Wafer Stage Encoder Layout for Reaction-Force Isolation
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Solution Overview
Problem
In exposure apparatuses for manufacturing electron devices, the measurement accuracy of the encoder system is degraded due to reaction forces when a planar motor-driven wafer stage is used with an encoder head placed inside the surface plate, affecting the precision and throughput of the exposure process.
Innovation Solution
A stage device with a measurement system that includes a first measurement member arranged on both the movable body and the second support member, which is fixed to the optical system, allowing for accurate positional measurement of the movable body within a two-dimensional plane while minimizing the influence of surrounding atmosphere fluctuations and reaction forces, using a guide surface that can be either contact or non-contact type, such as static gas bearings or magnetic levitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the encoder head is placed inside the surface plate with the planar motor-driven wafer stage, then the throughput and speed of the exposure operation are improved, but the measurement accuracy of the encoder system is degraded due to reaction forces
Solution Approach 1:
The encoder head is extracted from the surface plate and placed on the movable body (wafer stage). This separation removes the encoder head from the region affected by reaction forces generated by the planar motor, thereby preserving measurement accuracy while maintaining the high-speed, high-acceleration performance required for improved throughput.
Solution Approach 2:
The patent introduces a separate support structure (second support member) that carries the encoder head independently from the surface plate. This intermediary structure isolates the measurement system from the mechanical disturbances caused by the drive system, allowing both high productivity and high measurement precision to be achieved simultaneously.
2Speed
If the planar motor is used to drive the wafer stage with high acceleration for improved throughput, then the speed and acceleration are increased, but reaction forces degrade the measurement accuracy
Solution Approach 1:
The encoder head is extracted from the surface plate and mounted on the movable body itself, placing it outside the region where reaction forces from the planar motor affect the measurement. This allows the wafer stage to operate at high speed and acceleration without compromising measurement accuracy.
Solution Approach 2:
Instead of fixing the encoder head to the stationary surface plate (conventional approach), the patent inverts the arrangement by fixing the encoder head to the movable body. This inversion places the measurement system on the moving platform, isolating it from reaction forces generated during high-acceleration operation.
3Ease of operation
If the encoder head is placed on the surface plate for easy access and installation, then the ease of operation is improved, but the measurement accuracy is degraded by reaction forces from the drive system
Solution Approach 1:
The encoder head is extracted from the surface plate and relocated to the movable body. While this changes the installation location, it eliminates the harmful interaction with reaction forces, thereby improving measurement accuracy while maintaining reasonable accessibility for operation and maintenance.
Solution Approach 2:
A separate support structure (second support member) is introduced as an intermediary to carry the encoder head. This mediator provides a stable mounting platform that is isolated from the surface plate vibrations and reaction forces, achieving both ease of operation and high measurement precision.
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 positional control of the movable body with improved measurement accuracy and reduced degradation from reaction forces, enhancing the overall precision and throughput of the exposure process.
Implementation Method 1
a stage device that controls the position of a wafer within a two-dimensional plane using a planar motor by an electromagnetic force drive method
Implementation Method 2
a guide surface that can be either contact or non-contact type, such as static gas bearings or magnetic levitation
Data Source
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AI summary
Positional information of each of wafer stages (WST1 and WST2) during exposure and during alignment is measured directly under a projection optical system (PL) and directly under a primary alignment system (AL1), respectively, by a plurality of encoder heads, Z heads and the like, which a measurement bar (71) placed below surface plates (14A and 14B) has, using gratings placed on the lower surfaces of fine movement stages (WFS1 and WFS2). Consequently, high-precision measurement of the positional information of the wafer stages (WST1 and WST2) can be performed.