Multi-Tone Mask for Semiconductor Device Manufacturing
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Solution Overview
Problem
The existing manufacturing processes for thin film transistors, particularly those using oxide semiconductors, are costly and complex due to the need for multiple light-exposure masks in photolithography, which increases production costs and reduces productivity.
Innovation Solution
The use of a multi-tone mask that allows for multiple intensities of light transmission, reducing the number of masks required and simplifying the photolithography process through wet etching with a mixed solution of phosphoric acid, acetic acid, and nitric acid or an ammonia hydrogen peroxide mixture, enabling the formation of inverted staggered thin film transistors with an In--Ga--Zn--O based non-single-crystal film.
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 manufacturing precision can be maintained, but device complexity and manufacturing cost increase significantly
Solution Approach 1:
Multiple light-exposure masks are merged into a single multi-tone mask that can create multiple pattern levels simultaneously. The multi-tone mask contains regions with different light transmittance (first, second, and third regions) that correspond to different etching depths, allowing one mask to replace what previously required multiple masks and multiple exposure steps.
Solution Approach 2:
The multi-tone mask serves multiple functions in a single component: it defines different pattern regions (island-shaped, L-shaped, U-shaped), controls etching depth variations, and creates multiple mask layers through a single exposure process. This universal mask handles what previously required several specialized masks.
2Manufacturing precision
If multiple light-exposure masks are used in the photolithography process, then pattern definition accuracy is improved, but productivity decreases due to increased process steps
Solution Approach 1:
The multi-tone mask is prepared in advance with pre-defined regions of different light transmittance (first region with highest transmittance, second region with intermediate transmittance, third region with lowest transmittance). This preliminary structuring of the mask allows all pattern variations to be created in a single exposure step, eliminating the need for sequential mask changes and multiple exposure operations.
Solution Approach 2:
Multiple photolithography steps that were previously required for different pattern levels are merged into a single exposure step using the multi-tone mask. The single mask simultaneously exposes all regions with appropriate light intensities, reducing the process from multiple sequential steps to one concurrent step.
3Reliability
If conventional photolithography with multiple masks is used, then process control is maintained, but manufacturing cost increases due to mask design and fabrication expenses
Solution Approach 1:
The complex and expensive multi-mask system is extracted and replaced with a single multi-tone mask. By removing the need for multiple separate mask designs, fabrications, and alignments, the overall manufacturing cost is reduced while the essential process control is maintained through the integrated multi-tone mask design.
Solution Approach 2:
The mask design parameter changes from multiple binary masks to a single multi-tone mask with continuous or discrete light transmittance variations. This parameter change allows the mask to encode multiple pattern levels through light intensity modulation rather than requiring multiple physical masks, reducing material and fabrication costs.
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 lowers manufacturing costs and enhances productivity by reducing the complexity of the photolithography process, achieving high field effect mobility and on/off ratios in thin film transistors while maintaining high conductivity and stability.
Implementation Method 1
a mask layer formed using a multi-tone mask (also called as a high-tone mask) which is a light-exposure mask through which light is transmitted so as to have a plurality of intensities
Implementation Method 2
Each of the first and second etching steps is performed by wet etching in which an etching solution is used
Implementation Method 3
An oxide semiconductor film can be formed at temperatures of 300° C. or lower by a sputtering method
Data Source
AI summary
An object is to manufacture a semiconductor device including an oxide semiconductor at low cost with high productivity in such a manner that a photolithography process is simplified by reducing the number of light-exposure masks. In a method for manufacturing a semiconductor device including a channel-etched inverted-stagger 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 wet etching in which an etching solution is used.