Semiconductor Protection Element and MOS Transistor Common Diffusion
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Solution Overview
Problem
Conventional semiconductor devices face issues where variations in manufacturing conditions, such as mask misalignments and thermal diffusion time lag, cause the avalanche voltage of the lateral MOSFET to be lower than that of the protection element, leading to potential destruction by ESD surges.
Innovation Solution
A semiconductor device design where the protection element is formed in the same process steps as the MOS transistor, ensuring shared diffusion layer structures and impurity concentration profiles, resulting in equal avalanche voltages between the protection element and the MOS transistor, reducing variability and ensuring effective surge protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the protection element is formed in different process steps with different conditions from the MOS transistor, then the avalanche voltage of the protection element can be made lower than that of the MOS transistor, but manufacturing variations such as mask misalignment and thermal diffusion time lag cause the MOS transistor avalanche voltage to drop below the protection element avalanche voltage, resulting in failure to protect the MOS transistor
Solution Approach 1:
The protection element and MOS transistor are merged into a single integrated structure formed in the same process steps. The diffusion layers for both elements are created simultaneously using the same masks and thermal diffusion conditions, ensuring identical impurity concentration profiles. This merging eliminates the manufacturing variations that previously caused avalanche voltage mismatches, allowing the protection element to reliably activate before the MOS transistor while maintaining consistent voltage characteristics across production batches.
2Adaptability or versatility
If the N type diffusion layer for protection element avalanche voltage control is formed separately from the MOS transistor diffusion layers, then the protection element structure can be optimized for lower avalanche voltage, but the separate formation process introduces variability that may cause the MOS transistor avalanche voltage to become lower than expected
Solution Approach 1:
The same diffusion process and masks are used to form multiple diffusion layers serving different functions - the MOS transistor source/drain regions and the protection element avalanche control region are all created in unison. This universal approach ensures that all diffusion layers share identical impurity concentration profiles and formation conditions, enabling the protection element to be tuned for avalanche operation while guaranteeing that the MOS transistor maintains its designed voltage characteristics without variability.
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 minimizes variations in avalanche voltages between the protection element and the MOS transistor, effectively preventing damage from surge voltages and ensuring reliable operation by ensuring the protection element activates before the MOS transistor, thereby protecting it from ESD surges and other voltage spikes.
Implementation Method 1
The PN diode D3 in the protection element 50 operates in avalanche mode prior to the lateral MOSFET 49. Then, an avalanche current causes the PNP transistor Tr3 to operate.
Data Source
AI summary
In a conventional semiconductor device, protection of a to-be-protected element from a surge voltage is difficult because the to-be-protected element is turned on before a protection element due to variations in manufacturing conditions. In a semiconductor device of the present invention, a protection element and a MOS transistor have part of their structures formed under common conditions. N type diffusion layers of the protection element and the MOS transistor are formed in the same process, while the N type diffusion layer of the protection element has a larger diffusion width than the N type diffusion layer of the MOS transistor. With this structure, when a surge voltage is applied to an output terminal, the protection element is turned on before the MOS transistor, and thereby the MOS transistor is protected from an avalanche current.