Low-Temperature Polysilicon Thin Film Transistor Impurity Diffusion
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Solution Overview
Problem
In the manufacturing of low temperature polysilicon thin films, substrate impurities diffuse into the silicon film during the annealing process, degrading the semiconductor characteristics and causing protrusions with high aspect ratios on the surface.
Innovation Solution
A method involving multiple diffusion barrier layers and an impurity collection layer is used to block substrate impurities, along with recrystallization growth spaces to reduce protrusion sizes, employing a bottom gate configuration and laser annealing to form polysilicon layers with improved semiconductor properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser annealing is used to recrystallize amorphous silicon into polysilicon, then the semiconductor characteristics are improved, but substrate impurities diffuse into the silicon film degrading the characteristics
Solution Approach 1:
A buffer layer is introduced between the substrate and the amorphous silicon layer to act as an intermediary barrier. This buffer layer prevents substrate impurities from diffusing into the silicon film during laser annealing, while still allowing the laser energy to effectively recrystallize the silicon into polysilicon with improved semiconductor characteristics.
Solution Approach 2:
The structure is segmented into distinct layers: substrate, buffer layer, amorphous silicon layer, and optionally additional barrier layers. This segmentation isolates the silicon film from direct contact with the substrate, preventing impurity diffusion while maintaining the beneficial effects of laser annealing.
2Reliability
If laser annealing is performed to form polysilicon, then electric conductivity is improved, but protrusions with high aspect ratios form on the surface
Solution Approach 1:
The buffer layer is designed with specific local properties - it has sufficient thickness and appropriate material composition to prevent impurity diffusion and control surface morphology during recrystallization. The buffer layer's local quality at the interface region prevents the formation of high aspect ratio protrusions while maintaining good electrical conductivity in the polysilicon layer.
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 reduces substrate impurity diffusion and protrusion sizes, achieving acceptable semiconductor characteristics and smaller aspect ratios for the polysilicon thin films, enhancing the performance and consistency of the thin film transistors.
Implementation Method 1
excimer laser annealing is utilized and the excimer laser is used as a heat source. The laser beam irradiates the amorphous silicon thin film to make the amorphous silicon recrystallize and transform into polysilicon structure
Implementation Method 2
not only the silicon film is heated, and the glass substrate below the silicon film also absorbs heat so its temperature raises. Accordingly, the impurities in the glass substrate diffuse into the silicon film
Implementation Method 3
the impurities in the glass substrate diffuse into the silicon film and degrade semiconductor characteristic of the silicon film
Data Source
AI summary
A method of manufacturing a low temperature polysilicon thin film includes: forming a buffer layer on a substrate; forming a gate electrode on the buffer layer; forming a patterned raising layer on the gate electrode, wherein the patterned raising layer covers a top surface and a lateral surface of the gate electrode; forming a first diffusion barrier layer on the patterned raising layer; forming a second diffusion barrier layer on the first diffusion barrier layer; forming a silicon layer on the second diffusion barrier layer; annealing the silicon layer to form a polysilicon layer, wherein the polysilicon layer includes a patterned area and a to-be-removed area, the patterned area has the same pattern with the patterned raising layer, and the patterned area is whole directly above the patterned raising layer; and in the polysilicon layer, removing the to-be-removed area, and keeping the patterned area.