Abstract:
This invention relates to a broad beam ion deposition apparatus ( 100 ) including an ion source ( 101 ), a target ( 102 ), a tillable substrate table ( 103 ) and an auxiliary port ( 104 ). The target ( 102 ) is in the form of a carousel which carries a number of targets and the ion source ( 101 ) is configured to produce a substantially rectangular section beam ( 105 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application is a United States National Stage Application filed under 35 U.S.C. §371 of PCT Patent Application Serial No. PCT/GB2007/002537 filed on Jul. 6, 2007, which claims the benefit of and priority to Great Britain (GB) Patent Application Serial No. 0614499.2 filed on Jul. 21, 2006 and U.S. Provisional Patent Application Ser. No. 60/832,474 filed on Jul. 20, 2006, the disclosures of both of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to broad ion beam deposition (BIBD) apparatus and uses thereof. It is known to provide BIBD apparatus having an ion source, which feeds an ion beam through parallel grids to form a collimated beam that projects on a target to sputter material onto a substrate. Typically the target is deposed at about 45° to the main axis of the beam and the resultant sputtering occurs in a fairly wide arc with the relatively high degree of non uniformity. The ion beams so produced are generally circular in cross section and so either quite a lot of the target is not utilised or some of the beam will tend to pass by the edges of the target with the result that stray materials may be sputtered. Either way the efficiency is poor and so for the most part ion beam deposition has been a research tool or used in the manufacture of component parts where very specific film properties are essential and can only be achieved by this technique. This is because to date throughput has been very low and so only high value goods can bear the cost of such an operation. 
     It is known to have more than one target of different materials, mounted on a carousel in the form, for example, of a hexagon, to enable successive depositions but this tends to mean that the beam area at the target has to be further reduced to avoid stray impacts on the preceding and succeeding targets. 
     BRIEF SUMMARY OF THE INVENTION 
     From one aspect the invention consisting a broad ion beam deposition apparatus including: 
     (a) an ion source for producing an ion beam; and 
     (b) a rotatable target support for successfully aligning targets with the beam characterised in that the targets are generally rectangular and the ion source is arranged to produce a beam which is rectangular in cross section: 
     From another aspect the apparatus consists in the broad ion beam deposition apparatus including an ion source for producing an ion beam and a rotatable target support defining a plurality of target locations characterised in that the first location lies in the position which is, in use, in the shadow of a beam impinging on its succeeding location. 
     Preferably the target locations are spaced and inclined to the respective face of a notional regular geometric figure having a number of faces equal to the number of locations. For example, there may be eight locations. 
     From a further aspect the invention includes ion beam deposition apparatus including an ion source for producing an ion beam along a path, a target location in the path, a support for a substrate to one side of the path and an auxiliary process port to the other side of the path. 
     In many of the cases the ion source may include a chamber for containing a plasma and having an outlet for ions; and an accelerator mounted at the outlet for drawing a stream of ions from the plasma and forming them into a beam, in a direction, wherein the accelerator includes four spaced generally parallel grids, the second to fourth grids numbered in the direction being located by two sets of supports wherein one set supports the second and fourth grids and the other set supports the third grid. 
     The second grid does not need to be supported on the first grid, but instead its support can pass through an aperture of the first grid to engage the chamber wall or an extension thereof and indeed can sit in a recess in such a wall or extension. The insulator length can therefore be significantly extended. Similarly the support for the third grid can pass through the first grid. 
     In a preferred embodiment at least one of the supports of the first set includes an insulator extending from the second grid to the fourth grid and additionally or alternatively at least one of the supports of the second grid includes an insulator extending from a wall of the chamber which defines the outlet, or an extension thereof, to the third grid. Optionally, at least one of the supports of the other set may include an insulator extending from the third grid to the fourth grid. It is particularly preferred that the above mentioned insulators are present on all respective supports. 
     It is also preferred that at least some of the insulators include formations, which will create sputter shadows to prevent reverse sputtering creating a conductive path over the full length of the insulator. Such formations can also be formed in such a way as to increase the tracking length on the surface of the insulator. 
     In any of the above cases the first grid may be mechanically pre-stressed to present a concave or convex profile in the direction about one axis. The applicants have appreciated that the mechanical pre-stressing enables a precise design configuration to be achieved, which will not distort under heat, but which does not require expensive preheat treatments. As the pre-stressing is in one dimension it can be machined into the chamber wall or other component against which the first grid may be clamped, thus avoid expensive heat treatment. They further appreciated that, contrary to what is taught in 6346768, that a convex curve is desirable, because this will to some extent address plasma non-uniformity or allows the possibility of the plasma density being matched to a particular design configuration, because when pre-stressed the first grid will stay where it is designed to be. The concave profile can be used to provide a ‘hollow’ beam. 
