Direct Wafer Bonding Using Epitaxial (Al)GaInP Layer
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Solution Overview
Problem
Existing methods for joining semiconductor wafers, such as metamorphic and indirect bonding, face challenges with lattice mismatch, high temperature annealing requirements, and limitations in achieving both mechanical integrity, optical transparency, and low electrical resistance at the bond interface, particularly for GaAs and InP materials.
Innovation Solution
The use of an epitaxially grown (Al)(Ga)InP(As)(Sb) bonding layer for direct semiconductor bonding, which is lattice matched to the wafers, allowing for high mechanical strength, low electrical resistance, and high optical transmittance across the bonded interface, achieved at relatively low bonding temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If direct bonding is performed without intermediate layers, then mechanical strength and electrical conductivity are improved, but high temperature annealing (>500°C) is required for extended periods, reducing device performance
Solution Approach 1:
An epitaxially grown (Al)GaInP bonding layer is introduced as an intermediate layer between dissimilar semiconductor wafers (e.g., GaAs and InP). This bonding layer enables direct bonding at lower temperatures (300-500°C) while maintaining mechanical strength and electrical conductivity, eliminating the need for high-temperature annealing that would otherwise be required for direct bonding of lattice-mismatched materials.
Solution Approach 2:
The bonding layer's composition is optimized by adjusting the aluminum content and thickness parameters. The (Al)GaInP layer is grown with specific compositional gradients and thickness control (typically 1-10 micrometers) to achieve lattice matching between dissimilar substrates, enabling low-temperature bonding while maintaining electrical and mechanical properties.
2Temperature
If indirect bonding with dielectric layers (SiO2, Si3N4) is used, then bonding temperature is reduced, but the bonding interface becomes optically opaque and electrically insulating
Solution Approach 1:
The bonding layer is designed with specific material composition ((Al)GaInP) and thickness parameters that enable it to be both mechanically effective for bonding and optically transparent. By controlling the aluminum content and layer thickness, the bonding interface maintains high optical transmittance while providing the necessary mechanical strength at reduced bonding temperatures.
3Reliability
If indirect bonding with metal layers is used, then electrical conductivity is improved, but the bonding interface becomes optically opaque
Solution Approach 1:
The (Al)GaInP bonding layer functions as a composite material that combines the electrical conductivity of metals with the optical transparency of dielectrics. This single-layer composite structure eliminates the need for separate metal and dielectric layers, providing both electrical connectivity and optical transparency at the bonding interface simultaneously.
4Stability of the object's composition
If metamorphic layers with buffer layers are used, then lattice mismatch is reduced, but high densities of defects are introduced, reducing device performance
Solution Approach 1:
The epitaxially grown (Al)GaInP bonding layer serves as an intermediate layer that gradually transitions the lattice constant between dissimilar substrates. This controlled lattice transition minimizes defect formation compared to conventional buffer layers, maintaining high crystal quality and device performance while achieving lattice matching between dissimilar materials.
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 results in a bonded interface with mechanical strength greater than 4 J/m², electrical resistance as low as 0.3 Ohm-cm², and optical transmittance greater than 97%, enhancing the performance and efficiency of semiconductor devices.
Implementation Method 1
an epitaxially grown (Al)(Ga)InP(As)(Sb) bonding layer on GaAs and InP device or substrate
Implementation Method 2
high optical transmittance across the bonded interface
Data Source
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AI summary
The disclosure provides for a direct wafer bonding method including providing a bonding layer upon a first and second wafer, and directly bonding the first and second wafers together under heat and pressure. The method may be used for directly bonding an GaAs-based, InP-based, GaP-based, GaSb-based, or Ga(In)N-based device to a GaAs device by introducing a highly doped (A1)(Ga)InP(As)(Sb) layer between the devices. The bonding layer material forms a bond having high bond strength, low electrical resistance, and high optical transmittance.