Abstract
Laser thermal lithography is a good alternative method for forming small pattern feature size by taking advantage of the structural-change threshold effect of thermal lithography materials. In this work, the heat-diffusion channels of laser thermal lithography are first analyzed, and then we propose to manipulate the heat-diffusion channels by inserting thermal conduction layers in between channels. Heat-flow direction can be changed from the in-plane to the out-of-plane of the thermal lithography layer, which causes the size of the structural-change threshold region to become much smaller than the focused laser spot itself; thus, nanoscale marks can be obtained. Samples designated as "glass substrate/thermal conduction layer/thermal lithography layer (100 nm)/thermal conduction layer" are designed and prepared. Chalcogenide phase-change materials are used as thermal lithography layer, and Si is used as thermal conduction layer to manipulate heat-diffusion channels. Laser thermal lithography experiments are conducted on a home-made high-speed rotation direct laser writing setup with 488 nm laser wavelength and 0.90 numerical aperture of converging lens. The writing marks with 50-60 nm size are successfully obtained. The mark size is only about 1/13 of the focused laser spot, which is far smaller than that of the light diffraction limit spot of the direct laser writing setup. This work is useful for nanoscale fabrication and lithography by exploiting the far-field focusing light system.
Highlights
Formation of nanometric patterns on surfaces and thin films is often carried out with advanced nanolithography techniques, such as electron beam ablation, nanoimprint, and local scanning probe microscopy methods
The heat quantity that propagates along the out-of-plane channel of the thermal lithography layer and downward to the lower thermal conduction layer is proportional to the thermal conductivity of the Si layer (Ď Si ), expressed as
A light beam emitted from Ar + laser device was modulated into pulsed laser using acoustic optical modulator (AOM)
Summary
Formation of nanometric patterns on surfaces and thin films is often carried out with advanced nanolithography techniques, such as electron beam ablation, nanoimprint, and local scanning probe microscopy methods. To improve the pattern resolution in maskless laser direct writing, a number of methods, such as ultrafast laser pulse-based multi-photon absorption lithography with Îť/10 to Îť/20 resolution [1, 2] and two-beam lithography [3,4,5], have been proposed. For heat-mode lithography, which is based on the manufacturing technique for optical discs, the thermally induced structural change of the material occurs only at the center of the laser beam spot because of threshold effect. The thermal lithographic region size becomes smaller than the resolution limit of the focused laser beam spot because of the thermally-induced threshold effect of structural change; a fine pattern can be achieved using an inexpensive laser irradiation equipment. This rule can be broken through manipulating the heat-diffusion channel, such that the pattern feature size can be further reduced down to nanoscale
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