US 3607368 A
A device for vapor deposition containing as a vaporizer element, a wick formed of a lace-like body of graphite or carbides.
Description (OCR text may contain errors)
United States Patent  Inventor Johannes Jacobus Asuerus Ploos Van  Field of Search 1 17/106,
Amstel 107,46 CC,46 CB,46 CA; l18/48,49,49.1,49.5; Emmasingel, Eindhoven, Netherlands 2 19/273, 274, 275 [211 App]. No. 765,826  Filed Oct. 8, 1968 Rdel'ellces Clled  Patented Sept. 21, 1971 UNITED STATES PATENTS [7 1 Assignee Phillips orporation 2,665,225 1 1954 Godley 117/107 New 2,665,227 1/1954 Clough 6t 61.... 117/107 1 Pflomy 0t.l0, 1967 3,350,219 10/1967 Shaler 118/49.1 (x 1  Netherlands  6713713 Primary Exammer-Alfred L. Leavltt Assistant Examiner-William E. Ball W Attorney-Frank R. Trifari  METHOD OF COATING SUBSTRATES BY VAPOR DEPOSITION 6 Chums 3 Drawing Figs ABSTRACT: A method of coating substrates by vapor deposi-  U.S.Cl 117/106, tion. The material to be deposited is taken up in a lacelike 117/107, 219/274, 118/491, 118/495 body built up from graphite yarn heated to the vaporization [51 Int. Cl C23c13/12 temperature by the passage of electrical current :1 I I I J 9 Z f;
PATENIED saw a SHEET 1 0F 2 FIG.2
INVENTOR. JOHANNES J.A.PLOOS VAN AMSTEL METHOD OF COATING SUBSTRATES BY VAPOR DEPOSITION The invention relates to the coating of substrates by vapor deposition.
As is known, this is generally carried out in an atmosphere which is inert relative to the substance to be deposited in which, in order to check impediment of the vapor molecules on their way to the substrate, the gas pressure is chosen to be low and the method is usually carried out in a vacuum.
The vaporization of the substance to be deposited is usually effected by means of a vaporizer element which is heated by the passage of current.
According to some of the known methods, the substance is caused to vaporize on the surface of a heating element. A drawback hereof is that the substance can be present only in restricted quantities and hence the vapor deposition of thick layers or the continuous vapor deposition is not possible.
In other known methods this drawback is avoided by placing a large quantity of the substance to be vaporized directly or in a container inside a heating element which has the form of a helically wound filamentary body. However, a shadow effect of the heating body always occurs which hampers the obtaining of an even coating.
The use of a vaporizing element is also known already to which the substance to be vapor-deposited is applied continuously from a container during the vaporization process (American Pat. Spec. 2,665,227). In this method, an approximately horizontally arranged vaporizer element in the form of a rod is used which is provided with a channellike groove extending in the longitudinal direction in which the substance is allowed to flow from the container. This element is composed of a material which is readily wetted by the substance to be vapor-deposited so that it is coated with the substance, all over its surface. For many applications graphite was found to be suitable, if desired, converted superficially into a high-melting-point metal carbide.
A drawback of such vaporizer elements is that during use they have to be arranged approximately horizontally. In addition, the layer thickness of the substance to be vapor deposited in the groove is different from that on the further surface of the element. The result of this is a difference in vaporization at the area of the groove so that substrates arranged around the element are coated in different thicknesses dependent upon their position.
The invention is based on the recognition of the fact that the above-mentioned drawbacks can be avoided by using an electrically conducting vaporizer element which is built up from a porous material.
According to the invention, a vaporizer element is used for this purpose, which is constructed from a lacelike body of graphite yarn.
Such a material is commercially available and may be obtained, for example, by carbonizing rayon yarns, whether or not woven, knitted or twined, at temperatures above approximately 2000" C. for example an Article by MoLindsey in Design Engineering of 6 Apr. 1965 titled: Developments in Carbon and graphite Textiles f.e. Materials which advantageously can be used are told by Morganite Research and Development Ltd. UK. as graphite card grade 6301 G and 6303 G.
The invention relates to a method of coating substrates by vapor-deposition from the surface of a vaporizer element built up from graphite and heated by the passage of current, characterized in that the substance to be vapor-deposited is taken up in a vaporizer element consisting of a lace-body which is built up from graphite yarn and is then heated at a temperature at which said substance vaporizes.