     The grid is generally rectangular and the axis is the longitudinal axis. 
     At least some of the openings in a grid adjacent its periphery may be smaller in cross-section than those located in a central region. It had previously been thought that the outer holes or openings should be bigger to increase the current flow adjacent the walls of the plasma chamber, where the plasma density is reduced. The inventors have appreciated that, surprisingly, this is the wrong approach and their proposal will give a beam with reduced divergence. In general the cross-section of the openings may be proportional to the anticipated local plasma density. The source may include a plurality of plasma generators, which when the source is rectangular or elongate can be spaced along its length. 
     The ion source may include a plasma generator, a chamber having a volume for the plasma and a body located in the volume for creating local losses and thereby reducing local plasma density to determine the gradient of the plasma density across the volume. 
     In a preferred arrangement the plasma density is made more uniform across the chamber. 
     The Applicants have realised that there is, surprisingly, a completely different approach to the problem of plasma uniformity or achieving a preferred plasma gradient, which is to reduce the higher plasma density, which typically occurs towards the centre of the plasma, so that the density across the whole plasma is significantly more uniform or graduated as required. This can be used in combination with the traditional magnetic approach or alternatively it can be used alone. 
     Conveniently the body is generally planar and may lie in a general lateral plane in the chamber. The body may have one or more cut-outs or openings and indeed there may be more than one body. The bodies may be co-planar or alternatively they may be spaced and generally parallel. 
     In an alternative arrangement the body may be arranged generally axially within the chamber and there may be a number of spaced parallel bodies. 
     Where the body is located in an RF field it should be formed from an insulator. Otherwise the body may be a conductor. The body may be any suitable shape, but for manufacturing reasons a regular geometrical shape such as triangular, circular, diamond shaped, square or rectangular bodies are particularly suitable. Three dimensional and/or irregular shapes may be used. 
     The plasma source may be part of an ion source. Equally it may be substituted for antennae configurations or other plasma sources. Any appropriate mode of generating plasma may be used. 
     From a further aspect the invention consists in an ion source for creating a low power ion beam of 100V or less including a plasma generator having an input power of above about 100 W, a plasma chamber and at least a body located in the plasma chamber for absorbing power from a plasma contained in the chamber. 
     In this arrangement, the problems associated with running ion sources with very low input powers to created lower power beams can be overcome by running the source at higher powers and then using the body to absorb sufficient power to reduce the ion beam to the desired level. 
     Although the invention has been defined above it is to be understood that it includes any inventive combination of the features set out above or in the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The invention may be performed in various ways and specific embodiments will now be described, by way of example, with reference to the accompanying drawings in which: 
         FIG. 1  is a schematic view of ion deposition apparatus; 
         FIG. 2  is a schematic diagram of an ion gun; 
         FIG. 3  is a schematic view of the accelerator grid of the gun of  FIG. 2  on an enlarged scale; 
         FIG. 4  is a view from the front and one side of a grid assembly for use with the ion gun of  FIG. 2 ; 
         FIG. 5  is a plan view of the first grid for use with an ion gun of  FIG. 2 ; 
         FIG. 6  is a cross sectional view of the grid of  FIG. 5  along the line A-A with the curvature exaggerated; 
         FIG. 7  is an end view of the grid of  FIG. 5 ; 
         FIG. 8  is a cross sectional view through an accelerator grid showing one of a first set of supports; 
         FIG. 9  is a corresponding view to  FIG. 8  through one of the second sets of supports; 
         FIGS. 10 and 11  correspond to  FIGS. 8 and 9  respectively for an alternative embodiment; 
         FIG. 12  is a schematic view of a multi-antennae source; 
         FIG. 13  is a schematic cross section through a first embodiment of an ion source; and 
         FIG. 14  is a corresponding view through an alternative construction. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1  broad ion beam deposition apparatus, generally indicated at  100  includes an ion source  101 , a target carousel  102 , a tiltable substrate table  103  and an auxiliary port  104 . 
     As will be described in more detail below, the ion source  101  produces a substantially rectangular section beam  105  which is directed towards the target carousel  102 . The target carousel (support) carries a number of targets, for example eight, on tables (target holders)  106  on spaced generally radial legs  107 . In fact the legs  107  and tables  106  are slightly offset so that the target locations defined by the tables  106  are inclined to the faces, respectively, of a notional regular geometric figure (i.e., a regular polygon) having a number of faces (sides) equal to the number of locations and centred on the axis of rotation of the carousel  102 . It will be noted that the targets  108  are rectangular. Thus, in this example, in any given position of the target carousel  102 , the eight sides of a regular octagon intersect and pass through the target locations (tables  106  and/or targets  108 ), respectively, but each target location (table  106  and/or target  108 ) is inclined or skewed, front to back in the direction of rotation of the carousel  102 , relative to the side of the regular octagon passing therethrough such that the generally planar rectangular target  108  supported by the table  106  is similarly inclined. 
