In manufacturing semiconductor devices such as LSI and super-LSI or in manufacturing a liquid crystal display board or the like, a pattern is made by irradiating a light to a semiconductor wafer or an original plate for liquid crystal, but if a dust particle is attached to a photo mask or a reticle (hereinafter collectively referred to as “photo mask” for simplicity) which is used during the irradiation operation, the dust particle would block off or reflect the light so that the resulting pattern would have roughened edges or black stains on the base, which would lead to problems such as damaged dimensions, poor quality, and deformed external appearance.
Thus, these works are usually performed in a cleanroom, but it is still not easy to keep the photo mask clean all the time; therefore, a pellicle is attached to a surface of the photo mask as a dust-fender before light exposure is carried out. Under such circumstances, dust particles do not directly adhere to the surface of the photo mask but adhere only to the pellicle film, and since this film is sufficiently remote from the photo mask surface if the photo focus is set on a lithography pattern on the photo mask, the foreign particles on the pellicle film fail to transfer their shadows on the photo mask and thus no longer become a cause for problems to the image transfer performance.
In general, a pellicle is made by adhering a transparent pellicle film, which is made of a highly light transmitting material such as cellulose nitrate, cellulose acetate, fluorine-containing polymer and the like, to an upper annular end face of a pellicle frame made of aluminum, stainless steel, polyethylene or the like, using as the glue either a solvent capable of dissolving the pellicle film, which is applied to said upper annular end face (hereinafter this face is called “upper end face”) and then air-dried before receiving the film (ref. IP Publication 1), or an adhesive such as acrylic resin, epoxy resin or the like (ref. IP Publication 2). Further the other annular end face (hereinafter called “lower end face”) of the pellicle frame is covered with an agglutinant layer made of polybutene resin, polyvinyl acetate resin, acrylic resin, silicone resin or the like for attaching the pellicle frame to the photo mask, and over this agglutinant layer is laid a release liner (separator) to protect the agglutinant layer.
Now, in recent years, the semiconductor devices and the liquid display board have undergone further improvement in integration and densification. Currently, a technology of forming a fine pattern having a resolution level of 32 nm on a photo resist film is on the verge of realization. Such patterning can be effectively achieved by improved technologies such as the immersion exposure method, wherein the space between the semiconductor wafer or the original plate for liquid crystal on one hand and the projection lenses on the other is filled with a liquid such as super pure water and the photo resist film is exposed to an argon fluoride (ArF) eximer laser, or the double exposure method, which uses a conventional argon fluoride (ArF) eximer lasar, to which the photo resist film is exposed.
However, the next-generation semiconductor devices and the liquid display board are called on to have even denser patterning of a level of 10 nm or smaller, and there is scarce room for the conventional exposure technology depending on excimer laser to improve to answer such high demand of making a dense pattern of the level of 10 nm or smaller.
Now, as a most promising method for forming a pattern of a density of 10 nm or smaller, an EUV exposure technology which uses an EUV light of a dominant wavelength of 13.5 mm is in the spotlight. In order to achieve a pattern formation on the density level of as high as 10 nm or smaller on the photo resist film, it is necessary to solve the technical problems with regard to the choices of light source, photo mask, pellicle, etc., and in respect of light source and photo mask there have been considerable progress and various porposals have been made.
With respect to the pellicle that could improve yields of semiconductor device products or liquid crystal displays, IP Publication 3, for example, discloses a silicon film of a thickness of 0.1-2.0 micrometers to act as the pellcile film for EUV lithography which is transparent and does not give rise to optical distortion; however there remain unsolved problems in this film, which have prevented realization of the EUV light exposure technology.