EUV Photomask Black Border Surface Morphology
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Solution Overview
Problem
Current EUV photomasks suffer from reflectivity issues, causing radiation overlap and critical dimension drops due to incomplete absorption of EUV light and reflection of DUV radiation, which affects the precision of circuit designs.
Innovation Solution
Incorporating a modified surface morphology within a 'black border' region on the photomask to scatter DUV light away from the next mirror, reducing EUV reflectivity and preventing radiation overlap, achieved through a combination of substrate modification, multilayer reflective coatings, and absorber layer patterning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a reflective coating with absorber material is used in EUV photomasks, then EUV light absorption is improved, but DUV light reflection remains high causing radiation overlap
Solution Approach 1:
The patent applies different surface qualities to different regions of the photomask. The patterned design area maintains a smooth reflective surface for optimal EUV performance, while the border region is specifically modified with a roughened surface morphology. This local differentiation allows the border region to scatter DUV light away from mirrors while the patterned area continues to function with high EUV reflectivity and absorption control.
Solution Approach 2:
The patent converts the harmful DUV reflection into a beneficial scattering effect by intentionally roughening the border region surface. The roughness (5 nm to 200 nm RMS) that would normally be considered a defect is deliberately introduced to scatter DUV radiation away from subsequent mirrors, transforming the harmful reflective property into a useful light-directing function that prevents radiation overlap.
2Object-affected harmful factors
If absorber height is increased to improve EUV absorption, then EUV reflectivity decreases, but manufacturing complexity and CD control difficulty increase
Solution Approach 1:
The patent extracts the DUV reflection problem from the main patterned design area and relocates it to a separate border region. By confining the roughened surface morphology to only the border area (surrounding the patterned design but not interfering with it), the solution addresses DUV scattering without adding complexity to the absorber structure or height control in the critical patterned regions.
3Illumination intensity
If overlapping shots from neighboring fields are present, then background light increases on edges and corners, but critical dimension precision deteriorates
Solution Approach 1:
The roughened border region acts as an intermediary element between the patterned design and the surrounding environment. It serves as a light-management zone that scatters DUV radiation before it can reach subsequent mirrors and create harmful radiation overlap, thereby protecting the critical dimension precision of the patterned features from background light interference.
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 effectively reduces DUV reflectivity to less than 1.5%, minimizing critical dimension drops and improving the precision of circuit designs by preventing radiation overlap, while maintaining low EUV reflectivity.
Implementation Method 1
modifying a surface morphology of the black border region to cause light scattering of deep ultra violet light from reaching a next mirror
Implementation Method 2
current absorbers used in EUV lithography do not absorb all EUV light and, in fact, have a reflectivity of about 1-3%
Data Source
AI summary
The present disclosure relates to semiconductor structures and, more particularly, to modified surfaces of extreme ultraviolet lithography photomasks and methods of manufacture. The structure includes a reflective surface having a patterned design, and a black border region at edges of the patterned design. The black border region includes a modified surface morphology to direct light away from reaching a subsequent mirror.