Self-aligned emitter-base region in bipolar transistors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In BiCMOS technology, integrating bipolar transistors with CMOS transistors within a single integrated circuit poses a challenge in achieving high-speed performance, as the maximum frequency of oscillation (fmax) is limited by the base resistance of the bipolar transistor.
Innovation Solution
A method of forming a bipolar junction transistor with a self-aligned emitter-base region is developed, involving a semiconductor substrate with a uniform silicon nitride layer and a base layer, where silicon nitride spacers are formed adjacent to the emitter pedestal and an extrinsic base layer is deposited via selective epitaxy, reducing base resistance and enhancing speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional bipolar transistor fabrication is used, then integration with CMOS is achieved, but base resistance remains high limiting maximum frequency
Solution Approach 1:
A uniform silicon nitride layer is deposited over the emitter pedestal and base region before any patterning occurs. This preliminary deposition establishes a foundation for subsequent self-aligned spacer formation that will define the extrinsic base region boundaries without requiring additional alignment steps
Solution Approach 2:
Silicon nitride spacers are formed as intermediary structures that simultaneously serve as alignment references and physical boundaries for the extrinsic base region. These spacers mediate between the emitter pedestal and the base region, enabling precise definition of the base region boundaries through a single etch process
2Speed
If base resistance is reduced to increase maximum frequency, then transistor speed improves, but manufacturing precision requirements increase
Solution Approach 1:
The formation of silicon nitride spacers and exposure of the base region are merged into a single etch process. This combines two previously separate steps (spacer formation and base region definition) into one operation, eliminating alignment errors between steps while achieving the desired base region geometry for reduced resistance
Solution Approach 2:
The silicon nitride layer serves multiple functions: it acts as a sacrificial layer during processing, forms the basis for spacer structures, and defines the boundaries of the extrinsic base region. This multi-functionality reduces the number of separate manufacturing steps required
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
The approach results in a faster bipolar junction transistor with improved maximum frequency of oscillation (fmax) by lowering base resistance, facilitating easier integration with CMOS transistors and enhancing overall performance.
Implementation Method 1
performing a silicon nitride etch with the photomask to simultaneously form silicon nitride spacers adjacent to the emitter pedestal and exposing the base region
Implementation Method 2
depositing an extrinsic base layer via selective epitaxy, such that the extrinsic base layer is only within the exposed base region
Data Source
AI summary
Aspects of the invention provide a method of forming a bipolar junction transistor. The method includes: providing a semiconductor substrate including a uniform silicon nitride layer over an emitter pedestal, and a base layer below the emitter pedestal; applying a photomask at a first end and a second end of a base region; and performing a silicon nitride etch with the photomask to simultaneously form silicon nitride spacers adjacent to the emitter pedestal and exposing the base region of the bipolar junction transistor. The silicon nitride etch may be an end-pointed etch.