Wafer Bonding Connector with Nano-Twinned Ag-Cu Layers
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Solution Overview
Problem
Current wafer-to-wafer bonding techniques in the semiconductor industry face challenges such as high bonding temperatures, long processing times, and the need for vacuum environments, particularly when using copper as a bonding layer, which oxidizes easily and deteriorates the bonding process.
Innovation Solution
The use of a nano-twinned copper layer as a first metal layer, followed by a nano-twinned silver layer deposited using an electroless plating process, as a bonding layer. This configuration allows for selective deposition and reduces processing costs, enabling bonding at lower temperatures and shorter times under atmospheric pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper is used as a bonding layer, then electrical conductivity is improved, but oxidation resistance deteriorates
Solution Approach 1:
The patent uses a composite structure with a copper layer providing electrical conductivity and a silver layer providing oxidation resistance. The copper layer is deposited first to establish electrical connection, then a silver layer is deposited over it to protect against oxidation. This composite material approach allows the bonding structure to simultaneously achieve high electrical conductivity and oxidation resistance by combining the advantageous properties of both materials.
2Strength
If conventional bonding techniques are used, then bonding strength is achieved, but processing temperature and time increase
Solution Approach 1:
The patent changes the material parameters by using silver as the bonding layer material instead of conventional materials. Silver's unique properties allow bonding to occur at lower temperatures and shorter times while maintaining strong bonding strength. The electroless plating process also enables precise control of layer thickness and composition, optimizing the bonding interface for reduced processing requirements.
3Strength
If conventional bonding techniques are used, then bonding strength is achieved, but processing time increases
Solution Approach 1:
The patent utilizes silver's superior diffusion and bonding characteristics to achieve strong bonds in significantly reduced time. The electroless plating process enables rapid deposition of uniform silver layers with optimal thickness for fast bonding. This parameter optimization reduces the bonding time from conventional minutes to seconds while maintaining or improving bonding strength.
4Reliability
If vacuum environment is used for bonding, then bonding quality is improved, but equipment complexity and cost increase
Solution Approach 1:
The patent employs a disposable silver layer that sacrificially protects the copper layer during handling and bonding. This thin silver layer can be deposited quickly via electroless plating and provides sufficient protection against oxidation without requiring vacuum environments. The simplicity of atmospheric pressure processing eliminates complex vacuum equipment while the silver layer maintains bonding quality through its protective function.
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 the bonding temperature and time, allows for bonding under atmospheric pressure, and ensures a high-quality bond by maintaining a pure metal surface, thus improving the efficiency and cost-effectiveness of the wafer-to-wafer bonding process.
Implementation Method 1
a second metal layer over the first metal layer, the second metal layer and the first metal layer being made of different materials, in which the second metal layer has a nano-twinned structure with (111) orientation
Implementation Method 2
which oxidizes easily and deteriorates the bonding process
Implementation Method 3
performing a thermo-compression process to bond the first and second wafers
Data Source
AI summary
A method includes forming a first connector and a second connector over a first wafer and a second wafer, respectively, in which each of the first and second connectors are formed by forming an opening in a dielectric layer; depositing a first metal layer in the opening, in which the first metal layer has a nano-twinned structure with (111) orientation; and depositing a second metal layer over the first metal layer, the second metal layer and the first metal layer being made of different materials, in which the second metal layer has a nano-twinned structure with (111) orientation; attaching the first wafer to the second wafer, such that that the second metal layer of the first connector on the first wafer is in contact with the second metal layer of the second connector on the second wafer; and performing a thermo-compression process to bond the first and second wafers.