A pellicle that prevents adhesion of an adhesive pushed out from a pellicle frame to an original circuit pattern of a mask when mounting the pellicle to the mask. An end surface of the pellicle frame to be fixed to the mask has a taper-shaped notch formed by notching a rim along the entire peripheral surface of the pellicle frame in the peripheral direction. The adhesive is applied to the notch.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a pellicle which is bonded to a mask used
 in a photolithography process to protect the mask which process is a part
 of method for semiconductor integrated circuit fabrication.
 2. Description of the Related Art
 A mask is an original plate of a circuit pattern used for the transfer of a
 circuit pattern of a semiconductor integrated circuit onto a wafer, that
 is, the mask is a glass substrate having an original circuit pattern
 fabricated of opaque thin membrane formed thereon. To transfer the circuit
 pattern onto the wafer, the mask is set above a wafer, then ultra violet
 light, X-rays or the like are irradiated onto the mask.
 When foreign matter such as dust is adhering to the mask, the exact shape
 of the shadow of the foreign matter is transferred onto the wafer.
 Subsequently, defects are made in the circuit pattern transferred onto the
 wafer, resulting in a lowering of the reliability of the semiconductor
 integrated circuit. To prevent adhesion of foreign matter like this to the
 mask, a structure having a transparent protective membrane, called a
 pellicle, is mounted to the mask surface.
 FIG. 3 is a partially sectional view showing a structure of a conventional
 pellicle. As shown in FIG. 3, a pellicle 30 comprises a pellicle membrane
 31 which is a protective membrane fabricated from a transparent member, a
 pellicle frame 32 to hold the pellicle membrane 31 at a predetermined
 distance away from a surface of a mask 34, and an adhesive 33 to fix the
 pellicle frame 32 to the surface of the mask 34. The pellicle membrane 31
 is fabricated from a transparent thin membrane formed from nitrocellulose
 or the like, and prevents adhesion of foreign matter from outside onto the
 surface of the mask 34 by being fixed at a predetermined distance away
 from the surface of the mask. Even when foreign matter does adhere to the
 pellicle membrane 31, the shadow of the foreign matter is not transferred
 onto the wafer because the shadow of the foreign matter adhering to the
 pellicle membrane 31 is out of focus during exposure of the wafer since
 the pellicle membrane 31 and the mask 34 are spaced apart.
 To mount this type of pellicle 30 to the mask 34, first, a side of the
 pellicle 30 with the adhesive 33 applied thereto and a surface of the mask
 34 having an original circuit pattern formed thereon, are positioned
 face-to-face. Then, the pellicle 30 is press-adhered to the mask 34 by the
 application of a force against the mask 34 from above the pellicle 30.
 However, when this type of pellicle 30 is fixed to the mask, the adhesive
 33 is squeezed out due to the pressure applied to the pellicle 30, and a
 part of the adhesive 33 from an end surface of the pellicle frame 32
 adheres to the surface of the mask on the inside and outside of the
 pellicle frame 32. FIG. 4 is a schematic sectional view showing the
 squeezed adhesive 33' adhering to the surface of the mask 34 inside the
 pellicle frame 32. The adhesive 33' adhering to the surface of the mask 34
 inside the pellicle frame 32, as shown in FIG. 4, deteriorates due to
 exposure to the light from an exposure apparatus and loses its tackiness,
 and may move near to the original pattern of the mask due to vibration
 during transportation of the mask or the like. The problem has arisen that
 this deteriorated adhesive 33' causes defects in the mask 34 by adhering
 to the original pattern of the mask 34.
 In order to solve this type of problem, the technology described in
 Japanese Patent Application Laid-Open (JP-A) No. 6-19124 provides a
 pellicle such as that shown in FIG. 5 (FIG. 5 shows a pellicle which is
 mounted to the opposite surface of the mask to that in FIG. 4). A groove
 41a is formed on an end surface of a pellicle frame 41 facing a mask 43,
 and a pellicle is fixed to the mask 43 by an adhesive with which the
 groove 41a is filled. By utilizing this structure, bleeding of the
 adhesive onto the mask 43 inside the pellicle frame 41 is prevented.
