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New Methods—Experimental and Theoretical—To Control Thin Film Properties for Target Fabrication

R.W. Springer, B.J. Cameron, G.A. Reeves

Fusion Science and Technology / Volume 31 / Number 4 / Pages 449-455

July 1997

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A new ion beam technology has been developed which allows the specific control of a number of material parameters not previously or easily controlled during thin film fabrication. The new device is a modified Kaufman ion source. The principal differences are in the design of the grids, and the fact that the gun has an open bottom structure. An additional grid has been added on the bottom to contain the plasma and force the gun to be “unidirectional.” The gun operates by forming an electron driven plasma in the center, while allowing evaporated material to pass through this plasma. When the material moves through the plasma, it may also be ionized by the Penning process, or by electron impact. The voltage of the plasma, referenced to the substrate, may be adjusted from ∼100 volts to ∼1000 volts. As the ionized plasma and deposit leave the chamber, they pass by a hot filament which provides electrons to create a charge neutral beam. Thus both insulating and conducting materials may be deposited on both insulating and conducting substrates. Another important property that can be controlled using the FTIG is the orientation of the crystal structure. Films of MgO and YSZ have been deposited in an oriented state. These cubic structures can be “forced” to a preferred 111, 220, 200, or random orientation, depending on the rate of deposit and gun voltage. A practical example of a solved problem using new modeling techniques and the Flow Through Ion Gun (FTIG) is described. The problem is to apply a platinum coating to aluminum which forms an oxide and makes film adhesion difficult with noble metals. The FTIG was used to pre-clean the inside surface, and subsequently deposit gold. Due to the aspect ratio of the cylinder, two cleaning and deposit cycles were required. Platinum distributions from an electron beam gun were used to compute a thickness uniformity on the inside of the cylinder. The uniformity was computed and measured to be ∼10% from end to end. The film microstructure was compared with thin film ballistic computations using SIMBAD, and the agreement found to be excellent.

 
 
 
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