US3475315A - Cathodic sputtering apparatus wherein the sputtering plasma is generated by a plurality of electrically isolated circuits - Google Patents

Description

Oct. 28. I969 R. M. MOSESON 3,475,315

CATHODIC SPUTTERING APPARATUS WHEREIN THE SIUTTERING PLASMA IS GENERATED BY A PLURALITY OF ELECTRICALLY ISOLATED CIRCUITS 3 Sheets-Sheet 1 Filed April 11 1966 0 M v i A 065? M M0552 1/ am a Get. 28, 1969 R. M. MOSESON 3,475,315

CATHODIC SPUTTERING APPARATUS WHEREIN THE SPUTTERING PLASMA IS GENERATED BY A PLURALITY OF ELECTRICALLY ISOLATED CIRCUITS Filed April 11, 1966 3 Sheets-Sheet a fffi mm 4,,

{Kw W 5 I I f7 INVENTOR. F0550 M M03550 MiZa/M Oct. 28, 1969 R. M. MOSESON 3,475,315

CATHODIC SPUTTERING APPARATUS WHEREIN THE SPUTTERING PLASMA I S GENERATED BY A PLURALITY OF ELECTRICALLY ISOLATED CIRCUITS Filed April 11, 1966 3 Sheets-Sheet 5 623 1% 623323 14 dfli if 14 ,4! 1 7 f! a I 7/ 3 42 I INVENTOR. 1 7 7% Page fi/f 4mm ABSTRACT OF THE DISCLOSURE Two or more independent cathode-anode pairs are disposed in an evacuable enclosure for generating an ion plasma or discharge from each pair which coact with plasmas generated by other pairs to form a substantially continuous, interacting plasma over a target which can be used for its sputtering, heating or scrubbing. Each cathode-anode pair has a power supply which is independent from the power supplies employed with the other cathode-anode pairs. The cathode-anode pairs may be arranged to effect a plurality of opposed or unopposed discharges which are either parallel, crossed, or coincident with respect to each other.

The evacuable enclosure may be in the form of a sputtering module which can be connected with other modules to form a sputtering system. An unobstructed axis of the module provides for the transport of items to be sputtered or substrates to be deposited. A magnetic field may be impressed about a planar target material. The magnetic field has a uniform intensity in planes parallel to the surface of the target to provide control of the ion discharge and effect a very uniform rate of sputtering.

This invention relates to apparatus for sputtering, and more particularly, to sputtering apparatus suitable in the typical production situation.

In recent years the technique of sputtering either to clean the sputtered surface or to coat a substrate with the sputtered material has found ever increasing application in industry. A major factor for this is that neither the choice of the substance to be sputtered nor the choice of the substrate to be coated is in any way limited as to type of material. As a result, insulators such as glass, as well as metals, can be sputtered or coated.

My application Ser. No. 390,800, filed Aug. 20, 1964 now US. Patent 3,305,473 and entitled Sputtering discloses low voltage sputtering apparatus in whicha discharge or plasma of positive ions with a vertical axis is established between an anode and a cathode in a partially evacuated bell jar. A target, i.e., a material to be sputtered, is located to the side of the ion discharge and is biased negatively with respect to the anode. A substrate to be coated is located on the other side of the ion discharge, diametrically opposite the target, such that the surface to be coated faces the target. Ions are attracted to the target causing the target material to be sputtered upon the substrate. To control the uniformity of the ion discharge and thereby the uniformity of sputtering the target and of coating the substrate, the ion discharge is subjected to a magnetic field generated by an ordinary coil, i.e., a coil with a circular cross section.

Although good results have been achieved with the sputtering apparatus housed in a bell jar, as disclosed in my above-mentioned application, this bell jar arrangement is not particularly well-suited to a typical production situation, in which a number of sputtering stations 3,475,315 Patented Oct. 28, 1969 ice are usually employed to clean and to coat a substrate and the operations are often automated. For one thing, the obtainable width, uniformity, and density of the ion discharge are not suflicient for the demands of many production situations. For another thing, the apparatus is somewhat bulky and occupies more space than some production situations will allow. Moreover, the practical aspect that the equipment be flexible enough to use in different series of operations, to permit dismantlement and reorganization of the components to conform to changes in the operations, is implicit in well-designed production equipment.

