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Proceedings Paper

Low vacuum microscopy for mask metrology
Author(s): David C. Joy
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Paper Abstract

Because a photomask is typically a block of quartz partially covered a thin metal coating it charges significantly under an electron beam making CD metrology difficult and often imprecise. A solution to this problem can be found by performing the measurement in the presence of a low pressure of gas in a variable pressure scanning electron microscope (VPSEM). The gas is ionized by the emitted secondary electrons so producing both positive and negative ions which drift to the charged surface and neutralize it. This process is self controlling and requires no critical adjustments by the operator. With charging removed metrology can then be performed over a wide range of beam energies using either secondary or backscattered electron signals with excellent precision and accuracy. The presence of the gas atmosphere also eliminates beam induced contamination effects. If a chemically active precursor gas is injected into the system then the electron beam can also be used to edit and repair damaged masks.

Paper Details

Date Published: 24 May 2004
PDF: 8 pages
Proc. SPIE 5375, Metrology, Inspection, and Process Control for Microlithography XVIII, (24 May 2004); doi: 10.1117/12.532856
Show Author Affiliations
David C. Joy, Univ. of Tennessee/Knoxville (United States)
Oak Ridge National Laboratory (United States)

Published in SPIE Proceedings Vol. 5375:
Metrology, Inspection, and Process Control for Microlithography XVIII
Richard M. Silver, Editor(s)

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