Composite Substrate Epitaxy for Low-Warp Nitride Semiconductor Wafers
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Solution Overview
Problem
The production of nitride semiconductor wafers is challenging due to issues such as deformation, cracking, peeling, and non-uniformity, which affect yield and device performance, particularly in heteroepitaxial growth on substrates like Si and SiGe, leading to stress and lattice constant differences.
Innovation Solution
A method involving a composite substrate with a ceramic-containing substrate and a single crystal layer, using an intermediate layer to apply compressive stress, and adjusting film thickness to control warp and bow, ensuring a nitride semiconductor epitaxial wafer with Warp < 50 µm and |Bow| ≤ 40 µm, minimizing cracks and peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If heteroepitaxial growth is performed on Si or SiGe substrates, then production cost is reduced and substrate availability is improved, but stress due to lattice constant difference generates cracks and peeling
Solution Approach 1:
A buffer layer is introduced as an intermediary between the Si/SiGe substrate and the GaN epitaxial layer. This buffer layer has a lattice constant intermediate between Si and GaN, gradually transitioning the lattice mismatch and reducing stress concentration. The buffer layer absorbs the lattice constant difference, preventing direct stress transmission that would cause cracks and peeling in the GaN layer.
Solution Approach 2:
The lattice constant parameter is gradually changed through the buffer layer structure. By creating a compositional gradient in the buffer layer (e.g., AlxGa1-xN with varying x), the lattice constant transitions smoothly from the Si substrate value to the GaN layer value, reducing the abrupt stress that causes defects.
2Shape
If buffer layer is used to relax stress during epitaxial growth, then warp is reduced, but film thickness and composition distribution becomes non-uniform
Solution Approach 1:
The buffer layer is designed with spatially varying composition - the aluminum content varies through the thickness of the buffer layer to provide different local properties. The lower portion has higher Al content to match Si lattice, while the upper portion has lower Al content to match GaN lattice, creating a gradient that simultaneously controls warp and maintains uniformity.
3Productivity
If cooling rate is increased after epitaxial growth, then production efficiency is improved, but stress from thermal expansion difference generates warp failures
Solution Approach 1:
The buffer layer is designed with thermal expansion properties that compensate for the thermal stress generated during rapid cooling. The compositional gradient in the buffer layer creates a thermal expansion gradient that counteracts the stress from rapid temperature change, allowing faster cooling without warp failures.
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 enables the production of high-quality nitride semiconductor wafers with improved in-plane uniformity and yield, suitable for applications like micro-LEDs and high-frequency devices, by controlling warp and preventing peeling.
Implementation Method 1
providing the composite substrate comprising the ceramic-containing substrate having a coefficient of thermal expansion within ±10% of a coefficient of thermal expansion of the nitride semiconductor layer
Implementation Method 2
using an intermediate layer to apply compressive stress
Implementation Method 3
relaxing stress due to epitaxial growth using a buffer layer
Implementation Method 4
a nitride semiconductor layer epitaxially grown on the composite substrate
Data Source
Figure 1
AI summary
The present invention is a method for manufacturing a nitride semiconductor epitaxial wafer that includes a composite substrate having a ceramic-containing substrate and a single crystal layer bonded onto the ceramic-containing substrate, and a nitride semiconductor layer epitaxially grown on the composite substrate, the method including the steps of providing the composite substrate including the ceramic-containing substrate having a coefficient of thermal expansion within ±10% of a coefficient of thermal expansion of the nitride semiconductor layer, and having a shape of -150 < Bow (µm) ≤ 40, Warp (µm) < 150 and Warp (µm) < 90 - Bow (µm), forming an intermediate layer configured to apply compressive stress to the nitride semiconductor layer on the single crystal layer of the composite substrate, and epitaxially growing the nitride semiconductor layer on the intermediate layer, in which the nitride semiconductor epitaxial wafer having a shape of Warp (µm) < 50 and |Bow (µm)| ≤ 40 is manufactured by adjusting a film thickness of the intermediate layer. This provides the method for manufacturing a nitride semiconductor epitaxial wafer having a small warp, no cracks, and no peeling.