According to one aspect of the invention plural, independent ion discharges are established with respect to each other in sputtering apparatus so that they intermix somewhat to form a conglomerate mass of ions for sputtering a target. Depending upon the arrangement of anode-cathode pairs producing the ion discharges, it is possible to increase the width and density and improve the uniformity of the resulting ion mass. If the ion discharges have substantially parallel axes and are unopposed and uncrossed, a resulting ion mass with a width about twice as large as an individual ion discharge is obtainable. With opposed ion discharges, a substantial improvement of the resulting ion mass over the uniformity of an individual ion discharge can be achieved and, with crossed ion discharges, a resulting ion mass with an ion density about twice as large as an individual ion discharge is obtainable. In all cases it is necessary to realize the enumerated advantages that the ion discharges be independent from one another in the sense that they are produced by mutually electrically isolated circuits.

According to another aspect of the invention, a modular concept is implemented in sputtering apparatus by utilizing sputtering chambers with longitudinal, preferably horizontal axes. The sputtering chambers are interconnectable one with another to form an airtight sputtering system, in which the horizontal axes are in line. The sputtering chambers each have a main section with fittings on its ends to enable interconnection to other sputtering chambers or components. As a result, they can be connected in tandem to carry out any desired series of sputtering operations and later dismantled and reconnected to carry out a different series of operations. Thepassage along the longitudinal axes of the sputtering chambers is maintained unblocked by orienting the surface of the target and/or substrate substantially parallel to the longitudinal axes. The unblocked, inline nature of the sputtering chambers allows easy transport of targets and/or substrates from one station to another along the longitudinal axes by means of a conveyor belt or the like in an automated sputtering system. The sputtering chambers are preferably T-shaped, in which case a branch section, to which a vacuum pump can be connected, is joined to the main section approximately midway between its ends. Thus a T-shaped chamber permits convenient placement of the pump close to the site of the sputtering operation.

An anode-cathode system for establishing an ion mass to sputter the target comprises one or more anode-cathode pairs placed in the inside of the main section of each sputtering chamber. Each anode and its cathode are situated at diametrically opposite sides of the sputtering chamber such that the axis of the ion discharge they produce is transverse to the longitudinal axis of the main section.

It is particularly advantageous, although not necessary, to employ the practice of plural, independent ion discharges, as described above, in the sputtering chamber with a longitudinal axis, as described above. In this case, anode-cathode pairs can be stacked one next to the other along lines parallel to the longitudinal axis, which produces a very compact arrangement of components.

When the target surface is planar, it has been found that a magnetic field having uniform intensity in planes lying parallel to the surface of the target provides control of the ion discharge such that a very uniform rate of sputtering ensues. To provide this magnetic field, one or more magnets, such as coils, with elongated approximately elliptically-shaped cross sections are used. The cross sectional elongation of the magnet is sufliciently large with respect to the length of the target and the ion discharge so that the component magnetic field produced by current in the ends of the cross section of the coil have negligible effect on the resultant magnetic field applied to the ion discharge. Although a cross sectionally elongated magnet such as a coil can be employed to advantage with any type of sputtering apparatus including the bell jar arrangement of my above-mentioned application, it is particularly advantageous when used with a sputtering chamber with a longitudinal axis according to the invention, because the direction of the cross sectional elongation of the magnet is aligned with the longitudinal axis of the sputtering chamber. The magnet, therefore, requires hardly any more space than is necessary for the sputtering chamber itself.

These and other features of the invention are considered further in the following detailed description taken in conjunction with the drawings in which:

FIGS. 1A and 1B are top and side elevation views, respectively, of a T-shaped sputtering chamber;

FIGS. 2A and 2B are top and side elevation views, respectively, of schematic representations of the arrangement of the elements associated with the sputtering process in the chamber of FIG.1;

FIGS. 3A, 3B, 3C, and 3D are schematic circuit diagrams of alternative anode-cathode circuits used in the sputtering chamber of FIG. 1 to produce ion discharges; and

FIG. 4 is a side elevation view of a complete, closedpath sputtering system employing plural T-shaped chambers and interconnecting sections.

