Stock material or miscellaneous articles – Display in frame or transparent casing; or diorama including... – Peripheral enclosure or frame
Reexamination Certificate
2000-03-27
2002-04-09
Thomas, Alexander S. (Department: 1772)
Stock material or miscellaneous articles
Display in frame or transparent casing; or diorama including...
Peripheral enclosure or frame
C430S005000
Reexamination Certificate
active
06368683
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pellicle for photolithography, in particular, a pellicle for photolithography that realizes excellent light transmission and high resolution in the vacuum ultraviolet region.
2. Related Art
In the production of semiconductor devices such as LSIs and VLSIs or liquid crystal display panels, patterning has conventionally been attained by irradiating light on semiconductor wafers or substrates for liquid crystal panels. In this case, dust particles adhered to a substrate to be exposed with the light may cause a problem. That is, a transferred pattern may be deformed or edge lines of the pattern may be rugged without smoothness, because the dust particles may absorb or reflect the light. Therefore, dimension, appearance, quality and so forth of the pattern may be degraded, and thus performance and production yield of semiconductor devices and liquid crystal display panels may be degraded.
For this reason, these operations are usually performed in a clean room. However, because it is difficult to keep a substrate to be exposed by light always clean even in such a clean room, a pellicle well transmitting light is applied on a surface of substrate to be exposed by light in order to prevent adhesion of dust particles on the substrate.
When a pellicle is applied, dust particles do not adhere directly on the surface of substrate to be exposed with light, but on the pellicle membrane. Therefore, if the light is focused on the pattern of the substrate to be light-exposed during the photolithography process, the presence of such dust particles does not influence on the pattern transfer.
The pellicle has conventionally been produced by adhering a pellicle membrane made of a cellulosic organic resin well transmitting light such as nitrocellulose (cellulose nitrate) and cellulose acetate to a pellicle frame made of aluminum, stainless steel or the like, of which upper part is applied with a solvent well dissolving the pellicle membrane before setting and dried in air, or adhering the pellicle membrane to the frame with an adhesive comprising acrylic resin, epoxy resin or the like.
In recent years, as semiconductor devices have become further finer, resolution required in photolithography has gradually become higher. And in order to realize such resolution, light of shorter wavelength has gradually been used as a light source. Specifically, ultraviolet lights (g-line, wavelength of 436 nm and i-line, wavelength of 365 nm) are currently replaced with far-ultraviolet lights (KrF excimer laser, wavelength of 248 nm), and vacuum ultraviolet lights (ArF excimer laser, wavelength of 193 nm) and fluorine excimer laser (wavelength of 158 nm) are ready to be put into practical use in near future.
By the way, as the material of pellicle membranes, the aforementioned organic resins having functional groups such as carbonyl groups in their molecular structures have conventionally been used in order to obtain high transmission. However, these resins absorb lights having a wavelength of 200 nm or more and suffer from photodegradation. Therefore, amorphous fluorinated polymers not comprising these functional groups, and comprising only saturated bonds are used as the membrane material of pellicles for far-ultraviolet lights. However, although these amorphous fluorinated polymers show high transmission for a wavelength up to around 180 nm, they shows significant absorption and very poor transmission for lights of a wavelength smaller than the wavelength mentioned above. Therefore, it is difficult to use them for pellicle membranes for fluorine excimer laser.
On the other hand, silicon oxide, which is an inorganic substance, shows high transmission also for ultraviolet lights, and is used for the material of photomask and so forth. Use of silicon oxide for the material of pellicle membranes has also been proposed (see Japanese Patent Unexamined Publication (Kokai) Nos. 63-26251 and 2-62542). However, since usual silicon oxide shows significant absorption for a wavelength of 180 nm or less, it cannot be used as pellicle membranes for fluorine excimer laser.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the aforementioned problems, and its main object is to provide a pellicle for photolithography consisting of a pellicle membrane which shows high light transmission and excellent durability, even when it is irradiated with vacuum ultraviolet lights of a short wavelength, i.e., 160 nm or less.
The present invention has been accomplished in order to achieve the aforementioned object, and provides a pellicle for photolithography comprising at least a pellicle membrane adhered to a pellicle frame, characterized in that the pellicle membrane exhibits light transmission of 50% or more when it is irradiated by an excimer laser having a wavelength of 160 nm or less.
If a pellicle membrane shows a light transmission of 50% or more when it is irradiated by an excimer laser having a wavelength of 160 nm or less, it can maintain high light transmission and high resolution even when it is irradiated with a vacuum ultraviolet light of short wavelength. Therefore, it can be a pellicle of long life and high performance.
In a preferred embodiment of the aforementioned pellicle of the present invention, a material of the pellicle membrane may be an inorganic fluoride compound.
A pellicle membrane comprising an inorganic fluoride compound can surely maintain high light transmission even when it is irradiated with a vacuum ultraviolet light of short wavelength, and does not cause photodegradation. Therefore, it can be a pellicle of long life and high performance.
In the aforementioned preferred embodiment of the pellicle of the present invention, calcium fluoride or magnesium fluoride is preferably selected as the inorganic fluoride compound.
Calcium fluoride and magnesium fluoride intrinsically have a wide light transmission wavelength range, and show no substantial absorption for vacuum ultraviolet lights. Therefore, by using these compounds as the material of the pellicle membrane, a pellicle showing high transmission in that region can be obtained.
In another embodiment of the pellicle according to the present invention, the pellicle membrane may comprise silicon oxide containing 10 ppm or less of OH groups.
A pellicle comprising silicon oxide containing 10 ppm or less of OH groups as the material of the pellicle membrane can be used for laser beam of a short wavelength, i.e., 160 nm or less, for which conventional silicon oxide membranes cannot be used. In addition, it does not cause degradation, and hence it can maintain high transmission. Therefore, the pellicle can be a pellicle of long life and high performance.
Further, the present invention provides the pellicle for photolithography, wherein material of the pellicle membrane is silicon oxide doped with fluorine.
A pellicle comprising silicon oxide doped with fluorine as the material of the pellicle membrane can be used for laser lights of a short wavelength, 160 nm or less, for which conventional silicon oxide membranes cannot be used. Therefore, it can afford the same advantages as mentioned above.
OH group content of the silicon oxide doped with fluorine is preferably 10 ppm or less.
If the pellicle comprises silicon oxide having an OH group content of 10 ppm or less and doped with fluorine, the advantages mentioned above can be further enhanced by the effects of low OH group content and doping with fluorine.
According to the present invention, there is also provided the pellicle for photolithography wherein the pellicle membrane is adhered to the pellicle frame with an elastic adhesive.
Strain and deformation are likely to occur when a pellicle membrane consisting of an inorganic material, which is generally rigid, is used. By adhering the pellicle membrane to the pellicle frame with an elastic adhesive, such strain or deformation of the pellicle frame can be ameliorated.
In the aforementioned embodiment of the pellicle of the present invention, th
Oliff & Berridg,e PLC
Shin-Etsu Chemical Co. , Ltd.
Thomas Alexander S.
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