Thin Film Transistor Substrate Fabrication via Multi-Tone Mask Patterning
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Solution Overview
Problem
Current methods for fabricating thin film transistor substrates using multi-tone masks in four-photomask or three-photomask processes face issues with yield reduction due to the insolubility of transparent conductive layers in photoresist-stripping agents, leading to clogged equipment and increased costs.
Innovation Solution
A method involving the use of a multi-tone mask with different light transmittance regions to pattern photoresist layers, allowing for etching of passivation, ohmic contact metal, doped semiconductor, and insulating films, forming channels and contact holes without the need for lift-off processes, thereby reducing contamination and equipment clogging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a multi-tone mask is used in four-photomask or three-photomask processes to reduce the number of photomasks, then production costs are reduced, but yield is reduced due to clogged equipment from insoluble transparent conductive layers
Solution Approach 1:
The patent extracts and removes the transparent conductive layer using a selective etching process before photoresist stripping. This extraction eliminates the source of contamination that causes equipment clogging, thereby maintaining high yield while enabling the use of multi-tone masks for cost reduction.
Solution Approach 2:
The patent performs preliminary etching of the transparent conductive layer before the photoresist stripping step. This preliminary action prevents the accumulation of insoluble material that would otherwise clog equipment during subsequent processing, ensuring continuous production and high yield.
2Device complexity
If a multi-tone mask is used to pattern photoresist layers for etching, then the number of photomasks is reduced, but equipment becomes clogged and service life of photoresist-stripping agents decreases
Solution Approach 1:
The transparent conductive layer is extracted and removed before photoresist stripping. This extraction eliminates the contaminant that would otherwise accumulate in photoresist-stripping agents, preventing equipment clogging and extending the service life of these chemical agents.
Solution Approach 2:
The etching of the transparent conductive layer is performed as a preliminary action before photoresist stripping. This timing ensures that no insoluble material remains to contaminate the photoresist-stripping agents, thereby extending their usable life and reducing operational costs.
3Manufacturing precision
If lift-off processes are used with multi-tone masks, then patterning is achieved, but contamination increases and yield decreases
Solution Approach 1:
The transparent conductive layer is extracted through selective etching before lift-off processing. This extraction removes the material that would otherwise cause contamination during lift-off, thereby reducing harmful factors while maintaining patterning accuracy.
Solution Approach 2:
The etching of the transparent conductive layer is performed as a preliminary action before lift-off. This preliminary removal of contaminant material prevents contamination issues during the subsequent lift-off process, maintaining both precision and cleanliness.
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 enhances the yield of thin film transistor substrates by preventing contamination and extending the service life of photoresist-stripping agents, while reducing the number of photomasks required, thus lowering production costs.
Implementation Method 1
disposing a multi-tone mask over the second photoresist layer, followed by performing a lithography process to form the second photoresist layer into a patterned photoresist
Implementation Method 2
performing etching using the patterned photoresist so that a portion of each of the passivation film, the ohmic contact metal film, the doped semiconductor layer, the active semiconductor layer, and the insulating film
Data Source
AI summary
A method for fabricating a thin film transistor substrate includes: (a) forming a gate electrode on a substrate using a first photoresist layer; (b) forming an insulating film, an active semiconductor layer, a doped semiconductor layer, an ohmic contact metal film, a passivation film, and a second photoresist layer on the substrate to cover the gate electrode; (c) disposing a multi-tone mask over the second photoresist layer, followed by performing a lithography process to form the second photoresist layer into a patterned photoresist, which has different thicknesses at a location corresponding in position to the gate electrode and on two opposite sides of the location; and (d) performing etching using the patterned photoresist.