Nitride Semiconductor Substrate Surface Treatment for Crystalline Quality
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Solution Overview
Problem
Nitride semiconductor substrates, such as GaN, suffer from high crystal defects and surface damage, which impede the enhancement of device performance, particularly due to the mechanical hardness and chemical stability of nitride semiconductors, making it difficult to achieve high-quality surface polishing and reducing the effectiveness of existing CMP methods.
Innovation Solution
A nitride semiconductor substrate with a surface treatment method involving mechanical polishing, followed by chemical mechanical polishing (CMP) using colloidal silica or dry etching, and subsequent application of an ammonium fluoride solution with gallium oxide nanopowder, irradiated with ultraviolet rays to reduce surface damage and relieve strain, resulting in a significantly improved crystalline quality of the outermost surface layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If conventional CMP method is used on nitride semiconductor substrates, then surface flatness is improved, but surface quality and crystalline orientation are deteriorated due to residual damage and strain
Solution Approach 1:
The surface treatment process is segmented into multiple distinct stages: initial mechanical polishing for flatness, followed by CMP for fine finishing, then chemical treatment with ammonium fluoride solution, and finally UV irradiation. Each stage addresses specific surface issues without compromising the other aspects, thereby resolving the contradiction between flatness and quality.
Solution Approach 2:
The ammonium fluoride solution acts as an intermediary chemical agent that selectively removes damaged layers and relieves strain induced by previous polishing steps. The UV irradiation then serves as another intermediary that further repairs crystalline structure. These intermediary treatments bridge the gap between mechanical flatness achievement and crystalline quality preservation.
2Shape
If mechanical polishing is applied to nitride semiconductor substrates, then surface flatness is improved, but surface damage and strain are increased due to mechanical hardness and fragility
Solution Approach 1:
The process applies beforehand cushioning by using gentle chemical treatment with ammonium fluoride solution and UV irradiation immediately after mechanical polishing. These treatments preemptively remove and repair damage before it propagates into the bulk crystal, cushioning the substrate against further degradation while maintaining the flatness benefits.
Solution Approach 2:
The invention substitutes mechanical removal methods with chemical treatment methods. Instead of using further mechanical polishing to remove damaged layers, the process uses chemical etching with ammonium fluoride solution followed by UV irradiation, thereby eliminating the need for additional mechanical action that would cause further damage.
3Ease of manufacture
If hetero-substrate is used for nitride semiconductor growth, then device fabrication is simplified, but crystal defects and dislocations are increased due to lattice constant mismatch
Solution Approach 1:
The invention changes the substrate parameter from hetero-substrate to homo-substrate (nitride semiconductor single crystal substrate). This parameter change eliminates lattice mismatch issues while the surface treatment process further optimizes the substrate quality, thereby achieving both good manufacturability and high crystal quality.
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 surface treatment method achieves a remarkably excellent crystalline quality for the outermost surface layer compared to the inner region, inhibiting crystalline orientation variation within the surface layer, thereby enhancing the quality of nitride semiconductor substrates and devices.
Implementation Method 1
dripping onto the surface a not more than 2 mol % ammonium fluoride containing solution with not more than 100 nm particle diameter gallium oxide nanopowder added thereto, and irradiating the surface with ultraviolet rays over 1 hour, to apply friction to the surface
Implementation Method 2
irradiating the surface with ultraviolet rays over 1 hour
Implementation Method 3
chemical mechanical polishing (CMP) with colloidal silica or dry etching the surface to reduce damage caused by the mechanical polishing
Implementation Method 4
chemical mechanical polishing (CMP) with colloidal silica or dry etching the surface
Implementation Method 5
an FWHM in a surface layer region at depths of from 0 to 250 nm from the upper surface is narrower than an FWHM in an inner region at depths exceeding 5 μm from the upper surface, where the FWHMs are obtained by X-ray rocking curve measurement using diffraction off a particular asymmetric plane
Data Source
AI summary
A nitride semiconductor substrate includes two principal surfaces including an upper surface that is a growth face and a lower surface on its opposite side. An FWHM in a surface layer region at depths of from 0 to 250 nm from the upper surface is narrower than an FWHM in an inner region at depths exceeding 5 μm from the upper surface, where the FWHMs are obtained by X-ray rocking curve measurement using diffraction off a particular asymmetric plane inclined relative to the upper surface.