Seigi Suh

Electron beam lithography process using radiation sensitive carboxylate metalorganic precursors

A bilayer process has been developed for electron beam lithography using radiation sensitive metalorganic precursors as imaging layers in conjunction with organic planarizing layers. Upon electron beam irradiation, the precursor is converted to a metal oxide which serves as an etch mask for subsequent pattern transfer through the planarizing layer. In this article, a titanium(n-butoxide)2(2-ethylhexanoate)2 precursor was investigated that exhibits sensitivity and contrast of 495 μC/cm2 and 2.75, respectively, 10 keV accelerating potential. The sensitivity was further enhanced to 72 μC/cm2 using a pre-exposure thermal bake to partially convert the precursor to metal oxide prior to electron beam imaging. Additionally, it was found that combining the titanium(n-butoxide)2(2-ethylhexanoate)2 precursor with a similar precursor containing a higher atomic number metal center, barium(2-ethylhexanoate)2 in this work, also enhanced the sensitivity to 157 μC/cm2 for a 1:1 molar mixture of the precursors. After imagi...

Hybrid bilayer imaging approach using single-component metal-organic precursors for high-resolution electron beam lithography

A hybrid bilayer imaging approach has been developed which uses a thin radiation sensitive, single component, metal-organic precursor film in conjunction with a thicker organic planarizing etch barrier. Upon electron beam irradiation, the metal-organic precursors are converted to a metal-oxide etch mask and the pattern can be transferred through the organic etch barrier layer using an oxygen reactive ion etch. These novel precursors can also be converted to the metal-oxide using deep ultraviolet optical irradiation or thermal baking. Therefore, a combination of blanket conversion steps followed by the patterning process can be utilized in order to reduce imaging doses. In this work, results of characterizing a titanium(n-butoxide)2(2-ethylhexanoate)2 precursor are presented due to its combined properties of hydrolytic stability and moderate sensitivity. It was found that using a blanket thermal bake step of 1, 2, and 3 minutes at 150°C prior to electron beam exposure increased the sensitivity of the materials to 200, 90, and 72 µC/cm2 respectively. However, the contrast of the material decreased from 4.40 to 2.17 as a consequence of pre-exposure thermal baking. The etching characteristics of the metal-organic precursor were also studied in ashing and silicon dioxide etching plasmas. It was found that the etch rate in the different plasmas depends strongly on the extent of conversion of the metal-organic film. Films with higher extents of conversion to the metal-oxide provide higher etch resistance in general. The patterning capability with these metal-organic precursors is demonstrated on top of both silicon substrates and hard baked novolac films.

Direct thin-film imaging, DTFI, based on PMOD (photochemical metal-organic deposition) methodology

Considerable difficulties and limitations are associated with the patterning of thick photoresist layers to generate high aspect ratio features in MEMS fabrication. Moreover, a large number of steps is needed to achieve the patterned MEMS structures. The PMOD methodology takes advantage of direct patterning of a photoimageable, highly etch resistant inorganic metal oxide precursor to form the hard mask. A spin coated thin TiO2 film deposited onto a Novolac transfer layer has been evaluated. An etch ratio of 850:1 between Novolac resin and TiO2 thin-film has been achieved by oxygen gas RIE. One set of process parameters demonstrated vertical sidewalls on 10 m thick Novolac using a 20 nm patterned TiO2 thin-film. Photo resolution of the TiO2 films as small as 0.5 m has been demonstrated using a contact aligner. In addition to applying our process to silicon substrates, we have also demonstrated the feasibility of patterning on ceramic alumina substrates. The plasma-etch residues and the PMOD film were removed by wet chemical cleaning solutions developed at EKC Technology.