We found that the tip size of a tapered hollow micro-tube can affect the properties of an emitted Bessel light beam. In addition, the incident light polarization state was also found to influence the characteristics of the emitted light beam. From a lithography viewpoint, we looked at the correlation between an emitted Bessel light beam from a subwavelength annular aperture on metallic film and from a tapered hollow micro-tube. Intensity profiles were analyzed using finitedifference time-domain (FDTD) simulations and lithography experiments were undertaken. The approaches used to couple the incident light into the hollow micro-tube and to the subwavelength annular aperture are discussed. Effects from the waveguide mode were studied. Our results showed that the tube thickness of the tapered hollow micro-tube tip is an important factor in generating the Bessel light beam wavelength. We show that lithography can be used with a through-silicon-via (TSV) process in a far-field region while maintaining a near diffraction-limit spot size. Our tapered hollow tube design is useful for applications such as optical lithography, super resolution optical detection, and fabrication of high aspect ratio structures.
In this paper, we proposed a tapered hollow tube which can produce a near diffraction-limit spot and focus the incident
light in far-field region. From previous researches, the sub-wavelength annular aperture (SAA) made on metallic film
generates a Bessel beam in far-field region. Also, the traditional tapered fiber has been widely used in near-field
scanning optical microscope (NSOM) to achieve super-resolution in near-field. Combining these two concepts, tapered
hollow tube was shown to have great potential in creating a small sub-micron spot size and long depth of focus (DOF)
emitted light beam. By using the commercially available capillary and fiber heat-pulling method, it was found that tube
processed per design to be disclosed in this paper can achieve Bessel beam as well. It will be shown that the SAA-like
structure was actually implemented by the geometry of the tube tip. From FDTD simulation and experiment, the emitted
beam was identified to have more than 10 μm DOF and 250-300 nm focal spot excited by using the 408 nm laser source.
These results not only can help us pursue lithography applied to create through silicon via (TSV) process in far-field
region while maintaining near diffraction-limit spot size. The high throughput and side lobe became a serious problem
when continuous incident light was used. To circumvent this problem, the incident light from was changed from
continuous to pulse type and a suitable lithography experimental system designed by using three-axis displacement
platform was developed. All results will be detailed in this paper.