Nanoindentating Mechanical Responses and Interfacial Adhesion Strength of Electrochemically Deposited Copper Film

Abstract

The nanomechanical responses and interface adhesion of electrochemically plated copper ͑Cu͒ film have been investigated for the evaluation of interconnect reliability. The hardness and elastic modulus of the Cu film were measured by nanoindentation test as about 2.1 and 120 GPa, respectively. A dislocation burst phenomenon was observed and revealed the initiation of plastic deformation of the Cu film. The converted true stress-strain curve provided a stress criterion of 9.3 GPa for the plastic yielding of the Cu film. Besides, the creep behavior was also analyzed under nanoindentation test and showed a power law expression with a creep stress exponent of about 22. Moreover, the interfacial adhesion strength and delamination behavior between the Cu film and silicon carbide ͑SiC͒ etch stop layer have been studied using a four-point bending test. During delamination, cracks irregularly propagated along the Cu/SiC interface with blocking by the ductile Cu film. The fracture energy release rate for the delamination of Cu/SiC interface was measured as around 2-10 J/m 2 , affected by SiC deposition condition and testing parameter.Copper ͑Cu͒ with low electrical resistivity and high thermal conductivity has been widely adopted as multilevel interconnects in ultralarge-scale integrated ͑ULSI͒ circuits to reduce the problem of serious resistance-capacitance delay. 1 Copper metallization, mainly performed by electrochemical plating, has the advantages of low processing temperature, low cost, high throughput, good quality, and gap-filling capability, thus becoming attractive in the generation of 90 nm semiconductor manufacturing. 1-5 However, mechanical damages of the Cu films, such as film deformation and interface delamination caused by thermal stresses, chemical-mechanical polishing, or even wire bonding during chip packaging, severely suppress the processing yield and application reliability of microelectronic devices. 6-10 Film deformation and interface delamination detrimentally affect the performance of integrated circuits ͑ICs͒, especially with increasing integration density of ICs and thus increasing the amount of layer interface in the interconnect structures. A high resistance of the Cu films to the mechanical damages is thus strongly demanded to fit the strict requirements of next-generation semiconductor manufacturing. The true mechanical properties of the Cu films, including film strength and interface adhesion, therefore need to be clarified for the evaluation of the reliability of multilevel interconnects.However, due to the limit of conventional measurement equipment, the mechanical properties of nanoscale Cu thin films used in finely patterned interconnect structures have not been well studied. Nanomechanical analyses are required for further investigation of the true mechanical responses and deformation mechanisms of these thin films. An instrumented nanoindentation test has been widely applied for measurement of the hardness and elastic modulus of thin films and provides reliable results. 11,12 However, o...

Grain size effect on nanomechanical properties and deformation behavior of copper under nanoindentation test

“…Under indentation, the four Cu specimens deformed elastically at the beginning stage and then elastoplastically at the late stage of loading, and only elastically during unloading. [23][24][25][26][27]31 The 700 600 500 400 300 200 100 400 300 200 None 200 100 None Grain size ͑nm͒ 40 100 20 500 14 300 12 300 501 266 140 4530 1560 560 43 25 16 10 STDV 5030 2640 2950 1520 55 56 18 532 352 73 19 11 9 8 Hardness ͑GPa͒ elastic and elastoplastic behaviors are discussed in detail in the following section. From the loading/unloading curves of nanoindentation tests and the Oliver-Pharr relation, [19][20][21] the hardnesses H and effective elastic moduli E * ͑the same as the reduced modulus used in contact mechanics 20,21 ͒ of the Cu specimens were obtained, as listed in Table I and plotted in Fig.…”

“…19,20 In addition to basic experimental data such as that for hardness and elastic modulus, true mechanical responses, including stress criteria and the onset of plasticity ͑dislocation burst phenomenon͒, have been also examined. [21][22][23][24][25][26][27] Furthermore, nanoindentation is a convenient and well-controlled method for introducing highly localized mechanical deformation into materials. 28 To determine how the microstructure changes around an indented region under ultrafine scale normal contact further facilitates effective examination of material deformation and defect nucleation.…”

Effect of microstructure on the nanomechanical properties of Zn1−xCdxSe alloys

“…The nanoindentation test has been applied widely [12][13][14] as a tool to measure the hardness H and elastic modulus E, from which the true flow stress and fracture toughness can be determined to provide representative mechanical characteristics of the films [15][16][17][18]. Beryllium-based [19,20] and manganese-based [21] II-VI alloys have found increasing commercial application because of their favorable internal properties (e.g., increasing in hardness and/or Young's modulus).…”

Mechanical properties and deformation behavior of amorphous nickel-phosphorous films measured by nanoindentation test

“…Actually, by using nanoindentation, much more information can be obtained through which critical shear stress and fracture toughness can be extracted to reveal more representative mechanical properties of the films. [20][21][22][23][24][25] Therefore in this study, the instrumented nanoindentation test is applied not only to measure the mechanical properties of the electroless plated Ni-P films, but also to calculate the critical shear strength and energy release rate required for the initiation of early-stage plastic yielding on a nanometer scale. The Ni-P films deposited under different solution pH values are investigated to clarify the effect of P content on mechanical properties.…”