Removal of Resist Materials Using Acetic Acid

Abstract

Polymer film removal from silicon surfaces was investigated using acetic acid at low temperatures. The polymer materials studied included poly͑methyl methacrylate͒, poly͑4-hydroxystyrene͒, and commercial positive photoresist ͑Shipley 1813͒. All polymer films studied were removed by acetic acid at 35°C, apparently by dissolution and in some cases, lift-off from the polymer-silicon interface. If an adhesion-promoting layer such as hexamethyldisilazane was applied to the silicon surface prior to polymer application, a thin carbon-based residue remained on the silicon surface as detected by X-ray photoelectron spectroscopy. A proposed solubility removal mechanism was investigated by using propionic and trifluoroacetic acids, since these acids possess different solubility and reactivity properties than acetic acid. Acetic acid was the most efficient for polymer removal and was capable of removing B ϩ and P ϩ ion-implanted (10 12 atoms/cm 2 ) photoresist.

Fabrication of Copper Window Electrodes with ≈108 Apertures cm−2 for Organic Photovoltaics

“…At the same time the low concentration of Cu dopant at the uppermost surface of the 62 nm ZnO film would reduce the n‐type character of the oxide thus increasing the barrier to electron injection into the conduction band, which would manifest as an apparent reduction in the conductivity normal to the plane of oxide film. To confirm that an increase in the conductivity of the ZnO overlayer is the reason for the reduction in the large electrode sheet resistance, the ZnO layer on five month old electrodes with a sheet resistance of 9 Ω sq −1 was selectively removed by etching with acetic acid (Figure S7, Supporting Information) . After this treatment the sheet resistance increases to ≈40 Ω sq −1 , which confirms that the doped ZnO overlayer is the reason for the reduction in sheet resistance.…”

“…Glacial acetic acid simultaneously dissolves residual PMMA and any oxide layer at the surface of the copper film that may have formed if the etching processing is performed in air. Glacial acetic acid is known to preferentially remove copper oxides from the surface of copper leaving the metal surface residue free . Notably, for PMMA layers that are ≤25 nm thick acetic acid treatment alone is sufficient to completely remove the PMMA layer.…”

“…Glacial acetic acid is known to preferentially remove copper oxides from the surface of copper leaving the metal surface residue free . Notably, for PMMA layers that are ≤25 nm thick acetic acid treatment alone is sufficient to completely remove the PMMA layer. Together the process illustrated in Figure enables the fabrication of copper electrodes with a random distribution of ≈100 million circular apertures cm −2 , the average size of which can be altered by changing the concentration of the polymer blend, which enables control within the diameter range of 50–1000 nm (Figure S2, Supporting Information).…”

“…Notably, ≈40 Ω sq −1 is ≈10 Ω sq −1 higher than that of freshly etched Cu electrodes; 29.8 ± 0.7 Ω sq −1 . Such an increase is not however unexpected since: (i) the Cu that has diffused into the ZnO layer (and is thus removed upon etching) has reduced the thickness of the metal film; (ii) at the interface between the Cu film and the ZnO overlayer it is plausible that the Cu has been partially oxidized, forming a thin Cu oxide interlayer which would be readily etched by acetic acid, and so this would also reduce the Cu metal thickness.…”

Solvent enhanced resist flow for room temperature imprint lithography

“…4 There are several methods reported to produce nanoimprinted features at temperatures as low as room temperature, including using polystyrene, 5 hydrogen silsesquioxane ͑HSQ͒, 6 and lift-off resists. [10][11][12] The nature of the resist at room temperature is compared with that at a normal high temperature process, and the process conditions that provide successful results are evaluated. 8 Solvent vapor treatments can also be used to enhance the viscous plasticity of polystyrene at low temperature.…”