Half Tone Mask for Multi-Cycle Photolithography
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Solution Overview
Problem
Conventional photo masks are limited to single cycle photolithography processes and cannot achieve uniform patterning across larger dimensions, making them economically inefficient for multi-layer applications like TFT and CF in liquid crystal displays.
Innovation Solution
A half tone mask with a transparent substrate, a light shield layer, and light semitransmission portions that partially transmit light in a designated wavelength range, allowing for multiple photolithography cycles and uniform patterning without size limitations, fabricated using sequential photoresist layers and etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional photo mask with only light transmission portions and light shield portions is used, then the mask structure is simple, but it can only form one pattern layer and is limited to single cycle photolithography processes
Solution Approach 1:
The mask is segmented into three distinct functional layers: light transmission portions, light shield portions, and light semitransmission portions. This segmentation enables each layer to serve different purposes in multi-cycle photolithography processes, allowing the mask to form multiple pattern layers sequentially rather than being limited to a single cycle
Solution Approach 2:
The mask achieves multi-functionality by incorporating light semitransmission portions that can control light transmission in intermediate states. This universal design allows the same mask to be used across multiple photolithography cycles for forming different pattern layers (such as TFT and CF layers in LCD manufacturing), eliminating the need for separate masks for each cycle
2Productivity
If a gray tone mask with slit patterns is used to control light transmission, then multiple pattern layers can be formed, but the amount of light transmission is limited by the slit pattern design
Solution Approach 1:
Different portions of the mask are assigned different light transmission characteristics: light transmission portions for complete transmission, light shield portions for complete blocking, and light semitransmission portions for partial transmission. This local differentiation of quality allows precise control over light distribution for multiple pattern layers without being constrained by uniform slit pattern designs
Solution Approach 2:
The mask utilizes changes in the light transmission parameter by introducing light semitransmission portions with intermediate transmission characteristics. This parameter variation enables continuous control over the amount of light reaching different areas during multi-cycle photolithography, overcoming the binary transmission limitation of conventional gray tone masks
3Area of stationary object
If the mask size is increased beyond designated values, then larger display areas can be covered, but uniform patterning cannot be achieved
Solution Approach 1:
The invention addresses the size-uniformity contradiction by operating in a different dimensional space through the light semitransmission portions. These portions create intermediate light transmission zones that act as transition regions, allowing the mask to maintain uniform patterning control even when the overall mask area is enlarged beyond conventional limits
4Productivity
If multiple photolithography cycles are performed using conventional masks, then multiple pattern layers can be formed, but production time and costs increase
Solution Approach 1:
The mask merges multiple functional capabilities into a single structure, combining light transmission, light shielding, and intermediate light semitransmission portions. This merging enables the execution of multiple photolithography cycles using one mask instead of requiring separate masks for each cycle, thereby reducing production time and costs while maintaining the ability to form multiple pattern layers
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
Enables efficient and cost-effective multi-cycle photolithography processes, allowing for uniform patterning across various dimensions, reducing production time and costs, and facilitating the fabrication of flat panel displays.
Implementation Method 1
light semitransmission portions partially transmitting the irradiated light in the designated wavelength range
Implementation Method 2
forming light transmission portions for transmitting light and light shield portions for shielding light on the light shield layer by exposure, development, and etching
Data Source
AI summary
A half tone mask having a transparent substrate, a light semitransmission layer, and a light shield layer; and a method for fabricating the same. The halftone mask is applied to multiple cycles of a photolithography process, thus shortening a time taken to fabricate the mask and reducing the production costs of the mask. Since a desired pattern is uniformly formed through a light semitransmission layer of the half tone mask of the present invention according to the uniformity of a chrome oxide (CrxOy) film, i.e., the uniformity in sputtering, the halftone mask is not limited in size.