Lithography Position Detector Reflection Member Phase Compensation
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Solution Overview
Problem
The alignment accuracy of a wafer relative to the projection optical system in lithography processes is reduced due to fluctuations in the optical axis distance between the off-axis detection system and the projection optical system, leading to asymmetry in the alignment mark signal caused by phase differences in light beams incident on a reflection unit.
Innovation Solution
A position detector is designed with an optical system that includes a lens with positive refractive power and a reflection member made from materials with specific refractive indices and extinction coefficients, which reduces the phase difference and asymmetry in the alignment mark signal by minimizing the angle dependency of the reflection phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a light path folding mirror is used to shorten the baseline between the projection optical system and the OA detection system, then the alignment accuracy is improved by reducing baseline fluctuation, but the light flux becomes incident onto the reflection unit in a convergent or divergent state causing phase differences and signal asymmetry
Solution Approach 1:
The patent changes the optical parameters of the reflection unit by selecting materials with specific refractive indices and extinction coefficients. This material parameter selection compensates for the phase differences introduced by convergent or divergent light incidence, thereby maintaining signal symmetry while preserving the shortened baseline configuration
Solution Approach 2:
The reflection unit is constructed from composite material layers with carefully selected optical properties. By combining materials with different refractive indices and extinction coefficients, the system achieves wavelength-selective reflection that compensates for angle-dependent phase shifts, resolving the contradiction between baseline shortening and signal symmetry
2Measurement precision
If the optical axis distance (baseline) between the OA detection system and the projection optical system is reduced, then the fluctuation in baseline is reduced improving alignment accuracy, but the angle of incidence variation for light beams increases causing phase differences
Solution Approach 1:
The patent modifies the optical parameters of the reflection unit by selecting materials with specific refractive indices and extinction coefficients. This parameter optimization ensures that phase differences caused by varying angles of incidence are compensated, maintaining reliable phase consistency even when the baseline is shortened
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
The solution improves the symmetry of the alignment mark signal, enhancing the accuracy of position detection and reducing the sensitivity to fluctuations in the optical axis distance, thereby maintaining alignment accuracy.
Implementation Method 1
a reflection member configured to reflect a light flux that passes through the lens in a convergent state or a divergent state
Implementation Method 2
a lens that has a positive refractive power
Data Source
AI summary
A position detector configured to detect a position of an object to be detected. The position detector has an optical system configured to detect a mark on the object to be detected that includes a lens that has a positive refractive power, and a reflection member configured to reflect a light flux that passes through the lens in a convergent state or a divergent state. The reflection member is configured from at least one material of a material that exhibits a refractive index of less than 1.0 and an extinction coefficient of greater than 0.0, and a material that exhibits a refractive index of greater than 1.0 and an extinction coefficient of greater than 0.5.