ABLATION OF THIN POLYMER-FILMS ON SI OR METAL-SUBSTRATE WITH THE LOW INTENSITY UV BEAM OF AN EXCIMER LASER OR MERCURY LAMP - ADVANTAGES OF ELLIPSOMETRIC RATE MEASUREMENTS

Etching of thin dielectric films made of polymers (approximately 0.25 to several mu-m) on silicon or metal substrate is increasingly important for applications in microelectronics (e.g. via-hole formation) and for a basic understanding. With these film/substrate systems, it is demonstrated that the etch rate can be measured with angstrom accuracy with the aid of monochromatic ellipsometry. Therefore, measurements can be obtained for etching conditions that were beyond the possibilities of previous techniques [3]. It is shown that the low intensity of the lamp is sufficient to etch through polymers like polyimide, poly(phenylquinoxaline), polystyrene and polycarbonate when irradiation is done in air. It is called photo-oxidative etching since oxygen is necessary to attack the polymer film surface and to produce volatile molecules. High-intensity laser ablation can also be measured and interface effects (reflection or absorption of the substrate) can be evidenced. These precise measurements are crucial in the determination of the polymer mass balance of the etching mechanism.