Direct Die Bonding Structure for Low-Stress 3D Stacking
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Solution Overview
Problem
Conventional methods for stacking integrated device dies in 3D integration face challenges such as die damage from assembly stresses, difficulty in stacking dies with different thicknesses and high pin counts, and the use of thick low coefficient of thermal expansion materials, which are costly and difficult to manufacture.
Innovation Solution
The method involves direct gang bonding of elements without intervening adhesives, using a carrier with a polished surface to reduce thermal stresses and simplify the deposition process, and employing a sacrificial filler material to thin the structure while avoiding filling materials between elements, which allows for covalent bonding at room temperature and reduces fabrication costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional die thinning and 3D integration methods are used, then integrated device dies can be stacked, but product yield is limited due to die damage from assembly stresses
Solution Approach 1:
The patent removes the intermediate adhesive layer from the bonding process, enabling direct bonding between dies. This extraction of the adhesive layer eliminates the stress concentration and failure points that occur at adhesive-die interfaces during assembly, thereby preventing die damage and improving product yield
Solution Approach 2:
The patent performs preliminary surface preparation including polishing and activation of bonding surfaces before stacking. This preliminary action ensures surfaces are clean, smooth, and chemically activated, enabling direct covalent bonding that can withstand assembly stresses without die damage
2Adaptability or versatility
If conventional stacking methods are used, then dies can be assembled, but it is challenging to stack dies with different thicknesses and high pin counts
Solution Approach 1:
The patent changes the bonding mechanism from mechanical/adhesive-based to direct covalent bonding, which fundamentally alters how dies are joined. This parameter change enables accommodation of different die thicknesses and pin counts because the bonding occurs at the atomic level across the entire bonding surface rather than relying on mechanical interlocking or adhesive distribution
Solution Approach 2:
The direct bonding method creates a universal bonding interface that can bond any die surface regardless of thickness variations or pin configurations. The bonding process itself serves multiple functions: mechanical attachment, electrical isolation, and stress distribution, simplifying the overall stacking process
3Object-affected harmful factors
If thick low coefficient of thermal expansion materials are used in conventional methods, then thermal stresses are managed, but fabrication costs increase and manufacturing becomes difficult
Solution Approach 1:
The patent extracts and removes the thick low coefficient of thermal expansion material layer from the bonding structure. By enabling direct bonding between dies, the patent eliminates the need for this intermediate material layer, thereby reducing fabrication costs and manufacturing complexity while still managing thermal stresses through the direct covalent bond interface
Solution Approach 2:
The patent discards the conventional approach of using thick CTE-matching materials and recovers thermal stress management through direct die-to-die covalent bonding. The bonding interface itself becomes the thermal stress management mechanism rather than requiring separate material layers
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 enhances the yield and reliability of stacked die structures by minimizing thermal stresses and simplifying the manufacturing process, enabling the secure bonding of dies with different characteristics without the need for external pressure or voltage, while reducing fabrication costs.
Implementation Method 1
using a carrier with a polished surface to reduce thermal stresses
Implementation Method 2
enabling the secure bonding of dies with different characteristics without the need for external pressure or voltage
Data Source
AI summary
A bonded structure can comprise a first element and a second element. The first element has a first dielectric layer including a first bonding surface and at least one first side surface of the first element. The second element has a second dielectric layer including a second bonding surface and at least one second side surface of the second element. The second bonding surface of the second element is directly bonded to the first bonding surface of the first element without an adhesive.