# US 2008/0186466 A1 · Element for defocusing tm mode for lithography

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- Number: US 2008/0186466 A1
- Document ID: US20080186466A1
- Status: Published application
- Kind: A1
- Application number: 11/946,730
- Filed: 2007-11-28
- Published: 2008-08-07
- Earliest claimed: 2005-04-12
- Inventors: Gabriel Y. Sirat; Joseph Fisher
- Web page: https://patentgrep.com/patent/US20080186466A1

## CPC

- G03F 7/70966: {Birefringence}
- G03F 7/70308: {Optical correction elements, filters or phase plates for manipulating imaging light, e.g. intensity, wavelength, polarisation, phase or image shift}
- G03F 7/70566: {Polarisation control}
- G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)

## Abstract

A method for imaging a mask pattern with small features through a lithographic system includes an illumination source and providing a uniaxial material having an ordinary index of refraction and a different extraordinary index of refraction. The extraordinary mode is modified such that the extraordinary mode is defocused relative to the ordinary mode. Light from the illumination source is passed through the material and focusing the ordinary mode on an image plane and defocusing the extraordinary mode relative to the image plane.

## Claims

### Claim 1

A method for imaging a mask pattern with small features through a lithographic system:
providing an illumination source;
providing a uniaxial material having an ordinary index of refraction and a different extraordinary index of refraction;
modifying the extraordinary mode such that the extraordinary mode is defocused relative to the ordinary mode;
passing light from the illumination source through the material and focusing the ordinary mode on an image plane and defocusing the extraordinary mode relative to the image plane.

### Claim 2 (depends on 1)

The method of claim 1, further providing a photoresist in the image plane; and imaging the photoresist with the ordinary mode.

### Claim 3 (depends on 1)

The method of claim 1, wherein the uniaxial material is made of one of Sapphire, MgF2, KD*P, quartz or BBO.

### Claim 4 (depends on 3)

The method of claim 3, wherein the material is in the form of a planar plate member.

### Claim 5 (depends on 4)

The method of claim 4, wherein a mask is adjacent the uniaxial birefringent plate member and positioned between the mask and the photoresist.

### Claim 6 (depends on 5)

The method of claim 5, wherein the uniaxial birefringent plate is the substrate material of the mask.

### Claim 7 (depends on 5, 6)

The method of claim 5 or 6, further including passing the light through a uniaxial birefringent last optical element.

### Claim 8 (depends on 7)

The method of claim 7, wherein the last optical element is a plano-convex lens.

### Claim 9 (depends on 1)

The method of claim 1, utilized for fabricating a semiconductor device.

### Claim 10 (depends on 1)

The method of claim 1, wherein the uniaxial material is at least one of a plate, wedge or lens.

### Claim 11 (depends on 1)

The method of claim 1, wherein the material includes a last optical module having a plurality of elements, all the elements being made of the same uniaxial crystal;
wherein the first element of the last optical module is made of a uniaxial crystal with the optical axis of the crystal being aligned parallel to the optical axis of the optical system, a surface between the first and a second element carrying no optical power; and
the second element being made of the same uniaxial material as the first element with the crystal optical axis being inclined below 6 degrees relative to the optical axis;
wherein the crystal optical axis angle relative to the optical axis of the system and the surface shape of the second element being configured to reduce flare and flare non-uniformity on the image on the photoresist by adding additional flare to the image at positions with lower flare content.

### Claim 12

A lithographic system for imaging a mask pattern with small features through a lithographic system:
an illumination source;
a uniaxial material having an ordinary index of refraction and a different extraordinary index of refraction, the material being configured to focus the ordinary mode on an image plane and to modify the extraordinary mode such that the extraordinary mode is defocused relative to the ordinary mode;
a photoresist positioned at an image plane, wherein the ordinary mode from the illumination source is focused on the image plane and the extraordinary mode is defocused relative to the image plane.

### Claim 13 (depends on 12)

The lithographic system of claim 12, wherein the uniaxial material is formed from one of sapphire, MgF2, KD*P, quartz or BBO.

### Claim 14 (depends on 13)

The lithographic system of claim 13, wherein the material is in the form of a planar plate member.

### Claim 15 (depends on 14)

The lithographic system of claim 14, wherein a mask is adjacent the uniaxial birefringent plate member, the plate member being located between the mask and the photoresist.

### Claim 16 (depends on 15)

The method of claim 15, wherein the uniaxial birefringent plate is the substrate material of the mask.

### Claim 17 (depends on 15, 16)

The lithographic system of claim 15 or 16, further including passing the light through a uniaxial birefringent last optical element.

### Claim 18 (depends on 17)

The lithographic system of claim 17, wherein the last optical element is a plano-convex lens.

### Claim 19 (depends on 18)

The lithographic system of claim 18 wherein,
the illumination source includes a UV light source providing light; and further including:
a polarization system to control the polarization of the light;
an optical module to shape the spatial profile of the light;
optical elements including the last optical element placed along a geometric axis;
a wafer coated with the photoresist and positioned such that the photoresist is in the image plane of the projection objective; and
wherein the photoresist is kept at a distance from the last optical element to neutralize the decay of high frequency spatial components due to non propagating waves,
wherein the last optical element is in the form of a plano-convex lens, with the flat surface oriented facing the wafer,
wherein the material of the last optical element is made of uniaxial crystal,
wherein the optical axis of the uniaxial crystal is perpendicular to the bottom surface of the last optical element,
wherein an image is created in the photoresist in a preferred polarization, by the projection objective, and
wherein the extraordinary mode creates a uniform background in the photoresist.

