Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/34—Sputtering
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/34—Gas-filled discharge tubes operating with cathodic sputtering
  • H01J37/3411—Constructional aspects of the reactor
  • H01J37/3414—Targets
  • H01J37/3423—Shape
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/34—Sputtering
  • C23C14/3407—Cathode assembly for sputtering apparatus, e.g. Target

Definitions

• This invention relates to extended life sputtering targets and a method for using these extended life sputtering targets.
• Sputtering is a process that coats semiconductor wafers or other substrates within inert- gas-filled processing chambers. These chambers contain sputtering targets and an electrically biased wafer adjacent the sputtering target. An electric field within the chambers ionizes the inert gas and dislodges atoms from the target to deposit sputter target material on the wafer.
• processing chambers may contain magnetrons that generate annular groove patterns in portions of the sputtering targets. Unfortunately, these grooves can dramatically shorten a sputtering targets' life. Furthermore, the adverse effect of these grooves tends to become exaggerated for targets having increased diameters .
• a ring-enhanced design has proven effective for sputtering layers used to ' construct memory chips. Since memory chips typically contain only two metal layers, film uniformity is not critical for these memory applications. Unlike memory chip applications, logic chip applications often reguire greater film uniformity. Unfortunately, targets containing ring-enhanced designs fail to produce the stringent film uniformity required for some logic applications. This may result from the increased number of layers deposited or the device design rules. Furthermore, since there are more metal layers in logic applications, poor uniformity becomes accentuated with each succeeding layer when a manufacturer skips chemical mechanical polishing (CMP) of the deposited layers. As the stacked film uniformity decreases, photolithography on the upper layers becomes more difficult.
• CMP chemical mechanical polishing
• Film uniformity is also important from a device fabrication standpoint. There is often some degree of over-etch when etching the device. If the etching is greatest in the wafer's center and the film is thinner in the center, then there is an increased possibility of device yield loss. [0006] Furthermore, a lack of uniformity has a pronounced effect on film thickness and sheet resistance uniformity for large targets, such as those having a diameter in excess of 250 mm. In these large diameter targets, the rings can have a negative impact upon a target's useful life. As far as known, none of these ring-enhanced designs has received commercial acceptance for stringent device applications due to the above uniformity issue or other sputtering-induced defects .
• the sputtering target has a design for uniformly depositing a material on a substrate.
• the target contains a circular disk; and the disk has a radius and a top surface.
• the top surface has a center region within the inner half of the radius, an outer ring-shaped region within the outer half of the radius and a base region separating the center region from the ring-shaped region.
• the outer ring-shaped region has a projection height for extending the life of the sputtering target.
• the center region has a projection height of less than the projection height of the outer ring-shaped region for increasing the sputtering deposition rate on the substrate adjacent the center region.
• the method sputters a material on a substrate with a sputtering target or cathode.
• First ionizing an inert gas adjacent a cathode in a sputtering chamber prepares the chamber for sputtering.
• the cathode has an initial wafer to cathode spacing and a second wafer to cathode spacing for uniform sputtering.
• the second wafer to cathode spacing is greater than the initial wafer to cathode spacing.
• Dislodging atoms from the cathode with a rotating magnetron deposits a coating on the wafer using the initial wafer to cathode spacing.
• the initial spacing optimizes sputtering deposition uniformity for an initial period of time.
• the second wafer to cathode spacing optimizes sputtering deposition uniformity during a second period of time.
• Figure 1A is a top view of a sputtering target containing a disk-shaped center region.
• Figure IB is a cross section of the sputtering target of Figure 1A taken along line 1-1.
• Figure 2A is a top view of a sputtering target containing a ring-shaped center region.
• Figure 2B is a cross section of the sputtering target of Figure 2A taken along line 2-2.
• Figure 3 is a schematic drawing that illustrates locations for measuring wafer film thickness .
• Figure 4 illustrates the improved uniformity achieved with the center region design.
• Targets containing a raised outer ring and a lesser-raised inner region have resulted in improved sputter uniformity.
• This target has successfully performed with a conventional sputtering system and exhibits low sheet resistance (Rs) at the center of the wafer.
• Sheet resistance is an indirect method for comparing deposit thickness at several locations by measuring resistance to electrical flow.
• the target advantageously has an initial optimal wafer to cathode spacing for uniform sputtering and a second wafer to cathode spacing for uniform sputtering. The second wafer to cathode spacing is greater than the initial wafer to cathode spacing.
• This shift in optimal wafer to cathode spacing advantageously occurs after sputtering at least about thirty percent of the cathode' s life to further improve performance. Most advantageously, the shift occurs after sputtering at least about forty percent of the cathode's life.
• the exact distance of the initial and second location for optimum sputtering before and after the shift tends to vary from machine to machine.
• the target 10 contains a base region 12, a disk-shaped center region 14 and an outer ring-shaped region 16.
• ring-shaped region 16 extends upwardly adjacent an outer edge region 18 and outer edge 20.
• the outer edge region 18 has a thickness equal to the thickness of the base region 14.
• the ring-shaped region 16 can extend outwardly to the outer edge 20.
• the target 10 has a radius R extending from the center 25 to the outer edge 20.
