Phase Shift Mask Lift-Off Fabrication for Uniformity
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Solution Overview
Problem
Conventional phase shift masks suffer from non-uniform thickness of the phase shift layer due to etching processes, leading to poor yield and increased fabrication costs, and have more complex fabrication processes compared to binary masks.
Innovation Solution
The use of a lift-off process to form the phase shift layer, which reduces the complexity and non-uniformity issues associated with etching, and includes a mask structure with a transparent substrate, semi-transparent layer, and film layer to achieve improved light transmittance and phase angle uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an etching process is used to define the phase shift layer pattern, then the phase shift mask can be fabricated, but the etching process causes non-uniform thickness of the phase shift layer, resulting in poor yield
Solution Approach 1:
Instead of using etching to remove material and define the phase shift layer pattern (which causes non-uniform thickness), the patent inverts the approach by using a lift-off process. A sacrificial layer is deposited first, then the phase shift layer is deposited on top, and finally the sacrificial layer is removed from specific regions, causing the phase shift layer to lift off and be removed. This inversion of the conventional approach achieves uniform thickness while defining the pattern.
Solution Approach 2:
The patent applies preliminary action by first depositing a sacrificial layer (such as chromium or molybdenum) before depositing the phase shift layer. This sacrificial layer serves as a temporary foundation that enables uniform deposition of the phase shift layer. The sacrificial layer is then selectively removed in a subsequent step, causing the phase shift layer to lift off and be removed from those regions, achieving the desired pattern with uniform thickness.
2Measurement precision
If a phase shift layer is formed over the binary mask using conventional fabrication processes, then the resolution is improved, but the fabrication process becomes more complex with more steps, increasing the probability of defects and fabrication cost
Solution Approach 1:
The patent merges multiple fabrication steps into a more streamlined process. By using the lift-off approach, the formation of the phase shift layer pattern is combined with the deposition process itself, rather than requiring separate etching steps. This reduces the total number of process steps while maintaining the resolution benefits of the phase shift mask.
Solution Approach 2:
The patent extracts the problematic etching step from the fabrication process and replaces it with the lift-off approach. By removing the etching process entirely and using only deposition and sacrificial layer removal, the fabrication process becomes less complex while still achieving the desired phase shift layer pattern formation.
3Illumination intensity
If a phase shift layer is formed over the binary mask, then the light transmittance and phase angle can be controlled, but the non-uniform etching results in different transmittance and phase angle at different positions, reducing yield
Solution Approach 1:
The patent inverts the conventional approach of etching to define the phase shift layer pattern. By using deposition followed by lift-off, the phase shift layer is formed with uniform thickness across all positions. This ensures that light transmittance and phase angle are consistent throughout the mask, eliminating the variability caused by non-uniform etching and improving process yield.
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 improved precision and yield for photoresist patterns, reduced fabrication costs, and enhanced uniformity in light transmittance and phase angle, making the process more efficient and cost-effective.
Implementation Method 1
the only different between the light passing the phase shift layer and the light without passing the phase shift layer is the phase difference
Implementation Method 2
the transmittance at the third region is less than the transmittance at the second region
Data Source
AI summary
A mask including a transparent substrate, a semi-transparent layer and a film layer is provided. The transparent substrate at least has a first region, a second region and a third region. The semi-transparent layer covers the second region and the third region of the transparent substrate and exposes the first region. The film layer covers the halftone layer disposed at the third region, to make the transmittance of the third region lower than that of the second region. The halftone layer and the film can be made of phase shift layers, to form a phase shift mask. Besides, several fabrication methods of the mask are also disclosed to form the above-mentioned mask.