Semiconductor Device ESD Protection via Buried Layers
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Solution Overview
Problem
Conventional semiconductor devices face thermal breakdown due to poor heat dissipation and current concentration when subjected to surge voltages like electrostatic discharge (ESD), as the surface portion of the epitaxial layer has a low thermal conductivity and high on-current flow.
Innovation Solution
The semiconductor device incorporates an isolation region that divides the semiconductor layer into element-formation regions, with specific diffusion layers forming PN junctions of varying breakdown voltages, allowing current to flow through low-resistance paths and reducing thermal stress by using buried layers with high thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PN junction region is designed to break down at low voltage for ESD protection, then the protection capability is improved, but thermal breakdown occurs due to poor heat dissipation in the surface portion
Solution Approach 1:
The invention transitions the current flow path from a surface-level two-dimensional path to a three-dimensional path extending into the substrate. By forming a deep N-type diffusion layer that reaches the substrate, the patent creates a vertical current path that bypasses the thermally problematic surface region, effectively moving the heat dissipation problem to a different spatial dimension where thermal management is more effective.
Solution Approach 2:
The substrate acts as an intermediary thermal conductor between the PN junction breakdown region and the heat sink. The high thermal conductivity of the substrate material mediates the heat transfer from the breakdown junction, preventing localized thermal accumulation that would otherwise cause thermal breakdown in the low thermal conductivity surface portion.
2Reliability
If the on-current flows through the surface portion of the epitaxial layer, then the ESD protection function is achieved, but heat dissipation is poor leading to thermal breakdown
Solution Approach 1:
The invention introduces a vertical dimension to the current flow path by forming a deep N-type diffusion layer that extends to the substrate. This transforms the current path from a surface-confined horizontal flow to a three-dimensional path that penetrates through the epitaxial layer thickness, enabling heat to be conducted away in the vertical direction to the substrate heat sink.
Solution Approach 2:
The patent applies different material properties to different regions: the surface portion maintains its original low thermal conductivity for ESD protection, while the deep N-type diffusion layer region provides a high thermal conductivity path to the substrate. This local differentiation of thermal properties allows simultaneous ESD protection and effective heat dissipation.
3Reliability
If the junction breakdown voltage is lowered for protection, then ESD surge protection is improved, but current concentration increases causing thermal stress
Solution Approach 1:
The invention distributes the current flow into the third dimension by creating a deep vertical diffusion path. Instead of concentrating current in a shallow surface junction, the deep N-type diffusion layer extends the current distribution vertically through the epitaxial layer to the substrate, reducing current density and associated thermal stress in any single location.
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 design effectively protects semiconductor elements from ESD surges by managing current flow and heat dissipation, preventing thermal breakdown and ensuring efficient operation.
Implementation Method 1
the PN junction region 170 breaks down prior to the PN junction region 172 and thereby the diffused resistor 161 is protected
Implementation Method 2
a current path is formed between the first and second diffusion layers through the isolation region
Implementation Method 3
buried layers with high thermal conductivity
Data Source
AI summary
A conventional semiconductor device has a problem that an on-current of a parasitic transistor flows through a surface portion of a semiconductor layer and thus a semiconductor element undergoes thermal breakdown. In a semiconductor device according to the present invention, a protection element is formed with use of an isolation region and N type buried layers. A PN junction region in the protection element is formed on a P type buried layer of the isolation region. The PN junction region has a junction breakdown voltage lower than that of a PN junction region of a semiconductor element to be protected. This structure allows an on-current of a parasitic transistor to flow into the protection element, and thereby the semiconductor element is protected. In addition, the on-current of the parasitic transistor flows through a deep portion of the epitaxial layer, and thereby the protection element is prevented from thermal breakdown.