Bipolar Transistor Manufacturing via Selective Epitaxy
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Solution Overview
Problem
Existing methods for manufacturing semiconductor devices with bipolar transistors often result in devices with suboptimal RF properties due to high defect density, difficulty in selective etching of SiGe layers, and surface roughening, which affects the minimum distance between the emitter region and extrinsic base.
Innovation Solution
The method involves forming a high-crystalline semiconductor layer while keeping a part of the semiconductor body's surface free from the layer, using a cover layer that can be selectively etched relative to silicon, and depositing the high-crystalline layer using epitaxy or heat treatment to reduce defects and improve RF properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a SiGe layer is used to fill the hollow underneath the emitter region, then the minimum distance between emitter and extrinsic base can be reduced, but defect density increases and RF properties deteriorate
Solution Approach 1:
The patent removes the SiGe layer from the hollow region and replaces it with silicon material. This extraction of the problematic SiGe material eliminates the source of defects while maintaining the structural integrity needed for reduced emitter-to-base distance. The hollow is filled with silicon instead, which does not exhibit the same defect formation characteristics.
Solution Approach 2:
The patent changes the material parameter from SiGe to silicon in the hollow region. This parameter change fundamentally alters the material properties, eliminating the defect density issues associated with SiGe while preserving the geometric configuration that enables minimum distance reduction.
2Length of moving object
If a SiGe layer is used to fill the hollow, then the minimum distance between emitter and extrinsic base can be reduced, but selective etching becomes difficult
Solution Approach 1:
The patent extracts the SiGe layer that causes etching difficulties and replaces it with silicon material. This removal of the problematic material restores selective etching capability, as silicon can be etched selectively with respect to the surrounding structures, unlike SiGe which lacks this property.
3Volume of stationary object
If high-crystalline silicon is deposited on the surface adjoining the opening, then the hollow can be filled, but selective etching relative to underlying silicon becomes impossible
Solution Approach 1:
The patent applies different material qualities to different locations: the hollow is filled with high-crystalline silicon while the surface adjoining the opening is kept free from this deposition. This local differentiation ensures that the filled hollow provides structural support while maintaining etch selectivity at the surface region where selective etching is still required.
Solution Approach 2:
Instead of depositing high-crystalline silicon on the surface adjoining the opening and then trying to selectively remove it, the patent inverts the approach by keeping this surface region free from deposition. This inversion makes selective etching unnecessary in that region while still achieving the hollow filling objective.
4Productivity
If SiGe mixing crystal is exposed to oxygen during spacer formation, then the manufacturing process can proceed, but defects develop that worsen RF properties
Solution Approach 1:
The patent removes the SiGe mixing crystal from the structure by replacing it with silicon in the hollow region. This extraction eliminates the material that reacts adversely with oxygen during spacer formation, preventing defect development while allowing the manufacturing process to proceed without interruption.
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 reduces defect density, allows for closer doping atom diffusion to the emitter region, and enhances RF properties by maintaining a clean surface and minimizing extrinsic base resistance.
Implementation Method 1
depositing at least one epitaxial semiconductor layer on the surface of the semiconductor body in which the collector region is to be formed
Implementation Method 2
the high-crystalline layer is formed by means of a deposition process, in particular by means of epitaxy
Implementation Method 3
the cover layer is formed of a material which can be selectively etched relative to the silicon underlying layer
Implementation Method 4
the high-crystalline layer is formed by means of a portion of the low-crystalline semiconductor layer adjoining the hollow. This can be achieved by means of a heat treatment of the device
Data Source
AI summary
The invention relates to a method according to the part of the surface of the semiconductor body adjoining the opening and which is to be kept free is provided with a cover layer after which the high-crystalline layer is formed by means of a deposition process. The material of the cover layer can then easily be chosen such that it can be selectively etched relative to the silicon underneath. In addition, the cover layer can easily be selectively deposited on the relevant part of the surface because use can be made of an anisotropic deposition process. In such a process the cover layer is not deposited in the hollow and on the bottom of the hollow. It will be apparent that for the high-crystalline layer also other materials can be chosen such as SiGe having such low Ge contents that the SiGe cannot be etched selectively very well compared to the Silicon.