EP0010998B1 — Process for optically aligning patterns in two pl…

Claim 1

Independent Claim 167 words

Method of optically aligning patterns in two neighbouring planes using pattern markings marked on the two planes to be aligned, characterized in that it uses a pattern marking marked on the first plane and formed of at least one Fresnel zone lens of linear zones which are alternatively opaque and transparent and perpendicular to the alignment axis in the plane, and a reflecting pattern marking marked on the second plane; comprising a central zone perpendicular to the alignment axis, the alignment method consisting of illuminating the linear Fresnel zone lens by a parallel monochromatic light beam in a manner to form within the second plane a light track having substantially the same dimensions as the central zone of the pattern marked on that plane, detecting the radiation reflected by this second plane, and emerging from the linear Fresnel zone lens, and displacing the two planes one with respect to the other until the detected radiation passes through an extremum corresponding to the alignment of the two markings.

Claim 2

Dependent Claim 167 words

Method of optically aligning patterns in two neighbouring planes using pattern markings marked on the two planes to be aligned, characterized in that it uses a pattern marking marked on the first plane and formed of at least one Fresnel zone lens of linear zones which are alternatively opaque and transparent and perpendicular to the alignment axis in the plane, and a reflecting pattern marking marked on the second plane; comprising a central zone perpendicular to the alignment axis, the alignment method consisting of illuminating the linear Fresnel zone lens by a parallel monochromatic light beam in a manner to form within the second plane a light track having substantially the same dimensions as the central zone of the pattern marked on that plane, detecting the radiation reflected by this second plane, and emerging from the linear Fresnel zone lens, and displacing the two planes one with respect to the other until the detected radiation passes through an extremum corresponding to the alignment of the two markings.

Claim 3

Dependent Claim 29 words

Alignment method of claim 1, characterized in that the pattern marking marked on the second plane comprises a central zone having a reflection coefficient different from the surrounding zone.

Claim 4

Dependent Claim 50 words

Alignment method of claim 1, characterized in that the central zone of the pattern marking marked on the second plane is formed of elements having different reflection coefficients and extending in a direction perpendicular to the alignment direction for forming a reflection amplitude grid of constant pitch in this direction.

Claim 5

Dependent Claim 40 words

Alignment method of claim 1, characterized in that the central zone of the pattern marking marked on the second plane is engraved for forming a reflection phase grid of constant pitch extending in a direction perpendicular to the alignment direction.

Claim 6

Dependent Claim 89 words

Alignment method of any of claims 1 to 4, characterized in that, for an automatic alignment, the angle of incidence of the beam on the linear Fresnel zone lens is alternatively deflected on both sides of a medium position, the automatic alignment being obtained by controlling the relative displacement of the two planes by the output signal of a synchronous demodulator receiving a signal characteristic of the back-radiation reflected by the second plane and a signal synchronous with the deflection control signal of the beam incident on said lens.

Claim 7

Dependent Claim 46 words

Alignment method of any of claims 2 to 5, characterized in that the pattern marking marked on the second plane comprises, in addition to the central zone, lateral zones extending in the alignment direction and allowing an approximation of the central zone prior to precise alignment.

Claim 8

Dependent Claim 49 words

Alignment method of any of the preceding claims, characterized in that the alignment marking marked on the first plane comprises a plurality of Fresnel zone lenses of linear parallel zones, the corresponding pattern marked on the second plane comprising a plurality of central zones respectively associated with these lenses.

Claim 9

Dependent Claim 156 words

Device for performing the method of claim 1, characterized in that it comprises a monochromatic light source (30) and an optical projection device (31, 32, 34) for projecting radiation in a parallel beam onto a mask, a pattern marking (4) forming at least one linear Fresnel zone lens being marked on the mask forming opaque and transparent zones and a central reflecting zone parallel to the lens zones being marked on the sample (2) to be aligned with the mask (1), displacement means (21) for displacing the sample with respect to the mask along an axis normal to the marked central zone being provided for bringing the light track formed by the first order beam diffraction by the linear Fresnel zone lens into coincidence with the central zone of the pattern marked on the sample, the device further comprising a detector (37) detecting the radiation reflected by the sample, the coincidence corresponding to a signal extremum.

Claim 10

Dependent Claim 73 words

Alignment device of claim 8, characterized in that the central zone of the pattern marked on the mask forms a constant pitch reflecting grid, the radiation received by this grid being diffracted in the plane formed by the optical axis of the incident beam and the grid, the detector being arranged in the axis of the beam corresponding to one of the diffraction orders and inclined with respect to the incident radiation axis.

Claim 11

Dependent Claim 28 words

Alignment device of claim 9, characterized in that the detector is arranged along the optical axis of the first order diffracted beam of the constant pitch reflecting grid.

Claim 12

Dependent Claim 109 words

Alignment device of any of claims 8 to 10, characterized in that it comprises a device for deflecting the beam incident on the mask controlled by a deflection control signal, the optical projection device being a device without focus of such kind that the parallel beam illuminates the mask in the lens zone with variable incidence, the projected light track scanning the sample, whereby the detector supplies a variable amplitude signal applied to a synchronous demodulator to which a signal synchronous with the deflection control signal is applied, the output of the demodulator supplying an error signal used for controlling the relative displacement of the mask and the sample.

Claim 13

Dependent Claim 45 words

Alignment device of any of claims 8 to 11, characterized in that the pattern marking marked on the mask is formed of a plurality of parallel linear Fresnel zone lenses, the alignment pattern marked on the sample including parallel central zones associated with these lenses.

Claim 14

Dependent Claim 129 words

Alignment device of any of claims 8 to 12, characterized in that it comprises means for displacing the sample with respect to the mask along two perpendicular axes and by rotation, the mark comprising three pattern markings, two of the pattern markings each comprising at least one Fresnel lens of linear zones perpendicular to one of the alignment axes and the third pattern marking comprising at least one Fresnel lens of linear zones perpendicular to the other alignment axis, the pattern markings associated with the lenses being marked on the sample, the optical projection device projecting the radiation onto each of the markings in accordance with a determined procedure, a detector for detecting radiation emerging from the mask after reflexion on the sample being provided for each alignment direction.

Process for optically aligning patterns in two planes close to one another and alignment device to realize such a process

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