# US 6,721,039 B2 · Exposure method, exposure apparatus and device producing method

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- Number: US 6,721,039 B2
- Document ID: US6721039B2
- Status: Granted
- Kind: B2
- Application number: 09/757,489
- Filed: 2001-01-11
- Published: 2001-11-01
- Granted: 2004-04-13
- Earliest claimed: 2000-01-14
- Assignees: Nikon Corporation
- Inventors: Ken Ozawa
- Web page: https://patentgrep.com/patent/US6721039B2

## CPC

- G03F 7/70058: {Mask illumination systems}
- G03B 27/72: Controlling or varying light intensity, spectral composition, or exposure time in photographic printing apparatus
- G03F 7/70216: {Mask projection systems}
- 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)
- G03B: APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR (optical parts of such apparatus G02B; photosensitive materials or processes for photographic purposes G03C; apparatus for processing exposed photographic materials G03D)

## Abstract

In an exposure method which illuminates a first object with an exposure beam and exposes a second object through a projection system with the exposure beam passing through a pattern of the first object, a correlation between a light amount of the exposure beam detected at a measuring point on an optical path to the first object and a light amount of the exposure beam on an image plane of the projection system is previously obtained, and when an integrated exposure amount with respect to the second object is controlled based on the light amount of the exposure beam detected at the measuring point and the correlation at the time of exposure of the second object, a variation amount of transmittance of the projection system is forecast in accordance with a process condition and exposure progression, and the correlation is renewed based on the forecast variation amount of the transmittance.

## Claims

### Claim 1

An exposure method which illuminates a first object with an exposure beam emitted from a light source and exposes a second object through a projection system with the exposure beam that has passed through a pattern on the first object, comprising:
obtaining a correlation between a light amount of the exposure beam detected at a measuring point on an optical path between the light source and the first object and a light amount of the exposure beam on an image plane of the projection system;
obtaining, for each exposure process condition for exposing the second object, control parameters for forecasting a variation amount of a transmittance of an optical system disposed between the measuring point and the second object;
forecasting the variation amount of the transmittance of the optical system in accordance with the obtained control parameters; and
renewing the correlation based on the forecasted variation amount of the transmittance.

### Claim 2 (depends on 1)

An exposure method as recited in claim 1, wherein:
a light amount of the exposure beam with respect to the second object is indirectly obtained by multiplying a detected value of the light amount of the exposure beam detected at the measuring point by a coefficient indicating the renewed correlation; and
an exposure amount of the exposure beam is controlled such that the indirectly obtained light amount of the exposure beam with respect to the second object becomes a target exposure amount.

### Claim 3 (depends on 2)

An exposure method as recited in claim 2, wherein the optical system includes the projection system.

### Claim 4 (depends on 3)

An exposure method as recited in claim 3, wherein:
a wavelength of the exposure beam is 170 to 200 nm, and the projection system includes a refraction member made of a quartz glass.

### Claim 5 (depends on 4)

An exposure method as recited in claim 4, wherein:
the projection system includes at least one refraction member made of a fluorite for correcting chromatic aberration.

### Claim 6 (depends on 5)

An exposure method as recited in claim 5, wherein:
when the variation amount of the transmittance of the optical system is forecasted, at least one of an emitting time of the exposure beam and a non-emitting time of the exposure beam is considered.

### Claim 7 (depends on 4)

An exposure method as recited in claim 4, wherein:
the exposure beam is a pulsed light; and
the exposure process condition includes at least one of an illumination condition for the first object, a type of the pattern on the first object, a shape of an illumination region on the first object, a pulse energy of the exposure beam, and a cumulative period of use of an optical member of the optical system.

### Claim 8 (depends on 3)

An exposure method as recited in claim 3, wherein:
the forecasted variation amount of the transmittance of the projection system includes a forecasted variation amount that occurred while the projection system is irradiated with the exposure beam and a forecasted variation amount that occurred while the projection system is not irradiated with the exposure beam.

### Claim 9 (depends on 1)

An exposure method as recited in claim 1, wherein:
the control parameters include a variation ratio of the transmittance and a time constant of the variation of the transmittance with respect to an irradiation time of the exposure beam.

### Claim 10 (depends on 9)

An exposure method as recited in claim 9, wherein:
the exposure process condition includes a plurality of illumination conditions for illuminating the first object, and the variation rate of the transmittance and the time constant are obtained for each of the plurality of illumination conditions.

### Claim 11 (depends on 10)

An exposure method as recited in claim 10, wherein:
the plurality of illumination conditions include at least one of a circular zone illumination and a deformed illumination.

### Claim 12 (depends on 1)

An exposure method as recited in claim 1, wherein:
when a non-emitting time of the exposure beam exceeds a predetermined time, the transmittance of the optical system is measured, and a forecasted value of the variation amount of the transmittance of the optical system is reset.

### Claim 13 (depends on 1)

An exposure method as recited in claim 1, wherein:
when a predetermined time is elapsed, a transmittance distribution with respect to the exposure beam of the optical system is measured, and if a variation of the transmittance distribution exceeds a predetermined tolerance, the irradiation of the exposure beam is stopped, or an illumination region is entirely irradiated with the exposure beam.

