Orthoedge Mask Features for Lithography Focus Control
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Solution Overview
Problem
In semiconductor manufacturing, projection optical lithography faces challenges in achieving precise focus alignment due to phase errors induced by mask topography, leading to significant focus shifts and variations in the plane of best focus, especially at nanometer scales, which complicates the production of small feature sizes like 10 nm technology nodes.
Innovation Solution
The introduction of orthoedges on the mask, oriented perpendicularly to the feature edges, to counteract phase distortions by providing a compensating quadrature component to the actinic light, thereby canceling out phase errors and improving focus alignment across different feature sizes and pitches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional mask designs without orthoedges are used, then manufacturing process is simpler, but focus shifts and variations occur due to phase errors from mask topography
Solution Approach 1:
Orthoedges act as intermediary elements that mediate between the mask topography-induced phase errors and the desired focal plane alignment. These orthogonal edge features introduce compensating diffraction orders that serve as intermediaries to correct the phase distortions caused by the mask's finite thickness, thereby aligning the focal planes of different pattern types without fundamentally changing the mask substrate or illumination system.
Solution Approach 2:
The introduction of orthoedges creates intentional asymmetric features in the mask pattern. These asymmetric orthogonal edges generate specific diffraction components that are asymmetric in nature, and this asymmetry is precisely what is needed to counteract the symmetric phase errors introduced by the mask topography, enabling focus alignment across different pitch and pattern types.
2Ease of manufacture
If mask topography with finite thickness is present, then realistic mask fabrication is enabled, but phase errors are introduced causing focus shifts
Solution Approach 1:
The orthoedges convert the harmful phase errors into beneficial focus alignment. By introducing additional orthogonal edges that generate specific diffraction orders, the system transforms the problematic phase distortions caused by finite mask thickness into useful corrective elements. The orthoedges' diffraction components interfere with the original distorted waves to produce a corrected focal plane, effectively turning the mask topography's adverse effect into a solution.
3Length of moving object
If aggressive lithographic methods for small features are used, then technology node scaling is achieved, but focus control requirements become tighter
Solution Approach 1:
The orthoedges change the diffraction parameters of the light interacting with the mask. By adding these orthogonal edge features, the diffraction order spectrum is modified to include additional components that alter the interference pattern formation. This parameter change in the optical field enables the focal planes of different feature sizes and pitches to converge, providing tighter focus control necessary for aggressive technology node scaling without requiring changes to the lithography wavelength or numerical aperture.
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 focus shifts and variations, achieving a more stable and aligned focal plane for various feature sizes, enhancing the precision and reliability of semiconductor manufacturing at nanometer scales.
Implementation Method 1
the diffracted light imaged through a sophisticated optical system, and focused into a layer of light-sensitive photo-resist
Implementation Method 2
providing a compensating quadrature component to the actinic light, thereby canceling out phase errors and improving focus alignment
Data Source
AI summary
A method includes selecting a mask blank for lithographically forming a desired pattern of main features to be printed onto a wafer by projection lithography. First locations are identified in the desired pattern, the first locations being those which would produce on the wafer images impacted by phase distortions of actinic light through openings in the desired pattern. Second locations in the desired pattern are identified for the insertion of orthoedges. The orthoedges are provided to contribute an additional amplitude of actinic light to the images impacted by phase distortions when the actinic light is projected onto the wafer. The orthoedges are then inserted into the desired pattern at the second locations at orientations such that the orthoedges provide a quadrature component to the additional amplitude of actinic light having an opposite sign to the quadrature component of the actinic light producing the phase distortions. Finally, the mask blank is formed lithographically with the desired pattern modified through the insertion of the orthoedges.