In FIGS. 1A and 1B a T-chamber for sputtering is shown having a main horizontal section and a perpendicular branch section 11 joined to horizontal section 10 approximately midway between its ends. Horizontal section 10 has a flange 12 at one end, shown connected to a blankoff plate 13, and a flange 14 at its other end, shown connected to blankoff plate 15. Plate 13 and 15 seal off the ends of horizontal section 10. The end of branch section 11 is provided with a flange 16 for connection to a vacuum pump (not shown). The anode-cathode systems that produce the ion discharges within horizontal section 10 are situated such that each anode and its cathode are at diametrically opposite sides of horizontal section 10. Connecting housings 17 and 23 for the cathode elements are shown joined by their flanges to the outside wall of horizontal section 10 and feedthrough terminals 22 and 24, to provide electrical access to the anodes through airtight fittings, are shown mounted to and electrically isolated from the wall of horizontal section 10. Although cathode housings 17 and 23 are shown oriented so as to produce ion discharges with horizontal axes, the anode-cathode systems could be rotated so as to produce ion discharges with vertical axes or with axes at any other angles with the horizontal. A cooling coil 18 is wrapped around horizontal section 10 and cathode housings 17 and 23. At the top of perpendicular branch section 11 a door 19 is provided for access to the T- chamber. Targets and/or substrates can for example, be mounted through door 19 when open. Door 19 when closed, forms an airtight fitting with a seat 20 branch section 11. A glass window 21 in door 19 permits observation of the sputtering operation taking place in the T- chamber. Preparatory to sputtering, the T-chamber, which is completely airtight, is first evacuated to a pressure of about 10 torr, and then refilled with an ionizable gas such as argon to a pressure of about 10 torr. The ionizable gas is fed to the T-chamber through a conduit 58 from a tank not shown in the drawings by operating a valve 25.

In FIGS. 2A and 2B the approximate position of the elements involved in the sputtering operation is shown schematically. Within horizontal section 10 is an anodecathode system represented by an anode 33 at one side and diametrically opposite therefrom at the other side, a filament 35 constituting a cathode. Anode 33 is positively biased with respect to filament 35 by the series circuit comprising a battery 39 and a variable resistor 40. Filament 35 is heated by means of an alternating current power supply 37 to the point where it emits electrons that are drawn to anode 33. Collision of these electrons with the gas particles in the T-chamber causes a discharge of positive ions to develop between filament 35 and anode 33 along an axis 60. A second anode-cathode system within horizontal section 10 is represented by an anode 34 and a filament 36 constituting a cathode diametrically opposite from one another. Anode 34 is positively biased with respect to filament 36 by the series circuit comprising a battery 41 and a variable resistor 42. Filament 36 is heated by means of an alternating current power supply 38. A discharge of positive ions is thereby developed between anode 34 and filament 36 along an axis 26. Axes 60 and 26 are sufliciently close to one another that the ion discharges produced by the anode-cathode systems intermix. This is only one of various arrangements of plural anode-cathode systems which can be employed to advantage in the T-chamber or other type sputtering chamber. The various arrangements and their characteristics are discussed in detail in connection with FIGS. 3A through 3D. In the schematic representation of FIG. 1A the filaments appear in alignment with their respective anodes to facilitate illustration. It is advantageous in practice to locate the filaments beyond the bend in cathode housings 17 and 23, so the filaments are not in a direct line-of-sight with their anodes. This reduces unwanted sputtering from the filaments and contributes to longer filament life. A target 27, which is the material to be sputtered, is mounted in main section 10 to one side of the ion discharge by means not shown and is biased negatively with respect to anode 34 by means of the series circuit comprising a variable resistor 28 and a battery 29. Instead of a single target, plural targets, each biased with respect to an anode, could be employed. If the target material is an electrical insulator it would be advantageous to employ high frequency voltage to bias target 27. On the other side of the ion discharge, diametrically opposite to and facing target 27, is a substrate 30 to be coated. Ions are drawn to target 27 due to its bias potential, causing target 27 to be sputtered thus coating substrate 30. Magnets 31 and 56 are shown as coils with elongated, approximately elliptical cross sections that are voltagebiased by batteries 32 and 57 respectively. Magnets 31 and 56 are located on diametrically opposite sides of horizontal section 10 and are oriented such that they produce magnetic fields in the same direction, which is parallel to axis 60 of the ion discharge. The direction of elongation of the cross section of magnets 31 and 56 is parallel to axis 61 of section 10. The purpose of magnets 31 and 56 is to provide a magnetic field having a direction parallel to axis 60 of the ion discharge and an intensity uniform in planes lying parallel to the plane of the surface of target 27. It has been found that such a magnetic field causes a very uniform rate of sputtering for planar target surfaces and substrates.

