Solid Immersion Lens Metrology Gap Control
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Solution Overview
Problem
Current techniques face challenges in maintaining accuracy and precision while reducing the size of metrology targets in lithographic processing, particularly in controlling the small gap distances between optical elements and substrates, which is crucial for advanced lithographic techniques like scatterometry.
Innovation Solution
The method involves using a solid immersion lens (SIL) with a high numerical aperture to achieve near-field radiation, and by controlling the gap between the SIL and the substrate using polarization state detection and processing of reflected radiation to produce a position signal for precise alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the size of metrology targets is reduced to increase measurement precision, then measurement precision is improved, but controlling the gap distance between optical elements and substrates becomes more difficult
Solution Approach 1:
The patent introduces an intermediary optical element (solid immersion lens or hyper-NA objective) between the radiation source and the substrate. This intermediary enables near-field radiation with effective numerical aperture greater than 1, allowing precise measurement of small targets while maintaining controllable gap distances through its optical properties and design
Solution Approach 2:
The patent changes the optical parameters by using solid immersion lenses with refractive indices greater than 1, transforming the radiation into near-field radiation. This parameter change enables the system to achieve both high measurement precision on small targets and manageable gap distance control through the optical element's physical properties
2Measurement precision
If a solid immersion lens is used to achieve near-field radiation with high numerical aperture, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The solid immersion lens serves as an intermediary optical element that simplifies the overall system design by consolidating the functions of high numerical aperture generation and near-field radiation control into a single component, rather than requiring multiple complex optical elements
Solution Approach 2:
By changing the refractive index parameter of the optical element to greater than 1, the system achieves hyper-NA capability without increasing mechanical or structural complexity, as the enhanced optical performance emerges from the material property itself
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 allows for more precise and accurate measurements with smaller targets, enhancing the sensitivity and decoupling of parameters in lithographic processes, thereby improving the overall precision and reliability of metrology in lithographic apparatuses.
Implementation Method 1
providing incident radiation of a first polarization state by an optical component into an object... detecting, from incident radiation reflected from the interface... radiation of a second different polarization state arising from the reflection of incident radiation of the first polarization at the interface
Implementation Method 2
detecting, from incident radiation reflected from the interface and from the surface, radiation of a second different polarization state arising from the reflection of incident radiation
Data Source
AI summary
A method involving providing incident radiation of a first polarization state by an optical component into an interface of an object with an external environment, wherein a surface is provided adjacent the interface and separated by a gap from the interface, detecting, from incident radiation reflected from the interface and from the surface, radiation of a second different polarization state arising from the reflection of incident radiation of the first polarization at the interface as distinct from the radiation of the first polarization state in the reflected radiation, and producing a position signal representative of a relative position between the focus of the optical component and the object.