Encoder Device Retroreflector Optical Path Stability
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Solution Overview
Problem
Conventional encoder devices in photolithography processes face instability in measuring relative moving amounts due to changes in the height of the grating pattern surface of diffraction gratings, leading to reduced signal intensity of interference light.
Innovation Solution
An encoder device with a reflective-type diffraction grating that uses a specific optical configuration, including multiple reflecting units and photo-detectors, to measure relative moving amounts by detecting interference light generated between diffracted lights of different orders, thereby minimizing the impact of grating surface height changes on signal intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional encoder device uses a planar mirror to reflect diffracted light, then the device structure is simple, but the signal intensity of interference light decreases when the grating pattern surface height changes
Solution Approach 1:
The patent transitions from a two-dimensional planar mirror reflection to a three-dimensional retroreflector configuration. The retroreflector uses mutually orthogonal reflecting surfaces (first and second reflecting surfaces) to create a three-dimensional optical path that returns diffracted light along its incident path, compensating for height variations of the grating pattern surface and maintaining stable signal intensity.
Solution Approach 2:
The retroreflector acts as an intermediary optical element between the diffraction grating and the detector. It mediates the optical path by receiving diffracted light from the grating and returning it along the incident path, thereby isolating the measurement system from the effects of grating surface height changes and maintaining reliable signal intensity.
2Adaptability or versatility
If the grating pattern surface height changes, then the optical path length varies, but this causes relative shift between diffracted lights and reduces measurement precision
Solution Approach 1:
The patent converts the harmful effect of grating surface height changes into a beneficial configuration. By using a retroreflector with orthogonal reflecting surfaces, the system accepts variable optical path lengths caused by height changes and automatically compensates for them, transforming what would be a source of measurement error into a robust design feature that maintains measurement precision across varying conditions.
Solution Approach 2:
The retroreflector configuration provides beforehand cushioning against optical path variations. The mutually orthogonal reflecting surfaces are pre-configured to compensate for height changes before they affect the measurement, ensuring that diffracted lights return along their incident paths regardless of grating surface position variations.
3Measurement precision
If multiple diffracted lights are used for interference, then measurement resolution improves, but the optical system becomes more complex
Solution Approach 1:
The retroreflector serves multiple functions simultaneously: it reflects diffracted lights of various orders, compensates for optical path variations, and maintains the geometric relationship between incident and reflected beams. This multi-functionality allows the use of multiple diffracted lights for high-resolution interference measurement without proportionally increasing system complexity.
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 maintains high measurement precision and stability by reducing relative shifts between diffracted lights, ensuring consistent signal intensity and accuracy even with changes in the grating surface height, thus enhancing the encoder's performance in photolithography applications.
Implementation Method 1
a first diffracted light, which is generated, via diffraction of the measuring light, from the diffraction grating
Implementation Method 2
a first reflecting unit provided on the second member, causing a first diffracted light to come into the diffraction grating
Implementation Method 3
a first photo-detector configured to detect an interference light generated by interference between the second diffracted light and other light beam
Data Source
AI summary
There is provided an encoder device to measure a relative moving amount between first and second members. The encoder device includes: a reflective-type diffraction grating on the first member; a light source unit to radiate a measuring light; a first optical member on the second member; a first and second reflecting units on the second member that cause first and third diffracted lights generated via diffraction of the measuring light and having orders different from each other to come into the diffraction grating respectively, and cause second and fourth diffracted lights generated via diffraction of the first and third diffracted lights respectively to come into the first optical member; photo-detectors configured to detect interference lights between two diffracted lights and other light beam respectively; and a measuring unit to obtain the relative moving amount by using detection signals from the photo-detectors.