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 pericle frame (21), of the two edges of the pericle 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 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 films which is used in peeling off a film formed on a substrate in a production process and in adhering the peeled film to one side surface of a frame, and a jig used for peeling off the film formed. In recent years, protective films typified by pellicles have come to be increasingly provided on photomasks and reticles (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 pericle frame is cut off. At this juncture, first of all, the peeling the film off the substrate is conventionally carried out as follows: Pieces of a 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. 9. 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 pellicle 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. According to one aspect of the invention, there is provided a method of peeling off a thin film from a substrate by means of a jig, comprising the steps of: pressing a peeling jig, which is constituted by a flexible annular frame against the thin film applied on said substrate; and peeling said thin film together with said peeling jig from said substrate, characterised in that the annular frame has an adhesive applied thereon and is provided with at least one grasping portion such as a lug, handle, knob, or the like projecting laterally from the substrate at the periphery side of the frame or projecting upwardly at the periphery side of the frame; in that the annular frame has a Young's modulus of 15,000 - 30,000 kg/cm² and a bending strength of 50-120 g/10cm; and in that the peeling step comprises grasping the grasping portion of said peeling jig after said peeing jig and said thin film have been adhered together; and pulling upwardly the grasping portion of the peeling jig. 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. Preferably the method includes the steps of: adhering an adhesive tape at a peeling starting portion at a peripheral portion of the film applied on a substrate in such a manner as to cause the adhesive tape to project from the substrate; pressing the peeling jig against the thin film applied on the substrate, in such a manner that the peeling jig is placed on the adhesive tape; and grasping a portion of the peeling jig projecting outwardly from the adhesive tape, thereby to peel off the thin film from the substrate. Thus it is possible to peel off the film from the end surface even if the adhering portions of the jig on the substrate with the film applied thereon are offset to some degree or other. Conveniently the peeling jig has an adhesive applied on one surface thereof so as to be adhered to the film formed on the substrate, thereby overcoming the aforementioned drawback. According to a further aspect of the invention, the method further comprises the steps of: chamfering one or both of an edge of a pellicle frame formed by an inside surface thereof and an end surface thereof to which a pellicle film is to be adhered, and an edge of said pellicle frame formed by an outside surface thereof and said end surface thereof; applying an adhesive to said chamfered end surface of said pellicle frame; stretching and placing said pellicle film on said pellicle frame applied with said adhesive; and cutting off a portion of said pellicle film along said outside surface of said pellicle frame. Thus with the present invention in a method of peeling off a film an annular flexible provisional frame is 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 sides 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 3 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 swollen 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 plan view of a peeling jig of the invention adhered to a substrate with a film formed thereon; Fig. 2 is a cross-sectional view thereof; Fig. 3 is a cross-sectional view thereof during peeling; Figs. 4 to 6 are diagrams illustrating a method of testing the bending strength of the peeling jig, in which Fig. 4 is a top plan view of a test piece; Fig. 5 is a cross-sectional view prior to pulling; Fig. 6 is a cross-sectional view illustrating a state after pulling; Fig. 7 is a cross-sectional view of essential portions illustrating a state after a pericle film has been adhered; Fig. 8 is a cross-sectional view of essential portions illustrating a state after the pericle film has been adhered; and Fig. 9 is a cross-sectional view of essential portions of a conventional example. With 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, in accordance with the first aspect of the invention, 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. When peeling is carried out by using the aforementioned peeling jig, the adhesive is applied to that jig and the jig is pressed against the thin film on the substrate to effect adhesion, as described above. However, depending on a location or the viscosity of the adhesive, there are cases where the adhesive fails to be spread to the edge of the substrate. Accordingly, in this case, the peeling is effected from a point spaced from the edge of the substrate, and the aforementioned problem is liable to occur. It is possible to apply the adhesive in areas close to the peripheral edge of the peeling jig or to allow the adhesive to be spread sufficiently on the end surface when the jig is pressed against the film after applying an adhesive of good fluidity. In this case, the adhesive is often pressed out from the end surface, and a strong force is required in peeling off the film