Diffractive Optical Device Dipole Pupil Filter
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Solution Overview
Problem
Current pupil filters in semiconductor aligners face challenges with light transmission efficiency, coherence leading to fluctuating pattern sizes, and increased load on optical proximity correction due to smaller mask pattern pitches, which affect resolution and fabrication costs.
Innovation Solution
A diffractive optical device forming a dipole pupil filter with fan-like light transmissive areas symmetric about the center, an area of low light transmittance between them, and a light block area outside, optimized for parameters such as inner and outer diameters, angular aperture, and light intensity to enhance light transmission and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional round pupil filter is used, then light transmission is maintained, but resolution is insufficient for finer semiconductor devices
Solution Approach 1:
The pupil filter is segmented into multiple discrete light transmissive areas (first, second, third, and fourth light transmissive areas) arranged in a specific pattern, rather than using a continuous round aperture. This segmentation allows selective transmission of diffracted light orders while maintaining sufficient total light transmission, thereby improving resolution without completely sacrificing light efficiency.
Solution Approach 2:
Different regions of the pupil filter are assigned different functions: the first and second light transmissive areas transmit +1 and -1 order diffracted light respectively, while the third and fourth areas transmit +2 and -2 order light. This local differentiation of transmission characteristics enables precise control over the illumination angular spectrum, improving resolution for fine patterns while maintaining overall light efficiency.
2Manufacturing precision
If the mask pattern pitch is reduced for finer devices, then device density increases, but coherence increases causing pattern size fluctuations
Solution Approach 1:
The pupil filter transmits multiple discrete diffracted light orders (+1, -1, +2, -2) through separate light transmissive areas, creating a multi-valued angular spectrum. This segmentation of the angular spectrum prevents excessive coherence even when mask pitch is reduced, thereby stabilizing pattern size while maintaining adaptability to fine device dimensions.
Solution Approach 2:
The invention changes the angular spectrum parameters by transmitting multiple diffracted light orders with different angles. This parameter change in the illumination system allows the system to maintain stable pattern imaging across different mask pitch values, reducing sensitivity to pitch variations and minimizing pattern size fluctuations.
3Manufacturing precision
If multiple diffracted light orders are transmitted, then angular spectrum is enhanced for resolution, but device complexity increases
Solution Approach 1:
The pupil filter employs an asymmetric arrangement of light transmissive areas relative to the optical axis, with the first and second areas positioned at different angular locations than the third and fourth areas. This asymmetric configuration efficiently generates the required multi-valued angular spectrum while maintaining a relatively simple structure that can be fabricated using standard photolithography 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
This configuration maintains high light transmission efficiency, reduces pattern size fluctuations, and minimizes the load on optical proximity correction, achieving stable and high-resolution optical images for semiconductor fabrication.
Implementation Method 1
a diffractive optical device forming a dipole pupil filter with fan-like light transmissive areas symmetric about the center
Data Source
AI summary
The invention relates to a pupil filter used for the illumination optical system of a semiconductor aligner or the like that can prevent a decrease in the quantity of light having transmitted through it, enhance the efficiency of semiconductor exposure, reduce loads of correction by the optical proximity effect and yield a stable yet high-resolution optical image without engendering size fluctuations of a pattern imaged on a wafer depending on a mask pattern pitch. Specifically, the invention provides a diffractive optical device for the formation of a pupil filter used for the illumination optical system of an aligner adapted to direct light emanating from a light source to a mask via an illumination optical system and project a pattern on the mask onto an alignment substrate and exposing it to light via a projection optical system. The pupil filter formed by the diffractive optical device is a dipole pupil comprising two light transmissive areas (11). The two light transmissive areas (11) are in a fan-form configuration symmetric at a given distance from the center of the pupil filter, between them there is an area (12) of low light transmittance, and outside the two light transmissive areas (11) and the area (12) of low light transmittance there is a light block area (13).