Generally speaking the length (dimension parallel to axis 61) and height (dimension parallel to axis 60) of target 27, substrate 30, and the uniform region of the ion discharge are made about equal. The effect of the cross sectional elongation of the coils constituting magnets 31 and 56 is to remove end portions 52 and 53 of the coil cross section far from the region of the ion discharge within which uniformity is to be maintained. The resultant magnetic field within the region of the ion discharge to be maintained uniform, neglecting the magnetic field produced by end portions 52 and 53, is thus the sum of the magnetic field produced by side portions 54 and 55, which are approximately parallel. This resultant magnetic field has substantially uniform intensity in planes parallel to the surface of target 27. In the case of a target and substrate of a given width the more elongation of the cross section of the coil the better is the degree of uniformity of the sputtering rate and in the case of a coil with a given cross sectional elongation the narrower the target and substrate the better is the degree of uniformity of the sputtering rate.

Any other type of cross sectionally elongated magnet can be used instead of coils 31 and 56. For example, a cross sectionally elongated permanent bar magnet or a coil with a circular cross section, in which a ferromagnetic slug with an elongated cross section is placed, are also satisfactory.

The anode-cathode system for developing the ion discharge in the T-chamber can be composed of one or more anode-cathode pairs cooperating with each other and one or more targets. In all cases an anode and its cathode are located on opposite sides within horizontal section 10.

In FIG. 3A the electrical connections for two such anode-cathode pairs are shown employing the same numbers to identify elements as in FIGS. 2A and 2B. Anodes 33 and 34 are located on one side of section and cathodes 35 and 36 are located in line with anodes 33 and 34 respectively, on the diametrically opposite side of section 10. The filaments of cathodes 35 and 36 are heated by alternating- current sources 37 and 38, respectively. Anode 33 is positively biased with respect to cathode 35 by means of the series circuit comprising battery 39 and variable resistor 40, while anode 34 is positively biased with respect to cathode 36 by means of the series circuit, independent from the circuit for anode 33 and cathode 35, comprising battery 41 and variable resistor 42. The current flowing between each anode-cathode pair can be adjusted by its associated variable resistor. In this arrangement the two anode-cathode pairs produce two sideby-side, unopposed, uncrossed ion discharges which are independent from one another in the sense that they result from the flow of electrons in two independent circuits, namely anode 33, cathode 35, battery 39 and variable resistor 40 on the one hand, and anode 34, cathode 36, battery 41 and variable resistor 42 on the other hand. These anode-cathode pairs are arranged with respect to one another such that the contiguous edges of the ion discharges intermix somewhat with one another to form, in essence, a single conglomerate ion mass. The advantage of this arrangement is that, without increasing the anode-cathode bias voltage or reducing the ion density, an ion mass of about twice the width obtainable with a single anode-cathode pair can be achieved.

In FIG. 3B the two anode-cathode pairs are connected in a fashion identical to the connection of FIG. 3A, except that one of the anode-cathode pairs is rotated 180 degrees. As a result anode 33 and cathode 36 are side-byside at one side of section 10 and cathode 35 and anode 34 are side-by-side at the diametrically opposite side of section 10. In this arrangement, the one also shown in the T-chamber of FIGS. 1 and 2, the two anode-cathode pairs produce two side-by-side, opposed, uncrossed ion discharges which are independent from one another. When a single anode-cathode pair is employed the ion density is greater in the vicinity of the cathode than in the vicinity of the anode. The same is true of the arrangement of FIG. 3A. When the anode-cathode pairs are arranged to oppose one another as in FIG. 3B, and are placed such that the contiguous edges of their discharges intermix to some degree With one another, a conglomerated mass of ions forms having a width about twice that obtainable from a single anode-cathode pair and having much better uniformity than a single anode-cathode pair or the arrangement of FIG. 3A. Variable resistors 40 and 42 are employed to effect a change in the ratio between the anode-cathode currents, and thus a fine adjustment on the uniformity of the ion discharge. The improved uniformity of this arrangement may be viewed as resulting from an equalization between the higher density of the region of the ion discharge close to each cathode and the lower density of the region of the ion discharge close to the anode aside of it.

