Shearing Interferometer for Wavefront Aberration Detection
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Solution Overview
Problem
Current methods for detecting wavefront aberration in photolithography projection systems lack the precision needed to control feature line widths at the nanometer scale, essential for ultra-precise assembly and adjustment of projection objective lenses in advanced photolithography processes.
Innovation Solution
An apparatus comprising a light source, spatial filter, splitter plate with a transflective film, projection objective lens, spherical mirror, and interferometer is used to generate and measure ideal spherical waves, allowing for precise detection of wavefront aberration through shearing interference methods, capable of measuring both immersive and dry photolithography systems during alignment procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional interferometers are used for wavefront aberration detection, then the measurement can be performed, but the measurement precision is insufficient for sub-nanometer accuracy requirements
Solution Approach 1:
The patent segments the wavefront measurement process into multiple discrete steps: generating reference spherical waves through a spatial filter, splitting the beam via a splitter plate, introducing controlled shearing displacement, and recombining for interference detection. This segmentation allows each component to be optimized independently, achieving sub-nanometer measurement precision required for feature line width control.
Solution Approach 2:
The patent introduces a splitter plate with transflective film as an intermediary element that separates the incident beam into reference and measurement beams. This intermediary enables the shearing interferometry method by creating two coherent beams with a lateral displacement, allowing precise wavefront aberration measurement that conventional direct interferometers cannot achieve.
2Manufacturing precision
If the numerical aperture of the projection objective lens is increased beyond 0.93 to achieve smaller feature sizes, then resolution improves, but wavefront aberration control becomes more difficult
Solution Approach 1:
The patent performs preliminary wavefront aberration measurement and characterization before the actual photolithography exposure process. By using shearing interferometry to pre-measure and map the wavefront aberrations of the projection objective lens, the system can compensate for these aberrations through alignment adjustments and process parameter optimization, enabling precise feature size control even with high numerical aperture lenses (NA > 0.93).
3Measurement precision
If Point Diffraction Interferometer or Line Diffraction Interferometer is used, then wavefront aberration can be detected, but the device complexity and alignment difficulty increase
Solution Approach 1:
The patent creates a simplified copy of the complex wavefront measurement capability through shearing interferometry. Instead of using complex Point Diffraction or Line Diffraction Interferometers with multiple optical elements, the system uses a simple splitter plate to generate sheared beams that interfere with the original wavefront. This copying approach achieves the same measurement capability with significantly reduced device complexity and easier alignment.
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 solution enables sub-nanometer accuracy in wavefront aberration measurement, improving the precision of feature line widths achieved and facilitating ultra-precise assembly and adjustment of projection objective lenses, enhancing the resolution and performance of photolithography machines.
Implementation Method 1
a spatial filter configured to receive the illuminating beam and generate ideal spherical wave
Implementation Method 2
an interferometer configured to receive light reflected by the splitter plate and measure the wave front aberration
Implementation Method 3
a spherical mirror configured to reflect the output beam from the projection objective lens to the projection objective lens
Data Source
AI summary
Apparatus and methods for detecting wave front aberration of a projection objective lens in a photolithography machine are disclosed. The apparatus comprises: a light source system configured to generate an illuminating beam; a spatial filter configured to receive the illuminating beam and generate ideal spherical wave; a splitter plate arranged downstream to the spatial filter at a predetermined angle with respect to an optical axis of the spherical wave and having a transflective film being applied on a surface thereof; the projection objective lens configured to receive a beam from the splitter plate and generate an output beam; a spherical mirror configured to reflect the output beam from the projection objective lens to the projection objective lens, light passing through the projection objective lens being reflected by the splitter plate; and an interferometer configured to receive light reflected by the splitter plate and measure the wave front aberration of the projection objective lens.