DE1116015B - Method and device for cathodic spraying of a film onto a workpiece - Google Patents

Description

The invention relates to cathodic spraying of metals and dielectric films and relates to methods and devices for this purpose. In particular, the invention relates the improvement of a method in which the workpiece is placed in a vacuum chamber, which with two or more cathodes or electrodes are provided, which the substance or substances to be sprayed contain or consist of and by spraying a film of the substances or the substance onto the workpiece apply, with simultaneous relative rotational movement of the cathode or electrode and of the workpiece against each other.

Important applications of cathodic spray deposition, e.g. B. in the production of optical interference filters, require the deposition of multi-layer coatings of various substances.

In the known methods mentioned at the beginning, one works with devices in which the Workpiece rotates concentrically to the cathodes. This often results in error results due to Insufficient uniformity of the sprayed layers. Because of this unevenness that is known methods in many cases not applicable at all. If one then the other, likewise uses known method in which the workpiece on a solid base within a vacuum chamber and a stationary cathode made of the substance to be sprayed above the workpiece is suspended, the multilayer coating can also, but only by changing the cathode for each single layer can be generated. It is necessary to use the vacuum every time the cathode is changed and then bring it back to the desired value. This makes the work very complicated, time consuming and therefore costly.

The invention is based on the object of overcoming the disadvantages mentioned.

According to the invention, when using a method of the type mentioned at the outset, the object solved in that the cathode or electrode and the workpiece are arranged in planes which are longitudinal the axis of rotation at a certain distance from each other.

In order to apply a layer of films of different substances according to the method according to the invention form, it is necessary that there is at least one cathode or electrode under the cathodes and electrodes of the various substances is located.

The cathodes or electrodes are preferably in the form of segments, their included Method and device

for cathodic spraying of a film

on a workpiece

Applicant:

Edwards High Vacuum Limited,
Crawley, Sussex (UK)

Representative: Dipl.-Ing. H.Marsch, patent attorney,
Schwelm, Drosselstr. 31

Claimed priority:
Great Britain of October 28, 1955 (No. 30 944/55)

Leslie Arthur Holland, Crawley, Sussex

(Great Britain),
has been named as the inventor

Angles may be different within wide limits, e.g. B. 10 to 180 °, while the distance of the electrodes from one another, measured at an angle, must be chosen so that the uniform Distribution of the discharge is not disturbed. The desired distance can be required for each Number of cathodes or electrodes can be determined by a few simple experiments.

The invention also provides for the combination of cathodic spraying with vapor deposits, i.e. the formation of composite layers from sprayed-on films and films from vapor deposits, and for this purpose a heated melting pot with a substance to be evaporated can be used provided within the chamber and adjusted relative to the axis of rotation so that the required Film is deposited on the workpiece.

The drawing shows, for example, an embodiment of the invention, namely is

Fig. 1 is a schematic sectional elevation of a cathodic spray device according to the invention;

Fig. 2 is a plan view of the apparatus of Fig. 1;

Figure 3 is a schematic elevation of one known form of cathodic spray device in FIG

109 710/296

3 4

Section and shows in high magnification the change in size in order to achieve the greatest possible equilibrium

tion of the strength of a film made with it; ability of the coating to be achieved.

FIGS. 4 a and 4 b show two forms of the In this way it is possible to alternate

Device according to the invention usable Ka- layers by spraying from the cathodes and methods; 5 to be applied by vacuum evaporation.

