TARGET FOR CATHODE SPUTTERING

Abstract: A sputtering target and target assembly (12) includes a target member (10) having a substantially continuously concave top surface (17) and a bottom surface (18) with a central, downwardly directed hub (21) and at least three annular regions of differing radius of curvature (23, 27, 25). The shape of the target member (10) bottom surface (18) conforms to a backplate (11) to which it is mounted, thereby facilitating accurate mounting of the target member (10) during sputtering. The corresponding shapes of the target member (10) and backplate (11) promote maximum utilization of sputtering material.

Description: TARGET FOR CATHODE SPUTTERING Field of the Invention This invention relates to a target and target assembly for use in cathode sputtering. Background of the Invention Cathode sputtering refers to a process wh involves the coating of a wafer mounted within a processing chamber. An applied electric field posi tively biases the wafer with respect to an opposite mounted, negatively biased target made of the mater to be sputtered. A backplate supports the target. Upon introduction of an inert gas into the chamber a low pressure, the applied electric field ionizes the gas. As a result, positive ions from the gas bombar the target to cause sputtering of the target materia onto the wafer. A magnet or electromagnet located behind the target provides a magnetic field above th wafer facing surface of the target to confine the io "plasma" adjacent to the target. The magnetic field increases the efficiency of the sputtering process. Some typical materials used in sputtering include aluminum, aluminum alloys, gold, silver, copper, titanium, platinum, titanium-tungsten, and refractory metal suicides. Due primarily to the high purity required for sputtering, the cost of these sputtering materials is generally quite expensive, on the order of about $100 per pound of material. For this reason, maximum target material utilization is a major consideration in the design of sputtering equipment. Another important consideration relates to the effective coverage of trenches or via features of the wafer, either by planarizing an uneven surface or by adding another step-like layer. Some sputtering equipment employs a variation of the magnetic field, or multiple, non-planar erosion zones, or both, to coat wafer features in the desired manner. In addition to maximum target utilization and effective coverage of a wafer surface, other practical considerations such as target mounting and cost of manufacture also play an important role in the design of sputtering equipment. While some target shapes may provide excellent step coverage or planar- ization, these advantages may be offset by the diffi¬ culty or cost associated with properly mounting the target to a backplate. For the most part, the machining of targets is difficult, expensive and time consuming. However, as a general rule, simpler shap are easier to produce. It is an object of this invention to provi a cathode sputtering target with high target materia utilization capability and which is relatively easy mount to a backplate. It is another object of the invention to provide a sputtering target assembly that promotes maximum target utilization and ease in mounting without producing a corresponding sacrifice in effec tive wafer coverage or excessive manufacturing costs. Summary of the Invention The invention contemplates a single piece target member adapted to be mounted to a target backplate with a predetermined mounting surface configuration, the member having a substantially continuously concave top surface and a bottom surface configured to conform to the predetermined mounting surface configuration of the backplate. The shape of the target facilitates mounting and promotes maximum target utilization. The target member bottom surface includes a relatively shallow, central, downwardly directed hub r that fits within -a central recess in the backplate. r\ Radially outwardly of the hub, the target member bottom surface includes at least three annular regions. In one preferred embodiment, the inner region, or region adjacent the hub, and the outer region, which lies adjacent a peripheral edge of t h e disc shaped target member, are both convex, while an intermediate region located therebetween is substan¬ tially flat. According to another preferred embodi¬ ment, the inner annular region is substantially concave, and the outer annular region is substantiall convex and the intermediate annular region is flat. The substantially continuously concave top surface provides sufficient versatility for achieving effective step coverage and planarization. The botto surface construction creates increased cross-sectiona thickness in portions of the target member where the highest concentration of sputtering occurs, or those portions that are eroded the most over the useful lif