Optical system for the automatic alignment of two motifs comprising alignment marks of the grating type, particularly in direct photorepetition on silicon
Optical system for the automatic alignment of two motifs in which the alignment marks of a first fixed motif forming the reference are constituted by at least one pair of identical periodic optical gratings with a constant spacing P and having a predetermined distance dX from one another such that the equation dX=(n+ epsilon ) P is proved, n being an integer and epsilon a fraction of unity. An optical modulator, for example electro-optical means incorporating a Pockels cell alternately illuminate with the timing of the high frequency control signals, the said gratings in windows, whose position can be regulated in accordance with a given axis. The image of these windows is projected onto gratings carried on a second moving support to be aligned and produces orders of diffraction. An optoelectronic detector detects a predetermined order of diffraction. The high frequency-modulated output signals are transmitted to control circuits for producing the automatic alignment.