In FIG. 3C the two anode-cathode pairs are connected such that anode 33 is positively biased with respect to and in circuitwith cathode 36 and anode 34 is positively biased with respect to and in circuit with cathode 35. In this arrangement the two anode-cathode pairs produce two independent ion discharges which cross each other. In the region of the crossover of the two ion discharges an ion mass forms having a density increased approximately two fold. This same result can be achieved by placing the two anode-cathode pairs in other ways so that their ion discharges cross. For example, the anode-cathode pairs could be placed in the same plane at an angle with respect to one another. In terms of clock directions, one anode could be located at twelve oclock and its cathode at six oclock while the other anode could be located at three oclock and its cathode at nine oclock.

FIG. 3D shows an arrangement of anode-cathode pairs that combines the characteristics of the arrangements of FIGS. 3B and 3C. Anode 33 is separated into electrically connected parts 33a and 33b located on either side of and close to filament 36, and anode 34 is separated into electrically connected parts 34a and 34b located on either side of and close to filament 35. Anode 33 and anode 34 can alternatively each be constructed as a single unit with a hole through it. Filament 36 is then located at the hole in anode 33 and filament 35 is located at the hole in anode 34. In this way the independent ion discharges are superimposed upon one another over almost their entire length, producing a long conglomerate mass of electrons having improved uniformity and a density increased approximately twofold as compared to a single anodecathode pair.

It is vital to the arrangements shown in FIGS. 3A, 3B, 3C, and 3D that the anodes be electrically isolated from one another, as shown, i.e., that each anode-cathode pair has its own independent bias circuit to produce an independent ion discharge. Although the arrangement of FIGS 3A, 3B, 3C, and 3D are particularly advantageous when used in the T-chamber represented in FIGS. 1 and 2, because the anodes and cathodes can be placed one next to the other along the longitudinal axis of the main section, they can also be used to advantage in other types of sputtering apparatus, including the bell jar apparatus of my above-mentioned application. More than two anode-cathode pairs can also be employed in the arrangements of FIGS. 3A, 3B, 3C, and 3D with similar results.

A complete sputtering system composed of several stations for cleaning and coating substrates and adapted for automated operation is shown in FIG. 4. T- chambers 43 and 44 are connected together by a spacer section 45. An entrance T-chamber 46 is connected at one end to T- chamber 43 and at the other end to a blanking plate 63, while an exit T-chamber 47 is connected at one end to T-chamber 44, and at the other end to a blanking plate 64. The vertical sections of entrance chamber 46 and exit chamber 47 are connected together by an airtight conduit 48 such that a conveyor belt 49* or other means can easily transport substrates and/or targets to and from T- chambers 43 and 44 for sputtering operations. In accordance with principles well-known in the art of automation, entrance chamber 46 could be provided with means for placing and indexing substrates on conveyor belt 49 and exit chamber 47 could similarly be provided with means for removing the substrates after the operations are completed. A vacuum pump 50 is connected to the branch section of T-chamber 43 to evacuate the system, which is airtight. The branch section of T-chamber 44 is blanked off, but a second vacuum pump could instead be provided at this point if found necessary. Each T-chamber could house a single anode-cathode pair or plural anode-cathode pairs as discussed in connection with FIGS. 3A, 3B, 3C, or 3D.

What is claimed is:

1. A sputtering module comprising an evacuable chamber having a longitudinal axis, a plurality of means for establishing in the chamber a plurality of ion discharges transverse to its longitudinal axis, the axes of the discharges generally falling within a common plane, and which discharges at least partially merge with one another, each means for establishing the discharge being independent from the other and including an electrical circuit which is electrically isolated from the electrical circuit of the other, means for mounting a target material to be sputtered to the side of the plane of the axes of the ion discharges produced by the ion discharge establishing means such that an unblocked passage exists along the longitudinal axis permitting transport of items along it, means for applying to the target material an electric potential so as to draw ions from the ion discharge produced by the ion discharge establishing means, and means to transport items along the longitudinal axis.

