Seminar Jurusan 12 September 2013

12/Sep/

Engineering the photonic jet for direct laser micro-processing

Andri Abdurrochman1, 2, Sylvain Lecler1,*, Frédéric Mermet3, Patrick Meyrueis1, and Joël Fontaine4

1ICube, Université de Strasbourg – UMR – CNRS 7163, 300 Pôle API, Boulevard Sébastien Brant, BP 10413, 67412 Illkirch, Strasbourg, France

2Departement of Physics, Universitas Padjadjaran, Jl. Raya Bandung-Sumedang KM. 21, Jatinangor Sumedang 45363, Indonesia

3 Irépa Laser, Pôle API, Boulevard Sébastien Brant, 67412 Illkirch, Strasbourg, France

4 ICube, INSA de Strasbourg, bld de la Victoire, 67000 Strasbourg, France

*Corresponding author: sylvain.lecler@unistra.fr

Our research to improve the lateral resolution of direct laser micro-processing leads to new founds. It is because we are able to etch a glass, as well as a silicon wafer down to 1.3 µm, by applying photonic jet using 70 µm beam generated from a 28 ns near-infrared Nd:YAG laser and SiO2 spheres (ns = 1.5 with diameter between 3.93 and 38 µm) in ambient air. Numbers of laser pulses do not affect to these features size but laser fluencies does, and the distance between the surface of the sphere and material. Controlling this distance is enabling further advantages.

1. Introduction

In the micro-fabrication field, lithography (or photo-lithography) is mostly used to design circuits onto semiconductor surfaces. Typically the photo-lithography cost is typically about 30% of the manufacturing cost of an integrated circuit [1]. Then, it is followed by etching process which is using chemical agents called etchants (isotropic or anisotropic etchants). Etching is also classified as dry or wet etchings [2]. Some new methods have attracted a great deal of interest in micro-fabrication industry because of many potential benefits such as the chemical-free manufacturing environment. Such as: ion beam, electron beam and near-field optics technologies [3-6]. However these processes have to be conducted in vacuum and need expensive equipment. Another method, direct laser-etching (or laser-dry-etching) is very useful for selective removal of thin films [7]. But, due to the diffraction limit, the traditional laser optical heads are not available to fabricate further microstructures [8] without reducing the wavelength.

So, an optical spatial concentration phenomenon in the near-field, so called photonic jet, may have interest to resolve the barrier. In fact there are many reported attempt to apply the photonic jet for lithography (called nano-sphere lithography) [2] for marking/graving/etching. It is understandable, because:

1.     It yields greater intensity than the incident intensity (when Ds ≥ 2lo, for Ds: the sphere size and lo: the beam wavelength), at least 20 times [6, 9, 10].

2.     Its feature sizes are much smaller than the incident beam (wavelength) or the sphere diameter [6, 11-13] (it is also depend on the fluence of the incident beam [12]).

3.     The deviation feature sizes can be predicted from the free space computational [10].

Nevertheless, most of them are using ultrafast laser system (femto-/picosecond lasers) [6, 7, 10, 14-16] or shorter wavelength lasers (visible to UV or Near-UV) [6, 10-12, 15-18] or in special environment [18], which are not cost-effective as expected in many industrial processes. As we already know the ultrafast laser system yield better results (small spatial size), but it is a very expensive machine. It might increase the manufacturing-cost compared to the photo-lithography cost. In case of UV lasers, many people use these lasers because many materials can absorb the energy of UV light, but most of them are excimer lasers which require expensive gases and have short limited lifetime components. Therefore, a UV laser’s basic consumable and the overall operating will be very expensive; especially if it needs special operational environment.

In our research, we choose to consider specifically a 28 ns near-infrared Nd:YAG laser. Namely, these lasers are commonly used in industrial processes because the price is quite cheap and have well-packaged available sources. And for characterization we used Olympus® Vanox-T microscope and Zygo® profilometer.