GB2234265A

GB2234265A - Electroarcing vapour deposition apparatus

Info

Publication number: GB2234265A
Application number: GB9015513A
Authority: GB
Inventors: Papken Ehiezar Hovsepyan; Daniel Nikolov Djumaliiski
Original assignee: TECHNOLOGITCHEN INSTUTUTE VAKK
Current assignee: TECHNOLOGITCHEN INSTUTUTE VAKK
Priority date: 1989-07-13
Filing date: 1990-07-13
Publication date: 1991-01-30
Also published as: JPH03260064A; GB9015513D0; BG49771A1; DE4022308A1

Abstract

An electroarcing vapour deposition apparatus for application of coatings of pure metals, alloys and compounds such as carbides, nitrides and carbonitrides on tools and components comprises a vaporisable cathode 5 of rectilinear shape surrounded by a magnetic circuit in a first portion of which are mounted permanent magnets 3 forming the N pole of the magnetic system and to which is mounted a second portion 4 forming the S pole of the magnetic system, which S pole extends a predetermined distance in front of a vaporisable cathode and extends around the lateral surface of the cathode at a pre-determined distance therefrom to form an electrostatic screen. The front of the vaporisable cathode is intersected by magnetic force lines at an angle and the maximum value of the horizontal component of the magnetic induction achieved at the front surface of the vaporisable cathode, B PARALLEL max, is equal to 1.5 x 10<-2>T, with the second portion of the magnetic circuit being insulated from the first portion by means of an insulator of high reluctance 6 and being insulated from wall means defining a vaporising chamber by means of a further insulator 10, and being electrically connected to such wall via an RC group 11 as a result of which the second portion of the magnetic circuit serves simultaneously as a magnetic pole and an electrostatic screen. <IMAGE>

Description

f ELECTROARCING VAPOUR DEPOSITION APPARATUS This invention relates to a

vapour deposition apparatus for deposition of vacuum coatings of completely non-magnetic metals, alloys and compounds of metallic character such as nitrides, carbides and carbonitrides on tools and components thereof.

United States Patent 4559125 discloses an electroarcing vapour deposition apparatus having a rectangular vaporisable cathode formed of an electrically conductive material with the front of the cathode being surrounded by a protective ring formed of a material of high magnetic permeability. The front of the cathode is further protected by a second ring or a coating of a compound having a low capacity for emission of secondary electrons. A suitable such coating material is titanium nitride or boron nitride.

A disadvantage of such a cathode arrangement is that its production requires the use of specific materials which are difficult to work, such as titanium nitride and boron nitride. Moreover, the reliability of the evaporator itself is low because, during the evaporation process, the protective ring becomes covered by cathodic material,'thereby hindering its performance.

According to the present invention there is provided an electroarcing vaporiser comprising a cathode surrounded by a magnetic circuit in a first portion of which are mounted permanent magnets from the N pole of the magnetic system and to which is mounted a second portion forming the S pole of the magnetic system, which S pole extends a pre-determined distance in front of a vaporisable cathode and extends around the lateral 1 t f surface of the cathode at a pre-determined distance therefrom, such that the front of. the vaporisable cathode is intersected by magnetic force lines at an angle and the maximum value of the horizontal component of the magnetic induction achieved at the front surface of the vaporisable cathode, B I max, is equal to 1.5 x 10-2T, with the second portion of the magnetic circuit being insulated from the first portion by means of an insulator of high reluctance and being insulated from wall means defining a vaporising chamber by means of a further insulator, being electrically connected to such wall via an RC group as a result of which the second portion of the magnetic circuit serves simultaneously as a magnetic pole and an electrostatic screen.

The vaporisable cathode, which is generally water cooled, preferably possess a rectilinear cross-section, normally being of rectangular shape. The insulator between the first portion and second portion of the magnetic circuit will preferably have a thickness of from 0Amm to 0.5mm. Preferably the second portion of the magnetic circuit is not spaced apart from the vaporisable cathode by more than lmm.

An electroarcing vapour deposition apparatus of such construction, including a rectangular vaporisable cathode, lie in the greater reliability in retaining the cathodic spot reliably at the front of the vaporisable cathode owing to the interaction of the magnetic and electric fields present. Moreover, the utilisation of the cathode in such manner enables evaporators of greater length than hitherto to be produced.

