Economical Sputtering System To Produce Large-Size Composition-Spread Libraries Having Linear and Orthogonal Stoichiometry Variations

A multitarget sputtering machine with a water-cooled rotating substrate table has been modified to produce films on 75 mm × 75 mm wafers which map large portions of ternary phase diagrams. The system is unconventional because the stoichiometries of the elements sputtered on the wafer vary linearly with position and in an orthogonal manner. Subsequent screening of film properties is therefore quite intuitive, since the compositional variations are simple. Depositions are made under continuous rotation, so either intimate mixing of the elements (fast rotation) or artificial layered structures (slow rotation) can be produced. Rotating subtables mounted on the main rotating table hold the 75 mm × 75 mm substrates. Stationary mask openings over the targets and mechanical actuators that rotate the subtables in a precise manner accomplish the linear and orthogonal stoichiometry variations. Deposition of a film spanning the range SiSn x Al y (0 < x, y < 1), with Sn content increasing parallel to one edge on the wafer and Al content increasing in a perpendicular direction, is given to illustrate the effectiveness of the method. Since the system was easily and inexpensively built, it has enabled our research program in combinatorial materials synthesis to begin without large scale funding.