FIGS. 5 and 6 show multilayer deposits. Up to now it has been customary in spray devices to use the

to rectify the high voltage produced by the device according to the invention, thus a

places are; Spray only from the desired electrode

7-10 are graphs that may and may not follow the characteristics of the device of films, the metal parts located according to the invention. It has now

Application under different conditions shows that to avoid positive ion bombardment

are; of earthed metal parts it is not necessary that

Fig. 11 is a schematic elevational view of another high voltage supplied to be rectified when the

Arrangement for combining the cathodic two sides of an alternating current source opposite Spraying with the vapor deposition, and 15 isolating the earth with an isolated electrode in each

Figure 12 is a plan view of Figure 11 along which the vacuum chambers are connected. These work

Line XII-XII. then alternately as cathodes and anodes. A

With the cathodic spray device as it is in such a system with a large flat workpiece 1 and 2, a cylindrical Va- has been difficult to realize because when the electrode is off vacuum chamber 1 at its bottom an outlet 2 for connecting two halves of approximately semicircular shape with a vacuum, not shown, stands due to the change in the strength of the along pump. Near the bottom of the chamber is a layer deposited at the level of the workbench flat, circular work table 3 arranged, the spray pattern is generated on the workpiece. if This pattern is no longer around a workpiece that rotates together with the axis of the chamber falling axis 4 can revolve, and it is localized for the 25, and the deposit is, along one too Drive the table any, not shown, the center of the electrode and the table konzen device intended. tric circle measured, a uniform. the

On the ceiling of the chamber and electrically from it distribution of the film along a radial line

two cathodes 5 and 6 are isolated from different ones.

Materials attached, which are made moderate in several layers, so that the electrode

a flat workpiece 7 is formed down on the work table or its angle is changed,

should be beaten. The cathodes have the The device according to the invention can

Shape of segments that work an angle Θ one with non-rectified tension by adding

close and are separated from each other by an angle Φ two electrode segments are used with

removed. The cathodes are connected to an alternating current high voltage via a changeover switch 8 33 on each side.

with the negative pole 10 of a direct current are high-bound.

Connected voltage source, the positive pole of which is at 9. Of course, such a system can also have three

work connected to the vacuum chamber 1 and the earth by connecting three electrodes

that is. agrees, taking a similar cost saving for

To prevent a discharge from which the rectifier is present.

Surface of the cathodes facing away from the workpiece

Towards the ceiling of the chamber the cathodes of pieces of film of the same thickness are required, occasionally

removed from the ceiling of the chamber by the amount that borrowed it is also necessary to make films

is less than the "cathode dark room" as its strength is determined by a certain law

in patent 610,559. 45 changes. For the device according to the invention

With the help of the changeover switch 8 it can alternately follow that, since it is possible by suitable excites one or the other cathode and the shaping of the cathodes or electrodes To achieve the material in the form of a film of approximately uniform layer, it is also possible Uniform strength on the must be on the revolving, by appropriate design of the Ka table lying workpiece can be sprayed. If the 50 methods or electrodes increase the thickness of the film along a Film has reached the desired thickness, the radial line will change. With the well-known Sprühandere Cathode connected to the high voltage devices (Fig. 3) with a cathode 13 in the form and another film made from the material of the second of a large disk and a fixed table is the Electrode formed on the pre-existing film, applied film 14 within a small medium so that a multilayer coating results. 55 surface evenly, but then decreases towards the edge

It is also shown schematically and with the cathode to off, as shown at 15. this is the

11 designated steam source is provided, the result of edge losses on sprayed material

is correct to deposit layers by evaporation by lateral diffusion, as shown at 16, and it

and that from a container or melting pot for that is not possible, the type of film distribution too

material to be vaporized and an electrical 60 change, d. H. to make it completely uniform,

There is heating, the leads through the wall or even the distribution of the film in a

go through the chamber and change to an interchangeable device with a cathode disk,

Lead power source 12. because the distribution of the deposit by the geometry

As a result of the shape and the distance between the cathodes of the system is fixed.

it is of one another, possible to bring the melting pot in the 65 case of devices according to the invention with geKammer in a position such that the molded cathodes or electrodes and a umVerhältnis, the vertical distance h of the melting current workbench is it possible to change the pot of the axis of rotation of the table, the required speed of the cathode surface, from the center

the cathode measured after its outer end, to change according to Fig. 4 a and 4 b. It then becomes a Deposition is generated, the thickness of which varies in the radial direction, roughly corresponding to the radial rate of change the cathode area, changes.

