Polysilicon Film Surface Smoothing via Step-and-Repeat Laser
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Solution Overview
Problem
Conventional laser annealing methods for converting amorphous silicon to polysilicon films result in surface roughness, affecting the electrical reliability and uniformity of devices like MOS and TFT devices.
Innovation Solution
A method involving a lateral growth and step-and-repeat laser process where the substrate is moved in a predetermined step distance after each laser shot to melt and crystallize amorphous silicon, forming polysilicon with lateral growth crystal grains and nano-trenches, reducing surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional laser annealing methods are used to convert amorphous silicon to polysilicon, then the conversion process is achieved, but surface roughness increases due to protrusion formation
Solution Approach 1:
The laser beam is divided into multiple segments (first laser beam and second laser beam) with different functions. The first laser beam performs complete melting and crystallization to form polysilicon, while the second laser beam performs selective remelting to eliminate protrusions. This segmentation allows each beam to be optimized for its specific purpose, resolving the contradiction between achieving conversion and maintaining surface smoothness.
Solution Approach 2:
The invention changes the parameters of the laser processing by using two different laser beams with different characteristics. The first laser beam uses parameters optimized for complete melting (higher energy density), while the second laser beam uses parameters optimized for selective remelting (lower energy density). This parameter change enables the system to first achieve conversion and then improve surface quality, resolving the contradiction between conversion effectiveness and surface smoothness.
2Manufacturing precision
If conventional laser annealing methods are used, then polysilicon conversion is achieved, but electrical uniformity deteriorates due to surface roughness
Solution Approach 1:
The laser processing is segmented into two distinct stages performed by different laser beams. The first stage creates the polysilicon structure, while the second stage refines the surface by removing protrusions. This segmentation ensures that electrical uniformity is established in the first stage and then preserved and enhanced in the second stage, resolving the contradiction between manufacturing precision and reliability.
Solution Approach 2:
The first laser beam performs a preliminary action of complete melting and crystallization to establish the polysilicon structure and initial electrical properties. The second laser beam then performs a follow-up action to refine the surface and eliminate defects. This preliminary action ensures that the base structure is sound before surface refinement, resolving the contradiction between electrical uniformity and reliability.
3Manufacturing precision
If a single high-energy laser beam is used for complete melting, then polysilicon conversion is achieved, but surface protrusions are formed
Solution Approach 1:
The single high-energy laser beam is segmented into two functional beams: the first laser beam that performs complete melting for thorough conversion, and the second laser beam that performs selective remelting to flatten the surface. This segmentation allows the system to achieve both complete conversion and surface flatness by assigning different functions to different beam segments.
Solution Approach 2:
The laser parameters are changed between the two beams: the first beam uses high energy density parameters to achieve complete melting and conversion, while the second beam uses lower energy density parameters to selectively remelt only the protrusions. This parameter change enables the system to achieve complete conversion without permanent surface deformation, resolving the contradiction between conversion completeness and surface flatness.
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 produces a polysilicon film with reduced surface roughness, improving the electrical reliability and uniformity of devices, as evidenced by increased mobility and smoother surfaces compared to conventional methods.
Implementation Method 1
a first irradiation area of the substrate is irradiated by a first laser shot with sufficient energy to melt the amorphous silicon in the first irradiation area
Implementation Method 2
melt the amorphous silicon in the first irradiation area
Implementation Method 3
whereupon the melted amorphous silicon crystallizes to form polysilicon
Implementation Method 4
The invention achieves this object of the invention by providing a method for forming a polysilicon layer... by using a lateral growth and step-and-repeat laser process
Data Source
AI summary
A method of forming a polysilicon film having smooth surface using a lateral growth and a step-and-repeat laser process. Amorphous silicon formed in a first irradiation region of a substrate is crystallized to form a first polysilicon region by a first laser shot. Then, the substrate is moved a predetermined distance, and irradiated by a second laser shot. The polysilicon region is then recrystallized and locally planarized by subsequent laser shots. After multiple repetitions of the irradiation procedure, the amorphous silicon film formed on a substrate is completely transformed into a polysilicon film. The polysilicon film includes lateral growth crystal grains and nano-trenches formed in parallel on the surface of the polysilicon film. A longitudinal direction of the nano-trenches is substantially perpendicular to a lateral growth direction of the crystal grains.