Low vacuum microscopy for mask metrology

David C. Joy

doi:10.1117/12.532856

24 May 2004 Low vacuum microscopy for mask metrology

David C. Joy

Proceedings Volume 5375, Metrology, Inspection, and Process Control for Microlithography XVIII; (2004) https://doi.org/10.1117/12.532856
Event: Microlithography 2004, 2004, Santa Clara, California, United States

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.

Citation Download Citation

David C. Joy "Low vacuum microscopy for mask metrology", Proc. SPIE 5375, Metrology, Inspection, and Process Control for Microlithography XVIII, (24 May 2004); https://doi.org/10.1117/12.532856

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