Method of producing films and jig for producing the same

Abstract: The invention concerns a method of producing protective films or the like used as protective covers for photomasks or reticles. To peel a thin film (6) off a substrate (5), a peeling jig (8) constituted by a flexible annular frame (2) with an adhesive (10) applied thereon is pressed against the thin film applied on the substrate; a portion of the peeling jig is grabbed after the peeling jig and the thin film are adhered together; and the peeling jig and the film are peeled off the substrate. Before adhering the peeled film onto a side end surface of a pellicle frame (21), of the two edges of the pellicle frame, at least the edge formed by an inside surface thereof and the side end surface thereof is chambered.

Description: The present invention relates to a method of producing pellicles (protective films) which are used as protective covers for photomasks, reticles, or the like and a jig for producing the same and, more particularly, to a method of producing pellicles using films which are peeled from a substrate in a production process and in adhering the peeled film to one side surface of a frame. In recent years, protective films typified by pellicles have come to be increasingly provided on photomasks and reticiles (hereafter simply referred to as masks) for the purposes of protecting mask pattern surfaces and preventing foreign substances such as dust particles from being deposited thereon. To produce a pellicle according to a conventional method, a film is first formed on a substrate by spin coating or the like, is then peeled off, and is adhered on one side surface of a pellicle frame. Subsequently, a portion of the film projecting from the pellicle frame is cut off. At this juncture, first of all, peeling the film off the substrate is conventionally carried out as follows: Pieces of wide adhesive tape which has a small modulus of elasticity are adhered on a periphery of the film in the shape of # , and the film is peeled off carefully from one side by manually holding the adhesive tape. After the film has been released, the pieces of the adhesive tape provided on both sides of the film are manually held, and the film is placed on a pellicle frame with an adhesive applied on side end surfaces thereof and is adhered thereto. Since the film is thin, however, when it is peeled off, the film becomes partially elongated and is hence liable to become damaged unless the film is peeled off at a constant speed and uniformly in a direction perpendicular to the peeling direction. However it has not been easy to peel off the film uniformly at a constant speed without causing breakage. Secondly, the adhesion of the film onto the pellicle frame is conventionally carried out by holding with both hands the pieces of the aforementioned adhesive tape, adhered in the form of # around the periphery of the film to peel the film off the substrate, and by placing the film on the pellicle frame with its side coated with the adhesive facing upward. However, if the film is adhered by being simply placed on the pellicle frame, slackness is liable of occur on the film surface, and it is impossible to adhere the film uniformly on the entire surface of the side end surface of the frame, so that bubbles are liable to enter the adhered portion and an uneven surface can result. For this reason, it is desirable to install the film on the frame with the film set in a tense state by lightly and uniformly applying tension to the film from the four sides. However, it is not easy to apply tension to the film into a planar configuration in such a manner that excessive tension or slackness are not caused in the film surface. In addition, there are cases where the adhesive applied to the frame is extruded to the inner and outer sides of the frame, and the extruded adhesive causes the film to swell at an edge of the film, as shown in Fig. 6. If there is any such swollen portion, there is the possibility of the film becoming broken at the swollen portion when the pellicle is held by a device for installing the pellicle on the mask. To apply strong tension to eliminate any swelling of the film due to the extruded adhesive is not desirable since the film is liable to become broken. Thirdly, the protective films are generally cleaned by air jets at the time when they are produced or used (at the time when they are installed on the mask), and, at that time, the film surface vibrates. However, since the thickness of the pellicle film is very small, fracture can occur at the edge of the pellicle frame. As other methods of producing protective films, the following methods have been proposed: (1) a method in which a releasable film is formed on a substrate by using a material which is capable of undergoing sol-gel conversion, and a thin film is further formed thereon. This laminate is then immersed in warm water, and the releasable film is subjected to sol-gel conversion to cause the thin film to float in the warm water. Subsequently, this thin film is scooped up from the warm water by means of a frame, and is then subjected to heating and drying (Japanese Patent Laid-Open No. 182730/1984), (2) a method in which after a film is formed on a