Modeling topology formation during laser ablation

Hodapp, Theodore; Fleming, P.R.

doi:10.1063/1.368063

Cited by 21 publications

(20 citation statements)

References 41 publications

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“…However, for shallow craters formed in materials with low real refractive index, as in our investigation, both of these effects are expected to be very weak except near grazing incidence, particularly if there are fluence-dependent effects that further reduce the reflectivity and effective refractive index below their normal values. Such effects have been reported previously by Hodapp and Fleming,6 who observed significant reductions in the reflectivity of polyimide during 248-nm-wavelength excimer laser ablation at oblique incidence.…”

Section: ͑1͒supporting

confidence: 51%

“…This kind of ablation characteristic is well known from work on excimer laser ablation. 6,7 When considering the possible angular dependence of the total ablation depth h, we can ignore the effect of reflectivity variations ͑that affect h through the term F 0 ) except at extreme angles, for reasons already discussed in the context of the incremental depth. In addition, the effects of any angular dependence in F cr will be small except in regions of the crater where the fluence is close to the ablation threshold.…”

Section: ͑1͒mentioning

confidence: 99%

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On the angular dependence of focused laser ablation by nanosecond pulses in solgel and polymer materials

George

Onischenko

Holmes

2004

Applied Physics Letters

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Focused laser ablation by single laser pulses at varying angles of incidence is studied in two materials of interest: a solgel ͑Ormocer 4͒ and a polymer ͑SU8͒. For a range of angles ͑up to 70°f rom normal͒, and for low-energy ͑Ͻ20 J͒, 40 ns pulses at 266 nm wavelength, the ablation depth along the direction of the incident laser beam is found to be independent of the angle of incidence. This allows the crater profiles at oblique incidence to be generated directly from the crater profiles at normal incidence by a simple coordinate transformation. This result is of use in the development of simulation tools for direct-write laser ablation. A simple model based on the moving ablation front approach is shown to be consistent with the observed behavior. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1655702͔ Direct-write laser ablation using a focused laser beam is a highly promising technique for micromachining applications. Diode-pumped solid-state lasers have recently been employed for this purpose. This technique is particularly attractive for prototyping because it allows direct and rapid transfer from computer to workpiece without requiring an expensive mask. However, improved understanding of the fundamental ablation processes involved is required if this approach is to become more widely established. Direct-write micromachining involves the scanning of the focused laser beam over the surface of the workpiece along a predefined tool path, and overlap of multiple laser pulses on the surface is usually required to achieve the desired structure. In order to simulate arbitrary processes of this type and to predict their final surface shapes, it is necessary to understand the ablation of surfaces at nonnormal incidence. To investigate this aspect, we have studied the ablation behavior at varying angles of incidence in two interesting materials: a solgel ͑Or-mocer 4͒ and a polymer photoresist ͑SU8͒. Our study is confined to the angular dependence of the ablation depth due to single laser pulses incident on a previously unablated surface; material changes in the workpiece arising from multipulse ablation ͑such as increased surface roughness and incubation effects͒ are not considered.The samples consisted of thin ͑ϳ100 m͒ films of the solgel material ͑Ormocer 4͒ deposited on a borofloat glass substrate and SU8 polymer resist spun on a silicon wafer. The laser system ͑frequency quadrupled Nd:VO 4 ) produced 266-nm-wavelength, Q-switched pulses Ͻ40 ns in duration, with a pulse energy ranging from 10 to 100 J measured at the laser. It had an M 2 value Ͻ1.3, beam divergence Ͻ0.3 mrad, diameter ϳ2.5 mm, and polarization Ͼ100:1 horizontal. The repetition rate for most measurements was set to 20 kHz. The laser output was expanded ϫ3 and stopped down with an iris of about 7 mm diameter. After the scanning mirror, the beam was focused down using an f lens ( f ϭ160 mm). The beam was scanned at a sufficient speed to ensure the pulses were separated on the sample surface. The angle of incidence could be varied from 0°to 90...

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Section: ͑1͒supporting

confidence: 51%

Section: ͑1͒mentioning

confidence: 99%

On the angular dependence of focused laser ablation by nanosecond pulses in solgel and polymer materials

George

Onischenko

Holmes

2004

Applied Physics Letters

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“…The reflectivity of these steep features becomes important to the final ablated profile [25,26]. Actually, the surface reflectivity mainly depends on the incidence angle.…”

Section: Simulation Results and Discussionmentioning

confidence: 99%

Effect of two typical focus positions on microstructure shape and morphology in femtosecond laser multi-pulse ablation of metals

Wang

Mei

Jiang

et al. 2008

Applied Surface Science

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“…The model in (1) has been used previously to explain specific geometrical effects such as the variation of side-wall angle with fluence and illumination conditions [12,13] and the formation of conical structures due to micro-masking [14]. In recent years it has also been included in fluence calculations for photorefractive laser surgery [15].…”

Section: Models For Angular Dependence Of Ablation Ratementioning

confidence: 99%

A study of angular dependence in the ablation rate of polymers by nanosecond pulses

Pedder

Holmes

2006

Photon Processing in Microelectronics and Photonics V

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Measurements of ablation rate have traditionally been carried out only at normal incidence. However, in real-world applications ablation is often carried out at oblique angles, and it is useful to have prior knowledge of the ablation rate in this case. Detailed information about the angular dependence is also important for the development of ablation simulation tools, and can provide additional insight into the ablation mechanism. Previously we have reported on the angular dependence of direct-write ablation at 266 nm wavelength in solgel and polymer materials. In this paper we present a systematic study of angular dependence for excimer laser ablation of two polymer materials of interest for microfabrication: polycarbonate and SU8 photoresist. The results are used to improve simulation models to aid in mask design.

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Modeling topology formation during laser ablation

Cited by 21 publications

References 41 publications

On the angular dependence of focused laser ablation by nanosecond pulses in solgel and polymer materials

On the angular dependence of focused laser ablation by nanosecond pulses in solgel and polymer materials

Effect of two typical focus positions on microstructure shape and morphology in femtosecond laser multi-pulse ablation of metals

A study of angular dependence in the ablation rate of polymers by nanosecond pulses

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