摘要:

Electromigration performance of vias filled with Al-Si-Cu alloys on Ti glue layers was investigated in comparison with W-stud vias. In Al-Si-Cu filled vias, voids were formed at only a few locations in the test structure, while voids were formed at every via in W-stud via chains. It is supposed that Al moves through the Al-Si-Cu via during electromigration in spite of the existence of a glue layer at the via bottom. This phenomenon was observed only in the vias filled with Al-Si-Cu alloy. Al movement was prohibited in Al-Cu filled vias. In Al-Si-Cu filled vias, an Al-Ti-Si alloy was formed at the via bottom whileAl3Tiwas formed at Al-Cu filled vias. Al is speculated to move through this Al-Ti-Si alloy during electromigration. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54678

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electromigration void behavior in Al-0.1&percent;Sc and Al-0.5&percent;Cu alloys was compared by conducting tests in a High Voltage Scanning Electron Microscope (HVSEM). Wafer level test results showed that the median time to failure for the Al-Cu lines was ten times longer than that of the Al-Sc lines.In-situtests of the two alloys showed a similarity in void nucleation times but differences in void movement between the two sample sets; the interactions of voids withAl2Cutheta precipitates in Al-Cu lines were especially interesting. From our studies, it appeared that the addition of scandium to Al does not have the proposed benefits for electromigration resistance, as suggested by previous studies. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54632

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In this work, we have applied an overlying and underlying oxide layer interfaced with metal interconnection line for stress accommodation, which can lead to retardation of Al atom divergence. It is understood that the major reason for the improvement of electromigration lifetime is due to the tensile stress of overlying oxide acted as a counteractive force on the intrinsic tensile stress of Al interconnection line. In case of underlying oxide, the lower surface tension of oxide improves the wetting of metal deposits and it allows the metal grains to grow into larger sizes revealed by a focused ion beam (FIB) image. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54633

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electromigration in isolated 0.25 &mgr;m to 1.0 &mgr;m wide pure Cu fine lines on W has been investigated using both resistance and edge displacement techniques in the sample temperature range 221 °C–394 °C. The microstructures of the 1, 0.5 and 0.25 &mgr;m wide lines were polycrystalline, near-bamboo, and bamboo-like, respectively. The failure lifetimes were correlated to the sizes of voids formed in the vicinity of the cathode end of the line. The electromigration activation energy in bamboo-like Cu grain structure was found to be0.81±0.05 eVand the failure lifetime decreased as the metal linewidth decreased. These results suggest that mass transport of Cu during electromigration primarily occurs along the surfaces of the lines. The factor ofn,the current density dependencej−n,was found to range from 1 to 2 which depended on the magnitude of the current density. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54634

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Radioactive tracer diffusion data is presented which illustrates some of the more interesting questions that need to be further understood. For example, in Al, Cu and Au alloys, solute decreases the activation energy,Ql,for lattice diffusion while increasingQbfor boundary diffusion in the same test samples. Secondly, this is true only for diffusion in the alloy itself; for example,Qbfor Cu in pure Al boundaries is 0.4 eV while for Cu in All&percent;Cu alloy boundaries is 0.73 eV. Also, forQb,Sn in pure Cu is 0.8 eV, Cu in pure Cu is 0.92 eV, but in the Cu2&percent;Sn alloy Sn is 1.2 eV and Cu 1.39 eV quite substantial changes. Of note is the observation that solute atomic size does not appear to be the deciding feature. The systems selected for study represent smaller, larger and similar solute size for Cu in Al, Sn in Cu and Ta in Au, respectively. Preliminary work has been accomplished on measuring the electron energy loss (EELS) of Cu in Al2&percent;Cu grain boundaries, specifically to observe the electronic structure of Cu atoms in the boundaries. The data is consistent with a model including hybridization of Cu3dwith Cu, Als-states. The CuL2,3transition is similar, but not identical to that of Cu measured in a &THgr; phase particle. It is proposed that the increase in cohesive energy in the boundary produced by the hybridization has direct impact on diffusion energy. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54682

