Optical Element Thermal Wavefront Correction
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Solution Overview
Problem
Modern projection objectives for microlithography face challenges in correcting temporally and spatially varying higher-order wavefront aberrations, which are not effectively addressed by conventional mechanical manipulators, especially in regions near the pupil and field where stringent optical performance restrictions apply.
Innovation Solution
An optical element with electrically conductive tracks that can be heated locally to control the refractive index and form, allowing for dynamic correction of wavefront aberrations by varying the temperature profile, thereby enabling spatially and temporally resolved correction of imaging aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mechanical manipulators are used for wavefront correction, then low-order aberrations can be corrected, but higher-order and temporally variable aberrations cannot be effectively addressed
Solution Approach 1:
The patent replaces mechanical manipulators with a thermal field-based correction system. Electrical conductor tracks embedded in the optical element generate localized heat through Joule heating, creating temperature gradients that modify the refractive index distribution. This thermal-optical mechanism substitutes the mechanical deformation approach, enabling correction of higher-order and temporally variable aberrations with faster response and greater spatial resolution.
Solution Approach 2:
The patent changes the physical state parameters of the optical element by introducing controlled temperature variations. By applying electrical current to conductor tracks, localized temperature changes alter the refractive index (dn/dT effect) and physical dimensions (thermal expansion) of the optical material. This parameter change enables dynamic adjustment of wavefront correction for higher-order aberrations beyond the capability of static mechanical manipulators.
2Temperature
If fluid-mechanical heat pumps are used for temperature control, then heating capability is provided, but area coverage restrictions are violated
Solution Approach 1:
The patent extracts the heating function from external fluid-mechanical heat pumps and integrates it directly into the optical element itself. Electrical conductor tracks are embedded within the optical element, allowing localized heat generation at the precise location where temperature control is needed. This eliminates the need for external heating devices that would occupy space in the beam path and violate area coverage restrictions.
Solution Approach 2:
The optical element serves multiple functions: it maintains its primary optical function while simultaneously acting as a thermal actuator through embedded conductor tracks. The same optical element that transmits or focuses light also generates and distributes heat patterns for wavefront correction, eliminating the need for separate heating apparatus and preserving beam path area coverage.
3Use of energy by moving object
If conductor tracks are made wider for better heat distribution, then heating efficiency improves, but shading effects increase
Solution Approach 1:
The patent applies local quality by varying the conductor track dimensions and arrangements according to the specific heating requirements of different regions. Conductor track width, spacing, and pattern density are optimized locally to achieve the desired temperature distribution while minimizing overall shading. This localized optimization allows efficient heat generation in critical areas without uniformly increasing shading across the entire optical element.
Solution Approach 2:
The patent employs partial action by concentrating heating capacity only where and when it is needed for aberration correction, rather than providing uniform heating across the entire optical element. The conductor tracks are activated selectively in specific regions and time intervals, achieving sufficient heating efficiency for wavefront correction while keeping the overall shading effect minimal. This partial activation strategy balances heating efficiency with optical performance.
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 allows for precise correction of higher-order wavefront aberrations with minimal impairment to the optical performance, achieving phase changes sufficient for typical amplitudes in microlithography, while maintaining a small footprint to avoid shading effects, and can be applied across various wavelengths from UV to infrared.
Implementation Method 1
The optical element has at least one electrical conductor track, and the optical action of the optical element is capable of being influenced via the electrical conductor track
Implementation Method 2
The optical thickness of the optical element can be varied via the temperature dependence of the optical refractive index of the optical element. The phase variation Δφ is approximately proportional to the heated distance traversed in the optical element ΔZ, the temperature sensitivity of the optical refractive index dn/dT and the temperature variation ΔT
Implementation Method 3
In addition to the refractive index change, the thermally governed expansion of the optical element is also relevant to the alteration of the optical action of the optical element
Data Source
AI summary
The disclosure relates to an optical element configure to at least partial spatially resolve correction of a wavefront aberration of an optical system (e.g., a projection exposure apparatus for microlithography) to which optical radiation can be applied, as well as related systems and methods.