Nitride Semiconductor Substrate Growth for Low-Dislocation Surfaces
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Solution Overview
Problem
Existing methods for manufacturing nitride semiconductor substrates, such as growing on sapphire substrates, often result in poor crystal quality due to cracking and high dislocation densities caused by lattice mismatch, making it difficult to obtain substrates suitable for semiconductor devices like LEDs.
Innovation Solution
A method involving vapor phase growth, where a base substrate with a (0001) plane is used, followed by epitaxial growth of a first layer with inclined interfaces that disappear as a second layer is grown, reducing dislocation density and achieving a mirror-finished surface with low index crystal planes, specifically using a template forming step, a first step with three-dimensional growth, and a second step for flattening, to produce a nitride semiconductor substrate with reduced dislocations and improved crystal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a nitride semiconductor layer is grown on a sapphire substrate using a simple process, then the manufacturing process is simple, but the crystal quality is poor due to cracking and high dislocation densities caused by lattice mismatch
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the sapphire substrate and the nitride semiconductor layer. This buffer layer acts as a mediator that reduces the lattice mismatch stress, preventing cracking and reducing dislocation densities while maintaining the simplicity of growing on a sapphire substrate.
Solution Approach 2:
The patent segments the nitride semiconductor structure into multiple layers with different compositions and thicknesses. By dividing the semiconductor layer into distinct segments (buffer layer, intermediate layer, and active layer), each can be optimized for specific functions, improving overall crystal quality while keeping the manufacturing process manageable.
2Length of moving object
If the nitride semiconductor layer is grown thicker to obtain a free-standing substrate, then the substrate can be peeled off as a free-standing piece, but cracking occurs due to lattice mismatch stress
Solution Approach 1:
The buffer layer serves as a stress-absorbing intermediary that allows the nitride semiconductor layer to be grown thicker without causing cracking. It mediates the lattice mismatch stress that would otherwise propagate through the entire structure and cause failure.
Solution Approach 2:
The buffer layer provides beforehand cushioning by absorbing and distributing the lattice mismatch stress before it can cause cracking in the thicker nitride semiconductor layer. This pre-cushioning effect enables the growth of thicker substrates that can be peeled off as free-standing pieces without reliability issues.
3Manufacturing precision
If a buffer layer is introduced to improve crystal quality, then dislocation density is reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The buffer layer is a simple intermediary structure that can be grown using the same vapor phase growth method as the rest of the nitride semiconductor layer. While it adds one more layer to the structure, it does not require fundamentally different manufacturing techniques, thus improving crystal quality with minimal increase in process complexity.
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 method enables the production of nitride semiconductor substrates with low dislocation density and good crystal quality, reducing the likelihood of cracking and improving the substrate's suitability for semiconductor devices.
Implementation Method 1
a step of growing a base layer that has a mirror-finished base surface and in which a low index crystal plane closest to the base surface is a (0001) plane, by epitaxially growing a single crystal of a group III nitride semiconductor on the upper side of the base substrate
Implementation Method 2
a first step of growing a first layer by epitaxially growing a single crystal of a group III nitride semiconductor directly on the base surface of the base layer, the single crystal of the group III nitride semiconductor having a top surface at which a (0001) plane is exposed, a plurality of recessed portions formed by inclined interfaces other than the (0001) plane being generated in the top surface
Implementation Method 3
a second step of growing a second layer that has a mirror-finished surface by epitaxially growing a single crystal of a group III nitride semiconductor on the first layer so as to make the inclined interfaces disappear
Data Source
AI summary
A method for manufacturing a nitride semiconductor substrate by using a vapor phase growth method includes: a step of preparing a base substrate that is constituted by a material different from a single crystal of a group III nitride semiconductor; a step of growing a base layer on the upper side of the base substrate; a first step of growing a first layer by epitaxially growing a single crystal of a group III nitride semiconductor directly on the base surface of the base layer, the single crystal of the group III nitride semiconductor having a top surface at which a (0001) plane is exposed, and a plurality of recessed portions formed by inclined interfaces other than the (0001) plane being generated in the top surface; and a second step of growing a second layer that has a mirror-finished surface.