For a better understanding of the invention and to show how the same can be carried into effect, reference will now be made, by way of example only, to the accompanying drawings wherein:

1 Figure 1 shows a vertical cross section through an electroarcing vapour deposition apparatus according to the invention having a rectangular vaporisable cathode; and Figure 2 is a view of the device of Figure 1 taken in the direction of arrow A.

The vapour deposition apparatus of the invention comprises an electroarcing magnetron evaporator which incorporates a first portion 1 of a magnetic circuit which is of rectangular shape and which is electrically connected to the negative pole of adirect current (d.c.) source 2. In the lower part of the first portion 1 of the magnetic circuit are arranged permanent magnets 3 forming the N pole of the magnetic system of the evaporator.

The first portion 1 of the magnetic circuit passes into a second portion 4 which encloses a lateral nonactive surface of a vaporisable cathode 5 which is spaced apart from the surface of the second portion 4 by a distance C.

The first portion 1 and the second portion 4 of the magnetic circuit are formed of a material of high magnetic permeability and are electrically insulated from one another by means of a thin insulator therebetween which is from 0.2 to 0.3mm in thickness. The insulator is made of a strip material which does not exert any significant reluctance on portions 1 and 4 of the magnetic circuit.

The vaporisable cathode 5 is electrically connected with the first portion 1 of the magnetic circuit and is electrically insulated from the second portion 4 of the magnetic circuit by means of an insulator. The 1 X vaporisable cathode 5 is of rectangular form having a width B and length L and being-formed of the metal which is to be utilised for coating purposes.

The second portion 4 of the magnetic circuit forms the second or S pole of the magnetic system and extends forward to a distance h in front of the front surface of the cathode 5 at which vaporisation is to take place.

Figure 1 shows schematically the force lines of the magnetic field as they intersect the front surface ol the vaporisable cathode at a certain angle. Permanent magnets 3 are positioned between the rear surface of the vaporisable cathode 5 and the first portion 1 of the magnetic circuit and are so chosen that the maximum value of the horizontal component of the magnetic induction produced, B max, is equal to 1.5 x 10-2T.

The second portion 4 of the magnetic circuit is insulated by means of an insulator 10 from a cover 8 of a vacuum chamber defined by a wall 9 and is connected to the wall 9 electrically via an RC group 11 so that the wall 9 plays the part of an anode in the arrangement. On the cover 8 is mounted a sparking device 12 of the electromagnetic contact type.

Components 13 to be coated by vapour deposition are placed in the vacuum chamber to lie to the front of the vaporisable cathode 5. Various types, as required, of neutral gas such as argon or reactive gas, such as nitrogen, acetylene or methane, necessary for the vapour deposition process can be supplied into the vacuum chamber 9 via a metering valve 14.

Figure 2 serves to indicate the projection of the cathode spot upon the front surface of the vaporisable cathode 5.

1 An electroarcing magnetron vaporiser as shown in Figures 1 and 2 operates as follows:

The vacuum chamber defined by the wall 9 is evacuated to a pressure of the 2 x 10-3Pa and neutral gas (argon) and active gas (nitrogen, methane) are fed thereinto via a metering valve 14 until a pressure of the order of 5 x 10-2Pa is attained. Current supply to the sparking device 12 causes a short time contact to be created with the forward surface of the vaporisable cathode 5. On breaking the contact there are formed on the front of the cathode 5 cathodic spots characteristic for arc type discharge and which are sources of metal vapour produced from the material of the vaporisable cathode. A feature of cathodic spots is their continuous movement as the cathode travels, as a result of which they are retained upon the front or active surface of the cathode during operation of an arcing vapouriser deposition apparatus.

Within the apparatus, operation takes place as follows:

Insofar as a cathodic spot represents a region of metal plasma, it is distinguished by its own characteristic magnetic and electric field. This explains why upon movement thereof it is possible to exert an external magnetic field when knowing the principle for obtaining maximum magnetic induction of the external field.

The external magnetic field in the apparatus is obtained by means of the permanent magnets 3 and the first and second portions 1 and 4 respectively of the magnetic circuit, which enable a magnetic field to obtain whose configuration is analogous to the configuration of a known magnetron system. Owing to the fact that the second portion 4 of the magnetic circuit extends a distance h from the front surface-of the cathode 5, the magnetic force lines of the field intersect this surface at a certain angle with a maximum value of the horizontal component of the magnetic induction vector,, B 1 max equal to 1.5 x 10-2T. Since B 1 max is to be found at the forward surface of the vaporisable cathode 5, the cathodic spots are retained in position by the external magnetic field and are moved along the path 15 shown in

Figure 2. As a result of their travel along the indicated path over the entire width of the vaporisable cathode, the cathodic spots give rise to intensive vaporisation and to metallic vapours being obtained which are effective for the coating of the components 13. Such a configuration of the magnetic system might also be achieved for a circular cathode, but operation of a vaporiser with a rectangular cathode is much more effective and permits the coating of components of greater length.

