Copper Wiring Film Adhesion Layer for Thin Film Transistors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Copper wiring films used in thin film transistors (TFTs) exhibit exfoliation due to poor adhesion with silicon layers, particularly when exposed to hydrogen plasma during the production process, leading to reliability issues.
Innovation Solution
A two-layer metallic wiring film structure is employed, comprising an adhesion layer made of a copper alloy with added magnesium and oxygen, and a low-resistance layer of pure copper, where aluminum (Al) is included at a specific atomic percentage to enhance adhesion and prevent copper precipitation at the silicon interface, using sputtering with specific gas compositions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pure copper is used for the wiring film to achieve low resistance, then the resistance is reduced, but adhesion to silicon deteriorates causing exfoliation
Solution Approach 1:
The patent uses a composite structure consisting of a copper alloy adhesion layer (containing Cu, Al, and Mg) and a pure copper low-resistance layer. This composite material approach allows the adhesion layer to provide strong bonding to silicon while the pure copper layer maintains low electrical resistance, thus resolving the contradiction between adhesion reliability and low resistance requirement.
Solution Approach 2:
The patent applies different material compositions to different layers of the wiring film structure. The adhesion layer uses a copper alloy with specific elements (Al and Mg) to optimize bonding properties at the silicon interface, while the upper layer uses pure copper to minimize resistance. This local differentiation of material properties resolves the contradiction by assigning specific functions to specific regions.
2Reliability
If a copper alloy adhesion layer is used to improve adhesion to silicon, then adhesion is enhanced, but copper precipitates at the interface when exposed to hydrogen plasma
Solution Approach 1:
The patent modifies the compositional parameters of the adhesion layer by adding magnesium (Mg) in addition to aluminum (Al) in a specific ratio. This parameter change prevents copper precipitation at the silicon interface during hydrogen plasma exposure while maintaining strong adhesion. The specific composition (Cu-Al-Mg with controlled ratios) changes the chemical stability of the interface under plasma conditions.
Solution Approach 2:
The aluminum and magnesium elements in the adhesion layer act as intermediary elements between the silicon substrate and the pure copper layer. These intermediary elements prevent direct copper-silicon interaction that would cause precipitation during plasma treatment, while still maintaining strong adhesion. The Al-Mg alloy composition serves as a protective intermediary layer.
3Stability of the object's composition
If aluminum is added to the copper alloy to prevent copper precipitation, then interface stability is improved, but adhesion strength may be compromised
Solution Approach 1:
The patent optimizes the compositional parameters by adding magnesium (Mg) to the Cu-Al alloy system. This parameter change (adding Mg while controlling Al content) simultaneously achieves both interface stability during plasma treatment and strong adhesion to silicon. The specific composition ratio (Cu:Al:Mg) is tuned to balance these two competing requirements.
Solution Approach 2:
The patent creates a tri-element copper alloy composite (Cu-Al-Mg) that combines the benefits of aluminum (interface stability, prevention of copper precipitation) and magnesium (enhanced adhesion strength). This multi-element composite material resolves the contradiction by leveraging the complementary properties of different alloying elements.
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 improves the adhesion between the copper wiring film and silicon, preventing exfoliation even when exposed to hydrogen plasma, thereby increasing yield and reliability of the TFTs.
Implementation Method 1
a step of sputtering a target of a copper alloy having Al and copper in a vacuum atmosphere with a gas including a sputtering gas and oxidizing gas for forming an adhesion layer having copper, Al and oxygen on the ohmic contact layer
Implementation Method 2
sputtering a target of a copper alloy having Al and copper in a vacuum atmosphere with a gas including a sputtering gas and oxidizing gas for forming an adhesion layer having copper, Al and oxygen
Data Source
AI summary
A metallic wiring film, which is not exfoliated even when exposed to plasma of hydrogen, is provided. A metallic wiring film is constituted by an adhesion layer in which Al is added to copper and a metallic low-resistance layer which is disposed on the adhesion layer and made of pure copper. When a copper alloy including Al and oxygen are included in the adhesion layer and a source electrode and a drain electrode are formed from it, copper does not precipitate at an interface between the adhesion layer and the silicon layer even when being exposed to the hydrogen plasma, which prevents the occurrence of exfoliation between the adhesion layer and the silicon layer. If the amount of Al increases, since widths of the adhesion layer and the metallic low-resistance layer largely differ after etching, the maximum addition amount for permitting the etching to be performed is the upper limit.