Metallic Gate Electrode Grain Growth Control
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Solution Overview
Problem
Field effect transistors with aluminum gates tend to produce NOPO errors as gate length decreases, making components unusable for many applications, due to grain size growth during temperature treatment and electromigration.
Innovation Solution
A metallic gate electrode structure is used, with a thin first layer of aluminum and a second layer of a different metal, such as platinum, nickel, or titanium, to limit grain size growth, and a further layer of aluminum for the gate head, ensuring stable properties and preventing diffusion issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If gate length is reduced to achieve smaller dimensions, then device performance is improved, but NOPO errors increase making components unusable
Solution Approach 1:
By segmenting the gate electrode into functional layers, the invention enables reduced gate length operation. The second titanium layer specifically prevents grain growth in the narrow gate foot region, allowing the gate length to be reduced without incurring NOPO errors that would otherwise make the components unusable.
Solution Approach 2:
The invention changes the material composition parameters of the gate electrode, introducing a titanium diffusion barrier layer that fundamentally alters the grain growth behavior. This parameter change enables the gate length to be reduced while maintaining reliability by preventing the grain size growth that causes NOPO errors.
2Reliability
If aluminum layer thickness is increased to reduce electrical resistance, then conductivity is improved, but grain size growth is exacerbated
Solution Approach 1:
The aluminum gate electrode is segmented into a first layer and a third layer separated by a second titanium layer. This segmentation allows the aluminum layers to have sufficient thickness for low resistance while the titanium barrier prevents grain size growth, resolving the contradiction between conductivity and grain stability.
Solution Approach 2:
The second titanium layer serves as an intermediary that decouples the relationship between aluminum layer thickness and grain size. It allows the aluminum layers to be thick enough for low electrical resistance while blocking the grain growth pathway, thus resolving the contradiction between conductivity improvement and grain size stability.
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
This approach prevents NOPO errors and achieves long-term stable properties even with small gate lengths, maintaining low electrical resistance and avoiding impairment of semiconductor properties.
Implementation Method 1
the main reason for the occurrence of the NOPO defects mentioned is grain size growth of the aluminum that takes place during the temperature treatment and/or during operation as a result of electromigration
Implementation Method 2
The TiN layer suppresses the diffusion of Al into the gold layer
Implementation Method 3
The Ti layers between the TiN layer and the Al layer prevent diffusion of N from the TiN layer and nitriding of the aluminum caused thereby
Implementation Method 4
the gate electrode forms a Schottky contact on a GaAs semiconductor layer
Implementation Method 5
Aluminum has a particularly high conductivity and forms a connection to the semiconductor material that is particularly stable over the long term
Data Source
Figure 1a~1d
Figure 2
AI summary
The method involves isolating a metallic gate electrode with a base and a head, on a semiconductor layer (4) on a compound semiconductor substrate (1). The metal of the electrode is separated and a temperature treatment is performed at an increased temperature. A layer (G2) made of a metal is isolated on a layer (G1) of the electrode on the semiconductor layer, for limiting an increase of the grain size of aluminum in the layer (G1) during the temperature treatment. Metal in third layer (G3) on the layer (G2) is isolated. An independent claim is also included for a semiconductor device with a metallic gate electrode on a semiconductor layer.