摘要:

New experiments to determine electromigration drift velocity were badly needed in the 1970’s. One such experiment employed a series of aluminum islands, or strips, deposited on top of non-electromigrating but electrically conducting TiN. The experiments showed that the edge displacement near the cathode of the strips drifted as a result of electrical current passage. Figure 1 shows both a plan view as well as a graph of this displacement (1). The displacement is clearly seen to be a function of strip length, namely, longer strips showed larger edge displacement. Very short stripes, such as the one on the right in figure 1, did not show any signs of electromigration. It was this kind of experiments that led to the suggestion that there is a back flow of atoms counteracting the electromigration. The back flow originates from a free energy gradient (for example, a stress gradient) set up by atom crowding near the anode. The back flow was assumed to be stronger in short stripes since the energy gradient driving the back flow is the largest. Figure 1 shows that the edge displacement, or drift, decreases inversely proportional to the stripe length eventually reaching zero leading to credence to the theory. The back flow has generally beneficial effects since it reduces the damaging electromigration flow. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54679

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The wire delay in the deep-submicron era increases in proportion to the square of a scaling factork.The computer-aided design tool described here routes multilevel wires with variable width and spacings reduces the dependence of specified local net delay to dependence on1/kand reduces the dependence of specified global net delay to dependence onk.The increase in the number of specified nets in future LSIs makes LSI design prohibitively complex unless a multilevel interconnection using a low-resistivity material or a low-permittivity material is used. The design tool might also be useful in improving the electromigration hardness of the structure, but some of the parameters for this are still unknown. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54637

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

For Al-Cu VLSI interconnects at tungsten (W) plug contact/via areas, a new electromigration (EM) failure model has been established. A series of experiments were performed to verify the proposed model using novel test structures. This paper discusses the lifetime extrapolation using the model and experimental data which predicts that lifetimes of Al-Cu interconnects at use conditions are dominated by Cu drift, or incubation times. This paper also discusses EM experiment results obtained for the Al filled via which is a promising candidate for replacing W plug vias due to requirements of process simplification and cost reduction in multilevel metallizations. EM failure distributions from the Al filled vias show large standard deviations. This observation is explained through extensive failure analysis of EM-failed specimens. For performance improvement in high-speed logic devices, Cu metallization schemes are being developed. An application of the established failure model to the different metallization systems mentioned above is discussed for more realistic lifetime extrapolation. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54646

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Scaling of interconnect feature sizes changes the mass transport mechanisms that are responsible for electromigration failure of conductors. For deep submicron applications two of the most important issues related to electromigration are the dominant pathway for mass transport in a bamboo grain, and the influence of the Cu on the rate of drift of bamboo AlCu lines. This paper examines these issues, using the stripe drift technique to measure the drift velocity. We show that the dominant pathway for electromigration in bamboo grains is through the lattice at accelerated testing temperatures for conductor widths down to 0.6 &mgr;m. In Al-0.5&percent;Cu alloys, the drift velocity is unaffected by the presence of the Cu dopant, indicating that depletion of Cu atoms in solution does not affect the drift velocity in bamboo Al grains. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54660

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electromigration (EM) characteristics have been investigated with respect to the thickness of the wetting layer in Al-reflow process, the via etching schemes, and the types of glue layers in the W-plug vias. In Al-reflow vias, the thickness of the Ti wetting layer has a critical impact on EM performance. Thinner Ti wetting layers provided higher EM resistance due to lessTiAl3formation, resulting in lower local joule heating at the via interface. As a result, EM voiding for the thicker(∼300 Å)Ti wetting layers occurred at theTiAl3compound, while EM voiding for thinner(∼100 Å)Ti wetting layers occurred inside the vias. In W-plug vias, improvement of the electromigration resistance was achieved when via etching was stopped within the Ti/TiN bi-capping layers of the lower metal lines. On the other hand, when via interfaces were formed within the aluminum lines by etching through the TiN single capping layer, a novel electromigration failure mechanism was observed, resulting in inferior electromigration performance. This novel electromigration failure mechanism, being reported for the first time, is believed to be associated with atomic transport of aluminum through seams of W-plug vias. As a W-glue layer, a TiN glue layer led to improved via EM resistance compared to a Ti/TiN glue layer, presumably due to the lack of formation of titanium-fluoride during CVD-W deposition. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54674

