22-nm immersion interference lithography

Abstract

Immersion interference lithography was used to pattern gratings with 22-nm half pitch. This ultrahigh resolution was made possible by using 157-nm light, a sapphire coupling prism with index 2.09, and a 30-nm-thick immersion fluid with index 1.82. The thickness was controlled precisely by spin-casting the fluid rather than through mechanical means. The photoresist was a diluted version of a 193-nm material, which had a 157-nm index of 1.74. An analysis of the trade-off between fluid index, absorption coefficient, gap size and throughput indicated that, among the currently available materials, employing a high-index but absorbing fluid is preferable to using a highly transparent but low-index immersion media.

Interference lithography: a powerful tool for fabricating periodic structures

“…The period, d, of the resultant interference pattern depends on the www.lpr-journal.org Eq. (4) indicates that smaller periods can be achieved by either using a shorter wavelength source, increasing the angle between the interfering beams, or a combination of both.…”

“…Another method that can be used to fabricate smaller features with longer wavelength sources is immersion lithography [4]. Here the photosensitive layer is immersed in a fluid which leads to a reduction in the pattern periodicity by a factor corresponding to the refractive index of the immersion fluid, n. For example, water is a very attractive medium in this regard in that it has n = 1.44 at 193 nm [45].…”

“…Photolithography is widely used in microelectro-mechanical systems (MEMS) to create integrated circuits (IC). The combination of short wavelength light sources [2,3] and innovations such as immersion lithography [4][5][6][7][8] and phase shift masks [3,9] have pushed the feature size well into the nanometer scale.…”

The Thermodynamics of Defect Formation in Self-Assembled Systems

“…The photolithographic process has been continually developed to allow the size of devices to be decreased and the density of devices constantly increased so that individual transistor sizes have shrank from cm type sizes to around 50 nm. The trend in resolution enhancement was, for many years, achieved by reducing the dimensions of the mask patterns whilst simultaneously decreasing the wavelength of the radiation (light) (Bloomstein et al, 2006). Currently, techniques such as immersion technologies whereby a liquid (usually water) is placed directly between the final lens and photoresist surface resulting in a resolution enhancement defined by the refractive index of the liquid have allowed device engineers to pattern transfer feature sizes (65 or 45 nm generation) that are actually less than the wavelength of light used (193 nm).…”

Large-scale Patterning of Hydrophobic Silicon Nanostructure Arrays Fabricated by Dual Lithography and Deep Reactive Ion Etching

“…However, the spatial resolution is limited by the light source. Shorter wavelength lasers and immersion techniques have been used to fabricate nanostructures [7,8], but these two methods require complex sources and have limited exposure area.…”