Recessed Gate Dielectric Structure for Stable MOSFET Threshold Voltage
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Solution Overview
Problem
Recessed MOSFETs face reliability issues due to inconsistencies in current vs. voltage behavior caused by thinner gate dielectric layers near the corners of the gate electrode, leading to varying threshold voltages across the device.
Innovation Solution
A gate dielectric structure with thicker corner portions is implemented, comprising multiple layers that increase the thickness at the corners to prevent undesired current flow and ensure consistent voltage application, thereby enhancing the reliability of the recessed MOSFET.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the gate dielectric layer is made thinner to reduce device height in recessed MOSFETs, then the device can be integrated more densely, but the threshold voltage becomes inconsistent across the device due to corner effects
Solution Approach 1:
The gate dielectric structure is designed with non-uniform thickness, where corner portions have greater thickness than central portions. This local variation in dielectric thickness compensates for the corner effect, ensuring uniform threshold voltage across the entire gate electrode while maintaining overall device height reduction through the recessed structure.
2Reliability
If the gate dielectric layer is made thicker to ensure sufficient insulation, then reliability improves, but the device height increases and integration density decreases
Solution Approach 1:
Instead of uniformly increasing gate dielectric thickness throughout the device, the invention applies increased thickness only at corner portions where the gate dielectric directly contacts the trench isolation structure. This localized thickening provides sufficient insulation and eliminates corner effects while maintaining overall compact device height.
3Reliability
If the gate dielectric thickness is increased at corner portions, then threshold voltage consistency improves, but the manufacturing process becomes more complex
Solution Approach 1:
The gate dielectric structure is formed with thicker corner portions during the initial deposition process, before subsequent processing steps. This preliminary formation of the non-uniform dielectric structure simplifies later manufacturing steps by eliminating the need for additional corner-specific processing operations.
Data Source
AI summary
In some embodiments, the present disclosure relates to a semiconductor device that includes a well region with a substrate. A source region and a drain region are arranged within the substrate on opposite sides of the well region. A gate electrode is arranged over the well region, has a bottom surface arranged below a topmost surface of the substrate, and extends between the source and drain regions. A trench isolation structure surrounds the source region, the drain region, and the gate electrode. A gate dielectric structure separates the gate electrode from the well region, the source, region, the drain region, and the trench isolation structure. The gate electrode structure has a central portion and a corner portion. The central portion has a first thickness, and the corner portion has a second thickness that is greater than the first thickness.