Variable Liquid Lens Alignment Optics for Thick Resist and Warped Wafers
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Solution Overview
Problem
Current alignment systems in lithographic apparatuses face limitations such as fixed beam spot sizes, alignment failures with thick resists and warped wafers, undetectable Delta R effects, and the use of mechatronic elements that cause vibrations and heat generation, leading to inaccurate measurements.
Innovation Solution
The implementation of variable focal length lenses that adjust spot size and focus through voltage application, replacing fixed lenses and mechatronic elements to compensate for these shortcomings and improve alignment accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fixed beam spot size is used in alignment systems, then device complexity is reduced, but alignment precision deteriorates for thick resists and warped wafers
Solution Approach 1:
The patent applies dynamics by replacing fixed focal length lenses with variable focal length lenses that can dynamically adjust their focusing properties. This allows the beam spot size to be changed according to the specific measurement requirements, whether for thick resists, warped wafers, or standard substrates, thereby improving alignment precision without permanently increasing device complexity.
Solution Approach 2:
The patent implements parameter changes by enabling continuous adjustment of the focal length parameter of the lenses. This allows optimization of the beam spot size parameter for different measurement conditions, resolving the contradiction between maintaining simple fixed optics and achieving precise alignment measurements across varying substrate conditions.
2Measurement precision
If mechatronic elements are used for higher order rejection, then alignment accuracy is improved, but harmful factors increase due to vibrations and heat generation
Solution Approach 1:
The patent applies mechanics substitution by replacing mechatronic elements with purely optical variable focal length lenses for higher order rejection. This eliminates the mechanical moving parts that generate vibrations and heat, while maintaining the ability to achieve accurate alignment measurements through optical parameter adjustment alone.
3Productivity
If single illumination spot is used for multiple measurements, then device complexity is reduced, but measurement precision deteriorates due to serial measurement limitations
Solution Approach 1:
The patent implements universality by designing a variable focal length lens system that can perform multiple measurement functions with a single illumination spot. The lens can be adjusted to provide different spot sizes and focal positions, enabling the same optical path to handle various alignment measurement requirements without requiring multiple dedicated illumination systems.
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 variable focal length lenses enable adjustable spot sizes and focus, addressing alignment failures and reducing vibrations, thereby enhancing measurement precision and accuracy on thick stacks and warped substrates.
Implementation Method 1
variable focal length lenses that adjust spot size and focus through voltage application
Implementation Method 2
Toggling the voltage changes the curvature of a water-oil interface in the liquid lens, which in turn changes the direction of light passing through
Implementation Method 3
variable focal length lenses can also be applied to compensate for spot shift and Delta R effects
Data Source
AI summary
Systems and methods for providing variable spot size and variable focus at a substrate are described. Sets of variable focal length lenses can be added to an alignment system to allow for adjustment of the spot size and focus. A variable focal length lens is a liquid lens that is tunable based on application of voltage across the lens. Toggling the voltage changes the water-oil interface in the liquid lens, which in turn changes the direction of light passing through. For example, turning on the voltage across the lens shifts the light output direction to converging at a focal point. As a result, variable focal length lenses provide adjustment to compensate for the fixed spot size and focus shortcomings of the prior art. Furthermore, variable focal length lenses can also be applied to compensate for spot shift and higher order diffraction orders.