Polysilicon Layer Surface Roughness Minimization via Laser Annealing
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Solution Overview
Problem
The surface roughness of polysilicon layers in thin film transistors is undesirably high due to protrusions at grain boundaries, which affects the performance of display devices like OLEDs, LCDs, and PDPs.
Innovation Solution
A manufacturing method involving the irradiation of a first excimer laser beam to form a polysilicon layer with protrusions at grain boundaries, followed by removal of oxidation layers using a hydrogen fluoride solution, and subsequent irradiation with a second excimer laser beam to reduce surface roughness, achieving a minimized surface roughness polysilicon layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional laser annealing method is used to form a polysilicon layer, then the polysilicon layer can be formed efficiently, but the surface roughness becomes high due to protrusions at grain boundaries
Solution Approach 1:
An oxidation layer is formed on the polysilicon layer before the final laser annealing process. This preliminary oxidation creates a protective layer that prevents excessive protrusion formation at grain boundaries during subsequent laser irradiation, thereby reducing surface roughness while maintaining formation efficiency
Solution Approach 2:
The laser energy density is precisely controlled within a specific range (0.35-0.45 J/cm²) to optimize the annealing process. This parameter optimization ensures sufficient crystallization while minimizing grain boundary protrusions, resolving the contradiction between formation efficiency and surface quality
2Reliability
If the surface roughness of the polysilicon layer is reduced, then the performance of thin film transistors improves, but additional process steps are required
Solution Approach 1:
The oxidation process and laser annealing process are combined into an integrated treatment sequence. The oxidation layer formation is performed immediately before laser annealing without intermediate handling, merging two process steps into a cohesive workflow that reduces overall process complexity while achieving low surface roughness
Solution Approach 2:
By optimizing the laser energy density to a specific range (0.35-0.45 J/cm²), the process achieves both low surface roughness and high transistor performance without requiring additional complex process steps, thus improving reliability without significantly increasing device complexity
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 method effectively minimizes the surface roughness of the polysilicon layer, reducing the root mean square (RMS) to about 2-7 nm and peak-to-valley (RPV) to about 10-30 nm, thereby improving the performance and reliability of thin film transistors in display devices.
Implementation Method 1
irradiating a first excimer laser beam having a first energy density to an amorphous silicon layer including an oxidation layer thereon, to form a first polysilicon layer
Implementation Method 2
a hydrogen fluoride (HF) solution of about a 0.5% concentration may be coated on the first polysilicon layer including thereon the portions of the oxidation layer
Data Source
AI summary
A manufacturing method of a polysilicon layer of a thin film transistor of a display device, includes: irradiating a first excimer laser beam having a first energy density to an amorphous silicon layer including an oxidation layer thereon, to form a first polysilicon layer including thereon portions of the oxidation layer at grain boundaries of the first polysilicon layer; removing the portions of the oxidation layer at the grain boundaries of the first polysilicon layer; and irradiating a second excimer laser beam having a second energy density of 80% to 100% of the first energy density to the first polysilicon layer from which the portions of the oxidation layer at the grain boundaries thereof are removed, to form a second polysilicon layer as the polysilicon layer of the thin film transistor.