Direct current (D.C.) is usually employed to characterize the electromigration reliability of interconnects. However, D.C. characterization techniques might not reflect the actual reliability of interconnects that are carrying pulsed D.C. or A.C. (alternating current) signals during operation. This study investigates the effects of unipolar and bipolar pulsed current on the electromigration lifetime of copper (Cu) interconnects. A series of long period pulsed current (i.e. 2, 16, 32 and 48 hours) were applied to Cu interconnects. Lifetime enhancement is observed when the half-period of pulsed current is shorter than the medium-time-to-failure (t50) of D.C. stressed samples. Minor increase in resistance occurring in-between pulses for unipolar pulsed current stressed samples, and occurrence of damage healing in bipolar pulsed current stressed samples are reasons attributed for the observed enhanced lifetime. We obtained longer MTF when the period of the pulsed current is shorter.

Plasma modification of SiOCH low-k films is analyzed by means of Molecular Mechanics. It is shown that the most probable mechanism of SiOCH modification in He plasma is removal of hydrogen atoms from CH3 groups. The change of Si–O–Si bond angles depends on the amount of the formed –CH2* (CHx) groups. During the followed exposure in NH3 plasma, NH2* radicals bind CHx groups with Si forming a –CH2– Si–O–Si–O–Si–O–Si– chain. The end of this chain gets bound to its beginning through NH2. This process is the reason of pore sealing.

In our previous studies, thin Ti-rich diffusion barrier layers were found to be formed at the interface between Cu(Ti) films and SiO2/Si substrates after annealing at elevated temperatures. This technique was called “self-formation of the diffusion barrier,” which is attractive for fabrication of ultra-large scale integrated (ULSI) interconnects. In the present study, we investigated the applicability of this technique to Cu(Ti) alloy films which were deposited on the four low dielectric constant (low-k) dielectric layers which are potential dielectric layers of future ULSI-Si devices. The microstructures were analyzed by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS), and correlated with the electrical properties of the Cu(Ti) films. It was concluded that the Ti-rich interface layers were formed in all the Cu(Ti)/dielectric-layer samples. The primary factor to control composition of the self-formed Ti-rich interface layers was the C concentration in the dielectric layers rather than the formation enthalpy of the Ti compounds (TiC and TiSi). Crystalline TiC was formed on the dielectric layers with a C concentration higher than 17 at.%.

To better understand the factors governing the reliability of lead free solders during severe excursions in temperature, the hardness and elastic modulus of the micro-phases formed in a Sn-Ag-Cu/Cu solder joint were characterized using nanoindentation at temperatures from 25 to 175°C. The creep behaviour of the different micro-phases was also studied as function of temperature. The hardness and elastic modulus of Cu6Sn5, Cu3Sn had a weak dependence on temperature, while primary Sn, eutectic regions and electroplated Cu hardness and modulus were sensitive to temperature. Creep studies indicated that intermetallic were more creep resistant than softer phases that readily underwent creep, the type and rate of which was shown to be strongly temperature dependent.

The electromigration performance of Cu lines patterned by a Cl2 plasma-based etch process has been studied with the accelerated isothermal lifetime test. An electromigration activation energy of 0.6 eV and a current density acceleration exponent of 2.7 were obtained. Both the copper-silicon nitride cap layer interface and the copper grain boundary were active diffusion paths. The applied mechanical bending stress changed the electromigration void distribution in the film, which leaded to the shorter lifetime and lower activation energy.

In Copper back-end-of-line (BEOL), the “punchthru™ process” – removal of barrier material from via bottom during etch/re-sputter step, and gouging into the underlying Copper line - has been increasingly used in 65nm production for its superior reliability. However, with the adoption of porous low-k dielectric at 45nm node and beyond, the conventional punchthru process can cause physical damage to the porous dielectric, such as roughening of the trench bottom in dual damascene structures, micro-trenching in the bottom of single trenches, which may have reliability implications. This paper reported on the use of off-angular Tantalum neutral flux during the re-sputter process to improve the selectivity between the via and trench bottom in order to protect the trench bottom and via bevel, while still allowing sufficient gouging into the underlying Copper line. In addition, the plasma density and ion energy are adjusted to further optimize selectivity, and to eliminate any micro-trenching. Therefore, this paper demonstrated PVD high deposit/etch selectivity process based on transmission-electron microscopy (TEM) and studies of electrical test result. This approach has extended the PVD Tantalum barrier process to at least 32nm node.

