GaN Self-Supporting Substrate Slicing for Warp Reduction
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Solution Overview
Problem
The challenge lies in manufacturing a GaN self-supporting substrate with excellent crystal quality, minimal warp, and large diameter at a low cost, as existing methods face issues such as substrate warpage, cracking, and high dislocation density due to lattice and thermal expansion coefficient mismatches between sapphire and GaN, and require complex processing steps.
Innovation Solution
A method involving homoepitaxial growth of nitride semiconductors on a self-supporting seed substrate, followed by slicing the epitaxially grown substrate into two pieces to produce high-quality substrates, which avoids heteroepitaxial growth-related issues and simplifies the process, allowing for high productivity and cost-effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If GaN is directly epitaxially grown on a sapphire substrate, then the substrate can be used for growth, but a single-crystal film cannot be grown due to lattice constant difference
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the sapphire substrate and the GaN layer. This buffer layer mediates the lattice mismatch by providing a transition zone that gradually adapts the crystal structure from sapphire to GaN, enabling single-crystal film growth while maintaining ease of manufacture on sapphire substrates.
2Manufacturing precision
If a buffer layer is grown at low temperature to relax lattice distortion, then single-crystal GaN can be grown, but the substrate warps due to thermal expansion coefficient difference
Solution Approach 1:
The patent optimizes the buffer layer composition and growth parameters, specifically controlling the aluminum content gradient and thickness to minimize thermal expansion mismatch. By adjusting these parameters, the buffer layer maintains its lattice-matching function while reducing the thermal stress that causes substrate warpage.
3Manufacturing precision
If GaN is thickly grown on sapphire substrate to obtain self-supporting substrate, then lattice mismatch problems are solved, but inner strain relief causes substrate warp and breakage
Solution Approach 1:
The patent extracts the problematic sapphire substrate from the final structure by using a selective release layer. This release layer allows the thick GaN layer to be separated from the sapphire substrate after growth, eliminating the source of thermal expansion stress while maintaining the benefits of thick GaN growth for self-supporting capability.
4Ease of manufacture
If laser pulse is applied to delaminate GaN layer from sapphire substrate, then self-supporting GaN substrate can be obtained, but substrate cracking occurs during delamination
Solution Approach 1:
The patent introduces a selective release layer as an intermediary between the GaN layer and sapphire substrate. This release layer is designed to be selectively removable, allowing clean delamination of the GaN layer without applying stress that would cause cracking, thus enabling self-supporting substrate production while maintaining substrate integrity.
5Ease of manufacture
If different type of single crystal substrate is used to match lattice constant, then delamination becomes easier, but heteroepitaxial growth requires buffer layer and has temperature mismatch
Solution Approach 1:
The patent uses a disposable sapphire substrate that serves its purpose during growth and then is selectively removed. The sapphire substrate acts as a temporary, low-cost platform for growing high-quality GaN layers, after which it is discarded via selective etching of the release layer, avoiding the need for expensive reusable single-crystal GaN seeds.
6Ease of manufacture
If mask and low-temperature buffer layer are formed to grow GaN laterally, then self-supporting substrate can be obtained, but process becomes complicated and substrate warps
Solution Approach 1:
The patent combines the buffer layer function and the release layer function into a single integrated structure. The buffer layer is designed to simultaneously provide lattice matching during growth and serve as the selective release layer for later delamination, eliminating the need for separate mask and buffer layer formation steps, thus reducing process complexity while maintaining self-supporting substrate production.
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 nitride semiconductor self-supporting substrates with high crystal quality, reduced warp, and improved productivity, enabling the production of large-diameter substrates with low dislocation density and cost-effective manufacturing.
Implementation Method 1
a step of epitaxially growing the same type of nitride semiconductor as the seed substrate on the seed substrate
Implementation Method 2
a step of slicing an epitaxially grown substrate subjected to the epitaxial growth into two pieces in parallel to an epitaxial growth surface
Data Source
AI summary
The present invention provides a method for manufacturing a nitride semiconductor self-supporting substrate and a nitride semiconductor self-supporting substrate manufactured by this manufacturing method, the method including at least: a step of preparing a nitride semiconductor self-supporting substrate serving as a seed substrate; a step of epitaxially growing the same type of nitride semiconductor as the seed substrate on the seed substrate; and a step of slicing an epitaxially grown substrate subjected to the epitaxial growth into two pieces in parallel to an epitaxial growth surface. As a result, there is provided a method for manufacturing a large-diameter nitride semiconductor self-supporting substrate having an excellent crystal quality and small warp with good productivity at a low cost, etc.