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Usage of Conical Sputter Targets to Control Composition Homogeneities of Deposited Thin Layers Disclosure Number: IPCOM000014544D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2003-Jun-19
Document File: 2 page(s) / 44K

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  Usage of Conical Sputter Targets to Control Composition Homogeneities of Deposited Thin Layers


    Sputtered layers deposited from compounded targets tend to show compositional inhomogeneities, in particular if single substrate tools with circular sputter geometries are used. Here radial inhomogeneities originate from the rotational symmetry of the sputtering device in conjunction with emission characteristics being different for the different elements of the compound: to get radial thickness uniformity the mean racetrack radius of planar targets has to be larger than the mean substrate radius. The consequence is that the outer substrate edge gets primarily depositions from center emmisions, while the smaller substrate radii get more depositions from side emissions. Depending on the angular emission characteristics of the indiviual elements radial compositional inhomogeneities are generated. These inhomogeneities can be minimized by (magnetron) sputtering from concave conical targets. The cone angle offers another degree of freedom enabling the optimisation of layer thickness uniformity AND compositional homogeneity independantly of each other. Even nonuniformities to compensate for other radial effects can be created by purpose.

    Typical applications are for expample magnetic and magneto-optical storage layers. These are very sensitive to radial compositional inhomogeneities.

Application example

    Magnetic storage layers on thinfilm disks are magnetron sputtered using planar targets parallel to the substrate. The magnetic properties of those disks typically show radial gradients caused by layer nonuniformities. Radial coercivity ramps for example have been shown to originate from radially nonuniform Co/Pt ratios as generated by circular planar targets. The coercivity is known to be a strong function of the Co/Pt ratio. Geometric simulations demonsrtated that concave cone targets minimize or even can invert the radial Co/Pt ramps. For our alloys of typically Co(50-82%), Cr(8-25%), Pt(5-15%) and other small amounts of Ta, B, SiO2 or others (0.5-7 %) cone angles of
10...20 degrees...