LDMOS Field Oxide Geometry for Low On-Resistance Stability
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Solution Overview
Problem
LDMOS semiconductor devices face increased on-resistance and threshold voltage issues due to electron movement distance and defects in existing field oxide layer formation processes, such as LOCOS and chemical vapor deposition.
Innovation Solution
A semiconductor device with a field oxide layer formed using a two-stage thermal oxidation process, where a preliminary bird's beak-shaped layer is created and then expanded, resulting in a ring-shaped pattern that reduces electron movement distance and maintains stable threshold voltage by spacing the field oxide interface away from electron paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a field oxide layer is formed through a LOCOS process, then the breakdown voltage of the LDMOS device is improved, but the on-resistance increases due to increased electron movement distance through the drift region
Solution Approach 1:
The field oxide layer is formed with a convex upward surface portion, transitioning from a traditional planar structure to a three-dimensional elevated structure. This dimensional change allows the field oxide to protrude into the drift region without increasing the lateral electron movement distance, thereby maintaining low on-resistance while providing sufficient breakdown voltage protection.
Solution Approach 2:
The field oxide layer is selectively formed only in specific regions where high voltage protection is needed, rather than uniformly across the entire drift region. The convex upward structure concentrates the field oxide material in critical areas, providing localized electric field management that reduces on-resistance in non-critical areas while maintaining breakdown voltage where required.
2Manufacturing precision
If a field oxide pattern is formed by chemical vapor deposition and etching, then the electron movement distance is reduced, but the threshold voltage increases and current decreases due to defects from the processes
Solution Approach 1:
The patent replaces the chemical vapor deposition and etching processes with a thermal oxidation process. This substitution eliminates the defects associated with chemical deposition and mechanical etching, as thermal oxidation naturally forms a high-quality silicon oxide interface with the substrate, maintaining stable threshold voltage while achieving the desired field oxide pattern.
Solution Approach 2:
The invention changes the formation parameters by using thermal oxidation at controlled temperatures to create the field oxide layer with a convex upward profile. This parameter change allows precise control over the oxide thickness and surface geometry, achieving reduced electron movement distance without introducing process defects that would affect threshold voltage.
3Reliability
If the field oxide layer width increases downward, then the breakdown voltage is improved, but the device area increases
Solution Approach 1:
Instead of increasing the lateral width of the field oxide layer to improve breakdown voltage, the patent utilizes the vertical dimension by creating a convex upward structure. This allows the field oxide to extend vertically into the drift region, providing enhanced breakdown protection without increasing the horizontal device footprint, thus maintaining compact device area.
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
The solution reduces on-resistance and Hot Carrier Injection (HCI) effects, maintaining stable threshold voltage by minimizing electron movement distance and optimizing field oxide layer geometry.
Implementation Method 1
forming a field oxide layer on a substrate
Data Source
AI summary
A semiconductor device includes a field oxide layer formed on a substrate, a gate insulating layer formed on a surface portion of the substrate adjacent to one side of the field oxide layer, a gate electrode formed on the gate insulating layer and a portion of the field oxide layer, a source region formed in a surface portion of the substrate adjacent to one side of the gate electrode, and a drain region formed in a surface portion of the substrate adjacent to another side of the field oxide layer. A surface portion of the substrate on which the field oxide layer is formed is convex upward.