Double-Sided Epitaxial Layers for Latchup Resistance
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Solution Overview
Problem
Radiation exposure causes latchup in MOS circuits, leading to potential damage and operational interference in integrated circuits, particularly in applications like satellites and medical devices, due to parasitic bipolar transistors being triggered by radiation and adverse electrical noise.
Innovation Solution
The use of semiconductor devices with first and second lightly doped epitaxial semiconductor layers on opposite sides of a more heavily doped substrate, which mitigates auto-doping and warping issues during thermal processing, and provides a barrier to prevent parasitic bipolar transistor activation, thereby reducing latchup occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single epitaxial layer is formed on a heavily doped substrate, then latchup resistance is improved, but auto-doping and warping occur during thermal processing
Solution Approach 1:
The single epitaxial layer is divided into two separate epitaxial layers formed on opposite sides of the heavily doped substrate. This segmentation allows each epitaxial layer to be thinner and more lightly doped, providing better latchup resistance while reducing the total dopant quantity that causes auto-doping during thermal processing. The substrate acts as a separator between the two epitaxial layers, preventing dopant diffusion between them.
Solution Approach 2:
The solution transitions from a single-layer structure to a multi-layer structure by adding the second epitaxial layer on the opposite side of the substrate. This dimensional change allows the dopant concentration to be distributed across multiple layers rather than concentrated in one thick layer, reducing auto-doping effects while maintaining overall latchup resistance through the combined effect of both layers.
2Manufacturing precision
If the epitaxial layer is made more lightly doped to reduce auto-doping, then doping control is improved, but latchup resistance decreases
Solution Approach 1:
The lightly doped epitaxial structure is segmented into two separate layers on opposite sides of the substrate. Each layer can be optimally lightly doped for manufacturing precision while the combined effect of both layers provides sufficient latchup resistance. The substrate serves as a barrier that prevents dopant diffusion, maintaining the lightly doped state of both layers.
Solution Approach 2:
The latchup protection function is merged across two separate epitaxial layers. While each individual layer is lightly doped and provides limited latchup resistance on its own, the combination of both layers with the heavily doped substrate in between creates a more effective barrier against latchup than a single thick epitaxial layer would provide.
3Reliability
If a thick epitaxial layer is used to improve latchup resistance, then reliability is improved, but warping and auto-doping increase during thermal processing
Solution Approach 1:
The thick epitaxial layer is segmented into two thinner layers formed on opposite sides of the substrate. Each thinner layer produces less thermal stress and less dopant diffusion during processing compared to a single thick layer. The substrate acts as a stress-absorbing intermediate layer that helps maintain wafer flatness while the combined thickness of both epitaxial layers provides sufficient latchup resistance.
Solution Approach 2:
The heavily doped substrate acts as a counterweight to the thermal stress and dopant diffusion pressure from the epitaxial layers. By placing the substrate between two thinner epitaxial layers rather than having one thick layer, the substrate provides mechanical support and dopant diffusion barriers that counteract the warping and auto-doping effects that would occur with a single thick epitaxial layer.
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 solution effectively reduces latchup incidents and prevents auto-doping and warping, allowing for the fabrication of high-reliability and radiation-hardened integrated circuits that can operate without arcing issues in standard processing tools.
Implementation Method 1
forming a first epitaxial semiconductor layer of a first conductivity type on a first side of a semiconductor substrate of the first conductivity type, and forming a second epitaxial semiconductor layer of the first conductivity type on the second side of the semiconductor substrate
Data Source
AI summary
Disclosed examples include semiconductor devices and fabrication methods to fabricate semiconductor wafers and integrated circuits, including forming a first epitaxial semiconductor layer of a first conductivity type on a first side of a semiconductor substrate of the first conductivity type, forming a nitride or oxide protection layer on a top side of the first epitaxial semiconductor layer, forming a second epitaxial semiconductor layer of the first conductivity type on the second side of the semiconductor substrate, and removing the protection layer from the first epitaxial semiconductor layer. The wafer can be used to fabricate an integrated circuit by forming a plurality of transistors at least partially on the first epitaxial semiconductor layer.