of the target, thereby providing excellent target material utilization. Additionally, all of the annular regions of the bottom surface assist in cen¬ tering the target member onto the backplate during mounting. On a relative scale, this target is easier to manufacture than many others. Overall, the shape promotes excellent target utilization and simplified mounting to a backplate, without sacrificing wafer coverage or requiring excessive production costs. • In addition to surfaces with a smooth, continuous curvature, the phrase "substantially continuously concave" also encompasses surfaces with series of discrete steps to produce the overall same effect. These and other features will be more readily understood in view of the following detailed description of the drawings. Brief Description of the Drawings Fig. 1 is a cross-sectional view along a diameter of a sputtering target member in accordance with a first preferred embodiment of the invention. Fig. 2 is a top plan view of the target member shown in Fig. 1. Fig. 3 is a cross-sectional view along a diameter of a sputtering target member in accordance with a further preferred embodiment of the invention. Fig. 4 is a top plan view of the target member shown in Fig. 3. Detailed Description of the Invention Fig. 1 shows a concavo-convex target member 10 mounted to a backplate 11 that forms part of a cathode assembly 12 for use in a sputtering machine (not shown) . The sputtering machine may be of the type shown in applicant's U.S. Patent No. 4,909,695, which is expressly incorporated by reference herein i its entirety. The sputtering machine includes a wafe • support (not shown) mounted to an anode above the target member 10, and a magnet assembly (not shown) located beneath the backplate 11. Central threads 15 in the bottom of the backplate 11 are sized to thread- ably connect to the cathode of the sputtering machine. The target member 10 includes a substantial¬ ly continuously concave top surface 17 and a bottom surface 18 that is bonded to the backplate 11. In one preferred embodiment designed to sputter coat 6" diameter wafers, the target member has a 10.00" diameter, and the top surface 17 has a preferable radius of curvature of about 67.00". The bottom surface 18 includes a central, relatively shallow, downwardly directed hub 21 and three annular regions located radially outwardly of the hub 21. An inner annular region 23 adjacent the hub 21 preferably has a radius of curvature of about 10.00". An outer annular region 25, located adjacent an edge 26 of the member 10, preferably has a lower radius of curvature, i.e., about 3.00". An intermediate region located there¬ between 27 is substantially flat. For a target member 10 with a diameter of 10.00 inches, the diameter of the hub 21 is preferably about 1.00 inch. An outer boundary 30 of inner region 23 has a diameter of about 2.00 inches, and an outer boundary 31 of intermediate region.2-7 has a diameter of about 8.00 inches. The target member 10 has a relatively uniform thickness of about 0.562 inches at the hub 21. ithin region 23, the thickness of the target member 10 tapers to a minimum, at boundary 30. The thicknes at the external edge 35 of the target member 10 is about 0.250 inches. The shapes and dimension of the top surface 17 and the bottom surface 18 provide an annular zone 37 which, generally, is thicker than the rest of the member 10, except for hub 21. Zone 37 is preferably located above the area of maximum magnetic field strength. Hub 21 and zone 37 promote maximum target utilization. Depending upon the location and configura¬ tion of the magnetic field producing means, the targe diameter, and the type of coverage desired, the relative diameters and the surface shapes of the annular regions of bottom surface 18 may be varied to move zone 37 either radially inwardly or outwardly. For instance, according to another preferre embodiment of the invention, as shown in Figs. 3 and 4, target member 110 includes a top surface 117 and a bottom surface 118 which has a hub 121 and annular regions 123, 124 and 125 located radially outwardly therefrom. Hub 121 is similar in shape and dimension to hub 21, shown in Fig. 1. Annular region 123 is substantially convex in shape and has an outer diame¬ ter of about 7.00". If desired, region 123 may ' be further broken down into an inner upwardly angled section (similar to region 23 of Figs. 1 and 2) , a iddle flat section and an outer, downwardly angled section. Regardless of the specific shape, region 123 represents a substantially concave portion of bottom surface 118 that is located between hub 121 and the next radially outwardly located region, region 124. Intermediate annular region 124 is substan¬ tially flat, extends beneath region 123 and has an outer diameter of about 9.00 inches. Region 124 lies in the same plane as hub 121, a plane that is located about 0.552" below the uppermost