Semiconductor Laser Position Measuring Device
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Solution Overview
Problem
Conventional position-measuring devices, such as laser interferometers, face challenges in maintaining high accuracy due to refractive index fluctuations in the air, which may lead to unacceptable measuring value fluctuations, especially as accuracy requirements increase with positioning speeds in semiconductor manufacturing systems.
Innovation Solution
A position-measuring device utilizing a semiconductor laser with a great coherence length, operating in a pulsed single-mode operational mode, combined with asymmetrical scanning beam paths and a wavelength determination system for correcting wavelength-dependent errors, to provide precise position measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser interferometers are used for position measurement, then measurement capability is provided, but refractive index fluctuations in air cause unacceptable measuring value fluctuations on the order of nanometers
Solution Approach 1:
The patent replaces laser interferometers (optical measurement system sensitive to air refractive index) with a grating-based position measuring device that uses direct optical path length measurement through asymmetrical scanning, eliminating sensitivity to atmospheric refractive index fluctuations while maintaining nanometer-level precision
Solution Approach 2:
The patent changes the measurement principle from interferometric phase detection to direct optical path length measurement using asymmetrical scanning beam paths, fundamentally altering how position is determined to eliminate dependence on air refractive index stability
2Length of stationary object
If asymmetrical scanning beam paths are used to increase path length differences, then coherence length requirements increase to several millimeters or centimeters, but conventional light sources cannot provide sufficient coherence length
Solution Approach 1:
The patent changes the coherence length parameter of the light source from conventional short-coherence sources to a semiconductor laser with extended coherence length (>200 μm), enabling interference detection over the larger optical path length differences created by asymmetrical scanning beam paths
Solution Approach 2:
The patent employs a composite optical system combining asymmetrical scanning beam paths with a specialized semiconductor laser source, where the laser's extended coherence length compensates for the increased path length differences introduced by the asymmetrical configuration
3Duration of action of stationary object
If continuous wave operation is used, then measurement continuity is maintained, but memory jitter causes measuring inaccuracies
Solution Approach 1:
The patent implements pulsed operation of the semiconductor laser instead of continuous wave operation, using periodic measurement cycles that reduce memory jitter effects while maintaining sufficient measurement continuity for real-time position control in semiconductor manufacturing systems
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 ensures high precision and stability in position measurements by minimizing memory jitter and accommodating increased coherence lengths, allowing for the use of asymmetrical scanning beam paths and effective correction of wavelength-dependent errors, thereby addressing the limitations of conventional technologies.
Implementation Method 1
a light source which is arranged as a semiconductor laser having great coherence length, which operates in a pulsed manner in a single-mode operational-mode
Implementation Method 2
The light source is arranged as a semiconductor laser
Implementation Method 3
a light beam from a suitable light source is split up into a least two coherent partial beams of rays, which subsequently impinge upon a plurality of gratings in the scanning beam path before they are reunited and brought to interference
Data Source
AI summary
A position-measuring device is for determining the position of two objects which are arranged displaceably with respect to each other in at least one measuring direction, and a method is for the operation of such a position-measuring device. The position-measuring device includes a measuring graduation as well as a scanning device having a light source and one or a plurality of optical and/or optoelectronic components for generating displacement-dependent position signals. A semiconductor laser having great coherence length is provided as the light source, which is operated pulsed in a single-mode operational-mode.