摘要:

Using the concepts of linear elasticity the volume averaged stresses of an array of parallel metallic interconnects embedded in a passivation layer on a flat substrate are analysed. The calculation takes advantage of the proper boundary conditions and refers to lines with aspect ratio 1. Equations are derived which connect the volume averaged stresses in the metal and in the passivation to the so-called eigen-strains of the metal. These eigen-strains characterize the true (stress free) thermal strains and plastic deformation strains of the metal, thought to be not constrained by the surrounding passivation. The coefficients entering into these equations are determined from finite element calculations performed for various geometries and elastic properties of the passivation layer. Choosing the proper values of these coefficients allows the eigen-strains to be determined without further assumptions from experimentally measured metal X-ray stresses and from wafer curvature stresses. In this way a model independent judgement of the extent of voiding and/or plastic shear deformation of metal lines subjected to thermal stressing under a passivation layer can be obtained from experimental data. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50940

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The stresses induced in 1.2 &mgr;m thick Au films and lines during thermal cycling between room temperature (RT) and 450 °C have been investigated by X-ray diffraction methods. The biaxial or uniaxial stresses of films and lines varied between typically 200 MPa tensile stress at RT and 50 MPa compressive stress at 400 °C. The passivated lines show large tri-axial stresses varying between 450 MPa tensile stress at RT and≈300 MPacompressive stress at 400 °C. In contrast to the unpassivated lines a nearly elastic behaviour is observed during thermal cycling; the observed thermal stresses are in agreement with the expectations from the Eshelby theory. Details of the stress distribution are discussed in comparison to published results for Al. Special emphasis is given to specific differences to Al, which seem to be very advantageous for future applications of Au interconnects in addition to the superior electromigration resistence. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50929

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Plastic deformation in sub-micron wide Al-1&percent;Cu interconnects was studiedin situusing a straining device in the transmission electron microscope. Dislocation motion occurred readily in unpassivated lines but was non-existent in passivated lines due to the presence of encapsulating sidewalls. Instead, heterogeneous void nucleation occurred on straining to a critical limit. The void morphology was always near-hemispherical and the nucleation always took place at the line edges. Further stretching of the lines led to a rupture of the sidewalls away from the lines, resulting in immediate dislocation motion. Based on the configuration and motion of dislocations observed in these lines, a theoretical model is presented that predicts the critical resolved shear stress and the yield stress of a passivated Al line with columnar, bamboo grains. In arriving at the energy of the dislocation strain field due to a dislocation loop, use was made of the image forces on the dislocation segments due to the presence of four interfaces (that due to the substrate, the substrate oxide, the passivation, and the free interface). It is shown that the linewidth, the line thickness, and the grain orientation define the yield stress of these lines. The yield stress is predicted to increase with decreasing linewidth and line thickness. Passivation stiffness is predicted to play a stronger role than the passivation thickness in determining the yield stress of these lines. Orientation analysis performed on several wedge-shaped voids which had grown in the course of resistometric experiments, indicated that the void facets were bound by low energy planes and that the voids predominantly occurred in non-⟨111⟩ oriented grains. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50936

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Relaxation of thermally induced stresses in passivated line structures can lead to void formation, and it is strongly correlated with microstructural change in the lines. In this study bending beam technique has been used to measure the thermal stress relaxation behavior of passivated Al(1 wt. &percent; Cu) line structures with 3, 1, and 0.5 &mgr;m linewidths. Also the effect of microstructure on the stress relaxation behavior has been examined. Our data indicate that stress relaxation in Al(Cu) lines depends on line geometry and exhibits log(time) kinetics, consistent with a thermally activated dislocation glide mechanism. SEM and TEM techniques have been used to study stress-induced voiding as a function of aging time and temperature. One micron wide lines show most voiding and correlates well with stress relaxation data, whereas 0.5 &mgr;m wide lines show less voiding and correlation with stress relaxation data. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50937

