Half-tone proximity lithography

Abstract

The half-tone lithography using pixilated chromium masks in a projection stepper is an established technology in microoptics fabrication. However, the projection lithography tool is comparably expensive and the achievable lateral resolution is typically limited. By using pixel diffraction effects, binary and continuous profile lithography with submicron resolution can be installed on a conventional mask aligner. To achieve this goal the control of both, the angular spectrum of the illumination and the mask features is essential. We used a novel micro-optics based illumination system referred as "MO Exposure Optics System" in a SUSS MicroTec MA6 mask aligner for the dedicated shaping of the angular illumination distribution. In combination with an adapted lithography mask the formation of a desired intensity distribution in the resist layer is possible. A general mathematic model describes the relation between the angular spectrum of the mask illumination, pixel size and pitch in the mask, proximity distance and propagated field, which also includes special cases like Talbot imaging. We show that a wide range of different micro-optical structures can be optimized by controlling the light diffraction in proximity lithography. Parameter settings were found for submicron binary pattern up to continuous profile structures with extensions up to several tens of microns. An additional interesting application of this approach is the combination of binary and continuous profiles in single elements, e.g. micro lenses with diffractive correction or AR structures. Experimental results achieved for blazed gratings with a period of 2 microns are presented.

High-resolution proximity lithography for nano-optical components

“…Enabled by the flexible incidence angle and collimation control, direct self-imaging (Fig. 6) and self-imaging with pinhole arrays [138] as well as gray-scale lithography by self-imaging [139] (both Fig. 7) were demonstrated in 2010.…”

“…D-TL also claims to be able to address this range, but no results have been published so far. Blazed gratings with continuous saw tooth-like profile and micron-scale periods can be fabricated by Talbot lithography [139,144]. NFH has the potential to realize similar structures with very small periods [159].…”

“…Extensions of Talbot lithography: (a) Gray-scale lithography with binary masks for the realization of blazed gratings[139], (b) Generation of complex unit cell shapes with pinhole array masks and pattern definition by the angular spectrum of the illumination light[138].…”

Application of rigorously optimized phase masks for the fabrication of binary and blazed gratings with diffractive proximity lithography

“…Previous works 16 have demonstrated that diffractive proximity lithography can be used to fabricate blazed gratings with binary masks. To do so, the resist is exposed by the same aerial image multiple times.…”

Effective and flexible modeling approach to investigate various 3D Talbot carpets from a spatial finite mask

“…The utilization of two-photon effects in Talbot lithography allows the manufacturing of well-defined three-dimensional (3D) nanostructures [10]. The application of Talbot Lithography in a mask aligner system with an adapted illumination system allows the manufacturing of small pitched structures and sub-micron resolution also in an industrial fabrication environment [11,12]. With the introduction of displacement techniques, Talbot lithography offers the possibility for high-resolution patterning of large areas [13].…”