Low-Temperature Polysilicon Thin Film Impurity Barrier Interface
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Solution Overview
Problem
In the manufacturing of low temperature polysilicon thin films for liquid crystal display devices, substrate impurities diffuse into the silicon film during the annealing process, degrading the semiconductor characteristics and causing protrusions on the surface, which affect the performance of the thin film transistors.
Innovation Solution
A method involving the formation of a substrate impurity barrier interface between two silicon layers, where the second silicon layer is thicker than the first, and an impurity collection layer is used to trap substrate impurities, along with surface roughening and recrystallization growth spaces to reduce impurity diffusion and protrusion size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser annealing is used to transform amorphous silicon into polysilicon, then the semiconductor characteristics are improved, but substrate impurities diffuse into the silicon film degrading its characteristics
Solution Approach 1:
The silicon film is divided into multiple layers (first silicon layer, second silicon layer, third silicon layer) with different thicknesses and impurity concentrations. The first silicon layer (thinner, higher impurity concentration) acts as a sacrificial barrier that absorbs diffusing impurities, while the second silicon layer (thicker, lower impurity concentration) maintains good semiconductor characteristics. This segmentation allows the system to tolerate impurity diffusion in one layer while protecting the functional layers.
Solution Approach 2:
The first silicon layer serves as an intermediary barrier between the substrate and the second silicon layer. It intercepts and absorbs the impurities diffusing from the substrate during laser annealing, preventing them from reaching and degrading the semiconductor characteristics of the second silicon layer. The buffer layer also acts as an intermediary by providing a transition zone with controlled impurity absorption.
2Reliability
If the entire silicon film is made thick to maintain semiconductor characteristics, then impurity diffusion is reduced, but surface protrusions become larger affecting transistor performance
Solution Approach 1:
Different regions of the silicon film structure are assigned different thicknesses and impurity concentrations based on their specific functions. The first silicon layer near the substrate is thinner and has higher impurity concentration to absorb impurities. The second silicon layer in the middle is thicker with lower impurity concentration to maintain semiconductor characteristics. The third silicon layer at the surface is thinner to minimize surface protrusions. This local differentiation optimizes both impurity resistance and surface quality.
Solution Approach 2:
The solution moves from a single-dimensional (uniform thickness) to a multi-dimensional (layered structure with varying thicknesses) approach. By introducing vertical layering with different thicknesses and impurity concentrations, the patent simultaneously addresses impurity diffusion resistance and surface protrusion control that cannot be achieved with a uniform film structure.
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 effectively blocks substrate impurities from diffusing into the upper silicon layer, maintaining acceptable semiconductor characteristics and significantly reducing the size of surface protrusions, thereby improving the performance and uniformity of the low temperature polysilicon 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
forming a substrate impurity barrier interface between the first silicon layer and the second silicon layer, wherein the second silicon layer is thicker than the first silicon layer
Implementation Method 4
The laser beam irradiates the amorphous silicon thin film to make the amorphous silicon recrystallize and transform into polysilicon structure
Data Source
AI summary
A method of manufacturing a low temperature polysilicon thin film includes: forming a buffer layer on a substrate; forming a first silicon layer on the buffer layer; forming a second silicon layer on the first silicon layer, and forming a substrate impurity barrier interface between the first silicon layer and the second silicon layer, wherein the second silicon layer is thicker than the first silicon layer; and annealing the first silicon layer and the second silicon layer to form a polysilicon layer.