Compressible Porous Layer for Direct Bonding Defect Reduction
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Solution Overview
Problem
Direct bonding between two elements is hindered by the presence of particles at the bonding interface, which creates significant defects due to the difficulty in achieving perfectly clean and particle-free surfaces, especially in applications like 3D integration of electronic chips.
Innovation Solution
A compressible porous layer with an isothermal compressibility coefficient greater than 10^-10 Pa^-1 at 25°C is produced on one or both elements, allowing for local deformation and densification around particles, thereby reducing the size of defects at the bonding interface during direct bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If direct bonding is performed between two elements, then bonding strength is improved, but defects are generated due to particles at the bonding interface
Solution Approach 1:
A compressible porous layer is introduced as an intermediary between the two bonding surfaces. This layer absorbs particles and compensates for surface irregularities, preventing defect formation while maintaining bonding strength. The porous structure allows the layer to deform and conform to the actual bonding surface, effectively mediating the bonding process despite the presence of contaminants.
Solution Approach 2:
The compressible porous layer changes the physical parameters at the bonding interface by providing a compliant, deformable medium. The layer's compressibility allows it to adapt to surface variations and particle presence, transforming the rigid bonding interface into a more tolerant configuration that maintains contact pressure and bonding quality despite contaminants.
2Manufacturing precision
If surfaces are cleaned to remove particles, then bonding quality is improved, but manufacturing complexity increases
Solution Approach 1:
Instead of requiring perfect cleaning to eliminate particles, the compressible porous layer converts the presence of particles into a non-critical condition. The layer absorbs and isolates particles, transforming what would be bonding-destroying defects into manageable situations that do not compromise bonding quality, thereby simplifying the cleaning process requirements.
Solution Approach 2:
The use of a porous material provides a structure that can trap and isolate particles within its pore network. This porous architecture allows the bonding interface to tolerate particle presence by confining them within the porous structure rather than allowing them to directly interfere with the bonding contact, reducing the stringency of cleaning requirements.
3Stability of the object's composition
If a rigid bonding interface is used, then structural stability is improved, but defect propagation increases
Solution Approach 1:
The compressible porous layer acts as a flexible thin film at the bonding interface. This flexible layer can deform locally to accommodate particles and surface irregularities, preventing stress concentration and defect initiation. The flexibility allows the interface to maintain stability while absorbing local disturbances that would otherwise propagate as defects in a rigid structure.
Solution Approach 2:
The compressible porous layer provides beforehand cushioning by absorbing and distributing mechanical stresses before they can propagate through the bonding interface. The layer's compressibility allows it to act as a shock-absorbing medium that protects the bonding interface from defect propagation caused by particles or surface irregularities.
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 compressible porous layer effectively reduces the size of unbonded areas around particles, facilitating better contact and significantly minimizing defects in the bonding process, even in challenging applications like 3D chip integration.
Implementation Method 1
production of at least a first porous layer on at least one face of the first element, the first porous layer being compressible
Implementation Method 2
allowing for local deformation and densification around particles
Implementation Method 3
the material plastically deformed by the particle being further displaced at the periphery thereof
Data Source
Figure 1A~2A
Figure 2B~3B
Figure 3C~4C
AI summary
The method comprises forming a first porous layer (104) on a face of a first element (102), forming a first bonding layer (106) on the first porous layer, and soldering by direct bonding of a second element (202) with the first bonding layer. The first porous layer comprises a voluminal level of porosities of >= 10% and/or is made of a elastically deformable material with a Young modulus of = 20 GPa and/or a elastically deformable material with an elastic limit of = 350 MPa. A size of pores of the first porous layer is lower than or equal to a tenth thickness of the first porous layer. The method comprises forming a first compressible porous layer (104) on a face of a first element (102), forming a first bonding layer (106) on the first porous layer, and soldering by direct bonding of a second element (202) with the first bonding layer. The first porous layer comprises a voluminal level of porosities of >= 10% and/or is made of a elastically deformable material having a Young modulus of = 20 GPa and/or a elastically deformable material having an elastic limit of = 350 MPa. A size of pores of the first porous layer is lower than or equal to a tenth thickness of the first porous layer and/or less than a size of particles to be present at an interface in the bonding between the two elements at the time of the soldering by direct bonding. The first element and/or the second element comprise a substrate or an electronic chip. The method further comprises: forming a second compressible porous layer (204) on a face of the second element; forming a second bonding layer on the second porous layer; engraving a position of a connection stud, the first porous layer and part of the first element through the first bonding layer by photolithography between the step of formation of the first bonding layer and the step of soldering by direct bonding of the second element with the first bonding layer; depositing a electrically conducting material forming the connection stud in the position; performing chemical and mechanical planarization on the first bonding layer; and depositing a material layer to form a barrier with the diffusion of material of the connection stud prior to depositing the electrically conducting material in the position, where the electrically conducting material is then deposited on the barrier material layer. The soldering by direct bonding of the second member with the first bonding layer is obtained by a direct contacting of the first bonding layer against the second bonding layer. The second porous layer comprises a voluminal level of porosities of >= 10%, and/or is made of an elastically deformable material having a Young modulus of = 20 GPa and/or of an elastically deformable material having an elastic limit of = 350 MPa. The first porous layer comprises a thickness higher than a thickness of the first bonding layer, and/or the second porous layer comprises a thickness higher than the thickness of the second bonding layer. The formation of the first porous layer and/or the formation of the second porous layer comprise: an application of carbon doped silicon oxides deposited by a porous plasma-enhanced chemical vapor deposition; depositing a material to be engraved and intended to form the first porous layer and/or the second porous layer and then forming pores by chemical engraving and/or electrochemical material deposition; and depositing material of the first porous layer and/or the second porous layer by blowing pore-forming particles added to the deposited material, and removing the pore-forming particles after forming the pores within the material of the first porous layer and/or the second porous layer. The formation of the first bonding layer and/or the formation of the second bonding layer comprises depositing a material of the first bonding layer on the first porous layer and/or depositing of a material of the second bonding layer on the second porous layer, and heat treating a part of the first porous layer and/or the second porous layer using plasma or chemical, where the treated part of the first porous layer forms the first bonding layer and/or the treated part of the second porous layer forms the second bonding layer. The connection stud formed in the first element is attached by direct bonding with a connection stud in the second element at the time of soldering by direct bonding of the second element with the first bonding layer.