Anamorphic Projection System for Lithography CD Control
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Solution Overview
Problem
Lithographic apparatuses face challenges in controlling critical dimension (CD) and H-V difference of printed features due to field-dependent CD-pitch errors, which limit process latitude and introduce residual errors beyond tolerance.
Innovation Solution
Implementing anamorphic magnification in the projection system by adjusting the speed of the pattern image movement relative to the substrate during exposure, allowing for independent control of feature sizes along different directions, thereby minimizing H-V differences and maintaining CD uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If illumination is performed with linearly polarized radiation to print features, then the pattern can be transferred onto the substrate, but H-V difference occurs causing different printed line widths for horizontal and vertical lines
Solution Approach 1:
The patent applies asymmetry by introducing different scanning speeds in the x and y directions through anamorphic magnification. The projection system uses different magnification factors (Mx ≠ My) to create asymmetric scanning motion that compensates for the H-V difference caused by linearly polarized radiation, making the effective exposure symmetric despite the polarized illumination.
Solution Approach 2:
The patent changes the scanning speed parameters in the x and y directions to compensate for H-V difference. By adjusting the scanning speeds (vx, vy) through anamorphic magnification, the system modifies the effective exposure parameters to achieve uniform line widths for both horizontal and vertical features.
2Manufacturing precision
If the critical dimension of features is reduced to meet demand for smaller devices, then device density increases, but control over critical dimension becomes more difficult due to H-V difference
Solution Approach 1:
The patent replaces mechanical adjustments of the illumination system with a scanning speed adjustment mechanism. Instead of mechanically modifying the illumination optics to control CD, the system uses controlled scanning motion with anamorphic magnification to achieve the same effect, simplifying the mechanical complexity while improving CD control.
3Reliability
If modification of illumination system characteristic is performed to control H-V difference, then H-V difference is reduced, but CD-pitch characteristic varies over the image field
Solution Approach 1:
The patent uses dynamic scanning speed adjustment through anamorphic magnification to compensate for H-V difference. By making the scanning speeds in x and y directions dynamically adjustable and independent, the system can compensate for polarization effects without statically modifying the illumination system, thereby avoiding field-dependent CD-pitch variations.
Data Source
AI summary
In a lithographic printing process a substrate is moved, in the scanning direction, relative to a patterned beam of radiation being projected onto it during a scanning exposure of a pattern feature. An image of the pattern feature is blurred in the scanning direction. The effect of the blurring is used to reduce a difference of critical dimension between similar horizontal and vertical features. The effect on critical dimension may be obtained by providing an amount of anamorphic magnification to the projection system.