Wafer Edge Undercut Processing for Low-Chip 3D IC Thinning
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Solution Overview
Problem
Wafer edge trimming in 3D IC fabrication induces mechanical stresses causing microcracks and chipping, leading to reduced yield and low throughput due to a multi-stage cutting process.
Innovation Solution
A wafer processing method involving hybrid bonding, stealth laser dicing or lateral wafer edge cutting to form a narrow undercut region, followed by grinding to achieve a thin wafer thickness, reducing mechanical stresses and chipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wafer edge trimming process is performed to remove annular portion along outer periphery, then wafer edge imperfections are eliminated, but mechanical stresses are induced causing microcracks and chipping
Solution Approach 1:
The patent replaces the conventional mechanical trimming process with a laser-based processing method. The laser beam processes the wafer edge without physical contact, eliminating mechanical stresses and chipping that occur during traditional trimming. This substitution of mechanical system with optical/thermal field resolves the contradiction between achieving edge quality and avoiding mechanical damage.
Solution Approach 2:
The patent changes the processing parameters by using laser power, pulse duration, and scanning speed instead of mechanical feed rate and cutting depth. By controlling laser parameters such as power density and pulse width, the process achieves precise edge removal without inducing mechanical stresses, thus resolving the contradiction between edge quality improvement and stress-induced chipping.
2Manufacturing precision
If multi-stage cutting process is employed for wafer edge trimming, then edge quality is improved, but processing time increases resulting in low throughput
Solution Approach 1:
The patent combines multiple trimming stages into a single laser processing step. Instead of performing sequential mechanical trimming operations at different stages, the laser method achieves the complete edge removal in one continuous process, merging multiple operations into a unified process that maintains quality while reducing time.
Solution Approach 2:
The laser processing operates continuously along the wafer periphery without the need for stage changes or tool reconfigurations required in multi-stage mechanical trimming. The continuous laser scanning maintains constant processing action, eliminating idle time between stages and significantly improving throughput while maintaining edge quality.
3Ease of manufacture
If conventional wafer edge trimming is performed, then processing can be completed, but particulate contamination occurs and yield is reduced
Solution Approach 1:
By replacing mechanical cutting tools with laser processing, the patent eliminates the generation of mechanical particulates that contaminate the wafer surface. The laser ablates material through vaporization and ejection of molten material, avoiding the creation of fine particulate debris that would require additional cleaning steps and reduce yield.
Solution Approach 2:
The laser beam acts as an intermediary that transfers energy to the wafer material for removal without physical contact. This energy-mediated process avoids direct mechanical interaction that generates particulates, and the resulting material ejection can be controlled to minimize contamination, thus resolving the contradiction between completing processing and avoiding particulate contamination.
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 method simplifies processing, avoids particulate contamination, and enhances yield by minimizing wafer edge chipping, enabling higher throughput.
Implementation Method 1
the undercut region is formed by performing a stealth laser dicing process. a laser beam used during the stealth laser dicing process is focused at a region adjacent the front surface of the second wafer
Implementation Method 2
subjecting a rear surface of the second wafer to a grinding process, thereby thinning the second wafer to a pre-determined thickness
Data Source
AI summary
A wafer processing method is disclosed. A second wafer is bonded to a first wafer. An undercut region is formed along the periphery of a front surface of the second wafer. A grinding process is performed on a back surface of the second wafer, thereby thinning the second wafer to a predetermined thickness.