Photopolymers designed for high resolution laser ablation at a specific irradiation wavelength

We have developed novel photopolymers based on the triazeno chromophore group. The absorption properties can be tailored for a specific irradiation wavelength (e.g. 308 nm XeCl laser). With the introduction of a photolabile group into the main chain of the polymer we expected a mechanism which is mainly photochemical. This should result in high resolution etching with no thermal damage or chemical / physical modification to the material. The gaseous products of the photochemical decomposition were thought to assist the material removal, and to prevent the re-deposition of solid products which would contaminate the surface. We confirmed (SEM/AFM) that the irradiation of the polymer at 308 mn resulted in high resolution etching. No debris has been found around the etched comers. Maximum ablation rates of about 3 {mu}m / pulse were achieved due to the dynamic absorption behavior (bleaching during the pulse). No physical or chemical modifications of the polymer surface could be detected after irradiation at the tailored absorption wavelength, whereas irradiation at different wavelengths resulted in modified (physical and chemical) surfaces. The etching mechanism can be described as a laser induced microexplosion, revealed by ns-imaging. The etching of the polymer starts and ends with the laser pulse, shown by ns-interferometry, confirming that the acting mechanism is mainly photochemical at high fluences for our polymers. Our results demonstrate that the mechanism of ablation can be controlled by designing special polymers, which can be used as high resolution laser dry etching resists