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

By FIB, TEM, and EDS analyses, we observed the near-bamboo structured Al-Cu interconnect terminated with W plugs before and after electromigration (EM), and investigated Cu and Al atomic behavior during EM. While Cu atoms were supersaturated in the Al-Cu line before EM,&thgr;-Al2Cuprecipitates were found only in the anode side after EM. It indicates that transportation of Cu atoms from the cathode side toward the anode side occurred by electron wind. Amorphous layers of the order of 10 nm thickness were found to exist on both side walls of the Al-Cu line before and after EM. After EM, voids were found to be formed inside the amorphous layer along side walls of Al-Cu layer. It is supposed that interface between the amorphous layer and the Al-Cu line side wall is a dominant diffusion path of Al atoms in the case of near-bamboo structured Al-Cu line. We found that the surface of the void after EM was either (111) or (110) faceted plane. It is supposed that a diffusion path of Al atoms on the surface of the void cannot be explained only by the surface energy of lattice plane. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54680

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electromigration-stress of AlCu interconnects was analyzed in an isothermal, high current density Wafer-level test additionally equipped by a voltage noise spectroscopy analyzer. The present investigation indicates different phenomena of electron induced migration mechanisms. The degradation of the metal lines is related to characteristically temporal variations of the electrical resistivity. Analysis of variations of the resistivity in the early phase (1) as well as spectroscopy of low-frequency voltage noise in the following phases (2) and (3) reveal correlation to different diffusion processes in the metallization during the stress test. The estimated activation energiesEaderived from Arrhenius plots of resistance changesdR/dtand of noise measurements at 1 Hz are discussed. Hereby activation energy corresponds to electron induced volume diffusion (phase 1), grainboundary diffusion due to depletion of Copper precipitation (phase 2) and surface diffusion of Aluminum along the stress induced voids (phase 3). As a consequence for the requirement of device reliability a thermal maturing treatment was evaluated which enhances the stable precipitation ofAl2Cu-theta-phases at the grain boundaries and demonstrates improved lifetime of metal lines in electromigration testing. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54675

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The effects of underlying dielectric (phosphosilicate glass and borophosphosilicate glass) films to a humid air ambient on Al-Si-Cu film properties and electromigration (EM) performance in Al-Si-Cu/Ti/TiN/Ti layered films have been investigated as a function of the boron content and exposure time of the dielectric films. The Al(111) orientation in the layered films was found to improve drastically with increasing boron content and exposure time. The full width at half maximum value of an Al(111) x-ray rocking curve reached less than 1°. It was also found that the Al-Si-Cu surface becomes smoother and grain sizes increase as the Al(111) orientation improves. The improved Al(111) orientation was attributed to the improved Ti(002) orientation of the bottom Ti films. Further, it was demonstrate that interconnects fabricated from the improved layered film have excellent EM performance. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54681

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Aluminum (Al) reflow is suppressed in TiN/Ti/AlSiCu/Ti/TiON/Ti interconnects because the interfacial AlxTi layer hinders the migration of Al atoms during reflow annealing. Therefore, electromigration (EM) characteristics of sputtered TiN/Ti/AlSiCu/TiON/Ti interconnects with Al reflow were investigated. The sputtered interconnects with Al reflow treatment have a three times longer electromigration lifetime than the sputtered interconnects without Al reflow treatment. The difference in EM performance between the two metallizations cannot be explained merely by ⟨111⟩ orientation of Al crystallites and the grain size of Al. We verify that the most effective factor in electromigration performance is the stress relaxation between AlSiCu and TiON during reflow annealing. The negligible residual compressive strain has little influence on EM resistance of sputtered interconnects with Al reflow treatment. On the contrary, the residual compressive strain lowers the EM resistance in sputtered interconnects without Al reflow treatment. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54676

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The reservoir effect to electromigration characteristics of borderless vias was investigated. The tested samples were via chains consisting of the W plugs and AlCu lines. The AlCu line was extended over the via to a reservoir. The degradation of the EM reliability for a via without a reservoir which will cause current crowding is due to the via misalignment. In this work, we demonstrated that a long reservoir does not improve the via reliability effectively. The observation of vias showed that voids formed at various locations near the via. It is suggested that the void formation at various locations is depend on the current distribution near the via. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.54677

出版商:AIP    

年代:1998

数据来源: AIP