substrate, a pellicle frame with an adhesive applied thereto is pressed against the film to allow the film to become adhered thereto, and, after adhesion, the pericle frame is separated from the substrate together with the film, (3) a method in which, after a film is formed on a substrate, a frame with an adhesive applied thereto is placed on the laminate so as to be adhered. This structure is immersed in water to separate the film from the substrate, and the frame with the film secured thereto is lifted up from the water and is then allowed to dry (Japanese Patent Laid-Open No. 237450/1985) and (4) a method in which, after a film is formed on a substrate the substrate is soaked in deionized water to loosen the bonding. An aluminium peeling ring is attached to the film surface and used to peel off the film (document EP-A-0119387). However, in cases (1), (3) and (4) above, it is necessary to dry the film after it is recovered from the water, and these methods cannot be applied to a soluble film or a film whose surface has been provided with surface treatment with a soluble substance. Moreover, particularly in the case of the former method in which the thin film floating in the water is scooped up by the frame, creases or slackening are liable to occur in the film surface. In addition, in case (2) above, when the frame is pressed against the substrate, there is the risk of causing damage to the substrate, and the film is liable to become broken during cleaning by the air blow, as described above, Furthermore, the film must be peeled off in such a manner as to be lifted up from the portion where the inner side of the frame is adhered to the end surface of the substrate. However, since the space between the film and the substrate assumes the state of a vacuum, a strong force is required in peeling off the film. Hence there are cases where the film becomes broken, and the frame is subjected to deformation due to a strong force applied locally. A thin film support frame is described in US 4,579,616. The preamble of claim 1 is based on the disclosure of this document. According to one aspect of the invention, there is provided a method of producing a pellicle, using a pellicle frame having an inner surface, an outer surface and an end surface between said inner and outer surfaces with at least one edge of said end surface chamfered, said method comprising the steps of: applying an adhesive to said end surface; stretching and placing a pellicle film on said end surface to which said adhesive has been applied and cutting off a portion of said pellicle film along said outside surface of said pellicle frame; characterised in that said at least one edge of said end surface consists of at least the edge formed between said inner surface and said end surface of said pellicle frame; and in that in said adhesive applying step said adhesive is applied to said end surface in an area other than on the chamfered at least one edge. According to a further aspect of the invention, the method further comprises the steps prior to adhering said pellicle film to said pellicle frame, of adhering a provisional frame to said film formed on a substrate, peeling off said film from said substrate and holding said film using said provisional frame. Thus with the present invention a provisional frame may be adhered to a film formed on a substrate and this allows the film to be peeled off gradually and uniformly from adhered portions on both side as a portion thereof is held and peeled off. This facilitates peeling by means of a mechanical means such as a robot to permit the film to be peeled off at a fixed speed, and makes it possible to support the film in a planar state and with no waviness created therein, thereby overcoming the above-described drawbacks of the prior art. Further it can overcome problems that, when the film is pressed against a pellicle frame with tension lightly applied to the film, the film at an edge of the frame becomes swelled due to an extruded adhesive, and that the film becomes broken by the edge of the frame during air cleaning. This invention will be further described by way of non-limitative example with reference to the accompanying drawings in which:- Fig. 1 is a top view of a peeling jig adhered to a substrate with a film formed thereon; Fig. 2 is a cross-sectional view of Fig. 1; Fig. 3 is a cross-sectional view of Fig. 1 during peeling; Fig. 4 is a cross-sectional view illustrating a pellicle frame after a pellicle film has been adhered according to the method of the present invention; Fig. 5 is a cross-sectional view illustrating the pellicle frame of Fig. 4 before the pellicle film has been adhered; and Fig. 6 is a cross-sectional view of essential portions of a conventional example. For later use in an aspect of the present invention, a film is peeled from a substrate using a peeling jig constituted by a flexible annular frame with an adhesive applied thereon. The frame is pressed against the thin film applied on a substrate; grasping a portion of the peeling jig after the peeling jig and the thin film are adhered together; and peeling off the peeling jig and the film from the substrate, thereby peeling the thin film from the substrate. As the jig is flexible if a