Hilmar Esrom

New approach of a laser-induced forward transfer for deposition of patterned thin metal films

Abstract An excimer laser-induced forward transfer technique has been used for selective prenucleation of arbitrary substrate materials with palladium. Palladium acetate films on a quartz substrate were irradiated through the support causing simultaneous decomposition of the palladium acetate and deposition of palladium on a substrate at a short distance to the palladium acetate film. The palladium layer, only a few nanometres thick, can act as catalyst for subsequent chemical deposition of metallic films, e.g., copper, nickel, gold etc., of micrometer thickness.

Modification of surfaces with new excimer UV sources

Abstract Surface modification processes using various excimer UV sources are described. In addition to applications of excimer lasers, photolytic processes using newly developed incoherent excimer UV and vacuum UV sources are discussed. These UV sources, based on excimer formation in silent discharges, offer photolytic large area surface treatment at low temperature. Results are presented on the photoetching of polymer surfaces. In addition, metal deposition processes are discussed. In a two-step method, thin metal—organic films are used to obtain activated surface areas for subsequent electroless plating processes. The decomposition of thin solid films on arbitrary surfaces can be initiated by excimer lasers as well as by excimer lamps. It is concluded that laser irradiation involves pyrolytic decomposition effects while lamp exposure results mainly in photolytic decomposition of the precursor films. Direct activation of surfaces for electroless plating is demonstrated using high intensity excimer laser irradiation.

Metal deposition with a windowless VUV excimer source

Abstract A novel lamp configuration for generation of VUV excimer radiation is presented. A silent discharge between parallel dielectric tubes is used to excite the second continua of rare-gas dimers Ar∗2, Kr∗2 and Xe∗2 peaking at 126, 146 and 172 nm, respectively. Subjected to this radiation without intermediate windows palladium acetate films are photolytically decomposed leading to thin palladium layers that can be used as activators for electroless metal plating processes. Deposition rates are investigated as a function of discharge power, gas pressure and wavelength. Compared to earlier experiments with a VUV source consisting of a sealed quartz tube as discharge vessel deposition rates could be increased by two orders of magnitude.

Modification of polymers with UV excimer radiation from lasers and lamps

Photochemical dry etching and surface modification of various polymers, e.g. polymethylmethacrylate (PMMA), polyimide (PI), polyethyleneterephthalate (PET) and polytetrafluoroethylene (PTFE) were investigated with coherent and incoherent excimer UV sources. Ablation rates of PMMA were measured as a function of laser fluence and laser pulse at the wavelength λ = 248 nm (KrF*). Decomposition and etch rates of PMMA and PI were determined as a function of UV intensity and exposure time at three different wavelengths λ = 172 nm (Xe*2), λ = 222 nm (KrCl*) and λ = 308 nm (XeCl*). The transmittance of the polymeric films was determined with a UV-spectrophotometer after different exposure times. The morphology of the exposed polymers was investigated with scanning electron microscopy (SEM). The gaseous products occurring during UV exposure were measured using mass spectrometry (MS). Chemical surface changes of the photoetched PMMA were determined by X-ray photoelectron spectroscopy (XPS). The mechanism of the phot...

UV-induced decomposition of adsorbed Cu-acetylacetonate films at room temperature for electroless metal plating

Abstract Copper deposition on various substrates (ceramics, quartz, polymide) by excimer laser-induced decomposition of adsorbed copper acetylacetonate films was investigated. Electroless copper and nickel plating was used for enhancement of the selective laser-induced copper pattern. The combination of laser structuring with commercial electroless metal deposition is an interesting approach in producing circuit pattern and interconnects for application in hybrid technologies.

