SiGe HBT Drive Current via Carbon Strain Compensation
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Solution Overview
Problem
Current SiGe heterojunction bipolar transistors (HBTs) face issues with relaxation and dislocations due to high Ge gradients, leading to increased base current and collector-emitter leakage, limiting their use in high-current gain and high-frequency power amplifiers.
Innovation Solution
Incorporating carbon in various layers of the HBT, such as the subcollector, collector, base buffer, base, and emitter buffer layers, with concentrations greater than or equal to 5E20 cm−3, to induce tensile strain that compensates for compressive strain caused by Ge, thereby preventing relaxation and dislocation formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a high Ge gradient is used in the base layer to provide drift fields for high-frequency operation, then high-frequency operation is improved, but relaxation and dislocation formation occur leading to increased base current and collector-emitter leakage
Solution Approach 1:
Carbon is introduced as an intermediary element in the base layer to mediate between the Ge gradient requirements and strain stability. The carbon atoms interact with the Ge-Si lattice to compensate compressive strain while allowing the Ge gradient to persist for high-frequency operation, thus resolving the contradiction between speed and reliability
Solution Approach 2:
The patent changes the compositional parameter by incorporating carbon at specific concentrations (e.g., 1-5 at%) in the SiGe base layer. This parameter change modifies the strain state of the lattice, compensating compressive strain induced by Ge while maintaining the Ge gradient necessary for high-frequency operation, thereby preventing dislocation formation
2Ease of manufacture
If carbon is added at low concentration (e.g., 3E19 cm−3) to suppress dopant diffusion, then dopant diffusion is suppressed, but relaxation and dislocation formation still occur
Solution Approach 1:
The patent optimizes the carbon concentration parameter to a specific range (e.g., 1-5 at% or 3E20 to 1E21 cm−3), which is higher than the conventional low concentration (3E19 cm−3) used only for dopant diffusion suppression. This parameter change provides sufficient carbon atoms to compensate compressive strain and prevent relaxation, while still maintaining ease of manufacture through standard epitaxial growth processes
3Reliability
If the total Ge dose is kept under a critical limit to prevent relaxation, then relaxation is prevented, but current gain and high-frequency operation performance are limited
Solution Approach 1:
The patent changes the strain compensation mechanism by introducing carbon, which allows the Ge dose to exceed the conventional critical limit without causing relaxation. The carbon atoms compensate the compressive strain induced by high Ge concentrations, enabling higher Ge doses that improve current gain and high-frequency operation while maintaining relaxation prevention
Solution Approach 2:
The patent creates a composite SiGeC material system in the base layer, combining silicon, germanium, and carbon. This composite material approach allows leveraging the beneficial effects of high Ge concentration (improved productivity) while using carbon to compensate strain and prevent relaxation, thus resolving the contradiction between reliability and productivity
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 enhances the yield of the HBT by preventing recombination centers and short circuit paths, allowing for improved current gain and higher-frequency operation while reducing defects and precipitation.
Implementation Method 1
Incorporating carbon in various layers of the HBT, such as the subcollector, collector, base buffer, base, and emitter buffer layers, with concentrations greater than or equal to 5E20 cm−3, to induce tensile strain that compensates for compressive strain caused by Ge, thereby preventing relaxation and dislocation formation
Data Source
AI summary
A power SiGe heterojunction bipolor transistor (HBT) with improved drive current by strain compensation and methods of manufacture are provided. A method includes adding carbon in a continuous steady concentration in layers of a device including a subcollector layer, a collector layer, a base buffer layer, a base layer, and an emitter buffer layer.