Polysilicon TFT Contact Resistance via Metal Silicide
Solution Overview
Problem
Existing methods for manufacturing thin film transistors (TFTs) are costly due to the need for expensive equipment, such as doping apparatuses, to reduce contact resistance between source and drain regions and the polysilicon layer, which is not efficiently addressed.
Innovation Solution
A method involving a substrate with a polysilicon layer and metal silicide electrodes is used, where metal catalysts induce crystallization of the polysilicon layer, forming a metal silicide layer that reduces contact resistance without the need for expensive doping apparatuses, by incorporating a heat treatment process and additional metal layers for improved adhesion and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If expensive doping apparatuses are used to form lightly doped drain areas, then contact resistance between source and drain regions and polysilicon layer is reduced, but manufacturing cost increases
Solution Approach 1:
The patent extracts the essential function of reducing contact resistance from the expensive doping process and implements it through a simpler metal silicide formation process. The metal silicide layer is formed by depositing metal layers (such as titanium, cobalt, or nickel) and performing heat treatment, eliminating the need for complex doping apparatuses while achieving the same contact resistance reduction effect.
Solution Approach 2:
The patent replaces expensive, complex doping apparatuses with simpler, more affordable metal deposition and heat treatment equipment. The metal silicide layer serves as a cost-effective alternative to heavily doped regions, providing the necessary low contact resistance without requiring sophisticated doping infrastructure.
2Manufacturing precision
If metal layers are formed to cover amorphous silicon layer and metal catalysts, then polysilicon crystallization is induced, but metal catalysts between metal layer and amorphous silicon layer need to be removed
Solution Approach 1:
The patent combines multiple functions into the metal layer: it serves as both the crystallization catalyst carrier and the final source/drain electrode material. The metal layer is deposited to cover the amorphous silicon layer and metal catalysts, then heat treatment induces polysilicon crystallization while the metal layer transforms into metal silicide, eliminating the need for separate catalyst removal and electrode formation steps.
Solution Approach 2:
The metal layer performs multiple functions: it acts as a catalyst carrier during polysilicon crystallization, serves as the source/drain electrode material, and forms the metal silicide layer that provides low contact resistance. This multi-functional approach simplifies the overall manufacturing process by eliminating redundant steps.
3Reliability
If additional metal layers are formed to contact metal silicide layer, then adhesion and conductivity are improved, but manufacturing process becomes more complex
Solution Approach 1:
The patent optimizes the metal layer composition and thickness parameters to achieve both good adhesion and conductivity without requiring additional metal layers. By selecting appropriate metals (such as titanium, cobalt, or nickel) and controlling the layer thickness, the metal silicide layer itself provides the necessary adhesion to the polysilicon and conductivity for the source/drain electrodes.
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 simplifies the manufacturing process, reduces contact resistance, and improves the electrical properties of the TFTs, such as mobility and threshold voltage, without the use of expensive equipment.
Implementation Method 1
disposing metal catalysts on an upper surface of the amorphous silicon layer... transforming the amorphous silicon layer into a polysilicon layer
Implementation Method 2
transforming all portions of the metal layer into the metal silicide layer using a heat treatment process
Implementation Method 3
conditioning the metal layer to include a metal silicide layer
Implementation Method 4
The metal silicide layer may include a silicide of a material to getter the metal catalysts
Data Source
AI summary
A thin film transistor includes a polysilicon layer on a substrate, which includes a first area between second and third areas. A polysilicon layer is formed on the substrate, and a source electrode and a drain electrode are formed on the polysilicon layer in the first and third areas. Each of the source electrode and the drain electrode includes a metal silicide layer adjacent the polysilicon layer.