Double-T Gate Etching Structure for Lower Gate Resistance
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Solution Overview
Problem
The existing T-shaped gate preparation process for high-frequency high-electron-mobility transistors is tedious and difficult to control, leading to increased gate resistance and reliability issues, particularly in reducing the current collapse and virtual gate effects, which affect the high-frequency performance of radio frequency devices.
Innovation Solution
A double-T-shaped gate preparation method using double-layer passivation accurate etching, where two passivation layers are sequentially grown and etched to form a gate root, lower gate cap, and top gate cap, simplifying the process and improving control over metal thickness, thereby reducing gate resistance and enhancing breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the gate length is reduced to improve high-frequency performance, then the high-frequency performance is improved, but the gate resistance increases
Solution Approach 1:
The gate structure is segmented into three distinct parts: gate root, lower gate cap, and top gate cap. This segmentation allows each part to serve different functions - the gate root provides short gate length for high-frequency performance, while the gate caps provide extended metal coverage for reduced resistance
Solution Approach 2:
The gate structure transitions from a planar 2D configuration to a 3D vertical structure with multiple tiers. By stacking gate caps vertically above the gate root, the effective metal area is increased without extending the lateral gate length, thus reducing resistance while maintaining high-frequency performance
2Manufacturing precision
If the electron beam lithography tri-layer photoresist process is used to prepare T-shaped gate, then the gate pattern can be formed, but the process becomes extremely tedious requiring three times of exposure and development
Solution Approach 1:
The patent extracts and removes the complex multi-layer photoresist processing steps from the fabrication process. Instead of using three photoresist layers with multiple exposures and developments, the invention uses a simplified single-photoresist process combined with selective etching to achieve the same T-shaped gate pattern
Solution Approach 2:
The complex mechanical/photochemical process of multiple photoresist layers is replaced with a simpler chemical etching process. The selective etching method uses chemical reactions to differentiate between layers, eliminating the need for multiple photoresist coating, exposure, and development steps
3Manufacturing precision
If multiple baking and development processes are performed to prevent mixing between photoresist layers, then the T-shaped gate pattern can be obtained, but the process becomes more tedious and difficult to control
Solution Approach 1:
The patent introduces a sacrificial layer as an intermediary element that facilitates pattern formation without requiring complex photoresist processing. The sacrificial layer is temporarily deposited, patterned, and then removed to create the desired gate structure, simplifying the overall manufacturing process
Solution Approach 2:
The gate cap metal layer is deposited in advance before the gate root formation is completed. This preliminary action allows the gate cap to be pre-positioned and then used as a template or guide for subsequent etching steps, reducing the need for multiple photoresist processing cycles
4Reliability
If the double-T gate process is used to add gate cap on top of T-shaped gate, then the gate resistance is reduced and breakdown voltage is increased, but the process becomes more tedious and difficult to control
Solution Approach 1:
The patent merges the gate cap formation process with the gate root etching process. By using the same photoresist pattern and etching steps to define both structures simultaneously, the process complexity is reduced while still achieving the double-T gate structure with improved reliability
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 method effectively reduces gate resistance, suppresses current collapse and virtual gate effects, and increases breakdown voltage, improving the reliability and high-frequency performance of radio frequency devices by accurately etching and passivating the gate structure.
Implementation Method 1
performing a first exposure on the top passivation layer and etching the top passivation layer and the bottom passivation layer in a first exposure region from top to bottom to form a gate root region
Implementation Method 2
performing a second exposure on the top passivation layer and wet-etching the top passivation layer in a second exposure region to form a lower gate cap region
Implementation Method 3
performing metal evaporation and removing a photoresist to form a double-T-shaped gate structure in the two passivation layers
Data Source
AI summary
A preparation method of a double-T-shaped gate based on double-layer passivation accurate etching includes: sequentially growing two passivation layers on an epitaxial structure, where the two passivation layers include a bottom passivation layer and a top passivation layer; performing a first exposure on the top passivation layer and etching the top passivation layer and the bottom passivation layer in a first exposure region from top to bottom to form a gate root region; performing a second exposure on the top passivation layer and etching the top passivation layer in a second exposure region to form a lower gate cap region; and performing a third exposure on the top passivation layer to form a top gate cap exposure region and performing metal evaporation and removing a photoresist to form a double-T-shaped gate structure in the two passivation layers.