Single-Crystal Diamond Substrates With Mist CVD Buffer Layers
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Solution Overview
Problem
Current methods for producing single crystal diamond substrates face challenges in achieving large area, high quality, and low stress substrates due to lattice mismatch and difficulties in heteroepitaxial growth on suitable underlying substrates, leading to issues like hillocks, dislocation defects, and high production costs.
Innovation Solution
A method involving the use of a mist CVD process to form a single crystal Ir or MgO film as an intermediate layer on initial substrates such as Si, α-Al2O3, Fe, Ni, or Cu, with controlled off-angles and laminate films to mitigate lattice mismatch, followed by epitaxial growth of a single crystal diamond layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If HPHT method is used to synthesize single crystal diamond, then high purity and single crystallinity are achieved, but the substrate size is limited to approximately 8 mm square and production cost is high
Solution Approach 1:
The invention segments the substrate into multiple smaller HPHT-synthesized diamond substrates that are joined together to form a large-area mosaic substrate. This allows the benefits of HPHT synthesis (high purity, single crystallinity) to be maintained while achieving large overall substrate area through assembly of multiple segments.
Solution Approach 2:
The invention combines multiple small HPHT diamond substrates into a single large-area mosaic substrate by joining them together. This merging approach maintains the high crystallinity of individual substrates while achieving the desired large area for practical applications.
2Area of stationary object
If CVD method is used to grow diamond on polycrystal substrate, then large area (6 inches diameter) and high purity are achieved, but single crystallinity is difficult to obtain due to lattice mismatch
Solution Approach 1:
The invention introduces an intermediate layer between the polycrystal substrate and the diamond layer to serve as a mediator. This intermediate layer has lattice constants and thermal expansion coefficients that are intermediate between the substrate and diamond, reducing lattice mismatch and enabling heteroepitaxial growth of single crystal diamond on large-area polycrystal substrates.
Solution Approach 2:
The invention changes the lattice parameter matching by introducing an intermediate layer with suitable lattice constants. This parameter adjustment reduces the lattice mismatch between the polycrystal substrate and diamond, enabling single crystal growth over large areas.
3Area of stationary object
If heteroepitaxial growth is attempted on substrate with large lattice mismatch (e.g., Si), then growth is difficult due to 34.3% lattice constant difference, but large area production is desired
Solution Approach 1:
The invention introduces an intermediate layer as a mediator between the Si substrate and diamond layer. This intermediate layer has lattice constants that bridge the 34.3% mismatch between Si and diamond, enabling heteroepitaxial growth of single crystal diamond on large-area Si substrates that would otherwise be impossible.
4Area of stationary object
If mosaic method is used to join multiple HPHT substrates, then large area is achieved, but joint imperfections remain as a problem
Solution Approach 1:
The invention extracts and eliminates the problematic joint regions by growing a continuous single crystal diamond layer over the entire mosaic substrate. This overgrowth process covers the joint imperfections and creates a uniform single crystal surface, removing the joint quality issue from the final product.
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 enables the production of large-diameter, high-crystallinity single crystal diamond substrates with few defects and low stress, suitable for electronic and magnetic devices, at a lower cost, and allows for the creation of freestanding diamond structures.
Implementation Method 1
forming an intermediate layer comprising a single layer or a laminate film on the initial substrate containing at least a single crystal Ir film or a single crystal MgO film, wherein the single crystal Ir film or the single crystal MgO film composing the intermediate layer is formed by using a mist CVD method
Implementation Method 2
a combination of suitable materials, as an underlying substrate for forming the diamond with small differences in lattice constants and linear expansion coefficients with the diamond, has not been realized, for example, a difference in the lattice constant between the diamond and single crystal Si has even 34.3 %; therefore, it is very difficult to grow the diamond heteroepitaxially on a surface of the underlying substrate
Data Source
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AI summary
The present invention is a method for producing an underlying substrate for a single crystal diamond laminate substrate, the method includes the steps of providing an initial substrate, and forming an intermediate layer including a single layer or a laminate film on the initial substrate containing at least a single crystal Ir film or a single crystal MgO film, in which the single crystal Ir film or the single crystal MgO film composing the intermediate layer is formed by using a mist CVD method. This provides the method for producing an underlying substrate, in which a single crystal diamond layer can be formed with a large area (large diameter), high crystallinity, few hillocks, few abnormal growth particles such as twin crystals, few dislocation defects, etc., high purity, low stress, and high quality and applicable to an electronic and magnetic device.