edge 127 of the member 110. Radially outward from region 124, an outer¬ most annular region 125 angles upwardly to a location about 0.140" below edge 127. If desired, the angle may be varied slightly, either upward or downward, or the region 125 may be slightly convex. Similarly, while region 124 is preferably flat, it may also be either slightly convex or slightly angled. Together, regions 124 and 125 represent a substantially convex outer annular section of bottom surface 118. Zone 137 comprises all the volume above region 124 and adja¬ cently residing portions of regions 123 and 125. Zone 137 represents an.annular portion of the target member 110 that is generally thicker than the other portions, other than the hub 121. The overall effect produced by increased thickness at zone 137 and at hub 121 is the improvement in target material utilization at these inner and outer portions of the target. For either embodiment, a different diamete target member would be used to coat a different diameter wafer. For instance, a 12" target would be used for an 8" wafer. For targets of different diameter, the hub diameter would remain the same whi the diameters of the annular regions would be reduce proportionately in the remaining areas located annu- larly outward of the hub, assuming that the magnetic field was either upscaled or downscaled proportionat ly to provide maximum strength at the same relative locations above the target. As shown in Figs. 1 and 3, for either embodiment, the backplate 11 has a predetermined mounting surface configuration, and the target membe bottom surface is configured to conform in shape to the predetermined mounting surface configuration of the backplate. This facilitates mounting and bonding of the target member 10 to the backplate 11 by the manufacturer. While a preferred embodiment of the inven¬ tion has been described, it is to be understood that the invention is not limited thereby and that in ligh of the present disclosure, various other alternative embodiments will be apparent to a person skilled in the art. Accordingly, it is to be understood that changes may be made without departing from the scope ■ of t h e invention as particularly set forth and claimed. I claim:

Claims: 1. A sputter target comprising: a member adapted to be mounted to a target backp the backplate having a predetermined mounting surface conf uration and the member having a substantially continuously concave top surface or a top surface comprised of a series steps to produce a substantially concave surface and a bot surface configured to conform to the predetermined mountin surface configuration of the backplate. 2. The target of claim 1 wherein the bottom surface includes a central, downwardly directed hub positionable i in a complementarily configured central opening in the backplate. 3. The target of claim 2 wherein the bottom surface includes three annular regions located radially outwardly the hub. 4. The target of claim 3 wherein the bottom surface includes an inner convex annular region, an outer convex annular region, and a substantially flat intermediate annu region located therebetween. 5. The target of claim 3 wherein an innermost annular reg is substantially concave and an intermediate and an outerm annular region are substantially convex. 6. The target of claim 5 wherein the intermedi ate annular region is substantially flat and the outermost annular region is substantially convex. 7. A sputter target comprising: a member adapted to be mounted to a target backplate, the member having a substantially continu¬ ously concave top surface and a bottom surface with a central, downwardly directed hub for centering the member on the backplate and a plurality of annular regions located radially outwardly of the hub, whereb the hub and annular regions define target portions of greater cross-sectional thickness in areas of maximum target erosion to promote maximum target utilization. 8. A sputter target assembly comprising: a backplate for supporting a target during sputtering, the backplate having a predetermined mounting surface configuration including a central recess; a member having a substantially continuously concave top surface and a bottom surface configured to conform to the predetermined mounting surface config¬ uration of the backplate, including a central, down¬ wardly directed hub sized to reside within.the recess of the backplate. g_ The target of claim 8 wherein the bottom surface of the member and the predetermined mounting surface configuration of the backplate further include a plurality of complementarily configured annular regions located radially outwardly of the hub and the recess, respectively.

Inventors: HURWITT STEVEN D, MARX DANIEL R, HURWITT, STEVEN, D., MARX, DANIEL, R.
Applicants: MATERIALS RESEARCH CORP, MATERIALS RESEARCH CORPORATION
Application year: 1991
Main classification: C23C14
IPC codes: C23C14, H01J37