Semiconductor Isolation Structure for Thick Epitaxial Buried Layer Extraction
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Solution Overview
Problem
Conventional BCD processes face challenges in effectively isolating high-voltage devices from low-voltage devices due to difficulties in extracting buried layers as the epitaxial layer thickness increases, leading to circuit disconnection and increased manufacturing costs and complexity.
Innovation Solution
A method involving first and second ion implantations to form a buried layer and pre-dopant with higher thermal diffusion capability, followed by epitaxial growth and third ion implantation to form a deep well, allowing thermal annealing to connect the buried layer, pre-dopant, and deep well, ensuring effective isolation without significant process changes or additional equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the epitaxial layer is increased to improve breakdown voltage, then the isolation performance is improved, but the buried layer extraction becomes difficult causing circuit disconnection
Solution Approach 1:
The patent divides the extraction path into multiple segments: the deep well penetrating through the epitaxial layer, and the pre-dopant region forming a diffusion bridge. This segmentation allows each component to perform its function optimally - the deep well provides direct electrical connection while the pre-dopant ensures thermal diffusion connectivity, solving the extraction difficulty caused by thick epitaxial layers
Solution Approach 2:
The pre-dopant is formed in advance before final device fabrication. This preliminary action creates a pre-established diffusion path that facilitates subsequent thermal annealing and ensures connectivity between the deep well and buried layer, preventing circuit disconnection issues that would otherwise occur with thick epitaxial layers
2Ease of manufacture
If conventional ion implantation is used for buried layer extraction, then the process is simple, but thermal diffusion capability is insufficient causing connection failure
Solution Approach 1:
The patent changes the thermal diffusion parameter by introducing a pre-dopant with specifically engineered properties (higher thermal diffusion capability than the buried layer). This parameter change enables effective thermal annealing and ensures reliable connection between the deep well and buried layer, while maintaining process simplicity through ion implantation
3Reliability
If the epitaxial layer thickness is increased, then high-voltage device performance is improved, but manufacturing complexity and costs increase significantly
Solution Approach 1:
The patent merges multiple functions into the pre-dopant formation step: it creates the diffusion bridge, establishes the extraction path, and prepares the thermal annealing pathway. This merging approach maintains process simplicity while enabling thick epitaxial layer fabrication for high breakdown voltage devices
Solution Approach 2:
The pre-dopant acts as an intermediary between the deep well and the buried layer. It facilitates thermal diffusion and ensures connectivity without requiring direct contact between the deep well and buried layer, thereby simplifying the overall extraction process while maintaining reliable isolation
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
Enables smooth extraction of buried layers even with thick epitaxial layers, reducing processing costs and shortening manufacturing cycles while maintaining compatibility with existing processes.
Implementation Method 1
performing first ion implantation into a first area of a substrate to form a buried layer
Implementation Method 2
performing second ion implantation into a second area of the substrate to form a pre-dopant, where the second area is disposed around a periphery of the first area, and a thermal diffusion capability of ions in the pre-dopant is higher than a thermal diffusion capability of ions at the buried layer
Implementation Method 3
forming an epitaxial layer on a side, of the substrate, on which the buried layer and the pre-dopant are disposed
Implementation Method 4
performing, in correspondence to the second area, third ion implantation into the epitaxial layer to form a deep well
Implementation Method 5
performing thermal annealing, to thermally diffuse ions at the buried layer, in the pre-dopant, and in the deep well, so that the buried layer, the pre-dopant, and the deep well are sequentially connected
Data Source
Figure 1
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Figure 3B
AI summary
Embodiments of this application provide a device isolation structure and a manufacturing method thereof, and a semiconductor device. The manufacturing method includes: performing first ion implantation into a first area of a substrate to form a buried layer; performing second ion implantation into a second area of the substrate to form a pre-dopant, where the second area is disposed around a periphery of the first area, and a thermal diffusion capability of ions in the pre-dopant is higher than a thermal diffusion capability of ions at the buried layer; forming an epitaxial layer on a side, of the substrate, on which the buried layer and the pre-dopant are disposed; performing, in correspondence to the second area, third ion implantation into the epitaxial layer to form a deep well; and performing thermal annealing, to thermally diffuse ions at the buried layer, in the pre-dopant, and in the deep well, so that the buried layer, the pre-dopant, and the deep well are sequentially connected, where an internal area surrounded by the buried layer, the pre-dopant, and the deep well is a device area. In embodiments of this application, the deep buried layer beneath the thick epitaxial layer can be extracted, to effectively isolate the high-voltage device from the low-voltage device and be compatible with an existing process, thereby helping reduce processing costs and shorten a manufacturing cycle.