Asymmetric Transistor Layout for Strained Silicon Stress Optimization
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Solution Overview
Problem
Current semiconductor designs require significant design time and effort to optimize the mechanical stress effect in strained semiconductor materials, particularly in the border between the active region of a transistor and the shallow trench isolation, which affects current carrier mobility and saturation current.
Innovation Solution
The development of area-efficient layout designs for transistors with non-rectangular active regions and strategically placed gates to minimize the distance between stress-inducing structures and the gate, optimizing the placement of stress-inducing structures to enhance or reduce strain effects based on their electrical impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the distance between the stress-inducing structure (STI border) and the gate is reduced to enhance strain effects, then current carrier mobility and saturation current improve, but the design complexity and manufacturing precision requirements increase due to the non-rectangular active region configuration
Solution Approach 1:
The active region employs an asymmetric non-rectangular configuration where the distance from the gate to the first edge is intentionally made shorter than the distance to the second edge. This asymmetric layout strategically positions the stress-inducing STI structure closer to the gate on one side, maximizing strain effects on current carrier mobility while maintaining design manageability through systematic edge perpendicularity to the channel direction
Solution Approach 2:
The invention applies local quality by creating different distances from the gate to different edges of the active region. The first edge is positioned closer to the gate to induce beneficial compressive strain for enhanced carrier mobility, while the second edge maintains a larger distance. This localized variation in geometry optimizes strain distribution specifically where needed for performance enhancement
2Ease of manufacture
If standard rectangular active regions are used with conventional layouts, then manufacturing and design are simpler, but the mechanical stress effect is not optimized and transistor performance is limited
Solution Approach 1:
The invention changes the geometric parameters of the active region from the conventional rectangular shape to a non-rectangular configuration with edges perpendicular to the channel. By adjusting the distances from the gate to different edges (making the first distance shorter than the second), the layout optimizes the mechanical stress effect while maintaining manufacturing feasibility through systematic geometric modifications rather than complex arbitrary shapes
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
These designs enhance transistor performance by up to 20% in terms of I_Dsat, improving the utilization of strained silicon while maintaining functional integrity, with greater benefits for PMOS performance and some disadvantage for NMOS.
Implementation Method 1
STI oxide grown on silicon occupies more volume than the original silicon consumed. The difference causes strain as the oxide tries to push the adjoining silicon out of the way.
Implementation Method 2
The mobility of current carriers, electrons or holes, in semiconductors changes as stress is applied to the material. The material crystal is strained, or deformed.
Data Source
AI summary
A layout for a transistor in a standard cell is disclosed. The layout for a transistor includes an active region with at least one portion having a first edge and at least one portion having a second edge all perpendicular to a channel of the transistor; and a gate placed on top of the active region with a distance from an edge of the gate to the first edge being shorter than a distance from the edge of the gate to the second edge of the active region, wherein the active region is of a non-rectangular shape.