Investigation of the mechanism of the UV-induced palladium deposition process from thin solid palladium acetate films

The nature of the UV-induced decomposition process of thin solid palladium acetate films was investigated on different substrate materials (Al2O3, quartz, polyimide) with a pulsed KrF∗ excimer laser at λ = 248 nm and an incoherent Xe∗2 excimer source peaking at λ = 172 nm. Pulsed excimer laser deposition appears to be a process depending very much on the thermal properties of the substrate material and results always in discontinuous palladium layers. The decomposition caused by the incoherent excimer radiation is found to be independent of the thermal properties of the substrate material. It leads to smooth continuous palladium films. The transmission changes of the film during irradiation with incoherent VUV radiation were measured in the wavelength range 150 < λ < 400 nm after different exposure times. The change of transmission with exposure time is related to model calculations describing photolytic decomposition processes in thin solid films.

Decomposition mechanisms of thin palladium acetate film with excimer UV radiation

Pre-nucleation of surfaces with palladium from thin palladium acetate films on a range of substrate materials by UV-induced decomposition is described. The optical transmission of the films after irradiation with incoherent UV radiation from several excimer lamp sources provided information about the deposition rate at different UV intensities and exposure times using three different wavelengths: λ = 172 nm (Xe 2 * ), λ = 222 nm (KrCl * ), and λ = 308 nm (Xecl * ). The gaseous products produced during UV exposure were measured using mass spectrometry (MS). The decomposed products such as H 2 O, CO 2 , + CCH 3 , + COCH 3 and + CH 3 were observed. The decomposition mechanism of palladium acetate is discussed and a simple model calculation describing photolytic decomposition processes in the thin palladium acetate films is presented. Results will be compared to those obtained by laser and thermal decomposition of palladium acetate. The deposited palladium can act as an activator for subsequent pattemed chemical metal deposition techniques in which micrometer thick copper, nickel, or gold layers with good electrical resistivity are applied.

Excimer Laser-Induced Decomposition of Aluminum Nitride

A thin film of aluminum, detected by x-ray photoelectron spectroscopy, is left at the surface of aluminum nitride (AIN) substrates exposed to a high intensity excimer laser beam of UV radiation. Due to the presence of this film, there is a decrease in the surface resistivity of the substrate with increasing number of laser pulses. In addition, line profilometry shows a decrease of the surface roughness with the number of pulses. The thermal decomposition of AIN is assumed to take place in two stages. In the first, liquid aluminum is produced together with the evolution of gaseous nitrogen, and in the second, aluminum evaporates. Using a computer model to simulate the laser heating cycle, it is shown that the thickness of the aluminum film saturates at a given laser energy density. The saturation thickness is a strong function of the substrate absorption and reflectivity and, therefore, of the laser light frequency. The influence of the substrate roughness on the electrical resistivity of the aluminum film is discussed. The application of this process to direct laser writing in high density hybrid circuits is illustrated. During hole drilling by excimer laser, a thin aluminum film is continuously produced at the hole walls. This process can also be employed for substrate planarization.

Large area photochemical dry etching of polyimide with excimer UV lamps

Abstract Large area dry etching and surface modification of polyimide (PI) films was achieved with an incoherent excimer UV source. The transmittance change of thin PI films on fused quartz substrates was determined with an UV spectrophotometer after different exposure times at three different wavelengths: λ=172 (Xe∗2), 222 (KrCl∗) and 308 nm (XeCl∗), respectively. Etch rates of PI were measured at the different wavelengths as a function of UV intensity, exposure time and background pressure in the exposure reactor. The morphology of the exposed areas of the PI films was investigated with SEM. The results are compared with data obtained with mercury UV lamps and excimer laser experiments published by several groups.

Large Area Photochemical Dry Etching of Polymers with Incoherent Excimer UV Radiation

Photochemical dry etching and surface modification of different polymers, e.g., poly-methylmethacrylate (PMMA), polyimid (PI) and poly-ethylene terephthalate (PET) was achieved with an incoherent excimer UV source. Decomposition and etch rates of PMMA were determined as a function of UV intensity and exposure time at different wavelengths λ = 172 nm (Xe2*), λ = 222 nm (KrCI*) and λ = 308 nm (XeCI*). The morphology of the exposed area of PMMA was investigated with SEM. The etching of the polymers can be explained as a result of extensive photooxidation. The results are compared with data obtained from mercury lamp and excimer laser experiments.