FinFET Air Isolation Structure for Lower Parasitic Capacitance
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Solution Overview
Problem
The increase in parasitic capacitance between fin structures in FinFETs due to reduced distance between adjacent line-like fin structures leads to a resistance-capacitance (RC) effect that reduces operating speed, as conventional dielectric materials with high dielectric constants are inadequate for reducing this capacitance.
Innovation Solution
Incorporation of air spaces into the isolation structure between fin structures to reduce the overall dielectric constant, utilizing air's low dielectric constant to minimize parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the distance between adjacent fin structures is reduced to decrease transistor size, then the transistor area is reduced, but the parasitic capacitance between fin structures increases
Solution Approach 1:
The patent changes the dielectric parameter (dielectric constant) of the isolation material from conventional oxide materials (high dielectric constant) to air or vacuum (dielectric constant close to 1). This parameter change directly reduces the parasitic capacitance between adjacent fin structures, allowing closer spacing without sacrificing performance.
Solution Approach 2:
The patent employs a composite isolation structure combining air/vacuum regions with selective oxide regions. The air/vacuum provides low dielectric constant for reduced capacitance, while the oxide regions provide mechanical support and process compatibility, creating a composite material system that addresses multiple requirements simultaneously.
2Object-generated harmful factors
If air spaces are introduced to reduce dielectric constant and parasitic capacitance, then the parasitic capacitance is reduced, but the fabrication process complexity increases
Solution Approach 1:
The patent performs preliminary actions by forming the air/vacuum isolation regions during the early stages of fabrication, before depositing subsequent dielectric layers. The air gaps are created by selective removal of sacrificial materials or by direct deposition techniques, establishing the low-dielectric constant structure in advance to guide subsequent processing steps.
Solution Approach 2:
The patent uses intermediary materials such as sacrificial layers (e.g., silicon nitride, oxide) that are temporarily deposited to define the air gap regions, then selectively removed to create the vacuum/air isolation structures. These intermediary materials facilitate the formation of air spaces without requiring direct vacuum processing throughout the fabrication sequence.
3Ease of manufacture
If conventional oxide dielectric materials are used for isolation, then the isolation structure is simple to fabricate, but the dielectric constant remains high and parasitic capacitance is not reduced
Solution Approach 1:
The patent fundamentally changes the dielectric parameter by transitioning from high-k oxide materials to air/vacuum (k≈1) for the isolation regions. This parameter change is achieved through selective material removal or direct air-gap formation techniques, prioritizing electrical performance over conventional material simplicity.
Solution Approach 2:
The patent applies different dielectric qualities to different regions: air/vacuum in the isolation regions between fins for low capacitance, and conventional oxide materials in other regions for mechanical support and process compatibility. This local differentiation optimizes the overall device performance by placing the right material in the right location.
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
Effectively reduces parasitic capacitance and enhances the operating speed of FinFETs by using air isolation structures, which have a dielectric constant close to 1, thereby improving transistor performance.
Implementation Method 1
The air in a natural state substantially exists in the free space in a vacuum state and therefore, becomes air isolation structures. Air has a dielectric constant close to 1 and is barely a material with the lowest dielectric constant.
Data Source
Figure 1A~1C
Figure 1D~1F
Figure 2A~2C
AI summary
A fin transistor structure is provided. The fin transistor structure includes a first substrate. An insulation layer is disposed on the first substrate. A plurality of fin structures are disposed on the insulation layer. A supporting dielectric layer fixes the fin structures at the fin structures at waist parts thereof. A gate structure layer is disposed on the supporting dielectric layer and covers a portion of the fin structures.