Elevated Extrinsic Base Bipolar Transistor Selective Epitaxy
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Solution Overview
Problem
Conventional methods for forming bipolar junction transistors (BJTs) on semiconductor substrates result in rough surface topography, leading to processing and performance drawbacks due to the formation of extrinsic bases on intrinsic bases via conventional epitaxy, which is undesirable in small-scale devices.
Innovation Solution
The formation of a bipolar transistor structure with an elevated extrinsic base exclusively on crystalline regions of the base film, using selective epitaxy, where the extrinsic base is not formed on non-crystalline regions, and trench isolation is used to create a continuous boundary between the collector and the base film, improving surface smoothness and integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional epitaxy is used to form extrinsic base on intrinsic base, then the base structure is formed, but rough surface topography occurs on the extrinsic base
Solution Approach 1:
The patent applies selective epitaxy to grow the extrinsic base layer only on specific crystalline regions of the intrinsic base, rather than uniformly across the entire surface. This local quality approach ensures that the extrinsic base forms only where the underlying crystal structure supports smooth growth, eliminating rough surface topography while maintaining proper base structure formation for device functionality.
2Ease of manufacture
If conventional epitaxy is used to form extrinsic base, then the base structure is formed, but processing drawbacks occur due to rough surface topography
Solution Approach 1:
The patent changes the growth parameters by using selective epitaxy conditions that promote smooth surface formation. By controlling the epitaxial growth process to occur only on suitable crystalline substrates and not on isolated islands or amorphous regions, the method achieves both ease of manufacture through a single growth step and improved surface topography smoothness.
3Area of stationary object
If extrinsic base is formed on non-crystalline regions, then complete base coverage is achieved, but rough surface topography and performance drawbacks occur
Solution Approach 1:
The patent selectively forms the extrinsic base only on crystalline regions of the intrinsic base, excluding non-crystalline areas. This local quality approach ensures that the base coverage is concentrated on regions that support smooth epitaxial growth, achieving adequate functional coverage while eliminating the rough surface topography that would result from attempting to cover non-crystalline regions.
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 operational reliability and scalability by eliminating topographical features, improving the integration of vertical BJTs into integrated circuit layouts and reducing roughness, thereby enhancing device performance.
Implementation Method 1
The elevated extrinsic base may be formed exclusively on the crystalline region(s) of the base, e.g., by selective epitaxy
Data Source
AI summary
Aspects of the disclosure provide a bipolar transistor structure with an elevated extrinsic base, and related methods to form the same. A bipolar transistor according to the disclosure may include a collector on a substrate, and a base film on the collector. The base film includes a crystalline region on the collector and a non-crystalline region adjacent the crystalline region. An emitter is on a first portion of the crystalline region of the base film. An elevated extrinsic base is on a second portion of the crystalline region of the base film, and adjacent the emitter.