Projection Exposure Illumination Switching for Thermal Wavefront Control
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Solution Overview
Problem
Lithographic projection exposure methods face challenges in achieving high contrast and yield while minimizing thermally induced aberrations, which can reduce the lithographic process window due to localized illumination peaks and thermal heating effects in optical elements.
Innovation Solution
Operate a microlithographic projection exposure apparatus by repeatedly exposing a mask to different illumination settings, ensuring minimal overlap of pupil surfaces illuminated in each setting, and maintaining these settings for extended periods to prevent excessive wavefront aberrations caused by thermal heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If localized illumination distributions are used to achieve high contrast of imaged structures, then the contrast of imaged structures is improved, but thermal wavefront aberrations increase due to localized illumination peaks heating optical surfaces
Solution Approach 1:
The illumination system periodically switches between at least two different illumination settings during mask exposure. Each illumination setting produces a different illumination distribution in the pupil plane with minimal overlap (maximum 90% overlap) of illuminated pupil surfaces. This periodic switching prevents sustained localized heating of optical surfaces while maintaining high contrast imaging capability across multiple fields of semiconductor substrates
Solution Approach 2:
The illumination system changes operational parameters by switching between different illumination settings, each characterized by distinct illumination distributions in the pupil plane. These parameter changes include the spatial distribution pattern and intensity profile of illumination radiation, allowing the system to alternate between configurations that illuminate different regions of the pupil plane, thereby distributing thermal load across multiple optical surfaces
2Object-affected harmful factors
If the illumination system is switched frequently between different settings, then thermal wavefront aberrations are reduced, but the lithographic process window deteriorates due to insufficient exposure time per setting
Solution Approach 1:
The illumination system implements periodic switching between different illumination settings, where each setting is maintained for a sufficient duration to complete multiple field exposures. The switching period is optimized so that each illumination setting operates long enough to maintain stable thermal conditions and achieve complete mask scans, while still alternating frequently enough to prevent excessive localized heating
Solution Approach 2:
The illumination system maintains continuous useful action by ensuring that each illumination setting operates for an extended period sufficient to complete full mask scans and expose multiple semiconductor substrates. This continuous operation under each setting allows the lithographic process window to be fully utilized while the periodic switching between settings prevents thermal wavefront aberration accumulation
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 maintains a stable lithographic process window by reducing thermal wavefront aberrations, ensuring consistent imaging quality over time without significant losses.
Implementation Method 1
a mask is repeatedly exposed to an exposure radiation provided by an illumination system, and mask structures are imaged in the process on in each case one of a multiplicity of fields of a plurality of semiconductor substrates
Implementation Method 2
mask structures are imaged in the process on in each case one of a multiplicity of fields of a plurality of semiconductor substrates
Implementation Method 3
high-stress regions can be now created on optical surfaces with temperature peaks... different illumination distributions of the exposure radiation are present in a pupil plane of the illumination system... to prevent excessive wavefront aberrations caused by thermal heating
Data Source
AI summary
In a method for operating a microlithographic projection exposure apparatus, a mask is repeatedly exposed to an exposure radiation provided by an illumination system, and mask structures are imaged in the process on in each case one of a multiplicity of fields of a plurality of semiconductor substrates. During a period in which the repeated exposure of the mask takes place, the illumination system is used successively in at least two different illumination settings of the illumination system, in which different illumination distributions of the exposure radiation are present in a pupil plane of the illumination system, with a pupil surface illuminated in the first illumination setting having no overlap or an overlap of at most 90% of the respective illuminated pupil surface with a pupil surface illuminated in the second illumination setting, with the mask being fully exposed at least once in each of the different illumination settings.