Periodic ripples and dot patterns with spacing smaller than 200 nm have been produced on various highly absorbing polymers [poly(ethylene terephthalate), poly(butylene terephthalate), polystyrene, polycarbonate, etc.] using a polarized beam of an ArF and KrF excimer laser. The period of the structures increases with the wavelength used and with the angle of incidence of the beam, whereas the ripple direction is parallel to the polarization direction. The fluence interval in which the pattern can be produced is far below the ablation threshold of the polymer but probably allows a local melting or photolysis of the surface. For polystyrene, a strong influence of the presence of oxygen was observed, which leads to the conclusion that photooxidative processes play a major role in the structure growing mechanisms. Due to the small size (0.1 μm) of the structure scattering techniques using visible light (0.4–0.8 μm) could not be used in this study and scanning electron microscopy and transmission electron micro...

Characterization of submicrometer periodic structures produced on polymer surfaces with low‐fluence ultraviolet laser radiation

Excimer lasers sources of 193nm and 157 nm wavelength were used to obtain new photoablation etching rates for several materials of interest to the microelectronics industry. The harder 157nm radiation provided lower ablation rates and smaller threshold fluences for Polyimide and Polymethyl Methacrylate (PMMA) than with 193nm. For normally robust materials like quartz and Teflon (PTFE), the 157nm laser produced clean and smooth ablation sites with low threshold fluences of 620mJ/cm2 and 68mJ/cm2, respectively, features impossible to obtain with conventional excimer lasers at longer wavelengths. The data should help define new micromachining applications of these two materials for the electronic, optical or medical industry. Results are also reported for GaAs and InP based materials which are found to undergo moderate etch rates of 30-80nm/pulse at fluences of ∼3J/cm2, but suffer thermal damage and material segregation due to surface melting.

Photoablation Studies of Polymers, Quartz, and Semiconductors with Vacuum Ultraviolet Laser Radiation

The authors report a spatial control of the band gap in InGaAs∕GaAs quantum dots (QDs) using the combined effects of pulsed excimer laser irradiation and impurity-free dielectric cap induced intermixing technique. A large band gap shift of up to 180meV has been obtained under laser irradiation of 480mJ∕cm2 and 150 pulses to the SiO2 capped shallow QD structure, while the nonirradiated SiO2 and SixNy capped QDs only exhibit band gap shifts of 18 and 91meV, respectively.

Quantum dot intermixing using excimer laser irradiation

Excimer laser ablation of inorganic materials

V-3 – Laser-Driven Etching

The direct etching of GaAs substrates by excimer laser light has been studied at wavelengths of 193 nm (ArF). 248 nm (KrF) and 351 nm (XeF). For absorbed laser fluences greater than the direct etching fluence thresholds of 23 mJ cm-2 for ArF, 33 mJ cm-2 for KrF and 80 mJ cm-2 for XeF, the authors observe direct etching in air to depths of order one nanometre per pulse. For low-fluence exposures in either vacuum (10-2 Torr) or N2 (1 atm) environments the etch depth per pulse is less than a quarter of that observed when exposure takes place in air. For higher fluence exposures ( approximately 250 mJ cm-2) the etched regions show signs of melting. Using a line-narrowed KrF excimer laser and holographic interference techniques gratings of period 1.5 mu m were directly etched in GaAs substrates.

https://iopscience.iop.org/article/10.1088/0022-3727/21/5/003/pdf

G M Davis

Papers

Excimer laser direct etching of GaAs