Nano Lithography

Chapter 4

Lithography and Manipulation Based on the Optical Properties of Metal Nanostructures ¹

4.1. Introduction

Among lithography techniques that use an electromagnetic wave (of wavelength λ) to insulate a resist, optical lithography is undoubtedly the most attractive, for cost and simplicity reasons. Its main weak point is its resolution, limited for dense features at a value of λ/2n set by diffraction, n being the refraction index of the medium into which the electromagnetic field propagates. In practice, this value corresponds to about a hundred nanometers in UV lithography. With the aim of improving this resolution, for several years the main approach has been the reduction of λ (extreme UV lithography) and the increase of n (immersion lithography) [LIN 06]. However, these approaches are expensive and require the expending of considerable mid- and long-term economic and technological efforts.

An alternative solution consists of using the optical near-field, where evanescent and propagating waves coexist [COU 01]. While propagating waves are associated with the diffraction limit λ/2n by propagation of light and summing of the fields (the Huygens-Fresnel principle of far-field diffraction), evanescent waves (which result from the diffraction of light by the high spatial frequencies of an object [GOO 96]) can be associated with nanometric optical confinements.

Within the framework of the appearance of near-field optics techniques, several approaches to optical nano-sources ...