portion of the peeling jig is grasped and pulled away from the substrate, the peeling jig is separated from the substrate while being bent in the form of a cantilever, and the film adhered to the peeling jig is gradually peeled off from a peripheral edge portion of the substrate. A portion of the peripheral edge of the jig projecting laterally from the substrate may be grasped but preferably, however, a special portion such as lug, a handle, a knob, or the like is formed integrally with the jig, and that portion is grasped. As described above, the peeling jig is annular and flexible, so that if one portion of the peeling jig is grasped and peeled, the peeling jig bends in the form of a cantilever, and the film can be peeled off, and the peeling can be effected gradually. Hence, even a thin film which is liable to be torn if peeled off strongly at one time can be peeled off without being torn. In addition, by grasping a portion of the jig and simply pulling off the jig, the peeling can be performed uniformly at adhered portions that are perpendicular to the peeling direction, and the film can therefore be peeled off relatively uniformly even if the peeling jig is not pulled off at a plurality of locations. Accordingly, local slackening or excessive tension are unlikely to occur in the film surface. The film, which is peeled off from the substrate, is adhered to the jig, and is supported thereby, can be maintained in a planar state, and creases or slackening do not occur insofar as the jig is not twisted or deflected, so that handling can be facilitated. Furthermore, since it is possible to effect peeling by using a mechanical means such a robot by virtue of the above-described aspects, the invention contributes to labor saving and improves the operating efficiency. Moreover, since the peeling can be performed readily at a fixed speed, breakage is unlikely to occur in the film. The method is typically applicable to protective films provided on masks, but can be similarly applied to films in other fields as well. When the film applied on the substrate is peeled off, it is important to peel it from an edge of the substrate. If an attempt is made to peel it off from a point spaced from the edge of the substrate, the space between the substrate and the film assumes a vacuum, so that a relatively strong force is required, and when the air enters that space to cancel the vacuum, exfoliation occurs suddenly. Hence, damage to the film is likely to occur, resulting in breakage. As shown in Figs. 1 and 2, an adhesive tape 7 with a width of 20 mm and a length of 10 - 100 mm is first adhered at a peeling portion of a nitrocellulose film 6 formed on a glass substrate 5 by means of spin coating or the like, in such a manner as to protrude from a peripheral edge of the film 6. Subsequently, one of a pair of lugs 9, which are respectively provided on opposing sides of a peeling jig 8 constituted by a frame and on which an adhesive 10 is applied on an entire circumferential surface thereof, is grasped by a robot (a part of which is designated at reference numeral 11) from above, and is carried to above the substrate 5. With the side of the peeling jig 8 to which the adhesive 10 is applied facing downward, the peeling jig 8 is placed on the nitrocellulose film 6 and adhered thereto in such a manner that one of the lugs 9 adheres to and projects from the adhesive tape 7. The lug 9 projecting from the adhesive tape 7 is then grasped by the robot, and is peeled off at a fixed speed (Fig. 3). It was mentioned that a problem with prior art methods was the swelling of the glue and film at the edges of the pellicle frame. The following aspect of the invention reduces or eliminates this problem. With this aspect of the invention, one or both of an edge of a pellicle frame formed by an inside surface thereof and a end surface thereof to which a pellicle film is to be adhered; and edge of the pellicle frame formed by an outside surface thereof and the end surface thereof are chamfered i.e. cut away at an angle. The adhesive is applied to the chamfered end surface of the pellicle frame and the pellicle film is stretched and placed on the pellicle frame applied with the adhesive. Finally a portion of the pellicle film along the outside surface of the pellicle frame is cut off. The stretching of the pellicle film can be effected manually by grasping the adhesive tape used to peel off the film, in a manner similar to a conventional method. However, it is difficult to press the film against the pellicle frame and stretch the same by applying tension uniformly in such a manner that no excessive tension is applied to the film surface or no creases are formed therein. This problem can be overcome by provisionally taking up the film formed on the substrate, by means of a provisional frame, and by stretching the film on the pellicle frame using that provisional frame. Namely, an adhesive is applied to an annular provisional frame and the provisional frame is adhered to the film disposed on the substrate. After the film is peeled off using the provisional frame, the provisional frame is pressed against the pellicle frame or vice versa, or the two members are pressed against each other, thereby overcoming the