Bi-telecentric Projection Objective with Aspheric Lens Groups
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Solution Overview
Problem
Projection photolithography systems face challenges due to a large number of lenses leading to energy absorption and reduced transmittance, as well as sensitivity to mask surface defects caused by large object side telecentricity, which affects exposure quality.
Innovation Solution
A compact projection objective design with a reduced number of lenses and a bi-telecentric structure, comprising specific lens groups with aspheric surfaces, optimized to minimize lens count, enhance transmittance, and reduce sensitivity to mask defects, featuring a sequence of lens groups with positive and negative focal powers and strategically placed aspheric surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large number of lenses are used in the objective system, then the imaging performance can be improved, but the energy absorption increases and the overall transmittance decreases
Solution Approach 1:
The patent merges multiple lens functions into fewer lens elements by using aspheric surfaces with higher-order terms. The aspheric lens design integrates what would traditionally require multiple spherical lenses into single elements, reducing the total lens count from many to just five lens groups while maintaining imaging performance and reducing energy absorption.
2Ease of operation
If the objective system has a large object side telecentricity, then the chief ray angle is increased, but the sensitivity to mask surface defects is greatly enhanced
Solution Approach 1:
The patent changes the telecentricity parameter from large to small by optimizing the aspheric lens design. The fifth-order aspheric terms are specifically configured to reduce the chief ray angle at the object side, thereby decreasing sensitivity to mask surface defects while maintaining the desired optical performance.
3Volume of moving object
If multiple lens groups are used to achieve compact structure, then the volume is reduced, but the manufacturing complexity increases
Solution Approach 1:
The patent uses aspheric surfaces with fifth-order curvature terms instead of simple spherical surfaces. This allows each lens element to achieve complex light path control that would otherwise require multiple elements, reducing the overall number of lenses and compacting the structure while the aspheric profiles are manufactured using precision molding or grinding techniques.
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 results in a more compact and cost-effective optical structure with improved transmittance and reduced sensitivity to mask defects, optimizing aspheric lens design and manufacturing complexity while maintaining high exposure quality.
Implementation Method 1
a first lens group with a positive focal power, comprising a first lens sub-group with a negative focal power, wherein one lens of the first lens sub-group has an aspheric surface at a side close to the object side
Data Source
AI summary
A projection objective, used for projecting an object space to an image space. The objective includes, from the object space along an optical axis in sequence: a first lens set (G1) having positive focal power, a second lens set (G2) having negative focal power, a third lens set (G3) having positive focal power, a fourth lens set (G4) having negative focal power, and a fifth lens set (G5) having positive focal power. Aspheric lenses are provided in the first lens set (G1), the second lens set (G2), the third lens set (G3), the fourth lens set (G4), and the fifth lens set (G5). According to the design, the number of lenses is reduced, the structure of the objective is more compact, the transmittance of the objective is improved, the structural design of aspheric lenses is optimized, the asphericity of the aspheric lenses is reduced, the processing difficulty and costs for the aspheric lenses are reduced, and except for the above situations, the objective has a bitelecentric structure, and the sensitivity of the objective for micro irregularity defects on a mask surface is reduced.