Substrate Position Mark with Sub-wavelength Structures
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Solution Overview
Problem
Existing lithography systems face challenges in accurately determining the position of a substrate due to complexity, inaccuracy, and sensitivity to errors in focus and tilt, particularly when using multiple diffraction orders for position determination.
Innovation Solution
A substrate with an optical position mark featuring sub-wavelength structures and varying reflection coefficients, allowing for accurate position determination using a zero-th order reflected light beam, reducing sensitivity to errors and increasing process tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple diffraction orders are used for position determination, then measurement precision is improved, but device complexity increases and sensitivity to focus and tilt errors worsens
Solution Approach 1:
The patent extracts only the zero-th order reflected light beam from the multiple diffraction orders and uses it for position determination. This eliminates the need for complex multi-detector systems while maintaining measurement capability through the use of a checkerboard pattern that modulates the zero-th order beam intensity based on substrate position.
Solution Approach 2:
The patent changes the parameter being measured from the angular distribution of multiple diffraction orders to the intensity modulation of the zero-th order beam. The checkerboard pattern causes the zero-th order reflected light intensity to vary sinusoidally with substrate position, enabling accurate position determination through intensity measurement alone.
2Measurement precision
If multiple diffraction orders are used for position determination, then measurement precision is improved, but sensitivity to focus and tilt errors increases
Solution Approach 1:
The patent isolates the zero-th order reflected light beam from the other diffraction orders and uses exclusively this beam for position measurement. This extraction eliminates sensitivity to focus and tilt errors that affect higher-order diffraction beams, while the checkerboard pattern ensures the zero-th order beam intensity still varies sufficiently with position for accurate measurement.
3Ease of manufacture
If a Gaussian beam profile is used instead of a homogeneous disc-like profile, then ease of manufacture is improved, but measurement precision deteriorates
Solution Approach 1:
The patent changes the approach from relying on a specific beam intensity distribution shape to using the spatial modulation of the zero-th order beam intensity by the checkerboard pattern. The sinusoidal variation of reflected intensity with substrate position, caused by the alternating reflective and non-reflective squares, provides accurate position information regardless of whether the beam profile is Gaussian or homogeneous disc-like.
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 method provides high accuracy and reproducibility in substrate position determination, reducing the risk of design errors and improving the robustness of the position mark, enabling efficient and precise alignment in lithography systems.
Implementation Method 1
measuring an intensity profile of a zero-th order reflected light beam
Data Source
AI summary
The invention relates to a substrate comprising an optical position mark for being read-out by an optical recording head for emitting light of predetermined wavelength, preferably red or infra-red light, more in particular of 635 nm light, the optical position mark having a mark height, a mark length and a predetermined known position on the substrate, the optical position mark extending along a longitudinal direction and being arranged for varying a reflection coefficient of the position mark along said longitudinal direction, wherein the optical position mark comprises:a first region having a first reflection coefficient and a first width;a second region neighboring the first region and forming a first region pair, the second region having a second reflection coefficient and a second width, and the second reflection coefficient being different from the first reflection coefficient, wherein the first region comprises sub-wavelength structures in comparison with a wavelength of the predetermined wavelength light.