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Measurement of stress-induced void growth in submicron TiN/Al-0.5(wt)&percent;Cu-1(wt)&percent;Si/500 Å Ti metal lines 0.36, 0.40, 0.48 and 0.72 &mgr;m wide, at temperatures of 150 °C and 225 °C is reported. Void growth is correlated with measured resistance increases over time, and calibrated by comparison of final resistance changes with void sizes observed by scanning electron microscopy. Resistance measurements agree well with void growth caused by diffusive mass transport. Saturation in void growth corresponds generally to void spacing and interaction, but can also be affected by the position of Cu precipitates which extend completely across the line. A value for Al diffusivity is obtained from resistance shifts due to a single void. Considerable across-wafer variation occurred and is discussed. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50938

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effects of thermally cycling Al-Si-Cu VLSI metallization down to−196 °Chave been studied in unpatterned and patterned films with and without surface passivation using wafer curvature and x-ray diffraction techniques. Both passivated and unpassivated unpatterned metallization showed development of compressive stresses in the thin film after cooling to−196 °Cand warming to 22 °C. This was attributed to plastic deformation at−196 °Cleading to a reversal of stress from tensile to compressive upon warming to room temperature. The relaxation of this compressive stress was characterized at room temperature immediately after warming from−196 °Cand after cooling from anneals between 50 °C and 250 °C. The stress in patterned (1 to 2 &mgr;m line widths) thin films with passivation remained tensile, and this was attributed to a reduction in grain boundary area and inhibition of grain boundary diffusion. Therefore, the tensile stress was maintained even after thermal cycling several times between−196 °Cand 22 °C. Higher stress levels were observed on smaller line widths, and lower tensile stresses were observed on metal lines that exhibited stress voids. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50939

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Stress concentrations under W via plugs in a multilevel metal process have been calculated using finite element methods. It is seen that the stress under the W via plug is a sensitive function of the geometry and the presence of a TiN ARC (Anti-Reflective Coating). The stress under the plug is calculated to be approximately 50&percent; higher than in the surrounding material. In experiments where inspection after purely thermal (no electromigration) stressing was performed, a significantly greater probability of finding a void under the via than in the rest of the line was observed. Replacement of the W plug with Al reduces the stress significantly. In addition, an Al via would heve less tensile stress than the surrounding material and therefore not provide a preferred site for void nucleation. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50941

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Electromigration (EM) in realistic structures consisting ofTiAl3/Al/TiAl3sandwich lines and W studs is modeled in the circuit simulatorAS/X1using a modified Korhonen &etal;2model. Full 2D current crowding and Joule heating finite element analyses are performed and these effects are added onto the EM model. An EM activation energy of 0.87 eV is used, as obtained byHu3for both multi-grained and bamboo-like structures. The model matchest50data quite well for various current densities and temperatures. Sensitivity oft50toTiAl3thickness is analyzed. Comparisons are made for the model with and without Joule heating. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50942

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Narrow conductor lines used in microelectronic circuits at the chip level, are vulnerable to failure by stress migration (SM) and electromigration (EM). We outline a unified approach to model SM and EM damage in interconnects, where the gradients in the stress, electric potential, and concentration are considered as the driving forces for diffusion. We apply this framework analyze the Blech length effect and then proceed to show how EM, SM, and chemical diffusion act together in Cu depletion during accelerated testing. Finally we analyze several cases where SM and EM interaction enhances void nucleation and growth. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50923

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Electromigration in metallic interconnects produces sites of damage, such as voids and hillocks, which are, by definition, the sites of flux divergence in the lines. These flux divergences are usually due to inhomogeneities in the grain structure of the conductor line, where the damage development is controlled by grain boundary diffusion. Measurements of the spacing between voids and corresponding hillocks in Al, Al-1&percent;Si-0.5&percent;Cu and Al-2&percent;Cu interconnects are presented, showing that the distribution of the spacings is a function of current density and line width. These observations can be explained using a modified “Blech theory”. In particular, it was found that the threshold product of current density and spacing between flux divergences increases with increasing Cu content. It was observed that the failure mechanism changes as a function of test conditions: at low currents or in narrow lines the critical product is not reached and diffusion mechanisms other than grain boundary diffusion become predominant. Finally, the elements of a new damage-based electromigration model are presented, which predicts the lifetime of interconnects as a function of current density, threshold product and microstructure. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50924

出版商:AIP    

年代:1996

数据来源: AIP