     The combination of the rectangular section beam  105  and the inclined rectangular target  108  not only means that sputtering takes place substantially across the target, but also, as can be seen in  FIG. 1 , the preceding target, to that which is active at any time lies within the shadow with respect to the beam and hence no undesirable sputtering will take place. Further it is possible to introduce the target shielding indicated at  109  to protect the preceding target. It will be noted that that shielding is essentially wedge-shaped and may optionally be actuated so that its leading edge lies as close as possible to the face of the protected target. 
     The spaces  107   a  between the legs have a relatively high aspect ratio whereby any beam overspill on the upstream edge of a target will pass down the space and any resultant sputtered material will be retained within the space. 
     It will also be noted that the targets are spaced relative to each other and this, particularly with a rectangular beam, enables full-faced target cleaning to occur. Material sputtered from the active target impinges on the substrate  110  which is mounted on the tiltable substrate table  103 . It has been determined that the uniformity of sputtered layers on the substrate are very sensitive to the substrate angle, but that the optimum angle is target material dependent. The tiltable table therefore allows precise setting of the apparatus. It will be noted that the auxiliary port  104  is disposed substantially at right angles to the ion beam  105 , but faces the tiltable table  103 . This allows the possibility, when a sputter step has been performed, of deposition or ion beam processing, for example, for target cleaning to take place in between the sputter steps. The substrate can be tilted to the optimum position for such processing by the tiltable table  103  and then can be tilted back to the optimum position for sputtering. Alternatively an ion source located on the auxiliary port could be utilised during sputtering for the purpose of ion assisted deposition or surface modification. A substrate shield  111  can be located over the substrate or substrate location during cleaning. 
     It will be understood that the resultant apparatus is extremely flexible as the targets  108  can be made from different materials and, using the auxiliary port  104 , other process steps can take place between sputter steps. Thus in the single chamber, a series of fabrication steps can take place. 
     A particularly preferred ion source arrangement is described in connection with  FIGS. 2 to 9  and further embodiments are described in connection with  FIGS. 10 to 12 . 
     An ion gun;  101 , is schematically shown in  FIG. 2 . It comprises a plasma generator  11  driven from an RF source  12 , a plasma or source chamber  13 , having an outlet  14 , across which is mounted an accelerator grid  15 . The accelerator grid  15  comprises four individual grids. The first grid  16 , which is closest to the outlet  14  is maintained at a positive voltage by DC source  16   a , the second grid  17  is maintained strongly negative by DC source  17   a . The third grid  18  is maintained at a negative voltage, which is much lower than that of the second grid  17 , by DC source  18   a  and the fourth grid  19  is grounded. 
     For reasons highlighted below, the applicants are able to run the second grid  17  at around −2000V or even higher. This has a dual effect of creating a good electric lens, between plates  16  and  17 . The result of this is shown in  FIG. 3  where the ion beam  20  is focused between plates  16  and  17 . The high negative voltage on grid  17  also significantly accelerates the ions in the beam  20  and accordingly reduces the divergence creating effect of the transverse focusing forces over the operational length of throw of the ion beam  20 . 
     Grid  18  is at a much smaller negative voltage allowing the ground voltage of grid  19  to be achieved in two decelerating steps, without causing significant divergence of the beam  20 . 
     The positive, negative, negative, ground arrangement of the grids also significantly reduces the likelihood of a reverse electron current, which could cause voltage collapse and instability. 
       FIG. 4  shows a grid assembly. The grids  14  to  19  can be attached to the chamber  13  through frame assembly  21  and are themselves connected to the frame  22  as described below. Turning to  FIGS. 5 to 7  it should first be noted that the openings  23  in the grid  16  are smaller nearer the periphery than in the centre, for the reasons previously discussed. Secondly, as shown in  FIG. 6  grid  16  is mechanically pre-stressed in a slight longitudinal convex curve, which is exaggerated in the drawing, to overcome the heat effects previously mentioned. Conveniently this curvature, which may hardly be visible, may be machined into the chamber wall against which the first grid is clamped, thus avoiding expensive heat treatments. Alternatively the curve may be concave, which can produce a hollow beam. 
     It will be noted that in the frame  22  there are openings  23  through which supports pass and in which voltage connections such as indicated in  FIG. 4  at  24  may be attached. 
     It is proposed, as can be seen in  FIGS. 8 and 9 , that two different forms of supports should be used. Each support includes a central core which enables the support to be located in the wall  25  of the source chamber  13 . In each case the central core includes a screw  26 , a washer  27 , a sleeve  28  and a clamp  29 , which may be the frame  22 . As will be well understood by one skilled in the art, this arrangement can be used to hold the grids  16  to  19  in compression and to thus locate them vertically and laterally subject to interconnections between them. 
