Diffractive optical element and optical system incorporating the same

Claim 2

A diffractive optical element, comprising: a substrate; and a diffraction grating formed on the substrate, the pitch of said diffraction grating varying such that it progressively decreases outward over one region extending outward from a center towards a predetermined position and is then, in another region extending outward from the predetermined position towards the extremity of said diffraction grating, kept substantially constant, wherein the pitch of said diffraction grating varies according to a spline function as the phase distribution function of said diffractive optical element.

Claim 3

A diffractive optical element according to claim 1 , wherein a spherical or flat surface is formed in said one region and an aspherical surface is formed in said another region.

Claim 4

A diffractive optical element according to claim 1 , wherein, in the opposite surface to the surface on which said diffraction grating is formed, a spherical or flat surface is formed in a region corresponding to said one region and an aspherical surface is formed in a region corresponding to said another region.

Claim 5

A diffractive optical element according to claim 1 , wherein said substrate is transparent.

Claim 6

A diffractive optical element according to claim 1 , wherein said diffraction grating is a binary-type grating.

Claim 7

An optical system comprising: a diffractive optical element according to claim 1 .

Claim 8

An exposure apparatus comprising: an optical system according to claim 1 , wherein a device pattern is transferred on a wafer by the light through said optical system.

Claim 9

A process for producing a device, comprising the steps of: transferring a device pattern onto a resist on the wafer through the exposure apparatus of claim 7 ; and developing the wafer.

Claim 10

An optical system comprising: a first substrate having a diffraction grating, the pitch of said diffraction grating varying such that it progressively decreases outward over one region extending outward from a center towards a predetermined position and is then, in another region extending outward from the predetermined position towards the extremity of said diffraction grating, kept substantially constant; and a second substrate having a surface which comprises an aspherical surface formed in a region corresponding to said another region and a spherical or flat surface formed in a region corresponding to said one region, wherein the pitch of said diffraction grating varies according to a spline function as the phase distribution function of said diffractive optical element.

Claim 11

An optical system comprising: a first substrate having a diffraction grating, the pitch of said diffraction grating varying such that it progressively decreases outward over one region extending outward from a center towards a predetermined position and is then, in another region extending outward from the predetermined position towards the extremity of said diffraction grating, kept substantially constant; and a second substrate having a surface which comprises an aspherical surface formed in a region corresponding to said another region and a spherical or flat surface formed in a region corresponding to said one region, wherein the pitch of said diffraction grating varies according to a spline function as the phase distribution function of said diffractive optical element.

Claim 12

An optical system according to claim 9 , wherein said substrate is transparent.

Claim 13

An optical system according to claim 9 , wherein said diffraction grating is a binary-type grating.

Claim 14

An exposure apparatus comprising: an optical system according to claim 9 , wherein a device pattern is transferred on a wafer by the light through said optical system.

Claim 15

A process for producing a device, comprising the steps of: transferring a device pattern onto a resist on the wafer through the exposure apparatus of claim 12 ; and developing the wafer.