Vapourisers embodying the invention and of different length may be produced by a suitable selection of the number of permanent magnets 3 according to the length of the vaporisable cathode 5 provided.

Many of the characteristic conditions under which arc deposition apparatus operates, i.e. the conditions of the initial ignition of the arcing discharge, oxide formation at the forward and lateral surfaces of the cathode, etc., may provoke the appearance of cathodic spots upon the lateral, non-active surface of the vaporisable cathode. This is an undesirable phenomenon since it is usually connected with the interruption of the intended working regime. With an arrangement embodying the invention, the beginning of arcing discharge at the lateral surface of the cathode is averted by virtue of the second portion 4 of the magnetic 1 1 circuit being disposed at a distance C say of lmm from the cathode. Through the medium of the RC group 11, the second portion 4 forms part of an electrostatic screen.

Hence,, when a cathodic spot is formed upon the lateral surface of the cathode 5. the second portion 4 of the cathodic circuit assumes the potential of the cathode 5, owing to the charging of the condenser of the RC group 11. The resistance R limits the current of the circuit, thereby preventing the further existence of the cathodic spot. The second portion 4 of the magnetic system also constitutes the magnetic S pole of the magnetic system and therefore acts upon the magnetic field of the cathodic spot which has appeared on the lateral surface of the evaporating cathode 5 to return it to the front surface of the cathode. Thus the second portion 4 of the magnetic circuit has two functions, namely providing the magnetic S pole and providing an electrostatic screen, thereby stabilising the motion of the cathodic spots upon the forward surface of the vaporisable cathode 5 by a combination of magnetic and electrostatic effects.

Since a neutral gas, for example, argon, is supplied to the vacuum chamber through the metering valve 14, the metal vapours obtained as a result of the vaporisation of the cathodic material condense upon the components 13 to be coated as pure metal or alloy. If a gas such as nitrogen, methane or a mixture of both is supplied to the vacuum chamber, then nitride, carbide or carbo-nitride coatings respectively are obtained. owing to the interaction of the reactive gas with the metal vapour produced by vaporisation of the cathode.

a

Claims

1. An electroarcing vapour deposition apparatus comprising a cathode surrounded by a magnetic circuit in a first portion of which are mounted permanent magnets forming the N pole of the magnetic system and to which is mounted a second portion forming the S pole of the magnetic system, which S pole extends a pre-determined distance in front of a vaporisable cathode and extends around the lateral surface of the cathode at a predetermined distance therefrom. such that the front of the vaporisable cathode is intersected by magnetic force lines at an angle and the maximum value of the horizontal component of the magnetic induction achieved at the front surface of the vaporisable cathode, B11 max, is equal to 1.5 x 10-2T, with the second portion of the magnetic circuit being insulated from the first portion by means of an insulator of high reluctance and being insulated from wall means defining a vaporising chamber by means of a further insulator, being electrically connected to such wall via an RC group as a result of which the second portion of the magnetic circuit serves simultaneously as a magnetic pole and an electrostatic screen.

2. An apparatus, as claimed in Claim 1, wherein the vaporisable cathode is of a rectilinear crosssection.

3. An apparatus, as claimed in Claim 1 or 2, wherein the vaporisable cathode is water cooled.

4. An apparatus, as claimed in any preceding claim, wherein the insulator insulating the second portion from the first portion has a thickness from 0.1 to 0.

5 mm.

1 -g- 5. An apparatus as claimed in any preceding claim, wherein the second portion is not more than lmm apart from the lateral surface of the vaporisable cathode.

6. An electroarcing vapour deposition apparatus, substantially as hereinbefore described with reference to, and as shown in, Figures 1 and 2 of the accompanying drawings.

Published 1991 at The Patent Office. State House. 656/71 High Holborn. LDndonWC I R47P Further copies rmy be obtained frarr ri ted by Multiplex techniques ltd, St Mary Cray. Kent Sales Branch. Unit 6, Nine Mile Point. CwTnfelinfacb. Cross Keys, Newport, NPI 7HZ. P n