Patent DE-102009005972-A1 (DE)
Title: Creating a periodic pattern on or in a processing substrate, comprises exposing the processing substrate to an interfering radiation field, which forms itself in a space area by interacting partial fields of different diffraction orders
Inventor: BORCHERS BASTIAN
IPC: G02B5/18
Filed: 2009-01-23
Abstract: The method comprises exposing a processing substrate (18) to an interfering radiation field (16), which forms itself in a space area that is directly adjacent to a rear side of a front-side phase mask (10) illuminated with a laser radiation (14) by interacting partial fields of different diffraction orders. The processing substrate is spatially arranged from the rear side of the phase mask. A liquid film is arranged in an intermediate area (22) between the phase mask and processing substrate, is transparent for the laser radiation and directly contacts with the rear side of the phase mask. The method comprises exposing a processing substrate (18) to an interfering radiation field (16), which forms itself in a space area that is directly adjacent to a rear side of a front-side phase mask (10) illuminated with a laser radiation (14) by interacting partial fields of different diffraction orders. The processing substrate is spatially arranged from the rear side of the phase mask. A liquid film is arranged in an intermediate area (22) between the phase mask and the processing substrate, is transparent for the laser radiation and directly contacts with the rear side of the phase mask and/or the surface of the processing substrate to be processed. The intermediate gap is filled by the liquid film. The liquid film covers the rear side of the phase mask in an area-wise manner and does not contact with the processing substrate and/or the liquid film partially covers the surface of the processing substrate and does not contact with the phase mask. The intensity of the laser radiation is highly selected, so that the damage threshold of the processing substrate exposed to the radiation field is area-wisely exceeded. A resulting refractive index of the liquid film that is disposed in the intermediate area is adjusted in an adjusting step preceding the pattern creation by varying the temperature of the liquid film and/or by titrating a first liquid having a first refractive index with a second liquid having a second refractive index. The adjusting step is carried out onto an adjusting substrate, which is arranged oblique to the rear side of the phase mask and the resulting refractive index is adjusted, so that the intensity difference is minimized between the illumination maxima. During the adjusting step, the intensity of the laser radiation is sufficiently high to produce a spatially periodic material change of the adjusting substrate and the adjusting substrate is displaced parallel to its substrate surface. The implemented displacement positions are assigned and stored to the corresponding temperature- and/or titration steps. The processing substrate is displaced parallel to the normal direction of the rear side of the phase mask during the processing. The dimension of the displacement corresponds to a period or an integral multiple of a period of an intensity modulation of the radiation field in the normal direction of the rear side of the phase mask.