A titanium target is the material used as the sputtering source that is bombarded by high-velocity charged particles. It is a primary raw material for producing thin films and is widely used in applications such as integrated circuits, flat panel displays, solar cells, recording media, and smart glass. Because the final film performance is highly dependent on source quality, titanium targets must meet stringent requirements for purity and stability.
Material purity: 99.90%
Relative density of material: 100%
Target shapes: circular target, rotating target, rectangular target, spliced target
Maximum sizes: Ø200 mm; Ø200 × 60 mm; 200 × 200 mm; 200 mm × 1000 mm
(1) Purity
Purity is one of the most important performance indicators for a target because impurities in the target strongly affect the performance of the deposited film. Practical purity requirements vary by application. For example, as the microelectronics industry has advanced and wafer sizes and circuit densities have grown, process tolerance has tightened: a target purity of 99.995% that was once sufficient for 0.35 μm IC processes may no longer meet the demands of finer line widths such as 0.25 μm, 0.18 μm or 0.13 μm. For these smaller geometries, target purities of 99.999% or even 99.9999% may be required.
(2) Impurity content
Impurities within the target solid, and oxygen and water vapor trapped in pores, are the main contamination sources for deposited films. Different target materials and end uses impose different constraints on specific impurities. For instance, aluminum and aluminum-alloy targets used in the semiconductor industry often have stringent limits on alkali metal content and radioactive elements.
(3) Density
To reduce porosity in the target body and improve the properties of the sputtered film, high density is usually required. Target density affects the sputtering rate as well as the electrical and optical characteristics of the deposited film. Higher target density generally translates to better film performance. Increasing the density and mechanical strength of the target also helps it withstand the thermal stresses experienced during sputtering. Density is therefore a key quality metric.
(4) Grain size and grain size distribution
Targets are typically polycrystalline, with grain sizes ranging from micrometers to millimeters. For the same material, targets with finer grains sputter at higher rates than those with coarse grains. In addition, films deposited from targets whose grain size distribution is uniform tend to have more even thickness. Smaller grain size differences across the target yield better thickness uniformity in the sputtered coating.
Main grades of titanium target
TA0, TA1, TA2, TA9, TA10, ZR2, ZR0, GR5, GR2, GR1, TC11, TC6, TC4, TC3, TC2, TC1.
Processes such as plastic deformation, heat treatment and control of grain orientation are designed according to downstream application requirements. Targets undergo repeated deformation and annealing cycles to precisely control grain structure and orientation, followed by welding, machining, cleaning and drying, vacuum packaging and other finishing steps. Target manufacturing spans many processes, requires high technical expertise and substantial equipment investment, and only a limited number of enterprises operate at large scale.
Primary manufacturing methods for target materials include melting and powder metallurgy. Melting techniques include vacuum induction melting, vacuum arc melting and vacuum electron beam melting. Melted ingots are mechanically processed into targets; targets produced this way typically have low impurity content, high density, can be made at large scale, and are free of internal pores. However, when component metals have very different melting points or densities, obtaining a uniformly alloyed target can be difficult. Powder metallurgy methods—such as hot isostatic pressing, hot pressing and cold pressing followed by sintering—mix and sinter powders to form the target. Powder metallurgy yields relatively uniform composition and good mechanical properties, but tends to produce higher oxygen content.
Hot isostatic pressing
Powder or preformed billets are sintered under equal pressure at 800–1400 °C and 100–2000 kgf/cm². Advantage: high density and good physical and mechanical properties. Drawback: high equipment cost, high production cost and higher oxygen content in products.
Hot pressing method
Powder is placed in a graphite or alumina mold, axially pressed at 100–1000 kgf/cm² and sintered at 1000–1600 °C. Advantage: lower required forming pressure, lower sintering temperature and shorter sintering time. Drawback: high oxygen content variability, uneven oxygen distribution, and limited ability to produce large-size targets.
Cold pressing and sintering method
Raw powders are mixed with binders and dispersants, pressed, degreased and then sintered at 1400–1600 °C. Advantage: low capital investment, low cost, high product density, lower oxygen content and capacity for larger sizes. Drawback: strong sensitivity to powder characteristics.
Vacuum induction melting
Metal is melted by eddy currents induced during electromagnetic induction. Advantage: targets without gas pores and minimal defects; low impurity content, high density and potential for large-scale production. Drawback: when component metals have very different melting points or densities, achieving a uniform alloy composition is difficult.
Vacuum arc melting
An electric arc is used to melt metals and alloys in vacuum.
Vacuum electron beam melting
In a high-vacuum chamber, an electron beam from a gun bombards the charge; the electrons’ kinetic energy converts to heat and melts the furnace charge.
Titanium targets are widely used for decorative coatings, wear-resistant coatings, and in the electronics industry for coating optical discs such as CDs and VCDs and various magnetic media. Tungsten-titanium (W–Ti) films and W–Ti-based alloy films are high-performance coatings that bring together the high melting point, high strength and low thermal expansion of tungsten with titanium’s properties. W–Ti alloys have low resistivity, good thermal stability and oxidation resistance. Many devices require metal wiring (for example, Al, Cu and Ag), but these metals can oxidize, react with their environment, adhere poorly to dielectrics, and diffuse into substrates like Si and SiO₂ to form compounds at relatively low temperatures—behaviors that degrade device performance. W–Ti alloys are effective diffusion barrier layers for wiring because of their stable thermomechanical properties, low electron mobility, high corrosion resistance and chemical stability, making them especially suitable for high-current and high-temperature environments.
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