The investigation of laser induced forward transfer (LIFT) process using femtosecond pulsed laser comparing with that using excimer laser is reported. Ni thin film of several hundreds of nanometer thickness, which is deposited on fused silica substrate, was irradiated by single pulse of KrF excimer laser (wavelength: 248 nm, pulse width: 30 ns) or femtosecond pulsed laser (wavelength: 800 nm, pulse width: 120 fs), and transferred to a Si acceptor substrate. It is shown that laser beam profile affected the removal of thin film. It is revealed that adhesion of particles was inhibited using femtosecond pulsed laser in comparison with the case of excimer LIFT process.
Micro patterns of some μm size were fabricated by transferring metal thin films using Laser-Induced Forward Transfer (LIFT) technique. The oxygen composition ratio of deposited patterns fabricated by varying laser irradiation conditions was measured by using XPS. Then we investigated the dependence of the oxygen composition ratio of deposited patterns on the thin film-acceptor substrate distance and laser fluence. LIFT was performed using a single shot of KrF excimer laser (wavelength: 248nm, pulse width: 30ns). Sn thin film, with a few hundreds of nanometer thickness deposited on quartz substrate using electron beam evaporation method, were removed by laser irradiation, and deposited on acceptor substrate (Si wafer) after transfer in air under room temperature. As a result of XPS analysis of deposited patterns, it was revealed that the oxygen composition ratio depended on laser fluence and the distance from a thin film to an acceptor substrate and tended to increase and then fall with increase of laser fluence when the film-acceptor substrate distance was fixed. In order to investigate this tendency, we photographed the shadowgraph of the transferring thin film. From this investigation, it was revealed that higher fluence causes higher velocity. As the velocity becomes higher, the time from the beginning of removal to attachment on the acceptor substrate becomes shorter. So the higher laser fluence is, the lower the oxygen composition ratio is.
The purpose of this study is to investigate the correlation between Laser Induced Forward Transfer (LIFT) process observed experimentally and the deposited structure, especially the size accuracy. Ablated plume and shadowgraph of transferring materials were observed using image intensified CCD camera. The intensity of reflected He-Ne laser from the front and rear side of thin films, respectively, were measured using photodiode to investigate the behavior of thin film during laser pulse. Metal thin films (Au and Ni), with several tens - hundreds of nanometer in thickness deposited on quartz substrate using ion sputtering deposition method, were irradiated by KrF excimer laser (wavelength 248 nm, pulse width 30 ns). The measurement of the reflected He-ne laser shows that the film removal finishes during incident laser pulse. Ablated plume images and shadowgraphs of transferring materials show that the velocity of both the top of ablated plume and the transferring materials become faster in increase fo fluence, and that the transferring materials precede the plume. Optimum fluence exists at each film thickness to achieve high size accuracy of deposited structure. At lower fluence, the deposited structure shows bad feature due to incomplete removal from the support substrate. At higher fluence, the big shock causes the wide range of spread of deposited structure when the transferring particles have a collision with the acceptor substrate. At optimum fluence, the high size accuracy of deposited structure is achieved as the film-substrate distance is made as short as possible.