In this manner a very even coating of the whole vaporizer surface can be obtained, which is a condition for obtaining an even deposition on substrates arranged around the vaporizer. Any shadow effect of the material of which the element consists can be excluded by the fineness of the pores.
In connection herewith a vaporizer element is preferably used which is built up from yarns, the elementary strands of which have a thickness of under 20 microns.
The substance to be vaporized may be incorporated in the vaporizer element in comparatively large quantities. If very thick layers have to be vapor-deposited, or large numbers of substrates have to be coated in a continuous process however, it is of advantage to add a further quantity of the substance to the element during the vaporization process.
According to a useful embodiment of the invention a porous lacelike body is used which comprises a coaxial cavity. As a result of this it is possible to incorporate larger quantities of the substance to be vapor-deposited in the vaporizer.
Some substances, for example, copper, germanium and tim, do not react with the graphite material of the vaporizer. If such a substance is made to melt in the vaporizer, it penetrates through the pores in the wall to the outer surface on which an even layer is then formed. In this case it is recommendable to use a hollow vaporizer element which can easily be filled with the material to be vaporized.
With substances, for example, chromium, which poorly wet graphite, it is of advantage, in order to obtain an even vaporization, to convert the graphite entirely or superficially into metal carbide. As is known, many of these carbides can withstand the influence of very high temperatures and are more easily wetted by various substances. For this purpose are to be considered the carbides of metals of the promps IVa, Va and Vla of the periodic system of elements, particularly zirconium carbide, and in addition aluminum carbide.
However, cases may also present themselves in which the graphite and the substance to be vapor-deposited react with each other while forming carbides. This is the case notably in the above-mentioned carbide-forming metals. In itself this reaction is by no means objectionable because the carbide vaporizes at higher temperatures than the metals from which they are formed. If the carbides decompose at the vaporization temperature of the material, the vaporization may be continued after no free metal is present any longer in the vaporizer. The metal bound in carbide is then also vaporized and a graphite skeleton remains. This is significantly the case, for example with aluminum carbide.
Of course it is possible with these metals which do react with graphite, to convert the graphite body previously entirely or superficially into a carbide of a metal other than the metal which is to be vaporized. For example, the graphite may be converted into zirconium carbide, as a result of which an element of a very large strength is obtained, which can be used repeatedly for vapor-deposition of metals, for example, cobalt and chromium.
The supply to the vaporizer of the substance to be vapordeposited may be effected in a liquid and in a solid state, both prior to and during the vaporization.
According to a further aspect of the invention a device for coating substrates by vapor-deposition comprises a container in which the substance to be vaporized can be molten and from which the molten substance flows into a vaporizer element consisting of a lacelike body which is built up from yarns of graphite and/or a carbide. For this purpose the action of gravity and/or capillary action occuring may be used.
In some cases, for example, when silicon or germanium are supplied to an element which is'converted into silicon carbide, such a strong capillary action occurs that, if such an element is placed in the molten material with one extremity this will be sucked up into it.
For the filling with metal in the solid-state it is of course recommendable to use a vaporizer element which is provided with a coaxial cavity. The metal in the form of powder, grains or wire, can easily be provided in said cavity. For the continuous supply during the vaporization process, metal in the form of a wire is most suitable. This is the case also when replenishing the molten substance which is supplied to the vaporizer element through a container.
In order that the invention may be readily carried into effect, a few examples thereof will now be described in greater detail, with reference to the accompanying drawing in which FIG. 1 shows in perspective a hollow graphite lace and FIG. 2 I
shows a section of a part of a device for vapor-coating according to the invention. FIG. 3 shows a section of a device for vapor-coating according to the invention.
Two copper wires 2, thickness 0.5 mm., length 320 mm., are slid into a hollow graphite lace 1, length 400 mm., outside diameter approximately 2 mm., inside diameter approximately 1 mm., as shown on an exaggerated scale in FIG. 1 of the drawing, so that on either side approximately 40 mm. of the lace is free from metal.
This element is arranged horizontally in a vacuum and heated by a current of 13a. With an initial voltage of 20v. For maintaining this current which is necessary for maintaining a vaporization temperature of approximately 2000 C., the voltage must gradually be increased to approximately 90v.
The copper wires melt. The molten copper does not wet the graphite element but an even vaporization of copper around the element is obtained.
