TFT Electrode Metal Diffusion Barrier Structure
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Solution Overview
Problem
Copper diffusion into adjacent circuit elements or semiconductor layers in thin film transistors (TFTs) degrades the characteristics of pixel elements and TFTs, requiring effective prevention of metal atom spread.
Innovation Solution
A thin film transistor (TFT) structure with a gate electrode, gate insulating layer, semiconductor, and drain/source electrodes, where each electrode includes a first and second metal diffusion preventing layer with columnar grain structures and discontinuous grain boundaries to prevent copper diffusion, and a method for manufacturing such TFTs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper is used for wirings or electrodes to achieve lower electric resistance and higher resistance to electromigration, then electrical performance is improved, but copper atoms diffuse into adjacent elements or layers causing degradation of device characteristics
Solution Approach 1:
A metal diffusion preventing layer is introduced as an intermediary between the copper wiring/electrode and the adjacent semiconductor layer or circuit elements. This intermediate layer physically blocks copper atoms from diffusing into the semiconductor, thereby maintaining the electrical performance benefits of copper while preventing its harmful diffusion effects.
Solution Approach 2:
The electrode structure is segmented into multiple distinct layers: a copper layer for electrical conduction and a separate metal diffusion preventing layer for barrier functionality. This segmentation allows each layer to perform its specific function independently, with the copper providing low resistance and the barrier layer preventing diffusion.
2Reliability
If a metal diffusion preventing layer is introduced to prevent copper diffusion, then device reliability is improved, but the structure becomes more complex and manufacturing processes are extended
Solution Approach 1:
The metal diffusion preventing layer is designed to serve multiple functions simultaneously: it acts as a diffusion barrier to prevent copper migration, provides electrical isolation between layers, and serves as a foundation for subsequent electrode patterning. This multi-functionality reduces the need for additional separate layers or processes.
Solution Approach 2:
The formation of the metal diffusion preventing layer is merged with the existing electrode fabrication process sequence. The barrier layer is deposited and patterned in an integrated manner with the copper electrode formation, rather than as a completely separate process, thereby reducing overall manufacturing complexity.
Data Source
AI summary
A thin film transistor includes a gate electrode, a gate insulating layer on the gate electrode, a semiconductor on the gate insulating layer, and a drain electrode and a source electrode on the semiconductor and spaced apart from each other. Each of the drain electrode and the source electrode includes a first metal diffusion preventing layer which prevents diffusion of metal atoms, and a second metal diffusion preventing layer on the first metal diffusion preventing layer. At least one of the first and second metal diffusion preventing layers includes grains in a columnar structure, which are in a direction substantially perpendicular to a lower layer. First grain boundaries of the first metal diffusion preventing layer and second grain boundaries of the second metal diffusion preventing layer are substantially discontinuous in a direction perpendicular to the semiconductor.