2. A sputtering apparatus comprising an evacuable chamber, a plurality of means for establishing in the chamber a plurality of ion discharges extending along individul axes, the axes of the discharges generally falling within a common plane, and which discharges at least partially merge with one another, each means for establishing the discharge being independent from the other and including an electrical circuit which is electrically isolated from the electrical circuit of the other, means for mounting a substantially planar target material to be sputtered to the' side of the plane of the axes of the ion discharges, means for applying to the target material an electric potential to cause attraction of ions to it, and a coil having a cross section elongated in a direction substantially perpendicular to the axis of the ion discharge and substantially parallel to the target, the coil being oriented such that the magnetic field it produces acts upon the ion discharge.

3. A sputtering module comprising an evacuable horizontal main section with a longitudinal axis and a branch portion joining the main portion substantially midway between its ends, a plurality of means for establishing in the main section first and second ion discharges transverse to the longitudinal axis, the axes of the discharges generally falling within a common plane, each means for establishing the discharge being independent from the other and including an electrical circuit which is electrically isolated from the electrical circuit of the other, and situated with respect to one another such that they intermix somewhat to form a conglomerate discharge of ions, means for mounting a planar target material to be sputtered to the side of the plane of the axes of the ion mass, means for applying to the target material an electric potential to cause attraction of ions to it, and means for establishing in the region of the ion mass from which ions are attracted to the target material a magnetic field having a uniform direction and an intensity uniform in planes parallel to the target material.

4. A sputtering apparatus comprising:

(a) an evacuable chamber;

(b) means for introducing an ionizable atomosphere into the chamber;

(c) means for establishing in the chamber a first ion discharge;

((1) means for establishing in the chamber a second ion discharge, the first and second ion discharge establishing means including separate electrical circuits, and electrically isolated from the other and disposed such that the ion discharges they produce coact to form a conglomerate mass of ions at least over a target mounted on the target mounting means, the first and second ion discharge establishing means also being disposed such that the axes of the ion discharges they produce fall in a common plane; and

(e) means for mounting a target of material to be sputtered inside the chamber to the side of the plane of the ion discharges.

5. The sputtering apparatus claimed in claim 4 wherein means is provided for mounting a substrate within the chamber in position to receive material sputtered from a target mounted on the target mounting means, the target mounting means is disposed to mount a target to one side of the independent ion discharges produced by the first and second ion discharge establishing means; and means is provided for negatively biasing the target to attract ions from the independent ion discharges.

6. The sputtering apparatus claimed in claim 5 wherein the first and second independent ion discharge establishing means includes at least one anode and cathode pair for each independent ion discharge, and independent circuits for each anode-cathode pair operable to positively bias each anode with respect to its cathode.

7. The sputtering apparatus claimed in claim 6 wherein the first and second ion discharge establishing means are disposed to produce ion discharges which have substantially parallel axes and are unopposed and uncrossed.

8. The sputtering apparatus claimed in claim 6 wherein the first and second ion discharge establishing means are disposed to produce ion discharges which have parallel axes and are opposed and uncrossed.

9. The sputtering apparatus claimed in claim 8 wherein the first and second ion discharge establishing means are disposed to produce ion idscharges which are crossed.

10. The sputtering apparatus claimed in claim 9 wherein the first and second ion discharge establishing means are disposed to produce ion discharges which are unopposed.

11. The sputtering apparatus claimed in claim 6 wherein the first and second ion discharge establishing means are disposed to produce ion discharges which are coincident along at least a substantial portion of their axial lengths. 1

12. The sputtering apparatus claimed in claim 11 wherein the first and second ion discharge establishing means are disposed to produce ion discharges which are opposed.

References Cited UNITED STATES PATENTS 3,021,271 2/1962 Wehner 204l92 3,324,019 6/1967 Laegreid et al. 204-192 3,361,659 1/1968 Bertelson 204-492 ROBERT K. MIHALEK, Primary Examiner US. Cl. X.R. 204-192

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