Tilted Focus Testing in EUV Lithography via Reticle Tilting
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Solution Overview
Problem
Current tilted focus test methods are inefficient for extreme ultraviolet (EUV) radiation due to the difficulty in creating a tilted beam and require complex setups, such as blocking members or pellicles, which reduce system throughput and performance, especially when trying to determine relative defocus and correct substrate positioning in lithographic processes.
Innovation Solution
A method involving a lithographic apparatus with a tilting device that tilts a reflective mask or reticle to introduce a second projection beam with a different tilt relative to the first, allowing for the determination of defocus by measuring the lateral shift of the projected beams on the substrate, enabling efficient tilted focus testing even with EUV radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional tilted focus test methods are used with EUV radiation, then focus measurement can be performed, but the system requires complex setups with blocking members or pellicles that reduce throughput and performance
Solution Approach 1:
The invention extracts the beam tilting function from complex external components (blocking members, pellicles) and integrates it directly into the projection lens system through tilt-adjustable lens elements. This eliminates the need for separate tilting mechanisms and simplifies the overall system architecture while maintaining focus measurement capability.
Solution Approach 2:
The projection lens system is designed to perform multiple functions: normal imaging and tilted beam generation for focus testing. By incorporating tilt-adjustable lens elements into the projection lens, the system can switch between standard lithography operations and focus measurement modes without requiring separate dedicated equipment.
2Measurement precision
If blocking members or pellicles are introduced to create a tilted beam, then tilted focus testing is enabled, but system throughput and performance are reduced
Solution Approach 1:
The invention removes the need for physical blocking members and pellicles by implementing beam tilting through adjustable lens elements within the projection system. This extraction of the tilting function eliminates the throughput-reducing components while maintaining the ability to determine relative defocus accurately.
Solution Approach 2:
The mechanical approach of using physical blocking members to create tilted beams is replaced with an optical approach using tilt-adjustable lens elements. This substitution eliminates mechanical interventions that block or divert the beam, allowing continuous operation without throughput penalties.
3Measurement precision
If telecentric focus tests are performed, then absolute defocus can be determined, but relative defocus information including sign is lost
Solution Approach 1:
The invention introduces dynamic beam tilting capability that allows the projection lens to generate tilted beams for focus measurement. This dynamic adjustment enables the system to transition from static telecentric imaging to dynamic tilted beam imaging, providing both absolute and relative defocus information including the sign.
Solution Approach 2:
The invention changes the beam parameter from telecentric (perpendicular to substrate) to tilted (at an angle to substrate) by adjusting the lens elements. This parameter change enables the measurement of lateral beam shifts that provide relative defocus information with sign, complementing the absolute defocus measurement capability.
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 allows for rapid and accurate determination of defocus and relative positioning of the substrate with respect to the projection system, improving the efficiency and accuracy of focus correction in lithographic processes, particularly suitable for EUV applications where traditional methods fail.
Implementation Method 1
providing a reflective mask or reticle; using a tilting device for tilting the reflective mask or reticle
Data Source
AI summary
A method for performing a tilted focus test includes the steps of providing a target object, providing a projection beam of radiation using a radiation source, providing a reflective device to introduce a projected projection beam of radiation onto the target portion, introducing a first projected projection beam of radiation onto the target object using the reflective device in a first orientation, using a tilting device for tilting the reflective device to a second orientation to provide a second projection beam with a tilt relative to said first projection beam, introducing a second projected projection beam of radiation onto the target object, and determining a lateral shift of the first and second projected projection beams on the target object and determining from said lateral shift a defocus of the target object with respect to the projected projection beam.