Diluted Doping Profiles in High-Voltage Transistors
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Solution Overview
Problem
Power semiconductor devices, particularly high-voltage LDMOS and HVFETs, face challenges in achieving high breakdown voltage while maintaining reduced size and cost, as existing methods to decrease electric field concentration, such as enlarging the distance between drain extensions, increase device area and are counterproductive to size and cost reduction goals.
Innovation Solution
A method involving the implantation of dopants with specific masking techniques to create regions of reduced doping concentration between the center and edge of the drain, forming an epitaxial layer with a pn junction, and using masks with open and blocking portions to control dopant distribution, thereby reducing electric field concentration without increasing device area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the distance between drain extensions is enlarged to decrease electric field concentration, then breakdown voltage is improved, but device area increases
Solution Approach 1:
The patent applies local quality by creating a diluted doping region specifically in the drain extension area adjacent to the drain contact. This localized modification reduces electric field concentration only where needed (at the drain extension edges) without affecting other parts of the device, thereby avoiding the need to increase overall device area while still improving breakdown voltage.
Solution Approach 2:
The patent changes the doping concentration parameter by creating a diluted doping region with reduced dopant concentration compared to the standard drain extension. This parameter change (from high doping to diluted doping) reduces the electric field concentration effect, allowing the device to achieve higher breakdown voltage without increasing the physical dimensions of the drain extensions or device area.
2Reliability
If dopant distribution is modified to reduce electric field concentration, then breakdown voltage is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by forming the diluted doping region in the drain extension during the initial doping process, before subsequent fabrication steps. The masking pattern is designed beforehand to create the diluted region, and the dopant is implanted in a single step. This preliminary formation of the diluted doping profile simplifies manufacturing compared to attempting to create the same effect through multiple sequential doping steps or complex post-processing.
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 effectively increases breakdown voltage without enlarging the device area, improving robustness against premature breakdown and maintaining reduced size and cost, as demonstrated by simulations showing enhanced electric field spreading and increased breakdown voltage.
Implementation Method 1
a) implanting a first dopant in a substrate of a first conductivity type to form a first region of a second conductivity type in the substrate; b) implanting a second dopant into the substrate at a surface to form a second region of the first conductivity type; e) implanting the epitaxial layer with a third dopant and forming a third region of the second conductivity type in the epitaxial layer
Implementation Method 2
forming an epitaxial layer of the first conductivity type on the surface layer, wherein the surface layer is covered by the first epitaxial layer
Data Source
AI summary
A method of fabricating high-voltage semiconductor devices, the semiconductor devices and a mask for implanting dopants in a semiconductor are described.