AlN Buffer Layer on Silicon Substrate for GaN Devices
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Solution Overview
Problem
The use of silicon substrates for GaN semiconductor devices leads to lattice mismatch and thermal expansion issues, resulting in crystallinity defects, cracks, and surface morphology problems due to high tensile strain, which are not adequately addressed by existing buffer layers.
Innovation Solution
A method involving the formation of an initial buffer layer on a silicon substrate by heating it to a first temperature, then reducing it to a second temperature where an Al-containing gas is flowed without nitrogen, followed by increasing the temperature with both gases to form an AlN layer, ensuring the silicon lattice directly contacts the buffer layer, thereby reducing pinhole formation and enhancing crystallinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an initial buffer layer (AlN) is formed on the silicon substrate to address lattice mismatch and thermal expansion issues, then crystallinity is improved, but pinholes are formed due to growth temperature and lattice mismatch between silicon and AIN
Solution Approach 1:
An SiN film is formed on the silicon substrate before forming the AIN initial buffer layer to prevent pinhole formation. The SiN film acts as a preliminary protective layer that prevents the harmful interaction between silicon and AIN during high-temperature growth, thereby eliminating pinholes while maintaining crystallinity improvement.
Solution Approach 2:
The SiN film serves as an intermediary layer between the silicon substrate and the AIN initial buffer layer. This intermediate layer mediates the interaction between silicon and AIN, preventing direct harmful interactions that cause pinholes, while still allowing the AIN layer to provide its crystallinity-enhancing function.
2Reliability
If the n-type GaN layer is grown at high temperature on the silicon substrate, then device performance is improved, but cracks are caused by tensile strain during cooling
Solution Approach 1:
The growth temperature parameters are optimized to balance device performance and crack prevention. By controlling the temperature profile during GaN layer growth and subsequent cooling, the tensile strain that causes cracks is reduced while maintaining the high temperature conditions necessary for good device performance.
3Object-affected harmful factors
If an SiN film is formed between the AIN initial buffer layer and silicon substrate to prevent pinholes, then pinhole formation is reduced, but the silicon lattice does not directly contact the AIN lattice
Solution Approach 1:
The SiN film is formed with controlled thickness (about 5 Å to about 10 Å) to provide sufficient protection against pinhole formation while minimizing its interference with lattice contact. This partial application of the protective layer achieves the necessary pinhole prevention without completely blocking the lattice interaction needed for crystallinity.
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 prevents pinhole formation and improves surface morphology and crystallinity by allowing direct lattice contact and reducing thermal strain, resulting in enhanced semiconductor device performance.
Implementation Method 1
heating the silicon substrate to a first temperature in a chamber, reducing an internal temperature of the chamber to a second temperature that is lower than the first temperature
Implementation Method 2
flowing a first gas including Al in the chamber at the second temperature for a first predetermined period while a second gas comprising nitrogen is not supplied into the chamber, the second temperature being 750°C to 850°C, and flowing the second gas with the first gas for a second predetermined period
Implementation Method 3
flowing the second gas with the first gas for a second predetermined period at which the internal temperature of the chamber is increased to a third temperature that is higher than the second temperature
Data Source
Figure 1~2
Figure 3A~3B
Figure 4A
AI summary
A semiconductor device is disclosed. The semiconductor device includes a silicon substrate, an initial buffer layer disposed on the silicon substrate and including aluminum nitride (AIN), and a device layer disposed on the initial buffer layer and including a semiconductor compound, wherein there is no SiN between the initial buffer layer and the silicon substrate, and a silicon lattice of the silicon substrate directly contacts a lattice of the initial buffer layer.