US 2793609 A
Description (OCR text may contain errors)
May 28, 1957 TZU EN N ET AL 2,793,609
MEANS FOR THE DEPOSITION OF MATERIALS. BY EVAPORATION IN A VACUUM Filed Jan. 20, 1954 Inventor-r 7224/ 0 She/v 8 Jab/2 734/7 #9 982 1 Q Attorneyf United States Patent MEANS FOR THE DEPOSITION OF MATERIALS BY EVAPORATION IN A VACUUM Tzu En Shen, Ealing, London, and John Philip Huggett,
Forest Hill, London, England, assignors to British Dielectric Research Limited, London, England, a British company Application January 20, 1954, Serial No. 405,227
Claims priority, application Great Britain January 26, 1953 4 Claims. (Cl. 118-49) This invention relates to the deposition of material as a surface coating on articles by the aid of the production of vapour in a vacuum. It deals particularly with the form of the container in which the material is heated for the production of vapour and from which the vapour is directed towards the surface to be coated.
We have found that in working with the evaporation of certain materials, for instance the metals cadmium, zinc and magnesium, solid or liquid particles may be thrown off from the surface of the material in the container in the course of its melting and evaporation. These particles strike the surface to be coated and impair the regularity of the deposit thereon and may injure the surface itself. In accordance with the invention this defeet is overcome by inserting in the region between the material in the container and the entrance to an outlet passage a bafile which combines with the entrance to form a guide providing for the free flow of vapour be- ;tween the baffle and the entrance into the passage. The bafile cuts oflf the straight line paths between the surface .of the material in the container and the surface to be coated, thereby arresting solid or liquid particles thrown .off from the surface of the material. The outlet directs the vapour towards the surface to be coated.
This structural arrangement of bafile and outlet may be placed on or directly above the container and, in the former case, may be part of or be a separate attachment .to the container. It provides a passage which in the part .nearest the container presents by means of the bafiie an iobstructing surface on which any solid or liquid particles shot off from the metal will strike. It also provides guiding surfaces which lead the vapour past the obstruction and which beyond that obstruction direct it towards the surface to be coated.
The solid or liquid particles which strike the arresting cess localised heating may be applied to the surface or surfaces.
The invention is further described hereinafter with reference by way of example to the accompanying illustrations wherein:
Figure 1 is a diagrammatic drawing of a crucible provided with the essential features of the improved device;
Figure 2 is a view in section of a long narrow crucible showing the preferred arrangement, and
Figure 3 is a view upon an increased scale of part of the arrangement shown in Figure 2.
Referring to the arrangement shown in Figure 1 a crucible 1 contains a body of molten metal 2 and is surrounded by a heater coil 3 which maintains the liquid at the required temperature. The crucible cover 4 comprises portions 5 extending inwardly from the side walls and upwards to the entrance to a central vertical passage 6. A horizontal baflle plate 7 is supported above the surface of the metal 2 and below the entrance to the passage 6. This bafile plate completely interrupts the pasice sage of vapour in direct lines, represented by arrows 8, from the liquid surface to the passage.- Any solid or liquid particles leaving the metal surface will strike the baiiie or the portions 5 of the cover extending beyond the edges of the baffle. Vapour from the liquid will be deflected around the bafile along the paths 9 extending between the edges of the baffle and the'portions 5 of the cover to en ter the vertical passage and be discharged at the upper end as indicated by the arrow 10.- The surface to be coated will be positioned opposite the exit from the ver tical passage 6 and the complete device will be maintained in a vacuum in known manner. Any solid or liquid particles striking the underside of the bathe plate 7 or of the portions 5' of the cover will be retained there or thrown back or evaporated. In any event they will not pass outwards from the vertical passage 6.
In the preferred form of construction shown in Figures 2 and 3 the crucible 11 is a long narrow member arranged to discharge upward to cover a strip of the surface of a body which is placed above it and may be in motion across it. The crucible is provided with an external heating coil 18. Resting upon the upper part of the crucible is a titting 12 having an upward extension 13 through which extends the vertical passage 16. The fitting 12 has an external horizontal flange 14 by which it rests on the upper edge of the crucible 11 throughout the periphery thereof. Below this flange a downward extension 15 in line with the upper extension 13 fits inside the walls of the crucible. Below the lower end of the passage 16 which runs through the two extensions 13 and 15 there is arranged a bar 17 which is of about the same width or slightly wider than the width of the passage and has a length equal to the other transverse dimension of the passage. The walls of the passage at the lower end diverge on each side of this bar to meet the inside of the crucible. The bar 17 forms a barrier to the straight line movement of solid or liquid particles arising from the material in the crucible. The lateral widening of the passage at the lower end provides spaces at each side between the bar 17 and the mouth of the passage through which the vapour can stream. The bar 17 thus forms a complete bafile to solid particles projected upward from the surface of the material in the crucible but it does not unduly obstruct the flow of the vapour. A second heater coil 19 enclosing the upper extension 13 about the passage 16 provides localised heating to prevent condensation of the vapour on the passage walls.
In the arrangements which have been described by way of example the discharge is effected through straight vertical passages in alignment with the crucible, the escape of solid particles being prevented by the introduction of a separate bafile at the entrance to the passage.
What we claim as our invention is:
1. Apparatus for the deposition of vaporised material upon a surface in a vacuum, comprising a container for the material to be vaporised, an outlet passage for directing the vapour from the container to the surface to be coated, the passage having an elongated cross-section, and a cylindrical rod at the entrance to the passage having a diameter at least equal to the smallest transverse dimension of the passage and extending completely across the longest transverse dimension of the passage, the rod completely interrupting all straight line paths through the passage from the material in the container and providing paths for the flow of vapour between the rod and the entrance to the passage.
2. Apparatus for the deposition of vaporized material upon a surface in a vacuum, comprising a container for the material to be vaporized, an outlet passage for the vapour from the container, said outlet passage having a transverse sectional area less than that of the container, an entrance to said passage with walls converging from Patented May 28, 1957 the inner walls of the container to the passage, and a baflle positioned in the said entrance to interrupt all straight line paths through the passage from the material in the container and to provide paths for the flow of vapour between the baflie and the walls of the entrance.
3. Apparatus for the deposition of vaporized material upon a surface in a vacuum, comprising a container for the material to be vaporized, an outlet passage for directing the vapour from thecoutainer to the surface to be coated, the passage having a smaller cross-section than the container, an entrance to the passage converging from the container walls to the passage walls, and Within the entrance 2. bafile plate disposed transversely to the axis of the passage to interrupt all straight line paths through the 4 passage from the material in the container and to provide paths for the flow of vapour between the baffle plate and the Walls of the entrance.
4. Apparatus as claimed in claim 2, for the deposition of vaporised material upon a surface in a vacuum, in which there is provided" means for heating the walls of the passage to prevent the condensation of vapour thereon.
References Cited in the file of this patent UNITED STATES PATENTS 2,100,045 Alexander Nov. 23, 1937 2,416,211 Osterberg et a1. Feb. 18, 1947 2,439,983 Morgan et al. Apr. 20, 1948