US 3669871 A
Sputtering apparatus in which the sputtering cathode is concave to produce a focusing effect on dislodged particles and concentrate the particles toward a point. The substrate being coated is movably mounted to construct the desired coating configuration. A modification is to orient single crystal bits on the cathode surface to further enhance preferential directional emission during sputtering.
Claims available in
Description (OCR text may contain errors)
[ 1 June 13, 1972 Wurmet al .........204/l92 Sapoffet al............................204/192 to further enhance preferential ABSTRACT Sputtering apparatus in which the sputtering cathode is consurface 2 Claims, 2 Drawing Figures Primary Examiner-John H. Mack Assistant ExaminerSidney S. Kanter Attorney-K. P. Johnson and Hanifin and Jancin cave to produce a focusing effect on dislodged particles and concentrate the particles toward a point. The substrate being coated is movably mounted to construct the desired coating configuration. A modification is to orient single crystal bits on the cathode directional emission during sputtering.
..204/298 .i..C23c 15/00 .204/298, l92
CONCAVE SDURCE CATHODE  inventors: Jarl A. Elmgren; Robert R. R. Rodite,
both of Endwell, N.Y.
Assignee: International Business Machines Corporation, Arrnonk, N.Y.
Sept. 10, 1969 Appl. No.: 856,762
Int. References Cited UNITED STATES PATENTS 3,250,694 5/1966 Maissel et a1 Eimgren et al.
[541 SPUTTERING APPARATUS HAVING A 22 Filed:
PATENTEuJun 13 m2 x 4k. l
lNVE/VTORS JARL A. ELMGREN ROBERT R. R. RODITE /zf r7 ATTNEY SPUTTERING APPARATUS HAVING A CONCAVE SOURCE CATI-IODE BACKGROUND OF THE INVENTION In the art of vacuum deposition of thin film coatings for microcircuits, sputtering is a preferred method. Sputtering provides a coating that is relatively smooth, adheres well to the substrate surface, and is the same composition as the source material. Various materials that are either electrical insulators or conductors can be deposited by this method. The temperature characteristics of the target material are of minor concern because the process can be kept sufficiently cool as it proceeds.
A sputtered coating is generally deposited by spacing a planar workpiece with its coated surface parallel to the bombarded planar surface of the source electrode or target. The dislodged target particles then move to the surface of the workpiece and coat the entire surface. The thickness of the layer so formed decreases with distance from the center of the target. The reason for this, of course, is that the probability increases for particles dislodged by ion impact to miss the workpiece upon approaching the edge.
After thin films have been applied by the usual method, the coatings are selectively removed by etching to leave only specific areas in the form of circuit lines and lands or insulation thereover. The usual etching technique requires several intermediate processing steps to define and create the coated areas desired. In addition, a large portion of the sputtered material is not used and there is a significant quantity of target material sputtered onto nearby apparatus within the vacuum chamber. Attempts have been made to use masks to define coated areas but this method still requires frequent clean-up or mask replacement. Also, a sputtered coating is deposited at a relatively slow rate.
A variation in the usual sputtering arrangement is making the target in the form of a cylinder. The workpiece is placed on the longitudinal axis of the cylinder. Sputtered particles are loosened by ionized gas particles and are moving in all directions within the cylinder. This arrangement is particularly useful to coat the exterior surface of irregularly shaped objects. The cylindrical arrangement, however, still has the disadvantage of having little control over the direction taken by sputtered particles, so that the entire surface is coated.
Accordingly, a primary object of this invention is to provide sputtering apparatus by which the dislodged particles can be substantially focused and directed to a predetermined area on the workpiece.
A further object of this invention is to provide apparatus for applying focused sputtered coatings in varying configurations on a workpiece as desired by moving the workpiece during coating.
Other important objects of this invention include the provision of sputtering apparatus in which: neutral particles can be used to selectively coat a workpiece; sputtered material is conserved by concentrating and focusing the particles at the desired coating location; either electrically insulative or conductive materials can be selectively coated; and a concave source electrode is used to direct particles to the coating location desired.
SUMMARY OF THE INVENTION The foregoing objects are attained in accordance with the invention in its broad aspects by providing a sputtering target having a concave surface opposite the workpiece to be coated and thereafter producing ion bombardment of the target. A workpiece is spaced from the target along a centerline normal to the target concavity. When ionized particles bombard the concave target, they tend to impact along lines normal to the target surface or equipotential lines. Dislodged particles leave the target surface approximately at an angle equal to that of the impinging ion so that the result is a focusing of the particles toward the centerline of the concavity. By appropriately locating the workpiece at the point of greatest concentration of particles, a high deposition rate is possible and sputtered material can be confined to a relatively small area on the workpiece. A mask is used immediately above the workpiece to precisely define the coated area.
This arrangement provides several significant advantages. Coating efficiency is improved because of the higher deposition rate, and less extraneous coating occurs because of the focused particles, thus reducing clean-up requirements. By simultaneously controlling an X-Y positioning table for supporting the workpiece, a conductive line or insulation pattern can be generated with the concentrated stream of particles. This procedure eliminates several of the prior processing steps such as applying, exposing and developing photo-resist, and etching. The concave target can be used with either direct current or radio frequency (RF) sputtering arrangements.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings wherein:
FIG. 1 is an elevation view, partially in section, of a preferred embodiment of a sputtering apparatus constructed in accordance with the invention; and
FIG. 2 is an elevation view of an alternative target electrode, partially in section, that may be used in the apparatus of FIG. 1.
