Alloys electromigration

It will be shown that a more elegant and more easily applicable solution of the problem is given by choosing another reference system. Both the dilute alloy and the unperturbed host can be described with respect to a common reference system, which consists of the unperturbed part of the alloy system and for obvious reasons is called void system. This void system allows for a single-site evaluation of the matrix element describing the wind force in electromigration and the t-matrix element required for the calculation of the residual resistivity due to a saddle-point defect. 

Figure 1 A dilute alloy system, showing a substitutional impurity, an interstitial impurity and an electromigration defect, and its reference system, the unperturbed host system. Some charge transfer effects are shown. Lattice distortion effects are omitted.

Defect configurations in dilute alloys, studied up to now in the framework of multiple scattering theory, are such that a one-to-one correspondence exists between the atoms in the alloy and the reference system, the latter system regularly being the unperturbed host system. This one-to-one correspondence does not apply to the defect studied in substitutional electromigration, in which a host atom or an impurity can move to a neighbouring vacancy. 

Alloying element with CVD aluminum to reduce electromigration. 

To mitigate the problem, a diffusion barrier is incorporated between the aluminum and the silicon (see Sec. 5 below). It is also possible to replace aluminum by alloys of aluminum and copper or aluminum and silicon, which have less tendency to electromigration. These alloys are usually deposited by bias sputtering. However, they offer only a temporary solution as electromigration will still occur as greater densities of circuit elements are introduced. It was recently determined that improvements in the deposition of aluminum by MOCVD at low temperature with a dimethyl aluminum hydride precursor may reduce the problem.bl... 

Deposition of copper alloys such as copper/aluminum can be carried out starting from copper(l) and copper(Il) enolates. Copper alloys may be of technological and scientific interest as they can help avoiding problems caused by electromigration, corrosion and poor adhesion to dielectric substrates. ... 

The competitor to YBaCuO in this application is copper, which has a resistivity at 77 K of 0.24 /x 2cm, compared to a value at 300 K of 1.7 p2cm< In fact at room temperature, copper alloys with even higher resisitivity are used to reduce electromigration, which is practically eliminated at the lower temperatures. Thus copper offers a reduction in resistance of more than a factor of 6 at 77 K. 

Aluminum is often used as an alloy with a few atomic % Si and/or Cu to reduce electromigration (Fig. 1). This alloy is difficult to etch because copper does not form readily volatile compounds [73]. Fleating of the wafer to some 200 °C and intense ion bombardment to sputter off involatile products are then necessary to effect etching. Residual chlorine remaining on the wafer after aluminum etching can be deleterious because it can promote corrosion, especially in Al-Cu alloys. Hence wafer rinsing with DI water is common. Dry passivation by exposure to a fluorocarbon plasma has... 

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