Wafer Stage Alignment Using Inclined Interferometers
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Solution Overview
Problem
As semiconductor devices become highly integrated, the need for precise alignment of the wafer stage with the reticle becomes increasingly challenging due to narrower design rules, requiring more accurate measurement of the wafer stage's position during the exposing process.
Innovation Solution
The method involves using interferometers inclined at 45° to the X and Y axes to measure the wafer stage's coordinates, allowing for increased movement distance and improved accuracy by aligning diagonal lines of the wafer stage with these axes, utilizing linear motors and interferometers to accurately position the wafer stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the interferometer is arranged parallel to the moving direction of the wafer stage, then the measurement setup is simple, but the measurement precision is insufficient for highly integrated semiconductor devices
Solution Approach 1:
The interferometer is arranged at an angle (e.g., 45 degrees) relative to the moving direction of the wafer stage, rather than parallel to it. This angular arrangement creates a longer optical path length for the same stage displacement, thereby enhancing measurement precision without fundamentally changing the interferometer's structural configuration
Solution Approach 2:
The measurement system changes the geometric parameter of the interferometer's arrangement angle to optimize measurement precision. By adjusting the angle between the interferometer beam and the stage moving direction, the system achieves higher precision measurements suitable for narrow design rules in highly integrated semiconductor devices
2Measurement precision
If the wafer stage movement distance is increased to improve measurement accuracy, then the measurement precision improves, but the alignment complexity increases
Solution Approach 1:
By arranging the interferometer at an angle to the stage moving direction, the system effectively extends the measurement baseline without physically increasing the stage travel distance. This angular dimension change provides longer optical path length for measurement, improving precision while keeping the alignment process manageable
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 approach enhances the accuracy of wafer stage positioning, increasing the movement distance measured by interferometers, thereby enabling precise alignment and improving overlay accuracy between the wafer stage and reticle, leading to accurate pattern formation in semiconductor manufacturing.
Implementation Method 1
The interferometer may irradiate a light to the wafer stage. The interferometer may receive a light reflected from the wafer stage to measure the position of the wafer stage.
Data Source
AI summary
In a method of aligning a wafer stage, the wafer stage may be moved in an X-axis direction. A first coordinate of the wafer stage may be measured from a first measurement position inclined to the X-axis. The wafer stage may be moved in a Y-axis direction. A second coordinate of the wafer stage may be measured from a second measurement position inclined to the Y-axis. Thus, a movement distance of the wafer stage may be increased, so that the interferometers may accurately measure the position of the wafer stage.