DETAILED DESCRIPTION Referring to FIG. 1, there is shown sputtering apparatus comprising generally a vacuum chamber 10, a sputtering cathode l1, sputtering anode 12, workpiece 13 and support pedestal. Vacuum chamber 10 encloses the various elements and is formed by cylinder 16 suitably sealed between base plate 17 and cover plate 18. The chamber is capable of holding a high vacuum. The vacuum chamber may be constructed of the conventional materials, such as glass, metal or the like. Various required inputs and outputs to the vacuum chamber are made through base and cover plates 17 and 18; these include a duct 19 to a vacuum pump, inlet and outlet ducts 20, 21, respectively, for electron source coolant and duct 22 for a variable leak gas input for the inert ionizable gas. Ducts 23, 24 provide coolant for sputtering cathode 11. Other connections through the base and cover are for electrical conductors supplying the required energizing potentials and controls.
Sputtering cathode 11, sometimes referred to as the target, is dome-shaped, being formed as a symmetrical cavity having its surface 25 generated on a radius R with origin at point 27 on workpiece 13. The cathode is preferably made as base portion 28 with a layer 29 of the material to be sputtered. With this arrangement the sputtering material can be relatively thin and the base can be used for different source materials. The source materials can be applied by electroplating, laminating, vapor deposition, or mechanical clamping. The cathode base is suspended within the vacuum chamber from cover plate 18. Cathode base 28 is also formed with cooling passages 30 and, if desired, may comprise two or more assembled units to facilitate manufacture. Coolant is taken in via inlet duct 23, circulated through sputtering cathode 11, and removed via duct 24. Surrounding sputtering cathode ,11 is a conductive ground shield 33, also suspended from cover plate 18, which is maintained at or near ground potential to confine the dark space during sputtering.
The sputtering anode is an electrically conductive plate 12 having an aperture 38 and is adjustably secured to a support 39 fixed to base plate 17. The anode is maintained at ground potential and serves as a mask to permit sputtered particles to reach workpiece 13 only through the aperture. The size of aperture 38 will be varied according to the purpose of the material deposited, i.e., insulator or conductor, and the level of the anode above the workpiece will also be adjusted to control the size of the coated area and its edge definition.
Workpiece 13 is preferably supported on a table surface that can be moved along either or both of two axes during deposition. Such a table 40 is schematically shown on a pedestal and has a control cable 41 connected to external controls. The capability of table motion permits the generation of lines of varied configurations. Suitable X-Y positioning tables and controls are believed well-known, requiring no further explanation here.
To the left of the table is a filament 42 which provides a source of electrons, and filament housing 43. The filament is connected to a power supply 44 and housing 43 is connected to a source of coolant through ducts and 21. An electron anode 46 is supported in alignment with the opening of the filament housing and is connected to a source of suitable potential for emitting the plasma stream to, in turn, produce the ion sheath. The sputtering apparatus can be used either with or without the filament 42 and electron anode 46. Either DC or RF voltage can be applied to cathode 28 with the filament turned on. However, RF is preferred when operation without filament 42. The RF mode enables the sputtering of dielectric materials.
workpiece 13 is preferably placed at focal point 27 of the concavity which is the point of heaviest concentration of sputtered particles. Ions impact sputtering cathode surface 29 substantially normal thereto so that particles are dislodged at approximately the same angle. The configuration of surface 29 thus directs the particles toward the center of curvature or the point to be coated on the workpiece. Ion-particle collisions will occur which create some dispersion of the particles from their locus of concentration. The size of aperture 38 and its height above the workpiece aid in limiting the area coated by the sputtered particles. Occasional cleaning of anode 12 is required.
Although the concavity has been illustrated as defined by a radius from the workpiece, other configurations tending to concentrate the sputtered particles can be used. Parabolic and hyperbolic surfaces will also produce a high concentration of particles along a line coincident with the focal points.
The focusing effect of the shaped cathode 11 is of significant advantage because of the elimination of processing steps heretofore required for subtractive processes. This arrangement enables controlled deposition along desired circuit lines and lands merely by moving the workpiece with positioning table 40.
FIG. 2 shows a modification of sputtering cathode 11 which utilizes the known phenomenon of directional particle emission from crystalline structure. Particles of such coating material are ejected, as a result of ion bombardment, along preferential lines according to the orientation of the crystal faces. In FIG. 2, portions 60 of single crystal material, such as copper, are supported in a bulk layer 61 of the same material. Portions 60 are cut from a single crystal, oriented to expose the preferred face and embedded in the bulk metal with outer surfaces coincident in a common curved surface. The oriented crystal portions will further aid in the directionality of the ejected particles.
While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the forego ing and other changes in form and details may be made therein.
What is claimed is:
l. Sputtering apparatus for concentrating portions of dislodged, sputtered material toward a point comprising:
a first electrode having a surface area portion covered with said material to be sputtered, said entire covered surface area portion being shaped to form a single concavity;
a second electrode opposite said concavity of said first electrode and spaced to provide a glow discharge region therebetween adjacent said concave surface of said first electrode when energized, said second electrode being normal to the axis of said concavity and lying between the focal point of said concavity and said first electrode, and having an aperture therein on said axis for admitting said dislodged portions to said focal point;
means for introducing ionizable particles into said region energizing means connected to said electrodes for lOmZll'lg said particles to create a glow discharge between said electrodes and dislodged portions of said material to be sputtered; and
means for supporting a workpiece with an area to be coated with said portions at the focal point of said concavity on its axis.
2. Apparatus as described in claim 1 wherein said concavity surface lies on a radius from a point on the center axis of said concavity.