Asymmetric Bonding Layers for Reliable Semiconductor Wafer Joining
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Solution Overview
Problem
Metallic bonding processes for vertical hybrid integrated components require high contact pressures and stringent planarity and purity of wafer surfaces, making them challenging to initiate and maintain a reliable, uniform bond.
Innovation Solution
The use of asymmetrically structured starting layers with varying areal extents and thicknesses to create a noncongruent layout, allowing for a smaller initial contact area and higher pressure to break oxides, followed by lateral expansion and vertical pulling for uniform compression and bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high contact pressure is applied to ensure intimate contact for metallic bonding, then bonding reliability is improved, but the complexity of the bonding process increases due to strict requirements on wafer surface planarity and purity
Solution Approach 1:
A structured bonding layer is introduced as an intermediary between the two wafer surfaces to be bonded. This bonding layer compensates for surface imperfections and contaminants, enabling reliable metallic bonding without requiring extremely high contact pressures or strict surface planarity. The bonding layer materials (such as low melting point metals like In, Ga, or their alloys) facilitate bonding through controlled melting and solidification, acting as a mediator that reduces the complexity of the bonding process while maintaining bonding reliability.
2Reliability
If glass frit bonding is used to ensure hermetic sealing, then sealing reliability is improved, but the chip area required increases significantly
Solution Approach 1:
The bonding structure employs a composite material system combining a metallic bonding layer with a structured bonding layer containing low melting point materials (In, Ga, or their alloys). This composite approach achieves hermetic sealing with significantly reduced chip area compared to traditional glass frit bonding. The low melting point materials fill gaps and crevices during bonding, creating effective hermetic seals in a compact footprint, thus resolving the contradiction between sealing reliability and chip area.
3Ease of operation
If the contact area between bonding surfaces is increased to reduce pressure requirements, then ease of bonding is improved, but the ability to break oxides and contaminants decreases
Solution Approach 1:
The bonding process utilizes parameter changes by controlling the melting and solidification of low melting point materials (In, Ga, or their alloys) in the structured bonding layer. During bonding, these materials are heated to melt and flow, filling gaps and displacing oxides and contaminants. Upon cooling and solidification, they create strong, hermetic bonds. This phase change mechanism enables effective contaminant removal without requiring excessively high contact pressures or large contact areas, thus resolving the contradiction between bonding ease and contaminant removal effectiveness.
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 facilitates a reliable and uniform bonding process with reduced pressure requirements, ensuring a stable and hermetically sealed connection between semiconductor elements while accommodating non-planar bonding areas and enabling additional structural elements like electrodes or standoff structures.
Implementation Method 1
the wafer bond is established in this case with the aid of interdiffusion or by fusion of the bonding areas
Implementation Method 2
the wafer bond is established in this case with the aid of interdiffusion or by fusion of the bonding areas
Implementation Method 3
In the course of the bonding process, the bond front expands laterally, which is accompanied by a height reduction of the two starting layers
Data Source
AI summary
Measures are provided for improving and simplifying metallic bonding processes which enable a reliable initiation of the bonding process and thus contribute to a uniform bonding. The present method provides a further option for using bonding layers. The method in the case of which the two semiconductor elements are bonded to one another via a bond of at least one metallic starting layer and at least one further starting layer provides that the two starting layers are structured in such a way that the layer areas which are assigned to one another have differently sized areal extents. Moreover, the layer thicknesses of the two starting layers should be selected in such a way that the layer areas which are assigned to one another meet the material ratio necessary for the bonding process.