X-ray or gamma ray systems or devices – Specific application – Lithography
Reexamination Certificate
2002-06-10
2004-04-13
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Lithography
Reexamination Certificate
active
06721390
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a soft X-ray reduction projection exposure system, a soft X-ray reduction projection exposure method and a pattern formation method all using a soft X-ray beam as exposing light.
As the degree of integration of semiconductor integrated circuits is increased to further reduce the line width of circuits, lithography technique for forming a finer pattern is necessary.
Photolithography using KrF excimer laser (of a wavelength of 248 nm) is currently principally under development, and it is necessary to shorten the wavelength of exposing light in order to further increase the resolution.
It has been proved that a fine pattern with a width of 100 nm or less can be formed by photolithography using ArF excimer laser (of a wavelength of 193 nm) or F
2
laser (of a wavelength of 157 nm) having a wavelength shorter than that of the KrF excimer laser.
Also, EUV lithography using a soft X-ray beam (of a wavelength of 13.4 nm) capable of realizing resolution of 30 nm has recently been developed.
An exposure system for the EUV lithography includes, as disclosed in Japanese Laid-Open Patent Publication No. 01-010625, a light source for generating a soft X-ray beam, a reflecting mask and a reduction projection optical system for transferring a pattern of the reflecting mask onto a wafer. The reduction projection optical system includes a combination of several non-spherical reflecting mirrors. Furthermore, since light does not transmit the air in the wavelength region of a soft X-ray beam (principally a 4 nm through 20 nm wavelength band), the inside of the exposure system should be evacuated.
A conventional exposure system for the EUV lithography has a problem of contamination of the reflecting mirrors and the reflecting mask with organic substances. The contamination is caused principally by a decomposed substance from a resist film and an organic substance adhered onto the inside wall of the exposure system. In particular, an organic substance floating within the exposure system is decomposed by the soft X-ray beam during the exposure and the thus decomposed substance is adhered onto the surface of the reflecting mirror, so that a carbon film may be deposited on the reflecting mirror.
When a carbon film is deposited on the reflecting mirror, the reflectance of the reflecting mirror is lowered. Therefore, the optical characteristic of the reduction projection optical system is harmfully affected and specifically, for example, aberration is caused. For example, if a carbon film with a thickness of 1 nm is deposited on a reflecting mirror made from a multi-layer film composed of a molybdenum film and a silicon film, the reflectance is lowered from 65% to 64%.
Furthermore, if the carbon film deposited on the reflecting mirror has an uneven thickness, large aberration is caused.
SUMMARY OF THE INVENTION
In consideration of the aforementioned conventional problems, an object of the invention is, in a soft X-ray reduction projection exposure system, a soft X-ray reduction projection exposure method and a pattern formation method using a soft X-ray beam as exposing light, preventing a carbon film from depositing on the surface of a reflecting mask, an illumination optical system for irradiating the reflecting mask with the soft X-ray beam or a reduction projection optical system for imaging a pattern of the reflecting mask.
In order to achieve the object, the first soft X-ray reduction projection exposure system of this invention comprises a light source for generating a soft X-ray beam of a wavelength of a 4 through 20 nm band; a reflecting mask on which a desired pattern is formed; an illumination optical system for irradiating the reflecting mask with the soft X-ray beam; a reduction projection optical system for imaging the pattern of the reflecting mask on a wafer; and controlling means for controlling a partial pressure of a gas of a carbon compound to be 1.33×10
−8
Pa or less in at least one of a first region where the illumination optical system is disposed, a second region where the reflecting mask is disposed and a third region where the reduction projection optical system is disposed.
In the first soft X-ray reduction projection exposure system, the controlling means controls the partial pressure of the gas of the carbon compound to be 1.33×10
−8
Pa or less in at least one of the first region where the illumination optical system is disposed, the second region where the reflecting mask is disposed and the third region where the reduction projection optical system is disposed. Therefore, a degree of releasing carbon is higher than a degree of absorbing carbon on the surface of the illumination optical system disposed in the first region, the surface of the reflecting mask disposed in the second region or the surface of the reduction projection optical system disposed in the third region. Accordingly, the thickness of a carbon film deposited on the surface of the illumination optical system, the reflecting mask or the reduction projection optical system can be suppressed to approximately 0.1 nm or less. As a result, the optical characteristic can be prevented from degrading due to contamination, with an organic substance, of the surface of the illumination optical system, the reflecting mask or the reduction projection optical system.
In the first soft X-ray reduction projection exposure system, the controlling means preferably reduces a pressure in at least one of the first region, the second region and the third region individually.
Thus, the partial pressure of the carbon compound gas can be controlled in a short period of time in any particular region where the partial pressure of the carbon compound gas is desired to be controlled to be 1.33×10
−8
Pa or less among the first region, the second region and the third region.
In the first soft X-ray reduction projection exposure system, the controlling means preferably controls a total pressure to be 1.33×10
−4
Pa or less in any region where the partial pressure of the gas of the carbon compound is controlled to be 1.33×10
−8
Pa or less among the first region, the second region and the third region.
Thus, the thickness of a carbon film deposited on the surface of the illumination optical system, the reflecting mask or the reduction projection optical system can be suppressed to approximately 0.1 nm or less, and in addition, the surface of the illumination optical system, the reflecting mask or the reduction projection optical system can be prevented from being contaminated with an inorganic substance.
The second soft X-ray reduction projection exposure system of this invention comprises a light source for generating a soft X-ray beam of a wavelength of a 4 through 20 nm band; a reflecting mask on which a desired pattern is formed; an illumination optical system for irradiating the reflecting mask with the soft X-ray beam; a reduction projection optical system for imaging the pattern of the reflecting mask on a wafer; and capturing means for capturing a carbon compound generated in at least one of a first region where the illumination optical system is disposed, a second region where the reflecting mask is disposed and a third region where the reduction projection optical system is disposed.
In the second soft X-ray reduction projection exposure system, the capturing means captures the carbon compound generated in at least one of the first region where the illumination optical system is disposed, the second region where the reflecting mask is disposed and the third region where the reduction projection optical system is disposed. Therefore, the thickness of a carbon film deposited on the surface of the illumination optical system disposed in the first region, the surface of the reflecting mask disposed in the second region or the surface of the reduction projection optical system disposed in the third region can be suppressed. Accordingly, the optical characteristic can be prevented from degrading due to the contami
Matsuo Takahiro
Sasago Masaru
Church Craig E.
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
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