Sputtering is a technique used to produce a metallic layer in various manufacturing processes used in the semiconductor and the photoelectric industries. The properties of films formed during sputtering are related to the properties of the sputtering target itself, such as the size of the respective crystal grain and the formation of secondary phase with distribution characteristics. It is desirable to produce a sputter target that will provide film uniformity, minimal particle generation during sputtering, and the desired electrical properties.
Various sputtering techniques are used in order to effect the deposition of a film over the surface of a substrate. Deposited metal films, such as metal films on a flat panel display device, can be formed by a magnetron sputtering apparatus or other sputtering techniques. The magnetron sputtering apparatus induces plasma ions of a gas to bombard a target, causing surface atoms of the target material to be ejected and deposited as a film or layer on the surface of a substrate. Conventionally, a sputtering source in the form of a planar disc or rectangle is used as the target, and ejected atoms travel along a line-of-sight trajectory to deposit on top of a wafer whose deposition face is parallel to the erosion face of the target. Tubular-shaped sputtering targets can also be used, as described in co-pending application Ser. No. 10/931,203.
Sputtering targets may be desired which comprise materials or combinations of materials that cannot be made by conventional means such as rolling. In such cases, targets are made by hot isostatic pressing (HIP) powders. Ideally, the target is made in a single step. However, physical limitations of powder packing density and size of HIP equipment make it necessary to join smaller segments in order to produce large sputtering targets. For single-phase targets, conventional processing such as welding may be used; for multi-phase materials or where alloy formation is to be avoided for any reason, solid-state edge to edge bonding is preferred.
Interconnects in semiconductors and TFT-LCDs are evolving from aluminum and toward copper, thus new diffusion barriers are needed. Titanium provides excellent adhesion properties while the molybdenum contributes its dense barrier stability. Integrated circuits (for semiconductors and flat panel displays) use Mo—Ti as an underlayer or capping layer for aluminum, copper, and aluminum alloys to minimize hillocks formation, to control the reflectivity and provide protection from chemical attack during photolithography.
U.S. Pat. No. 5,234,487 describes methods of producing tungsten-titanium sputter targets with little or no β(Ti, W) alloy phase. U.S. Pat. No. 5,896,553 describes a titanium-tungsten sputter target which is substantially all single phase β(Ti, W). Neither patent discloses the use of other materials as substitutes for tungsten.
U.S. Patent Application Publication 20050189401 discloses a method of making a large Mo billet or bar for a sputtering target wherein two or more bodies comprising Mo are placed adjacent one another (e.g. stacked one on the other) with Mo powder metal present at gaps or joints between the adjacent bodies. The adjacent bodies are hot isostatically pressed to form a diffusion bond at each of the metal-to-Mo powder layer-to-metal joint between adjacent bodies to form a billet or bar that can be machined or otherwise formed to provide a large sputtering target. This patent publication discloses bonding of major side surfaces, not edge-to-edge bonding of plates.