Encoder Device Stabilizing Signal Intensity via Segmented Reflectors
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Solution Overview
Problem
Conventional encoder devices in photolithography processes face challenges in maintaining signal intensity due to changes in the height of the diffraction grating pattern surface, leading to instability in measuring relative moving amounts.
Innovation Solution
An encoder device with a reflective-type diffraction grating and a light source that generates measuring light, using a first and second reflecting member to direct diffracted light in a way that its incident angle is smaller than the diffraction angle, and photo-detectors to detect interference light for precise measurement of relative movement.
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 reflecting member is divided into multiple reflecting surfaces (first reflecting surface, second reflecting surface, third reflecting surface) that are spatially separated and oriented at different angles. This segmentation allows each surface to perform a specific function in redirecting the diffracted light, ultimately making the light incident perpendicularly on the grating pattern surface while maintaining structural organization.
Solution Approach 2:
The solution transitions from a simple planar mirror (two-dimensional surface) to a three-dimensional arrangement of multiple reflecting surfaces at different orientations. The first reflecting surface reflects light in a first direction, the second reflecting surface reflects it in a second direction, and the third reflecting surface reflects it in a third direction, creating a multi-dimensional optical path that achieves perpendicular incidence despite height variations.
2Length of stationary object
If the incident angle of diffracted light is large (equal to diffraction angle), then the optical path is direct, but the diffracted light shifts relative to reference light when grating height changes
Solution Approach 1:
The multiple reflecting surfaces are pre-arranged to counteract the potential shift caused by grating height changes. By designing the optical path to include these specific reflections before incidence, the system proactively compensates for height variations, ensuring that the diffracted light always incident perpendicularly on the grating pattern surface regardless of height changes.
Solution Approach 2:
The incident angle of the diffracted light is changed from the conventional diffraction angle to a smaller angle that enables perpendicular incidence. This parameter change in the optical path configuration allows the system to maintain measurement precision by ensuring that the diffracted light and reference light remain properly aligned even when grating height varies.
3Length of stationary object
If the optical path is long in laser interferometer, then measurement range is extended, but temperature fluctuation causes measured value variation
Solution Approach 1:
The patent replaces the conventional laser interferometer optical system with an encoder device that uses a diffraction grating and multiple reflecting surfaces. This substitution creates a more compact optical path structure that achieves the same measurement function while reducing the overall optical path length, thereby minimizing the impact of temperature fluctuations on measurement stability.
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 stabilizes the signal intensity and maintains high measurement precision by minimizing optical path variations and relative shifts of diffracted light, even with changes in the grating pattern surface height.
Implementation Method 1
a first diffracted light generated, via diffraction of the measuring light, from the diffraction grating
Implementation Method 2
a first reflecting member which is provided on the other of the first and second members, which has three reflecting surfaces and which reflects, via the three reflecting surfaces, a first diffracted light
Implementation Method 3
a first photo-detector which detects an interference light generated by interference between a double diffracted light and other diffracted light than the double diffracted light or a reference light
Implementation Method 4
a light-incident optical member which causes the measuring light to come into a grating pattern surface of the diffraction grating substantially perpendicularly
Data Source
AI summary
An encoder, which measures a relative moving amount of a second member relative to a first member, includes: a diffraction grating provided on the first member; a light-incident optical member causing a measuring light to come into a grating pattern surface of the diffraction grating substantially perpendicularly; a first reflecting member provided on the second member and reflecting a diffracted light generated from the diffraction grating; a first direction-changing member changing a direction of the diffracted light; a first photo-detector detecting an interference light generated by interference between a double diffracted light and other diffracted light than the double diffracted light or a reference light, the double diffracted light being generated, via diffraction of the diffracted light, from the diffraction grating; and a measuring section which obtains the relative moving amount of the second member relative to the first member by using a detection signal from the first photo-detector.