Scatterometer Focus Offset Mechanism for Lithography Metrology
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Solution Overview
Problem
The existing focus sensor measurements do not necessarily match the optimum focus position required for scatterometer measurements, leading to potential errors in focusing and alignment during lithographic processes.
Innovation Solution
A scatterometer system with a focusing arrangement, focus sensor, and focus controller that adjusts the relative positions of the focusing arrangement and substrate, and includes a focus offset mechanism to compensate for differences between adjustment and operational focusing conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a specialized focus sensor with a narrowband radiation source is used to determine the optimum height of the objective lens, then the focus measurement capability is improved, but the measured focus position may not exactly match the optimum focus position for the scatterometer detector
Solution Approach 1:
A focus offset arrangement is introduced as an intermediary component between the focus sensor and the scatterometer detector. This offset arrangement compensates for the discrepancy between the focus sensor's measured position and the actual optimum focus position for the scatterometer detector, thereby resolving the mismatch without requiring the focus sensor to directly measure the scatterometer's focus condition.
Solution Approach 2:
The system changes the parameter relationship between the focus sensor and scatterometer detector by introducing a configurable focus offset. This offset parameter allows the system to adjust the focus position compensation based on the specific optical characteristics and requirements of the scatterometer detector, enabling accurate focus positioning despite the inherent differences in measurement principles.
2Extent of automation
If the focus sensor is used to control the objective lens position, then the focusing process is automated, but focus errors may still occur due to optical differences between the sensor and scatterometer detector
Solution Approach 1:
The focus controller receives feedback from the focus sensor about the objective lens position and automatically adjusts the lens height. The focus offset arrangement provides additional feedback information about the discrepancy between sensor measurements and actual scatterometer focus conditions, enabling the system to correct focus errors while maintaining automation.
Solution Approach 2:
The focus offset arrangement acts as an intermediary correction mechanism between the automated focusing process and the actual scatterometer detection requirements. It translates the focus sensor's automated control signals into accurate focus positions for the scatterometer detector by compensating for optical differences.
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 solution ensures accurate focusing and alignment, reducing focus errors and improving measurement precision for critical dimensions and overlay measurements, allowing for more flexible design and enhanced metrology robustness.
Implementation Method 1
a focusing arrangement; a focus sensor; a focus controller responsive to said focus sensor to provide control signals effective to cause an actuator arrangement to adjust the relative positions of said focusing arrangement and the substrate which are required to focus a beam of radiation
Implementation Method 2
a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured
Data Source
AI summary
A scatterometer for measuring a property of a substrate includes a focus sensing arrangement including an arrangement (65) that directs a first beam of radiation onto a focusing arrangement, to be detected by a focus sensor arrangement (61). A focus controller (67) provides control signals representative of the relative positions of the focusing arrangement (15, 69) and the substrate (W), which are required to focus the first beam of radiation on the substrate. An actuator arrangement adjusts the position of the focusing arrangement dependent on the control signals. An irradiation arrangement directs a second beam of radiation onto the substrate using the focusing arrangement, a measurement detector (18) detecting the second radiation beam after reflection from the substrate. A focus offset arrangement adjusts the focus produced by the focusing arrangement to compensate for an offset between the focusing of the first beam of radiation and the second beam of radiation.