Manipulation of heat-diffusion channel in laser thermal lithography

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.

Direct Heat-Induced Patterning of Inorganic Nanomaterials

“…When silicon with high thermal conductivity is used as a substrate, the layer of patterned CdSe NCs cools more rapidly, just as observed in a previous study (Figure S21). 19 The suppression of in-plane heat conductivity is favorable for thermal patterning with high lateral resolution. The use of a thinner layer of patterned NCs also decreases thermal diffusion length in the less thermally conductive NC layer and facilitates material cooling through vertical thermal diffusion into the substrate (Figures S17−S21).…”

“…Recently, thermal lithography has attracted attention as a possible alternative to photolithography. Thermal scanning probes and pulsed lasers are used to induce localized temperature jumps, patterning materials through thermal ablation, crystallization, phase change, etching, oxidation, decomposition, or structural conversion of the target. − Thermal lithography is potentially capable of breaking the Abbe diffraction limit for patterning nanoscale features. For example, upon pulsed illumination with a laser beam focused into a diffraction-limited spot, fast nanoscale heat transfer creates a large transient temperature jump in the center of the illuminated spot relative to the temperature of the surrounding area.…”

Temperature dependent thermal conductivity and transition mechanism in amorphous and crystalline Sb2Te3 thin films

“…For data storage, the information bits are recorded and read out according to the structural change due to contrast of reflectance or resistance between crystalline and amorphous states, accordingly 13,14 . For laser thermal lithography, the patterns can be directly inscribed on the chalcogenide thin films due to laser-induced relief structures 15 , the lithographic patterns can be also etched through acid or alkali solutions due to the selective-etching between crystalline and amorphous states 16,17 . Besides, the chalcogenide phase change materials have been explored new functions, such as optically photonic devices, optical mask layer in reducing the spot and lithographic width 18–23 , and thermoelectric devices.…”

Laser‐Assisted Thermal Exposure Lithography: Arbitrary Feature Sizes

“…When thermal diffusion is restricted, the feature size can be smaller than the spot size due to the thermal threshold. [ 24 ] When the thermal diffusion occurs over a large area, thermal exposure can occur in regions outside of the spot. As shown in Figure 1d, the actual feature size may be 1.5 and 2 times the spot size.…”