For certain optical purposes it is necessary to place a metallic one on a circular glass plate To produce a coating whose optical density increases gradually along a radius, but along of a circle concentric to the center of the plate is measured uniformly. This can be done by can be made that the film thickness is gradually increased towards the periphery of the plate by increasing the thickness of the film the cathode is shaped in the manner shown at 17 in FIG. 4 a. Conversely, by shaping the cathode, as shown at 18 in Fig. 4b, the film thickness decreases gradually to the circumference of the plate.

The apparatus described with reference to Figure 1 is of particular value to the earth electrodes substance to be vaporized in varying degrees the width or divergence of the steam jet limit. To produce an even precipitation, all three types of Steam sources provide a uniform coating within reasonable limits if the source is in the above specified manner is set up opposite the workbench, provided that in the case a source according to c) the steam jet is not within

ίο such a small fixed angle is limited that the Working level is not fully exposed to the emitted steam.

When a turntable and steam source are used in conjunction with V-electrodes, as shown in FIG. 11, both electrodes 41 and the associated grounded glow discharge screen 42 prevent steam from reaching the work table, and if so, as can be seen in FIG shows that the steam source is located at the point marked B , there is a

generation of a film of the same thickness on a 20 step edge on the vapor shadow present, the

Workpiece covering the whole rotating table, for example, and this would be essential when the workpiece or object to be coated is in the form of a single large sheet.

generated by the electrode and its screen. This graduated shadow consists of a penumbra and an umbra, and when the work table revolves, those in the penumbra become

Smaller items, e.g. B. small disks, 25 lying parts of the workpiece can be arranged in a ring on the rotating table all the time to the steam, and in this case the inward
directed ends of the cathodes by removal
a small part of the pointed end of the electrode
be shortened so that at the inner ends of the 30 in the thickness of the deposited film, which is from

be exposed to the beam while the part of the workpiece that faces away from the axis of rotation part of the rotation of the table will be shielded. This results in a difference

Electrodes a concave edge surface is provided, the axis of which coincides with the axis of rotation of the work table. The discs can, for. B. be sun glasses on which an absorbent iron oxide film is sprayed with the aid of the device described. In the manufacture of sun glasses, it is common to provide the glasses with a graduated layer that optionally absorbs light so that the stronger light is taken into account, the maximum value from the sky in the middle of the workpiece to about half of the maximum value at the edge of the workpiece changes. However, when the steam source is at A , the size of the penumbra is limited by the dimensions of the area in which the steam is emitted, and that area is much smaller than when the source is at B , and by careful placement the source at point A it is possible to have a very

or from the sun on the upper part of the glasses 40 to achieve a uniform film.

falls. Such graded layers can thereby be achieved. In certain cases, however, it is desirable to use the

will keep that the glasses are placed in a circle on the work table, which is coaxial with the table, and cathodes are used to put the steam source at point B or at a point between A and B. It is z. B. known that certain substances in their deposition from steam

have the shape shown in Fig. 4 a or 4 b. After 45, assume a granular structure when the steam-

After the iron oxide film is sprayed on, the glasses are then coated with a film by vapor deposition coated with magnesium fluoride or silicon monoxide to reduce their reflection.

