SiGe Bipolar Transistor Emitter Doping Profile
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Solution Overview
Problem
Existing semiconductor devices with bipolar transistors require improved high-frequency behavior, as their speed is not sufficient for applications requiring very high cut-off frequencies.
Innovation Solution
The emitter region of the semiconductor device is extended with a mixed crystal of silicon and germanium up to the interface with the intermediate region, using arsenic doping atoms, which enhances the diffusion and creates a steeper n-type doping profile, while boron and carbon doping in the base region further improves the high-frequency behavior by retarding diffusion and maintaining a steep p-type profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the emitter region uses conventional silicon material with standard doping, then the manufacturing process is simple, but the cut-off frequency and high-frequency performance are insufficient
Solution Approach 1:
The emitter region is divided into two distinct zones: a first portion with standard silicon material and a second portion with silicon-germanium mixed crystal. This local differentiation allows the second portion to provide enhanced high-frequency performance through improved carrier diffusion, while the first portion maintains conventional characteristics, thus resolving the contradiction between performance improvement and structural complexity.
Solution Approach 2:
The invention introduces a composite structure in the emitter region by combining silicon and germanium to form a silicon-germanium mixed crystal. This composite material provides superior electrical properties for high-frequency operation compared to pure silicon, while the gradual transition between materials minimizes manufacturing complexity.
2Speed
If the Si-Ge sub-region is positioned away from the intermediate region, then the emitter structure is simpler, but the diffusion profile is less steep and speed is reduced
Solution Approach 1:
The Si-Ge sub-region is strategically positioned adjacent to the intermediate region before the doping process. This preliminary positioning creates a prepared structure that guides the diffusion of arsenic atoms during subsequent thermal processing, enabling the formation of a steep doping profile without requiring complex post-processing steps.
Solution Approach 2:
The invention changes the material composition parameter by introducing germanium into the silicon lattice in the second portion of the emitter region. This parameter change enhances the diffusion characteristics of n-type dopants, creating a steeper concentration gradient and improving carrier transport speed, thus resolving the contradiction between speed and structural complexity.
3Reliability
If phosphorus atoms are used for doping the emitter region, then the doping process is conventional, but the diffusion enhancement in Si-Ge material is insufficient
Solution Approach 1:
The invention changes the doping atom parameter from phosphorus to arsenic. Arsenic atoms exhibit enhanced diffusion characteristics in silicon-germanium mixed crystal compared to phosphorus, creating a steeper doping profile. This parameter change directly improves diffusion efficiency while maintaining the overall doping process framework.
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 configuration significantly increases the cut-off frequency (fT) and enhances the high-frequency performance of the transistor, with optimal results achieved at a germanium content of 40 at.% in the emitter region, and the use of arsenic and carbon doping results in a very steep doping profile, optimizing the transistor's speed and reducing end-of-range defects.
Implementation Method 1
the diffusion of more specifically n-type dopants appears to be enhanced in a material comprising a mixed crystal of Si and Ge compared to the diffusion speed in silicon
Implementation Method 2
the diffusion of more specifically n-type dopants appears to be enhanced in a material comprising a mixed crystal of Si and Ge compared to the diffusion speed in silicon
Data Source
AI summary
The invention relates to a semiconductor device with a substrate and a semiconductor body of silicon comprising a bipolar transistor with an emitter region, a base region and a collector region which are respectively of the N-type conductivity, the P-type conductivity and the N-type conductivity by the provision of suitable doping atoms, wherein the base region comprises a mixed crystal of silicon and germanium, the base region is separated from the emitter region by an intermediate region of silicon having a doping concentration which is lower than the doping concentration of the emitter region and with a thickness smaller than the thickness of the emitter region, and the emitter region comprises a sub-region comprising a mixed crystal of silicon and germanium which is positioned at the side of emitter region remote from the intermediate region.