• the inner half of the radius contains the center region 14 and the outer half of the radius contains the ring-shaped region 16.
• the center region 14 is within about the inner thirty-five percent of the radial distance from the center 25 and the outer edge 20 and most advantageously within about the inner thirty percent.
• the outer ring-shaped region 16 is most advantageously between seventy and ninety-five percent of the radial distance from the center 25 and the outer edge 20.
• Center regions formed with a solid disk-like projection of uniform height have proven effective.
• tapered regions 22 located between the base region 12 and the center region 14 and between the base region 12 and the ring-shaped region 16 serve to level- out sputtering in areas prone to non-uniform sputtering.
• flange 26 containing threaded openings 28 facilitates fastening of the sputtering target within a sputtering chamber.
• Figure IB illustrates the difference in projection height between the outer ring-shaped region 16 and the center region 14. The projection height is a measure of the difference in thickness between the base region 12 and the center region 14 or the outer ring-shaped region 16.
• the center region 14 has a projection height of at least less than about 20 percent of the outer ring-shaped region 16. For example, if the outer region 16 had a height of 5 mm, the center region 14 would have a height of 4 mm or less.
• the center region 14 has a projection height that has a projection height of about 20 to 80 percent of the outer region's projection height.
• FIGS. 2A and 2B illustrate an optional embodiment where the center region 14 includes a disk- shaped projection 30.
• the disk- shaped projection 30 contains a dimpled region 32.
• the dimpled region 32 has a thickness less than, equal to or greater than the base region 32.
• the dimpled region 32 has a thickness equal to the base region 12.
• the dimpled region 32 may have a circular, star-pattern or other symmetrical or semi-symmetrical shape.
• the dimpled region 32 has a symmetrical shape, such as the illustrated cylindrical shape. Comparative Example
• a partially spent 300 mm diameter AlCu (0.5%) target having two-concentric projecting rings (4 mm height) produced film thickness uniformity out of a narrow specification after approximately 800 kwh of sputtering with an Endura System using an A- Type magnet (target installed in chamber 4 and a standard set of shields)—this system also provided the sputtering device for the Example below.
• the system's magnetron contains several magnets that spin about an axis to generate a more uniform field. Unfortunately, the spinning magnetron produces higher sheet resistance values at the center of the wafer than on the outside diameter (6 mm from edge)—see Figure 3. This indicated a lower film thickness in the center of the wafer as compared to the outer area of the wafer.
• Table 1 measures Rs uniformity - (Percent 1 Sigma or one standard deviation) for a 200 mm oxide wafer at 49 sites using a 6 mm edge exclusion. Table 1
• Table 1 illustrates an unexpected shift in optimum wafer to cathode spacing resulting from reducing the inner ring height.
• the modified center design improved Rs uniformity.
• Table 2 data originate from operating the Endura system for 60 seconds at 10.6 kw, with an 18 seem chamber/15 seem backing plate flow of argon at a temperature of 300°C with a wafer to cathode spacing of 52 mm and a chamber pressure of 2 milliTorr.
• Delta measures the maximum difference in thickness (A) between the center reading and any of the four outside diameter readings top, left, bottom and right at locations near the outside diameter in accordance with Figure 3 (Standard Five-Point Test) . Testing at a greater number of sites tends to lower the standard deviation or sigma value. Therefore, since the Standard Five-Point Test tests at only five sites, it is much more stringent than alternative tests that measure thickness at several locations.
• Depositing approximately 1 micron films onto 200 mm thermal oxide wafers provided a basis for measuring targets' performance. Standard process conditions were used for the evaluation as follows :
• Rs uniformity was measured at 49 sites on the 200 mm wafers using a 4D automated 4 point probe. A 6 mm edge exclusion was used. The film thicknesses were measured at 5 location on each wafer in accordance with the Standard Five-Point Test. The initial testing was completed at 3, 7 and 15 kwh for Rs Uniformity (Table 3) and 3, 5, 7, 9, 12 and 15 kwh intervals for film thickness (Table 4). The film thickness and Rs Uniformity measurements were made at a standard wafer to cathode spacing of 52 mm. In addition, tests completed at 100, to 1400 kwh relied upon varied wafer to cathode distances (44 to 53 mm) to locate the optimum spacing for the deposition of low Rs uniformity films .
• Table 3 shows the Rs uniformity results for the target with different wafer to cathode spacings .
• Table 4 illustrates the uniformity in film thickness achieved with a wafer to cathode spacing of 52 mm.
• the data of Table 5 and Figure 4 illustrate a two-part method for optimizing sheet resistance or Rs uniformity.
• the optimal wafer to cathode spacing shifts inward in comparison to planar targets to 46 mm.
• the spacing increases to 52 mm.
• This shift enables sputtering manufacturers to maintain Rs uniformity at a level less than about 1.5 percent one sigma and a maximum delta thickness of about 250 A for the Standard Five Point Test. Most advantageously, it maintains Rs uniformity at a level less than about 1.3 percent one sigma.
• Table 6 provides film thickness data for various 200 mm Al/Cu.5% targets, measured at 100 kwh with optimum wafer to cathode ( /C) spacings. Table 6
• Targets containing a raised outer ring and a lesser-raised inner region facilitate improved sputter uniformity.
• This target has been successfully sputtered in a conventional sputtering system to produce high uniformity deposits.
• the target is particularly effective for aluminum and aluminum alloy sputter target designs.
• the target coats substrates with a maximum of about 1.5 percent sigma sheet resistance uniformity.
• it has a life of at least 1000 kwh in a spinning magnetron sputtering chamber using a type A magnet.
• the target has a life of at least 1200 kwh and has successfully tested to a life of at least 1400 kwh.

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