Cyclic Epitaxy for Bipolar Transistor Air Gap Isolation
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Solution Overview
Problem
Current fabrication processes for bipolar transistors with air gap isolation structures are complex and inefficient, particularly in forming effective base-collector isolation, which hampers transistor performance.
Innovation Solution
A method involving cyclical epitaxy to form an annular air spacer between the collector and silicon layers, followed by selective epitaxy to create doped semiconductor regions for the base and emitter, simplifying the process and improving isolation by reducing base-collector capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dielectric multilayer and multiple dry and wet etching operations are used to form air gap isolation, then air gap isolation structure is achieved, but the fabrication process becomes complex
Solution Approach 1:
The patent changes the fundamental approach from multiple etching operations to a single epitaxial growth process. By controlling doping parameters and growth conditions during epitaxy, the collector and base regions are formed simultaneously with inherent isolation, eliminating the need for complex dielectric multilayer stacking and multiple etching steps while achieving the same air gap isolation effect
Solution Approach 2:
The invention merges the formation of collector region, base region, and air gap isolation into a single integrated epitaxial growth step. The collector and base are formed concurrently with different doping types introduced during the same process, and the air gap is created as a byproduct of the lateral recess and selective growth, combining multiple functions into one operation
2Reliability
If conventional epitaxy is used to form collector and base regions, then semiconductor regions are formed, but access resistance increases
Solution Approach 1:
The patent modifies epitaxial growth parameters including temperature, pressure, gas flow rates, and doping concentrations to achieve simultaneous lateral recess and vertical growth. By optimizing these parameters, the process forms low-resistance collector and base regions with proper doping profiles while maintaining the air gap isolation, thereby reducing access resistance compared to conventional sequential epitaxy
Solution Approach 2:
The invention employs periodic alternation of doping gas introduction during the epitaxial growth cycle. Different doping gases are introduced at specific intervals to create the n-type collector and p-type base regions with precise doping profiles, enabling control over resistance characteristics while maintaining the benefits of simultaneous formation
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 method enhances transistor performance by reducing base-collector capacitance and allowing for higher doping levels without increasing access resistance, while maintaining compatibility with standard CMOS processes.
Implementation Method 1
performing a cyclical epitaxy process in the opening to simultaneously laterally recess the silicon layer to form an open region that annularly surrounds the opening and epitaxially grow a collector region made of semiconductor material doped with a first conductivity type from the top surface of the silicon substrate
Implementation Method 2
in the opening, further forming by selective epitaxy from a top surface of the collector region a base region made of semiconductor material doped with a second conductivity type
Data Source
AI summary
A bipolar transistor is supported by a single-crystal silicon substrate including a collector contact region. A cyclical epitaxy process is performed to provide a collector region of a first conductivity type on the collector contact region that is laterally separated from a silicon layer by an air gap. A second epitaxial region forms a base region of a second conductivity type. Deposited semiconductor material forms an emitter region of the first conductivity type. The collector region, base region and emitter region are located within an opening formed in a stack of insulating layers that includes a sacrificial layer. The sacrificial layer is selectively removed to expose a side wall of the base region. Epitaxial growth from the exposed sidewall forms a base contact region.