High Lateral Voltage Isolation Structure via Dual Trench Fill
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Solution Overview
Problem
Existing high lateral voltage isolation techniques in semiconductor chips face limitations due to film stress in dielectric films and charging effects caused by silicon islands between concentric trenches, restricting the maximum isolatable voltage.
Innovation Solution
Forming initial trenches around the active region, filling them with dielectric, and then removing semiconductor material between the trenches to create additional trenches, which are subsequently filled with dielectric, allowing for wider trenches without film stress and charging issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the trench width is increased to achieve higher lateral voltage isolation, then the voltage isolation capacity is improved, but film stress in the dielectric film increases excessively
Solution Approach 1:
The patent divides a single wide trench into multiple narrower concentric trenches (e.g., first trench 104, second trench 106, third trench 110). Each trench is narrow enough to avoid excessive film stress while collectively providing the required wide isolation width for high voltage capacity. The dielectric is deposited in each trench separately, ensuring stress remains within acceptable limits for each individual trench wall.
2Stress or pressure
If multiple concentric trenches are formed to reduce film stress, then film stress is reduced, but charging effects occur in the silicon bands between trenches
Solution Approach 1:
The patent removes the problematic silicon material between the concentric trenches by etching away the silicon bands that would otherwise form isolated islands. This extraction eliminates the source of charging effects while maintaining the beneficial narrow-trench structure for stress reduction. The trenches are then filled with dielectric material, and the region between initial trenches is also filled to create a continuous dielectric structure without isolated silicon regions.
3Reliability
If a single wide trench is formed to achieve high voltage isolation, then the voltage isolation capacity is improved, but the trench width exceeds the practical limit for CVD deposition
Solution Approach 1:
The patent segments the wide isolation region into multiple narrow trenches that can each be filled by standard CVD processes. The CVD dielectric deposition is performed separately in each trench, ensuring that the dielectric thickness in any single trench remains within the practical 3 um limit for CVD. The combined effect of multiple filled trenches achieves the equivalent of a much wider trench for high voltage isolation.
4Reliability
If the dielectric film thickness is increased to improve voltage isolation, then the voltage isolation capacity is improved, but film stress becomes excessive
Solution Approach 1:
The patent achieves high voltage isolation capacity not by increasing the thickness of dielectric in a single trench, but by segmenting the isolation into multiple trenches with moderate dielectric thickness. Each trench contains dielectric at acceptable thickness levels (avoiding excessive stress), while the cumulative width of multiple trenches provides the necessary voltage isolation capacity. This approach decouples the relationship between isolation capacity and dielectric thickness.
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 dielectric-filled trenches wider than 6 um, effectively increasing lateral voltage isolation capacity beyond previous limitations, reducing film stress and charging effects, and allowing for higher voltage isolation without anomalous device effects.
Implementation Method 1
depositing a dielectric into the trench using chemical vapor deposition (CVD)
Implementation Method 2
first growing a trench side wall oxide
Data Source
AI summary
In a SOI process, a high lateral voltage isolation structure is formed by providing at least two concentric dielectric filled trenches, removing the semiconductor material between the dielectric filled trenches and filling the resultant gap with dielectric material to define a single wide dielectric filled trench.