Thin Film Transistor Substrate Using Half Tone Mask Protective Layer
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Solution Overview
Problem
The manufacturing process of bottom gate thin film transistors often damages the active layer when forming source and drain electrodes, leading to back channel damage.
Innovation Solution
A method involving a photo-sensitive protective layer formed using a half tone mask during photolithography, which serves as an etching mask and stop layer to pattern the active layer, and optionally uses plasma ashing to expose portions of the active layer, improving electrical conductivity and reducing contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional photolithography with full-tone mask is used to pattern the active layer, then the manufacturing process is simple, but the source and drain electrodes damage the active layer causing back channel damage
Solution Approach 1:
The mask is segmented into three distinct regions: opaque region (for non-patterned areas), semi-transparent region (for recess formation), and transparent region (for patterned areas). This segmentation allows different portions of the photo-sensitive material layer to be differentially exposed, creating the photo-sensitive protective layer with recesses that prevents electrode damage to the active layer while maintaining process feasibility
Solution Approach 2:
The photo-sensitive protective layer with recesses is formed in advance before the source and drain electrode deposition. The recesses are pre-formed in the photo-sensitive protective layer at the locations where electrodes will be formed, so that when electrodes are deposited, they automatically align with the recesses and contact the active layer without causing back channel damage
2Reliability
If the photo-sensitive protective layer completely covers the active layer, then the active layer is protected from damage, but the source and drain electrodes cannot make good contact with the active layer
Solution Approach 1:
The photo-sensitive protective layer has non-uniform local properties: it is intact in some regions (providing protection) and has recesses in other regions (enabling electrode contact). The recesses are locally formed only at the source and drain electrode positions, allowing electrodes to contact the active layer through these localized openings while the rest of the active layer remains protected by the continuous photo-sensitive protective layer
3Reliability
If a half tone mask is used to form recesses in the photo-sensitive protective layer, then electrode contact with active layer is improved, but the manufacturing process complexity increases
Solution Approach 1:
The mask's optical parameters are changed by using a half tone mask instead of a full-tone mask. The half tone mask has semi-transparent regions with specific light transmission properties that allow controlled partial exposure of the photo-sensitive material layer. By adjusting the mask's optical density and exposure conditions, the recess depth and shape can be precisely controlled, improving electrical conductivity while maintaining manufacturing feasibility
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 method effectively forms electrodes without damaging the active layer, enhancing electrical conductivity and preventing undercut structures that could lead to poor contact, thus improving the reliability of thin film transistor substrates.
Implementation Method 1
performing a photolithography process on the photo-sensitive material layer by using a half tone mask to pattern the photo-sensitive material layer
Implementation Method 2
optionally uses plasma ashing to expose portions of the active layer
Data Source
AI summary
The invention provides a manufacturing method of a thin film transistor substrate including: sequentially forming a gate electrode, a gate insulating layer covering the gate electrode, an active material layer, and a photo-sensitive material layer on a first substrate; performing a photolithography process by using a half tone mask to form a protective layer which is above the gate electrode and has a first recess and a second recess; wet etching the active material layer by using the protective layer as a mask to form an active layer; removing a portion of the protective layer at bottoms of the first recess and the second recess to expose a first portion and a second portion of the active layer respectively; forming a first electrode connecting to the first portion; and forming a second electrode connecting to the second portion.