aforementioned problem. Since the film on the substrate is transferred onto the provisional frame, even if the provisional frame is manually held, it is possible to maintain the film surface in a planar state. Thus, it is possible to stretch the film on the pericle frame with tension applied to the film by simply pressing the provisional frame against the pericle frame or vice versa, or by simply pressing the two members against each other (see Fig. 4). The chamfering is carried out by providing a slanting surface or roundness to the edge, and when a slanting surface is provided, the slanting surface is formed with a chamfer C = 0.1 - 0.7 mm, preferably C = 0.2 - 0.4 mm. As shown in Figures 4 and 5, first, an edge formed by an inside surface of a pellicle frame 21 and an end surface to which a pellicle film 23 is to be adhered as well as an edge formed by an outside surface of the pellicle frame 21 and the end surface are chamfered, and an adhesive 22 is applied to the end surface of the pellicle frame 21 excluding chamfered portions 21a in such a way as to be piled up thereon. (Fig. 5). Before or after this application, a pelliclefilm 23 formed on the substrate is transferred onto a provisional frame 24, as described before. Subsequently, by grasping the provisional frame 24, the pellicle film 23 is placed on the side of the pellicle frame 21 to which the adhesive 22 is applied. The provisional frame 24 is depressed, or the pellicle frame 21 is lifted up, or the two members are pressed against each other, thereby adhering the pellicle film 23 onto the pellicleframe 21 (Fig. 4). Subsequently, a portion of the film 23 extruding from the pellicleframe 21 is cut off at the edge of the pellicle frame 21. If the chamfering C is less than 0.1mm, a swelling portion is created, as shown in Fig. 6, and when the pellicle is provided on the mask, there is the risk of the film becoming broken. Also, if the chamfering C is greater than 0.7mm, the adhesive surface becomes small, so that the adhesiveness weakens, and the film can exfoliate during air drying. In addition, as shown in Fig. 5, after the adhesive 22 is applied to the end surface of the pellicle frame 21 excluding the chamfered portions 21a, the pellicle film 23 is placed on the end surface, and tension is applied to the provisional frame or the pellicle frame, or both, the adhesive 22 is pressed out to the inner and outer sides of the frame, and is extruded to the chamfered portions 21a (see fig. 4). At this juncture, tension is applied in such a manner that the thickness of the pellicle film becomes smaller by 1 - 10%, preferably 3 - 7%. If the film is adhered in such a manner that the thickness of the pellicle film becomes smaller by 1% or less, creases are liable to be formed in the film. In addition, if the film is adhered by applying tension thereto in such a manner that the thickness of the pellicle film becomes smaller by more than 10%, the thickness of the film in the vicinity of the side end surface of the frame becomes small, so that the film is liable to become broken during air blow. Thus according to the invention, although the adhesive applied to the side end surface of the pellicle frame is extruded to the inside and outside of the frame, the extruded adhesive is pressed out to the chamfered portions and are received thereby, so that the film does not swell at the edge of the frame. Hence, at the time of handling of the film to be applied on to a mask, the problem that the film becomes broken or a similar problem can be overcome. In addition, during cleaning by air, even if the pellicle film vibrates, the breakage of the film at the edge of the frame can be prevented, or the number of cases of such breakage can be reduced.

Claims: A method of producing a pellicle, using a pellicle frame (21) having an inner surface, an outer surface and an end surface between said inner and outer surfaces with at least one edge (21a) of said end surface chamfered, said method comprising the steps of: applying an adhesive (22) to said end surface; stretching and placing a pellicle film (23) on said end surface to which said adhesive has been applied and cutting off a portion of said pellicle film along said outside surface of said pellicle frame; characterised in that said at least one edge of said end surface consists of at least the edge formed between said inner surface and said end surface of said pellicle frame; and in that in said adhesive applying step said adhesive is applied to said end surface in an area other than on the chamfered at least one edge. A method according to claim 1, further comprising the steps, prior to adhering said pellicle film to said pellicle frame (21), of adhering a provisional frame (24) to said film formed on a substrate, peeling off said film from said substrate and holding said film using said provisional frame (24). A method according to claim 1 or 2, wherein said chamfering is effected by providing a slanting surface (21a) with a chamfer C= 0.1 - 0.7mm.

Inventors: FUJIMOTO MAKOTO, KAYA TOSHIO, NAKAGAWA HIROAKI, FUJIMOTO, MAKOTO, KAYA, TOSHIO, NAKAGAWA, HIROAKI
Applicants: MITSUI CHEMICALS INC, MITSUI CHEMICALS, INC.
Application year: 1988
Main classification: G03F1
IPC codes: G03F1