Schottky Metal Gate Contact with Cavity for FET Stress Relief
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Solution Overview
Problem
Field-effect transistors (FETs) face reliability issues due to thermo-mechanical stress and electromigration of gate metal, leading to defects and premature failure, primarily caused by the mismatch of thermal expansion coefficients in complex material systems and chemical reactions that result in pit formation and leakage currents.
Innovation Solution
A gate structure for FETs featuring a substrate with an active layer, an intermediate layer having a recess for a Schottky metal contact element that completely fills the recess and includes an interior cavity, providing a diffusion barrier and mechanical stress relief, made of materials like SiC, GaAs, and InP, with preferred Schottky metals like Ir and Pt, and a dielectric cladding or passivation layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a metallic gate contact with high electrical conductivity is used, then switching speed is improved, but electromigration and diffusion of gate metal towards the semiconductor surface occurs, leading to reliability degradation
Solution Approach 1:
A Schottky metal layer (Ir, Pt, Ni, Os) is introduced as an intermediary between the highly conductive gate metal and the semiconductor active layer. This Schottky barrier layer prevents diffusion and electromigration of gate metal atoms towards the semiconductor surface while maintaining acceptable electrical conductivity for high-speed switching operation.
Solution Approach 2:
The gate contact structure employs a composite material system consisting of multiple layers: a highly conductive gate metal layer (Au, Cu, Al, Ag) combined with a Schottky barrier layer (Ir, Pt, Ni, Os). This composite structure combines the advantages of both materials - high conductivity from the gate metal and diffusion resistance from the Schottky barrier layer.
2Adaptability or versatility
If highly heterogeneous material systems are combined in a small space to achieve high performance, then device functionality is improved, but mismatch of thermal expansion coefficients causes high thermo-mechanical stress
Solution Approach 1:
The Schottky barrier layer acts as a mechanical intermediary layer between materials with different thermal expansion coefficients. This intermediate layer absorbs and distributes thermo-mechanical stress, preventing stress concentration and defect formation at material interfaces during device operation.
Solution Approach 2:
The invention changes the material parameter selection by introducing Schottky barrier metals (Ir, Pt, Ni, Os) with specific thermal and mechanical properties that bridge the gap between highly conductive gate metals and semiconductor materials. This parameter optimization reduces thermal expansion mismatch and associated stress.
3Speed
If the gate area is made short to achieve high operating frequencies, then frequency performance is improved, but the gate contact requires high conductivity which increases electromigration risk
Solution Approach 1:
The Schottky barrier layer serves as a protective intermediary that enables the use of highly conductive gate metals in short-gate high-frequency devices without suffering from electromigration. The barrier layer blocks atomic diffusion while allowing electrical current flow, solving the contradiction between conductivity requirements and electromigration resistance.
Solution Approach 2:
The gate contact uses a composite structure with a thin Schottky barrier layer (5-20 nm) combined with a highly conductive gate metal layer. This composite enables high-frequency operation by providing the necessary conductivity while the Schottky layer prevents electromigration, even in shortened gate geometries where current density is high.
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 solution significantly reduces thermo-mechanical stress and electromigration, enhancing the reliability and longevity of FETs by preventing diffusion of gate metals and absorbing mechanical deformations, thereby minimizing defects and leakage currents.
Implementation Method 1
the contact element is made of a Schottky metal and the contact element has an interior cavity completely enclosed by the Schottky metal
Implementation Method 2
providing a diffusion barrier and mechanical stress relief
Data Source
AI summary
This invention concerns a gate structure and a process for its manufacturing. In particular, the present invention concerns the gate structuring of a field effect transistor with reduced thermo-mechanical stress and increased reliability (lower electromigration or diffusion of the gate metal). The gate structure according to the invention comprises a substrate; an active layer disposed on the substrate; an intermediate layer disposed on the active layer, the intermediate layer-having a recess extending through the entire intermediate layer towards the active layer; and a contact element which is arranged within the recess, the contact element completely filling the recess and extending to above the intermediate layer, the contact element resting at least in sections directly on the intermediate layer; the contact element being made of a Schottky metal and the contact element having an interior cavity completely enclosed by the Schottky metal.