Multiphoton lithography

Multiphoton lithography

Multiphoton lithography (also known as direct laser lithography or direct laser writing) of polymer templates has been known for years by the photonic crystal community. Similar to standard photolithography techniques, structuring is accomplished by illuminating negative-tone or positive-tone photoresists via light of a well-defined wavelength. The fundamental difference is, however, the avoidance of reticles. Instead, two-photon absorption is utilized to induce a dramatic change in the solubility of the resist for appropriate developers.

Hence, multiphoton lithography is a technique for creating small features in a photosensitive material, without the use of complex optical systems or photomasks. This method relies on a multi-photon absorption process in a material that is transparent at the wavelength of the laser used for creating the pattern. By scanning and properly modulating the laser, a chemical change (usually polymerization) occurs at the focal spot of the laser and can be controlled to create an arbitrary three-dimensional periodic or non-periodic pattern. This method has been used for rapid prototyping of structures with fine features.

Since two-photon absorption is a second-order, non-linear process several orders of magnitude weaker than linear absorption, very high light intensities are required to increase the number of such rare events. For example, tightly-focused laser beams provide the needed intensities. Here, pulsed laser sources are preferred as they deliver high-intensity pulses while depositing a relatively low average energy. To enable 3D structuring, the light source must be adequately adapted to the photoresist in that single-photon absorption is highly suppressed while two-photon absorption is favored. This condition is met if and only if the resist is highly transparent for the laser light's output wavelength λ and, simultaneously, absorbing at λ/2. As a result, a given sample relative to the focused laser beam can be scanned while changing the resist's solubility only in a confined volume. The geometry of the latter mainly depends on the iso-intensity surfaces of the focus. Concretely, those regions of the laser beam which exceed a given exposure threshold of the photosensitive medium define the basic building block, the so-called voxel. Other parameters which influence the actual shape of the voxel are the laser mode and the refractive-index mismatch between the resist and the immersion system leading to spherical aberration.

References



Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • Jonathan Dowling — Infobox Scientist name = Jonathan P. Dowling birth date = birth place = Smithtown, New York residence = flagcountry|USA nationality = flagcountry|Ireland flagcountry|USA field = Physicist work institution = Louisiana State University alma mater …   Wikipedia

  • Photoresist — A photoresist is a light sensitive material used in several industrial processes, such as photolithography and photoengraving to form a patterned coating on a surface. Contents 1 Photoresist categories 1.1 Tone 1.2 Developing light wavelength …   Wikipedia

  • Near-field scanning optical microscope — Near field scanning optical microscopy (NSOM/SNOM) is a microscopic technique for nanostructure investigation that breaks the far field resolution limit by exploiting the properties of evanescent waves. This is done by placing the detector very… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”