Multi-tone Mask Photolithography for Oxide Semiconductor TFTs
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Solution Overview
Problem
The manufacturing process of thin film transistors using oxide semiconductors is complex and costly due to the need for multiple light-exposure masks in photolithography, which affects productivity and yield.
Innovation Solution
A method is developed to simplify the photolithography process by using a multi-tone mask that reduces the number of light-exposure masks required, employing a chlorine-based gas for etching, and forming In-Ga-Zn-O-based non-single-crystal films with a sputtering method at lower temperatures, achieving higher field effect mobility and simpler processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a photolithography process using multiple light-exposure masks is used to manufacture thin film transistors, then the manufacturing precision and pattern definition are improved, but the device complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent combines multiple light-exposure masks into a single multi-tone mask that can define multiple patterns simultaneously. This multi-tone mask contains different transmittance regions (first tone and second tone) that correspond to different threshold voltage requirements, allowing the formation of both high-threshold and low-threshold transistor regions in one exposure step, thereby reducing the total number of masks needed
Solution Approach 2:
The multi-tone mask serves multiple functions: it defines the gate electrode pattern, defines the source and drain electrode patterns, and differentiates between high-threshold and low-threshold transistor regions all in a single component. This universal mask replaces what would traditionally require multiple separate masks, simplifying the overall manufacturing process
2Manufacturing precision
If multiple light-exposure masks are used in the photolithography process, then the pattern definition is improved, but the productivity decreases due to increased process steps
Solution Approach 1:
The patent merges multiple sequential photolithography steps into a single parallel process by using a multi-tone mask that can define multiple different patterns simultaneously during one light exposure. This eliminates the need for multiple sequential mask alignment and exposure steps, directly increasing manufacturing throughput while maintaining precise pattern definition
Solution Approach 2:
The multi-tone mask is designed in advance with predetermined transmittance regions that correspond to the required pattern definitions. The different tone regions are pre-configured to create the appropriate threshold voltage characteristics, eliminating the need for multiple sequential patterning steps and accelerating the manufacturing process
3Manufacturing precision
If conventional photolithography with multiple masks is used, then the manufacturing precision is maintained, but the manufacturing cost increases due to mask design and fabrication expenses
Solution Approach 1:
The patent consolidates multiple expensive light-exposure masks into a single multi-tone mask, thereby reducing the total cost of mask design, fabrication, and inventory management. While the multi-tone mask itself is complex, it replaces multiple simpler masks, and the cost savings from eliminating redundant mask sets and alignment procedures outweigh the increased cost of the single multi-functional mask
Solution Approach 2:
The multi-tone mask is designed to perform multiple patterning functions simultaneously, making it a universal tool that replaces several specialized masks. This universal mask approach reduces the overall tooling cost by eliminating the need for multiple mask designs, each requiring separate fabrication and validation processes
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 results in a cost-effective and high-productivity semiconductor device with improved electrical characteristics, such as an on/off ratio of 10^9 and mobility of 10 or more, while reducing the complexity and cost of the manufacturing process.
Implementation Method 1
An oxide semiconductor film can be formed at temperatures of 300 °C or lower by a sputtering method or the like
Implementation Method 2
employing a chlorine-based gas for etching
Data Source
Figure 1A~1E
Figure 2A1~2A2
Figure 3A~3E
AI summary
In a method for manufacturing a semiconductor device including a channel-etched inverted-staggered thin film transistor, an oxide semiconductor film and a conductive film are etched using a mask layer formed with the use of a multi-tone mask which is a light-exposure mask through which light is transmitted so as to have a plurality of intensities. The etching step is performed by dry etching in which an etching gas is used.