Sub-wavelength Alignment Marks for Lithography Space Efficiency
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Solution Overview
Problem
Lithographic processes face inefficiencies due to large alignment marks in scribe lanes, which occupy valuable substrate space and are difficult to miniaturize without becoming transparent to alignment wavelengths, hindering mark stacking and pattern alignment accuracy.
Innovation Solution
The use of sub-wavelength periodic arrays of structures on the substrate, which are detectable by alignment beams but not by exposure beams, allowing for reduced scribe lane space usage and enabling mark stacking by creating artificial crystals with controlled optical properties for alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large copper areas are used in alignment marks, then alignment accuracy is maintained, but substrate space efficiency deteriorates due to increased scribe lane requirements
Solution Approach 1:
The alignment mark structures are divided into periodic arrays of smaller elements with sub-wavelength spacing. This segmentation allows the alignment marks to be detected by alignment beams while occupying significantly less substrate space, thereby resolving the contradiction between maintaining alignment accuracy and improving substrate space efficiency
Solution Approach 2:
The invention changes the physical parameters of alignment marks by using sub-wavelength periodic structures that are undetectable by exposure beams but detectable by alignment beams. This parameter change enables smaller alignment marks that maintain alignment functionality while reducing scribe lane requirements and improving substrate space utilization
2Productivity
If alignment marks are made transparent to certain wavelengths, then exposure efficiency is improved, but mark stacking capability deteriorates
Solution Approach 1:
The alignment mark structures are designed with local quality variations where the sub-wavelength periodic structures are transparent to exposure wavelengths while remaining detectable by alignment beams. This local quality differentiation enables both exposure efficiency and mark stacking capability to coexist
Solution Approach 2:
The invention effectively creates wavelength-selective transparency by using periodic structures with spacing smaller than the exposure wavelength but detectable by the alignment wavelength. This wavelength-dependent interaction enables the alignment marks to be transparent to exposure beams (improving exposure efficiency) while remaining visible to alignment beams (maintaining mark stacking capability)
3Area of stationary object
If scribe lane size is reduced to increase usable substrate area, then substrate space efficiency is improved, but alignment mark detectability deteriorates
Solution Approach 1:
By segmenting alignment marks into periodic arrays of sub-wavelength structures, the invention enables detection through diffraction effects rather than relying on large physical size. This segmentation allows alignment marks to be detected accurately even in reduced scribe lane spaces
Solution Approach 2:
The invention replaces the mechanical/direct optical detection method (relying on large physical mark size) with a wave-optics-based detection method where sub-wavelength periodic structures produce detectable diffraction patterns. This substitution enables alignment mark detectability to be maintained or improved even when physical mark size is reduced to fit smaller scribe lanes
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 reduces substrate space usage, maintains alignment accuracy, and allows for efficient mark stacking, improving the overall efficiency of lithographic processes by using sub-wavelength structures that are not transparent to alignment beams.
Implementation Method 1
the structures being separated by a distance that is less than the wavelength of an alignment radiation beam
Data Source
AI summary
Alignment marks for use on substrates. An exemplary implementation provides phase depth control. A grating mark, for example, can be etched on a silicon wafer with sub-wavelength segmentation in the spacing portion of the alignment grating's period. The sub-wavelength segmentation can be applied to the spaces or to the lines, or both, of an alignment grating to control the phase depth of the grating. By applying segmentation with a period smaller than the alignment light wavelength in either the space(s) and/or in the line(s) of the grating, the effective refractive index in that region can be manipulated. This change in the effective index will result in a change in the phase depth (optical path length). By varying the duty cycle of the sub-wavelength segmented region, the effective refractive index can be controlled, thereby providing selective control over the phase depth.