Amorphous Silicon Dehydrogenation for Uniform Polysilicon TFTs
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Solution Overview
Problem
The manufacturing process of thin film transistors for organic light emitting display devices faces issues with film characteristic deterioration due to hydrogen evaporation during the crystallization of amorphous silicon layers, leading to non-uniform polysilicon layers and degraded device characteristics, which result in uneven brightness and striped stains in the display.
Innovation Solution
A method is introduced to control the oxygen content in the dehydrogenation chamber to minimize the adsorption of oxygen and hetero elements on the amorphous silicon layer, ensuring a uniform crystallization process and reducing surface roughness, achieved by injecting an oxygen content control gas and exhausting oxygen to maintain a predetermined oxygen level, typically 100 ppm or less, during the dehydrogenation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the amorphous silicon layer is formed using PECVD method, then the processing speed is enhanced and cost is lowered, but hydrogen is contained in the amorphous silicon layer which evaporates during crystallization causing surface roughness and film characteristic deterioration
Solution Approach 1:
The patent applies preliminary dehydrogenation treatment to the amorphous silicon layer before laser crystallization. By removing hydrogen in advance through heating treatment at 400-450°C in a nitrogen atmosphere, the subsequent crystallization process produces a polysilicon layer with uniform surface characteristics and prevents hydrogen-related defects, thus resolving the contradiction between fast PECVD processing and film quality.
Solution Approach 2:
The patent uses a nitrogen atmosphere during the dehydrogenation process to prevent oxidation of the silicon layer while allowing hydrogen to be removed. The inert nitrogen environment protects the amorphous silicon layer from reacting with oxygen at elevated temperatures, enabling effective dehydrogenation without compromising the layer's integrity or introducing new contaminants.
2Reliability
If dehydrogenation process is performed by heating in normal pressure environment, then hydrogen is removed from amorphous silicon layer, but various hetero elements are adsorbed onto the surface of amorphous silicon layer causing non-uniform crystallization
Solution Approach 1:
The patent performs dehydrogenation in a nitrogen-filled chamber instead of normal pressure environment. The nitrogen atmosphere prevents adsorption of hetero elements (oxygen, water vapor, etc.) onto the silicon layer surface during heating, while still allowing hydrogen to be effectively removed. This ensures both hydrogen removal efficiency and prevents surface contamination that would cause non-uniform crystallization.
Solution Approach 2:
Nitrogen gas acts as an intermediary atmosphere during dehydrogenation. It mediates between the need to remove hydrogen (which requires heating) and the need to prevent surface contamination. The nitrogen environment allows thermal energy to remove hydrogen while blocking harmful hetero elements from adsorbing onto the silicon surface.
3Device complexity
If oxygen content in dehydrogenation chamber is not controlled, then the process is simple, but oxygen and hetero elements are adsorbed on amorphous silicon layer surface interrupting crystallization and degrading film characteristic
Solution Approach 1:
The patent controls the oxygen content in the dehydrogenation chamber by maintaining a nitrogen atmosphere with oxygen content of 100 ppm or less. This controlled inert environment prevents oxygen and other hetero elements from adsorbing onto the amorphous silicon layer surface during heating, ensuring uniform crystallization and smooth polysilicon layer formation without significantly complicating the process.
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 results in a polysilicon layer with low surface roughness and uniform silicon crystal grains, enhancing the device characteristics of thin film transistors, ensuring precise driving current supply to organic light emitting diodes and reducing striped stains, thereby improving the overall display quality.
Implementation Method 1
Hydrogen has a high vapor pressure, so that the hydrogen may easily evaporate... heating the inside of the chamber to perform a dehydrogenation process on the amorphous silicon layer
Implementation Method 2
forming a polysilicon layer by crystallizing the amorphous silicon layer using a laser... uniform silicon crystal grains
Implementation Method 3
injecting an oxygen content control gas and exhausting oxygen to maintain a predetermined oxygen level... reducing a content of oxygen in a chamber for performing a dehydrogenation process
Data Source
AI summary
Provided are a method of manufacturing a thin film transistor, a dehydrogenating apparatus for performing the method, and an organic light emitting display device including a thin film transistor manufactured by the same. A method of manufacturing a thin film transistor includes reducing a content of oxygen in a chamber for performing a dehydrogenation process of an amorphous silicon layer from a first value to a second value, inserting a substrate on which the amorphous silicon layer is formed into the chamber, heating the inside of the chamber to perform the dehydrogenation process on the amorphous silicon layer, and forming a polysilicon layer by crystallizing the amorphous silicon layer using a laser.