 However, in the pellicle structure described in the aforementioned JP-A-No.
 6-19124, the problem has been that it is difficult to adjust the amount of
 the adhesive 42 to be placed in the groove 41a. For example, too small an
 amount of the adhesive 42 makes it difficult to sufficiently fix the
 pellicle on the surface of the mask 43 because the adhesive 42 is not able
 to fully contact the mask 43. On the other hand, too large an amount of
 the adhesive 42 causes problems with the adhesive 42 being pushed out all
 over the end surface of the pellicle frame 41 from the groove 41a upon
 pressing the pellicle against the mask 43, and the pushed-out adhesive 42
 adheres to the mask 43 on the inside and outside of the pellicle frame 41.
 There has been a further problem that when the adhesive 42 is placed in
 the groove 41a like this, the bonding area of the mask 43 and the adhesive
 42 in the state shown in FIG. 5 is too small for a sufficient bond
 strength to be obtained.
 The aim of the present invention, therefore, is to provide a pellicle which
 does not cause lowering of reliability of the mask due to the adhesion of
 adhesive pushed out from a pellicle frame to a surface of a mask when
 fixing the pellicle to the mask.
 SUMMARY OF THE INVENTION
 The pellicle of the present invention is a pellicle stretched between a
 predetermined position and a surface of a mask, on the surface of which is
 formed an original pattern for transferring a circuit pattern onto a wafer
 using a photolithographic method, in order to prevent the adhesion of
 foreign matter to the original pattern formed on the surface of the mask,
 wherein the pellicle is provided with a pellicle frame. The pellicle
 includes a pellicle membrane that is transparent to exposure light, and a
 frame-shaped structure. The frame structure has a surface at a first end
 adhering to the periphery of the pellicle membrane and a surface of a
 second end adhering to the mask. The frame also has a notch portion
 running in the peripheral direction of the surface at the second end
 surface for allowing adhesive used during an adhesion process to escape in
 the peripheral direction.
 Namely, the pellicle of the present invention has a notch formed along the
 peripheral direction of a surface of the pellicle frame, which surface is
 to be bonded to the mask. By applying the adhesive to the notch, the
 adhesive can be released to the outside when mounting the pellicle to the
 mask, so that adhesion of the adhesive to the original pattern of the mask
 can be prevented.
 When adopting a pellicle with this type of structure, the notch may be a
 tapered surface that is sloped at a predetermined angle to the mask. Also,
 the notch may be shaped so as to have an arcuate sectional form.
 When adopting a pellicle with this type of structure, said notch may be a
 tapered surface which is sloped at a predetermined angle to said mask.
 Also, the notch may be shaped so as to have an arcuate sectional form.

DETAILED DESCRIPTION OF THE INVENTION
 Embodiments of the present invention are explained below with reference to
 the figures.
 (First Embodiment)
 FIG. 1A is a partially sectional view showing a structure of a pellicle
 according to a first embodiment of the present invention, and FIG. 1B is a
 sectional view showing the pellicle of FIG. 1A being mounted to a mask. A
 pellicle 10 of the present embodiment comprises a pellicle membrane 11,
 which is a protective membrane fabricated from a transparent member, a
 pellicle frame 12 to hold the pellicle membrane 11 a predetermined
 distance away from a mask 14, and an adhesive 13 applied to an end surface
 of the pellicle frame 12 to fix the pellicle frame 12 to the mask 14.
 The pellicle frame 12 is a frame fabricated from an aluminum alloy or the
 like, having a periphery smaller than the periphery of the mask 14. One
 end surface of the pellicle frame 12 is bonded to a surface of the
 pellicle membrane 11 near the membrane periphery. The pellicle membrane 11
 is a transparent thin membrane fabricated of nitrocellulose or the like
 and the thickness thereof is about 0.8 .mu.m. A rim along a peripheral
 surface 12d of another end surface 12b of the pellicle frame 12 is notched
 in a tapered-shape throughout the periphery of the end surface 12b so as
 to have an angle of 45.degree. to the end surface 12b. Hereinafter, this
 sloped portion is designed as a notch 12c. The adhesive 13 is applied to
 the entire surface of the notch 12c.
