Alignment of mask and semiconductor wafer using linear fresnel zone plate

Claim 1

A system for aligning a mask (24) carrying a pattern to a semiconductor wafer (20) to be patterned, said mask being positioned above the semiconductor wafer, said system comprising radiation source means (25, 26) for producing a radiation beam (25a) and for guiding the radiation beam thus produced so that the radiation beam irradiates the wafer through the mask located thereabove, focusing means (24a) provided on the mask for focusing the radiation beam incident thereto on a surface of the semiconductor wafer, diffraction means (20a) provided on the surface of the semiconductor wafer in correspondence to the focusing means for diffracting the radiation beam focused thereon in a form of a diffracted beam (25b) traveling in a predetermined direction relative to the wafer, detection means (27) held with a predetermined relationship with respect to the radiation source means and the mask, for detecting the diffracted beam, said detection means further producing an output signal having a level proportional to the intensity of the diffracted beam, stage means (22) for supporting the semiconductor wafer movably in a plane parallel to the surface of the wafer, and a controller (23) for moving the stage means responsive to the output signal of the detection means, characterized in that said focusing means comprises first linear Fresnel zone part (I) having a first focal length which in turn comprises a central zone (C, C′) and a plurality of parallel and alternating opaque and transparent bands disposed symmetrically about a central axis (l) passing through the central zone and a second linear Fresnel zone part having a second focal length substantially smaller than the first focal length, said second linear Fresnel zone part being provided in said first linear Fresnel zone part and comprising a plurality of parallel and alternating opaque and transparent bands disposed symmetrically with respect to a symmetrical axis (l).

Claim 2

A system for aligning a mask (24) carrying a pattern to a semiconductor wafer (20) to be patterned, said mask being positioned above the semiconductor wafer, said system comprising radiation source means (25, 26) for producing a radiation beam (25a) and for guiding the radiation beam thus produced so that the radiation beam irradiates the wafer through the mask located thereabove, focusing means (24a) provided on the mask for focusing the radiation beam incident thereto on a surface of the semiconductor wafer, diffraction means (20a) provided on the surface of the semiconductor wafer in correspondence to the focusing means for diffracting the radiation beam focused thereon in a form of a diffracted beam (25b) traveling in a predetermined direction relative to the wafer, detection means (27) held with a predetermined relationship with respect to the radiation source means and the mask, for detecting the diffracted beam, said detection means further producing an output signal having a level proportional to the intensity of the diffracted beam, stage means (22) for supporting the semiconductor wafer movably in a plane parallel to the surface of the wafer, and a controller (23) for moving the stage means responsive to the output signal of the detection means, characterized in that said focusing means comprises first linear Fresnel zone part (I) having a first focal length which in turn comprises a central zone (C, C′) and a plurality of parallel and alternating opaque and transparent bands disposed symmetrically about a central axis (l) passing through the central zone and a second linear Fresnel zone part having a second focal length substantially smaller than the first focal length, said second linear Fresnel zone part being provided in said first linear Fresnel zone part and comprising a plurality of parallel and alternating opaque and transparent bands disposed symmetrically with respect to a symmetrical axis (l).

Claim 5

A system as claimed in any one of claims 1 to 3 characterized in that said radiation beam comprises a coherent optical beam and said radiation source means comprises a laser (25) for producing the coherent optical beam.

Claim 6

A system as claimed in any one of claims 1 to 4 characterized in that said stage means (22) further supports the wafer (20) movably in a direction perpendicular to the surface of the wafer, the system further comprises means (24d, 28, 29) for measuring the distance between said mask (24) and the wafer and for producing a second output signal indicating the measured distance, and the controller (23) controls the movement of the stage means in the direction perpendicular to the plane of the wafer responsive to the second output signal.

Claim 8

A method of aligning a mask (24) carrying a semiconductor pattern to a semiconductor wafer (20) to be patterned according to the semiconductor pattern on the mask by using a dual focus linear Fresnel zone plate (24a) having a first focal length and a second focal length which is substantially shorter than the first focal length, comprising steps of focusing a radiation beam (25a) from a radiation source (25) held with a predetermined positional relationship with respect to the mask, on a surface of the wafer through the dual focus linear Fresnel zone plate by setting the distance between the mask and the wafer to the first focal length, moving the wafer relative to the mask in a plane parallel to the mask while observing a diffraction beam diffracted from a diffraction grating (20a) provided on the surface of the wafer in response to irradiation of the diffraction grating by the radiation beam focused at the first focal length by a detector (27) held with a predetermined positional relationship with respect to the radiation source and the mask until a predetermined intensity of the diffraction beam is observed, moving the wafer towards the mask so that the distance between the mask and the wafer is set to the second focal length of the dual focus linear Fresnel zone plate, and moving the wafer relative to the mask in a plane parallel to the mask while observing the diffraction beam by the detector held with the predetermined positional relationship with respect to the radiation source and the mask until the predetermined intensity of the diffraction beam is observed, characterized in that the predetermined positional relationship between the radiation source, detector and the mask is identical in the first step of moving the wafer parallel to the plane of the mask and in the second step of moving the wafer parallel to the plane of the mask.

Claim 9

A method of aligning a mask (24) carrying a semiconductor pattern to a semiconductor wafer (20) to be patterned according to the semiconductor pattern on the mask by using a dual focus linear Fresnel zone plate (24a) having a first focal length and a second focal length which is substantially shorter than the first focal length, comprising steps of focusing a radiation beam (25a) from a radiation source (25) held with a predetermined positional relationship with respect to the mask, on a surface of the wafer through the dual focus linear Fresnel zone plate by setting the distance between the mask and the wafer to the first focal length, moving the wafer relative to the mask in a plane parallel to the mask while observing a diffraction beam diffracted from a diffraction grating (20a) provided on the surface of the wafer in response to irradiation of the diffraction grating by the radiation beam focused at the first focal length by a detector (27) held with a predetermined positional relationship with respect to the radiation source and the mask until a predetermined intensity of the diffraction beam is observed, moving the wafer towards the mask so that the distance between the mask and the wafer is set to the second focal length of the dual focus linear Fresnel zone plate, and moving the wafer relative to the mask in a plane parallel to the mask while observing the diffraction beam by the detector held with the predetermined positional relationship with respect to the radiation source and the mask until the predetermined intensity of the diffraction beam is observed, characterized in that the predetermined positional relationship between the radiation source, detector and the mask is identical in the first step of moving the wafer parallel to the plane of the mask and in the second step of moving the wafer parallel to the plane of the mask.