Multi-Layer Buffer Structure for Nitride Semiconductor Crack Prevention
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Solution Overview
Problem
Nitride-based semiconductor devices face challenges with crack formation and dislocation density when grown on silicon substrates due to lattice mismatch and thermal expansion coefficient differences, leading to poor crystallinity and device performance.
Innovation Solution
A semiconductor buffer structure is developed using a multi-layered AlxInyGa1-x-yN layer configuration with specific lattice constant gradients and distributions to apply compressive stress, reducing tensile stress and preventing cracks, while also incorporating a crack prevention portion on the silicon substrate to mitigate edge-related defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a nitride thin film is grown on a Si substrate, then thermal conductivity is improved and large film growth is enabled, but dislocation density increases and cracks occur due to lattice mismatch and thermal expansion coefficient mismatch
Solution Approach 1:
The buffer layer is divided into multiple sub-layers (first buffer layer, second buffer layer, third buffer layer) with progressively varying compositions and lattice constants. This segmentation allows gradual transition from the Si substrate lattice structure to the nitride thin film lattice structure, reducing dislocation density and preventing cracks while maintaining thermal conductivity benefits.
Solution Approach 2:
Each buffer layer sub-layer has locally optimized composition and lattice constant tailored to its specific position in the structure. The first buffer layer has lower Al content and smaller lattice constant closer to Si, while subsequent layers have progressively higher Al content and larger lattice constants approaching the nitride film, creating locally adapted stress distribution that prevents crack formation.
2Reliability
If a sapphire substrate is used, then crack prevention is improved, but manufacturing cost increases and large size manufacturing becomes difficult due to warpage and low thermal conductivity
Solution Approach 1:
The multi-layer buffer structure acts as an intermediary between the Si substrate and the nitride thin film, providing gradual lattice constant transition and stress management. This intermediary structure enables the use of inexpensive, easily manufacturable Si substrates while achieving crack prevention previously only possible with expensive sapphire substrates.
Solution Approach 2:
The buffer layer composition parameters (Al content, In content, Ga content) are systematically varied across different layers to achieve progressive lattice constant changes. This parameter optimization allows the buffer layers to simultaneously match the Si substrate at the bottom interface and the nitride film at the top interface, enabling crack-free growth on cost-effective Si substrates.
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 reduces crack formation and dislocation density, enabling the growth of high-crystallinity nitride thin films on silicon substrates, thus improving the manufacturing feasibility and performance of nitride-based semiconductor devices.
Implementation Method 1
The buffer layer includes a first layer, a second layer and a third layer. The first layer includes AlxInyGa1-x-yN (0≦x≦1, 0≦y≦1, 0≦x+y≦1) and has a lattice constant LP1 smaller than a lattice constant LP0 of the silicon substrate. The second layer is formed on the first layer, includes AlxInyGa1-x-yN (0≦x≦1, 0≦y≦1, 0≦x+y≦1), and has a lattice constant LP2 greater than LP1. The third layer is formed on the second layer, includes AlxInyGa1-x-yN (0≦x≦1, 0≦y≦1, 0≦x+y≦1), and has a lattice constant LP3 smaller than LP2.
Implementation Method 2
Since a Si substrate has higher thermal conductivity than a sapphire substrate, the Si substrate is not warped greatly at a high temperature for growing a nitride thin film
Implementation Method 3
The silicon substrate may be doped with a dopant, and the dopant may include at least one of B, Al, Mg, Ca, Zn, Cd, Hg, and Ga. A doping concentration of the dopant may be determined such that the silicon substrate has a resistivity of about 1 Ωcm or less.
Data Source
AI summary
A method of manufacturing a semiconductor device includes forming a silicon substrate, forming a buffer layer on the silicon substrate, and forming a nitride semiconductor layer on the buffer layer. The buffer layer includes a first layer, a second layer, and a third layer. The first layer includes AlxInyGa1-x-yN (0≦x≦1, 0≦y≦1, 0≦x+y≦1) and has a lattice constant LP1 that is smaller than a lattice constant LP0 of the silicon substrate. The second layer is formed on the first layer, includes AlxInyGa1-x-yN (0≦x<1, 0≦y<1, 0≦x+y<1), and has a lattice constant LP2 that is greater than LP1 and smaller than LP0. The third layer is formed on the second layer, includes AlxInyGa1-x-yN (0≦x<1, 0≦y<1, 0≦x+y<1), and has a lattice constant LP3 that is smaller than LP2.