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electromigration induced resistance changes in short Al lines have been studied by high-resolution AC bridge measurements. The samples were pure, unpassivated Al lines having a length of 3, 5, 8, 12, 17 or 100 &mgr;m, a width of 2 &mgr;m and a film thickness of∼100 nm.Depending on current density and sample length the induced resistance changes fully recover or do not recover after removal of the DC stressing current. The transition from recoverable to non-recoverable behavior is clear-cut and is characterized by a constant critical current density—sample length product. Inspection of the lines after current stressing by atomic force microscopy revealed that non-recoverable resistance changes are caused by the growth of asinglevoid, hillock or hillock/void pair. Negative resistance changes correspond to the growth of a hillock and positive resistance changes to the growth of a void. The characteristic time of the relaxation process of the recoverable resistance changes scales with the sample length squared. The recoverable resistance changes are caused by the evolution of mechanical stress in the line during electromigration. A very good agreement is obtained between the observations and solutions of the stress evolution equation of Korhonen &etal; for a one-dimensional model consisting of a concatenation of grain boundary segments. The evolution of the stress is reflected in changes of the resistance by the piezoresistance effect. It is shown that the diffusion coefficient of the prevailing transport process can be determined from the characteristic time of the relaxation process. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54635

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In this paper, we propose a new model for alloying effects on electromigration in thin conductor lines. The mechanism considered is the action of material sinks and sources, modeled as a dislocation climb process. Mathematical expressions for the drift velocity and the stress evolution are derived and compared with experimental results on “Blech structures.” The agreement suggests that alloying elements may affect the electromigration behavior through their influence on dislocation mobility. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54636

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Void formation at the no current stressed area of Al interconnect was investigated by a modified Blech patterns which consisted of no current stressed area at the bending point. At the low current density conditions, a single void was formed at the end of no current stressed area (type A). With an increase in the current density, voids were formed near the boundary between the current stressed and the no stressed areas (type B). With the further increase in the current density, voids of type B extended into the no current stressed area (type C). One dimensional analysis of drift diffusion equation of vacancies suggested that vacancy concentration had the maximum at the boundary between the current stressed and the no current stressed areas. This was supported by the current reversal experiment in which a hillock was formed at the boundary. Type B void was formed by the accumulation of a huge number of vacancies at the boundary. On the other hand, type A void is considered to be formed by coalescence of small voids which were transported from the boundary by the vacancy concentration gradient. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54638

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We observed the erosion of &thgr;-phaseAl2Cuprecipitates and the growth of voids under electromigration (EM) stress (0.5–2 MA/cm2and 200–225 °C) in Al-2wt &percent;Cu lines using in-situ side-view TEM in conjunction with standard SEM. The sub-micron wide (0.5 to 0.8 &mgr;m) bamboo Al-Cu lines were on a TiN underlayer in a drift velocity measurement structure. Precipitates that were downstream of a sufficient Al source eroded without adjacent voiding, but precipitates without a sufficient source of Al, i.e., large ones near the cathode end, eroded and left voids. We discuss factors affecting the voiding that occurs before complete removal of Cu from the cathode end, including a stress model in which the end grain in a bamboo line is unable to withstand the tensile stress created by a shrinking precipitate. The results of these experiments indicate that for narrow, bamboo lines, largeAl2Cuprecipitates near the cathode are not very effective in delaying voiding. Furthermore, the voids did not necessarily form and/or grow at the very ends of the lines, rather, slightly downstream. The drift velocities seemed to be independent of the location, size, or existence of cathode-end precipitates and exhibited three different rate regimes. The near-steady-state drift velocity of 5.7 nm/hr at 200 °C andj=2 MA/cm2was comparable to those in the literature for bamboo lines. The variability in voiding location and the existence of different drift stages should be considered in EM reliability predictions for via structures. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54639

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Detailed statistical data of stress- and electromigration-induced void formation and growth inpassivatedAl-lines have been evaluated from in-situ TEM experiments for the first time. Experimental parameters such as grain size (0.5 &mgr;m to more than 3 &mgr;m, i.e. nearly perfect bamboo structure in the lines), relaxation time (0.1 to 20 h) and temperature (20–300 °C) and electromigration current density (without current up to∼2 MA/cm2) were varied. Some important results are: Void nucleation takes place exclusively at the passivation side walls in a very narrow temperature range about 50 °C below the annealing temperatureTA(450 °C–550 °C) on cooling. The growth rate of the relative total void volume in the lines is very dependent on time and temperature during isothermal relaxation consistent with previous data evaluated from macroscopic stress and strain measurements. Although nearly all pre-existing voids change their shape and/or position during an electromigration test the number of voids and their total volume is maintained in excellent agreement with recent X-ray measurementsduringelectromigration testing showing no changes in average strain or stress in the lines. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54640

出版商:AIP    

年代:1998

数据来源: AIP