In this manner copper mirrors with an even thickness of l p. are deposited in approximately 20 min. on glass substrates which are arranged at a distance of 80 mm. from the element. The graphite lace was a material sold by Morganite Research and Development Ltd. as graphitecord grade 6301 G according to the manufacturer this is a plaited cord about 2 mm. diameter. The electrical resistance is 0.45-0.69Qper cm. at room temperature, falling to about half this value at l50018000E- C. The weight of the cord' is approximately 1.3
I Example 2 A graphite lace as described in example 1 is filled with 1.7 gms. of germanium grains over a length of 300 mm.
By heating in a vacuum, the germanium which does not wet the graphite lace is caused to melt and vaporize in a vacuum.
This is carried out in a horizontal setup with a current of 12a. at a voltage increasing from 50 to 13 v. as a result of which a vaporization temperature of approximately 1700 C. is reached.
Even germanium mirrors, thickness 2.2. microns, are obtained in this manner in approximately minutes on glass substrates which are arranged at a distance of 80 mm. In quite an analogous manner 3 has also been processed to mirrors.
Example 3 A densely braided graphite lace 3, length 444 mm., as shown in FIG. 2, is threaded through an aperture 4 in the bottom of a crucible 5 and secured there by means of a knot 6. Aluminum 7 is provided in the crucible 5 and is kept in the molten state at approximately 800 C. As shown in FIG. 3 the crucible 5 is positioned in an oven 8. The lace 3 is brought under a weak tensile stress by the leaf springs 14 to which the lace 3 is connected through member 11 having an aperture 15 in which lace 3 is secured by means of a knot 12 and the means 13 for holding member 11. Substrate holders 10 are arranged around the lace 3. Electrical connections are made with spring 9 which is arranged between the crucible 5 and the inner wall of the electric oven 8 and the holding means 13. The device as shown in FIG. 3 is positioned in a vacuum chamber (not shown). The chamber is evacuated. The mass 7 consisting of aluminum is heated to a temperature of 800 C. by means of the oven 8. The lace 3 is heated to approximately 2000 C. with a current of 27a. with an initial voltage difference of 80v. between the springs 9 and the holding member B. Alu'mihum is sucked up from the crucible and reacts with the graphite while forming aluminum carbide. At the same time free aluminum is taken up in the element. With a current passage of 100a. and a voltage of 8v. a temperature of approximately 1200 C. is generated. On substrates which are arranged at a distance of 40 mm., aluminum mirrors, thickness 20 ,u., are vapor-deposited in this manner in 20 minutes.
During the vaporization process, the aluminum in the element is replenished by a capillary sucking from the crucible. By supplying aluminum wire to the Cl'UCllJ e the process can be Example 4 A rod of titanium, length 250 mm., thickness 2 mm., is slid into a hollow graphite lace as described in example 1. Heating is carried out in a vacuum by the passage of current.
At 60a. reaction occurs while forming titanium carbide, while a part of the titanium remains in the tubular element in a free state.
With a current of 60a. at 27 volt, the free titanium is deposited on glass substrates which are arranged at a distance of mm. Titanium mirrors, thickness 1 u, are then obtained in approximately 10 minutes.
Example 5 In a manner quite analogous to that described in example 4 a graphite lace is converted into a zirconium carbide element, the quantity of zirconium being chosen to be so that only a small excess of this metal remains.
The resulting hollow zirconium carbide element is filled with chromium in powder form and then heated in a vacuum to approximately 1200 C. by a current of 50a. with 20v.
Chromium mirrors, thickness approximately 1 [.L, are then obtained in 25 minutes on substrates which are arranged at a distance of 70 mm.
In the same manner mirrors of cobalt are realized.
What I claim is:
l. A method of coating substrates by vapor-deposition from the surface of a vaporizer element built up from graphite and heated by the passage of current, wherein the substance to be vapor-deposited is taken up in a vaporizer element consisting of a lacelike body which is built up from graphite yarn and is then heated at a temperature at which the said substance vaporizes.
2. A method as claimed in claim 1, wherein the elementary strands of the graphite yarn have a thickness of under 20 u.
3. A method as claimed in claim 1, characterized in that the vaporization process is carried out by means of a porous lacelike vaporizer element which is provided with a coaxial cavity.
4. A method as claimed in claim 1, characterized in that the substance to be vapor-deposited is replenished during vaporization.
5. A method as claimed in claim 1, characterized in that the graphite is converted into a metal carbide at least superficially. I
6. A method as claimed in claim 5, characterized in that the graphite is converted into zirconium carbide.