MOSFET Asymmetric Structural Configurations for Electrical Characteristics
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Solution Overview
Problem
Existing methods for creating metal oxide semiconductor field effect transistors (MOSFETs) with different electrical characteristics require complex and expensive fabrication processes.
Innovation Solution
A method involving a semiconductor substrate with distinct dopant concentration levels and regions, where a well region with a higher dopant concentration is formed within the substrate, along with body and source regions, to create transistors with varying electrical characteristics, such as threshold voltage and on resistance, using a series of implantation and annealing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If different dopant concentrations, gate oxide thicknesses, body region shapes, or source region dimensions are used to create MOSFETs with different electrical characteristics, then the electrical characteristics (threshold voltage, on resistance, transconductance) can be differentiated, but the fabrication process becomes expensive and complex
Solution Approach 1:
The patent applies local quality by creating a well region with a specific dopant concentration only in the first region of the semiconductor substrate, while the second region maintains the substrate's original dopant concentration. This localized dopant concentration difference creates MOSFETs with different electrical characteristics without requiring complex fabrication processes across the entire substrate. The well region is formed by implanting dopant atoms at specific locations and activating them through annealing, thereby achieving local property differentiation.
2Manufacturing precision
If multiple implantation and annealing steps are used to create different electrical characteristics, then transistor properties can be precisely controlled, but the manufacturing process becomes more complex and expensive
Solution Approach 1:
The patent segments the semiconductor substrate into distinct regions (first region with well structure, second region without well) and applies different dopant concentrations to each segment. The fabrication process is segmented into specific implantation steps (well implant, body implant, source implant) and annealing steps, where each step targets a specific region or function. This segmentation allows precise control of electrical characteristics while maintaining manufacturing simplicity by avoiding unnecessary process steps in regions where they are not needed.
Solution Approach 2:
The patent performs preliminary actions by first forming the well region through dopant implantation and activation annealing before creating the body and source regions. The well implant is performed at a higher dopant concentration and activated through annealing to create a stable foundation. Subsequent body and source implants are then performed on top of this pre-formed well structure, allowing precise control of final transistor characteristics while simplifying the overall process sequence.
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 allows for the fabrication of MOSFETs with different electrical characteristics without the need for expensive and complex processes, enabling the production of integrated circuits with transistors that exhibit distinct properties like zero temperature coefficient and asymmetric operation.
Implementation Method 1
implanting first conductivity-type dopant in the first region, but not the second region, of the semiconductor substrate layer to form a well implant; implanting second conductivity-type dopant in the well implant in the first region and in the semiconductor substrate layer in the second region to form a first body implant in the first region and a second body implant in the second region
Implementation Method 2
annealing to activate and diffuse the first and second conductivity-type dopants to form a well region in the semiconductor substrate layer from the well implant having a second dopant concentration level greater than the first dopant concentration level, a first body region in the well region from the first body implant and a second body region in the semiconductor substrate layer from the second body implant
Implementation Method 3
annealing to activate and diffuse the first and second conductivity-type dopants
Data Source
AI summary
First and second transistors with different electrical characteristics are supported by a substrate having a first-type dopant. The first transistor includes a well region within the substrate having the first-type dopant, a first body region within the well region having a second-type dopant and a first source region within the first body region and laterally offset from the well region by a first channel. The second transistor includes a second body region within the semiconductor substrate layer having the second-type dopant and a second source region within the second body region and laterally offset from material of the substrate by a second channel having a length greater than the length of the first channel. A gate region extends over portions of the first and second body regions for the first and second channels, respectively.