Multi-step Gate Structure for MOSFET Short Channel Effect
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Solution Overview
Problem
The decreasing size and channel length of transistors lead to a short channel effect, reducing the controlling ability of the conductive metal layer on the switching operation of the carrier channel, impeding the functioning of MOSFETs due to increased interaction between doped regions and the carrier channel.
Innovation Solution
A multi-step gate structure is introduced with a semiconductor substrate having a multi-step structure, featuring varying gate oxide layer thickness and dopant concentration, which allows for increased channel length by forming a mask layer, etching processes to create depressions, and implanting dopants to control the gate oxide layer and threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the transistor size and channel length are decreased to improve device integration, then the controlling ability of the conductive metal layer on the switching operation is reduced due to short channel effect
Solution Approach 1:
The patent introduces a multi-step gate structure with vertical steps into the semiconductor substrate, transforming the traditional planar gate into a three-dimensional structure. This dimensional change increases the effective channel length by adding vertical depth to the gate region, thereby extending the control path of the conductive metal layer over the carrier channel without increasing the lateral footprint of the device.
Solution Approach 2:
The gate structure is segmented into multiple steps at different depths within the semiconductor substrate. Each step creates a separate region that can be independently doped and controlled. This segmentation allows the gate to exert control over the carrier channel at multiple vertical levels, effectively increasing the total controlled channel length while maintaining compact lateral dimensions.
2Reliability
If the channel length is increased to mitigate short channel effect, then the device size increases which reduces integration density
Solution Approach 1:
Instead of extending the channel length horizontally which would increase device area, the patent extends the gate structure vertically into the substrate by creating multiple steps. This utilizes the vertical dimension to increase the effective channel length that the gate controls, thereby mitigating short channel effects without proportionally increasing the lateral device footprint and maintaining high integration density.
Solution Approach 2:
The multi-step gate structure nests multiple gate regions at different depths within the semiconductor substrate, similar to nested dolls. Each step is positioned within the vertical space of the substrate, allowing the gate structure to occupy three-dimensional space efficiently. This nesting approach increases the functional channel length while minimizing the lateral area occupied by the device.
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 multi-step gate structure effectively extends the channel length, mitigating the short channel effect and enabling better control over the threshold voltage and carrier channel operation.
Implementation Method 1
performing a thermal oxidation process to form a gate oxide layer on the multi-step structure
Implementation Method 2
a plurality of implanting processes to implant dopants into the semiconductor substrate under the multi-step structure
Data Source
AI summary
A multi-step gate structure comprises a semiconductor substrate having a multi-step structure, a gate oxide layer positioned on the multi-step structure and a conductive layer positioned on the gate oxide layer. Preferably, the gate oxide layer has different thicknesses on each step surface of the multi-step structure. In addition, the multi-step gate structure further comprises a plurality of doped regions positioned in the semiconductor substrate under the multi-step structure. The channel length of the multi-step gate structure is the summation of the lateral width and the vertical depth of the multi-step gate structure, which is dramatically increased such that problems originated from the short channel effect can be effectively solved. Further, the plurality of doped regions under the multi-step structure are prepared by implanting processes having different dosages and dopants, which can control the thickness of the gate oxide layer and the threshold voltage of the multi-step gate structure.