ULTRAVIOLET LASER ETCHING: DIATOMIC TEMPERATURES BY LASER-INDUCED FLUORESCENCE MEASUREMENTS.

Abstract

Studies have been carried out to distinguish between the thermal and electronic processes for several materials in laser-induced etching. It is found that laser-induced fluorescence provides detailed, reliable information about internal energies (temperatures) of diatomics including AlO, CN and C//2. In particular, laser impact on graphite produces C//2 with essentially the energies expected for thermally activated vaporization. The elevated C//2 kinetic energy is in principle understood on the basis of vaporization occurring as a three-step process, first as a dense collisional medium and only later in a supersonic, then freely expanding state. In contrast, laser impact on Al//2O//3 or polyimide leads to the sputtering of diatomics (AlO, CN, C//2) that have very low rotational energies and, at the same time, kinetic energies so high that they cannot be thermal. This contrast thus permits one to separate thermal from photochemical etching on the basis of diatomic particle energies within the plume while supporting the earlier conclusions about photochemical effects with the insulating materials.