Multi-Tone Mask Resist Thickness Control for Semiconductor Devices
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Solution Overview
Problem
The existing methods for manufacturing semiconductor devices, particularly transistors for active matrix liquid crystal display devices, require a large number of photolithography steps, leading to increased costs and potential yield reduction due to complex techniques like backside light exposure or lift-off methods, which often compromise the electric characteristics of transistors.
Innovation Solution
The use of a multi-tone mask in conjunction with plasma treatment to reduce the number of photolithography steps by forming resist masks with varying thicknesses, allowing for the simultaneous formation of gate electrodes, channel regions, and protective films using fewer photomasks, thereby reducing the complexity and cost of the manufacturing process while maintaining high display quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photolithography methods with multiple photomasks are used, then manufacturing precision is maintained, but the number of photolithography steps increases leading to higher costs and reduced productivity
Solution Approach 1:
The patent segments the photomask into multiple regions with different light transmission characteristics (transparent regions, semi-transparent regions, and opaque regions). This segmentation allows different portions of the resist to receive different amounts of light, creating multiple resist thickness levels from a single exposure step, thereby reducing the number of photolithography steps required
Solution Approach 2:
The patent applies local quality by creating regions with different light transmission properties within the same photomask. The semi-transparent regions allow partial light transmission to create intermediate resist thicknesses, while transparent regions allow full transmission for maximum thickness. This local variation in optical properties enables precise control over resist thickness distribution across different areas of the substrate
2Device complexity
If complex techniques like backside light exposure or lift-off method are used to reduce photolithography steps, then the number of photolithography steps decreases, but device complexity increases and yield reduces
Solution Approach 1:
The patent replaces complex mechanical processes (backside light exposure, lift-off methods) with a simpler optical approach using a multi-region photomask. The solution substitutes sophisticated mechanical manipulation of light and resist with a straightforward single-step photolithography process that uses optical property variations in the photomask to achieve the desired resist thickness patterns
Solution Approach 2:
The patent changes the optical parameters of the photomask by creating regions with different light transmission characteristics. By varying the light transmission parameter across different regions of the photomask, the process achieves multiple resist thickness levels without requiring multiple exposure steps or complex processing techniques
3Reliability
If more photomasks are used to maintain transistor characteristics, then electric characteristics are preserved, but production cost increases
Solution Approach 1:
The patent merges multiple photolithography steps into a single step by combining multiple functional regions (transparent, semi-transparent, and opaque regions) into one photomask. This consolidation allows the simultaneous formation of multiple transistor components with different resist thickness requirements in a single exposure and development process, thereby reducing the total number of photomasks needed and lowering production 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 allows for the manufacture of transistors with high display quality using fewer photomasks, reducing production costs and minimizing the impact on electric characteristics, while also reducing parasitic capacitance and enhancing the aperture ratio of the display device.
Implementation Method 1
a resist mask is formed thereover by performing light exposure with the use of a first photomask which is a multi-tone mask and development. The thickness of a resist remaining in each region after development can be controlled by the amount of transmitting light
Implementation Method 2
the resist mask is made to recede by plasma treatment such as ashing and the region of the resist mask with smaller thickness is removed
Data Source
AI summary
A conductive film to be a gate electrode, a first insulating film to be a gate insulating film, a semiconductor film in which a channel region is formed, and a second insulating film to be a channel protective film are successively formed. With the use of a resist mask formed by performing light exposure with the use of a photomask which is a multi-tone mask and development, i) in a region without the resist mask, the second insulating film, the semiconductor film, the first insulating film, and the conductive film are successively etched, ii) the resist mask is made to recede by ashing or the like and only the region of the resist mask with small thickness is removed, so that part of the second insulating film is exposed, and iii) the exposed part of the second insulating film is etched, so that a pair of opening portions is formed.