Ultraviolet laser ablation of polyimide films

Srinivasan, R.; Braren, Bodil; Dreyfus, R. W.

doi:10.1063/1.338834

Cited by 232 publications

(67 citation statements)

References 14 publications

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“…3 is the calculated transmission behavior using (8) with the following equation constants: d = 0.1 gm (film thickness), p = 4.5 x 1022 cm -3, and a~ = 5.5 x 10 -18 cm 2. The chromophore density used corresponds to roughly 20 absorbers per monomer in the polyimide solid (based on the material density [11]), a reasonable value given the complex molecular nature of the imide building block [12]. The small-signal absorption coefficient, c~ = pa 1 = 24.75 gm -~, is also in good agreement with the reported value.…”

Section: Discussionsupporting

confidence: 63%

“…6 are over a much smaller fluence range than the transmission measurement. Figure 7 shows etch data for repetitive-pulse KrF-laser irradiation of 125 gm thick Kapton (sheet polyimide) [12]. Although this is a slightly different experiment, the singlephoton model prediction is quite accurate over most experimental fluenees.…”

Section: Discussionmentioning

confidence: 95%

“…Note that the fluence region above 1 J/cm 2 where the theory diverges substantially from the experimental data is the same region where the thin-film transmission measurements become ambiguous. Higherorder nonlinear processes that are not considered in the simple theory may limit transmission at large pulse The experimental data are taken from [12]. The two curves are as in Fig.…”

Section: Discussionmentioning

confidence: 99%

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Transmission of polyimide during pulsed ultraviolet laser irradiation

et al. 1994

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Abstract. Experiments that demonstrate quantitatively the importance of laser absorption dynamics for ultraviolet laser ablation of organic materials are presented. Laser pulse transmission measurements have been performed on 0.1 jam spin-coated polyimide films at three ultraviolet wavelengths ( 193 nm, 248 nm, and 355 nm) over the fluence range l0 -3-10 J/cm 2. Target transmission is observed to increase with increasing fluence by a factor of --,5 at 193 nm, and a factor of ~ 10 at 248 nm. In contrast, transmission decreases by approximately one half during 355 nm target irradiation. These results are analyzed theoretically with a two-level model of chromophore absorption. This theory is also applied to reported pulsed UV-laser polyimide ablation data. It is shown that an accurate description of the fluence-dependent film absorption leads to a prediction of the etch depth versus pulse fluence relationship in good agreement with experimental data. PACS : 42.10, 81.60, 82.50 Pulsed ultraviolet-laser ablation has been shown in a multitude of studies to etch organic targets precisely, which in turn has led to widespread application of UV lasers in materials processing, microelectronics, and medicine. In order to optimize these procedures, as well as to assess possible risks of clinical laser use, the laser/material interaction must be well understood. One aspect of photoablation that has only lately become apparent is that the absorptive properties of the target can change during the intense laser irradiation [1][2][3][4]. Recently, two of the current authors presented a theoretical description of such dynamic optical properties [1,5] showing that these absorption changes could account for the commonly noted substantial discrepancy between experimental data and the etch depth versus laser fluence relationship predicted by Beer's law (i.e., the simple "blow-off" model [6] described below).However, other processes such as thermal diffusion could also affect the ablation depth/fluence behavior [7]. A recent theoretical analysis concluded that dynamic target optics were probably more important than thermal diffusion in affecting photoablation [8], yet this issue has not been conclusively resolved. The absolute magnitude of the optical effect cannot be deduced from the reports cited above because those studies were either qualitative in nature or limited in terms of incident laser fluence. For these reasons we have conducted the experiments described here, quantifying the change in absorption for thin films of polyimide (a common photoablation substrate) over a wide range of laser fluences at three distinct ultraviolet wavelengths. This paper thus provides the first quantitative experimental test of the ideas formulated in [1,5], i.e. that proper treatment of the radiation transport to include chromophore saturation and excited-state absorption is extremely important for determination of the etch depth per pulse in organic materials.

