Cut Metal Gate Process for Multiple Threshold Voltages
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Solution Overview
Problem
The semiconductor industry faces challenges in providing a sufficient number of tunable threshold voltages for transistors as existing approaches, such as high-k metal gates, are limited by the number of metal layers that can be reliably deposited and patterned, making it difficult to achieve multiple threshold voltages in smaller devices.
Innovation Solution
The use of a cut metal gate process where high-k metal gates are etched to create multiple portions, allowing for the tuning of threshold voltages by varying the proximity and size of dielectric features to the fins, enabling more versatile transistor designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-k metal gates are used to reduce gate leakage current and poly-silicon gate depletion, then device reliability is improved, but the number of available threshold voltage choices is limited to four to six
Solution Approach 1:
The gate electrode layer is divided into multiple segments along the channel length, with each segment having a different thickness. This segmentation allows each portion of the gate to independently control the threshold voltage for different regions of the channel, thereby providing multiple threshold voltage options (VT1, VT2, VT3) while maintaining the high-k metal gate structure's reliability benefits
Solution Approach 2:
Different regions of the gate electrode layer are given different local properties by varying the thickness of the gate electrode in different segments. The first, second, and third portions have different gate electrode thicknesses, creating local variations in electrical characteristics that enable multiple threshold voltages without compromising the overall gate structure's ability to reduce leakage current
2Adaptability or versatility
If the number of metal layers is increased to provide more threshold voltage options, then adaptability is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
Instead of adding multiple metal layers, the invention segments the single gate electrode layer into multiple thickness portions along the channel length. This approach achieves multiple threshold voltages by varying the effective gate thickness locally rather than by stacking multiple metal layers, thereby reducing device complexity while maintaining adaptability
Solution Approach 2:
The invention transitions from controlling threshold voltage through the vertical dimension (multiple metal layers stacked vertically) to controlling it through the horizontal dimension (different gate electrode thickness portions along the channel length). This dimensional shift reduces the number of metal layers required while providing the same or greater threshold voltage tuning capability
Data Source
AI summary
A semiconductor device includes first and second transistors each having a high-k metal gate disposed over a respective channel region of the transistors. The semiconductor device further includes first and second dielectric features in physical contact with an end of the respective high-k metal gates. The first and second transistors are of a same conductivity type. The two high-k metal gates have a same number of material layers. The first transistor's threshold voltage is different from the second transistor's threshold voltage, and at least one of following is true: the two high-k metal gates have different widths, the first and second dielectric features have different distances from respective channel regions of the two transistors, and the first and second dielectric features have different dimensions.