Variable Focus Project Lens for Lithography Depth-of-Focus
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Solution Overview
Problem
Conventional lithography scanners are limited by a fixed focus length, which results in a poor depth-of-focus (DOF) due to dramatic pattern density variations and feature height differences on semiconductor wafers, leading to decreased resolution in the lithography process.
Innovation Solution
A variable focusing project lens with multiple focus lengths is used, employing a liquid crystal layer and adjustable electrodes to tune the refractive index profile, allowing for different focus lengths within a single exposure field to accommodate varying feature heights, enabling improved depth-of-focus and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a fixed focus length is used in conventional scanners, then the exposure process is simple and fast, but the depth-of-focus is poor due to dramatic pattern density variations and feature height differences
Solution Approach 1:
The patent applies dynamics by making the focus length variable rather than fixed. The project lens is configured to provide multiple focus lengths within a single exposure field, allowing the optical system to dynamically adjust focus according to the topography of the substrate features. This resolves the contradiction by enabling the system to adapt focus length to match varying feature heights, thereby improving depth-of-focus while maintaining operational simplicity through automated control.
Solution Approach 2:
The patent changes the optical parameter of focus length from a fixed value to a variable parameter. By configuring the project lens to provide different focus lengths for different regions of the exposure field, the system can optimize focus for each specific area based on local feature height requirements. This parameter change directly improves manufacturing precision (depth-of-focus) while the automated lens control manages the complexity aspect.
2Manufacturing precision
If a fixed focus length is used, then the device structure is simple, but the resolution decreases in areas with significant pattern density and feature height variations
Solution Approach 1:
The patent applies local quality by providing different focus lengths for different regions (project pixels) of the exposure field. Each region of the project lens can be configured with an appropriate focus length matched to the local feature height and pattern density requirements. This localized optimization improves resolution in each specific area while the overall system manages complexity through systematic regional division and control.
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 solution enhances the lithography process by allowing multiple focus lengths within a single exposure field, effectively increasing the depth-of-focus and improving resolution, even in areas with significant pattern density and feature height variations.
Implementation Method 1
employing a liquid crystal layer and adjustable electrodes to tune the refractive index profile
Data Source
AI summary
A method of lithography includes obtaining a profile of a single field of a substrate that having a photoresist layer thereon, in which the profile includes a first feature and a second feature having different heights. A depth of focus distribution map is generated according to the profile. A project lens is tuned based on the generated depth of focus distribution map, such that the project lens provides a first focus length in a first project pixel of the project lens and a second focus length in a second project pixel of the project lens, wherein the first focus length and the second focus lengths. The single field of the substrate is exposed by using the tuned project lens.