3C-SiC Buffered Silicon Substrate for Crack-Free Nitride Epitaxy
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Solution Overview
Problem
Large diameter single crystal silicon substrates with nitride semiconductor layers face issues of warpage and cracking due to differences in linear expansion coefficients, and existing solutions like increasing substrate thickness do not provide a fundamental solution, leading to wafer damage and process contamination.
Innovation Solution
A method involving epitaxial growth of a 3C-SiC single crystal film on a single crystal silicon substrate, followed by a nitride semiconductor layer, with dislocations formed throughout the substrate to mitigate warpage and cracking, characterized by dislocation lengths greater than or equal to 1 mm and densities greater than or equal to 10/cm².
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the single crystal silicon substrate is increased to prevent warpage and cracking, then the substrate strength is improved, but the device process compatibility deteriorates and kerf loss increases
Solution Approach 1:
A 3C-SiC intermediate layer is introduced between the GaN nitride semiconductor layer and the Si substrate. This intermediary layer acts as a buffer that absorbs thermal expansion mismatch and prevents direct stress transmission to the thin Si substrate, enabling the use of regular thickness substrates (e.g., 775 μm) without warpage or cracking while maintaining device process compatibility.
Solution Approach 2:
The invention changes the material parameter of the intermediate layer from pure Si to 3C-SiC, which has different thermal and mechanical properties. This parameter change allows the intermediate layer to serve as a stress buffer, resolving the contradiction between substrate thickness for strength and thinness for process compatibility.
2Strength
If the thickness of the single crystal silicon substrate is increased to prevent warpage and cracking, then the substrate strength is improved, but the kerf loss increases
Solution Approach 1:
The 3C-SiC intermediate layer serves as a stress buffer that prevents warpage and cracking in regular thickness substrates, eliminating the need to increase substrate thickness. This resolves the contradiction by maintaining thin substrate dimensions (reducing kerf loss) while preventing substrate failure through the intermediary stress-absorbing layer.
3Ease of manufacture
If AlN is used as a buffer layer to grow GaN on Si substrates, then the nitride semiconductor layer growth is enabled, but melt-back of Al or Ga into the Si substrate occurs causing defects
Solution Approach 1:
The 3C-SiC intermediate layer is positioned between the GaN nitride semiconductor layer and the Si substrate, serving as a barrier that prevents melt-back of Al or Ga from the nitride layer into the substrate during high-temperature growth processes, thereby eliminating defects while enabling nitride semiconductor layer growth.
Solution Approach 2:
The 3C-SiC intermediate layer acts as a sacrificial buffer that protects the Si substrate from contamination. It is grown to a specific thickness (e.g., 50-200 nm) to provide sufficient protection against melt-back, serving its protective function during the critical growth phases.
4Shape
If dislocations are formed in the single crystal silicon substrate with specific density and length, then warpage is reduced, but the substrate structure becomes more complex
Solution Approach 1:
The 3C-SiC intermediate layer serves as a buffer that absorbs and distributes thermal stress during cooling from growth temperature, preventing warpage in the final device structure. This intermediary approach reduces warpage without requiring complex dislocation engineering in the Si substrate itself, maintaining relatively simple substrate structure.
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 method produces a single crystal silicon substrate with a nitride semiconductor layer having a large diameter of 200 mm or 300 mm, using a regular thickness, with reduced warpage and no cracks, effectively preventing melt-back of Al or Ga and ensuring stable device fabrication.
Implementation Method 1
a 3C-SiC single crystal film epitaxially grown on the single crystal silicon substrate
Implementation Method 2
a nitride semiconductor layer epitaxially grown on the 3C-SiC single crystal film
Implementation Method 3
dislocations are formed throughout the single crystal silicon substrate, a length (dislocation length) of each of the dislocations when seen in a planar projection onto the single crystal silicon substrate is greater than or equal to 1 mm, and a density of the dislocations is greater than or equal to 10/cm²
Data Source
AI summary
A single crystal silicon substrate with a nitride semiconductor layer, including: a single crystal silicon substrate; a 3C-SiC single crystal film epitaxially grown on the single crystal silicon substrate; and a nitride semiconductor layer epitaxially grown on the 3C-SiC single crystal film. Dislocations are formed throughout the single crystal silicon substrate, a length (dislocation length) of each of the dislocations when seen in a planar projection onto the single crystal silicon substrate is greater than or equal to 1 mm, and a density of the dislocations is greater than or equal to 10/cm2. This provides a single crystal silicon substrate with a nitride semiconductor layer having a large diameter such as 200 mm or 300 mm that is made using a regular thickness Si substrate and has less warpage and especially no cracks, and a method for producing such a single crystal silicon substrate with a nitride semiconductor layer.