GaN-on-Si Substrate Laminate with Twisted Handle Layer
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Solution Overview
Problem
The integration of Gallium Nitride (GaN) with Silicon in integrated circuits is hindered by their differing coefficients of thermal expansion and lattice mismatch, leading to cracks and fractures during the fabrication process, which results in wafer breakage and inefficiencies in forming high-quality epitaxial layers.
Innovation Solution
A substrate arrangement comprising a laminate with a [111] surface-oriented Silicon seed layer and a [0001] surface-oriented Gallium Nitride epitaxial layer, where the handle layer is twisted by an angle between 40° and 80° and tilted by 45° to 65° relative to the seed layer, decoupling fracture propagation risks and providing a robust substrate for epitaxial growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Gallium Nitride is integrated with Silicon substrate, then advantageous semiconducting material properties are achieved, but cracks and fractures occur due to thermal expansion mismatch and lattice mismatch
Solution Approach 1:
The substrate is divided into two separate layers: a Silicon handle layer and a Gallium Nitride epitaxial layer. This segmentation allows each layer to maintain its own crystal structure and thermal expansion characteristics, preventing crack propagation that would occur in a monolithic structure. The handle layer provides mechanical support while the epitaxial layer provides semiconducting functionality.
Solution Approach 2:
A seed layer is introduced as an intermediary between the Silicon handle layer and the Gallium Nitride epitaxial layer. This seed layer serves as a buffer that accommodates the lattice mismatch between Silicon and Gallium Nitride, enabling epitaxial growth while reducing dislocation density and preventing crack formation.
2Ease of manufacture
If handle layer and seed layer have same crystal orientation, then alignment is simplified, but fracture propagation risk increases
Solution Approach 1:
The handle layer and seed layer are deliberately given different crystal orientations (Silicon <100> vs. seed layer with specific orientation for GaN growth). This asymmetric orientation arrangement prevents fracture propagation by ensuring that cracks in one layer do not align with and propagate into the other layer, while still maintaining manufacturability through controlled epitaxial growth processes.
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 configuration reduces the risk of fractures spreading from the epitaxial layer to the handle layer, enhancing the robustness and reliability of the substrate for integrated circuit fabrication, particularly in high-voltage applications by minimizing capacitive coupling and improving high-frequency performance.
Implementation Method 1
the substrate having a surface configured to receive, by epitaxy, the epitaxial layer of semiconducting material
Implementation Method 2
The handle layer and seed layer may be wafer bonded together. Any wafer bonding process may be used, such as direct bonding or by way of the smart cut process.
Data Source
Figure 1~3
Figure 4~6
AI summary
A substrate arrangement comprising a substrate having a surface configured to receive, by epitaxy, an epitaxial layer of semiconducting material, the substrate comprising a laminate having a handle layer and a seed layer, the seed layer having a crystal orientation arranged to receive the epitaxial layer and the handle layer having a crystal orientation different to the seed layer.