Image Sensing Plane Tilt for Diffraction-Noise Suppression
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Solution Overview
Problem
The periodic structure of image sensing devices generates diffracted light noise that deteriorates detection accuracy in detection apparatuses.
Innovation Solution
The detection apparatus includes an image sensing device with a first periodic structure and an optical system that illuminates a detection target with a second periodic structure, where the optical axis is tilted to prevent diffracted light beams of adjacent orders from returning to the detection optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an image sensing device with a periodic structure is used, then the device can sense moire fringe patterns for alignment detection, but the periodic structure generates diffracted light noise that deteriorates detection accuracy
Solution Approach 1:
The patent applies asymmetry by tilting the image sensing plane relative to the optical axis, transforming the symmetric periodic structure into an asymmetric configuration. This tilt causes the diffracted light beams to be directed away from the optical axis, preventing them from returning to the detection optical system and thereby eliminating the noise while preserving the moire fringe detection capability
Solution Approach 2:
The patent introduces a dimensional change by tilting the image sensing plane from being perpendicular to the optical axis to being at an inclined angle. This adds a angular dimension to the system configuration, causing diffracted light to be redirected into different spatial dimensions where they cannot interfere with the detection signal
2Object-generated harmful factors
If the image sensing plane is tilted to suppress diffracted light, then noise is reduced, but the optical system complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the orientation angle of the image sensing plane relative to the optical axis. By adjusting this geometric parameter (the tilt angle), the system effectively redirects diffracted light away from the detection path without requiring additional optical components, thus suppressing noise while maintaining relatively simple system architecture
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 configuration suppresses noise components, enhancing detection accuracy by preventing interference fringes and flare, thereby improving alignment precision in lithography processes.
Implementation Method 1
The periodic structure generates diffracted light, and the diffracted light causes noise components in the image sensed by the image sensing device
Implementation Method 2
a normal of the image sensing plane is tilted with respect to an optical axis of the optical system such that the optical axis is located between diffracted light beams of adjacent orders
Implementation Method 3
light having entered the image sensing plane generates a plurality of diffracted light beams of different orders
Data Source
AI summary
A detection apparatus includes an image sensing device having an image sensing plane including a first periodic structure; and an optical system configured to illuminate a detection target including a second periodic structure different from the first periodic structure, and form an image of light from the detection target on the image sensing plane. Light having entered the image sensing plane generates a plurality of diffracted light beams of different orders in accordance with the first periodic structure. A normal of the image sensing plane is tilted with respect to an optical axis of the optical system such that the optical axis is located between diffracted light beams of adjacent orders not less than a first order among the plurality of diffracted light beams.