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Technology for fabricating layered oxide sensor structures

The contribution of the IET to the project was the development of the technology of optical metal/oxide multilayer sensors for the detection of environmentally important gases. Process sequence towards the fabrication of micrometer- and submicrometer-size grating-based structures involves deposition of metal/oxide multilayers, photolithography and etching.

Metal/oxide multilayer structures composed of metal films with thicknesses varying from 2 nm to 100 nm and 150-800 nm thick metal oxide layers were deposited by magnetron sputtering. Metals such as Pt, Pd, Ru, Au or Zn and oxides such as SnO2 or ZnO were deposited from metallic targets via Ar or reactive Ar/O2 sputtering, respectively. Depositions were performed in a multitarget sputtering system without breaking vacuum.

To achieve highly anisotropic etch profiles and smooth side-walls, sputter Ar-ion etching of metal/oxide multilayer structures was elaborated.

Since the conventional photoresist masks were not sufficiently selective during dry etching, appropriate hard metal (Ti, Cr, Ni or Al) or SiO2/metal/SiO2 trilevel mask were developed and successfully applied. The patterns were defined first in the hard mask and next transferred to the metal/oxide multilayers. Finally, the mask was removed with a selective etch revealing the underlying diffractive structure.

An alternative approach, designed to pattern metal/oxide multilayers with difficult to etch refractory metals, involved lift-off lithography and deposition of metal/oxide multilayers. Due to the fact that for lift-off lithography the substrates are covered with resist layers, deposition parameters were optimised to avoid unintentional heating during sputtering.

The achievements of this project should allow the development of more complex elements as well as other oxide-based devices.

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Institute of Electron Technology, Dept. of Semiconductor Processing for Photonics
Al. Lotnikow 32/46
02-668 Warsaw
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