Crystallization Mask for Laser Annealing of Amorphous Silicon
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Solution Overview
Problem
Conventional methods for crystallizing amorphous silicon into polysilicon for thin film transistors (TFTs) face issues with non-uniform grain boundaries, leading to stress on the gate insulating layer and degrading the electrical characteristics of TFTs, particularly in display devices like LCDs and OLEDs.
Innovation Solution
A crystallization mask with adjustable laser illumination using transmissive and opaque areas, including first and second slits, is employed to control the energy distribution of the laser beam, allowing for sequential lateral solidification and recrystallization processes that adjust grain boundaries and reduce surface stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If eximer laser annealing is used to crystallize amorphous silicon into polysilicon, then crystallization speed is improved (30-200 nanoseconds), but grain boundary uniformity deteriorates causing non-uniform grain sizes and electrical characteristic variations
Solution Approach 1:
The invention segments the laser beam into multiple beams arranged in a matrix pattern, where each beam crystallizes a specific region. This segmentation allows independent control of each beam's crystallization process, enabling uniform grain boundary formation while maintaining fast crystallization speed through parallel processing of multiple regions simultaneously.
Solution Approach 2:
The invention uses a movable mask that can be dynamically positioned to control the sequence and pattern of laser beam exposure. By dynamically adjusting the mask position and the activation sequence of laser beams, the process achieves uniform grain growth while maintaining the speed advantage of laser annealing, resolving the contradiction between speed and precision.
2Manufacturing precision
If sequential lateral solidification with slit mask is used to improve grain boundary uniformity, then manufacturing precision is improved, but device complexity increases due to mask movement and positioning requirements
Solution Approach 1:
The invention segments the crystallization process into multiple independent laser beams that can be selectively activated without mask movement. Each beam corresponds to a specific region and can be controlled independently, eliminating the need for complex mask positioning mechanisms while maintaining uniform grain boundary formation through parallel processing.
Solution Approach 2:
The invention introduces a matrix of controllable laser beams as an intermediary between the light source and the amorphous silicon layer. This intermediary system allows precise control of crystallization in each region without requiring physical mask movement, simplifying the overall device structure while achieving the desired manufacturing precision.
3Reliability
If high energy laser illumination is used to achieve complete melting and crystallization, then crystallization effectiveness is improved, but surface stress increases damaging the gate insulating layer
Solution Approach 1:
The invention applies different energy levels to different regions through the matrix of laser beams. By controlling the activation and energy of individual beams, each region receives precisely the amount of energy needed for effective crystallization without excessive energy that would cause harmful surface stress, thus protecting the gate insulating layer while maintaining crystallization effectiveness.
Solution Approach 2:
Instead of applying high energy to the entire area simultaneously, the invention uses partial action by activating only the necessary number of laser beams in the matrix for each processing step. This prevents excessive total energy input that would generate harmful surface stress, while still achieving complete melting and crystallization in the targeted regions through sufficient local energy delivery.
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 solution effectively reduces surface stress and improves the uniformity of polysilicon grain growth, enhancing the electrical characteristics and reliability of TFTs in display devices.
Implementation Method 1
The technique irradiates light with the wavelength, which can be absorbed by amorphous silicon, from an eximer laser into an amorphous silicon layer deposited on a substrate to melt the amorphous silicon layer at 1,400℃, thereby crystallizing the amorphous silicon into polysilicon
Implementation Method 2
melt the amorphous silicon layer at 1,400℃
Implementation Method 3
crystallizing the amorphous silicon into polysilicon
Implementation Method 4
A crystallization mask with adjustable laser illumination using transmissive and opaque areas, including first and second slits, is employed to control the energy distribution of the laser beam
Implementation Method 5
The first slits may include translucent films and the second slits are openings
Data Source
AI summary
A crystallization mask for laser illumination for converting amorphous silicon into polysilicon is provided, which includes: a plurality of transmissive areas having a plurality of first slits for adjusting energy of the laser illumination passing through the mask; and an opaque area.