LDMOS Transistors Vertical Double Drain Doping Profile
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Solution Overview
Problem
Conventional LDMOS transistors face challenges in optimizing power density and linearity without compromising other performance characteristics like efficiency and hot carrier injection reliability, as increasing power density often degrades linearity and reliability.
Innovation Solution
The implementation of a vertical double drain doping profile with a first lightly doped drain region extending under the gate and a shallower, second lightly doped N-type region, which allows for greater control over dopant concentration and electric field optimization, improving power density and linearity while reducing hot carrier injection effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the doping level of the lightly doped drain is increased to improve power density, then power density is improved, but hot carrier injection reliability deteriorates due to increased peak electric-field in the drain region
Solution Approach 1:
The patent applies local quality by creating distinct doping regions with different characteristics: a first lightly doped drain region with lower doping concentration to control peak electric field and maintain reliability, and a second shallower lightly doped region with higher doping concentration to improve power density. Each region is optimized for its specific function within the overall device structure.
Solution Approach 2:
The drain region is segmented into two separate lightly doped regions with different doping concentrations and depths. This segmentation allows independent optimization of each region's properties to simultaneously achieve good power density and hot carrier injection reliability, resolving the trade-off between these two parameters.
2Power
If the lightly doped drain region is extended beyond the gate electrode edge into the channel region to improve power density, then power density is improved, but linearity deteriorates substantially
Solution Approach 1:
The patent creates different doping concentrations in different spatial regions: the first lightly doped drain region extends under the gate with lower doping to maintain linearity, while the second shallower region provides higher doping for power density. This local differentiation resolves the contradiction between power density and linearity.
3Ease of manufacture
If a single N-type implant is used to form the lightly doped drain, then the process is simple, but it is difficult to simultaneously optimize power density, linearity, efficiency, and hot carrier injection reliability
Solution Approach 1:
The single N-type implant is segmented into two separate implantation steps: a first N-type implant creating a deeper, lightly doped region, and a second N-type implant creating a shallower, more heavily doped region. This segmentation provides the flexibility to independently optimize multiple performance parameters while maintaining a relatively simple two-step manufacturing process.
Solution Approach 2:
The patent changes the doping parameters by performing two separate N-type implants with different doping concentrations, depths, and lateral diffusion characteristics. This allows independent control of peak electric field (for reliability) and total dopant concentration (for power density), providing versatile performance optimization.
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 enhances power density and efficiency while maintaining improved linearity and reducing hot carrier injection reliability issues, providing better control over electric field distribution and current sinking ability.
Implementation Method 1
a first implant formed to a first depth in the substrate... The first implant may comprise an N-type dopant
Implementation Method 2
a second implant formed in the source region of the substrate, the second implant laterally diffused under the gate electrode into the channel region a predetermined distance
Implementation Method 3
a third implant formed to a second depth in the drain region of the substrate... The third implant may comprise an N-type dopant
Data Source
AI summary
Embodiments of laterally diffused metal oxide semiconductor (LDMOS) transistors are provided. An LDMOS transistor includes a substrate having a source region, channel region, and a drain region. A first implant is formed to a first depth in the substrate. A gate electrode is formed over the channel region in the substrate between the source region and the drain region. A second implant is formed in the source region of the substrate; the second implant is laterally diffused under the gate electrode a predetermined distance. A third implant is formed to a second depth in the drain region of the substrate; the second depth is less than the first depth.