Oxide Semiconductor Transistor Electrodes for Copper Diffusion Control
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Solution Overview
Problem
The use of Cu—Mn alloy films in oxide semiconductor transistors leads to copper diffusion issues, causing electrical characteristics deterioration and reliability concerns, especially on the back-channel side of bottom-gate structures, due to copper reattachment and diffusion effects.
Innovation Solution
Incorporating copper and silicon regions in the end portions of source and drain electrodes, with barrier metals like titanium, tungsten, or molybdenum to inhibit copper diffusion, and using insulating films with excess oxygen to reduce oxygen vacancies and enhance adhesion, thereby stabilizing the transistor's electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Cu—Mn alloy film is used as source/drain electrode to reduce resistance, then electrical conductivity is improved, but copper diffusion into oxide semiconductor film occurs causing transistor characteristics deterioration
Solution Approach 1:
A barrier metal film (titanium, tungsten, or molybdenum) is introduced as an intermediary layer between the Cu-Mn alloy electrode and the oxide semiconductor film. This barrier film prevents copper diffusion into the semiconductor while maintaining electrical conductivity, thus resolving the contradiction between using Cu-Mn for low resistance and preventing copper contamination.
Solution Approach 2:
The electrode structure is designed as a composite material system combining Cu-Mn alloy with barrier metal layers. This composite structure leverages the high conductivity of Cu-Mn while the barrier metal component prevents copper diffusion, achieving both low resistance and high reliability.
2Stability of the object's composition
If heat treatment is performed to form Mn oxide at interface, then adhesion is improved and oxygen vacancies are reduced, but copper reattachment from side surfaces occurs
Solution Approach 1:
The barrier metal film serves as a protective intermediary that prevents copper reattachment from side surfaces during and after heat treatment. Even when Mn oxide forms at the interface improving adhesion, the barrier film blocks copper migration paths, preventing reattachment harmful effects.
Solution Approach 2:
The barrier metal film is deposited beforehand to cover the electrode structure before heat treatment. This preliminary protective action ensures that even if heat treatment causes copper to become mobile, the pre-positioned barrier film prevents reattachment, maintaining interface stability without copper contamination.
3Ease of manufacture
If aluminum is used as wiring material, then ease of manufacture is improved, but resistance is high compared to copper
Solution Approach 1:
The wiring structure uses a composite material approach combining aluminum (for ease of manufacture and adhesion) with copper (for low resistance). This composite wiring achieves both manufacturing simplicity and low electrical resistance by leveraging the complementary properties of both metals.
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 results in transistors with improved electrical characteristics, such as enhanced on-state current and field-effect mobility, while reducing manufacturing costs and increasing productivity, by preventing copper diffusion and maintaining transistor reliability.
Implementation Method 1
barrier metals like titanium, tungsten, or molybdenum to inhibit copper diffusion
Implementation Method 2
using insulating films with excess oxygen to reduce oxygen vacancies
Implementation Method 3
heat treatment is performed on the Cu—Mn alloy film to form a Mn oxide at the joint interface
Implementation Method 4
Mn in the Cu—Mn alloy film diffuses toward the oxide semiconductor film and is preferentially bonded to oxygen contained in the oxide semiconductor film
Data Source
AI summary
A semiconductor device including an oxide semiconductor film that includes a transistor with excellent electrical characteristics is provided. It is a semiconductor device including a transistor. The transistor includes a gate electrode, a first insulating film, an oxide semiconductor film, a source electrode, a drain electrode, and a second insulating film. The source electrode and the drain electrode each include a first conductive film, a second conductive film over and in contact with the first conductive film, and a third conductive film over and in contact with the second conductive film. The second conductive film contains copper, the first conductive film and the third conductive film include a material that inhibits diffusion of copper, and an end portion of the second conductive film includes a region containing copper and silicon.