrate from the backside, bonding a second glass substrate to the backside, removing the first glass substrate, and reusing the first glass substrate for fabricating another backside-illuminated image sensor.