### Claim 14 (depends on 1)

A device producing method, comprising:
transferring a mask pattern onto a workpiece using the exposure method as recited in claim 1.

### Claim 15

An exposure apparatus that transfers a pattern of a first object onto a second object with an exposure beam generated by an exposure light source, comprising:
an illumination system which is disposed in an optical path of the exposure beam and which irradiates the first object with the exposure beam;
a projection system which is disposed in the optical path of the exposure beam and which irradiates a second object with the exposure beam that has passed through the pattern of the first object;
a first detector which is disposed in the illumination system and which detects a light amount of the exposure beam at a measuring point in the illumination system;
a second detector which is disposed at an image plane side of the projection system and which detects a light amount of the exposure beam on the image plane of the projection system;
an exposure amount control system which is connected to the first detector and the second detector, which stores a correlation between an output of the first detector and an output of the second detector and which controls an integrated exposure amount with respect to the second object based on the output of the first detector and the correlation; and
a forecasting control system which is connected to the exposure amount control system, which obtains, for each exposure process condition for exposing the second object, control parameters for forecasting a variation amount of a transmittance of an optical system disposed between the measuring point and the second object, which forecasts a variation amount of a transmittance of the projection system in accordance with the obtained control parameters, and which renews the correlation based on the forecasted variation amount of transmittance.

### Claim 16 (depends on 15)

An exposure apparatus as recited in claim 15, wherein:
the exposure amount control system indirectly obtains the light amount of the exposure beam with respect to the second object by multiplying a detected value of the light amount of the exposure beam detected at the measuring point by a coefficient based on the renewed correlation, and controls the exposure amount of the exposure beam such that the indirectly obtained light amount of the exposure beam with respect to the second object becomes a target exposure amount.

### Claim 17 (depends on 16)

An exposure apparatus as recited in claim 16, wherein:
the optical system includes the projection system.

### Claim 18 (depends on 17)

An exposure apparatus as recited in claim 17, wherein:
the optical system is disposed between the measuring point and the first object and further includes a part of optical members of the illumination system.

### Claim 19 (depends on 16)

An exposure apparatus as recited in claim 16, wherein:
the projection system is comprised of a plurality of optical members including a refraction member made of a quartz glass and at least one refraction member made of a fluorite for correcting chromatic aberration.

### Claim 20 (depends on 16)

An exposure apparatus as recited in claim 16, wherein the exposure process condition includes at least one of an illumination condition for the first object, a type of pattern on the first object, a shape of an illumination region on the first object, a pulse energy of the exposure beam, and a cumulative period of use of an optical member of the projection system.

### Claim 21 (depends on 20)

An exposure apparatus as recited in claim 20, wherein:
the forecasted variation amount of the transmittance of the projection system includes a forecasted variation amount that occurred while the projection system is irradiated with the exposure beam and a forecasted variation amount that occurred while the projection system is not irradiated with the exposure beam.

### Claim 22 (depends on 21)

An exposure apparatus as recited in claim 21, wherein:
when the variation amount of the transmittance of the projection system is forecasted, at least one of an emitting time of the exposure beam and a non-emitting time of the exposure beam is considered.

### Claim 23 (depends on 22)

An exposure apparatus as recited in claim 22, wherein:
the exposure process condition includes a plurality of illumination conditions for illuminating the first object, and the variation rate of the transmittance and the time constant are obtained for each of the plurality of illumination conditions.

### Claim 24 (depends on 15)

An exposure apparatus as recited in claim 15, further comprising an illumination condition switching member which is provided in the illumination system and which switches illumination conditions with respect to the first object, wherein:
the forecasting control system calculates a forecasted value of the variation amount of the transmittance of the optical system in accordance with the illumination condition.

### Claim 25 (depends on 15)

An exposure apparatus as recited in claim 15, further comprising a third detector which is disposed at the image plane side of the projection system and which measures a light amount distribution of the exposure beam, wherein:
the third detector measures the transmittance distribution of the projection system.

### Claim 26 (depends on 1)

An exposure method as recited in claim 1, wherein
the control parameters include a reference transmittance, and
the reference transmittance is a ratio, obtained in a state in which the first object is not disposed on the optical path of the exposure beam, of a light amount of the exposure beam detected at the measuring point to the light amount of the exposure beam on the image plane.

### Claim 27 (depends on 26)

An exposure method as recited in claim 26, wherein
the reference transmittance is obtained for said each exposure process condition.

### Claim 28 (depends on 23)

An exposure apparatus as recited in claim 23, wherein
the variation rate of the transmittance and the time constant are obtained for each of the plurality of illumination conditions.

### Claim 29 (depends on 28)

An exposure apparatus as recited in claim 28, wherein
the plurality of illumination conditions include at least one of a circular zone illumination and a deformed illumination.

### Claim 30 (depends on 15)

An exposure apparatus as recited in claim 15, wherein
the control parameters include a reference transmittance, and
the reference transmittance is a ratio, obtained in a state in which the first object is not disposed on the optical path of the exposure beam, of the output of the first detector which has received the exposure beam to the output of the second detector which has received the exposure beam.

### Claim 31 (depends on 30)

An exposure apparatus as recited in claim 30, wherein
the reference transmittance is obtained for said each exposure process condition.