The technology of 193nm immersion lithography has been progressing rapidly toward half-pitch 45 nm generation
device manufacturing. However, some intrinsic issues, the photoacid leaching and the watermark defect have remained
in the immersion process. Most of approaches to overcome them were the introduction of cover coating materials (top
coat) onto the resist film. Recently, we have established the non-top coat resist using novel two kinds of materials, a low
leaching PAG (PhotoAcid Generator) and a surface modifier. The hydrophobic photoacid generated from the low
leaching PAG decomposes by heating, and the acid migration changes to reduce the line-width roughness (LWR). The
surface modifier behaves as builded-topcoat by the distribution around resist surface and enhances the surface
hydrophobicity. Herein we propose the concept of novel PAG and surface modifier for immersion lithography.
The immersionspecific watermark defect is discussed in its formation mechanism and in the influence of materials and exposure process. The non-topcoat approach was the basis of the work, where the properties of resist surface itself played the key role. Water droplets left on the resist surface were considered to induce the watermark defect in two possible ways; (1) the droplet is carried over to PEB process and impact the resist properties under the heat, (2) the droplet already evaporates before the PEB leaving some residue on the surface. A notable reduction in the resist dissolution rate was observed in the former case, which could be due to either physical or chemical change in the resist materials triggered by the water, and thereby would result in an unavoidable patterning failure. Therefore it is essential not to leave any water droplets on the surface in preventing the watermark formation. A very much hydrophobic materials design was proven effective in achieving this. The watermark formation was correlated to the scanning speed of immersion showerhead and the defectivity was evaluated in this perspective. The receding contact angle of the resist surface was found to well correlate to the "allowable" scanning speed, and was concluded that the higher was the better. A resist material was newly designed by using a hydrophobic polymer on this basis and the resist demonstrated a promising results not only in the watermark defectivity but also in lithographic performance.
The depolarization of light in diffused medium was studied by observation of temporal profiles of orthogonally polarized components. The time dependence of depolarization of light in diffused medium was simulated by using the Monte Carlo method. The projection data of absorbers hidden in highly scattering medium were taken by the method for detecting photons which preserved initial polarization using a phase modulator. The floor level due to diffused light was significantly suppressed by our method. The reconstructed optical CT image exhibited high spatial resolution in comparison with the image from the projection data taken by a conventional method.
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