Reflective Photomask Pattern Uniformity via Reflectivity Compensation
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Solution Overview
Problem
Reflective photomasks used in EUV lithography for semiconductor manufacturing face challenges in achieving high uniformity of pattern sizes due to variations in reflectivity distribution, which affects the accuracy and consistency of pattern transfer onto wafers.
Innovation Solution
A reflective photomask with a multilayer structure comprising alternately stacked molybdenum and silicon films, along with a cap layer, features recessed portions acting as mask patterns, where the size of these patterns is adjusted based on reflectivity distribution to ensure uniformity, using a method that involves calculating and adjusting the mask pattern sizes through reflectivity analysis and MEEF values to improve pattern transfer accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a reflective photomask with multilayer structure is used for EUV lithography, then pattern transfer capability is improved, but pattern size uniformity deteriorates due to reflectivity distribution variations
Solution Approach 1:
The patent applies local quality by making the mask pattern sizes location-dependent according to the reflectivity distribution. Specifically, mask patterns in regions with higher reflectivity are made smaller, while those in lower reflectivity regions are made larger, so that all patterns transfer to the wafer with uniform size despite the non-uniform reflectivity across the photomask blank.
Solution Approach 2:
The patent changes the parameter of mask pattern size based on the reflectivity distribution. By calculating the reflectivity at different locations and adjusting the mask pattern dimensions accordingly, the invention compensates for reflectivity variations and achieves uniform pattern transfer. This involves modifying the physical dimensions of mask patterns as a function of location-specific reflectivity values.
2Manufacturing precision
If mask pattern sizes are adjusted based on reflectivity distribution, then pattern uniformity is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by measuring the reflectivity distribution and calculating the required mask pattern size adjustments before actual mask manufacturing. The reflectivity is measured at multiple locations across the photomask blank, and the mask pattern dimensions are predetermined based on these measurements and the desired uniform pattern transfer, thereby simplifying the subsequent manufacturing process.
Solution Approach 2:
The patent uses a measured reflectivity distribution map as a template or copy to guide the mask pattern design. By creating a digital model of the reflectivity variations and using it to calculate compensating size adjustments, the invention translates the physical reflectivity characteristics into design parameters without requiring complex manual adjustments during manufacturing.
3Ease of manufacture
If photomask blanks with non-uniform reflectivity are used, then manufacturing cost is reduced, but pattern transfer accuracy deteriorates
Solution Approach 1:
The patent converts the harmful effect of non-uniform reflectivity into a beneficial design parameter. Instead of discarding photomask blanks with reflectivity variations, the invention measures and utilizes these variations to calculate appropriate mask pattern size adjustments. This transforms what was previously a defect into a useful piece of information that enables accurate pattern transfer, thereby allowing the use of less expensive, non-uniform blanks.
Solution Approach 2:
The patent implements feedback by measuring the actual reflectivity distribution of each photomask blank and using this measurement to adjust the mask pattern design. The reflectivity data feeds into the pattern size calculation, creating a closed-loop system where the actual properties of the blank determine the compensating design adjustments, ensuring accurate pattern transfer regardless of blank uniformity.
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
The solution enhances the uniformity of mask patterns transferred onto wafers, allowing for more accurate and consistent semiconductor manufacturing, while also enabling the use of photomask blanks with non-uniform reflectivity distributions, reducing costs and Turn Around Time in the manufacturing process.
Implementation Method 1
A reflective photomask used for the lithography in the extremely-short wavelength region comprises, for example, a multilayer film mirror, which includes alternately stacked molybdenum (Mo) layer and silicon (Si) layer
Implementation Method 2
a light-absorbing body
Data Source
AI summary
A reflective photomask includes a substrate and a reflective layer on the substrate. The reflective layer has a top surface opposite to the substrate and a reflectivity distribution on the top surface. The reflective layer includes mask patterns, the mask patterns having sizes depending on the reflectivity distribution. The mask patterns include a first pattern and a second pattern, the first pattern having a first space size smaller than a second space size of the second pattern. The first pattern is provided in a first region of the top surface, and the second pattern is provided in a second region of the top surface, wherein a reflectivity in the first region is lower than a reflectivity in the second region.