### Claim 20 (depends on 19)

The method of claim 19, wherein the material is one of a plate, wedge or lens.

### Claim 21 (depends on 19)

A semiconductor wafer processed using the apparatus of claim 19.

### Claim 22 (depends on 19)

The apparatus of claim 19, wherein the optical elements provide telecentricity, within 5 degrees, for all points across an object imaged by the lithography apparatus.

### Claim 23 (depends on 19)

The apparatus of claim 19, wherein the optical crystal axis is within 5 degrees from the perpendicular to the bottom plane of the last optical element.

### Claim 24

A lithographic apparatus having a projection objective for imaging a pattern provided in an object plane of the projection objective onto an image plane of the projection objective suitable for microlithography projection exposure machines comprising:
a UV light source providing light;
a polarization controller to control the polarization of the light;
an optical module to shape the spatial profile of the light;
a mask to define a pattern;
optical elements including a last optical element placed along a geometric axis;
a wafer and a photoresist coated on the wafer placed such that the photoresist is positioned at the image plane of the projection objective; and
an immersion liquid filled in between the last optical element and the wafer, wherein the last optical element is in the form of a plano-convex lens, with the flat surface oriented facing the wafer and up against the immersion liquid,
wherein the material of the last optical element is made of uniaxial crystal,
wherein the optical axis of the uniaxial crystal is perpendicular to the bottom surface of the last optical element,
wherein an image is created in the wafer in a preferred polarization, by the projection objective,
wherein unwanted polarization creates a uniform background in the photoresist.

### Claim 25 (depends on 24)

The apparatus of claim 24, wherein the optical elements provide telecentricity, within 5 degrees, for all points across an object imaged by the lithographic apparatus.

### Claim 26 (depends on 24)

The apparatus of claim 24, wherein the optical crystal axis is within 5 degrees from the perpendicular to the bottom plane of the last optical element.

### Claim 27 (depends on 24)

The apparatus of claim 24, wherein the last optical element comprises sapphire.

### Claim 28 (depends on 24)

The apparatus of claim 24, wherein the last optical element comprises quartz.

### Claim 29 (depends on 24)

The apparatus of claim 24, wherein the lithographic system uses double exposure and/or double patterning.

### Claim 30

A method of immersion lithography comprising:
providing a UV light source providing light;
providing a polarization controller to control the polarization of the light;
providing an optical module to shape the spatial profile of the light;
providing a mask to define a pattern;
providing optical elements including a last optical element placed along a geometric axis;
a wafer and a photoresist coated on the wafer placed such that the photoresist is positioned at the image plane of the projection objective; and
filling an immersion liquid between the last optical element and the wafer;
wherein the last optical element is in the form of a plano-convex lens, with the flat surface oriented facing the wafer and up against the immersion liquid,
wherein the material of the last optical element is made of uniaxial crystal,
wherein the optical axis of the uniaxial crystal is perpendicular to the bottom surface of the last optical element;
creating an image on the wafer in a preferred polarization,
creating a uniform background in the photoresist from unwanted polarization.

### Claim 31 (depends on 30)

The method of claim 30, wherein the optical elements provide telecentricity, within 5 degrees, for all points across an object imaged by the lithographic apparatus.

### Claim 32 (depends on 30)

The method of claim 30, wherein the optical crystal axis is within 5 degrees from the perpendicular to the bottom plane of the last optical element.

### Claim 33 (depends on 30)

The method of claim 30, wherein the last optical element comprises sapphire.

### Claim 34 (depends on 30)

The method of claim 30, wherein the last optical element comprises quartz.

### Claim 35 (depends on 30)

The method of claim 30, wherein the lithographic system uses double exposure and or double patterning.

### Claim 36 (depends on 30)

A semiconductor wafer processed using the method of claim 30.

### Claim 37

A projection objective for imaging a pattern provided in an object plane of the projection objective onto an image plane of the projection objective suitable for microlithography projection exposure machines, comprising:
a UV light source providing light;
a polarization controller to control the polarization of the light;
an optical module to shape the spatial profile of the light;
a mask to define a pattern;
optical elements including a last optical element placed along a geometric axis;
a wafer and a photoresist coated on the wafer placed such that the photoresist is positioned at the image plane of the projection objective; and
wherein the photoresist is kept at a distance from the last optical element to neutralize the decay of high frequency spatial components due to non propagating waves,
wherein the last optical element is in the form of a plano-convex lens, with the flat surface oriented facing the wafer,
wherein the material of the last optical element is made of uniaxial crystal,
wherein the optical axis of the uniaxial crystal is perpendicular to the bottom surface of the last optical element,
wherein an image is created in the wafer in a preferred polarization, by the projection objective,
wherein unwanted polarization creates a uniform background in the photoresist.