Abstract: A laser irradiation device generates a linear laser beam extending in one direction, which is irradiated toward the substrate 20 to be processed. The length Lh of the emitted linear laser beam in the major axis direction is adjusted in accordance with a size of the substrate 20 to be processed or the area to be processed within the substrate 20. The adjustment of the length Lh is performed by altering the distance X between a pair of cylindrical lenses 43 and 5 of the optical system for adjusting the generated laser beam in the direction corresponding to the length Lh direction of the linear laser beam, in accordance with the required length Lh. The alteration of the distance X is performed by altering the position of one of the cylindrical lenses 43 and 5 within the optical path in forward and backward direction. The lens is, for example, one having more flexibility of layout in the optical system than the other.

Abstract: A mask is mounted on one surface of a ceramic green sheet which is supported on an X-Y table. The mask is provided with a plurality of through hole transmissive portions. A pulsed laser beam is applied to the mask. The size of the laser beam is sufficiently large to encompass at least several of said through hole transmissive portions. The laser beam passes through the through hole transmissive portions and simultaneously forms a plurality of through holes in the ceramic green sheet. Because the mask is located on (or at least substantially adjacent) the surface of the ceramic green sheet, the size and shape of the through holes will be approximately identical to the size and shape of the through hole transmissive portions, thereby precisely controlling the size and shape of the through holes.