SOS Substrate Low Defect Density via Ion Implantation
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Solution Overview
Problem
The high defect density in silicon-on-sapphire (SOS) substrates due to lattice constant mismatch limits their use in high-frequency devices and large-scale semiconductor applications, making it difficult to produce sophisticated and downscaled devices with low defect densities.
Innovation Solution
A method involving ion implantation, surface activation, bonding, and visible light irradiation to form a bonded SOS substrate with a defect density of approximately 10^4 pieces/cm², which includes forming an ion-implanted layer, activating the surfaces, bonding the substrates, heating them, and irradiating with visible light to make the interface brittle for transferring the silicon film to the sapphire substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If heteroepitaxial growth is used to form SOS substrate, then silicon layer can be formed on sapphire substrate, but defect density increases due to lattice constant mismatch
Solution Approach 1:
The patent applies preliminary action by forming an amorphous silicon layer through ion implantation before the final crystallization step. This amorphous layer serves as a defect-free intermediate state that allows subsequent single-phase crystallization to proceed without propagating lattice mismatch defects, thereby achieving low defect density in the final SOS substrate.
Solution Approach 2:
The patent utilizes phase transitions by converting silicon from crystalline to amorphous state through ion implantation, then back to crystalline state through single-phase growth. This phase transition approach allows the silicon layer to be reformed without inheriting the lattice mismatch defects that would occur in direct heteroepitaxial growth, resolving the contradiction between manufacturability and defect density.
2Manufacturing precision
If double solid phase growth method is used to reduce defects, then defect density decreases to 10^6-10^7 pieces/cm2, but it remains insufficient for highly downscaled devices
Solution Approach 1:
The patent employs phase transitions by intentionally creating an amorphous silicon layer through ion implantation, then utilizing single-phase crystallization to transform it back to crystalline state. This controlled phase transition approach achieves defect density of 10^4 pieces/cm2 or less, surpassing the double solid phase growth method and enabling scalability to highly downscaled devices.
Solution Approach 2:
The patent applies parameter changes by modifying the crystallization process parameters - specifically using single-phase growth at controlled temperatures rather than the two-stage process. This parameter optimization achieves lower defect density (10^4 pieces/cm2 or less) compared to double solid phase growth (10^6-10^7 pieces/cm2), thereby improving both manufacturing precision and device scalability.
3Reliability
If heteroepitaxial SOS substrate is used for high frequency devices, then low dielectric loss is achieved, but high defect density limits use to small individual parts only
Solution Approach 1:
The patent utilizes phase transitions to first convert crystalline silicon to amorphous state through ion implantation, then revert to crystalline state through single-phase growth. This process eliminates the lattice mismatch defects inherent in heteroepitaxial growth while preserving the low dielectric loss properties of SOS substrates, enabling both high reliability and low defect density for advanced device applications.
Solution Approach 2:
The patent applies the extraction principle by removing the problematic crystalline structure through ion implantation-induced amorphization, then reconstructing a defect-free crystalline layer. This extraction of the defective crystalline phase and replacement with a freshly crystallized layer achieves defect density of 10^4 pieces/cm2 or less, enabling SOS substrates to be used for sophisticated and downscaled devices while maintaining low dielectric loss.
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 method results in an SOS substrate with a significantly reduced defect density, enabling the production of high-speed semiconductor devices with minimal parasitic capacitance and allowing for larger substrate diameters while maintaining low defect densities, suitable for complex arithmetic processing and high-frequency devices.
Implementation Method 1
implanting ions into a silicon substrate or a silicon substrate with an oxide film thereon to form an ion-implanted layer
Implementation Method 2
irradiating visible light from a sapphire substrate side of the bonded body to the ion-implanted layer of the silicon substrate or the silicon substrate with the oxide film thereon for making an interface of the ion-implanted layer brittle
Data Source
AI summary
A bonded SOS substrate having a semiconductor film on or above a surface of a sapphire substrate is obtained by a method with the steps of implanting ions from a surface of a semiconductor substrate to form an ion-implanted layer; activating at least a surface from which the ions have been implanted; bonding the surface of the semiconductor substrate and the surface of the sapphire substrate at a temperature of 50° C. to 350° C.; heating the bonded substrates at a maximum temperature from 200° C. to 350° C. to form a bonded body; and irradiating visible light from a sapphire substrate side or a semiconductor substrate side to the ion-implanted layer of the semiconductor substrate for embrittling an interface of the ion-implanted layer, while keeping the bonded body at a temperature higher than the temperature at which the surfaces of the semiconductor substrate and the sapphire substrate were bonded.