Selective Laser Crystallization of Amorphous Semiconductor Films
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Solution Overview
Problem
Current methods for integrating drive and pixel TFTs in liquid crystal displays face challenges such as high manufacturing costs and display unevenness due to the need for precise positional accuracy in laser irradiation for crystallizing amorphous silicon to polycrystalline silicon, which is difficult to achieve, especially in small displays with complex layouts.
Innovation Solution
A method involving the formation of a gate electrode and gate insulating film on a transparent substrate, followed by an amorphous semiconductor film, a light-transmissive insulating film, and a metal film with openings, where laser light is used to selectively crystallize the amorphous semiconductor film through the light-transmissive film, allowing for high-accuracy conversion of amorphous to crystalline silicon in specific regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser irradiation is used to convert amorphous silicon to polycrystalline silicon in drive circuit regions, then drive capability is improved, but manufacturing precision deteriorates due to difficulty in achieving precise positional accuracy
Solution Approach 1:
A light-transmissive insulating film is introduced as an intermediary layer between the amorphous silicon film and the metal mask. This film has a refractive index higher than air, enabling effective laser light absorption in the amorphous silicon film while allowing the metal mask to function as a precise light-shielding pattern formation film. The intermediary film resolves the contradiction by facilitating laser crystallization without requiring direct contact between laser and substrate, thereby achieving both drive capability improvement and manufacturing precision.
Solution Approach 2:
The refractive index parameter of the medium between the laser source and the amorphous silicon film is changed from air to a light-transmissive insulating film with higher refractive index. This parameter change enhances laser light absorption efficiency in the amorphous silicon film, enabling effective crystallization with lower laser power and improved positional accuracy, thus resolving the technical contradiction.
2Speed
If polycrystalline silicon TFT is used for both pixel TFT and drive TFT, then drive speed is improved, but display unevenness occurs due to characteristic variations and leak current
Solution Approach 1:
The invention applies local quality by using different semiconductor material types in different regions: polycrystalline silicon is formed only in drive circuit regions where high drive speed is required, while amorphous silicon is maintained in pixel regions where uniformity is critical. The light-transmissive insulating film with metal mask patterning enables selective local crystallization, allowing each region to have optimized characteristics for its specific function.
3Adaptability or versatility
If amorphous silicon is converted to polycrystalline silicon only in drive circuit regions, then different TFT characteristics are achieved, but manufacturing cost increases due to complex manufacturing management
Solution Approach 1:
The invention merges the light-transmissive insulating film formation process with existing manufacturing steps, combining multiple functions into a single layer. The metal mask is formed using standard photolithography techniques already present in the manufacturing line. This integration approach enables selective crystallization without adding significant manufacturing complexity or cost, resolving the contradiction between adaptability and ease of manufacture.
4Manufacturing precision
If laser irradiation position is precisely aligned with drive circuit region, then selective crystallization is achieved, but productivity deteriorates due to repeated movement and alignment operations
Solution Approach 1:
The light-transmissive insulating film and metal mask pattern are formed in advance during the standard manufacturing process, before laser irradiation. This preliminary action creates a pre-configured light-shielding pattern that guides laser irradiation, eliminating the need for complex real-time alignment operations and repeated substrate movement, thus resolving the contradiction between manufacturing precision and productivity.
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 enables the selective crystallization of semiconductor films with high accuracy, allowing for the close arrangement of drive and pixel TFTs, reducing manufacturing costs and display unevenness, while maintaining productivity and reducing the frame region dimensions in liquid crystal displays.
Implementation Method 1
irradiating laser light onto both a region of the light-transmissive insulating film exposed by the opening and the metal film, which is used as a mask for shielding the laser light; and performing laser annealing to make the laser light to be absorbed through the light-transmissive insulating film into a region of the amorphous semiconductor film exposed by the opening, so that the amorphous semiconductor film is heated and converted to a crystalline semiconductor film
Implementation Method 2
performing laser annealing to make the laser light to be absorbed through the light-transmissive insulating film into a region of the amorphous semiconductor film
Implementation Method 3
a metal film having an opening on the light-transmissive insulating film; irradiating laser light onto both a region of the light-transmissive insulating film exposed by the opening and the metal film, which is used as a mask for shielding the laser light
Implementation Method 4
performing laser annealing to make the laser light to be absorbed through the light-transmissive insulating film into a region of the amorphous semiconductor film exposed by the opening, so that the amorphous semiconductor film is heated and converted to a crystalline semiconductor film
Implementation Method 5
the amorphous semiconductor film is heated and converted to a crystalline semiconductor film
Data Source
AI summary
A method of crystallizing an amorphous semiconductor film, the method comprising the steps of: forming a gate electrode on a transparent insulating substrate; forming a gate insulating film on the transparent insulating substrate and on an upper part of the gate electrode; forming an amorphous semiconductor film on the gate insulating film; forming a light-transmissive insulating film on the amorphous semiconductor film; forming a metal film having an opening on the light-transmissive insulating film; irradiating laser light onto both a region of the light-transmissive insulating film exposed by the opening and the metal film, which is used as a mask for shielding the laser light; and performing laser annealing to make the laser light to be absorbed through the light-transmissive insulating film into a region of the amorphous semiconductor film exposed by the opening, so that the amorphous semiconductor film is heated and converted to a crystalline semiconductor film.