Nitride Semiconductor Buffer Layer for Substrate Warpage Reduction
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Solution Overview
Problem
The growth of nitride semiconductor layers on sapphire substrates often results in crystal defects due to lattice constant and thermal expansion coefficient differences, leading to substrate warpage, which affects device processes like lithography and increases costs as substrate size increases.
Innovation Solution
A method involving the formation of protrusions on the substrate surface, followed by the growth of a single crystal layer with controlled cracks, which acts as a buffer to reduce stress and warpage by managing the lattice constant and thermal expansion coefficient differences between the substrate and the nitride semiconductor layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a sapphire substrate is used for nitride semiconductor growth, then stability in crystal growth atmosphere and price are improved, but crystal defects occur due to lattice constant and thermal expansion coefficient differences
Solution Approach 1:
A buffer layer is introduced as an intermediary between the sapphire substrate and the nitride semiconductor layer. This buffer layer mediates the lattice constant and thermal expansion coefficient differences, reducing strain and preventing crystal defects while maintaining the cost advantages of using sapphire substrates.
Solution Approach 2:
The composition and thickness of the buffer layer are optimized to gradually transition from the sapphire substrate parameters to the nitride semiconductor parameters. By controlling the buffer layer's material composition and thickness, the strain is progressively reduced, improving crystal quality without changing the substrate material.
2Productivity
If substrate diameter is increased to reduce device cost, then manufacturing efficiency is improved, but substrate warpage is accelerated due to strain accumulation
Solution Approach 1:
The buffer layer acts as a stress-absorbing intermediary that prevents strain accumulation across large substrate areas. By distributing and mitigating the thermal expansion and lattice mismatch strains, the buffer layer enables larger substrate diameters to be used without excessive warpage, thereby reducing device cost.
Solution Approach 2:
The buffer layer is designed with thermal expansion properties that bridge the gap between the sapphire substrate and nitride semiconductor. This gradual transition in thermal expansion coefficients reduces strain during cooling from growth temperature, preventing warpage even on large-diameter substrates.
3Reliability
If buffer layer thickness is increased to reduce defects, then crystal quality is improved, but misfit dislocations occur at the buffer layer interface
Solution Approach 1:
Instead of simply increasing buffer layer thickness, the composition parameters of the buffer layer are optimized. The buffer layer composition is gradually adjusted to match the nitride semiconductor, allowing effective strain reduction at optimal thicknesses without generating misfit dislocations.
Solution Approach 2:
The buffer layer is designed as a composite structure with varying composition gradients. This composite approach allows the buffer layer to simultaneously manage strain and prevent dislocation formation by creating a gradual transition in material properties rather than a abrupt interface.
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
The approach effectively reduces substrate warpage, improving the accuracy of device processes and reducing costs by facilitating more uniform and stable nitride semiconductor layer growth, even on larger substrates.
Implementation Method 1
the other one is strain due to the thermal expansion coefficient difference between the substrate and a growth layer during a cooling process from a growth temperature to a room temperature
Implementation Method 2
One is strain due to the lattice constant difference between the sapphire substrate and the nitride semiconductor
Implementation Method 3
a single crystal layer with controlled cracks, which acts as a buffer to reduce stress and warpage
Data Source
AI summary
According to one embodiment, stacked layers of a nitride semiconductor include a substrate, a single crystal layer and a nitride semiconductor layer. The substrate does not include a nitride semiconductor and has a protrusion on a major surface. The single crystal layer is provided directly on the major surface of the substrate to cover the protrusion, and includes a crack therein. The nitride semiconductor layer is provided on the single crystal layer.