Graded AlInGaN Buffer for Silicon Substrate Crack Prevention
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Solution Overview
Problem
Conventional nitride-based semiconductor devices using sapphire substrates are expensive and prone to warping due to low thermal conductivity, while those using silicon substrates face issues with dislocation density and cracking due to lattice mismatch and thermal expansion coefficient differences.
Innovation Solution
A semiconductor buffer structure comprising multiple layers of AlxInyGa1-x-yN with specific lattice constants and thickness relationships is used on a silicon substrate to apply compressive stress, reducing the likelihood of cracks in nitride thin films and enhancing crystallinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sapphire substrate is used for nitride-based semiconductor devices, then the device can be manufactured, but the cost is high and the substrate is prone to warping due to low thermal conductivity
Solution Approach 1:
The patent replaces expensive sapphire substrates with silicon substrates that can be mass-produced at lower costs. The silicon substrate serves as a temporary platform for growing nitride semiconductor layers, which can then be transferred to final devices, effectively making the substrate a disposable manufacturing aid rather than a permanent component.
Solution Approach 2:
The patent modifies the substrate material parameter from sapphire to silicon, fundamentally changing the thermal and mechanical properties of the substrate system. This parameter change enables better thermal conductivity and reduced warping during the high-temperature epitaxial growth process.
2Temperature
If a silicon substrate is used instead of sapphire substrate, then thermal conductivity is improved and warping is reduced, but dislocation density increases due to lattice constant mismatch
Solution Approach 1:
The patent introduces an AlN buffer layer as an intermediary between the silicon substrate and the nitride semiconductor layers. This buffer layer acts as a mediator that gradually transitions the lattice constant from silicon to nitride, reducing the abrupt mismatch and thereby decreasing dislocation density in the final semiconductor layers.
Solution Approach 2:
The patent employs a graded buffer layer where the aluminum nitride content is gradually increased from the silicon substrate interface toward the nitride semiconductor layer. This gradual parameter change in composition creates a progressive lattice constant transition, minimizing dislocation formation.
3Area of stationary object
If a silicon substrate is used, then larger substrate size can be achieved, but cracks occur due to tensile stress from thermal expansion coefficient mismatch
Solution Approach 1:
The patent modifies the thermal expansion characteristics of the substrate-film system by introducing aluminum nitride buffer layers with intermediate thermal expansion coefficients. This gradual parameter transition reduces the thermal stress differential, preventing crack formation in large-area substrates during temperature cycling.
Solution Approach 2:
The patent creates a composite structure consisting of silicon substrate, AlN buffer layers, and nitride semiconductor layers. This composite material system combines the advantages of silicon (large size, high thermal conductivity) with the benefits of aluminum nitride (intermediate thermal expansion, good lattice match), resulting in a crack-resistant structure for large-area devices.
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 buffer structure effectively compensates for stress and prevents cracking in nitride semiconductor films, allowing for the growth of high-crystallinity films on silicon substrates, enabling the production of large-area semiconductor devices.
Implementation Method 1
a dislocation density may be increased due to a mismatch in lattice constants between the Si substrate and the nitride thin film
Implementation Method 2
tensile stress generated by the mismatch in thermal expansion coefficients between the Si substrate and the nitride thin film
Implementation Method 3
the buffer layer may be configured to apply a compressive stress to the nitride semiconductor layer
Data Source
AI summary
A semiconductor buffer structure may include a silicon substrate and a buffer layer that is formed on the silicon substrate. The buffer layer may include a first layer, a second layer formed on the first layer, and a third layer formed on the second layer. The first layer may include AlxInyGa1-x-yN (0≦x≦1, 0≦y≦1, 0≦x+y≦1) and have a lattice constant LP1 that is smaller than a lattice constant LP0 of the silicon substrate. The second layer may include AlxInyGa1-x-yN (0≦x<1, 0≦y<1, 0≦x+y<1) and have a lattice constant LP2 that is greater than the lattice constant LP1 and smaller than the lattice constant LP0. The third layer may include AlxInyGa1-x-yN (0≦x<1, 0≦y<1, 0≦x+y<1) and have a lattice constant LP3 that is greater than the lattice constant LP1 and smaller than the lattice constant LP2.