When pulsed, ultraviolet laser radiation falls on the surface of an organic polymer or biological tissue, the material at the surface is spontaneously etched away to a depth of 0.1 to several micrometers. In the process, the depth of etching is controlled by the width of the pulse and the fluence of the laser, and there is no detectable thermal damage to the substrate. The material that is removed by etching consists of products ranging from atoms to small fragments of the polymer. They are ejected at supersonic velocities. This dry photoetching technique is useful in patterning polymer films. It is also under serious investigation in several areas in surgery.

https://science.sciencemag.org/content/sci/234/4776/559.full.pdf

Ablation of Polymers and Biological Tissue by Ultraviolet Lasers

Irradiation of organic polymers by short pulses of far‐UV (e.g., 193 nm) laser light causes ablative photodecomposition (APD) of the material. This etching process occurs cleanly leaving behind a well‐defined pit. Longer wavelength (e.g., 532 nm) laser light also ablates material from a polymeric solid. However, this process is distinct from APD in that the sample near the pit is distorted and melted. Microscopic models are presented here for both the photochemical and thermal processes. The photochemical model predicts that well‐defined pits will be formed, that narrow angular distributions of the ablated material should be observed, and that the average perpendicular ejection velocity will be 1000–2000 m/s. The thermal model predicts melting or distortion of the solid and a broad angular distribution of the ejected material.

Laser ablation of organic polymers: Microscopic models for photochemical and thermal processes

Thermal coupling and etch rate measurements are reported for polyethylene terephthalate and polyimide films irradiated at excimer laser wavelengths of 193, 248, and 308 nm. Thermal energy balance is observed up to a threshold fluence but above this the energy absorbed remains approximately constant, the excess energy being carried away by the ablated material. The ablated material appears to have a temperature >103 K as determined by calculations based on the thermal energy loading and relaxation time estimated from IR measurements. These results provided useful information on the interaction mechanism.

Excimer laser ablation and thermal coupling efficiency to polymer films

Laser interactions with the cornea.

Nitrocellulose functions as a self‐developing photoresist which can be patterned using pulsed excimer laser radiation. The material exhibits a threshold fluence for ablation of 20 mJ/cm2 at a wavelength of 193 nm; this threshold results in higher contrast than can be obtained with most conventional photoresists. The effect of varying the laser wavelength has been examined. A simple model of ablative development has been used to predict the etch rate. The processing stability of the resist has been increased without changing the optical development rate by the addition of a dopant. The resolution of the resist is better than 0.3 μm.

Self‐developing UV photoresist using excimer laser exposure

Nitrocellulose films have been shown to function as self‐developing resist layers that are sensitive to both low‐energy ( 25:1 have been demonstrated using a stencil mask and an argon ion beam; the resolution obtained was mask limited. The sensitivity of the resist to 2‐keV Ar+ ions is 36 μm/min at beam currents of 1 mA/cm2, allowing exposure times of 1 s for 0.5 μm of resist. The material is capable of functioning as a mask material for typical semiconductor dry etching processes.

P. D. DeGraff

Papers

Self‐developing resist with submicrometer resolution and processing stability