As described in connection with FIG. 1, V-shaped cathodes can be used to spray-on To produce films in connection with layers that are deposited by evaporation. If there are no cathodes, atoms would be on the receiving surface under one hit a large angle of incidence, that is the angle of the beam with respect to the perpendicular to the acted upon Area. This effect arises from the fact that the obliquely striking atoms are on the outer surfaces previously deposited cores or on projections of the surfaces, which then in a increase faster than in a direction that is inclined in relation to the impinged plane than in a direction parallel to this.

the most favorable position of the steam source to achieve 55 len direction. If the steam source is in the position of the greatest possible uniformity of the thickness of the treatment A and h = r , the angle of incidence can vary between 0 and about 60 °, and at which

The vapor deposition corresponds approximately to a distance from the plane of rotation of the workpiece which is equal to the radius of the turntable, ie r - h, as indicated in FIG. 11. This most favorable location is dependent on a number of factors including the steam delivery characteristics of the steam source. There are three main types of steam emission sources known, namely a) a point source that emits the steam uniformly in all directions, b) an area that emits steam within a fixed angle 2π , and c) a directional source in which the On the sides of a melting pot with a higher value, the steam can form a film with a granular structure. The result may be that the precipitate that arises from the steam is hard and dense in the middle of the workpiece plane, and soft and porous at the edges. By setting up the steam source at position B or between A and B , the maximum value of the angle of incidence is reduced and the formation of granular parts is prevented or at least considerably reduced. On the other hand, if the steam source is set in this way, it is more difficult to remove the electrodes

and to choose the steam source opposite the workpiece table so that the thickness of the steam film in the The center is no larger than at the edges, as explained earlier. However, if the workpieces are small objects that are arranged in a ring on the workpiece carrier, the enlarged one The strength of the precipitation in the middle of the workpiece carrier is not so annoying, and you can Regard the thickness of the film on the individual small objects as roughly even.

The invention is generally used in the field of electronic metal deposition and dielectrics are used. Two particular examples of such an application are as follows:

a) Manufacture of multilayer interference filters

Interference filters with different spectral characteristics are continually due to the successive deposition of dielectrics of different optical thickness. For example, a mirror that has a high in a wavelength range Has reflectivity and a high transmittance in another wavelength range, be prepared in such a way that layers of materials with high and low Refractive index deposited, with each layer having the same optical thickness. It's difficult with that obtainable substances to produce particularly durable filters of this type by evaporation in a vacuum. the Invention now makes it possible to produce the most durable layers that can be found in both the evaporation process Vacuum as well as cathodic spraying can be used. Most fabrics with high refractive index, which can be evaporated in a vacuum, either lacks durability, or they are optically absorbent. But you can produce substances with a high refractive index by that a metal is sprayed on in an oxygen-containing atmosphere according to the known technique, so that an oxide deposit forms. This technique is known as "reactive spraying," but it is not suitable for the production of permanent oxide coatings with a low refractive index (-1.3), as these apparently of course not occurring. But it can be an extraordinarily long-lasting material of low value Refractive index (magnesium fluoride) can be produced as a film by evaporation in a vacuum.

Thus, in one embodiment of the invention, the cathode is made of titanium and the steam source is charged with magnesium fluoride. The device is connected to a pump system, which makes it possible to first carry out a gas discharge in an oxygen-containing atmosphere at intermediate pressures for spraying and then to reduce the pressure to a pressure suitable for evaporation in a vacuum (-0.1 μHg). This process can then be repeated several times, so that a multilayer coating is produced, as can be seen in FIG. 5, in which a glass base 19 is provided with a coating in which layers 20 of tritanium oxide with a high refractive index deposited by spraying Change layers 21 made of magnesium fluoride, which are deposited by evaporation in a vacuum and have a low refractive index. In the prior art, it would be necessary to spray the titanium oxide layer in a particular device and then move the workpiece to another device to deposit the magnesium fluoride by evaporation, etc., until the required number of alternating layers is applied so that arduous and very time-consuming work results.

