Design of Two-Dimensional Optical Alignment Signals Robust to Diffractive Effects

Mask alignment is one of the most critical processes in photolithography. Prior to the shadow projection, the alignment between the lithographic mask and the silicon wafer is needed. In contact and proximity photolithography, a method to achieve the alignment with submicron or even nanometer resolut...

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Bibliographic Details
Published in:Journal of lightwave technology 2008-06, Vol.26 (12), p.1702-1707
Main Authors: Saez-Landete, J., Salcedo-Sanz, S., Cruz-Roldan, F., Amo-Lopez, P., Blanco-Velasco, M.
Format: Article
Language:English
Subjects:
Alignment
Applied sciences
Codes
Coding, codes
Degradation
Design engineering
Diffraction
Electronics
Exact sciences and technology
Genetic algorithms
Gratings
Information, signal and communications theory
Lithography
Masks
Mathematical models
Microelectronic fabrication (materials and surfaces technology)
Optical communication
Optical design
optical device fabrication
Optical diffraction
optical position measurement
optical transducers
optimization methods
Photolithography
position measurement
Robustness
Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
Signal analysis
Signal and communications theory
Signal design
Signal resolution
Silicon
Silicon wafers
Telecommunications and information theory
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Summary:Mask alignment is one of the most critical processes in photolithography. Prior to the shadow projection, the alignment between the lithographic mask and the silicon wafer is needed. In contact and proximity photolithography, a method to achieve the alignment with submicron or even nanometer resolution consists of superimposing two identical 2-D zero reference codes and registering the optical output signal. In order to increase the resolution of the system, the size of the code must be reduced and the diffractive effects become strong. The signal is then degraded and the precision of the alignment is reduced. In this paper, the effect of the diffraction in 2-D codes is analyzed, the degradation of the signal is characterized and its effect is modelled by means of a simple and fast computing parameter. Finally, we propose a genetic algorithm to optimize this parameter and design 2-D codes robust to diffractive effects. We propose the use of these codes to increase the resolution of alignment systems.
ISSN:0733-8724
1558-2213
DOI:10.1109/JLT.2008.919428