Femtosecond pulsed light polarization induced effects in direct laser writing 3D nanolithography

We demonstrate how the coupling between (i) polarization of the writing laser beam, (ii) tight focusing and (iii) heat conduction affects the size, shape and absorption in the laser-affected area and therefore the polymerization process. It is possible to control the sizes of 3D laser-produced structure at the scale of several nanometers. Specifically we were able to tune the aspect ratio of 3D suspended line up to 20% in hybrid SZ2080 resist. The focal spot of tightly focused linearly polarized beam has an elliptical form with the long axis in the field direction. It is shown here that this effect is enhanced by increase in the electronic heat conduction when polarization coincide with temperature gradient along with the absorption. Overlapping of three effects (i- iii) results in the difference of several tens of nanometers between two axes of the focal ellipse. Narrow line appears when polarization and scan direction coincide, while the wide line is produced when these directions are perpendicular to each other. The effect scales with the laser intensity giving a possibility to control the width of the structure on nanometer scale as demonstrated experimentally in this work. These effects are of general nature and can be observed in any laser-matter interaction experiments where plasma produced by using tight focusing of linear-polarized light.