2D Channel FET Contact Structure With Lower Schottky Barrier
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Solution Overview
Problem
Two-dimensional (2D) channel field-effect transistors (FETs) face high contact resistance due to low contact area between the 2D channel and source/drain regions, high van der Waals gap, and high Schottky barrier height, which are challenging to address with existing materials and integration processes.
Innovation Solution
A channel last process is employed where a gate opening is formed through a transition metal layer, treated with a chalcogen material to create a transition metal chalcogenide 2D channel, generating a high mobility channel with a gradient distribution that reduces the Schottky barrier height and increases contact area, thereby lowering contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional source/drain contact scheme is used with 2D channel, then the device structure is simple, but the contact resistance is high due to low contact area and high Schottky barrier height
Solution Approach 1:
The patent applies local quality by creating a gradient distribution of transition metal chalcogenide materials specifically at the source/drain contact regions. This gradient structure provides different material compositions at different locations: the 2H phase with higher carrier density at the contact interface reduces Schottky barrier height, while maintaining the desired channel properties elsewhere. This localized material optimization reduces contact resistance without requiring complete structural redesign of the entire device.
Solution Approach 2:
The patent changes material parameters by transitioning from conventional metals to transition metal chalcogenides with specific phase structures (2H phase). This parameter change includes modifying the crystal structure, carrier density, and work function of the contact material. The 2H phase transition in materials like MoTe2 or WTe2 creates a metallic state with higher carrier concentration, which directly reduces the Schottky barrier height at the 2D channel interface, thereby lowering contact resistance.
2Reliability
If the contact area between source/drain and 2D channel is increased, then contact resistance decreases, but the van der Waals gap increases leading to higher contact resistance
Solution Approach 1:
The patent employs composite materials by combining transition metal chalcogenide layers (such as MoTe2, WTe2) with the 2D channel material (like MoS2 or WS2). This composite structure creates a heterostructure where the transition metal chalcogenide provides both mechanical bridging across the van der Waals gap and electrical contact optimization. The composite material system simultaneously addresses the mechanical gap issue and the electrical contact resistance through its unique interfacial properties and gradient composition.
3Reliability
If transition metal chalcogenide with gradient distribution is formed, then Schottky barrier height is reduced and contact resistance is lowered, but the manufacturing process complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-forming the transition metal chalcogenide layer with the desired gradient distribution before final device assembly. The gradient structure is created in advance through controlled deposition or phase transition processes, ensuring the contact-optimizing material configuration is established prior to subsequent manufacturing steps. This preliminary structuring simplifies later processing by eliminating the need for complex in-situ gradient formation during device fabrication.
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 approach results in 2D channel FETs with significantly reduced contact resistance, improving device performance by enhancing mobility and reducing van der Waals gaps, while allowing for flexible selection of source/drain region metals.
Implementation Method 1
High Schottky barrier height (SBH) between the S/D regions and the 2D channel also contributes to the high contact resistance. The chalcogen treatment can generate a gradient distribution of the TMC material at the two ends of the 2D channel. The gradient distribution can realize a semiconductor-semimetal-metal work function (WF) transition from the 2D channel to the S/D regions. The transition can reduce SBH, i.e., SBH tuning, between the 2D channel and the S/D regions to result in low contact resistance.
Implementation Method 2
Low contact area at edge interfaces and van der Waals gap between top and bottom interfaces give rise to high contact resistance. The diffusion of chalcogen atoms into the thin metal layer can also reduce the van der Waals gap between the top and bottom surfaces of the 2D channel, and further reduce the contact resistance.
Implementation Method 3
The thin metal layer is treated with a chalcogen material, e.g., sulfur (S), selenium (Se), or tellurium (Te), to form a 2D channel. The chalcogen treatment can generate a high mobility channel in the center of the 2D channel.
Data Source
AI summary
The present disclosure describes a 2D channel FET with low contact resistance and a method for forming such a structure. The method includes depositing a dielectric layer on a semiconductor substrate, depositing a metal layer on the dielectric layer, and depositing a hard mask layer on the metal layer. The method further includes forming a gate opening by removing a portion of the hard mask layer and a portion of the metal layer. The method further includes depositing a spacer material layer on sidewalls of the gate opening and forming a channel, the channel including a TMC layer, at a bottom of the gate opening. The method further includes forming a gate structure on the channel and in the gate opening and removing the hard mask layer.