Strained MOS Transistor Oxidation and Trenching for Hole Mobility
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Solution Overview
Problem
Existing methods for forming strained MOS transistors, particularly those with small dimensions, face challenges in maintaining compressive strain along the transistor length while minimizing strain in the width direction to enhance hole mobility, which is crucial for increasing transistor speed.
Innovation Solution
A method involving the formation of a strained semiconductor layer, either silicon-germanium or silicon, where thermal oxidation creates bars along the transistor width direction and insulating trenches along the length direction, maintaining lengthwise strain while releasing widthwise strain, thereby optimizing transistor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If compressive strain is applied along the drain-source direction to increase hole mobility, then transistor speed is improved, but compressive strain in the width direction decreases hole mobility
Solution Approach 1:
The patent segments the strain distribution by direction, creating distinct strain states along the length and width directions through the specific sequence of oxidation and trench formation, allowing independent optimization of mobility in each direction
Solution Approach 2:
The patent applies different strain characteristics to different spatial directions within the same semiconductor layer, creating local quality variations where lengthwise compressive strain and widthwise strain relief coexist to optimize hole mobility
2Reliability
If known methods are used to form strained transistors, then strain can be introduced, but various problems arise particularly in transistors with very small dimensions
Solution Approach 1:
The patent performs thermal oxidation before forming insulating trenches, creating oxide bars that pre-establish the strain configuration. This preliminary action simplifies subsequent processing and ensures proper strain distribution in miniaturized transistors
Solution Approach 2:
The patent introduces a temporal dimension to the strain formation process by sequencing operations (oxidation first, then trenching), which transforms the complexity of simultaneous multi-directional strain control into a manageable sequential process
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 results in improved hole mobility, particularly in P-channel MOS transistors, leading to faster transistor operation without compromising the strain in shorter transistors, thus enhancing overall performance.
Implementation Method 1
thermally oxidizing the strained layer across its entire thickness to form two bars extending in the transistor gate width direction
Data Source
AI summary
A strained semiconductor layer is produced from a semiconductor layer extending on an insulating layer. A thermal oxidization is performed on the semiconductor layer across its entire thickness to form two bars extending in a direction of a transistor width. Insulating trenches are formed in a direction of a transistor length. A strain of the strained semiconductor layer is induced in one implementation before the thermal oxidation is performed. Alternatively, the strain is induced after the thermal oxidation is performed. The insulating trenches serve to release a component of the strain extending in the direction of transistor width. A component of the strain extending in the direction of transistor length is maintained. The bars and trenches delimit an active area of the transistor include source, drain and channel regions.