 A method of mounting a pellicle 10 having this type of structure to the
 mask 14 is explained below. First, as a shown in FIG. 1A, the surface of
 the pellicle 10 with the adhesive 13 applied thereto is positioned to face
 a surface 14a of the mask 14 on which an original circuit pattern (not
 shown) is formed. Then pressure against the pellicle 10 from the pellicle
 membrane 11 side is applied in a direction A of FIG. 1A to press-adhere
 the end surface 12b of the pellicle frame against the surface 14a of the
 mask 14. Thus, as shown in FIG. 1B, the end surface 12b of the pellicle
 frame 12 is fixed to the mask 14 by the adhesive 13 applied to the notch
 12c closely contacting the mask 14. By mounting the pellicle 10 to the
 mask 14 in this way, the original circuit pattern formed on the surface
 14a of the mask 14 is covered by the pellicle 10, and thereby adhesion of
 foreign matter onto the mask 14 can be prevented. In the state shown in
 FIG. 1B, even when foreign matter adheres to the pellicle membrane 11, the
 shadow thereof is not transferred onto a wafer because the foreign matter
 is out of focus during exposure since the pellicle membrane 11 is spaced a
 predetermined distance away from the surface of the mask 14.
 To mount the pellicle 10 to the mask 14, a pressure of about 30 kg/cm.sup.2
 is applied to the pellicle 10. Therefore, the adhesive 13 applied to the
 pellicle frame 12 is squeezed by the pressure and may spread around the
 pellicle frame 12. Even in a case like this, the adhesive 13 only spreads
 outward from the pellicle 10 along the notch 12c since the adhesive 13 is
 applied only to the notch 12c, which is sloped with respect to the end
 surface 12b. Thus, adhesion of the spread adhesive 13 onto the portion of
 the original circuit pattern of the mask 14 inside the pellicle frame 12
 can be prevented. Thus, defects in the mask caused by adhesion onto the
 original circuit pattern of the adhesive, which has lost its tackiness due
 to exposure to an exposure light, can be prevented.
 FIG. 2A is a sectional view showing a structure of a pellicle according to
 a second embodiment of the present invention, and FIG. 2B is a sectional
 view showing the pellicle of FIG. 2A being mounted to a mask. The pellicle
 according to the second embodiment is characterized by an adhesive
 application surface formed by notching a rim, along the periphery of an
 end surface of a pellicle frame, to have an arcuate sectional form. Other
 portions of the pellicle are the same as the pellicle of the first
 embodiment.
 A pellicle membrane 11 is bonded to an end surface 22a of a pellicle frame
 22 of the pellicle 20 in the same way as in the first embodiment. A rim
 along a peripheral surface 22d of another end surface 22b of the pellicle
 frame 22 is notched so as to have an arcuate sectional form, as shown in
 FIG. 2A. An adhesive 13 for fixing the pellicle 20 to a mask 14 is applied
 to the entire adhesive application surface 22c formed by notching the rim
 of the pellicle frame 22b.
 To mount the pellicle having this type of structure onto the mask 14,
 pressure is applied to the pellicle 20 to press-adhere the pellicle 20
 against the mask 14 in the same way as in the first embodiment. Thus, the
 pellicle frame 22 is fixed to the mask 14 by the adhesive 13. At this
 time, the adhesive 13 is squeezed by the pressure applied to the pellicle
 20, and a part of the adhesive 13 may spread around the pellicle frame 22.
 However, in the pellicle 20 of the present embodiment, the adhesive 13 is
 spread outward only from the pellicle 20 because the adhesive 13 is
 applied only to the adhesive application surface 22c formed by notching
 the end surface 22b of the pellicle frame 22. Thus, adhesion of the
 adhesive 13 to the original circuit pattern (not shown) formed on the
 surface of the mask inside the pellicle frame 22, can be prevented, and
 thereby the occurrence of defects in the mask can be prevented.
 According to the present invention, the adhesion of an adhesive pushed out
 of a pellicle frame onto a surface of a mask inside the pellicle frame
 when mounting a pellicle to the mask can be prevented.