Polarization Adjustment for Microlithography Image Placement
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Solution Overview
Problem
Current microlithographic projection exposure apparatuses face significant challenges in reducing image placement errors, particularly due to higher asymmetric aberrations like coma, which are sensitive to feature pitch and orientation, limiting the effectiveness of uniform correction methods.
Innovation Solution
An optical system with a polarization adjustment device that changes the input state of polarization to elliptical output states, controlled by a unit that selects the appropriate polarization based on feature pitch and orientation to compensate for image placement errors, often arranged near a pupil surface of the optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If uniform correction methods are used for image placement errors, then the correction process is simple, but the correction effectiveness is limited due to pitch and orientation sensitivity
Solution Approach 1:
The patent applies local quality by making the polarization state spatially varying across the pupil plane. Different regions of the pupil are assigned different polarization states (elliptical with different orientations) to compensate for the spatially varying image placement errors that depend on feature pitch and orientation. This is achieved through a polarization adjustment device that creates a non-uniform polarization distribution in the pupil plane, allowing different local areas to be corrected according to their specific requirements.
2Manufacturing precision
If polarization adjustment device is added to correct image placement errors, then correction effectiveness improves, but device complexity increases
Solution Approach 1:
The patent achieves multi-functionality by designing the polarization adjustment device to simultaneously correct multiple types of image placement errors with a single device. The device can generate various elliptical polarization states with different orientations and ellipticities, allowing it to address pitch-dependent and orientation-dependent errors uniformly across different feature types. This eliminates the need for separate correction mechanisms for different error types, reducing overall system complexity despite the advanced functionality.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the polarization state parameters (ellipticity, orientation, and phase) across the pupil plane to compensate for image placement errors. The polarization adjustment device modifies these parameters spatially and spectrally, allowing the same device to correct errors for features with different pitches and orientations by changing the local polarization parameters rather than using multiple fixed correction elements.
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 image placement errors by compensating for pitch and orientation-dependent displacements, achieving significant corrections even when the same elliptical output state is used for different masks, thereby improving the precision of feature imaging in microlithography.
Implementation Method 1
a polarization adjustment device which is capable of changing an input state of polarization to different elliptical output states of polarization
Data Source
AI summary
A method of reducing image placement errors in a microlithographic projection exposure apparatus includes providing a mask, a light sensitive layer and a microlithographic projection exposure apparatus which images features of the mask onto the light sensitive surface using projection light. Subsequently, image placement errors associated with an image of the features formed on the light sensitive surface are determined either by simulation or metrologically. Then an input state of polarization of the projection light is changed to an elliptical output state of polarization which is selected such that the image placement errors are reduced.