Dynamic Projection Objective Aberration Control
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Solution Overview
Problem
Conventional microlithographic projection exposure methods face challenges in ensuring high-quality imaging on substrates with uneven surfaces, leading to increased reject rates due to insufficient focus and imaging errors caused by substrate and mask surface irregularities.
Innovation Solution
A step-and-scan projection exposure method that dynamically adjusts the imaging properties of the projection objective by varying aberrations, such as field curvature, during the scanning operation to compensate for substrate and mask surface unevenness, using manipulators to change the optical effects of field elements like mirrors and refractive elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional microlithographic projection exposure methods are used, then the imaging process is simple and fast, but imaging quality deteriorates on substrates with uneven surfaces due to focus errors and aberrations
Solution Approach 1:
The patent applies dynamics by dynamically adjusting the imaging properties of the projection objective during the scanning operation. The aberrations, particularly field curvature, are varied in real-time to compensate for substrate and mask surface unevenness, transforming a static optical system into an adaptive one that maintains focus quality across uneven surfaces
Solution Approach 2:
The patent changes optical parameters of the projection objective during exposure. Specifically, the aberrations (particularly field curvature) are modified as a function of time and position to match the surface profile deviations. This parameter adjustment allows the optical system to adapt to varying surface heights, maintaining imaging quality despite substrate or mask irregularities
2Manufacturing precision
If the projection objective dynamically adjusts imaging properties by varying aberrations, then imaging quality on uneven substrates improves, but the complexity of the projection objective increases
Solution Approach 1:
The projection objective is transformed from a static to a dynamic system by introducing time-varying aberration adjustments. Manipulators modify the optical path during scanning, enabling the objective to adapt its imaging properties in real-time according to the surface profile, thereby handling uneven substrates without sacrificing image quality
Solution Approach 2:
Manipulators serve as intermediary devices between the control system and the optical elements of the projection objective. These manipulators physically adjust components like mirrors or refractive elements to introduce controlled aberrations that compensate for surface unevenness, acting as mediators that translate surface profile data into optical corrections
3Productivity
If scanning operation is used instead of step-and-shoot, then productivity improves, but maintaining focus across the exposure area becomes more difficult with uneven surfaces
Solution Approach 1:
The patent combines scanning operation with dynamic aberration adjustment, where the optical system continuously adapts during the scan. As the beam moves across the exposure area, the manipulators adjust the field curvature and other aberrations in real-time to maintain focus on uneven surfaces, enabling high-speed scanning without sacrificing focus quality
Solution Approach 2:
The system uses feedback from surface profile measurements to control the manipulators. The known surface topology (from prior measurement or real-time sensing) feeds into the control system, which then adjusts the optical aberrations accordingly during scanning, creating a closed-loop system that maintains focus despite surface variations
Data Source
AI summary
A projection exposure method includes exposing an exposure area of a radiation sensitive substrate with at least one image of a pattern of a mask in a scanning operation. The scanning operation includes moving the mask relative to an effective object field of the projection objective and simultaneously moving the substrate relative to an effective image field of the projection objective in respective scanning directions. The projection exposure method also includes changing imaging properties of the projection objective actively during the scanning operation according to a given time profile to change dynamically at least one aberration of the projection objective between a beginning and an end of the scanning operation.