Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-12-03
2004-06-08
Rosasco, Stephen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06746806
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of manufacturing a mask blank and a mask each of which is used in a lithography process on fabricating a semiconductor device or the like and, in particular, to a mask blank and a method pertinent to KrF excimer laser, ArF excimer laser, or F
2
excimer laser.
With fineness of a semiconductor circuit and the like, it is a recent trend that requirements have been directed to using an exposure source of a short wavelength in lithography and using lenses of a high numerical aperture (NA) in an exposure apparatus. However, it is to be noted that a high numerical aperture (NA) of the exposure lenses and a depth of focus reside in a trade-off relationship.
In order to attain a depth of focus, flatness required for a photo mask has become severe more and more and should be recently reduced to a range from 0.3 &mgr;m to less than 0.5 &mgr;m.
In the meanwhile, the flatness of the photo mask depends on bending strength of the transparent substrate, flatness of a substrate prior to deposition of any films, and internal stress of films that form a circuit pattern and the like. Among others, the internal stress of the films has raised a serious problem. Herein, flatness is defined by a difference between a highest point and a lowest one from an average plane determined on a surface used for exposure and can be given by measuring a configuration of a substrate by the use of an optical interferometer. The internal stress is given by the following formula (1):
Eb2/[6(&ngr;−1)rd] (1)
where E is representative of Young's modulus; b, a thickness of a substrate; &ngr;, a Poisson's ratio; r, a variable component of a radius of curvature of the substrate; and d, a thickness of a thin film.
In order to satisfy the flatness required for the photo mask, the film for forming the circuit pattern has the internal stress preferably not greater than 5×10
8
Pa when use is made of a synthetic quartz substrate of 6 inches square that has a thickness of 0.25 inch and that has films of 70 nm thick.
The internal stress of the films for the circuit pattern is generated during a process of manufacturing a photo mask blank that may be called a substrate with films and that serves to form a photo mask. Taking this into consideration, it has been found out that flatness should be improved in a photo mask blank so as to establish excellent flatness of the photo mask.
Herein, consideration is made about a method of controlling stress of the films for forming the circuit pattern. A method of controlling such stress can include a method of adjusting during a stage of depositing the film and a method of adjusting after deposition of the film.
In the method of adjusting during the deposition stage, a difficulty is present about making adjustment of the stress compatible with keeping characteristics necessary for the photo mask blank. Such characteristics may be an optical characteristic, chemical durability, and the like. Especially, it is often difficult to adjust the stress by deposition conditions in the case where the internal stress is compressive stress.
On the other hand, the instant has already filed Japanese Patent Application No. 2000-277215 and has proposed a method of reducing compressive stress in films for forming the circuit pattern. According to this method, a mask blank is manufactured by utilizing heat treatment carried out after deposition of films.
As any other conventional treatment methods, consideration is made about a method of using a clean oven, a method of using a hot plate, a method of using a lamp heater.
In Japanese Unexamined Patent Publication No. Hei 7-104457, namely, 104457/1995, disclosure is made about a method of manufacturing a half tone phase shift mask. Specifically, the method deposits a translucent film and thereafter forms a stabilization layer on the translucent film. The stabilization layer serves to protect a variation of characteristics in the translucent film that might occur due to irradiating light by a mercury lamp, heating, oxidizing, and due to irradiation of exposure light.
Alternatively, disclosure is also made in Japanese Unexamined Patent Publication No. Hei 8-220731, namely, 220731/1996 about a technique of stabilizing a translucent film of a half tone phase shift mask. According to this technique, the translucent film is irradiated by light, heat, an electromagnetic wave, a particle beam after deposition in an atmosphere of a vacuum, a rare gas, or a reactive atmosphere. In this case, a light source for irradiating light and the like may be, for example, either one of a heavy hydrogen lamp, a Xe lamp, and an excimer laser source, or a combination thereof.
Among the above-mentioned conventional methods, the heat treatment method should heat the transparent substrate to a high temperature not lower than 400° C. with the film deposited on the transparent substrate, so as to reduce or alleviate the internal stress of the film. Such a high temperature inevitably lengthens heating and cooling time and lowers productivity.
When heat treatment is carried out by the use of the heat processing apparatus, there is a temperature limit. Consequently, a reduction effect of the internal stress is insufficient for flatness required for the photo mask.
In addition, the light irradiation for the above-mentioned stabilization is not enough to reduce the internal stress because the film can not be heated to a temperature sufficient to alleviate the internal stress.
SUMMARY OF THE INVENTION
It is a first object of this invention to provide a method of manufacturing a mask blank, wherein a time needed for improving an internal stress is very short and the internal stress is remarkably improved.
Especially, this invention makes it possible to improve an internal stress of a film that has a difficulty of improving the internal stress and provides the method of manufacturing the mask blank, wherein the internal stress of the film is largely improved.
It is another object of this invention to provide a method of manufacturing the mask blank, which can reduce the internal stress in the film and also improve optical characteristics of the film.
It is still another object of this invention to provide a mask blank or a mask that is not greater than 0.5 &mgr;m in flatness.
In order to accomplish the above-mentioned objects, this invention has the following constitution.
(Constitution 1)
A method is for use in manufacturing a lithography mask blank on a transparent substrate. According to this invention, the method comprises the steps of depositing, on the transparent substrate, at least one light absorption film which has a property of absorbing a laser of a predetermined wavelength, and irradiating a laser beam of the predetermined wavelength onto the light absorption film to heat the light absorption film and to thereby alleviate its internal stress.
(Constitution 2)
The mask blank according to Constitution 1 is a phase shift mask blank and the light absorption film is formed by a translucent film which serves as a phase shift film of the phase shift mask blank so as to attenuate exposure light of predetermined intensity.
(Constitution 3)
The mask blank mentioned in Constitution 1 has at least one shield or opaque film and the light absorption film is formed by the opaque film.
(Constitution 4)
In the method according to either one of Constitutions 1 through 3, the laser beam is irradiated onto the mask blank so that the transparent substrate with the light absorption film has flatness not greater than 0.5 &mgr;m.
(Constitution 5)
A lithography mask blank according to Constitution 5 is manufactured by the method mentioned in either one of Constitutions 1 through 4.
(Constitution 6)
A lithography mask according to Constitution 6 is manufactured by the use of the mask blank mentioned in Constitution 5.
In order to accomplish the above-mentioned objects, the transparent substrate after deposition of the light absorption film is irradiated by a laser beam in this invention to heat the
Hoya Corporation
Rosasco Stephen
Sughrue & Mion, PLLC
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