Rounded SOI Isolation Trenches for High Voltage
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Solution Overview
Problem
Existing methods for fabricating isolation trenches on SOI substrates often result in sharp trench edges that concentrate field strength, leading to voltage peaks, especially at higher supply voltages, due to the lack of effective edge geometry patterning.
Innovation Solution
A two-step etch process is employed, involving anisotropic etching to form the trench and subsequent isotropic etching to create under-etched areas at the sidewalls, followed by thermal oxidation to form a rounded oxide layer at the trench bottom transition area, effectively reducing field concentration without altering the upper trench edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a standard etch process is used to create isolation trenches, then the trench is efficiently formed, but sharp edges are created that concentrate field strength and cause voltage peaks
Solution Approach 1:
The patent applies curvature by rounding the trench edges through a two-step etch process. The first anisotropic etch creates the vertical trench, and the second isotropic etch rounds the edges by etching in all directions equally. This curvature eliminates sharp edges that concentrate field strength, thereby resolving the contradiction between efficient trench formation and field strength concentration.
Solution Approach 2:
The etch process is segmented into two distinct steps: an anisotropic etch step for vertical trench formation and an isotropic etch step for edge rounding. This segmentation allows each step to optimize for its specific function, maintaining productivity while eliminating the harmful sharp edges.
2Object-affected harmful factors
If chamfering is applied at the beginning and end of the etch process to reduce field strength peaks, then voltage peaks are reduced, but the etch process becomes complex and difficult to control
Solution Approach 1:
The patent changes the etch parameters by using two different etch types (anisotropic and isotropic) with distinct directional characteristics. This parameter change allows edge rounding to be achieved through the inherent properties of the etch processes rather than complex chamfering steps, reducing process complexity while still eliminating voltage peaks.
3Object-affected harmful factors
If edge rounding is applied to all trench edges, then field strength concentration is reduced, but unnecessary rounding at upper edges increases process complexity
Solution Approach 1:
The patent applies local quality by using the directional nature of anisotropic and isotropic etching to round only the critical edges where field strength concentration occurs. The anisotropic etch maintains vertical walls while the isotropic etch selectively rounds the bottom edges, applying rounding only where necessary rather than uniformly to all edges, thus avoiding unnecessary process complexity.
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 simplifies the edge rounding process, reducing voltage peaks by increasing oxidation rates at the trench edges, thereby enhancing the planarization and reducing complexity while maintaining control over the edge geometry, resulting in cost-effective fabrication of rounded isolation trenches.
Implementation Method 1
after performing the etch process, thermally oxidising surfaces of the trench and the under-etched areas
Implementation Method 2
the oxygen diffusion can occur at two surface areas, thereby resulting in an overall increased oxidation rate in the edge region
Data Source
AI summary
The aim of the invention is to integrate low-voltage logic elements and high-voltage power elements in one and the same silicon circuit. Said aim is achieved by dielectrically chip regions having different potentials from each other with the aid of isolation trenches (10). In order to prevent voltage rises at sharp edges on the bottom of the isolation trenches, said edges are rounded in a simple process, part of the insulating layer (2) being isotropically etched.