Técnicas e Instrumentos de Recolección de Datos

The Gilgamesh system, as seen in Figure 11a), combinatorially sputtered three guns (US Gun II, US Inc., San Jose, Ca) with 2” targets placed in a triangular arrangement on-axis to a 3” substrate holder. The distance from the center of each target to the center of the substrate was 2.5” in the plane of the substrate and ~1.5”

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perpendicular to this plane. Base pressure were at least 2 microtorrs and sputtering pressures of Ar usually 10 millitorrs. For underlayer and single-layer deposition, two other guns were employed. A 4th gun of similar make was located 60° clockwise of this flange and a 5th S-gun (Sputtered Films, Inc. Santa Barbara, CA), which utilized ring-like targets, was 120° counter-clockwise of the flange. Both the 4th and 5th gun were ~5” from the substrate holder to ensure as uniform a film thickness as possible. All guns were water-cooled. Four dc power supplies, one connected to each gun, could control the power, current, and voltage to each gun. In most cases, current was adjusted to change the sputtering rate.

The substrate holder was suspended from the lid and had 4 sides at right angles to each other. Two of the sites held slots for 3” wafer placement so that they would be directly facing the guns. Halogen bulbs could radiatively heat these substrates up to 700°C with the temperature monitored by type-K thermocouples. Most of the films were hot-sputtered at 500°C to reach thermodynamic equilibrium on the surface and in the bulk before cooling down. The cool-down time to a removal temperature of 50°C was approximately 2-3 hours. A third site held a quartz-crystal monitor (QCM) fixed in a position corresponding to the middle of a 3” wafer when placed in one of the substrate holders. By sensing the change in mass depositing on the crystal through detecting changes in its resonant frequency vibrations, the QCM could give a real-time reading of the sputter rate. This was used to adjust the sputtering rates of each gun in the same pumpdown as the deposition. The 4th site had a DC motor attached to an un- heated substrate holder for constant composition sputtering from multiple guns.

The 3-gun arrangement was the workhorse of the system, depositing films that covered at least 60% of the composition space of a ternary diagram. As mentioned before, each gun was centered 2.5” off the center of the substrate. When sputtered separately, each would deposit a film whose rate of deposition decreased the farther

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away from the gun. This decreasing rate could be fit to a decaying exponential of form y = A*exp(-R/d), where A and d were constants related to sputtering conditions and R the distance from the center of the target in the plane of the substrate. A sample plot for Pd, with a desired rate of 0.5 Å/s in the middle of the substrate, is shown in Figure 12a). The rate often decreases towards the edge of each the substrate closest to the gun due to a combination of shadowing from the substrate holder and a temporary node from the ‘racetrack’ configuration of sputtering on the target. However, areas this near the edge were not used in testing and disregarded. As follows from this simple modeling, the rate translated to a 2-D fit would be:

Rategun(x, y) ~ A*exp(-√[(x – xc)2 + (y – yc)2]/d) (2.1)

where xc and yc were the coordinates of the center of each gun. Geometrically, one

could think of a sputtering cone of exponential slant perpendicular to the substrate plane. Its intersection would produce exponentially decaying rates in a circular pattern centered around each target in the plane of the substrate, as demonstrated by Figure 12b). Of course, the decay of these rates was not identical for each deposition. They varied according to the atoms in each target, current and voltage used, pressure of the Ar gas, and so forth. In addition, re-sputtering from Ar reflecting off heavier targets before knocking off atoms on the substrate has been known to decrease the experimental rate of loosely bound atoms [58].

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Figure 12. Pd Deposition rate in Gilgamesh system from one of the US Guns for a QCM-predicted rate of 0.5 A/s and current of 60 mA in the middle of the wafer. In a), the rate is compared vs. a direct line from the target. A ~ 27.4 Å/s and d ~ 13.6 mm. The highlighted area is either off of the 3" wafer or an edge region that is not used in testing or characterization. In b), this thickness is generalizaed to the 2D wafer surface (borders in black) from the bottom gun in the ternary setup. Since this involves on-axis sputtering, the rate can be approximated as coming from a point source cone perpendicular to the substrate intersecting its plane in circular rate contours.

Figure 13. W Deposition rate in Fenris system from one of the US Guns for a QCM- predicted rate of 1 A/s in the middle. In a), the rate is compared vs. a direct line from the target. A ~ 7.94 Å/s and d ~ 30.3 mm. In b), this rate is generalizaed to the 2D wafer surface (borders in black) from the bottom gun in the ternary setup. Since this involves off-axis sputtering, the rate can be approximated as coming from a point source cone parallel to the substrate intersecting it in elliptical rate contours with c, or the added factor to the axis perpendicular to the target, hovering around 0.8.

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