LDMOS Well and Isolation Structure for Higher Breakdown Voltage
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Solution Overview
Problem
Existing LDMOS designs face challenges in achieving high breakdown voltage while maintaining manufacturing efficiency and compatibility with other processes, requiring additional masks and process steps, and the breakdown voltage is insufficient to meet demand.
Innovation Solution
A semiconductor structure design with a first well, a second well, and an isolation structure where the lower surface of the isolation structure is partially or completely uncovered by the wells, allowing for increased breakdown voltage without additional photomasks, and maintaining compatibility with existing manufacturing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the doping concentration of the N-type well and/or P-type well is reduced to achieve high breakdown voltage, then the breakdown voltage is improved, but the manufacturing complexity increases due to requiring more masks and process steps
Solution Approach 1:
The patent divides the semiconductor structure into multiple wells (first well, second well, third well) with different doping concentrations arranged in sequence. This segmentation allows each well to have optimized doping levels without requiring additional photomasks, as the spatial separation replaces the need for sequential doping steps that would otherwise require multiple masks.
Solution Approach 2:
The patent transitions from a two-dimensional planar structure to a three-dimensional vertical structure by stacking multiple wells at different depths. This dimensional change enables the achievement of high breakdown voltage through vertical doping concentration gradients rather than relying on additional lateral photomasking steps.
2Reliability
If the doping concentration of the N-type well and/or P-type well is reduced to achieve high breakdown voltage, then the breakdown voltage is improved, but the manufacturing cost increases
Solution Approach 1:
The patent segments the doping profile into multiple distinct wells that can be formed using existing photomask sets already required for other device features. This eliminates the need for additional dedicated photomasks for well formation, thereby reducing manufacturing costs while achieving the desired doping concentration gradients for high breakdown voltage.
Solution Approach 2:
The multiple wells serve multiple functions: they establish the doping concentration gradient needed for high breakdown voltage, provide current conduction paths, and define active device regions. This multi-functionality eliminates the need for separate process steps dedicated solely to well formation, reducing overall manufacturing costs.
3Reliability
If the doping concentration is reduced to achieve high breakdown voltage, then the breakdown voltage is improved, but the process compatibility with other manufacturing processes deteriorates
Solution Approach 1:
The patent segments the device structure into multiple wells that align with standard photomask layers used in conventional CMOS and LDMOS fabrication. This segmentation allows the doping profiles to be integrated into existing manufacturing workflows without requiring specialized or non-compatible process steps.
Solution Approach 2:
The patent modifies the doping concentration parameters of existing well structures to create a vertical gradient (higher concentration in first well, lower in second well) that achieves high breakdown voltage. These parameter changes are applied to standard process steps rather than introducing new incompatible processes.
4Productivity
If existing LDMOS structure is used to achieve high breakdown voltage, then the current delivery capability is maintained, but the breakdown voltage remains insufficient to meet demand
Solution Approach 1:
The patent segments the doping profile into multiple wells with progressively decreasing concentrations from first to second well. This segmentation creates an optimized electric field distribution that simultaneously maintains high current delivery capability through the first well and achieves high breakdown voltage through the lower-concentration second well.
Solution Approach 2:
The patent applies local quality optimization by having different doping concentrations in different spatial regions (first well vs. second well). The first well maintains higher doping for current conduction, while the second well has lower doping for breakdown voltage enhancement, achieving both requirements locally in different parts of the same structure.
Data Source
AI summary
A semiconductor structure is provided. The semiconductor structure includes a substrate, a first well in the substrate and having a first side surface, a second well in the substrate and having a second side surface, a third well in the substrate, an isolation structure in the substrate and between the first well and the second well, a drain region in the first well, a source region in the third well, and a gate structure on the substrate. The second well is between the first well and the third well. The first side surface of the first well faces the second side surface of the second well. The first side surface of the first well is apart from the second side surface of the second well.