Patent Number: 039881539
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to a method of manufacturing thin film iris diaphragms for use in corpuscular beam apparatus such as electron microscopes and vidicons which iris diaphragms consist of a metal layer containing at least one opening in order to pass a beam of particles. 2. Prior Art Iris diaphragms have been previously made from two separately manufactured components comprising a metal layer and a substrate or carrier plate. The metal layer is produced by depositing the metal on a profile surface of a template using a vapor metal deposition technique conducted under vacuum conditions. After forming the layer on the template, it is removed and secured to the substrate or carrier plate such as by brazing. Since the rate of fouling of an iris diaphragm increases with the thickness of the metal layer, the metal layer must be as thin as possible. Due to this requirement for a thin layer, the above described process has a high risk of damage to the metal layer as it is being removed from the template and during the step of securing it to the carrier or substrate. In addition thereto, the above described process requires templates which are complex and expensive to manufacture and which can only be used a few times. To overcome the above mentioned problems in the manufacture of iris diaphragms, it has been suggested to produce the diaphragms with the following method. A metal film is deposited directly on a carrier using for example electro-deposition methods with an appropriate mask. The carrier is subsequently etched in the area adjacent to the opening of the thin metal layer by a positive etching technique. Since the etching agent can only attack the unprotected areas of the carrier plate, the metal film or layer and the carrier must be made of different metals. While this process overcomes several difficulties experienced with the previous method, the different in the coefficience of thermal expansion and the difference in the thermal conductivity of the two metals used for the carrier member and the thin film subjects the iris diaphragm to distorsion when used in an apparatus subjected to temperature fluctuations. Thus, the thin film iris diaphragms produced by the proposed method are unsuitable for corpuscular beam apparatuses of the kind in which major temperature fluctuations will occur. SUMMARY OF THE INVENTION The present invention is directed to a method of manufacturing thin film iris diaphragms which have a film as thin as possible and have improved mechanical strength so that they retain their shape even in the presence of substantial temperature fluctuations. In addition, the method of the present invention enables production of iris diaphragms having a complicated structure as well as a plurality of iris diaphragms with minimum manufacturing expenses. To accomplish these tasks, the present invention is directed to a method of manufacturing an iris diaphragm having a thin metal layer with at least one opening therethrough and an integral reinforcing portion of the same metal which is set back from the edge of each of the openings in the thin metal layer with the method comprising the step of providing a surface, forming a first mask on said surface, said mask leaving a portion of the surface exposed with the exposed surface having a configuration of the thin metal layer of the iris diaphragm, applying a thin metal coating to the exposed surface, forming a second mask on the first mask and thin metal layer, said second mask having a configuration of the reinforcing portion and covering a portion of the thin metal layer adjacent the edge of each opening therein, depositing a thick metal layer of the same metal as the thin metal layer to form the reinforcing portion and then removing the iris diaphragm from the surface and the masks. Preferably, the surface on which the first mask is applied is a metal base film applied either directly on a surface of a substrate or onto a bonding layer which has been applied to the substrate. By applying the first mask on the metal base film, the various metal layers may be applied by electrodepositing techniques. Since high resolution can be obtained by a photographic printing operation, each of the masks is preferably formed by utilizing a photo-sensitive material which is exposed and developed to form a mask of the desired configuration. In addition, the use of photographic printing to form the mask enables forming iris diaphragms having complicated shapes. For example ones with extremely small openings or central collectors. The use of photographic techniques also enables forming a plurality of iris diaphragms on the same substrate. The method of the present invention enables the utilization of the same metal for both the thin film and the reinforcing portions so that the temperature fluctuations do not effect the shape of the thin film iris diaphragms. In addition, the process allows producing the thin film or layer to be extremely thin in the neighborhood of the openings so that the thin film iris diaphragm exhibits less tendency to become fouled during operation. Even with this thin metal film or layer of the diaphragm, the mechanical sensitivity is reduced due to the presence of the reinforcing portion so that handling of the thin iris diaphragm no longer presents the problems with regard to damage thereto.