Compensatory Optical Device for Soft X-ray Inspection
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Solution Overview
Problem
Current metrology techniques in lithographic processes face challenges in accurately measuring small product structures due to the blurring of measurement spots caused by slope errors in reflective optics, especially in the soft X-ray regime, leading to inaccurate results and inefficiencies in focusing and positioning.
Innovation Solution
An inspection apparatus and method that spatially modulates the wavefront of measurement radiation to compensate for non-uniform manufacturing defects in optical elements, using a compensatory optical device such as a spatial light modulation device to improve focusing and positioning accuracy, particularly for soft X-ray or EUV radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reflective optics are used to focus measurement radiation in the soft X-ray regime, then focusing capability is achieved, but slope errors cause blurring of the measurement spot
Solution Approach 1:
A compensatory optical device is introduced as an intermediary element between the measurement radiation source and the target. This device compensates for the blurring effects caused by slope errors in the reflective optics, allowing the system to maintain measurement precision despite manufacturing limitations in the optical elements
Solution Approach 2:
The patent changes the wavelength parameter of the measurement radiation to the soft X-ray regime (1-50 nm), which enables penetration through thick process layers while using reflective optics operated at grazing incidence angles to achieve focusing capability
2Productivity
If larger metrology targets are used for optical metrology, then measurement is feasible, but measurement accuracy decreases due to indirect relationship with real product structures
Solution Approach 1:
The patent changes the wavelength parameter to soft X-ray range, enabling the use of smaller metrology targets that more closely match the scale of real product structures, thereby improving measurement accuracy while maintaining optical measurement speed advantages
3Measurement precision
If SEM is used to measure small product structures directly, then measurement accuracy is improved, but measurement time increases significantly
Solution Approach 1:
The patent uses soft X-ray radiation (1-50 nm wavelength) instead of visible or UV light, enabling direct optical measurement of small product structures at high speed while maintaining accuracy comparable to SEM through the shorter wavelength's superior resolution capability
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
Enhances the precision and accuracy of measurement spot focusing, reducing blurring and improving the control of measurement radiation, thereby providing more reliable and precise metrology results for small product structures.
Implementation Method 1
a compensatory optical device operable to spatially modulate the wavefront of the measurement radiation so as to compensate for a non-uniform manufacturing defect in said optical arrangement
Implementation Method 2
an optical arrangement for focusing the measurement radiation onto said target structure, the optical arrangement comprising at least one optical element being arranged to receive said measurement radiation at a grazing incidence
Implementation Method 3
detecting scattered radiation resulting from the illumination of the target with the measurement radiation
Data Source
AI summary
Disclosed is an inspection apparatus and associated method for measuring a target structure on a substrate. The inspection apparatus comprises an illumination source for generating measurement radiation; an optical arrangement for focusing the measurement radiation onto said target structure; and a compensatory optical device. The compensatory optical device may comprise an SLM operable to spatially modulate the wavefront of the measurement radiation so as to compensate for a non-uniform manufacturing defect in said optical arrangement. In alternative embodiments, the compensatory optical device may be located in the beam of measurement radiation, or in the beam of pump radiation used to generate high harmonic radiation in a HHG source. Where located in the beam of pump radiation, the compensatory optical device may be used to correct pointing errors, or impart a desired profile or varying illumination pattern in a beam of the measurement radiation.