Polycrystalline CVD Diamond Nucleation for Semiconductor Thermal Management
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Solution Overview
Problem
The existing methods for growing polycrystalline diamond on non-diamond substrates result in high near-substrate thermal boundary resistance, limiting the thermal performance of semiconductor devices, particularly in high-power electronic and optoelectronic applications where efficient heat management is crucial.
Innovation Solution
The method involves using nanocrystalline diamond powder for seeding, alternating CVD diamond growth and non-diamond carbon etch steps, and a pre-growth etching step to reduce void formation, non-diamond carbon content, and increase diamond grain size, thereby minimizing thermal boundary resistance between the semiconductor substrate and the polycrystalline CVD diamond layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional CVD diamond growth methods are used on non-diamond substrates, then diamond layers can be formed, but high near-substrate thermal boundary resistance occurs due to void formation, non-diamond carbon content, and small grain sizes in the nucleation layer
Solution Approach 1:
The substrate surface is pre-treated with oxygen plasma before diamond nucleation to remove organic contaminants and create a clean surface. This preliminary action prevents the formation of non-diamond carbon phases and voids during subsequent diamond growth, directly addressing the nucleation layer quality issues that cause thermal boundary resistance
Solution Approach 2:
The invention employs a two-stage CVD process with different parameters: Stage 1 uses low carbon concentration (1-5% methane in hydrogen) and low power (300-500W) to promote grain growth over nucleation, while Stage 2 uses higher carbon concentration (10-20% methane) and higher power (700-1000W) for bulk diamond growth. This parameter optimization minimizes void formation and non-diamond carbon while maximizing grain size in the nucleation layer
Solution Approach 3:
The CVD process alternates between diamond deposition and non-diamond carbon etching cycles during the nucleation phase. This periodic action removes amorphous carbon and graphite phases that form during initial growth, purifying the nucleation layer and reducing thermal boundary resistance while maintaining good grain structure
2Temperature
If the diamond nucleation layer is made thicker to improve thermal conductivity, then more diamond material is present, but void formation and non-diamond carbon content increase, worsening thermal boundary resistance
Solution Approach 1:
The invention uses low carbon concentration (1-5% methane) and low power (300-500W) during the nucleation stage to promote lateral grain growth rather than vertical thickness increase. This parameter regime creates a thin nucleation layer with large grains and minimal voids, achieving low thermal boundary resistance without requiring thick diamond layers
Solution Approach 2:
The invention creates different quality zones within the diamond structure: a thin, high-quality nucleation layer with large grains and minimal defects directly on the substrate, followed by a thicker bulk diamond region. Each zone is optimized for its specific function, with the nucleation layer specifically engineered to minimize thermal boundary resistance
3Object-generated harmful factors
If nanocrystalline diamond powder seeding is used, then diamond grain size increases and thermal boundary resistance decreases, but the process complexity increases with multiple etching and growth steps
Solution Approach 1:
The substrate is pre-seeded with nanocrystalline diamond powder before CVD growth, creating numerous nucleation sites that promote uniform diamond grain formation. This preliminary seeding action eliminates the need for complex in-situ nucleation control during CVD, simplifying the overall process while achieving low thermal boundary resistance through improved grain structure
Solution Approach 2:
The invention combines substrate seeding with continuous CVD diamond growth in an integrated process flow. The seeded substrate is immediately placed in the CVD chamber for continuous diamond deposition, maintaining process continuity and avoiding separate discrete steps, thereby reducing overall process complexity while achieving the desired grain 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
This approach significantly reduces thermal boundary resistance, enhancing the thermal conductivity of semiconductor device structures by improving the quality and thickness of the diamond nucleation layer, thus improving the thermal performance of semiconductor devices.
Implementation Method 1
seeding a surface of the substrate... growing a diamond nucleation layer on the surface
Implementation Method 2
growing a diamond nucleation layer on the surface using a chemical vapour deposition (CVD) technique... growing a thicker layer of polycrystalline CVD diamond material
Implementation Method 3
using alternating CVD diamond growth and non-diamond carbon etch steps... etching at least a part of the diamond layer... etches non-diamond phases preferentially over diamond phases
Data Source
Figure 1~2
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AI summary
A semiconductor device structure comprising: a layer of III-V compound semiconductor material; a layer of polycrystalline CVD diamond material; and an interface region between the layer of III-V compound semiconductor material and the layer of polycrystalline CVD diamond material, the interface region including a diamond nucleation layer of polycrystalline CVD diamond which is formed during an initial nucleation phase of polycrystalline CVD diamond growth over a substrate comprising the layer of III-V compound semiconductor material, wherein the diamond nucleation layer is such that a Raman signal generated by a laser focused on a region comprising the diamond nucleation layer exhibits an sp3 carbon peak at 1332 cm-1 having a full width half-maximum of no more than 5.0 cm-1, wherein the diamond nucleation layer is such that said Raman signal further exhibits one or both of the following characteristics: (i) an sp2 carbon peak at 1550 cm-1 having a height which is no more than 20% of a height of the sp3 carbon peak at 1332 cm-1 after background subtraction when using a Raman excitation source at 633 nm; and (ii) the sp3 carbon peak at 1332 cm-1 is no less than 10% of local background intensity in a Raman spectrum using a Raman excitation source at 785 nm, and wherein an average nucleation density at a nucleation surface of the diamond nucleation layer is no less than 1 x 108 cm-2and no more than 1 x 1012 cm-2.