SOI Trench Isolation Sidewall Spacer and Bottom Liner
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Solution Overview
Problem
SOI MOSFET devices exhibit lower drive currents due to oxidation of trench isolation sidewalls, which applies compressive stress and degrades performance, and sharp trench corners contribute to leakage current.
Innovation Solution
The use of a protective tensile stressor spacer structure on sidewalls to prevent oxidation and a bottom trench liner to manage stress, combined with anisotropic etching to round trench corners, reduces compressive stress and enhances drive current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If trench isolation is formed in SOI structures, then isolation between devices is achieved, but sidewall oxidation occurs causing compressive stress and reduced drive current
Solution Approach 1:
A liner layer is deposited on the trench sidewalls to act as an intermediary barrier that prevents oxidation. The liner material (such as nitride or oxide) is selectively placed on vertical sidewalls while leaving horizontal surfaces exposed, thereby mediating between the need for isolation and the need to prevent harmful oxidation-induced compressive stress
Solution Approach 2:
The liner is applied selectively only on trench sidewalls with different properties for different surfaces: vertical sidewalls receive the liner to prevent oxidation, while horizontal surfaces (trench bottom and top) remain exposed. This local differentiation allows the structure to have different functional qualities in different regions, preventing harmful compression while maintaining isolation
2Ease of manufacture
If sharp trench corners are present, then manufacturing simplicity is maintained, but leakage current increases due to corner effects
Solution Approach 1:
The trench corners are rounded or curved instead of being sharp, which eliminates the corner effects that cause leakage current. The anisotropic etching process naturally produces rounded corners by etching vertical walls faster than horizontal surfaces, transforming the sharp corner geometry into a curved profile that prevents harmful electrical leakage
3Object-generated harmful factors
If anisotropic etching is used to round trench corners, then leakage is reduced, but manufacturing complexity increases
Solution Approach 1:
The anisotropic etching process is self-selective, automatically rounding corners and shaping the trench profile based on crystallographic orientation without requiring additional masking or patterning steps. The process uses the material's own properties to achieve the desired geometry, eliminating the need for complex external control mechanisms
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 increases drive current by minimizing sidewall oxidation and corner effects, leading to improved transistor performance with reduced leakage and enhanced tensile stress.
Implementation Method 1
oxidation of trench isolation sidewalls, which applies compressive stress and degrades performance
Implementation Method 2
a bottom trench liner to manage stress
Implementation Method 3
anisotropic etching to round trench corners
Data Source
AI summary
A method for making a semiconductor device is provided which includes (a) providing a layer stack comprising a semiconductor layer (211) and a dielectric layer (209) disposed between the substrate and the semiconductor layer, (b) creating a trench (210) which extends through the semiconductor layer and which exposes a portion of the dielectric layer, the trench having a sidewall, (c) creating a spacer structure (221) which comprises a first material and which is adjacent to the sidewall of the trench, and (d) forming a stressor layer (223) which comprises a second material and which is disposed on the bottom of the trench.