Projection Exposure Wavefront Control via Cyclical Encoder Error Compensation
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Solution Overview
Problem
Existing projection exposure apparatuses face limitations in wavefront correction accuracy due to cyclical errors in phase-based optical encoders, which hinder precise manipulator settings and can introduce unintended aberrations during exposure.
Innovation Solution
A production control method that selectively establishes actuator travels of manipulators, considering cyclical errors of phase-based optical encoders, allowing actuator travels to be substantially longer than the cyclical error periodicity, ensuring that cyclical errors at the start and end of the travel are identical, thereby eliminating their influence on the manipulator adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase-based optical encoders are used for measuring manipulator position, then measurement precision is improved, but cyclical errors are introduced that limit manufacturing precision
Solution Approach 1:
The control apparatus pre-determines actuator travels to ensure that the sum of the actuator travel and the initial encoder value results in a final encoder value with the same cyclical error component as the initial value. This preliminary planning of actuator travels compensates for cyclical errors before they affect the wavefront correction precision.
2Manufacturing precision
If manipulator settings are adjusted for wavefront correction, then wavefront correction accuracy is improved, but cyclical errors in encoder measurements introduce unintended aberrations
Solution Approach 1:
The control apparatus converts the harmful cyclical errors into a manageable parameter by determining actuator travels that result in the same cyclical error at the end position as at the start position. This approach transforms the periodic error into a neutral factor that cancels itself out over complete actuator cycles, eliminating unintended aberrations while maintaining wavefront correction accuracy.
3Measurement precision
If actuator travels are restricted to be shorter than cyclical error periodicity, then measurement accuracy is maintained, but device complexity and operation difficulty increase
Solution Approach 1:
The control apparatus changes the parameter of actuator travel length from being restricted to small values to allowing longer travels, compensating by calculating travels that maintain the same cyclical error phase at start and end. This parameter change enables longer, more efficient actuator travels while maintaining measurement accuracy through intelligent travel planning.
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
Enables precise control of manipulators during exposure time intervals, reducing unintended aberrations and improving wavefront correction accuracy without relying on wavefront measurements, allowing for accurate imaging of mask structures on substrates.
Implementation Method 1
The measuring systems for measuring the changes in pose are based on an optical distance measurement at a suitable measurement wavelength. Such a measuring system comprises at least one phase-based optical encoder for measuring changes in the pose of the manipulable optical element or of a portion thereof by evaluating phase information from a measurement signal captured at a measurement wavelength.
Data Source
AI summary
A production control method controls the operation of a microlithographic projection exposure apparatus comprising a projection lens; a wavefront manipulation system comprising a manipulator and an optical encoder, the wavefront manipulation system configured to controllably influence the wavefront of the projection radiation, and a controller configured to control the manipulator of the manipulation system by generating an actuator travel command which defines a change in the spatial pose along an actuator travel of the optical element. The controller in at least one error-optimized mode of operation selectively establishes actuator travels of the manipulator with consideration being given to cyclical errors of the phase-based optical encoder of the wavefront manipulation system, in such a way that a second cyclical error at the end of an actuator travel substantially corresponds to a first cyclical error at the start of an actuator travel.