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Section: Discussionsupporting

confidence: 63%

Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 99%

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Transmission of polyimide during pulsed ultraviolet laser irradiation

et al. 1994

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“…Srinivasan et al 31,33 also observed that various gas phase species from diatomics to high molecular weight products were generated from poly(methyl methacrylate) (PMMA) by 193 nm light and concluded that monomers were efficiently generated at fluences from 0.01 to 0.5 J/cm 2 with a high quantum yield for direct photochemical bond breaking. 29 In other work, 34 Srinivasan and co-workers noticed that a single UV photon per monomer in a polymer surface does not produce many gas phase species smaller than monomers. These observations indicate that at low PAR values monomers are efficiently generated from the polystyrene nanospheres, but more atomic species are produced either directly from the particle surface or from the monomers generated as PAR increases.…”

Section: Discussionmentioning

confidence: 99%

Photochemical Interaction of Polystyrene Nanospheres with 193 nm Pulsed Laser Light

et al. 2005

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The photochemical interaction of 193 nm light with polystyrene nanospheres is used to produce particles with a controlled size and morphology. Laser fluences from 0 to 0.14 J/cm 2 at 10 and 50 Hz photofragment nearly monodisperse 110 nm spherical polystyrene particles. The size distributions before and after irradiation are measured with a scanning mobility particle sizer (SMPS), and the morphology of the irradiated particles is examined with a transmission electron microscope (TEM). The results show that the irradiated particles have a smaller mean diameter (∼25 nm) and a number concentration more than an order of magnitude higher than nonirradiated particles. The particles are formed by nucleation of gas-phase species produced by photolytic decomposition of nanospheres. A nondimensional parameter, the photon-to-atom ratio (PAR), is used to interpret the laser-particle interaction energetics.

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“…Laser-induced fluorescence measurements indicate that diatomic fragments C 2 and CN are also formed, at least transiently, during ablation [273]. Larger molecules (e.g., C 60 ) up to visible carbon particles are also formed [274]. The soot is partly redeposited around the ablation crater and consists of amorphous carbon with some crystalline features.…”

Section: Laser Application Of Polymersmentioning

confidence: 97%

Laser Application of Polymers

Lippert

2004

Polymers and Light

150

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Laser ablation of polymers has been studied with designed materials to evaluate the mechanism of ablation and the role of photochemically active groups on the ablation process, and to test possible applications of laser ablation and designed polymers. The incorporation of photochemically active groups lowers the threshold of ablation and allows high-quality structuring without contamination and modification of the remaining surface. The decomposition of the active chromophore takes place during the excitation pulse of the laser and gaseous products are ejected with supersonic velocity. Time-of-flight mass spectrometry reveals that a metastable species is among the products, suggesting that excited electronic states are involved in the ablation process. Experiments with a reference material, i.e., polyimide, for which a photothermal ablation mechanism has been suggested, exhibited pronounced differences. These results strongly suggest that, in case of designed polymers which contain photochemically active groups, a photochemical part in the ablation mechanism cannot be neglected. Various potential applications for laser ablation and the special photopolymers were evaluated and it became clear that the potential of laser ablation and specially designed material is in the field of microstructuring. Laser ablation can be used to fabricate three-dimensional elements, e.g., microoptical elements.Keywords Laser ablation · Ablation mechanism · Photopolymers · Polyimide · Spectroscopy This was not always true, of course. For many years, the laser was viewed as "an answer in search of a question". That is, it was seen as an elegant device, but one with no real useful application outside of fundamental scientific research. In the last two to three decades however, numerous laser applications have moved from the laboratory to the industrial workplace or the commercial market. Lasers are unique energy sources characterized by their spectral purity, spatial and temporal coherence, and high average peak intensity. Each of these characteristics has led to applications that take advantage of these qualities: -Spatial coherence: e.g., remote sensing, range finding and many holographic techniques. -Spectral purity: e.g., atmospheric monitoring based on high-resolution spectroscopies. -and of course the many other applications in communication and storage, e.g., CDs.All of these high-tech applications have come to define everyday life in the late twentieth century. One property of lasers, however, that of high intensity, did not immediately lead to "delicate" applications but rather to those requiring "brute force". That is, the laser was used in applications for removing material or heating. The first realistic applications involved cutting, drilling, and welding, and the laser was little more advanced than a saw, a drill, or a torch. In a humorous vein A.L. Schawlow proposed and demonstrated the first "laser eraser" in 1965 [4], using the different absorptivities of paper and ink to remove the ink without damaging the und...

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Ultraviolet laser ablation of polyimide films

Cited by 232 publications

References 14 publications

Transmission of polyimide during pulsed ultraviolet laser irradiation

Transmission of polyimide during pulsed ultraviolet laser irradiation

Photochemical Interaction of Polystyrene Nanospheres with 193 nm Pulsed Laser Light

Laser Application of Polymers

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