The results of copper Chemical Mechanical Planarization (CMP) experiments with a model slurry chemistry based on the combination of Glycine-water-Benzotriazole (Gly-H2O2-BTA), and different types of composite A (silane coupling agents between the polymer core and the silica shell) and B (electrostatic attraction between the polymer core and the silica shell) abrasives, are presented. While the presence of BTA allows a ten-fold reduction in the static etch rate from 95 nm/min. to 10 nm/min., combining oxidizer and complexing agent leads to removal rates higher than 400 nm/min. Different surface morphology and RMS roughness are observed after polishing with composite abrasives and different peroxide concentrations. Oxidizer concentrations as low as 0.1 vol.% lead to high non-uniformity and defectivity values. In particular, composite B performs better than pure colloidal/fumed silica during copper CMP using the IC-1000 pad, giving comparable Material Removal Rate (MRR), but a better surface finish due to the contribution of the elasticity of the polymer in gently transferring the applied load to the wafer surface. Cu CMP with pure polymer particles is a promising alternative to the hard inorganic material especially if combined with suitable surfactants that act from both particle stabilization and friction reduction / lubrication improvement perspectives.

The use of the medium/high-hardness pad IC-1000 is compared to the use of a soft Politex pad. In the former case, differences in terms of MRR, MRS roughness, and total defects are observed between the composite abrasives A and B; in the latter case, the behaviour of the two composites is similar. In the case of a soft pad in combination with composite abrasives, there is a remarkable improvement in the defectivity without any loss in MRR.

As revealed by SEM inspection of the composite particles collected in the slurry drain after CMP, for all the composites, the silica shell coverage is not disrupted by the shear forces and chemistry during the 1 min. polishing. Consequently, the stability and agglomeration properties of the particles in the complex Cu CMP chemistry can be helpful in explaining the experimental results in terms of MRR and surface finishing.

This work describes the effect of addition of O2 and NH3 to the N2 ambient used during the UV cure process of low-k materials. The effects of O2 give an acceleration of the cure process, resulting in increased film modulus and shrinkage. The use of NH3 resulted in a retardation of UV cure, explained by the higher absorption cross section of NH3 at the wavelengths used.

Optimum conditions of annealing atmosphere and temperature for the reduction of Mn content from the Cu-Mn alloy layer in Cu-Mn self-forming barrier process were investigated. Mn was selectively oxidized at the surface by annealing in Ar gas containing an impurity level of O2 (<0.01ppm). Resistivity of the film was decreased to 2.0 μΩcm after annealing. On the other hand, internal oxidation of Cu-Mn alloy was observed with no external protective surface oxide layer in Ar containing more than 10 ppm of O2. An optimum oxygen concentration is found to be in between 0.01 and 10 ppm in 1atm of Ar gas at 350 °C.

A manganese oxide layer was formed by thermal chemical vapor deposition(CVD) on a tetraethylorthosilicate (TEOS) oxide substrate. The thickness of the Mn oxide layer could be varied 2.6 to 10 nm depending on deposition temperature. Heat-treated samples of PVD Cu / CVD Mn oxide /SiO2 indicated no interdiffusion. The CVD Mn oxide was found to be a good diffusion barrier layer.

In this paper, we report a novel method to improve aluminum interconnect electromigration performance, reduce metal line sheet resistance (Rs) and reduce via contact resistance (Rc) in a minimum pitch design. We report the effects of bottom redundancy layers on electrical line and via resistance and upstream electromigration performance. We studied 4 metallization stacks: (I) Ti/TiN/AlCu/Ti/TiN, (II) Ti/TiN/Ti/AlCu/Ti/TiN (annealed at 400°C for 20 minutes), (III) a flash process/stack I, (IV) stack III with aluminum deposition temperature of 250°C. Aluminum deposition temperature in stacks I, II, and III are 200°C. Bottom Ti/TiN, AlCu, and Top Ti/TiN layers have the same thickness for all these stacks. Metal line Rs and via contact resistances (Rc) of stack IV are 5% and 10% lower, respectively, than stack I. Stack II metal line sheet resistance is 15% higher than stack I, which is attributed to Al consumption in the TiAl3 formation during 400°C/20minutes annealing. Electromigration performance is best with stack IV followed by III, II, then I.

Drift of metal ions in low-k dielectrics was investigated by Triangular Voltage Sweep (TVS) measurements on planar capacitors with different gate materials: Al, Ta, Ru, Ti, Cu, Pt and a-Si.