The Effects of Al(111) Crystal Orientation on Electromigration in Half-Micron Layered Al Interconnects

INTRODUCTIONAluminum thin films are widely used as interconnect materials in microelectronic devices. Electromigration in thin films, especially aluminum and its alloys, is an important subject because of the increased reliability requirements of very large-scale integration circuits. As interconnect-feature sizes continue to decrease, reliability issues related to electromigration failure have received much of attention. 1-4 Alloying aluminum with copper has widely been used to improve electromigration resistance. The electromigration life of Al thin films is highly dependent on median grain size, grain-size distribution, and crystallographic texture. 5 A stronger (111) texture is associated with an increase in the number of low-angle and coincidence-site lattice boundaries. Because these boundaries have a lowintergranular, atomic-transport rate, they can slow down electromigration. 6 It is well documented that the strength of this texture is strongly correlated with the lifetime of interconnections and that a strong (111) texture guarantees good resistance against electromigration failure. 7-9As indicated by several publications, layered metallization has a potential for overcoming many problems, such as electromigration failures and hillock formation, 10,11 associated with common monolithic metallization. A layered structure consisting of Al and a refractory metal, such as Ta, Ti, TiN, Ti/TiN, W, or TiW, was also reported to provide high reliability. 12 This structure promotes better mechanical strength and suppresses aluminum migration. 12 It was also reported that a strongly textured underlayer leads to a similarly strong (111) texture in the aluminum-based conductors. 9,13 The mechanism for this texture inheritance has been proposed as a lattice matching between the underlayer and the metal film. 9,14 Hence, Al (111) texture can be improved by increasing Ti texture. 15 One way to improve Ti texture is to increase the energy of incident-Ti adatoms. In this paper, we tried to increase the energy of incident-Ti adatoms by applying radio-frequency (RF) bias to the substrate during Ti deposition and also by controlling the Ar pressure during sputtering. In addition, RF plasma-cleaning effects of the substrate were also investigated. EXPERIMENTAL PROCEDUREThe 50-nm-thick Ti films and 500-nm-thick Al films were sequentially deposited on thermally oxidized silicon wafers by direct-current (DC) magnetron-sputtering at room temperature. Figure 1 shows a schematic diagram of a three-target, DCThe influence of sputtering pressure and radio-frequency (RF) bias power on the texture of Al/Ti thin films has been investigated. The Al/Ti thin films were deposited sequentially onto thermally oxidized Si wafers in a direct-current (DC) magnetron system. The RF bias was applied during Ti deposition. The texture of Al thin films was quantified by -2 scans and rocking curves of xray diffraction (XRD). The Al thin films deposited on bias-sputtered Ti underlayers showed an epitaxial growth and strong (111) texture. The Al (111) tex...

Section: Discussionmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Texture enhancement of Al films on Ti underlayers by radio-frequency bias sputtering

Park

Kim

2002

“…As the Ti (002) texture improves, the Al (111) texture accordingly improves, mainly because of the small lattice mismatch of about 3% between the Ti (002) and the Al (111) planes. 22 In experiments, using the higher ion energy, e.g., 8 kV, a decrease in the degree of (002) texture of the Ti films was observed when the ion flux was increased. Hence, ion irradiation in the above experiment played at least two major roles.…”

Section: Texture Analyses Of the Ti Underlayermentioning

confidence: 98%

Ion bombardment-induced high orientation of Al/Ti films for surface acoustic wave device applications

Pan

Niu

et al. 2005

Al/Ti films were deposited on 128°Y-X LiNbO 3 substrates by electron-beam (e-beam) deposition. Low-energy Ar ion beam bombardment was employed during the Ti underlayer deposition. Influence of low-energy beam bombardment on the texture of Al/Ti films was investigated by x-ray diffraction (XRD) analysis. It was found that Al films deposited on Ar-ion bombarded Ti underlayers possessed excellent (111) texture. With the textured Al/Ti films, a 2.3-GHz range image-impedance connection surface acoustic wave (SAW) filter was successfully fabricated.

“…The Al (111) texture accordingly decreases, which can most probably be ascribed to the small lattice mismatch of $3% between the Ti (002) and the Al (111) planes. 12 As a result, Al-Zr/Ti films with a preferred orientation were easier to obtain at a lower sputtering pressure. We obtained highly textured Al (111) films on a Ti underlayer using the IBAD technique.…”

Section: Effect Of Microstructure On Lifetime Of Al-zr/ti Electrode Fmentioning

confidence: 99%

Improvement in Power Durability of Al Electrode Films Used in SAW Devices by Zr Additive and Ti Underlayer

Pan

2007

In order to improve the power durability of Al electrode films and obtain fine-dimensional control in high-frequency surface acoustic wave (SAW) devices, two-layered Al-Zr/Ti electrode films were investigated on 128°Y-X LiNbO 3 substrates by sputter deposition. The results indicated that Al-Zr/Ti electrode films had improved electromigration (EM) reliability compared to Al/Ti electrode films and their lifetime was strongly dependent on the microstructure and Zr concentration. Al-Zr/Ti electrode films with a strong Al (111) texture exhibited longer EM lifetime than polycrystalline films. The Al-Zr/Ti electrode film with an ideal Zr concentration of 0.2 wt.% and a sputtering pressure of 0.25 Pa had a strong Al (111) texture, and its lifetime was approximately four times longer than that of Al/Ti films tested at a current density of 5 · 10 7 A/cm 2 at 200°C. Furthermore, the Al-Zr/Ti films were easily etched in reactive ion etching and fine-dimensional control was realized during pattern replication for high-frequency SAW devices.