Patent Number: 039881539
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT The principles of the present invention are particularly useful in producing an iris diaphragm 1 illustrated in FIGS. 1 and 2. The iris diaphragm 1 is a one piece component and consists of a thin metal layer or film 2 and a reinforcing portion or consolidating film 3 which are both formed of the same metal and are integral with each other at a boundary surface 4 which is illustrated by chain lines. At the center of the thin metal layer 2 is a circular iris aperture 5. The reinforcing portion or consolidating film 3 is set back from the edge of the opening or aperture 5 to form a concentric enlarged passageway or aperture 6. As illustrated, the edge of the opening 5 is extremely smooth and has no ragged formations, and therefore fouling of a beam of particles passing through the aperture 5 is minimized. To manufacture the iris diaphragm 1, the preferred method includes providing a glass substrate 7 having an upper surface on which a bonding layer 8 of nickel chrome (CrNi) is applied in the thickness of 0.01 .mu.m. On the bonding layer 8 a metal base film 9, such as copper, of a thickness of about 0.1 .mu.m is applied either by vaporization or an atomizing operation. The bonding layer or film 8 was selected from a material which is a metal or metal alloy which will improve adhesion between the glass substrate 7 and the metal base film 9. With the proper selection of the bonding layer or film 8, it is possible to employ metals for a base film 9 which metal would readily peel from the substrate 7. However, for certain metals used as the base metal film, the presence of a bonding layer 8 is not necessary. After applying the metal base film 9, a first mask 10 is applied to masked portions of the base metal film 9 and leave unexposed portions corresponding to the thin metal layer 2 of the iris diaphragm 1. Preferably, the first mask 10 is provided by a photographic process comprising covering the base film 9 with a coating of a photographic varnish which is resistant to electrodeposition. This coating of photographic varnish is applied in a thickness of approximately 2 .mu.m and is then selectively exposed by illumination and developed to provide the mask with the negative image of the thin metal layer 2 and to expose the base film 9 with a configuration of the thin metal layer 2. As illustrated, the mask 10 has a portion 10' to define the opening 5 and a concentric outer portion. As illustrated in FIG. 4, after producing the first mask 10, the exposed areas of a metal base film 9 which are left exposed or are not covered by the first mask 10 receive a thin metal layer 2 which is built up to a thickness of approximately 1.5 .mu.m. Preferably, the thin metal layer 2 is formed by electro-deposition of gold on the base film 9. The portion 10' of the mask causes the formation of aperture 5 in the layer 2. Subsequent to forming the thin metal layer 2, a second mask 11 is applied on portions of the first mask 10 and portions of the thin metal layer 2. As illustrated, the second mask 11 is a negative image of the reinforcing or consolidating layer 3 and has a portion 11' which covers a portion 10' which forms the opening or aperture 5 in the base metal layer 5 and also covers a circular portion of the thin metal layer 2 which is adjacent to the edge of the opening 5. Preferably, the second mask 11 has a thickness of about 5 to 10 .mu.m and is formed by applying a coating of photographic or photo-sensitive varnish, exposing by illuminating select areas of the photographic varnish and developing to leave the particular mask structure 11 illustrated in FIG. 5. Subsequent to forming the mask 11, a second thick layer of metal 3 is deposited on the thin layer 2 to form the reinforcing portion or consolidating layer 3. The thick layer is formed of the same metal, such as by electro-depositing of gold, and has a thickness of from 3 to 10 .mu.m. As illustrated, the outer portion of the mask 11 coincides and is aligned with the outer portion of the mask 10 so that the thin layer 2 and the reinforcing portion 3 have the same outer circumference. The mask 11 will delimit the outer edge of the reinforcing portion 3. If the outer annular zone of the mask 11 were omitted, then the layer 3 forming the reinforcing portion will overlap and extend passed the edge of the layer 2. However, this will not interfere with the use of the iris diaphragm 1 in a corpuscular beam apparatus. As illustrated in FIG. 6, the masks 10 and 11 have been removed and the iris diaphragm 1 is still disposed on the base film 9. To remove the iris diaphragm from the substrate 7 and the metal layers 8 and 9, the metal base film 9 is selectively etched away. In the above description, the iris diaphragm was formed of gold and it has been found advantageous to use copper for the metal base film 9 and nickel chrome as a bonding layer 8 on the glass substrate 7. Other materials can be used to form the iris diaphragm. For example, to form the iris diaphragm of nickel, silver should be used as a metal base film 9. If copper is to be used for the iris diaphragm, then the base film is not required and the various copper layers to form the thin metal layer 2 and the reinforcing portion 3 can be applied by other depositing procedures such as vaporizing or atomizing operations. While the above described method as illustrated in FIGS. 3-6 was directed to a method for producing a single iris diaphragm on the glass substrate 7, it is possible to simultaneously manufacture a very large number of iris diaphragms, for example between 500 and 2000 on a single glass substrate. This is accomplished by sequentially forming a plurality of the photographic masks in the coating of photo-sensitive material during the steps of forming the first mask. During the step of forming the second mask, a second mask is formed for each one of the first masks and aligned therewith. The method of the present invention enables production of an iris diaphragm which on one hand has a metal film or layer that is as thin as possible and yet on the other hand has improved mechanical stability and strength so that it is not subject to damage during handling. Since the thick layer forming the reinforcing portion 3 is of the same material as the thin layer 2, the iris diaphragm 1 is less susceptible to distorsion and loss of shape when subjected to substantial temperature fluctuations which may occur in a corpuscular beam apparatus. It is also noted that since the thin metal layer forming the thin film or layer 2 of the diaphragm is not handled prior to the application of the reinforcing portion, the thickness of this layer can be extremely thin without risking damage due to subsequent handling. Although various minor modifications may be suggested by those versed in the art, it should be understood that I wish to employ within the scope of the patent granted hereon, all such modifications as reasonably and properly come within the scope of my contribution to the art.