Epitaxial Base Structure for High-Voltage Shallow-Snapback ESD BJTs
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Solution Overview
Problem
Conventional bipolar junction transistor (BJT) based ESD protection devices face challenges in achieving high breakdown voltages and shallow snapback performance, particularly in vertical NPN or PNP BJT technology, which is essential for effective electrostatic discharge protection without risking latch-up.
Innovation Solution
The semiconductor device employs an epitaxial layer with a stack of lightly doped and heavily doped layers as the base region, allowing for high trigger voltage and shallow snapback performance, achieved through epitaxial deposition methods that provide precise control over doping concentration and thickness, reducing forward current gain and leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vertical NPN or PNP BJT technology is used for ESD protection devices, then high current driving capability is achieved, but high breakdown voltages (higher than ~10V) and shallow snapback performance are difficult to achieve
Solution Approach 1:
The base region is segmented into three distinct epi-layers with different doping concentrations (first epi-layer: lightly doped, second epi-layer: heavily doped, third epi-layer: lightly doped). This segmentation allows independent optimization of each layer's properties to achieve both high breakdown voltage (through lightly doped outer layers) and shallow snapback (through the heavily doped middle layer that reduces forward current gain).
Solution Approach 2:
Different regions of the base are given different doping concentrations to serve different functions: the first and third epi-layers have low doping concentrations to provide high breakdown voltage, while the second epi-layer has high doping concentration to reduce forward current gain and enable shallow snapback. This local quality differentiation resolves the contradiction between achieving high breakdown voltage and shallow snapback performance.
2Reliability
If the holding voltage is reduced to achieve shallow snapback, then the risk of latch-up is reduced, but the breakdown voltage performance deteriorates
Solution Approach 1:
The base is divided into three epi-layers where the outer lightly doped layers (first and third epi-layers) maintain high breakdown voltage, while the inner heavily doped layer (second epi-layer) reduces forward current gain to enable shallow snapback. This segmentation allows simultaneous achievement of high breakdown voltage and low holding voltage without compromise.
3Ease of manufacture
If conventional single-layer epitaxial structure is used, then manufacturing is simpler, but precise control over doping concentration and thickness for optimal ESD performance is difficult
Solution Approach 1:
The single epitaxial growth process is segmented into three distinct deposition steps, each creating an epi-layer with a specific doping concentration. This allows precise control over the doping profile and thickness of each layer while maintaining the efficiency of in-situ epitaxial growth, resolving the contradiction between manufacturing simplicity and doping precision.
4Reliability
If the base region doping concentration is increased to reduce forward current gain for shallow snapback, then snapback performance improves, but breakdown voltage decreases
Solution Approach 1:
The base is segmented so that the second epi-layer (heavily doped) provides the high doping concentration needed to reduce forward current gain and achieve shallow snapback, while the first and third epi-layers (lightly doped) maintain the high breakdown voltage. This spatial segmentation of doping concentrations resolves the contradiction between snapback performance and breakdown voltage.
Solution Approach 2:
The base region exhibits local quality variations with different doping concentrations at different positions: heavily doped in the middle region (second epi-layer) for shallow snapback, and lightly doped in the outer regions (first and third epi-layers) for high breakdown voltage. This local quality approach simultaneously achieves both performance requirements.
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 enables the semiconductor device to achieve high trigger voltage and shallow snapback performance, reducing the risk of latch-up and providing effective ESD protection with low dynamic resistance and clamping voltage, suitable for various ESD applications.
Implementation Method 1
depositing an epitaxial layer on a semiconductor substrate, wherein the semiconductor substrate is of a first conductivity type, and the epitaxial layer is of a second conductivity type that is opposite to the first conductivity type
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
There is provided a semiconductor device 100 and a method of manufacturing the same. The method comprises: depositing an epitaxial layer 6 on a semiconductor substrate 4, wherein the semiconductor substrate 4 is of a first conductivity type, and the epitaxial layer 6 is of a second conductivity type that is opposite to the first conductivity type, wherein depositing the epitaxial layer comprises depositing a first epi-layer 1 of a first doping concentration C_1, a second epi-layer 2 of a second doping concentration C_2 and a third epi-layer 3 of a third doping concentration C_3, and wherein the semiconductor substrate 4 and the first epi-layer 1 form a first P-N junction 10 at their interface, and the second epi-layer 2 is arranged between the first and third epi-layers 1, 3, and the second doping concentration C_2 is higher than each of the first doping concentration C_1 and the third doping concentration C_3; and forming a doped region 8 of the first conductivity type at a surface of the third epi-layer 3, such that the doped region 8 and the third epi-layer 3 form a second P-N junction 12 at their interface.