Projection optical system, exposure apparatus incorporating this projection optical system, and manufacturing method for micro devices using the exposure apparatus

Abstract

In a projection optical system which forms an image of a first plane on a second plane, using extreme ultraviolet illumination light, an object of the invention is to form an image on the first plane on the second plane under suitable conditions. This projection optical system comprises a first diffractive optical element arranged in an optical path between the first plane and the second plane; a second diffractive optical element arranged in the optical path on the side of the second plane from the first diffractive optical element; and an optical system having a negative power, arranged in the optical path between the first diffractive optical element and the second diffractive optical element.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to a projection optical system for forming an image of a first plane on a second plane, an exposure apparatus incorporating this projection optical system and used at the time of transferring a mask pattern onto a substrate in a lithography process for manufacturing devices or micro devices, such as semiconductor devices or liquid-crystal display devices, and a manufacturing method for micro devices using this exposure apparatus to manufacture micro devices such as semiconductor devices, imaging devices, liquid-crystal display devices or thin film magnetic heads.[0003] 2. Description of the Related Art[0004] When micro devices such as semiconductor devices are manufactured, there are used a batch exposure type projection exposure apparatus (stepper or the like) in which a minute pattern image formed on a reticle as a mask is transferred onto a wafer (or a glass plate) on which a resist is applied, via a projection ...

AI Technical Summary

Benefits of technology

[0015] According to this projection optical system, an optical system having a negative power is arranged in the optical path between the first diffractive optical element and the second diffractive optical element, so as to adjust the angle of incidence of the luminous flux which is incident to the second diffractive optical element. Therefore, the luminous flux can be diffracted according to the diffraction characteristic of the second diffractive optical element, and as a result, the image on the first plane can be formed on the second plane with high precision. Hence, the system is especially suitable for forming an image of a minute pattern, in particular, a pattern of 0.1 .mu.m or less on the second plane.

[0017] According to this projection optical system, the axial luminous flux on the first plane is converted to a substantially parallel luminous flux, and shone onto the first diffractive optical element, and the axial luminous flux on the first plane via the first diffractive optical element is again converted to a substantially parallel luminous flux and guided to the second diffractive optical element. As a result, the image on the first plane can be formed on the second plane with high precision. Moreover, the first diffractive optical element and the second diffractive optical element have a chromatic aberration characteristic opposite to that of a chromatic aberration caused by the front optical system, the rear optical system and the optical system having a negative power, and do not affect the Petzval's condition. Hence the chromatic aberration can be corrected favorably. As a result, the system is especially suitable for forming an image on the first plane on the second plane with high precision. Furthermore, since correction of chromatic aberration is performed only by the diffractive optical element, several lenses arranged in the optical path for correcting the chromatic aberration are not required, thereby keeping down cost increase. Also, even if chromatic aberration cannot be corrected by lenses, due to a restriction on the glass material of the lenses, chromatic aberration can be corrected by using a diffractive optical element having an aberration characteristic opposite to that of lenses. Furthermore, since two diffractive optical elements, namely the first diffractive optical element and the second diffractive optical element, are used to obtain a power required for correction of chromatic aberration by each diffractive optical element, even if values of chromatic aberration in the front optical system, the rear optical system and the optical system having a negative power are varied, chromatic aberration can be properly corrected.

[0019] According to this projection optical system, by satisfying the above described conditions, a projection optical system having a large numerical aperture, but having no imaging performance degradation due to the angular characteristic can be realized. Hence sufficient correction of chromatic aberration can be realized. Moreover, by satisfying the above described conditions, the pitch of the diffractive optical elements is not refined so much, and diffractive optical elements having a relatively wide pitch and which are easy to manufacture can be used.

[0020] Furthermore, a third aspect of the present invention is a projection optical system (PL) having a plurality of optical elements arranged along an optical path between a first plane (P1) and a second plane (P2) for forming an image on the first plane (P1) on the second plane (P2), wherein at least one diffractive optical element (D1, D2) having a diffraction pattern surface (PL1, PL11) formed on one surface and a correction surface (PL2, PL22) formed on an other surface is arranged along the optical path, and the correction surface (PL2, PL12) corrects a manufacturing error on the diffraction pattern surface (PL1, PL11).

[0032] According to this exposure apparatus, the pattern image formed on the mask arranged on the first plane can be formed with high precision on the photosensitive substrate arranged on the second plane. As a result, the apparatus is extremely suitable for forming a minute pattern, especially, a minute pattern of 0.1 .mu.m or less on the wafer.

[0034] According to this manufacturing method for micro devices, as in the above described exposure apparatus, the pattern image formed on the mask arranged on the first plane can be formed with high precision on the photosensitive substrate arranged on the second plane. As a result, the method is extremely suitable for manufacturing micro devices where it is necessary to form a minute pattern, especially, a minute pattern of 0.1 .mu.m or less on the wafer.

Problems solved by technology

However, even if the numerical aperture of the projection optical system is increased over and above what is required, if illumination light having a long wavelength is used, there is naturally a limit to improvement of the resolution.

However, even if the numerical aperture is high, if aberration occurs, there is a problem in forming minute patterns.

This method however, requires a multiplicity of lenses, and hence invites a reduction in transmittance, and an increase in the cost for manufacturing the projection optical system cannot be avoided.

As a result, this is not desirable in view of improving transmittance and cost reduction.

With the diffractive optical element having a cross-section in a saw-tooth pattern or a stepwise pattern, occurrence of unnecessary diffracted light which does not contribute to image forming cannot be avoided due to form error or the like.

When the wavelength of illumination light becomes short with shortening of the wavelength of the light source, the kinds of usable glass material are limited due to absorption of light, and if the wavelength becomes 180 nm or below, the only glass material practically usable is fluorite.

Therefore, under illumination light having such a short wavelength, correction of chromatic aberration becomes impossible with a construction having only dioptric lenses.

Hence the production thereof becomes difficult.

However, for a projection optical system for forming a pattern having a resolution of 0.1 .mu.m or less, using extreme ultraviolet illumination light having a large numerical aperture, measures have not heretofore been taken for exhibiting sufficient imaging performance, taking into consideration incident angle characteristics and manufacturing error of the diffractive optical element.

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