Lateral Bipolar Transistor Base Resistance Reduction
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Solution Overview
Problem
In the design of semiconductor integrated circuits, there is a challenge in optimizing the performance of CMOS and bipolar devices with reduced dimensions, particularly in achieving reduced base resistance in CMOS-based lateral bipolar junction transistors, which is essential for improving the flexibility and performance of mixed mode devices like BiCMOS circuits.
Innovation Solution
The solution involves a CMOS-based lateral bipolar junction transistor design that includes an emitter region, a base region surrounded by a gate, a collector region with shallow trench isolation, and an extension region that merges with the base contact, reducing base resistance by creating a low resistance path for current flow while maintaining compatibility with CMOS processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a typical lightly doped drain (LDD) MOS transistor structure is used to form lateral bipolar transistor, then CMOS compatibility is achieved, but base resistance remains high
Solution Approach 1:
The patent applies local quality by creating a heavily doped extension region (n-type for NPN or p-type for PNP) specifically at the base contact area, while maintaining the lightly doped LDD structure in other regions. This localized heavy doping reduces base resistance at the contact point without affecting the overall CMOS process compatibility or the lightly doped drain characteristics in the channel region.
Solution Approach 2:
The extension region is formed during the LDD doping process itself, performing the base contact doping preparation in advance. The extension region merges with the base contact region, so the low resistance path is already established before final base contact formation, eliminating the need for additional heavy doping steps.
2Speed
If base width is reduced to improve switching speed, then frequency response improves, but base resistance increases
Solution Approach 1:
The patent solves the base resistance problem by transitioning from a one-dimensional vertical doping profile to a two-dimensional structure with a laterally extending extension region. This extension region creates an additional conduction path in the lateral dimension, reducing base resistance without increasing the vertical base width, thereby maintaining fast switching speed while lowering resistance.
3Reliability
If extension region is added to reduce base resistance, then bipolar performance improves, but device complexity increases
Solution Approach 1:
The extension region merges with the base contact region, combining two functions into a single continuous doped region. This merging eliminates the need for separate extension and contact regions, simplifying the fabrication process and reducing device structural complexity while still achieving reduced base resistance and improved bipolar performance.
Solution Approach 2:
The extension region serves multiple functions: it acts as part of the lightly doped drain structure during LDD formation, provides a heavily doped base contact path for low resistance, and merges with the base contact region to simplify the overall structure. This multi-functionality reduces the need for additional specialized structures.
Data Source
AI summary
A lateral bipolar junction transistor formed in a semiconductor substrate includes an emitter region; a base region surrounding the emitter region; a gate disposed at least over a portion of the base region; a collector region having at least one open side and being disposed about a periphery of the base region; a shallow trench isolation (STI) region disposed about a periphery of the collector region; a base contact region disposed about a periphery of the STI region; and an extension region merging with the base contact region and laterally extending to the gate on the open side of the collector region.