adhered to the edge surface of the substrate. For that reason, sudden exfoliation occurs, possibly damaging the film. Hence, when adhering the jig, it is necessary to effect positioning in such a manner that the adhesive reaches to the edges of the end surface but does not project therefrom. However, such positioning involves a delicate operation and is difficult to effect. A further embodiment of the invention overcomes the aforementioned problem, and makes it possible to peel off the film from the end surface even if the adhering portions of the jig on the substrate with the film applied thereon are offset to some degree or other. According to this embodiment an adhesive tape is adhered at a peeling starting portion at a peripheral portion of the film applied on a substrate in such a manner as to cause the adhesive tape to project from the edge of the substrate. A peeling jig constituted by a flexible annular frame with an adhesive applied thereon is pressed against the thin film applied on the substrate, in such a manner that the peeling jig is placed on the adhesive tape; and a portion of the peeling jig projecting outwardly from the adhesive tape is used to peel off the thin film from the substrate. Thus it is unnecessary to effect adhesion by accurately positioning the peeling jig in such a manner that the peeling jig will be aligned with the end surface of the substrate. If the peeling jig is suitably positioned on the substrate in such a manner that the peeling jig is merely placed on the adhesive tape adhered at the peeling starting position, the peeling off of the film from the end surface becomes possible even if the position of the peeling position is offset to some degree or other. Consequently, the number of cases where the film becomes damaged during peeling off is substantially reduced, so that the production yield improves. In the above-described aspects of the invention, the reason why a flexible peeling jig is used is that, if the jig is formed of a rigid material, the peeling is carried out at once over the entire surface of the film, so that a strong force is required, and the film is hence liable to become broken. Nevertheless, it is undesirable if the jig is highly resilient and very flexible, or has small resiliency and is difficult to bend. If the film is highly resilient and is very flexible, when a portion of the jig is grabbed by a robot to carry the film, the free end of the jig droops and it becomes difficult to place the jig correctly on the film disposed on the substrate. As a result, the adhering portions are liable to become offset, or it becomes impossible to effect adhesion of the entire portions. Also, when the film peeled off the substrate by adhering the jig thereto is adhered to a frame in a following process, the film is liable to undergo deflection or slackness owing to the deflection of the jig, making it impossible to stretch the film on the frame. Thus, deteriorated handling efficiency results. Meanwhile, if the resiliency is small and the jig is difficult to bend, the peeling of the film cannot be effected continuously and tends to be carried out intermittently. In consequence, numerous creases tend to be formed in a direction perpendicular to the peeling direction. Suitably, according to the present invention, the peeling jig for peeling off a film formed on a substrate, comprises an annular frame having a Young's modulus of 15,000 - 35,000 kg/cm² and a bending strength of 50 - 120 g/10 cm. An adhesive is applied on one surface thereof so as to be adhered to the film formed on the substrate. Since the peeling jig is suitably flexible, it is possible to effect the peeling off of the film continuously and progressively, and, since the peeling jig does not bend excessively, handling can be facilitated. A bending strength referred to here means tension measured as follows: As shown in Fig. 4, using an annular frame 2 having an inside diameter of 180 mm, an outside diameter of 220 mm, a length of the jig including lugs 1 formed projectingly at opposite sides thereof being 300 mm, and a thickness of 1.5 mm, one of the lugs 1 is fixed, as shown in Fig. 5, and one end of a cord 3 with a length of 600 mm is connected to the other lug 1, while the other end of the cord is pulled vertically at a fixed point, and the deflection at point a becomes 100 mm. A peeling jig embodying the invention is shown in Figures 1 to 4. 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 2, as shown in Fig. 4, 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). When a peeling test in accordance with this embodiment was conducted 150 times, the number of cases in which it was able to peel off the nitrocellulose film without being broken off was 145, and the success rate was 96.7%. When a peeling test was conducted without using the adhesive tape 7, in the same manner as the above-described embodiment, the number of successful cases was 25 with respect to 100 times of peeling, and the success rate was only 25%. For the peeling jig 8, a material having a Young's modulus of 15,000 - 35,000 kg/cm² and a bending strength of 50 - 120 g/10 cm is used. Accordingly, no nitrocellulose film in which creases are formed in a direction perpendicular to the peeling direction was obtained. In addition, the nitrocellulose film 6 which is supported by the jig 8 at the peripheral portion thereof maintains a substantially planar configuration even if one end of the jig 8 is supported in the form of a cantilever. For this reason, handling can be facilitated at the time when the film is stretched on a frame in a following process. Next, comparative