Novel Laser Ablation Resists for Excimer Laser Ablation Lithography. Influence of Photochemical Properties on Ablation

Abstract

The ablation characteristics of various polymers were studied at low and high fluences. The polymers can be divided into three groups, i.e., polymers containing triazene and ester groups, the same polymers without the triazene group, and polyimide as reference polymer. At high fluences, similar ablation parameters, i.e., etch rates and effective absorption coefficients, were obtained for all polymers. The main difference is the absence of carbon deposits for the designed polymers. At low fluences, very pronounced differences are detected. The polymers containing the photochemically most active group (triazene) exhibit the lowest threshold of ablation and the highest etch rates, followed by the designed polyesters and then polyimide. Neither the linear nor the effective absorption coefficients reveal a clear influence on the ablation characteristics. The thermal properties of the designed polymers also have only minor influence on the ablation activity. The amount of detected gaseous products follows the same trend as the ablation activity, suggesting a combined mechanism of photochemical decomposition and volume increase for the designed polymers. The different behavior of polyimide might be explained by a pronounced thermal part in the ablation mechanism.

Time-resolved techniques as probes for the laser ablation process

“…The following polymers were studied: a special designed triazene polymer, which exhibits excellent laser ablation characteristics (sharp ablation edges, no debris, low threshold fluence and high etch rates at low fluences [24,25]) and an energetic polymer, which performed very well in laser plasma thruster experiments [26].…”

Laser Application of Polymers

“…The modeling of ablation depths at high fluences is not sensitive to the underlying mechanisms of ablation itself. At such fluences ablation rates of most polymers are quite similar [90] and are determined by screening of the radiation by the ablated products [80,82] or generated plasma [91].This above described volume photothermal model was only applied for polyimide and does not take into account that photochemical decomposition is possible. This model, like all other thermal models, needs many material parameters for the calculations.…”

“…This approach allowed a continuous variation of the triazene content in the polymer. Polymers with 0, 1,5,20, 35,50,60,75,90, and 100 percent of the triazene-containing polyester have been synthesized [123].Designed polymers of the last generation are based on the triazene polymers (structure B I in Scheme 1) but containing a second functional group, which enables selective photocross-linking without destruction of the triazene chromophore. For this purpose it is crucial that both steps, i.e., photocross-linking and laser ablation, can be separately performed using differScheme 2 Synthesis scheme of the interfacial polycondensation used for the preparation of the nitrogen-containing polymers.…”

Sub-micron surface patterning by laser irradiation through microlens arrays

“…On the other hand, laser processing is one of the promising tools in non-contact material processing that gives the advantages of low cost and suitable for processing of any kind of materials [7,8]. Conventional laser processing technique by focusing the laser light using a lens only can achieve features in micron range [9].…”