2X Projection Objective Lens Groups for Large Field Lithography
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Solution Overview
Problem
Current semiconductor processing technologies face challenges in achieving high-throughput projection optical systems with millimeter-level resolution and large exposure fields, particularly in adapting for reticle sizes with magnifications higher than 1X, such as 2X, while effectively correcting aberrations like distortions, field curvatures, and chromatic aberrations.
Innovation Solution
A 2X projection objective is designed with a multi-lens system comprising four lens groups (G31, G32, G33, G34) made of high and low refractive index materials, optimized through specific focal length and Abbe number ratios to correct aberrations and ensure telecentricity, achieving a partial field of view of not less than 100 mm and suitable for I-line light with a wavelength band of ±5nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large exposure field design is adopted to achieve high throughput, then productivity is improved, but device complexity increases due to the need for more lenses and complex optical paths
Solution Approach 1:
The optical system is divided into four distinct lens groups (G31, G32, G33, G34) with specific positive refractive powers, where each group contains a specific number of lenses (4, 6, 4, 6 respectively). This segmentation allows the large exposure field requirement to be met while distributing the optical complexity across manageable modules, making the system both high-throughput and manufacturable.
2Adaptability or versatility
If magnification of 2X is adopted to adapt for reticle size, then adaptability is improved, but manufacturing precision requirements increase due to stricter aberration correction needs
Solution Approach 1:
Different lens groups are assigned different numbers of lenses and specific refractive power characteristics tailored to their local functional requirements. For example, G32 and G34 each have 6 lenses with specific positive powers to handle particular aberration correction tasks, while G31 and G33 have 4 lenses each. This local optimization enables 2X magnification adaptability while managing manufacturing precision requirements through distributed functional specialization.
Solution Approach 2:
The patent employs a composite lens structure where each lens group contains multiple lenses with different refractive powers and Abbe numbers. This composite approach within each lens group enables sophisticated aberration correction (including chromatic and spherical aberrations) necessary for 2X magnification, while distributing the precision requirements across multiple elements rather than demanding ultra-precision from a single element.
3Manufacturing precision
If multiple lens groups with specific refractive powers are used to correct aberrations, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
Each of the four lens groups (G31, G32, G33, G34) with positive refractive powers serves multiple functions: they collectively provide the required 2X magnification, individually and collectively correct various aberrations (spherical, chromatic, astigmatism), and maintain telecentricity on both object and image sides. This multi-functionality of each lens group reduces the need for additional specialized components, achieving superior aberration correction without proportionally increasing device complexity.
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 achieves a 2X projection objective with improved resolution and correction of distortions, field curvatures, and chromatic aberrations, ensuring sufficient exposure light intensity and millimeter-level resolution with a simpler structure and fewer lenses compared to existing systems.
Implementation Method 1
a first lens group G31 having a positive refractive power; a second lens group G32 having a positive refractive power; a third lens group G33 having a positive refractive power; and a fourth lens group G34 having a positive refractive power
Data Source
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AI summary
A lithography projection objective (30) for focusing and imaging a pattern of a reticle onto a wafer including, from the reticle and along an optical axis: a first lens group G31 having a positive refractive power; a second lens group G32 having a positive refractive power; a third lens group G33 having a positive refractive power; and a fourth lens group G34 having a positive refractive power. These four lens groups form a 2X magnification design which has a partial field of view of not smaller than 100 mm; a wavelength band of I-line±5nm can ensure a sufficient exposure light intensity. Moreover, the present invention also achieves, with a relatively simple structure, the demanded millimeter-level resolution as well as the correction of distortions, field curvatures, astigmatisms and chromatic aberrations in a large field.