examples in which peeling jigs of materials other than that described above will be described below. Comparative Example 1 When 2.65µ-thick nitrocellulose films each formed on the glass substrate were peeled off at a rate of 10 mm/sec by using a metallic jig having a Young's modulus of 40,000 kg/cm² and a bending strength of 150 g/10 cm, it was not possible to peel off each of the films continuously, and the state was such that the film was peeled off intermittently. As a result, films in which numerous creases were formed perpendicularly to the peeling direction were obtained. Comparative Example 2 When a synthetic resin-made jig having a Young's modulus of 50,000 kg/cm² and a bending strength of 20 g/10 cm, was used, at the time when one lug of the jig was grabbed and carried by the robot, the following deteriorated handling features were encountered: The free end of the nitrocellulose film drooped, which caused the adhering position to be offset, and made it impossible to cause the overall jig to be adhered accurately to the film on the substrate. In addition, it was not possible to stretch the film subsequently in a frame. 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. A further 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. 7). 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 0.1 - 0.7 C, preferably 0.2 - 0.4 C. As shown in Figures 7 and 8, 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. 8). Before or after this application, a pellicle film 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 pellicle frame 21 (Fig. 7). Subsequently, a portion of the film 23 extruding from the pellicle frame 21 is cut off at the edge of the pellicle frame 21. If the chamfering is smaller than 0.1, a swelling portion is created, a shown in Fig. 9, and when the pellicle is provided on the mask, there is the risk of the film becoming broken. Also, if the chambering is greater than 0.7, the adhesive surface becomes small, so that the adhesiveness weakens, and the film can exfoliate during air drying. In addition, as shown in Fig. 8, 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. 7). 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 with this aspect of 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 peeling off a thin film from a substrate by means of a jig, comprising the steps of: pressing a peeling jig (8), which is constituted by a flexible annular frame (2) against the thin film (6) applied on said substrate; and peeling said thin film together with said peeling jig from said substrate, characterised in that the annular frame (2) has an adhesive (10) applied thereon and is provided with at least one grasping portion, such as a lug (9), a handle or a knob, projecting laterally from the substrate (5) at the periphery side of the frame or projecting upwardly at the periphery side of the frame; in that the annular frame has a Young's modulus of 15,000 - 30,000 kg/cm² and a bending strength of 50-120 g/10cm; and in that the peeling step comprises grasping the grasping portion of said peeling jig after said peeling jig and said thin film have been adhered together; and pulling upwardly the grasping portion of the peeling jig. A method of peeling off a film (6) by means of a jig according to claim 1, further comprising the steps of: adhering an adhesive tape (7) at a peeling starting portion at a peripheral portion of said film (6) applied on said substrate (5) in such a manner as to cause said adhesive tape to project from said substrate; and pressing the peeling jig (8) against said thin film applied on said substrate, in such a manner that said peeling jig is placed on said adhesive tape. A peeling jig (8) for peeling off a film (6) formed on a substrate (5), characterised by consisting of a flexible annular frame (2) provided with at least one grasping portion, such as a lug (9), a handle or a knob, projecting laterally from said substrate at the periphery side of the frame or projecting upwardly at the periphery side of the frame, said annular frame having a Young's modulus of 15,000-35,000 kg/cm² and a bending strength of 50-120 g/10cm. A peeling jig according to claim 3, characterised by an adhesive (10) applied on one surface thereof so as to be adhered to said film formed on said substrate. A method according to claim 1 or 2, further comprising the steps of: chamfering one or both edges of a pellicle frame (21) formed by an inside surface thereof and an end surface thereof to which a pellicle film (23) is to be adhered and an edge of said pellicle frame formed by an outside surface thereof and said end surface thereof; applying an adhesive (22) to said chamfered end surface of said pellicle frame; stretching and placing said pellicle film on said pellicle frame applied with said adhesive; and cutting off a portion of said pellicle film along said outside surface of said pellicle frame. A method according to claim 5, wherein said pellicle film is peeled off and held by a provisional frame (24) by adhering said provisional frame to said film formed on said substrate, before said film is adhered to said pellicle frame. A method according to claim 5 or 6, wherein said chamfering is effected by providing a slanting surface (21a) at an angle of 0.1 - 0.7C. A method according to claim 6, wherein said provisional frame (24) is a peeling jig in accordance with claim 3 or 4.

Inventors: FUJIMOTO MAKOTO, KAYA TOSHIO, NAKAGAWA HIROAKI, FUJIMOTO, MAKOTO, KAYA, TOSHIO, NAKAGAWA, HIROAKI
Applicants: MITSUI PETROCHEMICAL IND, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1988
Main classification: G03F1
IPC codes: G03F1