The local texture in three types of patterned, thin-film, Al and AlCu interconnections on Si semiconductor devices is investigated by electron backscatter diffraction. Two types of standard planar metal structures were investigated: (1) blanket Al and (2) blanket Al–0.5 wt % Cu on TiN/Ti underlayers. Both were deposited on amorphous SiO2 substrates followed by reactive ion etching to define 0.45–10 μm wide lines and >10×10 μm2 pads. Damascene structures were also investigated in which Al–0.5 wt % Cu films were deposited into preformed Ti-lined amorphous SiO2 trenches, 0.3–5.0 μm wide by 0.4 μm deep, followed by chemical–mechanical polishing to remove the metal overburden. For these three types of structures, distinctly different behaviors were observed: the two planar metal samples exhibited either little change or a large increase in their (111) fiber texture strength with decreasing linewidth, while the damascene samples showed a marked decrease in the (111) fiber texture with decreasing linewidth and feature size. In addition, a novel trimodal (111) texture distribution was found in 0.3 μm wide damascene lines in which appreciable TiAl3 formed.
The microstructure was measured for AlCu lines, formed using either a traditional planar metal subtractive etch process or a newly developed hot AlCu-trench-damascene process. It was found that 0.35 μm wide damascene AlCu lines formed a large grained bamboo microstructure with little or no Al (111) texture. The local crystallographic texture was measured in a scanning electron microscope using electron backscatter pattern analysis often referred to as backscatter Kikuchi diffraction. Damascene structures consisted of AlCu films deposited at greater than 400 °C onto Ti or Ti/TiN into preformed amorphous SiO2 trenches, 0.3–5.0 μm wide by 0.4 μm deep, followed by aluminum chemical mechanical polishing to remove the metal overburden. Standard planar metal control samples consisted of blanket Al or AlCu films deposited onto either an amorphous SiO2 substrate or onto SiO2/Ti/TiN substrates, followed by subtractive etching to define 0.45–10 μm wide lines as well as large (e.g., 10×10 μm2) pads. The planar metal samples exhibited either little change or a slight strengthening of their (111) fiber texture with decreasing line width; this was in sharp contrast to the damascene films in which a marked weakening in the (111) fiber texture with decreasing line width was found. In addition a trimodal (111) texture distribution developed in trenches where TiAl3 intermetallic formed. The role of intermetallic formation (TiAl3), elevated (>400 °C) AlCu deposition temperature, large bamboo grain size, local AlCu crystallographic texture and differences in sidewall coverage between subtractive etched and trench-damascene processed AlCu on film microstructure are examined.
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