Defect-Layer Collector Structure for High-fmax Semiconductor Devices
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Solution Overview
Problem
Conventional semiconductor devices, such as bipolar junction transistors (BJTs) and heterojunction bipolar transistors (HBTs), face a trade-off between collector junction capacitance (Cjc) and off-state collector-base breakdown voltage (BVcbo), limiting their maximum frequency of oscillation (fmax) and frequency response in high-frequency applications.
Innovation Solution
The semiconductor device design includes a defect layer with dislocation loops and a launcher layer between the collector and base regions, optimized dopant concentrations, and a spacer region to reduce collector junction capacitance while maintaining high breakdown voltage, achieved through specific doping and recrystallization processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional BJT and HBT structures are used, then the device can be manufactured with standard processes, but the collector junction capacitance (Cjc) cannot be reduced without compromising the off-state collector-base breakdown voltage (BVcbo)
Solution Approach 1:
The collector region is segmented into multiple doped regions (first doped region, second doped region, third doped region) with different doping concentrations and depths. This segmentation allows each region to contribute differently to the overall device performance: the first doped region provides high doping for low capacitance, while the second and third doped regions provide graded doping profiles that maintain high breakdown voltage. The defect layer is positioned within the first doped region to further reduce capacitance without compromising structural integrity.
Solution Approach 2:
Different regions of the collector are given different local properties through selective doping. The first doped region has high doping concentration (1e19 to 1e21 atoms/cm³) to reduce capacitance, while the second and third doped regions have lower doping concentrations (1e17 to 1e19 atoms/cm³) to maintain breakdown voltage. The defect layer is locally introduced in the upper portion of the first doped region to specifically target capacitance reduction at the collector-base junction interface.
2Speed
If the collector junction capacitance (Cjc) is reduced to achieve higher maximum frequency of oscillation (fmax), then the off-state collector-base breakdown voltage (BVcbo) is compromised
Solution Approach 1:
The doping concentration parameter is varied across different regions of the collector. The first doped region has high doping concentration (1e19 to 1e21 atoms/cm³) to reduce capacitance and increase fmax, while the second and third doped regions have lower doping concentrations (1e17 to 1e19 atoms/cm³) to maintain high breakdown voltage. This parameter change creates a graded doping profile that simultaneously optimizes both speed and voltage handling capabilities.
Solution Approach 2:
The defect layer acts as an intermediary structure within the first doped region. It provides a transition zone that reduces the effective capacitance at the collector-base junction while the graded doping profile in the second and third doped regions maintains the electric field distribution necessary for high breakdown voltage. The launcher layer also serves as an intermediary that facilitates carrier injection while managing the trade-off between capacitance and breakdown characteristics.
3Reliability
If a defect layer is introduced in the collector region to reduce capacitance, then the device performance at high frequency is improved, but the manufacturing process complexity increases
Solution Approach 1:
The defect layer is formed through preliminary ion implantation and annealing processes before final device assembly. The ion implantation introduces defects at specific depths and concentrations, and the subsequent annealing process activates these defects and creates the desired defect layer structure. This preliminary action simplifies later fabrication steps by pre-establishing the capacitance-reducing defect structure before final device completion.
Solution Approach 2:
Traditional mechanical or physical methods of creating defect layers are replaced with ion implantation and thermal annealing processes. Instead of mechanically introducing defects, ion beams are used to implant atoms that create controlled defect structures. The thermal annealing process then activates these defects through diffusion and recrystallization, replacing mechanical defect introduction with a combination of ion bombardment and thermal processing that offers better control and repeatability.
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 design enhances the maximum oscillation frequency (fmax) and collector-emitter breakdown voltage, improving the frequency response and performance of semiconductor devices for high-frequency applications.
Implementation Method 1
The defect layer may include dislocation loops coalesced below the upper surface of the defect layer
Implementation Method 2
a first doped region formed in a lower portion of the first semiconductor region, a second doped region formed over the first doped region
Implementation Method 3
achieved through specific doping and recrystallization processes
Data Source
AI summary
A semiconductor device includes a semiconductor substrate, a first semiconductor region of a first semiconductor type, formed within the semiconductor substrate, wherein the first semiconductor region includes a first doped region formed in a lower portion of the first semiconductor region and a second doped region formed over the first doped region in an upper portion of the first semiconductor region. A defect layer having an upper surface formed in an upper portion of the first doped region. A second semiconductor region of a second semiconductor type is formed over the first semiconductor region.