Deep ultraviolet laser direct write for patterning sol-gel InGaZnO semiconducting micro/nanowires and improving field-effect mobility

Abstract

Deep-UV (DUV) laser was used to directly write indium-gallium-zinc-oxide (IGZO) precursor solution and form micro and nanoscale patterns. The directional DUV laser beam avoids the substrate heating and suppresses the diffraction effect. A IGZO precursor solution was also developed to fulfill the requirements for direct photopatterning and for achieving semi-conducting properties with thermal annealing at moderate temperature. The DUV-induced crosslinking of the starting material allows direct write of semi-conducting channels in thin-film transistors but also it improves the field-effect mobility and surface roughness. Material analysis has been carried out by XPS, FTIR, spectroscopic ellipsometry and AFM and the effect of DUV on the final material structure is discussed. The DUV irradiation step results in photolysis and a partial condensation of the inorganic network that freezes the sol-gel layer in a homogeneous distribution, lowering possibilities of thermally induced reorganization at the atomic scale. Laser irradiation allows high-resolution photopatterning and high-enough field-effect mobility, which enables the easy fabrication of oxide nanowires for applications in solar cell, display, flexible electronics, and biomedical sensors.

Figure 1. Direct write of IGZO micro and nanopatterns.

(a) Molecular structure of the zinc methacrylate precursor. Schematic description of patterning methods used including (b) patterning by irradiating DUV laser beam on sample through a binary amplitude mask and (c) patterning by using interference lithography with DUV laser and phase masks. The material acts as a negative tone photoresist and patterns are obtained after development.

Figure 2. Typical example of IGZO patterns.

AFM images of patterns obtained by binary amplitude mask lithography (a,b) and interference lithography (c) Material composition was In:Ga:Zn = 4:1:2. Widths of structures are respectively (a) 5 μm, (b) 800 nm and (c) 300 nm.

Figure 3. Laser patterning and electrical properties of material.

(a) The height of IGZO thin film with laser or DUV-lamp irradiation prepared with irradiation through binary mask with line width of 800 nm. (b) The transfer characteristic of IGZO TFT with DUV-laser-write periodic multiple channel lines. The thermal annealing temperature is 600 °C. Channel width and length are 1000 μm and 300 μm, respectively. (c) AFM image of multiple line channels produced by laser irradiation through binary mask. The period is 10 μm.

Figure 4. Effect of DUV annealing on electrical properties.

(a) Mobility, (b) threshold voltage, and (c) subthreshold swing of DVU-laser-write and of STD IGZO TFTs are plotted as a function of post thermal annealing temperature. Average value and standard deviation are extracted from three independent devices with identical condition.

Figure 5. Impact of DUV and thermal treatmant on material structure.

(a) Schematic representation of different types of oxygen atoms present in the material and their relative proportion determined by XPS after spin-coating, DUV irradiation with 2 J and 24 J, thermal annealing at 300 °C and 600 °C and DUV irradiation followed by thermal annealing (600 °C). Raw XPS spectra and results from deconvolution are given in Figure S4. The AFM image of surface of (b) samples prepared by thermal annealing and (c) that of samples prepared by DUV annealing.