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Title:Electron beam interactive oxide films for nanometer scale lithography
Author(s):Hollenbeck, James Lowell
Doctoral Committee Chair(s):Buchanan, Relva C.
Department / Program:Materials Science and Engineering
Discipline:Materials Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Electronics and Electrical
Physics, Condensed Matter
Engineering, Materials Science
Abstract:A number of oxide thin films produced by rf sputtering have been found to show high resolution lithographic characteristics when exposed under high dose rate conditions in a scanning transmission electron microscope. Holes and lines less than 10 nm in dimensions have been formed in amorphous films of Al$\sb2$O$\sb3$, Y$\sb2$O$\sb3$, Sc$\sb2$O$\sb3$, $\rm 3Al\sb2 {O\sb3}{\cdot}{2SiO\sb2}$ and $\rm {MgO}{\cdot}{Al\sb2}{O\sb3}$ through the direct removal of material during exposure. Complete exposure in these films was produced in less than 80 ms using a dose rate of $1 \times 10\sp5$ A/cm$\sp2$. In addition to the requirement of amorphous film structure the material characteristics found to be important in determining film response included high ionic character, high heat of formation and incorporation of inert gas into the structure. The high resolution characteristics in amorphous Al$\sb2$O$\sb3$ films allowed the production of 5.0 nm holes with a minimum center-to-center spacing of 8.9 nm.
The effects of film thickness, inert gas incorporation and exposure parameters were studied using amorphous Al$\sb2$O$\sb3$ films. An optimum thickness was found to occur at approximately 90 nm where the dose required for exposure was $25 \times 10\sp2$ C/cm$\sp 2$ ($\sim$25 ms). Argon concentrations could be controlled over the range of approximately 1.0-2.5 At.% and films containing larger amounts of Ar showed improved sensitivity. Increasing the dose rate of exposure resulted in decreased time and increased total dose requirements for exposure. No threshold current densities for material removal were observed above $1 \times 10\sp3$ A/cm$\sp2$. A qualitative model of the exposure process has been developed which describes material removal as a sequence of events involving the desorption of surface species, generation of bulk defects, preferential diffusion of cations and rapid expulsion of oxygen and inert gas from the exposed volume. Such a model is consistent with observations made during and after exposure of oxide resist materials.
Evaluation of amorphous Al$\sb2$O$\sb3$ and AlF$\sb3$ films exposed under the same conditions revealed similar dose requirements in the two materials, however, the exposure process appears to be slightly different. Less extensive damage to unexposed regions of Al$\sb2$O$\sb3$ films have shown them to have superior characteristics for exposure of line patterns.
Issue Date:1989
Rights Information:Copyright 1989 Hollenbeck, James Lowell
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9010889
OCLC Identifier:(UMI)AAI9010889

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