Lithographic Apparatus Asymmetric Spectral Control
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Solution Overview
Problem
Conventional lithographic techniques face challenges in controlling CD-focus error and process latitude due to asymmetry in CD-focus dependency, which limits the depth of focus and increases sensitivity to focus and exposure variations.
Innovation Solution
A lithographic apparatus with a radiation system providing an asymmetric spectral intensity distribution, controlled by a bandwidth-controller, adjusts the spectral distribution based on data from different focal positions to enhance symmetry and match focus behavior across systems, thereby reducing CD-focus error and improving process latitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional symmetric spectral intensity distribution is used, then the lithographic process is simple, but the CD-focus dependency is asymmetric which limits process latitude
Solution Approach 1:
The patent applies asymmetry by intentionally creating an asymmetric spectral intensity distribution to compensate for the asymmetric CD-focus dependency. The controller adjusts the spectral distribution to be asymmetric, which counteracts the inherent asymmetry in the lithographic process, thereby extending the usable focus range and improving process latitude.
Solution Approach 2:
The patent changes the spectral parameters by adjusting the spectral intensity distribution across different wavelengths. The controller modifies the spectral parameters dynamically to optimize the focus behavior, transforming the symmetric spectral distribution into an asymmetric one that compensates for process variations.
2Length of stationary object
If the depth of focus is increased through conventional means, then more features can be printed simultaneously, but the CD-focus error increases due to asymmetry
Solution Approach 1:
The patent uses asymmetric spectral distribution to balance the focus behavior at different focal positions. By making the spectral intensity distribution asymmetric, the system achieves more symmetric CD-focus dependency, allowing extended depth of focus while maintaining critical dimension control across the extended range.
Solution Approach 2:
The controller uses feedback from measured CD-focus dependency data to adjust the spectral intensity distribution. The system measures the actual focus behavior and dynamically modifies the spectral parameters to compensate for deviations, thereby maintaining precision across an extended depth of focus range.
3Reliability
If the spectral bandwidth is increased to extend depth of focus, then process robustness improves, but the asymmetry in CD-focus dependency worsens
Solution Approach 1:
The patent intentionally introduces asymmetry in the spectral intensity distribution to counterbalance the asymmetry in CD-focus dependency. By carefully designing the asymmetric spectral shape, the system achieves both extended depth of focus (improved robustness) and symmetric focus behavior (maintained precision) simultaneously.
Solution Approach 2:
The controller dynamically adjusts spectral parameters including bandwidth and intensity distribution shape. By changing these parameters based on measured process conditions, the system maintains optimal balance between robustness and precision, preventing the worsening of focus behavior symmetry even as bandwidth increases.
Data Source
AI summary
A CD-pitch dependency for a lithographic pattern printing process is related to the spectral intensity distribution of radiation used for projecting the pattern. A CD-pitch dependency can vary from one system to another. This can result in an iso-dense bias mismatch between systems. The invention addresses this problem by providing a lithographic apparatus including an illumination system for providing a projection beam of radiation, a projection system for projecting a patterned beam onto a target portion of a substrate, and a substrate table for holding the substrate, with a controller to provide an adjustment of the spectral distribution of radiant intensity of the projection beam. The adjustment of the spectral intensity distribution is based on data relating to an iso dense bias, and includes a broadening of the spectral bandwidth or a change of shape of the spectral intensity distribution.