Stresses in Cu Thin Films and Ag/Ni Multilayers - Harvard School of ...
Stresses in Cu Thin Films and Ag/Ni Multilayers - Harvard School of ...
Stresses in Cu Thin Films and Ag/Ni Multilayers - Harvard School of ...
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Chapter 2<br />
The Elastic Properties <strong>of</strong> <strong>Cu</strong> Th<strong>in</strong> <strong>Films</strong><br />
Us<strong>in</strong>g a tensile tester especially designed for free-st<strong>and</strong><strong>in</strong>g films, Huang [106] found<br />
that the Young moduli <strong>of</strong> electron beam evaporated films were about 20% lower than those<br />
calculated from the elastic constants found <strong>in</strong> the literature (such as those from L<strong>and</strong>olt-<br />
Börnste<strong>in</strong> [12], Simmons <strong>and</strong> Wang [207], or Hunt<strong>in</strong>gton [108]). Table 2.1 shows that this<br />
“deficit” is well documented <strong>and</strong> only observed <strong>in</strong> polycrystall<strong>in</strong>e films.<br />
A variety <strong>of</strong> reasons for this modulus deficit have been hypothesized. They <strong>in</strong>clude<br />
elastic anisotropy (from preferred orientation), porosity, gra<strong>in</strong> boundary compliance, gra<strong>in</strong><br />
boundary crack<strong>in</strong>g, reversible microplasticity, dislocation anelasticity, <strong>and</strong> gra<strong>in</strong> bound-<br />
ary slid<strong>in</strong>g [107]. We studied the orig<strong>in</strong> <strong>of</strong> the modulus deficit by measur<strong>in</strong>g the biaxial<br />
modulus <strong>of</strong> sputtered copper films on substrates us<strong>in</strong>g the wafer curvature method. Before<br />
discuss<strong>in</strong>g how the measurement is made, it is important to first underst<strong>and</strong> the stress-<br />
temperature pr<strong>of</strong>ile.<br />
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