Mask and apparatus used for alignment purposes in photolithography

Claim 2

A mask bearing a pattern formed as variations in the reflectivity of transmissivity of the mask for reproduction on a layer of photosensitive material spaced from the mask by exposing said photosensitive layer to light reflected from or transmitted through said mask, wherein said mask also has at least one fiducial mark comprising means defining a plurality of elements the reflectivity or transmissivity of which is different from the surrounding parts of said mask, said elements being so arranged that, when illuminated, the diffraction effects at the edges of said elements cooperate to provide a single dense image of said fiducial mark.

Claim 3

The mask of claim 1 wherein said elements of said fiducial mark are shaped as elongate parallel lines arranged side by side in at least one row extending transverse the direction of said elements.

Claim 4

The mask of claim 2 wherein said elements are of such a size and so spaced that when they are illuminated said diffraction patterns of adjacent elements overlap and cancel to provide said single dense image of said fiducial mark.

Claim 5

The mask of claim 2 wherein said elongate elements are inclined to the direction of said row of said elements forming said fiducial mark.

Claim 6

The mask of claim 4 wherein said elements are inclined at 45* to said direction fo said row of said elements.

Claim 7

The mask of claim 2 wherein said fiducial mark comprises at least two rows of said elongate elements, the direction of said two rows being mutually perpendicular and said two rows intersecting, said elements of said two rows extending all in the same direction.

Claim 8

The mask of claim 6 wherein there are no means defining said elongate elements at said intersection of said two rows of said fiducial mark.

Claim 9

The mask of claim 2 wherein said fiducial mark comprises a plurality of rows of said elongate elements, said plurality of rows extending in two perpendicular directions and forming a grid on said mask, said elongate elements of said plurality of rows all extending in the same direction.

Claim 10

The mask of claim 8 wherein said pattern on said mask is formed solely in the interstices between rows of said grid of fiducial marks and is repeated in each of the interstices of said grid.

Claim 11

Apparatus for use in the manufacture of planar semi-conductors, comprising: means for adjustably mounting an element of semi-conductor material bearing a layer of photosensitive material thereon, in a given orientation, a mask bearing a pattern formed as variations in the transmissivity of said mask for reproduction on said layer of photosensitive material by exposing said layer of photosensitive material to light transmitted through said mask, said mask also having at least one fiducial mark comprising means defining a plurality of elements the transmissivity of which is different from that of the surrounding parts of said mask, said elements being so arranged that when said mask is illuminated the diffraction effects at the edges of said elements cooperate to provide a single dense image of said fiducial mark, means for mounting said mask spaced from said element of semiconductor material in a predetermined relative orientation therewith, means for illuminating the mask with radiation of a wavelength to which the photosensitive layer is insensitive so that light transmitted through said mask falls on said element, and means sensitive to the relative positions of the image of said fiducial mark on said semiconductor element, and a fiducial mark previously formed on said semiconductor element to effect automatically alignment of said two fiducial marks.

Claim 12

Apparatus for use in the manufacture of planar semi-conductors, comprising: means for adjustably mounting an element of semi-conductor material bearing a layer of photosensitive material thereon, in a given orientation, a mask bearing a pattern formed as variations in the transmissivity of said mask for reproduction on said layer of photosensitive material by exposing said layer of photosensitive material to light transmitted through said mask, said mask also having at least one fiducial mark comprising means defining a plurality of elements the transmissivity of which is different from that of the surrounding parts of said mask, said elements being so arranged that when said mask is illuminated the diffraction effects at the edges of said elements cooperate to provide a single dense image of said fiducial mark, means for mounting said mask spaced from said element of semiconductor material in a predetermined relative orientation therewith, means for illuminating the mask with radiation of a wavelength to which the photosensitive layer is insensitive so that light transmitted through said mask falls on said element, and means sensitive to the relative positions of the image of said fiducial mark on said semiconductor element, and a fiducial mark previously formed on said semiconductor element to effect automatically alignment of said two fiducial marks.

Claim 13

The apparatus of claim 10 wherein said means sensitive to said relative positions of said two fiducial marks includes at least one photoelectric detector in front of which there is located a screen having fiducial marks formed as variations in the transmissivity thereof which are complementary to the variations in the transmissivity of said mask which form said fiducial marks.

Claim 14

The apparatus of claim 11 wherein said elements of said fiducial mark on said mask are formed as opaque regions in a transparent mask, and said complementary screen has a correspondingly shaped transparent region in an otherwise opaque screen.

Claim 15

The apparatus of claim 11 wherein there are further provided means for vibrating said complementary screen transverse the direction of incident light, and means for providing a reference signal the frequency and phase of which are related to the frequency and phase of vibration of said screen.

Claim 16

The apparatus of claim 11 wherein there is provided a prismatic refractor in the path of the light from said semiconductor element to said complementary screen, and means for rotating said refractor and providing a reference signal the frequency of which is related to the angular velocity of said refractor.

Claim 17

The apparatus of claim 14 wherein said prismatic refractor is in the form of a parallel sided plate inclined with respect to the direction of incident light from said semiconductor element.

Claim 18

The apparatus of claim 11, wherein said fiducial mark on said mask is in the form of a grid pattern of elements and said fiducial mark on said complementary screen is in the form of a corresponding grid pattern of openings.

Claim 19

The apparatus of claim 16, further comprising a lens between said complementary screen and said photoelectric detector for focusing substantially the whole of the light transmitted through said screen onto said photoelectric detector.

Claim 20

The apparatus of claim 11 wherein there are provided two separate fiducial marks on said mask and two photo detectors for sensing the alignment of said two fiducial marks on said mask with two separate fiducial marks on said sEmi-conductor element.