Recessed Gate Structure Multi-Step Channel Length
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Solution Overview
Problem
The continuous reduction in transistor size leads to a short channel effect, where the interaction between doped regions and the carrier channel under the gate oxide layer impairs the control of the conductive metal layer, reducing the transistor's functionality due to the reduced channel length.
Innovation Solution
A recessed gate structure with a multi-step structure is formed in a recess, allowing for varying gate oxide layer thickness and dopant concentration, which increases the channel length by forming a mask layer, etching to create depressions, and implanting dopants to control the gate oxide layer thickness and threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the transistor size and channel length are continuously reduced to improve integration density, then the productivity and device density are improved, but the short channel effect occurs due to increased interaction between doped regions and carrier channel, reducing the control ability of the gate
Solution Approach 1:
The patent introduces a vertical dimension by forming a recess in the semiconductor substrate and creating a multi-step structure within the recess. This transforms the conventional planar gate structure into a three-dimensional recessed gate structure, effectively increasing the channel length in the vertical direction while maintaining the same lateral footprint, thus improving device density without sacrificing gate control
2Reliability
If the channel length is increased to reduce the short channel effect, then the control ability is improved, but the device density and integration are reduced
Solution Approach 1:
The patent utilizes the vertical dimension by forming a recess in the semiconductor substrate and creating a multi-step structure within the recess. This allows the channel to extend vertically through multiple steps, effectively increasing the channel length without occupying additional lateral space, thus maintaining high device density while improving gate control
3Ease of manufacture
If a conventional planar gate structure is used to maintain simple fabrication, then the ease of manufacture is improved, but the short channel effect cannot be effectively controlled in scaled devices
Solution Approach 1:
The patent divides the recess into multiple steps, creating a multi-step structure where each step can have different gate oxide thicknesses and dopant concentrations. This segmentation allows independent optimization of different regions to control the short channel effect while maintaining compatibility with standard fabrication processes
Solution Approach 2:
The patent implements local quality by allowing different regions of the multi-step structure to have different gate oxide layer thicknesses and dopant concentrations. This enables tailored optimization of each step's electrical characteristics to specifically address short channel effects in scaled devices
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
The recessed gate structure effectively increases the channel length, reducing the short channel effect by allowing for precise control of the gate oxide layer thickness and dopant concentration, thereby enhancing the transistor's switching operation.
Implementation Method 1
performing a thermal oxidation process to form a gate oxide layer in the recess
Implementation Method 2
performing a plurality of implanting processes to implant dopants into the semiconductor substrate under the multi-step structure
Data Source
AI summary
A recessed gate structure comprises a semiconductor substrate, a recess positioned in the semiconductor substrate, a gate oxide layer positioned in the recess and a conductive layer positioned on the gate oxide layer, wherein the semiconductor substrate has a multi-step structure in the recess. The thickness of the gate oxide layer on one step surface can be different from that on another step surface of the multi-step structure. In addition, the recessed gate structure further comprises a plurality of doped regions positioned in the semiconductor substrate under the multi-step structure, and these doped regions may use different dosages and different types of dopants. There is a carrier channel in the semiconductor substrate under the recessed gate structure and the overall channel length of the carrier channel is substantially the summation of the lateral width and twice of the vertical depth of the recessed gate structure.