Nitride Semiconductor Substrate Warpage Reduction via Buffer Layer Deformation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The formation of nitride semiconductor substrates on sapphire or silicon substrates faces challenges such as warpage due to low thermal conductivity and lattice mismatch, leading to stress and dislocation issues, which complicates the fabrication of large-sized substrates with high crystallinity and crack-free nitride films.
Innovation Solution
A method involving the formation of a buffer layer on a growth substrate to deform its surface convexly, followed by growing nitride semiconductor layers with controlled deformation forces to mitigate stress, and removing the growth substrate within a process chamber to achieve a flat substrate surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a nitride film is grown on a silicon substrate to form a heterogeneous semiconductor substrate, then thermal conductivity is improved compared to sapphire substrate, but lattice mismatch between substrate and nitride film leads to increased dislocation density
Solution Approach 1:
A buffer layer is introduced as an intermediary between the silicon substrate and the nitride film. This buffer layer has a lattice constant intermediate between silicon and gallium nitride, serving as a transition that reduces the lattice mismatch. The buffer layer absorbs the lattice constant difference gradually, thereby reducing dislocation density while maintaining the thermal conductivity benefits of the silicon substrate.
Solution Approach 2:
The lattice constant parameter is changed progressively through the buffer layer structure. By creating a gradient in lattice constant from the silicon substrate through the buffer layer to the nitride film, the abrupt parameter change is softened. This gradual parameter transition reduces the generation of dislocations at the interfaces.
2Temperature
If a nitride film is grown on a silicon substrate, then thermal conductivity is improved, but difference in thermal expansion coefficient produces tensile stress that may cause cracks in the nitride film
Solution Approach 1:
The buffer layer acts as a mediator that accommodates the difference in thermal expansion coefficients between silicon and nitride. During thermal cycling in the MOCVD process, the buffer layer absorbs the differential expansion stress, preventing it from being transmitted directly to the nitride film and causing cracks.
Solution Approach 2:
The buffer layer provides beforehand cushioning against thermal stress by being positioned between the silicon substrate and the nitride film before the nitride film is grown. This pre-positioned cushioning layer absorbs the thermal expansion mismatch stress that occurs during the high-temperature MOCVD growth process and subsequent cooling, preventing crack formation in the nitride film.
3Area of stationary object
If a large-sized sapphire substrate is formed by epitaxial growth process, then substrate size is increased, but low thermal conductivity of sapphire substrate results in warpage under high temperature environment
Solution Approach 1:
The silicon substrate serves as a disposable growth substrate that enables the formation of large-sized nitride semiconductor structures. After the nitride film and buffer layer are grown, the silicon substrate is removed, leaving the desired large-sized nitride structure. This approach allows achieving large substrate sizes without being constrained by the thermal conductivity limitations of sapphire 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
This approach effectively reduces substrate warpage and dislocation density, enabling the growth of crack-free nitride films with high crystallinity on silicon substrates, facilitating the production of large-sized nitride semiconductor substrates with improved thermal and electrical conductivity.
Implementation Method 1
forming a buffer layer on a surface of a growth substrate within a first process chamber, the buffer layer deforming the surface of the growth substrate to have a convex shape
Implementation Method 2
growing a first nitride semiconductor layer on the buffer layer within the first process chamber, growing a second nitride semiconductor layer on the first nitride semiconductor layer within a second process chamber
Data Source
AI summary
A method of fabricating a nitride semiconductor substrate including forming a buffer layer on a surface of a growth substrate, growing a first nitride semiconductor layer on the buffer layer, growing a second nitride semiconductor layer on the first nitride semiconductor layer, and removing the growth substrate may be provided. The forming a buffer layer may deform the surface of the growth substrate to have a convex shape. The forming a buffer layer and the growing a first nitride semiconductor layer may be performed within a first process chamber. The growing a second nitride semiconductor layer and the removing the growth substrate may be performed within a second process chamber.