A novel negative-tone bilayer scheme has been developed using organometallic imaging materials in conjunction with organic planarizing layers. Precursor films containing the radiation sensitive organometallics are spin coated and converted to a metal oxide through electron beam exposure to form an etch mask for pattern transfer. After exposure, the unexposed regions are washed away using an appropriate developer solution and the etch mask pattern is transferred through the organic planarizing layer by an oxygen reactive ion etch (RIE). In this work, a multicomponent organometallic precursor Ba(Sr,Ti) [Ba(2-ethylhexanote), Sr(2-ethylhexanote), Ti(IV)(diisopropoxide) (bisacetylacetonate)] is evaluated as a possible imaging material for bilayer lithography applications. The sensitivity of the 1:1:2 (molar ratio of metals) Ba(Sr,Ti) precursor was found to be 56.5 (mu) C/cm2 with a contrast of 16.1 at 10keV accelerating potential. In order to enhance the sensitivity, partial conversion of the precursor to the metal oxide prior to electron beam exposure through thermal baking was investigated. It was found that a 30 second thermal bake at 150 degree(s)C enhanced the sensivity to 23.3 (mu) C/cm2 but decreased the contrast to 4.2. Also, blanket etch studies on exposed samples found that the remaining organic ligands in the precursor are further converted to the metal oxide upon exposure to the O2 plasma causing shrinkage of the etch mask. After shrinkage, the precursor offers excellent etch selectivity as compared to hard baked novolac. This bilayer process is demonstrated by printing 200 nm line and space patterns using electron beam patterning.
A novel class of photosensitive organometallic precursor materials is used to pattern thin film mixed-metal oxide structures. In this work a photosensitive organometallic precursor is coated onto a silicon substrate and exposed to ultraviolet light through a mask to form patterned oxide structures. This is a negative-tone process in which the unexposed areas can be washed away using a developer solvent. In this work, lithographic contrast curves were measured to characterize the sensitivity and contrast of thin films composed of a mixture of the organometallic precursors for the oxides barium, strontium and titanium. Experiments directed at finding methods to increase the photo-speed of these materials were also conducted. It was found that partial pre-exposure conversion of these films using thermal baking could be used to enhance the sensitivity of these materials. A pre-exposure bake performed at 150 degrees C for 15 seconds was found to decrease the required exposure dose by a factor of two. Dielectric properties were measured for photochemically converted oxide films via electrical measurements on parallel plate capacitor devices. X-ray photoelectron spectroscopy (XPS) was used to quantify the relative amounts of carbon present in the finished films, and it was determined that thermally processes films had higher levels of carbon contamination.