Multi-layer filters made up of layers of sprayed titanium oxide and vaporized magnesium fluoride are made, are extraordinarily durable, and around titanium dioxide within a reasonable range To be able to spray out time, very high current densities must be used. A very permanent one Coating can now be made more easily by using the easier-to-spray bismuth oxide which is provided on a thin layer of magnesium fluoride produced by evaporation. Such coatings are expediently used in mirrors in optical systems that are used for unification or separation of colored images, e.g. B. for optical systems used in testing and transmitting devices be used in color television. Layers of vaporized magnesium fluoride and sprayed Bismuth oxide is also used on the surfaces of imitation gemstones to create a sparkle by interference and color.

b) Manufacture of conductive metal films

It is known that the electrical conductivity and optical transparency of thin films Certain metals are larger when the underlying glass layer is prior to the deposition of the metal film is covered with a film of certain oxides. It is also known that the metal deposit can be produced either by evaporation in a vacuum or by spraying. The metal oxide film however, usually has to be prepared by cathodic spraying if a reduction of the oxide should be avoided.

In the device according to the invention, two cathodes are used, namely one made of metal, by which the required oxide is formed, and the other from gold. (If the alternating current is higher Voltage, each "cathode" would contain two electrodes.) It is then possible on a glass base 22 (Fig. 6) first spray the metal oxide layer 23 and then the gold layer 24, so that without mechanical change of the cathode or lateral displacement of the workpiece carrier compared to the Cathode uniform deposits are obtained.

7 to 10, there are shown graphs obtained by experiments in carrying out the present invention, which show characteristics of the films deposited by spraying. Thus, the curves in Fig. 7 show the relationship between the electrical resistance of a nickel film in "ohms per square" (ordinate) and the radial distance in inches (abscissa) from the center of a circular plate on which the film is deposited. The term "ohms per square" means the resistance of a square part of the film when measured with electrodes that extend completely along two opposite sides of the square. Such a measurement does not depend on the dimensions of the square because when the size of the square is e.g. B. increases, although the distance between the electrodes also increases, but also the length of the electrodes in a corresponding manner

grows so that the measured actual resistance between the electrodes remains constant. The cathode used is a simple semicircular cathode, which is at a distance d above a circular work table that rotates at 30 revolutions per minute. The spraying takes place in argon at a voltage of 3 kV and a current of 0.5 Amp. For a period of 30 to 60 seconds. Curves 25, 26, 27, 28 and 29 show the characteristics of the nickel film obtained when the distance d = ³ U " (19.05 mm), 1", (25.4 mm), I ¹ A "(31, is In Fig. 75 mm), 1 ¹ It "(38.1 mm) and 1 ^s h" (44.45 mm). 8 curves are shown which show the optical transmission of nickel films under similar conditions as the reference are sprayed to FIG. 7 described, wherein the ordinate represents the Lichtdurchlaßprozente measured at λ = 5460 Ao. the curves 30,31 and 32 represent the transmission characteristic of the nickel film is that for a 30 seconds währendem spraying at distances d ³ A "(19.05 mm), 1" (25.4 mm) and IV4 "(31.75 mm) is obtained while the curve. 33 indicates the characteristics of the film which is obtained after one minute of spraying and at a distance of d = 1 ¹ It " (38.1 mm).

The curves of FIG. 9 were obtained under similar conditions as in FIG. 7, but a cathode in the form of a 90 ° segment of a circle was used. Curves 34, 35 and 36 were obtained with a spraying time of 30 seconds and distances d = ³ U " (19.05 mm), 1" (25.4 mm) and I ¹ A "(31.75 mm) while curve 37 was obtained with a one minute spray and a distance d of ¹¹ It " (38.1 mm).

Finally, the curves of FIG. 10 show the electrical resistance of a circular film of cadmium oxide deposited by reactive spraying for 2 minutes in an argon-oxygen mixture, the cathode being similar to that used to produce the curves in FIG ° sector, but the tip of which was rounded. The speed of rotation of the workbench is 30 revolutions per minute, the voltage 3 kV and the current 0.5 Amp. Curves 38, 39 and 40 were at distances d = ³ U " (19.05 mm), 1" (25.4 mm) or 1 W (38.1 mm).

