Dual Composition Shallow Trench Isolation for Stress Decoupling
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Solution Overview
Problem
Existing stress-generating structures in semiconductor transistors are inefficient in transmitting stress to the channel region, and they fail to decouple longitudinal and transverse stress directions, which limits the enhancement of charge carrier mobility and transconductance in MOSFETs.
Innovation Solution
A shallow trench isolation structure with a dual composition is introduced, where a first shallow trench isolation portion and a second portion have different materials and stress-generating properties, allowing for the application of biaxial and bidirectional stresses to enhance charge carrier mobility by selectively choosing the materials and their orientations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a conventional stress-generating structure is used, then stress is applied to the channel region, but the stress transmission is inefficient and the magnitude of stress decays rapidly with depth
Solution Approach 1:
The isolation structure is divided into multiple segments with different materials: a first isolation material in the shallow trench and a second isolation material in the deeper region. This segmentation allows each material to be optimized for its specific function, with the first material providing stress generation and the second material providing stress transmission to deeper regions, thereby resolving the contradiction between stress transmission efficiency and stress magnitude at depth.
Solution Approach 2:
The invention uses a composite isolation structure combining two different isolation materials with distinct properties. The first isolation material (e.g., silicon nitride) generates stress, while the second isolation material (e.g., silicon oxide) transmits stress efficiently to deeper regions. This composite approach enables both efficient stress transmission and maintained stress magnitude at depth, resolving the technical contradiction.
2Adaptability or versatility
If a single-material isolation structure is used, then the structure is simple, but it cannot decouple longitudinal and transverse stress directions
Solution Approach 1:
Different regions of the isolation structure are assigned different materials with specific properties: the first isolation material is placed in the shallow trench region to generate stress in specific directions, while the second isolation material is placed in deeper regions to transmit and control stress in different directions. This local differentiation enables independent control of longitudinal and transverse stress directions, resolving the contradiction between adaptability and complexity.
Solution Approach 2:
The isolation structure is segmented into functional zones with different materials, allowing independent optimization of stress generation and stress transmission in different directions. The first material zone handles one stress direction while the second material zone handles another direction, enabling decoupled control without excessive complexity.
3Device complexity
If stress is transmitted through gate spacers, then the stress-generating structure is simple, but the stress magnitude decays rapidly with depth into the substrate
Solution Approach 1:
The invention introduces a second isolation material as an intermediary between the stress-generating first isolation material and the substrate. This intermediary material is specifically designed to transmit stress efficiently to deeper regions, preventing the rapid decay of stress magnitude with depth while maintaining the simplicity of the overall stress-generating structure.
Solution Approach 2:
By combining a stress-generating material (first isolation material) with a stress-transmitting material (second isolation material), the invention creates a composite structure that maintains stress magnitude at depth. The first material provides the stress source while the second material acts as a transmission medium, resolving the contradiction between structural simplicity and stress maintenance at depth.
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 effectively enhances charge carrier mobility in both p-type and n-type transistors by efficiently transmitting and managing stress, improving the performance of MOSFETs by optimizing the stress distribution along the lengthwise and widthwise directions.
Implementation Method 1
a first shallow trench isolation portion laterally abutting lengthwise sidewalls of a middle portion of the active area; and a set of two second shallow trench isolation portions, each laterally abutting lengthwise sidewalls and widthwise sidewalls of end portions of the active area, wherein the first shallow trench isolation portion and the set of two second shallow trench isolation portions comprise different materials
Data Source
AI summary
A shallow trench isolation structure containing a first shallow trench isolation portion comprising the first shallow trench material and a second shallow trench isolation portion comprising the second shallow trench material is provided. A first biaxial stress on at least one first active area and a second bidirectional stress on at least one second active area are manipulated separately to enhance charge carrier mobility in middle portions of the at least one first and second active areas by selection of the first and second shallow trench materials as well as adjusting the type of the shallow trench isolation material that each portion of the at least one first active area and the at least one second active area laterally abut.