     One of the supports, which constitutes the first set, as previously mentioned, is illustrated at  30 . This further includes two annular insulators  31  and  32 . It will be seen that the insulator  31  is able to pass through the grid  16  to sit in a recess  33  in the wall  25 . It then passes upwardly through an opening  34  in the second grid  17  to support the third grid  18 . The insulator  32  in turn sits on the grid  18  to support the grid  19 . This effectively decouples the second grid from the third grid in mechanical terms whilst providing a long insulator  33  between the chamber  25  and the third grid  18 . 
     A member of the second set of supports is illustrated in  FIG. 9  at  35 . Here the lower annular insulator  36  supports the second grid  17  and the upper annular insulator  37  in turn supports the fourth grid  19 . In this way both the second and third grid as dimensionally referenced to the wall  25  and the fourth grid  19 , but without being engaged with each other. This enables the insulator  36  to pass through the first grid  16 , rather than sitting on it so that the advantage of the recess  33  can once more be gained and it also allows for the convex curve to be introduced into the grid  16  without losing accuracy in the positioning of the remaining grids. 
       FIGS. 10 and 11  illustrate an alternative arrangement in which the fourth grid  19  is not supported on the third grid  18  and the sleeve  28  is provided with a shoulder  38  to clamp the third grid  18 . 
     The grids  16  to  19  are described as generally parallel despite the curvature of the grid  16 . As that grid is generally planar in configuration the phrase will be well understood by those skilled in the art. 
     In  FIG. 12  a single large (e.g. 150 mm×900 mm) chamber  13  is supplied by three plasma generators  11 . As illustrated the generators  11  are MORI® sources supplied by Aviza Technology Inc., but any suitable generator may be used. The accelerator grid is shown at  15 . Multiple generator sources of this type can be used for provide broad beam for processing large substrates e.g. flat screen displays. 
     The Applicants have also developed a surprisingly simple system for adjusting the local plasma density within the ion source so as either to achieve enhanced uniformity across the width of the source or, for some particular processing techniques, to provide a predetermined gradient of plasma density. For example it may be desirable to have an inverted density distribution with the lowest density towards the centre of the source. 
     The Applicants have inserted a body  39  to extend laterally across a general central portion of the chamber  13 . The size, shape and location of the body  39  are selected to absorb the sufficient power from the plasma struck in the chamber so as to reduce locally the plasma density in such a way that the density of the plasma, as seen by the grid  15  is essentially uniform across the width of the chamber  14  or to achieve some desired profile of non-uniformity. 
     The size, shape and location can be determined empirically. The body  39  may be provided with openings or perforations  40  to allow for local fine tuning. 
     When a lateral body of this type is used, it will also affect the flow of ions through the chamber, as well the presence or absence of opening  40 . This can be used to displace ion flow towards the chamber walls again enhancing uniformity. More than one body can be used and the addition of further bodies  39  will often persist in fine tuning. 
     As has already been mentioned, the ion source is only one example of a plasma generation device and the principles discussed above can equally well be applied to other plasma generation devices. 
     As well as being used to alter the level of non-uniformity within the plasma, a body or bodies  39  can be used to absorb power from the ion beam. This can be particularly effective for applications where low energy process beams (eg 100V or below) are required. Typically applications requiring low energy process beams demand a plasma density in the region of 0.2 mAcm −2 , with good uniformity. However this means that they tend to be operated at input powers in the region of 20 W where it is extremely difficult to control the device. In contrast, the Applicants have appreciated, that by utilising the arrangement shown in  FIG. 1 , the ion source can be operated in a well controlled region e.g. an input power of 150 W. The body or bodies  39  are then designed to absorb sufficient power and provide the appropriate uniformity. 
     If power absorption or control of plasma density is the sole requirement, then the body or bodies  39  may be aligned longitudinally with in the chamber  14  as illustrated in  FIG. 2 . Arrangement lying between the orientations of  FIGS. 1 and 2  may also be utilised. 
     The positioning requirements vary depending on the geometry of the apparatus, but in general the insert should not be place too close to the antenna region of primary plasma generation such that it affects the flow of plasma into the chamber  13 . Equally if the body  39  is too close to the grid  15  or process plane, it may effectively block the grid  15 . Within these limits the longitudinal position of the body may be selected in accordance with the effect that is desired. There is some suggestion from experiment, that the diffusion length of the expansion box is sensitive to changes of the insert axial location of the order of 5 mm. A diffusion length of half the radius of the insert, measured across the short axis of the chamber  13 , has proved to be acceptable. In general it has been found that it is useful to have an insert which follows the symmetry of the chamber  13 .