Stitching Submicron Periodic Patterns over a Planar Substrate and a Roller by Utilizing Step-and-Align Interference Lithography
Date Issued
2011
Date
2011
Author(s)
Chen, Yung-Pin
Abstract
A Step-and-Align Interference Lithography (SAIL) system is developed for fabricating continuous submicron periodic patterns over a silicon wafer with diameter of 100 mm and a metal roller with radius of curvature 25 mm. By utilizing two-beam interference lithography to expose submicron periodic patterns in a small square area and the position stages with high precision control system to stepwise move or rotate the substrate, the small exposure regions are stitched to be large-area submicron periodic patterns.
The SAIL system is composed of two fabrication modes; plane mode and roller mode, which can be used to fabricate and stitch the interference patterns on a planar sub-strate and a roller, respectively. A flip bending mirror is used to control the propagation direction of laser beam, and then the interference patterns exposed in the plane or roller mode can be switched conveniently. The optical module in each mode has three functions; beam stabilization function to trace and stabilize the laser beam’s drifting from the argon ion laser placed on a separate table, beam expansion function to expand a small laser beam to a large-area collimated Gaussian beam, and two-beam interference function to have two beams interfered with equal intensity by splitting the expanded beam via a beamsplitter on the substrate coated with photoresist.
To obtain uniform exposure dose distribution over the whole large area after step-wise stitching the small exposure regions, a beam profile is designed to have the unit ex-posure area with designed dose distribution. However, there is no beam shaper to trans-form the laser beam into the designed beam. A metal mask with a square open window set up before the substrate is used to truncate the central region of the expanded Gaussian beam whose intensity distribution is more uniform to be the unit exposure area. The Gaussian intensity distribution is smoother in the small region of the expanded beam, which has large tolerance for the overlapping misalignment of two incident beams. Even though the overlapping misalignment is about 2 mm, the interference contrast in the overlapping area could still be higher than 0.99.
The interference patterns with period about 700 nm and 800 nm are stitched suc-cessfully over the wafer and the roller. There are about 90 unit exposure areas stitched over the wafer and 120 unit exposure areas stitched over the roller, which take half an hour and an hour, respectively. The process times are much shorter than those of other fabrication methods for making submicron periodic patterns such as e-beam lithography. Although the reflectance spectra of the fringes in the single interference regions and the overlapping regions vary owing to some disturbances, the connection of the submicron periodic fringes and the continuity of fringes for a long distance are verified by utilizing the OM and the SEM. The one- and two-dimensional patterns with the period smaller than 300 nm can be fabricated in the single interference regions without stitching by uti-lizing the optical interference lithography module.
Subjects
Step-and-align interference lithography(SAIL)
submicron periodic structures
large area
roller
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