It can be seen that it is seen with the help of a cathode Spray system according to the invention is possible either sprayed metal films or sprayed Metal oxides with or without interposed layers obtained by evaporation in vacuo to be applied one after the other to the surface of a workpiece, the sprayed films optionally be of approximately the same thickness or, in the case of suitably shaped cathodes, a certain alternating thickness can have. The geometrical shape of the cathode electrodes is suitable for the use of alternating current high voltage, as this saves the need for an expensive rectifier.

The invention is not limited to the particular methods and devices described, rather, z. B. instead of a rotating work table and fixed electrodes, a stationary table and electrodes rotating around the axis of the table are used.

Claims (13)

PATENT CLAIMS: 1. A method for the cathodic spraying of a film of one or more given substances onto a workpiece, the workpiece being brought into a vacuum chamber which is provided with two or more cathodes or electrodes which contain or consist of the substance or substances to be sprayed and by spraying a film of the substance or substances onto the workpiece with simultaneous relative rotational movement of the cathode or electrode and the workpiece against one another, characterized in that the cathode or electrode and the workpiece are arranged in planes which are along the axis the rotational movement are at a certain distance from each other. 2. The method according to claim 1, characterized in that the workpiece on a rotating Work table is and the cathodes or electrodes have segment shape and in one Angular distance from each other at a parallel to the table but at an axial distance of lying on it arranged level. 3. The method according to claim 2, characterized in that that the electrode system consists of two or more electrodes or two or more Sets of electrodes is made, each with a pole of an alternating current supply higher Voltage are connected. 4. The method according to claim 3, characterized in that further electrodes or sets of electrodes made of another substance are present that form a film of this other substance Spray on the workpiece by applying the high voltage from one of the electrodes or electrode sets is switched to the other electrodes or electrode sets. 5. The method according to any one of the preceding claims, characterized in that on the Workpiece another film is made by deposition of steam from a steam source which is set up inside the vacuum chamber. 6. Device for cathodic spraying of a film on one or more given substances a workpiece according to the method according to claim 1 to 5, wherein a vacuum chamber (1), a work table (3) in this serving to carry the workpiece, two or more cathodes or electrodes (5, 6), which consist of the substance or substances in question and in one perpendicular distance to the table (3) are provided, characterized in that that means are provided which allow a relative rotational movement of the cathode or electrode (5, 6) with respect to the work table (3) in planes that are spaced from one another along the axis of the relative rotational movement. 7. Apparatus according to claim 6, characterized in that the table (3) about an axis (4) revolves, which goes vertically through its center, the cathodes or electrodes (5, 6) firmly in one parallel to the table, but arranged along the table axis (4) at a distance from the table Lie flat and the individual cathodes or electrodes in different angular positions are arranged opposite the axis. 109 710/296 8. Apparatus according to claim ?, characterized in that the cathodes or electrodes Are designed segment-like, the included angle of the segments is chosen so that a from the cathode or electrode onto a workpiece lying on the table and rotating with it The film that is sprayed on is approximately uniform in thickness. 9. Apparatus according to claim 7, characterized in that that the individual cathodes or electrodes are shaped so that they change a film of over the surface of the workpiece Generate strength. 10. The method according to claim 7, 8 or 9, characterized in that the table has several Can accommodate workpieces arranged in a ring concentric to the axis of rotation of the table are. 11. Device according to one of claims 6 to 10, characterized in that within the Vacuum chamber a source of steam for lowering hit a film on one or more lying on the table and revolving with it Workpieces is arranged. 12. The apparatus according to claim 11, characterized in that the steam source consists of a heated melting pot for receiving the substance to be evaporated and opposite the Table and the cathodes or electrodes are arranged so that the precipitated from the vapor Film is roughly uniform in thickness. 13. Device according to one of claims 6 to 12, characterized in that the electrode system contains two or more electrodes or two or more sets of electrodes, which are connected to the relevant poles of an alternating current of high voltage can. Considered publications:
German patent specification No. 542404. For this purpose 2 sheets of drawings © 109 710/296 10.61